Direct observation of vinyl hydroperoxide

摘要

Many alkyl-substituted Criegee intermediates are predicted to undergo an intramolecular 1,4-hydrogen transfer to form isomeric vinyl hydroperoxide species (C=COOH moiety), which break apart to release OH and vinoxy radicals. We report direct detection of stabilized vinyl hydroperoxides formed via carboxylic acid-catalyzed tautomerization of Criegee intermediates. A doubly hydrogen-bonded interaction between the Criegee intermediate and carboxylic acid facilitates efficient hydrogen transfer through a double hydrogen shift. Deuteration of formic or acetic acid permits migration of a D atom to yield partially deuterated vinyl hydroperoxides, which are distinguished from the CH3CHOO, (CH3)(2)COO, and CH3CH2CHOO Criegee intermediates by mass. Using 10.5 eV photoionization, three prototypical vinyl hydroperoxides, CH2=CHOOD, CH2=C(CH3)OOD, and CH3CH=CHOOD, are detected directly. Complementary electronic structure calculations reveal several reaction pathways, including the barrierless acid-catalyzed tautomerization reaction predicted previously and a barrierless addition reaction that yields hydroperoxy alkyl formate.