Deuterium NMR Studies of Guest Solubilization in Liquid Crystals/Photochemistry of Cyclopropenes

Abstract

<p>The direct solution photochemistry of 1,3,3-trimethylcyclopropene and 1-t-butyl-3,3-dimethylcyclopropene has been investigated. Primary photoproducts consisting of alkynes, allenes, and 1,3-dienes are formed from vinylcarbene intermediates, a result of cleavage of the C₁ - C₃ or C₂ - C₃ bond. Cleavage of the more substituted (C₁ - C₃) bond to yield a vinylcarbenes can account for > 80% of observed products. Most of the products are formed via 1,2- and 1,4-hydrogen migrations from the intermediate vinylcarbenes.</p> <p>Photolysis of 1,3,3-trimethylcyclopropene-1-¹³C supports the intermediacy of vinylcarbenes in product formation from singlet excited cyclopropenes. In addition, evidence which strongly suggests the importance of a second pathway for formation of alkyne products from alkylcyclopropenes has been obtained. This pathway involves the intermediacy of vinylidene, formed by 1,2-hydrogen migration/ring opening (sequential or concened) from the singlet excited-state of cyclopropene.</p>