DICYANOCARBENE - TRIPLET AND SINGLET STRUCTURES AND ENERGETICS
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Dicyanocarbene, C(CN)2, is thought to have a linear triplet state as its electronic ground state. Here ab initio electronic structure theory has been used to test this hypothesis. A double basis set (with d functions on the central carbon in some cases) was employed in conjunction with one (for the 3Bi state) and two (1A1 state) configuration self-consistent-field wave functions. The predicted 3B1 structure is re(CC) =1.41 , r(CN)=1.15 , and (CCC)=133 when the CCN atoms are constrained to be collinear. Similarly for the 1A1 state, theory predicts re(CC)=1.42 A, re(CN)=1.16 , and (CCC)=115. The barriers to linearity for the triplet and singlet states are 9 and 10 kcal/mol. Exploration of the two equivalent CCN angles suggests optimum values of ~177 and ~174 for 3B1 and 1A1. Finally the triplet state is estimated to lie ~14 kcal below the singlet state. 1977, American Chemical Society. All rights reserved.