An ab Initio Study of Potentially Aromatic and Antiaromatic Three

J. Am. Chem. SOC. 1991, 113, 3689-3696

3689

An ab Initio Study of Potentially Aromatic and Antiaromatic Three-Membered Rings Yong-Cwan Byun, Svein Saebo,* and Charles U. Pittman, Jr.* Contribution from the Department of Chemistry, Mississippi State University, Mississippi State, Mississippi 39762. Received June 18, I990

Abstract: Ab initio calculations were performed on 18 threemembered ring systems including 11 closed-shell and Seven open-shell systems. The geometries of all systems were completely optimized on the RHF/6-31G** level. Both known and unknown closed-shell molecules were investigatedincluding the cyclopropenyl cation, C3H3+,1, the azirinyl cation, C2H2N+,2, the diazirinyl cation, CHN,', 3, the triazirinyl cation, N3+,4, and its acyclic isomers, borirene, C2H3B,5, borazirene, CH2NB, 6, boradiazirine, N2BH, 7, azadiboridine, NB2H3, 8, the borazarinyl cation, CHNB', 9, azirene, C2H3N,10, and the diazaridinyl cation, CH3N2+, 11. Open-shell systems studied included the cyclopropenyl radical, C3H3', 12, the azirinyl radical cation, C2H3N'+, 13, the diazirinyl radical, CHN,', 14, the triazirinyl radical cation, N3H'+, 15, the borazirinyl radical, CHNB', 16, the azadiboridinyl radical cation, NB2H