ISSN:
0018-019X
Keywords:
Chemistry
;
Organic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
On ultraviolet irradiation of the cyclopent-2-enyl methyl ketones 1a-c at -54° ≤ t ≤ 139°, photo-CIDNP. effects of the starting ketones, the 1,3-acetyl shifted isomers (2), and radical disproportionation and combination products (4-7) were observed. These effects show a unique dependence of the polarization phase on temperature which is a novel feature in photo-CIDNP. studies. The results of the investigation, which also included experiments using triplet quenchers, triplet sensitizers and radical scavengers, are rationalized in terms of Schemes 2 and 3.α-Cleavage is a major excited-state reaction of 1a-c on direct irradiation. Temperature-activated α-cleavage (kaS(t)) to the radical pair R · · R′1 and intersystem crossing (kisc) to the T2 state are among the competing S1 deactivation processes. The T2 state in turn cleaves (kaT2) to R · · R′3 A ‘low-temperature range’ with kisc ≫ kaS(t) and a ‘high-temperature range’ with kaS(t) ≫ kisc exhibiting preferential reactivity from the T2 and S1 states, respectively, can be defined for all three β,γ-unsaturated ketones 1a-c.
Additional Material:
3 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/hlca.19790620624
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