Directional Preferences of Approach of Nucleophiles to Sulfonium Ions

An analysis of the crystal environments of sulfonium ions shows that short nonbonded contacts (secondary bonds) to sulfur tend to occur along the extensions of the C‐S primary bonds. Non‐bonded contacts to the C ( a )‐atoms of sulfonium ions are not especially short and do not show any striking directional preference, except in sulfonium ions derived from methionine where a specific intramolecular interaction between a carboxyl O‐atom and the C (γ)‐atom may represent an incipient stage of the internal nucleophilic displacement leading to formation of homoserine and mercaptan.