Theoretical studies on structures and electronic state of alkyl-substituted ethyl cations

This paper describes the gas phase structural details for a series of alkyl-substituted ethyl cations 1-11 by mainly natural bond orbital (nbo) analysis. for the simplest ethyl cation,two kinds of optimized structures (nonclassical 1 and classical 2) were found to have minima on the potential surface,and the nonclassical 1 was more stable than the corresponding classical 2 by 1.19 kcal/mol at møller-plesset (mp) level calculations in the gas phase. the calculated values of wiberg's bond index revealed that the central ethylic c1-c2 bonds of the nonclassical cations 1,6,7,and 10 have 1.10-1.46 bond multiplicities. the compliance constant (cii) values indicated that the cation center c1 of nonclassical 2-butyl cation 6 (0.209 å/mdyn) acquires stronger hyperconjugative stabilization from c2-r3 (c-h) bond than that of the nonclassical ethyl cation 1 (0.388 å/mdyn). moreover,the gas phase stabilities for the alkyl-substituted ethyl cations 1-11 were also estimated by the hydride affinities based on isodesmic equations. © 2013 toshiaki shimasaki et al.