AN AB-INITIO QUANTUM-CHEMICAL STUDY ON THE STRUCTURE, STABILITY AND POLYMERIZATION OF C-28 AND ITS DERIVATIVES

STO-3G calculated reaction energies of the radical reactions producing C28Hn (n = 1, 2, 3, 4) from the unstable C-28 are used to discuss the stabilization of these derivatives. The influence of the nature of va rious groups X (X is F, OH, NH2, Cl, CH3, iPr, CN, CF3 and tBu) on the stabilization of C-28 is investigated using the isodesmic reactions i n which one or more hydrogens of C28H4 are substituted by X. In genera l, all our calculations predict that C-28 is stabilized by the additio n of hard monovalent atoms (or groups) such as H and F on the four dan gling bonds. When applying the Hard and Soft Acids and Bases (HSAB) pr inciple to these isodesmic reactions, C28H3 is predicted to be harder than CH3. The stability of C28H3 and the localization of its unpaired electron suggest that this molecule may be used as a monomer in a radi cal polymerization. The stability analysis of the dimer, trimer, tetra mer and pentamer (in linear or branched form) shows that these molecul es are stable with strong C-28-C-28 bonds. (C) 1997 Elsevier Science B .V.