33S and 17O NMR of compounds containing the S02 moiety. A generalization of the 'chlorine effect'

33S and 17O chemical shifts of substrates CH3SO2Y for Y = Br, I, SeC6H4 and p-CH3C6H4SO2Y for Y = F, Cl, Br, I are reported. Evidence is provided for the existence of n → σ ∗ conjugative interactions between the oxygen lone-pair molecular orbitals of the sulfonyl group and the vacant σ ∗ (S-Y) MO. The trend of oxygen chemical shifts is rationalized in terms of conjugative interactions and electronegativity effects which may operate in the same or in opposite directions.