On the nitration of 2‐benzylthiophene and the spectroscopic behaviour of nitro‐2‐benzylthiophenes

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Abstract
Nitration of 2‐benzylthiophene with nitric acid (molar ratio 1:1) in acetic anhydride gave only nitro‐2‐benzylthiophenes, indicating the benzene ring is unreactive to this electrophilic substitution. The main reaction product was 2‐benzyl‐5‐nitrothiophene (about 87%) the amounts of the 3‐nitro and 4‐nitro isomers were about 10% and 3%, respectively. These percentages, determined by glc and nmr techniques, were found to be constant using various nitration conditions. The syntheses of the nitro‐2‐benzylthiophenes are described, together with some spectroscopic properties.The uv spectra confirm that the conjugation of the nitro group in the α position is greater than in the β position. The isomer structures have been assigned by nmr chemical shifts and coupling constant of the thiophene protons. Also infrared spectra are briefly considered.