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Setting Limits on Supersymmetry Using Simplified Models
Published on: November 15, 2013
Karplus Equation for (3)JHH Spin-Spin Couplings with Unusual (3)J(180°) < (3)J(0°) Relationship
R H Contreras1, R Suardíaz1, C Pérez1
1Departamento de Física, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires and CONICET, Buenos Aires, Argentina, Departamento de Química Física, Facultad de Química, Universidad de la Habana, La Habana 10400, Cuba, and Departamento de Química Física Aplicada, Facultad de Ciencias, Universidad Autónoma de Madrid, 28049 Madrid, Spain.
Abstract:
Vicinal (3)JHH coupling constants for monosubstituted ethane molecules present the unusual relationship (3)JHH (180°) < (3)JHH (0°) when the substituent contains bonding and antibonding orbitals with strong hyperconjugative interactions involving bond and antibond orbitals of the ethane fragment. This anomalous behavior is studied as a function of the substituent rotation for three model systems (propanal, thiopropanal, and 1-butene) at the B3LYP/TZVP level. The consistency of this level of theory to study this problem is previously established using different ab initio methods and larger basis sets. The origin of the unusual (3)JHH(180°) - (3)JHH(0°) relationship is attributed to simultaneous σ/π hyperconjugative interactions σCα-Hα → π*Cc═X, and σCα-Cβ → π*Cc═X. These interactions depend on the substituent rotation and their effects are different for (3)JHH(180°) than for (3)JHH(0°). The modelization carried out shows an increase of those effects as the substituent changes from weaker (CH═CH2) to stronger (CH═S) electron acceptor π*C═X.
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