The rotational angle dependence of 5JmH,SH in benzenethiol
It is suggested that the five-bond spin–spin coupling constant between the sulfhydryl proton and the ring proton in the meta position is given by [Formula: see text]. Here θ is the angle by which the S—H bond twists out of the benzene plane and angular brackets indicate expectation or average values, determined by the twofold barrier to internal rotation about the C—S bond. [Formula: see text] is the π electron contribution and has a maximum at θ = 90° and [Formula: see text] is the σ electron contribution with a maximum at θ = 180° (zig-zag orientation). For eight para substituted derivatives of benzenethiol, the 5J numbers can be reproduced by this equation, which also agrees with the observed couplings in 2-hydroxybenzenethiol. In this compound θ lies near 90°. It appears that this approach will allow an extension of the J method to the evaluation of two-term potential functions in, for example, ortho substituted benzene derivatives.