Heats of Formation of the Annulene Dianion and Neutral Molecule

Article abstract of DOI:10.1021/ja00539a001

The enthalpy of reaction of the disodium salt of <16>annulene with water and the heat of combustion of neutral <16>annulene were both measured calorimetrically.These measurements were utilized in a thermochemical cycle to yield the heat of reaction of sodium metal with <16>annulene to give the solid dianion salt.The enthalpy of reaction of the dianion with water (-10.9 kcal/mol) is much less exothermic than that for the dianion of <8>annulene.The results indicate that the <16>annulene dianion is greatly stabilized via aromatization.Further, its relative thermodynamic stability over that of the <8>annulene dianion has been attributed to a reduced electron-electron repulsion force in the larger annulene dianion.The combustion measurements indicate that the neutral <16>annulene does not possess any conjugative stability.The heat of combustion of <16>annulene (-2182.2 kcal/mol) is more exothermic by 9 kcal/mol than that for two <8>annulenes.