Relations structure-reactivity and the positive steric effects of ortho substituents in arenesulfonyl chlorides

This work aims to unravel the origin of the positive ortho-effect in solvolysis reactions of hindered arenesulfonyl chlorides. The alcoholysis in methanol, ethanol,  propanol and iso-propanol, at 313 K, of hindered X-ArSO₂Cl (X=4-Me; 4-Br-; H-; 2,4,6‑Me₃-; 2,6‑Me₂‑4-t-Bu-; 2,3,5,6-Me₄-; 2,4,6‑Me₃-3-NO₂-; 2,4,6-i-Pr₃-) was investigated. X-ray analysis was carried out in solid crystals of hindered arenesulfonyl chlorides and arenesulfonates. The hypothesis of C-H···O intramolecular interactions in these compounds was discussed. A S_N2‑like transition state, with nucleophilic assistance of a second alcohol molecule was proposed. Empirical data support the change from nucleophile’s backside attack to frontal attack when moving from unhindered compounds to ortho‑alkyl substituted.