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  • 1990-1994  (1,717)
  • 1980-1984
  • 1991  (1,717)
  • Analytical Chemistry and Spectroscopy  (1,511)
  • Physical Chemistry  (205)
  • Nuclear reactions
Source
Material
Years
  • 1990-1994  (1,717)
  • 1980-1984
Year
Keywords
  • 1
    Electronic Resource
    Electronic Resource
    The origin and abundances of the chemical elements revisited (1991)
    Springer
    The astronomy and astrophysics review 3 (1991), S. 1-46 
    Details
    ISSN: 1432-0754
    Keywords: Nucleosynthesis ; Nuclear reactions ; Stars: abundances ; Interstellar Medium: abundances ; Cosmology ; Galaxies: evolution of
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary The basic scheme of nucleosynthesis (building of heavy elements from light ones) has held up very well since it was first proposed more than 30 years ago by E.M. Burbidge, G.R. Burbidge, A.G.W. Cameron, W.A. Fowler, and F. Hoyle. Significant advances in the intervening years include (a) observations of elemental and a few isotopic ratios in many more extrasolar-system sites, including metal-poor dwarf irregular galaxies, where very little has happened, and supernovae and their remnants, where a great deal has happened, (b) recognition of the early universe as good for making all the elements up to helium, (c) resolution of heavy element burning in stars into separate carbon, neon, oxygen, and silicon burning, with fine tuning of the resulting abundances by explosive nucleosynthesis in outgoing supernova shock waves, (d) clarification of the role of Type I supernovae, (e) concordance between elements produced in short-lived and long-lived stars with those that increased quickly and slowly over the history of the galaxy, and (f) calibration of calculations of the evolution and explosion of massive stars against the detailed observations of SN 1987A. The discussion presupposes a reader (a) with some prior knowledge of astronomy at the level of recognizing what is meant by an A star and an AGB star and (b) with at least a mild interest in how we got to where we currently are.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00873456
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  • 2
    Electronic Resource
    Electronic Resource
    Factor analysis in chemistry, (2nd edition), E. R. Malinowski, Wiley-Interscience, 1991. ISBN 0-471-53009-3. Price £43.70 (1991)
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 5 (1991), S. 545-545 
    Details
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cem.1180050607
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  • 3
    Electronic Resource
    Electronic Resource
    Recent developments in multivariate calibrationInvited Paper. (1991)
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 5 (1991), S. 129-145 
    Details
    ISSN: 0886-9383
    Keywords: Multivariate calibration ; Biased regression ; Partial least squares (PLS) ; Principal component regression (PCR) ; Model validation ; Non-linear calibration ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: With the goal of understanding global chemical processes, environmental chemists have some of the most complex sample analysis problems. Multivariate calibration is a tool that can be applied successfully in many situations where traditional univariate analyses cannot. The purpose of this paper is to review multivariate calibration, with an emphasis being placed on the developments in recent years. The inverse and classical models are discussed briefly, with the main emphasis on the biased calibration methods. Principal component regression (PCR) and partial least squares (PLS) are discussed, along with methods for quantitative and qualitative validation of the calibration models. Non-linear PCR, non-linear PLS and locally weighted regression are presented as calibration methods for non-linear data. Finally, calibration techniques using a matrix of data per sample (second-order calibration) are discussed briefly.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cem.1180050303
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  • 4
    Electronic Resource
    Electronic Resource
    Real-time filtering of data from mobile, passive remote infrared sensors with principal component models of backgroundInvited Paper. (1991)
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 5 (1991), S. 147-161 
    Details
    ISSN: 0886-9383
    Keywords: Digital filtering ; Real-time analysis ; Kalman filtering ; Infrared spectroscopy ; Principal components regression ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Real-time monitoring of pollutant levels from a mobile measuring platform requires fast, flexible data analysis methods. This paper reports a method for rapid analysis of passive remotely sensed infrared data with the aid of a Kalman filter. The background spectra produced by emission from the atmosphere are modelled at the start of the data collection sequence with a simple principal components model obtained by eigenanalysis of the initial ‘blank’ data taken with the spectrometer. The species of interest are included in the state space model by a separate measurement of their infrared spectra. It is demonstrated that for best filter performance in detecting the simulated pollutant species SF6 in the atmosphere, a filter model with two principal components describing the emission background works best. The filter ‘maps’ of SF6 closely follow the integrated spectral intensities measured after removal of suitable backgrounds.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cem.1180050304
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  • 5
    Electronic Resource
    Electronic Resource
    Examining large databases: A chemometric approach using principal component analysisInvited Paper. (1991)
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 5 (1991), S. 163-179 
    Details
    ISSN: 0886-9383
    Keywords: Principal component analysis ; Factor analysis ; Chemometrics ; Exploratory data analysis ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Principal component analysis is used to examine large multivariate databases. The graphical approach to exploratory data analysis is described and illustrated with a single example of chemical composition data obtained on environmental dust particles. While the graphical approach to exploratory data analysis has certain advantages over the numerical procedures, the empirical approach described here should be viewed as complementary to the more robust treatments that statistical methodologies afford.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cem.1180050305
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  • 6
    Electronic Resource
    Electronic Resource
    Experimental design in chemometricsInvited Paper. (1991)
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 5 (1991), S. 181-192 
    Details
    ISSN: 0886-9383
    Keywords: Chemometrics ; Systems theory ; Experimental design ; Multivariate analysis ; Measurement science ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Chemometrics is defined as the application of mathematical and statistical methods to chemical systems. Systems theory is seen to be useful for organizing and categorizing the inputs to and outputs from chemical systems. Advances in measurement science in the 1950s and 1960s, particularly in analytical chemistry, created a need for a multivariate approach to data analysis. Early chemometrics emphasized the use of structure-finding methods for existing data sets. In many instances, data sets can be obtained from designed experiments. Such data sets are more likely to contain the desired information and the data can usually be acquired at less cost. Renewed interest in statistical process control will provide many new, more robust data sets in the future.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cem.1180050306
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  • 7
    Electronic Resource
    Electronic Resource
    Simultaneous analysis of Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) by spectrophotometry and the Kalman filter (1991)
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 5 (1991), S. 193-199 
    Details
    ISSN: 0886-9383
    Keywords: Kalman filter ; Chemometrics ; 5-Br-PADAP ; Metallic ions ; Simultaneous spectrophotometric determination ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This paper describes the simultaneous determination of cobalt, nickel, copper, zinc and cadmium by spectrophotometry and the Kalman filter method. Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) react with 5-bromo-2-(2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP) in the presence of cationic surfactant cetyl pyridinium bromide (CPB) to form five different coloured ternary complexes. The absorption curves of these complexes overlap severely in the scanning range 500-620 nm. The Kalman filter algorithm is successfully applied to resolve the overlapped absorption curves and therefore makes the simultaneous determination of these metallic ions possible without tedious pretreatment. The proposed method is applied to analyse the titled elements in synthetic samples and in environmental samples such as hair, fingernail and river water samples with satisfactory results.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cem.1180050307
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  • 8
    Electronic Resource
    Electronic Resource
    Step function technique for estimating data uncertainty in experimental results (1991)
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 5 (1991), S. 201-209 
    Details
    ISSN: 0886-9383
    Keywords: Uncertainty ; Step function ; Additive model ; Transformation ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An additive model is used to express the observed value of a sample characteristic as the sum of the true sample characteristic and a value of the data collection error, commonly known as experimental error. The data uncertainty of the experimental results (or of a survey data set) is defined as the expected squared error. The expected squarred error may change with the sample characteristic, e.g. the error moment could be concentration-dependent. The relationship between the error variance and the analyte concentration may not be very distinct. In such a case the data transformation to stabilize the error moments may not be appropriate. A step function is proposed as an alternative way to represent the second moment of the error. The data uncertainty is defined as the weighted average of the step values of the second raw moment of the error, using the appropriate proportions of the routine samples as weights. The data uncertainties associated with the different data collection stages were evaluated by using regional soil survey data.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cem.1180050308
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  • 9
    Electronic Resource
    Electronic Resource
    Expectation-maximization algorithm for regression, deconvolution and smoothing of shot-noise limited data (1991)
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 5 (1991), S. 211-225 
    Details
    ISSN: 0886-9383
    Keywords: Shot noise ; Expectation-maximization ; Regression ; Deconvolution ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A simple algorithm for deconvolution and regression of shot-noise-limited data is illustrated in this paper. The algorithm is easily adapted to almost any model and converges to the global optimum. Multiple-component spectrum regression, spectrum deconvolution and smoothing examples are used to illustrate the algorithm. The algorithm and a method for determining uncertainties in the parameters based on the Fisher information matrix are given and illustrated with three examples. An experimental example of spectrograph grating order compensation of a diode array solar spectroradiometer is given to illustrate the use of this technique in environmental analysis. The major advantages of the EM algorithm are found to be its stability, simplicity, conservation of data magnitude and guaranteed convergence.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cem.1180050309
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  • 10
    Electronic Resource
    Electronic Resource
    Estimation of errors in absorbance ratio measurements (1991)
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 5 (1991), S. 291-298 
    Details
    ISSN: 0886-9383
    Keywords: Absorbance ratio ; Statistical confidence ; Quality control ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ratio measurements are commonly used to address a variety of analytical problems in environmental, forensic and pharmaceutical laboratories. In absorbance ratioing techniques, analytical chemists rely on the spectral features of the analyte(s) of interest. The absorbances at two wavelengths are monitored and the ratio of these two absorbances is computed. This ratio is then used to confirm the identity of the analyte(s) of interest, the purity of a product of the overlap of chromatographic peaks. These decisions often have far-reaching consequences (e.g. the identification of the source, biogenic or petrogenic, of hydrocarbons in biological tissues or water). Given the cost and the liabilities associated with such decisions, it is unfortunate that these ratios are seldom reported with any statistical confidence. The purpose of this study is to delineate the parameters that affect absorbance ratio measurements. The models that can be used to estimate the statistical confidence in these measurements are derived and evaluated experimentally. The results show that these models can estimate the relative standard deviations in absorbance ratios accurately. They can also estimate the effect of signal-to-noise ratio and the choice of wavelengths on the precision of absorbance ratios.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cem.1180050315
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  • 11
    Electronic Resource
    Electronic Resource
    Likelihood techniques for interlaboratory calibration in the national stream survey (1991)
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 5 (1991), S. 299-308 
    Details
    ISSN: 0886-9383
    Keywords: Errors in variables ; Orthogonal regression ; Latent variables ; Acid rain ; Acidic deposition ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Techniques for testing for and estimating relative bias between two laboratories are developed and applied to a survey of the chemistry of streams in the United States. The design of the quality assurance program allows estimation of linear corrections for bias as well as testing of the hypothesis of linearity. Designs of this type are useful, but improvements are suggested.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cem.1180050316
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  • 12
    Electronic Resource
    Electronic Resource
    On confidence intervals for the product of three means of three normally distributed populations (1991)
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 5 (1991), S. 309-319 
    Details
    ISSN: 0886-9383
    Keywords: Confidence intervals ; Products of normal random variables ; Risk/exposure modeling ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In many environmental applications, such as exposure assessment and risk modelling, the desired estimate is a random variable computed as the product of three independently distributed random variables. These variables may not necessarily have the same mean and variance. The method for finding the 100(1 - α)% confidence interval for the mean of the product random variable has been proposed by some practitioners as the product of the 100(1 - α)% confidence interval of the three means. In this paper we show that the distribution of the product of three independent normal variables is not normal. We find the mean and variance of the product distribution. Further, we show that although the mean of the product is equal to the product of the means, the product of the three confidence intervals is not a good approximation of the confidence intervals for the mean of the product variable. The confidence interval of the mean of the product variable may be estimated by computer simulation. An algorithm for estimating the confidence interval for the mean of the product random variable is given. The program implementing this algorithm is given as an appendix.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cem.1180050317
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  • 13
    Electronic Resource
    Electronic Resource
    Comparison of two screening methods for the detection of volatile organic compounds in ground water (1991)
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 5 (1991), S. 321-331 
    Details
    ISSN: 0886-9383
    Keywords: Screening ; Ground-water quality ; Monitoring ; Volatile organic compounds (VOCs) ; Optimization ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: It is shown that the presence of 31-35 commonly measured volatile organic compounds (VOCs) in ground water can be detected with small error rates by using screening methods which analyze for a subset of such VOCs. A study of selected data sets indicates that analytical determinations of only from two to eight VOCs will suffice to detect 95% of all VOC hits. It is also shown that a serially optimal algorithm for selecting the VOCs for screening is very nearly as accurate as a globally optimal algorithm and much easier to implement. These conclusions are supported by empirical evidence from two drinking-water data sets and one hazardous waste site data set. Additional research areas are also outlined.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cem.1180050318
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  • 14
    Electronic Resource
    Electronic Resource
    Masthead (1991)
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 5 (1991) 
    Details
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cem.1180050401
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  • 15
    Electronic Resource
    Electronic Resource
    Diary (1991)
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 5 (1991), S. i 
    Details
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cem.1180050402
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  • 16
    Electronic Resource
    Electronic Resource
    A bootstrap resampling scheme for using the canonical correlation technique in rank estimation (1991)
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 5 (1991), S. 333-343 
    Details
    ISSN: 0886-9383
    Keywords: Rank estimation ; Bootstrap resampling ; Canonical correlation ; Excitation-emission matrix ; Singular value decomposition ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Rank estimation by canonical correlation analysis in multivariate statistics has been proposed as an alternative approach for estimating the number of components in a multicomponent mixture. A methodological turning point of this new approach is that it focuses on the difference in structure rather than in magnitude in characterizing the difference between the signal and the noise. This structural difference is quantified through the analysis of canonical correlation, which is a well-established data reduction technique in multivariate statistics. Unfortunately, there is a price to be paid for having this structural difference: at least two replicate data matrices are needed to carry out the analysis.In this paper we continue to explore the potential and to extend the scope of the canonical correlation technique. In particular, we propose a bootstrap resampling method which makes it possible to perform the canonical correlation analysis on a single data matrix. Since a robust estimator is introduced to make inference about the rank, the procedure may be applied to a wide range of data without any restriction on the noise distribution. Results from real as well as simulated mixture samples indicate that when used in conjunction with this resampling method, canonical correlation analysis of a single data matrix is equally efficient as of replicate data matrices.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cem.1180050403
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  • 17
    Electronic Resource
    Electronic Resource
    Three-way methods for the calibration of chromatographic systems: Comparing PARAFAC and three-way PLS (1991)
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 5 (1991), S. 345-360 
    Details
    ISSN: 0886-9383
    Keywords: Three-way PCA ; Three-way PLS ; PARAFAC ; Trilinear ; Unfolding ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: For the calibration of chromatographic systems, different methods can be used. One class of methods utilizes three-way approaches. The calibration problem is stated in such a way that the decomposition of a three-way array can serve for the prediction of retention on new stationary phases.Two three-way approaches are presented: the Unfold-PCA and PARAFAC models. The theory of both methods is presented and the differences are highlighted, the main difference being that PARAFAC is a trilinear decomposition whereas Unfold-PCA is not. Both three-way methods are evaluated on a small data set consisting of retention measurements of eight solutes at six mobile phase compositions on six stationary phases. The differences in performance of the two models are minor.For calibration purposes, two variants of the methods are discussed: three-way PLS and an extension of PARAFAC. Again the theory and differences between the two methods are explained. The predictive performance of the two methods is compared using the same data set as earlier. The differences in predictive performance, however, are minor. Both methods are capable of predicting 98% of the variation in the test sets. Yet, there are other considerations when comparing methods than predictive performance, e.g. the quality of the predictions.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cem.1180050404
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  • 18
    Electronic Resource
    Electronic Resource
    Estimation in compositional data analysis (1991)
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 5 (1991), S. 361-374 
    Details
    ISSN: 0886-9383
    Keywords: Closure ; Normalization ; Multivariate trimming ; Minimum distance ; Bootstrap ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Compositional data arise naturally in several branches of science, including chemistry, geology, biology, medicine, ecology and manufacturing design. In chemistry, these constrained data seem to occur typically when raw data are normalized or when output is obtained from a constrained estimation procedure, such as might be used in a source apportionment problem. It is important not only for chemists to be aware that the usual multivariate statistical techniques are not applicable to constrained data, but also to have access to appropriate techniques as they become available. The currently available methodology is due principally to Aitchison and is based on log-normal models. This paper suggests new parametric and non-parametric approaches to significantly improve the existing methodology. In the parametric setting, some recent work of Rayens and Srinivasan is extended and a practical regression model is proposed. In the development of the non-parametric approach, minimum distance methods coupled with multivariate bootstrap techniques are used to obtain point and region estimators.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cem.1180050405
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  • 19
    Electronic Resource
    Electronic Resource
    A test of three fitting criteria for multiresponse non-linear modeling (1991)
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 5 (1991), S. 375-387 
    Details
    ISSN: 0886-9383
    Keywords: Determinant criterion ; Multiresponse non-linear fitting ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This work evaluates objective functions for multiresponse non-linear modeling using computer simulations. Tests are performed under a variety of signal-to-noise ratios and noise variance-covariance structures. The standard error of prediction for the model parameters, computed from 50 trials, is used for performance comparisons. The full rank and rank-deficient problems are considered. For the full rank problem one model was investigated, a first-order two-step consecutive reaction model, and two objective functions were considered, the total sum of squares and the determinant criterion. No distinction could be made between the two objective functions for this model.For the rank-deficient case two models were investigated, a first-order two-step consecutive reaction as in the full rank case, and a pH titration model described by the Henderson-Hasselbalch equation. Three objective functions were investigated for the rank-deficient case, the total sum of squares, a weighted total sum of squares and the determinant criterion. The total sum of squares was found to perform poorly under all conditions tested compared to the weighted total sum of squares and the determinant criterion. The determinant criterion was found to perform much better than the other two criteria when the data have a combination of a low signal-to-noise ratio and high variance-covariance noise structure.
    Additional Material: 7 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cem.1180050406
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  • 20
    Electronic Resource
    Electronic Resource
    The chemometrics team of MITAC (Micro and Trace Analysis Center), University of Antwerp, Belgium (1991)
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 5 (1991), S. 405-409 
    Details
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cem.1180050408
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  • 21
    Electronic Resource
    Electronic Resource
    Comparison of pattern recognition descriptors for chemical acoustic emission analysis (1991)
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 5 (1991), S. 389-403 
    Details
    ISSN: 0886-9383
    Keywords: Acoustic emission ; Pattern recognition ; Feature selection ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Features used to characterize acoustic emission signals from chemical systems are evaluated with regard to their potential for pattern recognition. Eight chemical systems involving phase transitions, hydration, dissolution and effervescence are employed and treated as separate signal classes. These are compared pairwise and the discriminatory capabilities of about 50 features are investigated by computing Fisher weights. Time domain and frequency domain descriptors are examined. Correlations among the features evaluated are also reported. Recommended descriptors are the mean and median frequencies, frequency bandwidth, number of level crossings (0% and 25%), crest factor (time and frequency domains), half-life, kurtosis and normalized percentiles of the signal and its power spectrum. The effectiveness of the recommended descriptors is demonstrated through the separation of signal classes in two different systems (melting ice and an enzyme-catalyzed gas formation reaction) by principal components analysis.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cem.1180050407
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  • 22
    Electronic Resource
    Electronic Resource
    Scientific computing and automation (Europe) 1990 (Proceedings of the Scientific Computing and Automation (Europe) Conference, 12-15 June 1990, Maastricht, The Netherlands), edited by E. J. Karjalainen for the series Data Handling in Science and Technology, 6, Elsevier Science Publishers, Amsterdam, 1990, 514 pp., ISBN 0-444-88949-3, US$220.00/Dfl. 385.00 (1991)
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 5 (1991), S. 411-412 
    Details
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cem.1180050409
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  • 23
    Electronic Resource
    Electronic Resource
    UNSCRAMBLER 11, version 3.10: A program for multivariate analysis with PLS and PCA/PCR. Available from CAMO AS, Jarlevn. 4, Trondheim, Norway. Price $3000; academic discount price $1500 (1991)
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 5 (1991), S. 413-415 
    Details
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cem.1180050410
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  • 24
    Electronic Resource
    Electronic Resource
    Announcement (1991)
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 5 (1991), S. 416-416 
    Details
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cem.1180050411
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  • 25
    Electronic Resource
    Electronic Resource
    Masthead (1991)
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 5 (1991) 
    Details
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cem.1180050501
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  • 26
    Electronic Resource
    Electronic Resource
    Diary (1991)
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 5 (1991), S. i 
    Details
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cem.1180050502
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  • 27
    Electronic Resource
    Electronic Resource
    Rapid estimation of the number of coeluting components in liquid chromatography by factor analysis (1991)
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 5 (1991), S. 417-434 
    Details
    ISSN: 0886-9383
    Keywords: Factor analysis ; Power density distribution ; Chromatography ; Absorption spectroscopy ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Evaluation of the results of factor analysis of sets of spectroscopically detected chromatograms is carried out by examining the shapes of the abstract factors. This is done either by visual inspection or by analysis of the power density spectra produced from them. Owing to constraints imposed by the column function and the spectroscopic instrument function, the information content of the chromatograms necessarily occurs at low spatial frequencies. As a consequence, it appears as relatively broad features in the abstract chromatograms and as a peak in the low-frequency region of the corresponding power density plot. On the basis of examination of the power density distribution, a well-defined distinction is made between primary and secondary abstract factors. The major uncertainty encountered in determining the number of chemical components appears to arise from effects of contaminants in reagents.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cem.1180050503
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  • 28
    Electronic Resource
    Electronic Resource
    A class-modelling technique based on potential functions (1991)
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 5 (1991), S. 435-453 
    Details
    ISSN: 0886-9383
    Keywords: Class-modelling methods ; Potential functions ; Pattern recognition ; Discriminant analysis ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A probabilistic and distribution-free class-modelling technique is developed from potential function discriminant analysis. In the multidimensional space of variables the class boundary is built either by the sample percentile of the probability density estimated by means of potential functions, or by the estimate of the ‘equivalent’ determinant of the variance-covariance matrix. The equivalent determinant is that of a hypothetical multivariate normal distribution whose mean probability density was obtained by potential functions. The bases of this modelling rule are evaluated by means of Monte Carlo experiments. The results on four datasets are used to measure the performances of this method, which equal and sometimes exceed the performances of parametric class-modelling methods based on linear and quadratic discriminant analysis which were used for comparison.
    Additional Material: 15 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cem.1180050504
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  • 29
    Electronic Resource
    Electronic Resource
    Correspondence analysis and adsorbate selection for chemical sensor arrays (1991)
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 5 (1991), S. 455-465 
    Details
    ISSN: 0886-9383
    Keywords: Correspondence analysis ; Cluster analysis ; Optimization ; Eigenanalysis ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Carey et al. utilized principal components analysis (PCA) to analyze frequency shift data obtained from piezoelectric sensors formed by coating quartz crystals with 27 different GC stationary phases and tested using 14 analytes. The objective of the analysis was to determine an optimal reduced set of coatings for detection of the analytes. The results were correlated with those obtained from cluster analysis. In this paper the data are re-analyzed using correspondence analysis (CA). The advantage of using CA include a symmetric treatment of sensor coatings and analytes and better identification of the representation of the analytes in terms of the detection components. The results obtained by the conjunctive use of PCA, a varimax rotation and cluster analysis were obtained by CA.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cem.1180050505
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  • 30
    Electronic Resource
    Electronic Resource
    Fuzzy multivariate rule-building expert systems: Minimal neural networks (1991)
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 5 (1991), S. 467-486 
    Details
    ISSN: 0886-9383
    Keywords: Expert system ; Neural network ; Fuzzy entropy ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A fuzzy multivariate rule-building expert system (FuRES) has been devised which also functions as a minimal neural network. This system builds rules from training sets of data that use feature transformation in their antecedents. The rules are constructed using the ID3 algorithm with a fuzzy expression of classification entropy. The rules are optimal with respect to fuzziness and can accommodate overlapped and underlapped clusters of data. The FuRES algorithm combines the benefits obtained from simulated annealing and gradient optimization, which provide robustness and efficiency respectively. FuRES classification trees support OR logic in their inference. The system automatically generates meaningful and consistent certainty factors during rule construction. Unlike other neural networks, FuRES uses local processing which furnishes qualitative information in the rule structure of its classification trees and variable loadings of the weight vectors.
    Additional Material: 18 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cem.1180050506
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  • 31
    Electronic Resource
    Electronic Resource
    Masthead (1991)
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 5 (1991) 
    Details
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cem.1180050601
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  • 32
    Electronic Resource
    Electronic Resource
    Diary (1991)
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 5 (1991), S. i 
    Details
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cem.1180050602
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  • 33
    Electronic Resource
    Electronic Resource
    Multivariate calibration when data are split into subsets (1991)
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 5 (1991), S. 487-501 
    Details
    ISSN: 0886-9383
    Keywords: Calibration ; Locally linear models ; Discrimination ; Optimality ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A calibration situation is considered where the calibration data are split into subsets with good linear relationship between y and x within each group. Different strategies for good prediction in this case are proposed. Modifications for collinear data are considered and a simple simulated data set is used for illustration.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cem.1180050603
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  • 34
    Electronic Resource
    Electronic Resource
    Rank-order analysis for robust multiresponse, multiblock comparisons: Evaluation of herbicide interactions (1991)
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 5 (1991), S. 503-521 
    Details
    ISSN: 0886-9383
    Keywords: Antagonism ; Bounded ordinal scale ; Herbicide interaction ; Inter block comparisons ; Non-parametric ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Studies of interactions among bioactive compounds are often difficult to interpret unambiguously. A priori assumptions about the nature of such interactions can seriously distort analysis of the data. By applying a rank order analysis appropriate to the naturally ordinal scale of response to xenobiotic insult, several co-herbicides were successfully identified from among numerous candidates in an experiment involving multiple blocks, rates and species. Moreover, underlying herbicide interactions were substantiated and identified which were not apparent by more traditional parametric analysis.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cem.1180050604
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  • 35
    Electronic Resource
    Electronic Resource
    Diary (1991)
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 5 (1991), S. i 
    Details
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cem.1180050102
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  • 36
    Electronic Resource
    Electronic Resource
    Tutorial to robust statistics (1991)
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 5 (1991), S. 1-20 
    Details
    ISSN: 0886-9383
    Keywords: Averaging ; Median ; Outliers ; Regression ; Residuals ; Robustness ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In this tutorial we first illustrate the effect of outliers on classical statistics such as the sample average. This motivates the use of robust techniques. For univariate data the sample median is a robust estimator of location, and the dispersion can also be estimated robustly. The resulting ‘z-scores’ are well suited to detect outliers. The sample median can be generalized to very large data sets, which is useful for robust ‘averaging’ of curves or images. For multivariate data a robust regression procedure is described. Its standardized residuals allow us to identify the outliers. Finally, a survey of related approaches is given. (This review overlaps with earlier work by the same author, which appeared elsewhere.)
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cem.1180050103
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  • 37
    Electronic Resource
    Electronic Resource
    Use of the Wronskian determinant in the study of multicomponent systems (1991)
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 5 (1991), S. 21-35 
    Details
    ISSN: 0886-9383
    Keywords: Wronskian determinant ; Multicomponent systems ; Derivative spectroscopy ; Spline functions ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The use of Wronskian determinants in the study of multicomponent systems is proposed. The general theory is presented and applied to the spectrophotometric determination of the number of linearly independent components-absorbers. A detailed study of a two-component system is presented and analysed. Numerical methods for smoothing and differentiation of digitized spectra via cubic splines are used.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cem.1180050104
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  • 38
    Electronic Resource
    Electronic Resource
    Splitting of calibration data by cluster analysis (1991)
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 5 (1991), S. 49-65 
    Details
    ISSN: 0886-9383
    Keywords: Calibration ; Cluster analysis ; Local linearity ; Mahalanobis distance ; Residual distance ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The topic of the present paper is the splitting of calibration data into subgroups with improved linearity in each group. The method proposed is based on a criterion which is a weighted average of a Mahalanobis distance and a squared regression residual. The algorithm used to find the solution is based on fuzzy clustering. Two examples are given to illustrate the theory.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cem.1180050106
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  • 39
    Electronic Resource
    Electronic Resource
    Generalized simulated annealing for calibration sample selection from an existing set and orthogonalization of undesigned experiments (1991)
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 5 (1991), S. 37-48 
    Details
    ISSN: 0886-9383
    Keywords: Optimization ; Simulated annealing ; Calibration ; Experimental design ; Multicomponent analysis ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Generalized simulated annealing (GSA) is an optimization procedure for locating the global optimum (maximum or minimum) of multidimenisonal continuous functions. GSA has been modified for optimization of discrete functions. Selection of calibration samples from an existing set defines discrete optimization and GSA is used to select optimal sets of calibration samples for specific analysis samples. The procedure is applied to near-infrared spectra. When compared to using the complete set of 37 calibration samples, concentration prediction errors were reduced 50%-100% by using select sets of two to seven calibration samples. Additionally, GSA was able to improve a poorly designed experiment. GSA devised augmented experimental designs such that the overall experimental design (original plus augmented) was more orthogonal than the original.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cem.1180050105
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  • 40
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    Electronic Resource
    Computational methods in the chemical sciences, A. F. Carley and P. H. Morgan, Ellis Horwood, Ltd, Chichester, U.K., 1989. ISBN 0-85312-746-8 (1991)
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 5 (1991), S. 68-69 
    Details
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cem.1180050108
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    Electronic Resource
    Computerized multiple input chromatography, M. Kaljurand and E. Küllik, Ellis Horwood, Chichester, U.K., 1989. No. of pages: 225. ISBN 0-7458-0120-X. Price £45.00 (1991)
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 5 (1991), S. 67-67 
    Details
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cem.1180050107
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  • 42
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    Electronic Resource
    Editorial (1991)
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 5 (1991), S. 71-71 
    Details
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cem.1180050203
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  • 43
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    Electronic Resource
    The use of a ratio method as an alternative to constrained deconvolution (1991)
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 5 (1991), S. 85-95 
    Details
    ISSN: 0886-9383
    Keywords: Deconvolution ; Gold's ratio ; Iterative deconvolution ; Chromatographic deconvolution ; Peak restoration ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This paper will consider the use of an iterative ratio technique called Gold's ratio method as an alternative to iterative constrained deconvolution methods for the restoration of overlapped and noisy chromatograpic peaks. The study will consist of first describing the technique and then evaluating its performance with respect to Jansson's deconvolution procedure. A Hewlett-Packard 5890A gas chromatograph will be used to generate most of the test data. The evaluation criteria will include convergence rates, peak area errors and variances, retention time variances and noise performance.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cem.1180050205
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  • 44
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    Electronic Resource
    Comparison of measurement methods based on a model for the error structure (1991)
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 5 (1991), S. 523-536 
    Details
    ISSN: 0886-9383
    Keywords: Measurement errors ; Method comparison ; Mean square successive difference ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Comparison of methods is a technique often used for investigation of systematic errors of measurement methods. As concerns the design and analysis of such comparisons, much variety of opinion and practice exists. In one approach a few specimens are measured several times by different operators in different laboratories (reproducibility conditions) and in another approach several specimens are measured on one or a few occasions by one operator in the same laboratory (repeatability conditions). In this paper a model for the error structure of measurements is formulated and it is emphasized that one has to distinguish between two types of systematic errors: the first type depends only on the level of the measured quantity and the second type is specific for the separate specimens. On the basis of this model the information which can be obtained from the different designs of method comparisons is discussed. A new approach for the analysis of method comparisons with many specimens is also proposed.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cem.1180050605
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  • 45
    Electronic Resource
    Electronic Resource
    Announcement (1991)
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 5 (1991), S. 69-69 
    Details
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cem.1180050109
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  • 46
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    Electronic Resource
    Some issues in chemometrics with environmental applications (1991)
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 5 (1991), S. 121-128 
    Details
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cem.1180050302
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  • 47
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    Electronic Resource
    Laboratorio di Chemiometria, University of Perugia, Italy (1991)
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 5 (1991), S. 537-543 
    Details
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cem.1180050606
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  • 48
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    Diagnostika Sostava Materialov Rentgenodifrakcionnimi I Spektralnymi Metodami (Identification of materials by X-ray diffraction and spectroscopical Techniques) (in Russian), M. S. Nakhmanson and V. G. Feklitschev, Mashinostroenie, Leningrad, 1990. 357 pages. ISBN 5-217-00915-2, Rubl 5.40 (1991)
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 5 (1991), S. 546-547 
    Details
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cem.1180050608
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  • 49
    Electronic Resource
    Electronic Resource
    Masthead (1991)
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 5 (1991) 
    Details
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cem.1180050101
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  • 50
    Electronic Resource
    Electronic Resource
    Masthead (1991)
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 5 (1991) 
    Details
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cem.1180050201
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  • 51
    Electronic Resource
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    Diary (1991)
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 5 (1991), S. i 
    Details
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cem.1180050202
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  • 52
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    A new serial method for searching the optimum operating conditions of a technological process (1991)
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 5 (1991), S. 73-84 
    Details
    ISSN: 0886-9383
    Keywords: Optimization ; Technological process ; COMPLEX algorithm ; ANTICOMPLEX algorithm ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new program, named ANTICOMPLEX, has been specially written for searching the optimum conditions of a technological process. The algorithm is based on an iterative procedure with, at each step, a random sampling for a better exploration of the hyperspace of the parameters. Since the process is considered as a ‘black box’, the program operates by successive reductions of the variation domains with a strategy derived from some function optimization (COMPLEX). This approach is very flexible and the experimenter can stop the investigation at any series of experiments according to the desired accuracy for the optimum region. This program has been successfully tested on several real processes. This paper gives a complete description of the approach together with two illustrations on simulated processes.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cem.1180050204
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    The Laboratory for Chemometrics, University of Washington, Seattle (1991)
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 5 (1991), S. 113-116 
    Details
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cem.1180050207
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  • 54
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    Announcements (1991)
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 5 (1991), S. 117-119 
    Details
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cem.1180050208
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    Regression on multivariate images: Principal component regression for modeling, prediction and visual diagnostic tools (1991)
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 5 (1991), S. 97-111 
    Details
    ISSN: 0886-9383
    Keywords: Multivariate images ; Principal component regression ; Multivariate image regression ; Regression model ; Predicted image(s) ; Prediction quality scatter plot ; Visual diagnostic tools ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Regression between two blocks (usually called ‘dependent’ or Y and ‘independent’ or X) of data is a very important scientific and data-analytical tool. Regression on multivariate images is possible and constitutes a meaningful addition to existing univariate and multivariate techniques of image analysis. The regression can be used as a modeling tool or for prediction. The form of the regression equation chosen is dependent upon problem specification and information at hand. This paper describes the use of principal component regression (PCR). Both model building and prediction are presented for continuous Y-variables. The final goal is to supply new image material that can be used for visual inspection on a screen. Also, visual tools for diagnosis of model and prediction are provided, often based on derived image material. Examples of modeling and prediction are given for six channels in a seven-channel satellite image.
    Additional Material: 14 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cem.1180050206
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    Masthead (1991)
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 5 (1991) 
    Details
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cem.1180050301
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    Box-Cox transformations in the analysis of compositional data (1991)
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 5 (1991), S. 227-239 
    Details
    ISSN: 0886-9383
    Keywords: Unit-sum constraint ; Mixing proportions ; Ratio data ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The statistical analysis of compositional data is of fundamental importance to practitioners in general and to chemists in particular. The existing methodology is principally due to Aitchison, who effectively uses two transformations, a ratio followed by the logarithmic, to create a useful, coherent theory that in principle allows the plethora of normal-based multivariate techniques to be used on the transformed data. This paper suggests that the well-known class of Box-Cox transformations can be employed in place of the logarithmic to significantly improve the existing methodology. This is supported in part by showing that one of the most basic problems that Aitchison managed to overcome, namely the specification of an interpretable covariance structure for compositional data, can be resolved, or nearly resolved, once the ratio transformation has been applied. Hence the resolution is not directly dependent on the logarithmic transformation. It is then verified that access to the general Box-Cox family will allow a more accurate use of the normal-based multivariate techniques, simply because better fits to normality can be achieved. Finally, maximum likelihood estimation and some associated asymptotics are employed to construct confidence intervals for ratios of the true, unknown compositional constituents. Heretofore this had not been done even in the context of the logarithmic transformation. Applications to real data are presented.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/cem.1180050310
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    Finding causes of outliers in multivariate environmental data (1991)
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 5 (1991), S. 241-248 
    Details
    ISSN: 0886-9383
    Keywords: Multivariate kurtosis ; Generalized distance ; Multivariate outliers ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Multivariate outliers in environmental data sets are often caused by atypical measurement error in a single variable. From a quality assurance perspective it is important to identify these variables efficiently so that corrective actions may be performed. We demonstrate a procedure for using two multivariate tests to identify which variable ‘caused’ each outlier. The procedure is tested with simulated data sets have have the same correlation structure as selected water chemistry variables from a survey of lakes in the Western United States. The success rates are evaluated for three of the variables for sample sizes of 50 and 100, significance levels of 0.01 and 0.05 and various amounts of mean shift. The procedure works best for highly correlated variables.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cem.1180050311
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    A statistical procedure to evaluate clean-up standards (1991)
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 5 (1991), S. 249-261 
    Details
    ISSN: 0886-9383
    Keywords: Asymptotic power ; Clean-up standard ; Gamma distribution ; Likelihood ratio test ; Uniformly most powerful unbiased test ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The object of this paper is to develop a suitable statistical procedure to evaluate clean-up standards at hazardous waste sites. Under the assumptions that contaminant masses at a site follow a gamma distribution and that the data from the pre-remediation baseline sample as well as from the interim or final sample taken after a certain period of operation are both distributed as gamma with the same shape parameter but different scale parameters, we derive a uniformly most powerful unbiased test of the hypothesis that a specified percentage of contaminant mass has been reduced. A large-sample approximation of the exact test procedure and a comparison with the likelihood ratio test are provided.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cem.1180050312
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    The quality of mean and variance estimates for normal and lognormal data when the underlying distribution is misspecified (1991)
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 5 (1991), S. 263-271 
    Details
    ISSN: 0886-9383
    Keywords: Mean ; Variance ; Lognormal ; Optimal estimators ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Theoretical and simulation results are employed to evaluate mean and variance estimates for normal data when a lognormal distribution is assumed and for lognormal data when a normal distribution is assumed. Misspecifying the distribution leads to the use of suboptimal estimation methods. However, the results show that the suboptimal methods still produce estimators of good quality (low bias and variance) relative to the minimum variance unbiased estimators for each distribution, at least when practical efficiency is considered.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cem.1180050313
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    Correspondence analysis used in the evaluation of lakewater chemistry in the Adirondacks (1991)
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 5 (1991), S. 273-290 
    Details
    ISSN: 0886-9383
    Keywords: Correspondence analysis ; Eastern Lake Survey - Phase I data ; Acidic deposition ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Correspondence analysis (CA) was applied to lakewater data in order to study the effects of acidic deposition on the geochemical composition of lakes in the Adirondacks. The lake chemistry data analyzed were taken from the Eastern Lake Survey - Phase I (ELS-I) conducted by the U.S. Environmental Protection Agency. CA was used to identify ‘outlying’ lake samples as well as ‘superflous’ and ‘unresolved’ analytes. Correlational relationship among analytes were also examined.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cem.1180050314
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    Masthead (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991) 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040101
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    Geometry of 2-benzopyrylium and pyrylium cations calculated by semi-empirical methods. Crystal and molecular structure of 1,3-dimethyl-6,7-dimethoxy-2-benzopyrylium perchlorate (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 7-12 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: X-ray data on the crystal and molecular structure of 1,3-dimethyl-6,7- dimethoxy-2-benzopyrylium perchlorate show a good correlation with the geometry of the same cation calculated by the MINDO/3 and MNDO methods with total optimization of all geometrical parameters. The geometry of substituted pyrylium cations was determined by the MNDO and AM1 methods. On the basis of the data obtained, some effects of benzo [c] annelation are displayed for the 2-benzopyrylium cation in comparison with the pyrylium cation.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040103
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    Micellar catalysis of the intramolecular aminolysis of the β-lactam antibiotic cephaclor (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 19-24 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The rate of intramolecular degradation of cephaclor, involving the attack of the amino group at C-17 (N-18) on the β-lactam carbonyl, was increased up to 50-fold by neutral (polyoxyethylene-23 lauryl ether; Brij) and zwitterionic [3-(N-dodecyl-N, N-dimethylammonium) propane 1-sulphonate; (SDP)] micelles. The rate of OH- attack on cephaclor was increased 2-3-fold by Brij and SDP micelles. In the absence of micelles the rate of intramolecular degradation of cephaclor increased by up to 2-fold by addition of organic solvents. Distance calculations, based on the crystal structure of the antibiotic, showed that the intramolecular degration can only proceed in a conformation involving a cis-amide bond (N-14 - C-15). Micellar catalysis of the intramolecular degradation process was proposed to be due to the stabilization of the reactive conformation.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040105
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    Development of a model to explain the influence of the solvent on the rate and selectivity of diels-alder reactions (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 48-52 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Solvophobic and polarity parameters are used to explain the endo/exo selectivity of the reaction between cyclopentadiene and methyl acrylate. A good linear regression model with Sp and ETN is obtained. The existence of an intrinsic correlation between the Sp and ETN values, which makes the interpretation of the results difficult, is shown. A comparison of the results with other previously reported showed that the relative influence of Sp and ETN on selectivity depends on the nature of the reagents.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610040108
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    Aggregation of amphiphilic molecules in water. I. α-phenylethylamine: 1H and 13C NMR study (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 58-66 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The concentration dependence of the 1H and 13C NMR chemical shifts in D2O and in CDCl3 solutions were determined for (±)-α-phenylethylamine (I). Aqueous solutions of (-)-I and (+)-I, 50% enantiomerically enriched in (-)- and (±)-2, 2, 2,-trifluoro-1-phenylethanol and the (+)- and (-)-N-formyl derivatives of I, were also studied. 1H nuclear Overhauser enhancements were used to check the conformations of the solutes at various concentrations and 1H T1 values were used to monitor the changes in molecular tumbling in solutions. The results are interpreted in terms of a spontaneous aggregation of solute molecules in water, with the possible determination of the critical micelle concentration. The time-dependent splittings in the 1H NMR spectra suggest further, more detailed, studies of the structures of the aggregates and the possibility of chiral recognition in water.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610040110
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    Evaluation of solvent effects on the dissociation of aliphatic carboxylic acids in aqueous N,N-dimethylformamide mixtures according to the scaled particle theory (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 87-95 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The standard Gibbs energies of transfer, ΔGt° from water to water-N,N-dimethylformamide mixtures for the dissociation process of several organic acids (formic, acetic, propionic, n-butyric, isobutyric, n-valeric, isovaleric, 2-methylbutyric and trimethylacetic acids) obtained from the pKa* values are discussed in terms of the extended Scaled Particle Theory from quantum mechanical calculations in order to estimate the cavity and electrostatic contributions. The residual energy term was correlated with the hydrogen bond acceptor density and the Kamlet-Taft β parameters. The main contribution to ΔGt° was due to dipolar and specific interactions.
    Additional Material: 6 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040204
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    The 11C/14C kinetic isotope effect method. The 11C/14C kinetic isotope effect in the SN2 reaction of N,N-dimethyl-p-toluidine with labelled methyl iodide (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 77-86 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Methodological aspects of the determination of 11C/14C kinetic isotope effects (KIEs) were investigated using the reaction of N, N-dimethyl-p-toluidine with labelled methyl iodide in methanol at 30 °C as model system. The primary 11C KIE was determined to be 1.202 ± 0.008 for this reaction. The isotope effect was determined by a one-pot technique based on liquid chromatographic fractionation of the reactant and product followed by liquid scintillation counting of the 11C and 14C radioactivity in these fractions. The KIE value obtained agrees well with the value predicted from a previously determined 12C/14C-KIE for the same reaction. Theoretical model calculations of both carbon KIEs were performed using the BEBOVIB IV program. Transition-state models ranging from reactant- to product-like were employed in the calculations, and three different reaction coordinate models with more or less pronounced Walden inversion of the methyl hydrogens were investigated.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610040203
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    Cross-interaction constants as a measure of the transition state structure. Part 15. Kinetic isotope effects in the SN2 reactions of 2-phenylethyl derivatives with deuterated aniline nucleophiles (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 101-106 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Kinetic isotope effects (KIE) were determined for the reactions of 2-phenylethyl and 1-methyl-2-phenylethyl benzenesulphonates with deuterated aniline nucleophiles in acetonitrile at 65.0 °C. The results are in good agreement with the transition state (TS) structures proposed based on the sign and magnitude of the cross-interaction constants, pxz, between the substituents in the nucleophile (X) and the leaving group (Z). In the reactions of 2-phenylethyl derivatives, all three reaction pathways, kr, kt and kΔ, were found to be contributing competitively; the inverse secondary KIE observed with a stronger nucleophile changed into the primary KIE with a weaker nucleophile owing to the predominant contribution of the four-centre TS in the kf path. For the reactions of the 1-methyl-2-phenylethyl series, the kr path played a major role, the contribution from the front-side nucleophilic attack, kf, being negligible. In both reaction series, the aryl participation was important for the p-CH3O-substituted substrate.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040206
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    Addition of hydroxylamine to cyclohexanone and bicyclic ketones. Steric, electronic and hydrogen bonding effects on the general mechanism of addition of amines to carbonyl compounds (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 107-112 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Three different types of pH-rate profiles were observed for the addition of amines to carbonyl compounds, depending on the relative predominance, at weakly acidic pH, of either a concerted or a stepwise mechanism. The predominant mechanism depends on the basicity of the amine and the mutual equilibrium affinity for adduct formation between the carbonyl compound and the amine. The reaction of hydroxylamine with cyclohexanone and bicyclic ketones was studied in order to examine the roles of steric and electronic effects in this mechanism. Cyclohexanone and 3-chlorobicyclo [2.2.1] heptan-2-one exhibit the profile expected for a single change in the rate-determining step with increasing pH from uncatalysed attack of the amine on the carbonyl group to hydronium ion-catalysed dehydration of the carbinolamine. In contrast, both bicyclo [2.2.1] heptan-2-one and bicyclo [2.2.2] octan-2-one show an unexpected profile with two negative breaks and five kinetically significant regions. This profile is explained by stabilization of the zwitterionic intermediate T± by intramolecular hydrogen bonding, leading to the formation of the carbinolamine by a stepwise mechanism at weakly acidic pH.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610040207
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    Crystal and molecular structure of pyrylium salts. IV. Crystal and molecular structure of 2,6-diphenyl-4-(4-carboxyphenyl)pyrylium perchlorate. Interrelations between structural parameters due to substituent effects (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 121-124 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The crystal and molecular structure of 2,6-diphenyl-4-(4-carboxyphenyl)pyrylium perchlorate was solved by x-ray diffraction, yielding structural parameters of high precision (estimated standard deviations for bond length ≤ 0.5 pm, for bond angles ≤ 0.2°). Comparison with other 4-substituted derivatives of 2,6-diphenyl-4(4-carboxytphenylpyrylium) perchlorate shows regularities in the variations of structural parameters following classical views of substituent effects.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610040209
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    Structure and dynamics of dicyandiamide: A theoretical study (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 125-134 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Ab initio MO methods have been used to study the structures and energetics of dicyandiamide, [(NH2)2C=N—C≡N], its isomers, protonated species, radical anions, transition structures for internal conformational change and transition structures for isomerization. Structures were optimized at the HF/STO-3G, HF/3-21G and HF/6-31G* levels; selected barrier heights for smaller analogues were also computed at the MP4SDTQ/6-31G* level. The most stable isomer of dicyandiamide has the cyano group on the imine nitrogen [1, (NH2)2C=NC≡N]; the other isomer [2, HN=C(NH2)NH—C≡N] lies 12.8 kcal mol-1 higher. Inversion at the imino nitrogen proceeds by a linear, in plane process with a barrier of 32.5 kcal mol-1. The amino rotation barriers are 19 kcal mol-1 (single NH2) and 40 kcal mol-1 (both NH2 in a conrotaory or a disrotatory fashion; if the NH2 groups are allowed to pyramidalize the disrotatory barrier drops to 20 kcal mol)-1. Protonation occurs preferentially on the imine nitrogen (PA = 219.7 kcal mol-1 for 1); the proton affinities PA of the amino nitrogens are 25-30 kcal mol-1 lower. Isomerization between 2 and 1 would go via a 1,3-sigmatropic hydrogen shift, but the barrier is high (48.3 kcal mol-1); protonation reduces the hydrogen shift barrier by ca 15 kcal mol-1. However, the most likely mechanism for isomerization involves protonation of the imine nitrogen in 2 followed by deprotonation of the cyano-substituted nitrogen to form 1, circumventing the energetically costly 1,3-sigmatropic hydrogen shift. When an electron is transferred to dicyandiamide, a sizeable fraction of the resonance stabilization of the guanidine moiety is lost.
    Additional Material: 7 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610040302
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    The grignard reaction of α-diketones. Radical intermediates as the determinant of carbon- and oxygen-attacked products (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 158-162 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Although carbon (normal)- and oxygen (abnormal)-attacked products are usually afforded in the Grignard reaction of α-diketones, the relative ratio of the two are strongly dependent on the structure of the Grignard reagents. The product-determining factors are discussed on the basis of the intermediate radicals formed from α-diketones and Grignard reagents.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610040306
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    Masthead (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991) 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040401
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    Kinetics of oxidation of hydrocarbons by quinolinium dichromate (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 217-224 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Quinolinium dichromate (QDC) oxidizes hydrocarbons (toluenes and phenanthrenes) smoothly in dimethylformamide in the presence of acid. The rate of the reaction was first order in each substrate, oxidant and acid. The effects of variations in solvent composition and temperature were studied. The rate data obeyed Hammett's relationship and the values of ρ were -0.20 for toluenes and -1.79 for phenanthrenes. Induced polymerization of acrylonitrile and the reduction of mercury(II) chloride were not observed. For the oxidation of toluenes, a kinetic isotope effect, kH/kD = 5.13, was observed. The initial reaction for the oxidation of toluenes involved hydrogen abstraction, forming an intermediate which was rapidly converted to the product, the corresponding aldehyde. For the oxidation of phenanthrene, the experimental data have been rationalized in terms of a hydride ion transfer in the ratedetermining step.
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    URL: http://dx.doi.org/10.1002/poc.610040404
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    Isotope effects in acid-catalyzed aromatic hydrogen exchangePresented in part at the 68th CIC Chemical Conference, Kingston, Canada, June 1985, paper no. OR-C3-4. (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 233-241 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Deuterium- or tritium-substituted aromatics undergo isotope exchange in fairly concentrated aqueous sulfuric acid media. The rate constant for this process is complex, being composed of that for the slow electrophilic attack, and the isotope effect on the breakup of the Wheland intermediate. Using experimental rate constant data for both deuterium and tritium exchange on the same substrate, the excess acidity method and the Swain-Schaad relationship, true protonation rate constants and isotope effects have been separated out for several positions in several simple aromatic substrates. Most of the electrophilic attack rate constants are described by a Hammett-type linear free energy relationship with a ρ+ of - 6.5. The average observed deuterium isotope effect on Wheland intermediate breakup was 5.3. Using rate constants obtained at different temperatures, enthalpies and entropies of activation were also obtained for benzene, naphthalene and thiophene; the activation entropy averaged - 8 cal mol-1 K-1. Some evidence was found for general acid catalysis at the higher acidities.
    Additional Material: 7 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610040406
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  • 77
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    Masthead (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991) 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040501
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  • 78
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    Conversion of flavanones into chalcones in alkaline medium. Kinetic and spectroscopic studies (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 263-270 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The conversion of flavanone and 7-hydroxyflavanone in alkaline water and heavy water and of the same compounds and of 4′ -nitroflavanone in alkali-methanolic media into the corresponding substituted chalcones was studied kinetically and spectroscopically. Treatment of kinetic data in this work and data for the reverse reaction determined previously allowed the estimation of the partial rate coefficients for each step and of the free-energy changes for the three systems studied. To disentangle isotope effects, the conversion of [3-D2]-flavanone was also studied. The present results confirm a previously suggested mechanism for the spontaneous reaction and afford essential information that may contribute to a more detailed understanding of the mechanism of the enzyme-catalysed reaction.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610040502
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  • 79
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    Kinetic modelling of the low-temperature photo-oxidation of hexafluoropropene (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 293-300 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: By kinetic simulation, the significant features of the mechanism of the low-temperature photo-oxidation of hexafluoropropene were elucidated and the rate constants for the major elementary reactions of the intermediate fluorinated peroxy and alkoxy radicals were determined through a best-fit procedure. Comparison with analogue reactions in non-fluorinated systems showed a significant increase in reactivity for the self-reaction and double bond addition by peroxy radicals and β-scission by alkoxy radicals, which are discussed in terms of fluorine substituent effects.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610040506
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  • 80
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    Masthead (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991) 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040601
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  • 81
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    New ideas on phase transfer catalysts: SN2 reaction with a solid ionophoric salt (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 336-340 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A new mechanism of substitution between n-hexyl bromide (RBr) and solid potassium chloride in toluene under phasetransfer catalysis conditions is suggested, involving the formation of intermediates, adsorbed on the solid phase, viz., two binary (KCl·QX and KX·QBr) and two ternary (QX·KCl·RBr and QBr·KX·RCl) complexes. According to this mechanism, the catalytic activity of onium salts (QX) in the substitution changes in the order QI 〉 QBr 〉 QCl. The nature of the catalyst cation has little or no effect on the reaction rate. A general rule is proposed according to which in this reaction the substrate is attacked by a stronger nucleophile whereas a weaker nucleophile accepts the leaving group of the substrate. These and earlier data are interpreted in term of the SN2 process occurring on the solid-phase surface. The structure of the ternary complexes and the role of the phase-transfer catalyst are discussed.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610040603
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  • 82
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    Origin of apparent swain-schaad deviations in criteria for tunneling (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 361-366 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Vibrational analysis calculations have been conducted in an effort to understand the origins of apparently anomalous relationships reported between kH/kT and kD/kT kinetic isotope effects. The actual isotopic substitutions used in previous work are more complex than a simple comparison between H/T and D/T isotope effects. The relationships between the actual isotope effects determined in these studies amount to tests of two standards of conventional isotope effect theory, the rule of the geometric mean (or the lack of isotope effects on isotope effects) and the Swain - Schaad rule. Model calculations illustrate the importance of violations of the rule of the geometric mean (over Swain - Schaad deviations) arising in models that incorporate both explicit reaction-coordinate coupling of two isotopic sites and reaction-coordinate tunneling. Implications for experimental studies of turneling using apparent Swain - Schaad exponents are discussed.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610040607
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  • 83
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    The schiff base between pyridoxal-5′-phosphate (PLP) and hexylamine. Formation of the unprotonated form of the imine by reaction of the unprotonated PLP and free amine (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 372-380 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Electrochemical and spectrophotometric studies of the pyridoxal-5′ -phosphate hexylamine Schiff base (PHSB) in strongly basic media were carried out. The equilibrium constant and rate constants of the formation and hydrolysis of the unprotonated imine from the unprotonated pyridoxal-5′ -phosphate and free amine were determined by linearscan cyclic voltammetry. The acid-base dissociation constant of the imine group was obtained by spectrophotometric measurements. Absorption bands for the free imine and the conjugate acid are characterized by a log-normal distribution. These studies are for general application to the quantitative characterization of non-enzymatic model compounds.
    Additional Material: 10 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610040609
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  • 84
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    Factors affecting the reversibility of the electrophilic step in olefin bromination. The case of 5H-dibenzo [a, d] cycloheptene (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 387-398 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The tendency of ion-pair intermediates generated by treatment of trans-10-bromo-10, 11-dihydro-11-hydroxy-5H-dibenzo [a, d] cycloheptene (5) with HBr to release Br2 giving 5H-dibenzo [a, d,] cycloheptene (1) has been evaluated. The observed 9:1 ratio between ion-pair collapse to the trans-dibromide (7) and Br2 release to olefin 1, as compared with the 3:7 ratio found with the 5H-dibenz [b, f] azepine-5-carbonyl chloride system, has been interpreted as indicating a much lower propensity for reversibility of ion-pair formation in the bromination of 1. The structural parameters obtained by x-ray diffraction of the dibromide 7 show for this compound an angle strain at C-10 and C-11 analogous to that found in trans-10, 11-dibromo-10, 11-dihydro-5H-dibenz [b, f,] azepine-5-carbonyl chloride. Olefin 1 adds Br2 in 1,2-dichloroethane at 25°C according to a third-order rate law, with k3 = 30(3) M-2 s-1. About 10% of 5-bromo-5H,-dibenzo [a, d] cycloheptene, arising from collapse of a dibenzo [a, d] tropylium ion intermediate (9), is formed in this reaction besides the expected trans-dibromide 7. Spectral evidence for the formation of 9, arising by rearrangement of a first formed weakly bridged ionic intermediate in the reaction of 1 with Br2, is presented. the results obtained with the 5H-dibenzo [a, d,] cycloheptene system have been rationalized on the basis of the formation of very weakly bridged intermediates having a much lower tendency to revert back to olefin and Br2 with respect to the corresponding symmetrically bridged bromonium ions.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610040611
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  • 85
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    SRN1 Reactions of nucleophiles with radical clocks: Rate constants for some radical-nucleophile reactions (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 404-412 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Treatment of o-3-(but-3-enyloxy)benzene (1) with anions -SPh, -PPh2 and -PO(OEt)2 in ammonia, acetonitrile or dimethyl sulphoxide gives both direct substitution and cyclized products. The formation of the latter confirms the intermediacy of the o-3-(but-3-enyloxy)phenyl radical (2) and confirms that the reactions follow the SRN1 pathway. The kinetics of the coupling of the aryl radical 2 were determined by comparison with the known rate of cyclization of 2. Similar experiments with the neopentyl bromide, 6-bromo-5,5-dimethylhex-1-ene, and its 3-oxa derivative also gave cyclized and uncyclized products, thus confirming that the SRN1 mechanism applies to the reactions. Approximate rate constants for the coupling of a neopentyl radical with the nucleophiles -SPh and -PPh2 have thus been determined.
    Additional Material: 5 Tab.
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    URL: http://dx.doi.org/10.1002/poc.610040703
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  • 86
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    Short Communications. Biphenyl-3,4′-Dinitrene (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 459-462 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Photolysis of biphenyl-3,4′ -diazide in a rigid glassy matrix at 77 K yields quintet state biphenyl-3,4′ -dinitrene with zero-field splitting parameters of |D/hc- = 0.153 cm-1 and |E/hc| = 0.019 cm-1 determined by electron spin resonance spectroscopic studies. Curie plot studies are consistent with assigning the quintet to be the ground state in this species. This finding confirms qualitative connectivity-based predictions for this general connectivity type of openshell system, and is in qualitative agreement with spectral INDO-CI computational predictions for both planar and twisted geometries of the dinitrene.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610040708
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  • 87
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    The α-bromocyclohexanone ring: The relationship between its conformation and the ultraviolet and infrared absorption of the keto group (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 420-438 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A series of diterpenoids whose C-ring was an α-bromocyclohexanone showed a discontinuity in the relationship between the Br—C—C=O torsion angle and the Br…O contact distance at about 50°, below which the Br…O distance remained effectively constant at about 3.0 Å. This effect is caused by the non-compressibility of the van der Waals radii of the Br and O atoms. Analysis of the parameters for all compounds in the Cambridge Data File containing an α-bromocyclohexanone ring confirmed this phenomenon. Once the Br…O distance approaches 3.0 Å, the Br—C—C and C—C=O angles are forced open to accommodate the Br…O compression strain as the torsion angle is further reduced. An approximate value of the Br…O distance, d in Å, can be estimated for any torsion angle, ø, by the empirical equation d2 = R - S cos φ + T cos2 φ where R = 11.73, S = 3.62 and T = 0.75. There is a linear relationship between the Br…O separation and both the infrared vibration frequency v and the ultraviolet absorption wavelength δmax of the C=O group: the greater the distance, the lower is the frequency v and longer the wavelength δmax. Thus measurement of the ultraviolet and infrared spectra of a compound containing an α-bromocyclohexanone system can yield information about the Br…O distance and hence the conformation of the six-membered ring. There are also systematic trends in the effect on the spectroscopic properties of the keto group that accompany changing the halogen from fluorine through to iodine. When the halogen is axial, its electronegativity has a maximum influence on the C=O vibration frequency by a ‘through-bond’ inductive process. When the halogen is equatorial, it exerts a steric compression on the non-bonded electrons in the 2p orbital of the oxygen atom. This enhances hybridization to the sp2 state and this simultaneously strengthens the C=O bond and enlarges the n → π* energy gap. This ‘through-space’ influence is simply a process of steric compression, dependent on the size of the halogen atom. It accounts well for all of the systematic trends in both infrared and ultraviolet frequencies of the C=O group when the halogen is equatorial and eclipses the C=O bond.
    Additional Material: 11 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610040705
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  • 88
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    Masthead (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991) 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040801
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  • 89
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    Treatment of electrostatic effects within the molecular mechanics method. 3. Double bonds and conjugated systems (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 467-478 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The previously developed general method (IDME), which includes calculation of electrostatic and solvation effects on conformational equilibria, has been extended to molecules containing double bonds and conjugated systems. It was applied in connection with MM2 studies to the calculation of the charge distributions and dipole moments, and to the conformational energies of some β-substituted cyclohexenes, exo-methylenecyclohexanes and benzocycloheptenes. Conformational equilibria and dipole moments were well calculated. It was concluded that electrostatic interactions do not play a major role in determining conformational preferences in these compounds. On the other hand, the energies of the preferred conformations of the ten-membered ring in (E)-3β-acetoxy-5,10-seco-1(10)-cholesten-5-one are poorly calculated without the IDME procedure, and fairly well with it.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610040802
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  • 90
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    Theoretical models for the reduction of arylmethyl halides by triorganotin hydridesPreliminary presentation of results at combined 45th Northwest-10th Rocky Mountain Regional Meeting of the American Chemical Society, Salt Lake City, UT, 13 June 1990. (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 485-491 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Two mechanistic pathways have been proposed for halogen atom transfer from the benzylic positions of halomethylarenes to triorganotin radicals. These are direct atom abstraction, which might involve an extremely polar transition state, and single electron transfer followed by bond cleavage. AM1 semi-empirical calculations have been utilized to model the rate-determining step of these processes. A wide range of related families of compounds have been studied, including substituted halomethylbenzes, selected halomethyl-substituted polycyclic aromatic hydrocarbons and oxygen- and nitrogen-containing chloromethyl-substituted heteroaromatic systems. Although these calculations are relatively simple, the present results corroborate the view that chlorine and bromine atom transfer from the benzylic position to triorganotin radicals involves a direct atom abstraction in the rate-determining step whereas reduction of the corresponding iodides proceeds via an electron-transfer mechanism.
    Additional Material: 8 Tab.
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    URL: http://dx.doi.org/10.1002/poc.610040804
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  • 91
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    Ambident electrophilicity of alkyl aryl phosphates (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 516-522 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Hydrolysis of dimethyl aryl phosphates, (MeO)2P(O)OAr where the ArO group is derived from N-methyl-8-hydroxyquinolinium or 4-hydroxy-(N,N,N-trimethylanilinium) ion, proceeds with the cleavage of the P—OAr and Me—O bonds. The effect of external factors on the relative contributions of those two reaction pathways was studied. The increase in temperature favours, owing to the difference in activation entropies, the reaction at carbon. The addition acetone to the aqueous reaction medium slows down the reaction at carbon more rapidly than the reaction at phosphorus, indicating higher hydration requirements of the dealkylation transition state. In water-triffuoracetic acid mixtures only the P—OAr bond cleavage is acid catalysed; the catalytic effect is superimposed on the general, decelerating medium effect. Specific nucleophilic catalysis was demonstrated for the Me—O bond fission by thiosulphate ion (ca 60-fold acceleration), and for the reaction at phosphorus by fluoride ion (ca 500-fold acceleration).
    Additional Material: 6 Tab.
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    URL: http://dx.doi.org/10.1002/poc.610040807
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    Masthead (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991) 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040901
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  • 93
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    Short communication. Structural studies of bromine adducts of 1,2- and 1,4-bis(phenylseleno)benzenes. Evidence for the (TB, MC) structure of 1,2-(PhSeBr2)2C6H4 (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 523-525 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: 1,2-Bis(phenylseleno)benzene reacted with equimolar amount of bromine to yield a trigonal bipyramidal (TB) adduct, in contrast to the molecular complex (MC) structure of selenanthrene with bromine. Whereas the structure of 1,4-(PhSeBr2)2C6H4 was (TB, TB) at the two selenium atoms, that of the 1,2-derivative was demonstrated to be (TB, MC), the first example of an MC structure of PhSeC6H4Y with Br2 [Y = 2-PhBr2Se(TB)]. Both electronic and steric effects of the group must play an important role in MC formation. Rapid structural exchange in this tetrabromide, (TB, MC) ⇄ (MC, TB), was also observed.
    Additional Material: 2 Tab.
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    URL: http://dx.doi.org/10.1002/poc.610040808
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  • 94
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    Conformations of pentan-1-OL, hexan-1-OL and their thio analogues (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 536-540 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Empirical linear relationships between standard Gibbs free energy, ΔG298°, and parachor and between standard entropy, S298°, and parachor are presented for the aliphatic series H(CH2)nX with X = CH3, CH=CH2, C≡CH, Cl, OH, SH, SCH3 and SC2H5. In the series with X = OH and SH significant deviations of points for n = 4 and 5 are observed. INDO quantum-chemical analysis points to the formation of cyclic conformers of butan-1-ol, pentan-1-ol and their corresponding thio analogues. The formation energy of the cyclic conformers (higher for thiols than for alcohols) is proportional to the sum of deviations from the linearity of the points under discussion.
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    URL: http://dx.doi.org/10.1002/poc.610040903
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  • 95
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    Review commentary. Solvation, the electrophilic driving force of ionic bromination of ethylenic compounds. The addition-solvolysis analogy (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 527-535 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Solvation is the main driving force of electrophilic bromination since it is impossible to obtain a bromonium ion from bromine and alkene in the gas phase, whereas it is a very fast reaction in solution. The role of a protic solvent in this addition was investigated experimentally by extended Winstein-Grunwald relationships, kinetic solvent isotope effects and R, the rate ratios in two solvents of similar ionizing powers but different nucleophilicities. It is shown that electrostatic medium effects and electrophilic assistance to bromide ion departure are the main rate-determining factors of the reaction. These two contributions are roughly independent of the double bond substituents. Nucleophilic solvent assistance to positive charge development is also found; however, it provides only a small acceleration, the magnitude of which depends on alkene structure. This nucleophilic solvent involvement is annulled when crowded substituents inhibit approach of the solvent to the cationic part of the transition state or when positive charge is delocalized by conjugated electron-donating groups. These several solvent roles are identical in nature and in magnitude with those observed in heterolytic solvolysis. In halogenated solvents, the driving force of bromination arises from catalysis by a second bromine molecule which assists heterolysis of the bromine-bromine bond, leading to the bromonium-tribromide ion pair. Similar halogen catalysis occurs also in some solvolyses. Finally, return is also found in both reactions; reversible formation of bromonium ions is observed when their nucleophilic attack, the productforming last step, is made energetically difficult either by steric inhibition or by poor nucleophilicity of the trapping nucleophiles. Similarities and differences between electrophilic bromine addition and limiting solvolysis are discussed in terms of respective intermediate stabilities and heats of formation.
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  • 96
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    Photochemical transformations. 49.For Part 48, see Ref. 1. Solvent effects on singlet ionic and triplet photoreactions of some bridged polycyclic chlorides: Comparison with ground-state reactionsDedicated to Professor Kurt Schaffner on his 60th birthday. (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 541-546 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Direct irradiations of 2-chloro-6,7 : 8,9-dibenzotricyclo [3.2.2.02,4] nona-6,8-diene (5-Cl) were conducted in cyclohexane, acetic acid and wet acetonitrile. The products are 1-methylfluoranthene (8) in all three solvents, the allylic chlorides 8-chloro-7-methylene-2,3 : 5,6-dibenzobicyclo [2.2.2] octa-2,5-diene (3-Cl) and 7-chloromethyl-2,3 : 5,6-dibenzobicyclo [2.2.2] octa-2,5,7-triene (2-Cl) in acetic acid and acetonitrile and solvolysis product amides in wet acetonitrile. Compound 5-Cl had previously been shown to be the product of triplet sensitization of 2-Cl and 3-Cl, so that the singlet reaction reverses that of the triplet. The formation of 8 from 5-Cl was quenched with piperylene, whereas that of the allylic chlorides was not. Quantum yields of products and singlet lifetimes in the three solvents were measured. The solvent effects are discussed. Deuterium-labeling results on the formation of 5-Cl from 2-Cl and of 8 from 5-Cl are reported.
    Additional Material: 1 Tab.
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    URL: http://dx.doi.org/10.1002/poc.610040904
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    Methyl substituent effects on the dissociation energies of Si—X bonds (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 562-565 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Empirical expressions are obtained for bond dissociation energies (BDEs) of alkylsilanes and their derivatives. It is pointed out that the sensitivity of the BDEs of Si—X bonds to methyl substitution depends on the electronegativity of the substituent X. When X is an atom or group with low or moderate electronegativity, the Si—X BDE is insensitive to methyl substitution, but when X is a halogen atom or OH, the Si—X BDEs increase with increasing methyl substitution.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040906
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  • 98
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    Kinetics and mechanism of the cleavage of phthalimide in buffers of tertiary and secondary amines. Evidence of intramolecular general acid-base catalysis in the reactions of phthalimide with secondary amines (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 547-561 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The reaction rates of the cleavage of phthalimide (PTH) were studied at 30°C in buffer solutions of trimethylamine, triethylamine, triethanolamine, carbonate, piperidine, dimethylamine, morpholine, piperazine and N-methylpiperazine at different pH values. The reactivity of carbonate, triethylamine and triethanolamine toward PTH could not be detected under the experimental conditions applied. However, triethylamine revealed nucleophilic reactivity toward non-ionized PTH (SH). The steric requirements of triethylamine and triethanolamine are ascribed to the absence of nucleophilic reactivities of these amines toward SH. Secondary amines show nucleophilic reactivity toward both SH and ionized PTH (S-). The absence of nucleophilic reactivity of trimethylamine and the presence of nucleophilic reactivity of secondary amines toward S- are attributed to the occurrence of intramolecular general acid-base catalysis due to the presence of a mobile proton at the nucleophilic site of the nucleophile. Intermolecular general base catalysis was observed in the reactions of SH with all secondary amines except piperidine and such catalysis could be detected in the reactions of S- with morpholine, piperazine and N-methylpiperazine. Nucleophilic second-order rate constants for the reactions of secondary amines with SH (k1) and S- (k2) reveal the Brønsted plots of slopes of ca 0.8 and 0.3, respectively. Similarly, the general base-catalysed third-order rate constants (k4) for the reactions of secondary amines with SH yield a Brønsted plot of slope 1.2. These observations suggest the occurrence of diffusion-controlled trapping stepwise and pre-association stepwise mechanisms in the aminolysis of non-ionized and ionized phthalimide, respectively.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040905
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  • 99
    Electronic Resource
    Electronic Resource
    Multiplicities of π-ylide ground states: Computational evidence for a breakdown of aromaticity arguments (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 566-572 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: AM1 and 3-21G computations, on the lowest singlet state of selected π-ylides, support the earlier conclusion that π-ylides are highly polar with highly reactive side-chains. The computations also indicate that the corresponding triplet states are lower in energy and have substantially reduced polarity. Contrary to the expectations derived from Hückel calculations, AM1 and 3-21G calculations suggest that the best π-ylide structures have non-aromatic rings. The heats of isomerization contradict earlier conclusions reached using topological resonance energies. π-Ylides are expected to afford different product structures depending on the electronic state of the π-ylide involved in a given cycloaddition reaction.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040907
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  • 100
    Electronic Resource
    Electronic Resource
    Protein immobilization by aminolysis of cellulose xanthate esters (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 573-578 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: P-Nitrobenzyl cellulose xanthate (CelXNB) was obtained with a degree of substitution (DS) in the range 0.5-3. The first order rate constant for hydrolysis of CelXNB at 25°C, extrapolated to zero buffer concentration, is hydroxide ion catalysed, whereas the water-catalyed path is about 2000 times faster than that observed for p-nitrobenzyl ethylxanthate (EXNB), probably owing to the highly ordered cybotactic region of cellulose. Aminolysis of CelXNB produces the corresponding thioncarbamate ester; for simple alkylamines, the second-order rate constants are similar to those obtained for EXNB. The secod-order rate constants are similar to those obtained for EXNB. The second-order rate constants at pH 11 for immobilization of bacterial α-amylase and bovine serum albumin were 13.4 and 112 1 mol-1 s-1, respectively, unexpectedly high values when compared with simple alkylamines, even considering the concentration of external reactive groups of the proteins. CelXNB with low DS should release 1 mol of p-nitro-α-toluenethiol for every mole of protein that becomes immobilized. The net weight increase of the cellulose matrix allows the calculation of the absolute molecular weight of the protein. Preliminary results support this assumption.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040908
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