BOAT FORM CONTRIBUTIONS IN CROWDED PIPERIDINES: THEORETICAL AND EXPERIMENTAL STUDY
A. Thangamani1, J. Jayabharathi2, A. Manimekalai3
1 Annamalai University
2 Annamalai University, jtchalam2005@yahoo.co.in
3 Annamalai University
Ключевые слова: N-nitroso-2,6-bis(2?-furyl)piperidines, conformations, 1H NMR, 13C NMR, semiempirical AM1 calculations
Страницы: 658-668
Аннотация
The preferred conformations of N-nitroso-t(3)-alkyl-r(2),c(6)-bis(2′-furyl)-piperidin-4-ones 1-3 [alkyl = CH3, C2H5 and CH(CH3)2] and N-nitroso-t(3),t(5)-dimethyl-r(2),c(6)-bis(2′-furyl)piperidin-4-one 4 in solutions were assigned by means of 1H and 13C NMR studies. The results derived from NMR spectra indicate the presence of an equilibrium mixture of boat conformation B1 and alternate chair conformation CA for the E isomers of 1-3 and Z isomers of 2-3. For the Z isomer of 1 boat form B2 is predicted to be the major conformer. The N-nitroso-3,5-dimethyl derivative 4 exists in the boat form B1 only. Conformational analysis performed through semiempirical molecular orbital calculations also supports the conformations for 3-4. The presence of one conformer in the equilibrium can be predicted to a reasonable accuracy by theoretical studies in 1-2. The effects due to N-nitrosation on 1H and 13C chemical shifts are also interpreted in terms of these conformations. The conformation of isopropyl group at C(3) was also predicted by spectral and theoretical studies.
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