Reaction mechanism in crystalline solids: kinetics and conformational dynamics of the Norrish type II biradicals from α-adamantyl-p-methoxyacetophenone.
J Am Chem Soc
; 134(2): 1115-23, 2012 Jan 18.
Article
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| MEDLINE
| ID: mdl-22145996
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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MEDLINE
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En
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J Am Chem Soc
Año:
2012
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Article
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Estados Unidos