Conformation analysis of small molecules with PCILO methods

Abstract
The conformational potential of n‐butane, ethyl methyl ether, n‐propanol, methyl propyl ether, and 1,2‐dimethoxyethane was calculated with different PCILO algorithms as well as with ab‐initio SCF–LCAO–MO computations. Compared with ab‐initio calculations, the conformational potentials obtained by PCILO methods on the same geometries are too flat. In particular, the barrier at 0˚ (synperiplanar conformation) is much too low at the second‐ and third‐order level. This is mainly a consequence of the second‐order delocalization corrections. Since the PCILO algorithms are not capable of reproducing conformational potentials obtained from ab‐initio calculations, only qualitative predictions are possible.