Ab initio studies of the C 2H 2BN potential energy surface

Abstract

The C 2H 2BN potential energy surface has been investigated at the MP2-level using the 6-311G** basis set. The potential surface proved to be very complex permitting only partial characterization. Sixty-six stationary points, including 42 energy minima and 24 transition states, were found. The linear ( C ∞ v ) isomer HCC–B −N +–H, 9, was the most stable species identified. The most stable cyclic structure was the non-planar isomer 46, consisting of two fused three-membered rings. Isomer 46 is 12.9 kcal/mol more stable than the planar four-membered ▪ ring structure, 4. The planar isomer 4 has a short cross-ring CB distance and could be considered as an example of a long sought after system with a planar four-coordinated carbon. Planar four-membered ring isomer 5 has shorter CN and CB (and longer CC and BN) lengths than 4 and was only 6.7 kcal/mol less stable. Planar four-membered ring, 7, ▪ was 18.7 kcal/mol less stable than 4 and it exhibits alternating single and double bonds. The C 2 v isomer 18, H 2CBCN (CBCN portion linear) was found to be a local minimum, lying 17.3 kcal/mol above the global minimum 9 and is proposed to be observable under proper conditions. Isomer 18 can be represented by the valence bond structure, 3, H 2CB–CN. In addition to 9, 46, 4, and 18, other candidates for experimental detection are the linear isomers HCC–NBH, 10, HCNBCH, 11, and HNCCBH, 12, the acyclic C 2 v structures H 2CBNC, 19, H 2CCNB, 21, and H 2CCBN, 22, and the three-membered ring structures ▪, and ▪, 62. 10, 11, 12, 19, 21, 22, 60 and 62 are less stable than 9 by 17.5, 61.6, 35.2, 27.5, 59.6, 77.5, 73.2 and 78.4 kcal/mol, respectively.