NMR Spectral Studies of some Six-membered and Seven-membered Saturated Hetero Cyclic Compounds: Calculation of Torsional Angles from Vicinal Coupling Constants - using Altona’s Equation and its Comparison with DAERM Method

S Rosy Christy

doi:10.17485/ijst/2014/v7sp3.14

Abstract

Some six and seven membered saturated hetero cyclic compounds were prepared; from their vicinal coupling constants, proton - proton Torsional angles were calculated using Altona's Equation. 1H NMR spectra were recorded in DMSO - d6. The chemical shifts were compared with those in CDCl3. The COSY, NOESY and 13C-1H correlation spectra had been recorded to assign the signals unambiguously. Thereafter, torsional angles were calculated using electronegativity values of the substituents; the electronegativity value of oxygen was taken to be 3.50. Calculations were made accurately.

Highlights

Some six and seven membered saturated hetero cyclic compounds were prepared; from their vicinal coupling constants, proton - proton Torsional angles were calculated using Altona’s Equation. 1H NMR spectra were recorded in DMSO - d6
Ever since Barton pointed out the importance of conformational analysis, there has been a rapid development in the conformational analysis of various systems
Nuclear magnetic resonance spectroscopy is a powerful tool for such analysis. 1H, 13C, 15N, 17O and 33S are the nuclei used for analysis1

Summary

Intoduction

Ever since Barton pointed out the importance of conformational analysis, there has been a rapid development in the conformational analysis of various systems. Diamagnetic anisotropy arises due to ring currents and affects the chemical shift This can cause either shielding or deshielding of a proton. The introduction of a vicinal axial substituent causes the resonance of an equatorial proton to move upfield by 0.1–0.3 ppm (Type A) and the resonance of an axial proton to move downfield by about 0.ppm (Type B). The effect of an equatorial methyl group on the resonance of an axial proton on the adjacent carbon has been calculated to be about 0.4 ppm by comparing the chemical shifts of carbinol protons of Trans 2 - Methylcyclohexanes [4] and Trans 4 - t-butylcyclohexanol [5]. It is seen that the effect of a substituent on the chemical shift of ring protons depends on its configuration. The influence of a substituent on the chemical shifts of ring protons can be used for configuration assignments

Proton - Proton Coupling Constants

Two – dimensional NMR Spectroscopy

Scope of the Present Investigation

Result and Dicussion