THE ELUSIVE ANTIAROMATICITY OF MALEIMIDES AND MALEIC-ANHYDRIDE - ENTHALPIES OF FORMATION OF N-METHYLMALEIMIDE, N-METHYLSUCCINIMIDE, N-METHYLPHTHALIMIDE, AND N-BENZOYL-N-METHYLBENZAMIDE

In order to understand the antiaromaticity of maleimides, the enthalpi es of formation and sublimation of N-methylmaleimide, N-methylsuccinim ide, N-methylphthalimide, and N-benzoyl-N-methylbenzamide were measure d. The numerical values of enthalpies of formation for these compounds in the solid state are -329.3 +/- 1.4, -469.8 +/- 1.6, -325.0 +/- 2.1 , and -239.6 +/- 3.8 kJ mol(-1), respectively, while the corresponding values in the gaseous state are -256.0 +/- 1.5, -389.7 +/- 1.6, -233. 9 +/- 2.2, and -119.5 +/- 3.8 kJ mol(-1), respectively. The values of enthalpies of sublimation for the same compounds are 73.3 +/- 0.5, 80. 1 +/- 0.3, 91.1 +/- 0.5, and 120.1 +/- 0.4 kJ mol(-1), respectively. W e find that the antiaromaticity of maleimides is only modest.