Abstract
Hydrogen atom abstraction by photoexcited carbonyl compounds has played a central role in the development of a general picture of how photochemical reactions occur. Scaiano reviewed the bimolecular process in 1973;1 in the mid-70‘s one of us authored two reviews that covered excited state reactivity2a and reactions of photogenerated biradicals.2b The past 15 years have seen many new developments in the area of hydrogen abstraction. The emergence of nanosecond and picosecond laser spectroscopy has allowed the direct study not only of the reactive triplet states but also of the radicals, biradicals, and radical-ions that are produced as intermediates during photochemical hydrogen transfer processes. Very accurate rate constants are now known for a variety of hydrogen abstraction processes. The competition between hydrogen and electron transfer has been addressed far more quantitatively than was possible earlier. Environmental effects on hydrogen transfer have been used to determine information about the structures of organized media. Conformational effects both on intramolecular hydrogen abstraction itself and on the reactions of biradicals have been explored more thoroughly than previously. The study of solid compounds with known crystal structures and the arrival of simple molecular mechanics programs have been of great benefit in this regard. The reactions of biradicals, in particular the mechanism for intersystem crossing and product formation, have become a topic of major interest. New biradical rearrangements appear regularly in all of the journals. Synthetic organic chemists have begun to utilize photorearrangements initiated by hydrogen transfers. With the current intense interest in synthetic applications of intramolecular radical reactions, it is almost a certainty that initiation by hdyrogen abstraction will be used more routinely for natural products synthesis.
Original language | English |
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Title of host publication | Organic Photochemistry |
Publisher | CRC Press |
Pages | 227-366 |
Number of pages | 140 |
Volume | 11 |
ISBN (Electronic) | 9781351426565 |
ISBN (Print) | 0824785614, 9780824785611 |
DOIs | |
State | Published - 1 Jan 2017 |