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Journal of Chemistry
Volume 2013 (2013), Article ID 406904, 9 pages
Research Article

Theoretical Studies on Structures and Electronic State of Alkyl-Substituted Ethyl Cations

1Department of Life and Environmental Sciences, Faculty of Engineering, Chiba Institute of Technology, Narashino, Chiba 275-0016, Japan
2Instrumental Analysis Division, Center for Supports to Research and Education Activities, Kobe University, 1-1 Rokkodai-cho, Nada, Kobe 657-8501, Japan

Received 17 May 2013; Accepted 10 July 2013

Academic Editor: Adriana Szeghalmi

Copyright © 2013 Toshiaki Shimasaki et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


This paper describes the gas phase structural details for a series of alkyl-substituted ethyl cations 111 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 ( ) 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 111 were also estimated by the hydride affinities based on isodesmic equations.