Effect of alkyl substituents on photorelease from butyrophenone derivatives

The Journal of Organic Chemistry
Sivaramakrishnan MuthukrishnanAnna D Gudmundsdottir

Abstract

Photolysis of 1a yields 4a in argon-saturated methanol, whereas 1b is photostable. Laser flash photolysis of 1a in acetonitrile shows formation of biradical 2a (lambda(max) = 340 nm, tau = approximately 60 ns), which undergoes intersystem crossing to form Z-3a (lambda(max) = 380 nm, tau = 270 ns) and E-3a (lambda(max) = 380 nm, tau = 300 ms). Z-3a regenerates the starting material, whereas E-3b undergoes intramolecular lactonization to release the alcohol moiety and form 4a. Similar laser flash photolysis of 1b shows formation of biradical 2b (lambda(max) = 340 nm, tau = 1.9 micros in acetonitrile), which is longer-lived than 2a is. However, 2b only undergoes intersystem crossing to form Z-3b (lambda(max) = 380 nm, tau = 4.3 micros). Calculations demonstrate that intramolecular pseudo hydrogen bonding between the OH moiety and the radical centered on the isopropyl carbon in 2b and the bulkiness of the isopropyl group prevent the necessary rotation to form E-3b. In comparison, 2a does not form an intramolecular pseudo hydrogen bond between the methylene radical center and the OH group, and as a consequence, it undergoes intersystem crossing to form both E- and Z-3a.

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Citations

Jul 26, 2013·Chemical Reviews·Manabu Abe
Apr 12, 2016·Photochemistry and Photobiology·Anushree DasAnna D Gudmundsdottir
Nov 5, 2014·The Journal of Physical Chemistry. B·Sujan K SarkarAnna D Gudmundsdottir
Aug 14, 2018·Photochemistry and Photobiology·Anushree DasAnna D Gudmundsdottir
Mar 13, 2012·Photochemical & Photobiological Sciences : Official Journal of the European Photochemistry Association and the European Society for Photobiology·Qian LiAnna D Gudmundsdottir
Aug 14, 2021·Science·Justin JurczykRichmond Sarpong
Oct 17, 2013·The Journal of Organic Chemistry·Disnani W GamageAnna D Gudmundsdottir
Jul 8, 2011·The Journal of Organic Chemistry·Sridhar RajamAnna D Gudmundsdottir
Sep 8, 2011·The Journal of Organic Chemistry·Ranaweera A A Upul RanaweeraAnna D Gudmundsdottir
Jul 22, 2014·The Journal of Physical Chemistry. a·R A A Upul RanaweeraAnna D Gudmundsdottir

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