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The structure and dissociation pathways of protonated methanol: An ab initio molecular orbital study
Author(s) -
Nobes Ross H.,
Radom Leo
Publication year - 1982
Publication title -
organic mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.475
H-Index - 121
eISSN - 1096-9888
pISSN - 0030-493X
DOI - 10.1002/oms.1210170711
Subject(s) - chemistry , protonation , dissociation (chemistry) , methyl radical , ab initio , hydrogen atom , methanol , ab initio quantum chemistry methods , molecular orbital , bond dissociation energy , transition state , computational chemistry , photochemistry , molecule , radical , ion , catalysis , organic chemistry , alkyl
Ab initio molecular orbital calculations with moderately large polarization basis sets and including valence‐electron correlation have been used to examine the structure and dissociation mechanisms of protonated methanol [CH 3 OH 2 ] + . Stable isomers and transition structures have been characterized using gradient techniques. Protonated methanol is found to be the only stable isomer in the [CH 5 O] + potential surface. There is no evidence for a tightly‐bound complex, [HOCH 2 ] + …H 2 , analogous to the preferred structure [CH 3 ] + …H 2 of [CH 5 ] + . Protonated methanol is found to possess a pyramidal arrangement of bonds at the oxygen atom with a barrier to inversion of 8kJ mol −1 . The lowest energy fragmentation pathways are dissociation into methyl cation and water (predicted to require 284 kJ mol −1 with zero reverse activation energy) and loss of molecular hydrogen (endothermic by 138 kJ mol −1 but with a reverse activation barrier of 149 kJ mol −1 ). The results offer a possible explanation as to why production of [CH 2 OH] + from the reaction of methyl cation with water is not observed. Other dissociation processes examined include loss of a hydrogen atom to yield the methylenoxonium radical cation or methanol radical cation (requiring 441 and 490 kJ mol −1 , respectively) and loss of a proton to yield neutral methanol (requiring 784 kJ mol −1 ).