Library

X
feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    Electronic Resource
    Electronic Resource
    Geminale Substituenteneffekte. VIII.VII. Mitt. K. Rakus, S. P. Verevkin, H.-D. Beckhaus, C. Rüchardt, Chem. Ber., 127 (1994) 2225. Standardbildungsenthalpien von Acetalen (1995)
    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 337 (1995), S. 93-98 
    Details
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Geminal Substituent Effects. VIII. Enthalpies of Formation of AcetalsThe standard enthalpies of combustion ΔHc° (1 or c) of the α-phenyl-substituted acetals (1) and diacetals (2) were measured calorimetrically. The enthalpies of vaporisation or sublimation ΔHvap or ΔHsub of 1-2 were obtained from the temperature function of the vapor pressure measured in a flow system, and the standard enthalpies of formation are obtained thereof: ΔH°f (1 or c) and ΔHf° (g) (in kJ mol-1) for 1a = -308.40 ± 0.52(1), -248.94 ± 0.88; 1b = -343.48 ± 0.72 (1), -288.5 ± 1.5; 1c = -267.4 ± 1.3 (1), -205.3 ± 1.3; 1d = -343.8 ± 2.1 (c), -261.9 ± 2.2; 1e = -397.02 ± 0.86 (c), -311.3 ± 1.2; 1f = -414.52 ± 0.80 (1), -350.68 ± 0.86; 2a = -564.8 ± 2.4 (c), -467.1 ± 2.5; 2b = -547.6 ± 1.6 (c), -414.9 ± 2.7; 2c = -717.1 ± 7.5 (c), -587.0 ± 8.0. The results are combined into values of two strain free group increments CH[20, CPh] = -59.7 and C[20, CPh, C] = -71.3 kJ mol-1; and compared to the aliphatic series of acetals.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prac.19953370122
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 2
    Electronic Resource
    Electronic Resource
    Substituenteneffekte auf die C—C-Bindungsstärke, 16. Thermische Stabilität und Bildungsenthalpie von β-Dicarbonylverbindungen.  -  Stabilisierung von α,α′-Diketoalkyl-Radikalen (1995)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1995 (1995), S. 41-51 
    Details
    ISSN: 0947-3440
    Keywords: Enthalpies of formation ; Geminal substituents, energetic interaction of ; Bond cleavage, C—C, kinetics of ; Radicals, stability of ; Increments, thermochemical ; Bond strength, substituent effects on ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Substituent Effects on the CC Bond Strength, 16.  -  Thermal Stability and Enthalpies of Formation of β-Dicarbonyl Compounds.  -  Stabilisation Enthalpies of α,α′-Diketoalkyl RadicalsThe geminal interactions of the two carbonyl groups in seven β-diketones of the type 8-9 and 11-13 were estimated from their enthalpies of formation, which were deduced from their heats of combustion and enthalpies of vaporization. The radical stabilisation enthalpies RSE of the α,α′-diketoalkyl radicals 9-13 were obtained from the enthalpies of activation ΔH≠ of thermal CC bond cleavage of eight model compounds of the type 9-13 by their comparison with ΔH≠ of comparable hydrocarbons of similar strain. For non-cyclic α,α′-diacyl-alkyl radicals and six-membered cyclic ones RSE = 54.8 ± 1.3 kJ mol-1 was determined, which indicates an additive stabilisation by two carbonyl groups.
    Additional Material: 11 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199519950108
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 3
    Electronic Resource
    Electronic Resource
    Substituent effects on the CC bond strength, 18Part 17: Ref.. Stabilization of alkyl radicals by 4-pyridyl, 1-naphthyl or 2-naphthyl substituents in α-positionDedicated to Professor Manfred Schulz on the occasion of his 65th birthday. (1995)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1995 (1995), S. 881-884 
    Details
    ISSN: 0947-3440
    Keywords: Bond cleavage, C—C, kinetics of ; Radicals, stability of ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The formation of the α-substituted radicals 7-9 with the 4-pyridyl (7), 1-naphthyl (8), and the 2-naphthyl (9) substituent by thermolysis of their dimers 1-3 in solution was investigated. The activation parameters of the homolysis of the central CC bond were obtained from kinetic measurements of the thermal cleavage of 1-3 in the presence of radical scavengers. These data were compared with those obtained from the thermolysis of alkanes which cleave into α-alkyl branched radicals, and which lose the same amount of strain during the dissociation. The „strain-free“ radical stabilization enthalpies of the α-substituted radicals [RSE = 7.9 ± 1.8 (7), 12.0 ± 1.4 (8), and 8.7 ± 1.9 kcal/mol (9)] were obtained in this way.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.1995199505128
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 4
    Electronic Resource
    Electronic Resource
    Geminal substituent effects, 11. The anomeric effect in orthoesters  -  the concept of geminal pairwise interactions for the interpretation of standard enthalpies of formationDedicated to Professor Rolf Huisgen on the occasion of his 75th birthday. (1995)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1995 (1995), S. 2059-2067 
    Details
    ISSN: 0947-3440
    Keywords: Anomeric effect ; Enthalpies of formation ; Geminal substituents, energetic interaction of ; Increments, thermochemical, of orthoesters ; Group increments, interpretation of ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: New enthalpies of formation ΔHf^(g) are provided for the series of orthoesters 2a-2f, 3 and 4 from their enthalpies of combustion ΔHc^ and their enthalpies of vaporization ΔHvap^ or enthalpies of sublimation ΔHsub^. From these data and from literature data the following new thermochemical increments were calculated [kJ · mol-1]: CH[O3] - 106.4, C[O3, C] -103.7, and C[O3, Ph] -124.5. In addition the increment C[O4] - 167.1 was calculated from literature data for ΔHf^(g) of the orthocarbonates 9a and 9b. The anomeric stabilization derived from these results and from previous results for acetals and ketals are reported in Table 3. - A new concept of additive structural increments for the quantitative analysis of the group increments of hydrocarbons, ethers, acetals, and ketals is proposed. It is shown that the increments for CH3, CH2, CH, and C groups with their different neighboring atoms (see Table 4) are determined by the number of hydrogen atoms in the group and by the number of pairwise geminal interactions between all atoms attached to the central carbon atom. - Using this procedure for orthoesters and orthocarbonates, deviations from additivity for the geminal interaction between oxygen atoms, i.e. the anomeric effect, are observed.
    Additional Material: 10 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.1995199512291
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 5
    Electronic Resource
    Electronic Resource
    Thermolabile hydrocarbons, 34. Part 33: Ref.[1a].. Kinetics of the generation of 1,3-di-tert-butylallyl radicals by thermal CC bond cleavage reactions (1995)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1995 (1995), S. 515-522 
    Details
    ISSN: 0947-3440
    Keywords: Bond cleavage, C-C, kinetics of ; Allyl radicals, stability of ; Calculations, molecular mechanics ; Enthalpies of formation ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The title radicals were generated by thermal decomposition of (E,E)-meso- and (E,E)-(±)-5,6-di-tert-butyl-2,2,9,9-tetramethyl-3,7-decadiene (4a, b), (E)-5-(1,1-dimethylethyl)-2,2,6-trimethyl-6-phenyl-3-heptene (6), and (E)-5-(diphenyl-methyl)-2,2,6,6-tetramethyl-3-heptene (7). The activation parameters of these reactions were calculated from the rate constants which were followed over a 40°C temperature range. The enthalpies of formation of 4a, b were determined from the enthalpies of combustion and enthalpies of vaporization, those of 6 and 7 by MM2 calculation. From these data and their comparison with those of comparable saturated hydrocarbons of similar strain the radical stabilization enthalpy of the title radical RSE = 11.4 ± 1.5 kcal/mol was determined, which is in good agreement with results obtained from other model compounds (12.6 kcal/mol) previously.
    Additional Material: 8 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199519950371
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 6
    Electronic Resource
    Electronic Resource
    Bimolecular Formation of Radicals by Hydrogen Transfer, 13.Part 12; Ref. Uncatalyzed Transfer Hydrogenation of Azulene and the Initiation of the Azulene-Naphthalene Rearrangement (1997)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 2055-2063 
    Details
    ISSN: 0947-3440
    Keywords: Retrodisproportionation ; Molecule-induced radical formation ; Semiempirical calculations ; Hydrogen transfer ; Rearrangements ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: From the uncatalyzed transfer-hydrogenation of azulene 1 with the hydrogen donors 9,10-dihydroanthracene (4), 7H-benz[de]anthracene (5) and 9,9-diphenyl-10,10-dideuteroanthracene (6) at 340-375°C in diphenyl ether, two isomeric octahydroazulenes and, in addition, naphthalene and tetralin are obtained. From product studies, kinetics, isotopic labelling experiments and semiempirical MO calculations, a nonchain stepwise radical mechanism is proposed, which is initiated by H-atom transfer from the donor to azulene. The proposed mechanism for the formation of naphthalene and tetralin via azulene-naphthalene rearrangement under these conditions is a combination of the Scott mechanism and the Alder “walk” mechanism, which are initiated by the hydrogen-transfer step.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199719971008
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 7
    Electronic Resource
    Electronic Resource
    Anwendung von Kraftfeldrechungen, IV. Ein Kraftfeld für die Berechnung von Struktur und Bildungsenthalpie von Alkylbenzolen und sein Verläßlichkeitstest an hochgespannten Diphenylethanen (1983)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 116 (1983), S. 86-96 
    Details
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Application of Force Field Calculations, IV. A Force Field for the Calculation of the Structures and Heats of Formation of Alkylbenzenes and its Test of Reliability on Highly Strained DiphenylethanesAllinger's force field MM26) was expanded to the calculation of the molecular structures and heats of formation of alkylated benzenes by additional parameters. Calculations on highly congested diphenylethanes were performed. These compounds are distinguished by long C—C-bonds, by large bond angle deformations and by high strain enthalpies (up to 45 kcal · mol-1). The excellent agreement between calculational results and experimentally determined data proves high reliability of the extended force field. - Furthermore strain-free increments for phenyl groups are given to put the strain enthalpies of phenyl and alkyl groups on the same scale.
    Notes: Zur Berechnung von Struktur und Bildungsenthalpie von Alkylbenzolen wurde das Kraftfeld MM2 von Allinger6) mit Parametern ergänzt. Testrechnungen wurden durchgeführt an hochverzweigten Diphenylethanen, die sich auszeichnen durch stark gedehnte C—C-Bindungen, aufgeweitete Bindungswinkel und hohe Spannungsenthalpien (bis zu 45 kcal · mol-1). Die ausgezeichnete Übereinstimmung der Rechenergebnisse mit experimentellen Daten belegt die hohe Verläßlichkeit des erweiterten Kraftfeldes. - Außerdem wurden spannungsfreie Inkremente für Phenylgruppen angegeben, um die Spannungsenthalpie einheitlich für Alkyl- und Phenylgruppen angeben zu können.
    Additional Material: 8 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19831160110
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 8
    Electronic Resource
    Electronic Resource
    Substituenteneffekte auf die C—C-Bindungsstärke, 1. Struktur und Spannungsenthalpie tetrasubstituierter Bernsteinsäuredinitrile (1983)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 116 (1983), S. 1017-1041 
    Details
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Substituent Effects on the C—C-Bond Strength, 1. Structure and Strain Enthalpy of Tetrasubstituted SuccinonitrilesEleven Succinonitriles, tetrasubstituted by alkyl or aryl groups, were prepared, partially as pure meso- and DL-diastereomers. For four of them standard heats of formation ΔHfo and strain enthalpies Hsp were determined from heats of combustion. Their values were used together with data from the literature to deduce the CN-base value required for the computation of heats of formation ΔHfo of nitriles and dinitriles with Allinger's MM2 force field. In addition rotational barriers, conformational equilibria, dipole moments and structures were determined by force field calculations. The agreement with experimental data as e. g. the X-ray structures of 7d und 7g was good. The relationships between strain and structure are discussed.
    Notes: Elf durch Alkyl- oder Arylgruppen tetrasubstituierte Bernsteinsäuredinitrile wurden, teilweise als meso- und DL-Diastereomere, dargestellt. Durch Verbrennungskalorimetrie wurden von vier Bernsteinsäuredinitrilen Bildungsenthalpien ΔHfo und Spannungsenthalpien Hsp bestimmt, die es, zusammen mit Literatur-Werten ermöglichten, das Kraftfeld MM2 zur Berechnung der Bildungswärmen ΔHfo von Nitrilen und Dinitrilen zu parametrisieren. Mit dem Kraftfeld wurden zusätzlich Rotationsbarrieren, Konformationsgleichgewichte, Dipolmomente und Strukturen berechnet. Die Übereinstimmung mit experimentellen Werten, u.a. den Röntgenstrukturanalysen der Dinitrile 7d und 7g, ist gut. Die Zusammenhänge zwischen Strukturparametern und Spannungsenthalpien werden diskutiert.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19831160319
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 9
    Electronic Resource
    Electronic Resource
    Substituenteneffekte auf die C—C-Bindungsstärke, 2. Die thermische Stabilität tetrasubstituierter Bernsteinsäuredinitrile (1983)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 116 (1983), S. 1042-1057 
    Details
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Substituent Effects on the C—C-Bond Strength, 2. The Thermal Stability of Tetrasubstituted SuccinonitrilesRate constants and activation parameters for the thermolysis reaction of ten, partly cyclic tetraal-kylsuccinonitriles and of meso-2,3-dimethyl-2,3-diphenylsuccinonitrile were determined. Relationships between ΔG≠ (300°C), ΔH≠ and ΔS≠ of the thermolysis reaction on the one hand and the change in strain enthalpy during bond dissociation on the other are pointed out. A force field procedure for the estimation of the strain in α-cyanoalkyl radicals is presented. A quantitative separation of the steric and resonance effects responsible for the thermal dissociation process was achieved successfully. A resonance energy of 5.3 kcal · mol-1 was deduced for tertiary α-cyanoalkyl radicals in agreement with the most recent literature data.
    Notes: Die Zerfallskonstanten und Aktivierungsparameter der Thermolyse von zehn, teilweise cyclischen Tetraalkylbernsteinsäuredinitrilen und von meso-2,3-Dimethyl-2,3-diphenylbernsteinsäuredinitril wurden bestimmt. Die Beziehungen zwischen ΔG≠ (300°C), ΔH≠ und ΔS≠ der Thermolyse einerseits und der Änderung der Spannungsenthalpie im Dissoziationsprozeß andererseits werden aufgezeigt. Ein Kraftfeldverfahren zur Abschätzung der Spannungsenthalpie von α-Cyanalkylradikalen wird beschrieben. Es ist gelungen, die für die Triebkraft der Dissoziation der Bernsteinsäuredinitrile verantwortlichen sterischen Effekte von den Resonanzeffekten der Radikale quantitativ zu separieren. Für die Resonanzenergie tert. α-Cyanalkylradikale ergibt sich der Wert 5.3 kcal · mol-1 in Übereinstimmung mit den neuesten Lit.-Daten.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19831160320
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 10
    Electronic Resource
    Electronic Resource
    Thermolabile Kohlenwasserstoffe, XXV1). Zusammenhänge zwischen thermischer Stabilität, Spannung und Struktur von 1,1′-Diphenyl-1,1′-bicycloalkylen (1984)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 117 (1984), S. 3303-3319 
    Details
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Thermolabile Hydrocarbons, XXV1). Relationships between Thermal Stability, Strain, and Structure of 1,1′-Diphenyl-1,1′-bicycloalkylsThe products and activation parameters of the thermolysis reaction of the title hydrocarbons 1a (n = 4-8) and 1b (n = 12) were determined. Strain enthalpies and structural data of the compounds 1a and of the radicals 2a, which are generated on thermolysis, were obtained from force field calculations. For 1a (n = 8) a crystal structure analysis was carried out.  -  The importance of i-strain action is estimated from the relationship between ΔG≠ of the thermolysis reaction and the strain enthalpy of 1 from which the ring strain of the corresponding cycloalkane was substracted as a correction factor. In addition, a linear correlation between ΔG≠ and the change in strain enthalpy (MM2 results) in the course of the dissociation process was found. The large variation in ΔS≠ can be rationalized by consideration of the change in internal mobility (MM2 results) during the dissociation process.
    Notes: Die Produkte und Aktivierungsparameter der Thermolyse der Kohlenwasserstoffe 1a (n = 4-8) und 1b (n = 12) wurden bestimmt. Die Spannungsenthalpien und Strukturdaten der Verbindungen 1a und der beim thermischen Zerfall entstehenden Radikale 2a wurden durch Kraftfeldberechnungen ermittelt. Für 1a (n = 8) wurde eine Kristallstrukturanalyse durchgeführt.  -  Die Beziehungen zwischen ΔG≠ der Thermolyse und den um die Ringspannung korrigierten Spannungsenthalpien gestatten eine quantitative Analyse der i-strain-Wirkung. Außerdem wird eine lineare Korrelation zwischen ΔG≠ und der Änderung an Spannungsenthalpie im Dissoziationsprozess nach Kraftfeldrechnungen aufgezeigt. Stark unterschiedliche Aktivierungsentropien werden durch die Änderung der inneren Beweglichkeit im Zuge des Dissoziationsprozesses, die aus Kraftfeldrechnungen abschätzbar ist, verständlich.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19841171115
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...