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Pyramidal inversion mechanism of simple chiral and achiral sulfoxides: A theoretical study
Author(s) -
Marom Hili,
Biedermann P. Ulrich,
Agranat Israel
Publication year - 2007
Publication title -
chirality
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.43
H-Index - 77
eISSN - 1520-636X
pISSN - 0899-0042
DOI - 10.1002/chir.20417
Subject(s) - chemistry , racemization , sulfoxide , substituent , computational chemistry , chirality (physics) , inversion (geology) , molecule , crystallography , stereochemistry , organic chemistry , quantum mechanics , chiral symmetry breaking , physics , nambu–jona lasinio model , quark , paleontology , structural basin , biology
The pyramidal inversion mechanism of simple sulfoxides was studied, employing ab initio and DFT methods. The convergence of the geometrical and energetic parameters of H 2 SO and DMSO with respect to the Hamiltonian and basis set was analyzed in order to determine a computational level suitable for methyl phenyl sulfoxide ( 3 ), methyl 4‐cyanophenyl sulfoxide ( 4 ), diphenyl sulfoxide ( 5 ), 4,4′‐dicyanodiphenyl sulfoxide ( 6 ), benzyl methyl sulfoxide ( 7 ) and benzyl phenyl sulfoxide ( 8 ). The DFT B3LYP/6‐311G(d,p) level was chosen for further calculations of larger sulfoxides. The barriers Δ E ‡ calculated for the pyramidal inversion mechanism of sulfoxides 3 – 8 are in the range of 38.7–47.1 kcal/mol. These values are in good agreement with the experimental barriers for racemization via the pyramidal inversion mechanism. A resonance effect of a phenyl ring selectively stabilizes the transition state conformations, decreasing the energy barrier for pyramidal inversion by about 3 kcal/mol, compared to a similar molecule without a phenyl substituent. Introducing electron withdrawing groups (cyano) at the para positions of the phenyl ring(s) causes a further decrease of the energy barrier. Chirality, 2007. © 2007 Wiley‐Liss, Inc.