Meisenheimer-type adducts from thiophene derivatives. Part 4. Reaction of sodium methoxide with 2-methoxy-5-methyl-3-nitrothiophene in methanol

Abstract

The rate and equilibrium constants for the formation of the Meisenheimer-type adduct from 2-methoxy-5-methyl-3-nitrothiophene (1a) and sodium methoxide in methanol have been measured at 20 °C. The adduct (2a) is nine times more stable and is formed about three times faster than the ‘unsubstituted’ adduct (2b), confirming the unusual role that a methyl substituent can play in reactions where it is necessary to delocalize a negative charge. 13C N.m.r. chemical shifts of (1a) and (2a) have also been determined. An interpretation of all the results is offered on the basis of polarity variation of the methyl group.