Structure and Dynamic Behavior of Crowded Cis Vicinal [(N,N-Dimethylamino)cyclopentyl]trimethylammonium Salts and Related Compounds
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- 作者：Gideon Fraenkel ; Sharon Boyd ; Albert Chow ; and Judith Gallucci
- 刊名：Journal of the American Chemical Society
- 出版年：1996
- 出版时间：December 18, 1996
- 年：1996
- 卷：118
- 期：50
- 页码：12804 - 12811
- 全文大小：262K
- 年卷期：v.118,no.50(December 18, 1996)
- ISSN：1520-5126
文摘
Carbon-13 NMR spectra of[cis-2-(N,N-dimethylamino)cyclopentyl]trimethylammoniumiodide (4a) andtriflate (4b) in acetone-d6 and inCD3NO2 show inversion of the amine withrotation about the ring-N bond to beunusually slow with 
H
andS (4b inacetone-d6) of 17 kcal/mol and 14 eu, similar tothe values for cis-2-tert-butyl-1-(N,N-dimethylamino)cyclopentane(3) in Et2O-d10 of 16kcal/mol and 17 eu, indicating that steric and notelectrostatic interactions are responsible for the slow rates. Inaddition, the N+ methyls of 4a and4b, which aremagnetically nonequivalent by 13C NMR at low temperatures,undergo signal averaging with increasing temperature,the result of rotation dynamics around the ring-N+bonds giving for 4b in acetone-d6H and S,respectively,of 7.2 kcal/mol and -9 eu. Similar values are found fortert-butyl rotation in 3 inEt2O-d10. Around roomtemperaturefor 4a and 4b,1J(14N,13C) is resolvedand found to be ca. 3.6 Hz. With decreasing temperature, thiscoupling isaveraged by progressively faster 14N electric quadrupoleinduced relaxation. Line shape analysis of the 13CNMRspectra shows Ea for the correlation time to be2-2.7 kcal/mol. X-ray crystallography of 4b and(cis-2-tert-butylcyclopentyl)trimethylammonium triflate (7) showsthe rings to adopt the half-chair structure with vicinalsubstituents located at the puckered carbons. In 4b,the N+Me3 group is pseudoequatorial withthe NMe2 grouppseudoaxial; whereas, in 7, the tert-butyl groupis pseudoequatorial with the N+Me3 grouppseudoaxial. Interestingcorrelations are noted of 13C NMR shifts of individualmethyls with their crystallographic structuralassignments.
H andS (4b inacetone-d6) of 17 kcal/mol and 14 eu, similar tothe values for cis-2-tert-butyl-1-(N,N-dimethylamino)cyclopentane(3) in Et2O-d10 of 16kcal/mol and 17 eu, indicating that steric and notelectrostatic interactions are responsible for the slow rates. Inaddition, the N+ methyls of 4a and4b, which aremagnetically nonequivalent by 13C NMR at low temperatures,undergo signal averaging with increasing temperature,the result of rotation dynamics around the ring-N+bonds giving for 4b in acetone-d6H and S,respectively,of 7.2 kcal/mol and -9 eu. Similar values are found fortert-butyl rotation in 3 inEt2O-d10. Around roomtemperaturefor 4a and 4b,1J(14N,13C) is resolvedand found to be ca. 3.6 Hz. With decreasing temperature, thiscoupling isaveraged by progressively faster 14N electric quadrupoleinduced relaxation. Line shape analysis of the 13CNMRspectra shows Ea for the correlation time to be2-2.7 kcal/mol. X-ray crystallography of 4b and(cis-2-tert-butylcyclopentyl)trimethylammonium triflate (7) showsthe rings to adopt the half-chair structure with vicinalsubstituents located at the puckered carbons. In 4b,the N+Me3 group is pseudoequatorial withthe NMe2 grouppseudoaxial; whereas, in 7, the tert-butyl groupis pseudoequatorial with the N+Me3 grouppseudoaxial. Interestingcorrelations are noted of 13C NMR shifts of individualmethyls with their crystallographic structuralassignments.