How different can the bond angles be in two conformers?

In our previous studies, a rule was formulated referring to how the internu clear 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 t wo conformer mixtures) showed that it works well for the internuclear dista nces but is poor in predicting the bond angle changes. We undertook a syste matic 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 system s 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 degrees in different conformers and the directi on of change mostly contradicts the above mentioned rule. (C) 2001 Elsevier Science B.V. All rights reserved.