Structures and stabilities of cyclic and β-substituted carbocations C2H4Z+, C3H6Z+, and C4H8Z+, where Z is NH2, PH2, AsH2, OH, SH and SeH

Add time:09/09/2019    Source:sciencedirect.com

Structures have been optimised using ab initio molecular orbital calculations for cyclic ions 1 and β-substituted ions 2 where R1 and R2 are the three possible combinations of H and CH3 and Z is NH2, PH2, AsH2, OH, SH and SeH. The 3–21G basis set was used for ions with Z = NH2, OH, SH, and PH2, and the MINI 1 basis set for ions containing SeH and AsH2. Unsymmetrically substituted rings have C1Z bonds which are longer than C2Z and this difference is overemphasised by the small basis set calculations. All bridged ions are lower in energy than the β substituted ions except for the combination of R1 = R2 = CH3 and Z = OH+. For Group VI elements the ability of substituents to bridge increases with the size of the bridging atom, i.e., OH < SH < SeH. The opposite trend is found for substituents containing elements from Group V where the order is NH2 > PH2 ≈ AsH2.

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