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Reaction mechanism in crystalline solids: kinetics and conformational dynamics of the Norrish type II biradicals from α-adamantyl-p-methoxyacetophenone.

Authors
Type
Published Article
Journal
Journal of the American Chemical Society
1520-5126
Publisher
American Chemical Society
Publication Date
Volume
134
Issue
2
Pages
1115–1123
Identifiers
DOI: 10.1021/ja2090004
PMID: 22145996
Source
Medline
License
Unknown

Abstract

In an effort to determine the details of the solid-state reaction mechanism and diastereoselectivity in the Norrish type II and Yang cyclization of crystalline α-adamantyl-p-methoxyacetophenone, we determined its solid-state quantum yields and transient kinetics using nanocrystalline suspensions. The transient spectroscopy measurements were complemented with solid-state NMR spectroscopy spin-lattice relaxation experiments using isotopically labeled samples and with the analysis of variable-temperature anisotropic displacement parameters from single-crystal X-ray diffraction to determine the rate of interconversion of biradical conformers by rotation of the globular adamantyl group. Our experimental findings include a solid-state quantum yield for reaction that is 3 times greater than that in solution, a Norrish type II hydrogen-transfer reaction that is about 8 times faster in crystals than in solution, and a biradical decay that occurs on the same time scale as conformational exchange, which helps to explain the diastereoselectivity observed in the solid state.

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