Abstract
Although 1-(o-tolyl)-1-benzoylcyclopropane (I) and 2-(o-tolyl)-2-benzoyloxirane (II) are structurally analogous, they go through dramatically different reaction pathways upon absorption of photons. I yields a single photoproduct, while 2H2-substituted II gives birth to three different photoproducts. The structural and kinetic features of the entire reaction intermediates have been measured with laser flash techniques. I at T1 undergoes intramolecular hydrogen transfer at 2.3 × 108 s-1 from the methyl group to the carbonyl group to form a biradical intermediate, which transforms into a cyclized photoproduct (φ 0.14; 5 × 107 s-1). However, the carbonyl group of II at T1 can abstract a hydrogen atom from the oxiranyl ring (6 × 107 s-1) as well as from the methyl group (2.3 × 108 s-1). The biradical intermediate from the former process immediately rearranges into a photoproduct (φ 0.025), while the one from the latter transforms into a new oxiranyl ring-opened intermediate (1.1 × 108 s-1) or a cyclized photoproduct (φ 0.075; 3.3 × 108 s-1). The new intermediate rearranges into another photoproduct (φ 0.025; 3.7 × 107 s-1). The dramatic changes of II are theoretically attributed to the drastic increase in the acidity and instability of the three-membered ring with oxygen substitution.
Original language | English |
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Pages (from-to) | 3555-3563 |
Number of pages | 9 |
Journal | Journal of Physical Chemistry A |
Volume | 105 |
Issue number | 14 |
DOIs | |
State | Published - 12 Apr 2001 |