Nitrile-forming eliminations from (E)-2,4-(NO 2) 2C 6H 2CH=NOC 6H 4-2-X-4-NO 2 (1a-e) promoted by R 3N in MeCN have been studied kinetically. The reactions are second-order and exhibit Brönsted β = 0.83-1.0 and |βlg| = 0.41-0.46. The results have been interpreted in terms of highly E1cb-like transition state with extensive Cβ- H bond cleavage and limited Nα-OAr bond cleavage. Comparison with existing data reveals that the structure of the transition state changes from E2-central to highly E1cb-like either by the change of the β-aryl group from Ph to 2,4-dinitrophenyl under the same condition or by the base-solvent system variation from EtO --EtOH to Et 3N-MeCN for a given substrate (1a-e).
- E2 and E1cb-like
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