A Gaussian-2 ab initio study of [C₂H₅S]⁺ ions: II. fragmentation pathways of CH₃SCH₂⁺ and CH₂CHSH₂⁺ r

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• 作者：Chiu ; S.-W. ; Cheung ; Yu-San ; Ma ; Ngai Ling ; Li ; Wai-Kee ; Ng ; C.Y.
• 关键词：Gaussian-2 theory ; [C₂H₅S]⁺ ions ; Unimolecular dissociations ; Ion-molecule complexes ; Ion-radical complexes
• 刊名：Journal of Molecular Structure: THEOCHEM
• 出版年：1999
• 出版时间：August 9, 1999
• 年：1999
• 卷：468
• 期：1-2
• 页码：21-37
• 全文大小：407 K

文摘

Gaussian-2 ab initio method was performed to examine the five modes of unimolecular dissociation of CH₃SCH₂⁺ (1⁺) and CH₂CHSH₂⁺ (5⁺): 1⁺→CH₃+H₂CS⁺ (1); 1⁺→CH₃⁺+H₂CS (2); 1⁺→CH₄+HCS⁺ (3); 5⁺→H₂S + [C₂H₃]⁺ (4); and 5⁺→H₃S⁺+C₂H₂ (5). Both reactions 1 and 2, with endothermicities 359 and 395 kJ mol⁻¹ respectively, proceed without a reverse barrier. Loss of CH₄ from 1⁺ (reaction 3) proceeds via a transition state resembling an ion–radical complex CH₃/H₂CS⁺. The elimination reaction has an energy barrier of 332 kJ mol⁻¹. Loss of H₂S from 5⁺ (reaction 4) initially proceeds through either cleavage of the C–S bond or formation of the ion–molecule complex H₂S/[C₂H₃]⁺ (8⁺/9⁺), followed by dissociation of the complex. The endothermicity of reaction 4 is calculated to be 245–261 kJ mol⁻¹. Reaction 5, the lowest energy process among the dissociation pathways studied in this work, proceeds via intermediates 9⁺ and H₃S⁺/C₂H₂ (10⁺). Its rate-determining step 5⁺→9⁺ has an energy barrier of 220 kJ mol⁻¹.