Ab initio calculations at MP2/cc-pVTZ level show that the trifluoromethyl group has a strong destabilizing effect on the nonclassical, σ-bridged cyclobutylmethyl cations. The GIAO-MP2 derived 13C NMR chemical shifts indicate substantial charge delocalization from the neighboring cyclobutyl ring for carbocations with an α-fluorolkyl group as compared to the 1-cyclobutylethyl cation, and this enhanced charge delocalization in case of the α-(trifluoromethyl)cyclobutylmethyl cation would lead to the ring-opening rearrangement to form the relatively more stable nonclassical primary cyclobutylmethyl cation, in which the carbocation center is farthest from the strongly electron-withdrawing trifluoromethyl group.
P. Reddy et al., "Ab Initio Structural Studies of Cyclobutylmethyl Cations: Effect of Fluoroalkyl Groups on the Relative Stability of the Carbocations," Arkivoc, vol. 2018, no. 2, pp. 233 - 240, Arkat, Dec 2017.
The definitive version is available at https://doi.org/10.24820/ark.5550190.p010.313
Keywords and Phrases
Ab initio; Carbocations; Cyclobutylmethyl cation; Fluoroalkyl; GIAO-MP2; Trifluoromethyl
International Standard Serial Number (ISSN)
Article - Journal
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01 Dec 2017