- C-H Hyperconjugation in α-chlorocarbocations
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The lowering of Cβ-H stretching frequencies in carbocations 1a-d and 2a-c induced by hyperconjugation was tested as a possible probe for estimating the electron donating ability of α-substituents. Conclusions are based on the results of high level quantum chemical calculations confirmed with experimental FT-IR spectra. Because the decrease in the Cβ-H stretching frequency is comparable in 1b and in 1c, and in 2b and 2c respectively, it follows that α-substitution by a methyl group or by chlorine stabilizes a carbocation with almost the same effectiveness.
- Mesic, Milan,Novak, Igor,Sunko, Dionis E.,Vancik, Hrvoj
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- Molecular structure and pseudorotation of 1,1-dichlorocyclopentane as determined by gas-phase electron diffraction and ab initio calculations: A large amplitude treatment
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The molecular structure of 1,1-dichlorocyclopentane (DCICP) has been investigated by means of gas-phase electron diffraction and ab initio calculations. Although the electron diffraction data could be fairly well reproduced by a Cs (envelope) model we found it more pertinent to apply a pseudorotation model to account for the dynamic and large amplitude motion in DClCP. On the basis of this model we analyzed the dependency of the ring geometric parameters and vibrational mean amplitudes on the phase angle φ. For a better elucidation of this distinct dependency we developed particular equations which describe the dependency of the distribution of the delocalized net charges throughout the ring on the phase angle φ. The joint electron diffraction and ab initio study has led to the following ra structural parameters of DClCP (Cs conformer): r(C-Cl)ax = 1.787(3) A, r(C-Cl)eq = 1.769(3) A, average r(C-C) ring = 1.535(1) A, r(C-H)av = 1.114(5) A, ∠(C5-C1-C2) = 103.0(9)°, ∠(Cl-C-Cl) = 108.6(3)°, and ∠(H-C-H) = 104.6(26)°. The puckering amplitude for the five-membered ring was determined to be q = 0.400(11) A. The quantum mechanical calculations were carried out by utilizing the Hartree-Fock, density functional B3PW91, and perturbation MP2 methods and applying the following basis sets: cc-pVDZ, 6-31G(d,p), 6-311G(df,pd), 6-311+G(d,p), 6-311++G(d,p), 6-311+G(2df,2pd), and 6-311++G(2df,2pd). For the purpose of comparison and systematic study, we optimized the geometries and calculated the charge distributions using the natural population analysis (NPA) and Mulliken population analysis (MPA) of 1,1-difluorocyclopentane, 1,1-dibromocyclopentane, and their corresponding monohalogenated derivatives.
- Dakkouri, Marwan,Typke, Volker,Schauwecker, Tilman
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- Cobalt Catalyzed Reductive Spirocyclopropanation Reactions
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Cobalt pyridine?diimine (PDI) complexes catalyze the reductive spirocyclopropanation of terminal 1,3-dienes. gem-Dichlorocycloalkanes serve as carbene precursors and Zn is used as a terminal electron source. The reaction is effective for a range of gem-di
- Werth, Jacob,Berger, Kristen,Uyeda, Christopher
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supporting information
p. 348 - 352
(2019/11/28)
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- Chlorination of oximes in hydrogen fluoride: formation of gem-dihalogenoalkanes
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The action of chlorine on oximes in hydrogen fluoride as a medium gives gem-dihalogenoalkanes.The reaction proceeds through the intermediate formation of gem-chloronitrosoalkanes.The relative proportions between gem-dichloro, -difluoro and -fluorochloro compounds are dependent on the presence of a cosolvent.The use of other oxidants, such as nitric oxide, dinitrogen tetroxide or nitrosyl chloride, gives similar compounds: - Keywords: Chlorination, Oximes; Hydrogen fluoride; Dihalogenoalkanes; NMR spectroscopy, Mass spectrometry
- Tordeux, Marc,Boumizane, Khalid,Wakselman, Claude
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p. 207 - 214
(2007/10/02)
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