Sengupta, Debasis and Bhattacharyya, Anuradha and Sumathi, R and Chandra, AK (1995) Further studies on Norrish type II reactions including a reaction in the first excited singlet state and cyclization of 1:4 biradicals. In: Journal of Photochemistry and Photobiology A: Chemistry, 86 (1-3). pp. 161-170.
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The Norrish type II processes of methyl-2,2-dimethyl- cyclopropyl ketone, alpha-alkoxy acetones and alkyl pyruvates have been examined using the AM1 semi-empirical molecular orbital method with complete geometry optimization at the partial configuration interaction level in the restricted Hartree-Fock (RHF) frame. The results reveal that the methyl-substituted cyclopropyl ketone has a constrained geometry favourable for hydrogen abstraction from the gamma-position relative to the carbonyl group in the excited singlet state. The presence of the ether oxygen atom in the beta-position relative to the carbonyl group in alkoxy acetones and alkyl pyruvates leads to increased reactivity relative to alkyl monoketones and diketones respectively. The cyclization of 1:4 biradicals has been studied in the unrestricted Hartree-Fock (UHF) frame, and the results reveal that the 1:4 biradical derived from alkoxy acetones readily cyclizes to form oxetanols. On the other hand, in the 1:4 biradicals derived from methyl-substituted cyclopropyl ketone, the three-membered ring breaks readily to form an enol intermediate. Delocalization of an odd electron in 1:4 biradicals derived from alkyl pyruvates is thought to make cyclization difficult.
|Item Type:||Journal Article|
|Additional Information:||Copyright of this article belongs to Elsevier Science.|
|Keywords:||Norrish type II reactions;Excited singlet state;Cyclization; 1:4 biradicals|
|Department/Centre:||Division of Chemical Sciences > Inorganic & Physical Chemistry|
|Date Deposited:||18 May 2011 07:54|
|Last Modified:||18 May 2011 07:54|
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