R. J. Abraham, N. Aboitiz, Marco Filippi
Jul 1, 2015
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Journal
Magnetic Resonance in Chemistry
Abstract
A refined Lanthanide‐Induced‐Shift Analysis (LISA) is used with molecular mechanics and ab initio calculations to investigate the conformations of benzamide (1), N‐methylbenzamide (2), N,N‐dimethylbenzamide (3) and the conformational equilibria of 2‐fluoro (4), 2‐chloro (5) and N‐methyl‐2‐methoxy benzamide (6). The amino group in 1 is planar in the crystal but is calculated to be pyramidal with the CO/phenyl torsional angle (ω) of 20–25°. The LISA analysis gave acceptable agreement factors (Rcryst ≤ 1%) for the ab initio geometries when ω was decreased to 0°, the other geometries were not as good. In 2, the N‐methyl is coplanar with the carbonyl group in all the geometries. Good agreement was obtained for the RHF geometries, with ω 25°, the other geometries were only acceptable with increased values of ω. In 3, good agreement for the RHF and PCModel geometries was found when ω was changed from the calculated values of 40° (RHF) and 90° (PCModel) to ca. 60°, the X‐ray and B3LYP geometries were not as good.