Molecular structure of N-methylpyrrole studied by gas electron diffraction using rotational constants and liquid–crystal NMR spectroscopy

In our previous studies, a rule was formulated referring to how the internuclear distances and the bond angles in a second conformer differ from those in the most stable one. A test of this rule on 36 molecules (existing as two conformer mixtures) showed that it works well for the internuclear distances but is poor in predicting the bond angle changes. We undertook a systematic analysis of some of the molecules showing the highest angular changes using ab initio methods. It was found that the X–C–Y bond angles in systems like CH2X–YH, where Y=O, S and CH2X–YH2, where Y=N, P (X=CH3, F, Cl) can differ as much as 5.8° in different conformers and the direction of change mostly contradicts the above mentioned rule.