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Destabilized carbenium ions: α‐Carbamoyl‐α,α‐dimethylmethyl cations
Author(s) -
Wolf Rainer,
Grützmacher HansFriedrich
Publication year - 1990
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/poc.610030506
Subject(s) - chemistry , protonation , ion , amide , kinetic energy , dissociation (chemistry) , metastability , decomposition , proton affinity , medicinal chemistry , computational chemistry , stereochemistry , organic chemistry , physics , quantum mechanics
The formation and unimolecular reactions of the especially electron‐deficient α‐carbamoyl carbenium ions [(CH 3 ) 2 CCONH 2 ] + (a 1 ) and [(CH 3 ) 2 CCON(CH 3 ) 2 ] + (a 2 ) have been studied by mass spectrometric techniques. The ions a are formed by electron impact‐induced dissociation from the relevant isobutyric amides α‐substituted by I, Br and Cl, respectively, but the carbonyl protonated methacrylamides b 1 and b 2 are cogenerated. A similar mixture of ions a and b is obtained by CI(CH 4 ) of the corresponding methacyrlamides. The metastable ions decompose by the loss of CO exhibiting in particular a large kinetic energy release (KER) and by the elimination of NH 3 and HN(CH 3 ) 2 , respectively. It is shown that isomeric ions of structures a and b interconvert prior to decomposition and that the energy barrier separating the isomeric ions is small. Hence the kinetic stability of the tertiary α‐carbamoyl‐α,α‐dimethylmethylcations is reduced compared with other types of α‐acyl carbenium ions. This effect can be attributed to the increased proton affinity of the amide group.