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Conformation and reactivity of α‐oxo‐ketenes: Ab initio and semiempirical (AM1, PM3) calculations
Author(s) -
Janoschek Rudolf,
Fabian Walter M. F.,
Kollenz Gert,
Oliver Kappe C.
Publication year - 1994
Publication title -
journal of computational chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.907
H-Index - 188
eISSN - 1096-987X
pISSN - 0192-8651
DOI - 10.1002/jcc.540150203
Subject(s) - conformational isomerism , ab initio , chemistry , ketene , computational chemistry , steric effects , molecule , ab initio quantum chemistry methods , reactivity (psychology) , stereochemistry , organic chemistry , pathology , medicine , alternative medicine
Ab initio MP2/6‐31G*//MP2/6‐31G* and semiempirical AM1 and PM3 calculations on a series of differently substituted α‐oxo‐ketenes are used to investigate E / Z ‐isomerism and rotational barriers in these molecules. Sterically crowded derivatives are found to exist solely as s‐ E conformers. The unusual stability of these derivatives thus can be attributed to their inability to adopt the s‐Z conformation required for the normal α‐oxo‐ketene reactions. With respect to structures and energies, the PM3 method (especially in the case of highly crowded molecules) is found to be less reliable than AM1. Ab initio HF/3‐21G and PM3 vibrational frequencies appear to be of sufficient accuracy for a distinction between s‐Z and s‐ E conformers. In this respect, the AM1 method appears less reliable. © 1994 by John Wiley & Sons, Inc.