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  • 1
    Digitale Medien
    Digitale Medien
    A critique on overstory/understory comparisons based on transition probability analysis of an old growth spruce-fir stand in the Appalachians (1985)
    Springer
    Plant ecology 64 (1985), S. 37-45 
    Details
    ISSN: 1573-5052
    Schlagwort(e): Abies ; Betula ; Compositional stability ; Gap phase dynamics ; Picea ; Southern Appalachians ; Transition probability analysis
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Compositional stability in forests has traditionally been evaluated by comparing understory with overstory composition. Such comparisons have generally been qualitative. Transition probability analysis has recently allowed quantitative prediction of future community states. We used transition probability analysis of an undisturbed spruce-fir forest to evaluate the sensitivity of the overstory/understory comparison to underlying assumptions. The predictions of future composition differed widely depending on understory size class used, ecological situation (gap versus forest plots), and stand descriptor (density versus frequency). Species longevities and interactions between understory and overstory species also affected the predictions. Understory data generally led to a predicted increase in importance for the most tolerant species (Abies fraseri) and the conclusion that a previous disturbance allowed the least tolerant species (Betula lutea) to become established. Inventory of stems in gaps led to a predicted increase in importance for the least tolerant species (Betula) and the conclusion that disturbance frequency was increasing in the stand. Data incorporating more detailed observations of the gap capture process led to the inference that this old growth stand was in compositional equilibrium. In this community, the species that was densest in the understory species (Abies) had the shortest lifespan and thus, the fastest canopy turnover rate. This lead to counter-intuitive behavior in the models; in some cases Abies had a 40% higher relative density in the understory than in the overstory at equilibrium.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00033452
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  • 2
    Digitale Medien
    Digitale Medien
    The Structures of [X2Y—N—YX2]+ Cations (X = F, Cl; Y = S, Se). A Comparison of X-ray and ab Initio Studies[1] (1995)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 128 (1995), S. 35-40 
    Details
    ISSN: 0009-2940
    Schlagwort(e): Selenium-nitrogen compounds ; Sulfur-nitrogen compounds ; Calculations, ab initio ; Chemistry ; Inorganic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The structures of cationic species of the series [X2Y—N—YX2]+ (X = F, Cl; Y = S, Se) have been computed ab initio using all electron treatments for first-row elements and sulfur and quasi-relativistic pseudopotentials for Se and Cl. Splitvalence basis sets with polarization and diffuse functions were employed. The MP2 results for the (non-isostructural!) cations [Cl2Se—N—SeCl2]+ (1: Cs) and [F2S—N—SF2]+ (2: C2v) are in excellent agreement with the experimental (X-ray) observations. Both structures represent local minima. A deeper minimum for either of the cations is represented by another C2v isomer which for crystal lattice energy reasons is stable in the isolated state only. The geometries of the hitherto unknown species [Cl2S—N—SCl2]+ (3) and [F2Se—N—SeF2]+ (4) have been assessed by ab initio HF calculations. In analogy to 2, cations 3 and 4 are predicted to prefer C2v symmetry. Therefore, 1 exhibits unusual structural features. According to strictly localized natural bond orbital analysis (NBO), the central nitrogen atoms in 1 and 2 possess two lone pairs of electrons (LP: one sp hybrid and one p orbital). The relatively short Se—N and S—N bond distances in 1 (1.741-1.760 Å) and 2 (1.551 Å) can best be attributed to LP(N)→s̰*(Y—X) negative hyperconjugation (1: Y = Se, X = Cl; 2: Y = S, X = F).
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/cber.19951280106
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  • 3
    Digitale Medien
    Digitale Medien
    The x-ray structure determinations and semiempirical PM3 calculations of two chloro(piperidyl)cyclotri(phosphazenes)Prior to publication the results presented in this paper were made available to the DRA (UK). (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Heteroatom Chemistry 8 (1997), S. 267-271 
    Details
    ISSN: 1042-7163
    Schlagwort(e): Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Single crystals of 2,4,6,6-tetrachloro-2,4-bis(piperid-yl)cyclotri(phosphazene) (1a) and of 2,4,6-trichloro-2,4,6-tris(piperidyl)cyclotri(phosphazene) (2a) were grown from petroleum ether solution. The structures of both compounds were determined by single-crystal X-ray diffraction analyses. Compound 1a crystallizes in the monoclinic space group P 21/n with Z = 4 and unit cell dimensions a = 9.3994(4), b = 19.204(3), c = 11.5664(4) Å, and β = 108.718(4)°. Compound 2a crystallizes in the triclinic space group P 1 with Z = 4 and unit cell dimensions a = 12.8289(2), b = 13.8856(2), c = 14.63810(10) Å, and α = 100.7621(5), β = 91.0094(2), γ = 113.9757(6)°. The experimentally obtained structural parameters for the covalent molecules 1a and 2a compare well with those calculated at the semiempirical PM3 level of theory. These results give credence to the PM3 calculated structures of 2,4,6,6-tetraazido-2,4-bis(piperidyl)cy-clotri(phosphazene) (1b) and 2,4,6-triazido-2,4,6-tris(piperidyl)cyclotri(phosphazene) (2b) for which presently there are no experimental data available. Non-SI units employed: 1 kcal≍4.184 kJ, 1 Å = 10-10 m (since these units are still used in computational chemistry, we employed them throughout this article). © 1997 John Wiley & Sons, Inc. Heteroatom Chem 8: 267-271, 1997.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
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  • 4
    Digitale Medien
    Digitale Medien
    The preparation and x-ray structure of [P(C2H5)4]+[N3]- and the attempted preparation of [PH4]+[N3]- (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Heteroatom Chemistry 9 (1998), S. 129-132 
    Details
    ISSN: 1042-7163
    Schlagwort(e): Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Tetraethylphosphonium azide, [P(C2H5)4 ]+[N3 ]-, was prepared from tetraethyl phosphonium bromide and silver azide. Single crystals of [P(C2H5)4 ]+[N3 ]- were grown from dichloromethane/THF (10:1) solution. The structure was determined by single-crystal X-ray diffraction analysis. [P(C2H5)4 ]+[N3 ]- crystallizes in the monoclinic space group C 2/c with Z = 4 and unit cell dimensions a = 12.961(6), b = 6.835(3), c = 12.378(6) Å, and β = 100.57(4)°. The attempted preparation of phosphonium azide [PH4]+[N3]- from phosphonium iodide and silver azide lead instead to the formation of PH3 and HN3. The instability of [PH4]+[N3]- with respect to PH3 and HN3 is in accord with thermodynamic considerations according to which the reaction PH3(g) and HN3(g) to yield [PH4 ]+[N3 ]- is thermodynamically unfavorable. (Non SI units employed: kcal ≈ 4.184 J, Å = 10-10 m.) © 1998 John Wiley & Sons, Inc. Heteroatom Chem 9:129-132, 1998
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
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  • 5
    Digitale Medien
    Digitale Medien
    A new synthetic route to Se2NOl3 leading to a new modification of this chloride nitride of trivalent selenium (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Heteroatom Chemistry 7 (1996), S. 195-198 
    Details
    ISSN: 1042-7163
    Schlagwort(e): Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Se2NCl3 was prepared in 58% yield by the reaction of SeCl4 with Se2[N(SiMe3)2]2. This method provides a new and convenient one-day and one-pot synthesis for the preparation of this neutral chloronitride of trivalent selenium. The low-temperature structure was determined by a single-crystal X-ray diffraction analysis. The compound crystallizes in the monoclinic space group P 21/a with Z = 4 and unit cell dimensions a = 7.605(3), b = 8.7643(20), c = 8.966(3) Å, and β = 93.23(3)°. The structure is made up of essentially planar Se2NCl3 molecules (C2v symmetry) that are packed in a coplanar fashion to form one-dimensional chains. There are strong intermolecular interactions with short intermolecular Se···Se distances of 3.82 Å, which is significantly shorter than the sum of the covalent radii (4.0 Å). This explains the golden color and the metallic luster of this compound. Se2NCl3 was first reported in 1992 by K. Delmicke et al. to form transparent red crystals (orthorhombic, space group P bca, a = 12.290(6), b = 8.046(4), c = 24.336(12) Å) without significant intermolecular interactions (Se···Se, 4.10 Å). Therefore, Se2NCl3 is polymorphic, crystallizing either in the orthorhombic or in the monoclinic system. © 1996 John Wiley & Sons, Inc.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
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  • 6
    Digitale Medien
    Digitale Medien
    Preparation and characterization of arsine derivatives: X-ray crystal structures of As (SitBuMe2)3, As (SiMe3)2(SiPh3), Et3Ga · As(SiMe3)2(SiPh3), and As(SePh)3 (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Heteroatom Chemistry 7 (1996), S. 409-416 
    Details
    ISSN: 1042-7163
    Schlagwort(e): Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: As(Si1BuMe2)3 (1) was prepared by the salt-elimination reaction between (Na/K)3As and 1BuMe2SiCl. Mixing LiAs(SiMe3)2 with Ph3SiCl (1:1) yielded As(SiMe3)2(SiPh3) (2) in a good crystalline yield. Reaction of 2 (1:1) with Et3Ga gave the expected Lewis acid-base adduct Et3Ga · As(SiMe3)2(SiPh3) (3). The 1:1 mole ratio reaction of In(SePh)3 with As(SiMe3)3 resulted in a ligand redistribution around the indium and arsenic centers to afford As(SePh)3 (4) in a low yield. The solid-state structures of 1-4 have been established by single-crystal X-ray analysis. Crystal data for 1, monoclinic space group P 21/c, with a = 11.112(2), b = 17.453(2), c = 14.199(2) Å, β = 114.89° for Z = 4; 2, orthorhombic space group P c21n, with a = 9.236(1), b = 16.612(2), c = 16.803(4) Å for Z = 4; 3, monoclinic space group P 21/c, with a = 16.799(1), b = 11.199(2), c = 19.413(3) Å, β = 112.22(1) for Z = 4; 4, trigonal space group R &3macr;, with a = 12.863(5), c = 18.96(1) Å for Z = 6. © 1996 John Wiley & Sons, Inc.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
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  • 7
    Digitale Medien
    Digitale Medien
    Conformational analysis of 2-OAryl-2-oxo-4,6-dimethyl- and -4-methyl-1,3,2λ5-dioxaphosphorinanes. Spectroscopic, X-Ray, and solid-state 13C and 31P studies (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Heteroatom Chemistry 8 (1997), S. 509-516 
    Details
    ISSN: 1042-7163
    Schlagwort(e): Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Results of IR and 1H, 13C, and 31P NMR studies of the anancomeric title compounds (2-5) and compound 1 (Scheme 1) are analyzed to search for the existence of high-energy boat or twist-boat conformations in the equatorial epimers. While the difference in frequencies (Δν)P=O between the axial and equatorial compounds and 13C NMR JPOCC and anti JPOCCH3 values suggest the participation of twist-boat conformations for the equatorial isomers, coupling constants in 1H NMR JH4H5a or JH6H5a and JH4H5e or JH6H5e of the equatorial isomers 2e-4e along with the lack of a large 3JPH in 31P NMR are consistent with predominant chair conformations. In addition, an X-ray structure of the equatorial 2-p-nitrophenoxy-2-oxo-cis-4,6-dimethyl-1,3,2-dioxaphosphorinane (4e) showed that the molecule adopts a chair conformation with no severe ring flattening in the OPO region in the solid state. X-ray structures of trans-4 and trans-5 displayed chair conformations with mild ring flattening especially in the axial methyl region, presumably as a result of the steric methyl-oxygen interaction. CPMAS 13C and 31P NMR spectra of 4a and 4e provide evidence against the presence of a significant contribution of a twist-boat conformation in solid equatorial 4e. The NMR spectral analysis of 1e, on the other hand, suggests a substantial contribution of a twist conformation as well as, possibly, some contribution of the inverted chair. © 1997 John Wiley & Sons, Inc. Heteroatom Chem 8:509-516, 1997
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
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  • 8
    Digitale Medien
    Digitale Medien
    The structure of potassium hydrogentartrate: A combined X-ray, semiempirical, and ab initio study (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Heteroatom Chemistry 9 (1998), S. 307-310 
    Details
    ISSN: 1042-7163
    Schlagwort(e): Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Single crystals of potassium hydrogentartrate, (2R,2R)-KO2C(CHOH)2CO2H, were taken from a three-year-old wine bottle. The structure was determined by low-temperature single-crystal X-ray diffraction analysis using a Siemens SMART diffractometer. (2R,2R)-KO2C(CHOH)2CO2H crystallizes in the orthorhombic space group P212121 with Z = 4 and unit cell dimensions a = 7.6065(5), b = 7.7599(5), and c = 10.6054(7) Å. The structure of an isolatedhydrogentartrate anion, (2R,2R)-[O2C(CHOH)2-CO2H]-, was calculated at the semiempirical AM1 and PM3 levels of theory with a VSTO-3G* basis set and in addition ab initio at the self-consistent level of theory using a standard 6-31G(d, p) basis set (Non-SI units employed: kcal ≈ 4.184 kJ, Å = 10-10 m).© 1998 John Wiley & Sons, Inc. Heteroatom Chem 9:307-310, 1998
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
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  • 9
    Digitale Medien
    Digitale Medien
    IodazidDiese Arbeit wurde von der NATO (T.M.K. und P.S.W., CRG 920034). dem Fonds der Chemischen Industrie, der Deutschen Forschungsgemeinschaft (KL 636/2-2) und dem Bundesminister für Bildung und Wissenschaft (Graduiertenkolleg „Synthese und Strukturaufklärung niedermolekularer Verbindungen“) gefördert. (1993)
    Weinheim : Wiley-Blackwell
    Zeitschrift für die chemische Industrie 105 (1993), S. 289-290 
    Details
    ISSN: 0044-8249
    Schlagwort(e): Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/ange.19931050228
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  • 10
    Digitale Medien
    Digitale Medien
    Synthese und Struktur der ersten Titan(IV)-α-Aminosäure-KomplexeDiese Arbeit wurde von der Deutschen Forschungsgemeinschaft, dem Fonds der Chemischen Industrie und der NATO (CRG 920034) gefördert. Wir danken Prof. Dr. J. Passmore für die Ermöglichung der Aufnahme von 14N/15N-NMR-Spektren und Herrn Dipl.-Chem. M. Kempf für die Aufnahme des DCI-Massenspektrums. Beiden Gutachtern danken wir für wertvolle Hinweise. (1994)
    Weinheim : Wiley-Blackwell
    Zeitschrift für die chemische Industrie 106 (1994), S. 1587-1589 
    Details
    ISSN: 0044-8249
    Schlagwort(e): Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/ange.19941061436
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