Isotopic exchange in heterocyclic quaternary salts. II. (1) Hydrogen‐deuterium exchange ln active c‐methyl groups

Abstract The non‐catalysed H‐D exchange in heterocyclic quaternary ammonium salts (1–3) was studied by 1 H‐nmr. Exchange occurs only at the C‐CH 3 group, at a rate decreasing in the order X = C(CH 3 ) 2 , Se, CH=CH, S, NCH 3 . In substituted benzothiazolium salts the exchange rates decrease in the series Y = NO 2 , Cl, H, OCH 3 . Chemical shifts (δ) of C‐CH 3 and N‐CH 3 groups decrease in the same sequence. Both exchange rate constants and chemical shifts can be related ta Hammett σp‐ values of the Y substituents. The mechanism p of the exchange reaction is briefly discussed.