AbstractIn 7‐benzyl‐6‐mercaptopurine the benzylic methylene resonates at a lower magnetic field compared to other N‐benzyl groups and can be easily characterized. This deshielding effect is attributed to the magnetic anisotropy of the carbon6‐sulphur bond. In trifluoroacetic acid a slow proton‐exchange is observed for 1‐and 3‐benzyl‐6‐mercaptopurines but not f