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.