Karplus Equation for 3JHH Spin−Spin Couplings with Unusual 3J(180°) < 3J(0°) Relationship

• DOI: 10.1021/ct800145h
• Publication Date: 2008-08-14T08:01:46Z
• Authors: R. H. Contreras; R. Suardíaz; C. Pérez; R. Crespo-Otero; J. San Fabián; J. M. García de l...
• Keywords: Antibonding molecular orbital; Natural bond orbital

Vicinal (3)JHH coupling constants for monosubstituted ethane molecules present the unusual relationship (180°) < (0°) when substituent contains bonding and antibonding orbitals with strong hyperconjugative interactions involving bond antibond of fragment. This anomalous behavior is studied as a function rotation three model systems (propanal, thiopropanal, 1-butene) at B3LYP/TZVP level. The consistency this level theory to study problem previously established using different ab initio methods larger basis sets. origin (3)JHH(180°) - (3)JHH(0°) attributed simultaneous σ/π σCα-Hα → π*Cc═X, σCα-Cβ π*Cc═X. These depend on their effects are than (3)JHH(0°). modelization carried out shows an increase those changes from weaker (CH═CH2) stronger (CH═S) electron acceptor π*C═X.