Solution and Solid-State Photodimerization of Some Styrylthiophenes

Bernard S. Green, Lilly Heller

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Abstract

The Pyrex-filtered uv irradiation of trans-1-phenyl-2-(2-thienyl)ethene (4), irans-1-(2,4-dichlorophenyl)-2-(2-thienyl)ethene (7), and trans-1-(3,4-dichlorophenyl)-2-(2-thienyl)ethene (8) has been performed in the crystalline state and in benzene solution. The solid-state behavior is crystal lattice controlled: 4 and the two crystal modifications of 8 are light stable; 7 yields the topochemically expected mirror-symmetric dimer 9. Contrary to a previous report, 4 undergoes photodimerization in solution and one of the photoproducts has been assigned the centrosymmetric structure 23. The two dichloro derivatives also afforded solution photodimers and there is a striking substituent effect on their solution photobehaviors. The 2,4-dichloro isomer, 7, yields only the two dimers 9 and 11, both of cis,anti,cis stereochemistry. By contrast, the 3,4-dichloro isomer, 8, yields all four cyclobutane isomers possible from the union of trans monomers: two all-trans isomers, 16 and 17, and two cis,anti,cis isomers, 14 and 15. The photodimerization rates in benzene solution of 7, 4, 8, and trares-stilbene were in the ratio 1.0:2.1:2.4:15. Attention is drawn to a correlation between the monomer crystal structures and their solution photodimerization.

Original languageEnglish
Pages (from-to)196-201
Number of pages6
JournalJournal of Organic Chemistry
Volume39
Issue number2
DOIs
StatePublished - 1 Jan 1974
Externally publishedYes

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