Photodimerization of cis-Cinnamic Acids and cis-Cinnamides in Crystalline State and Aqueous Solution

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Veerakanellore, Giri Babu
cis-Cinnamic acids; cis-Cinnamides; Topochemical postulates; Solid-state photochemistry; Geometric isomerization;; cis-Cinnamic acids; cis-Cinnamides; Topochemical postulates; Solid-state photochemistry; Geometric isomerization; "in and on water" photoreactions
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The research work presented in this thesis describes the photochemical reactions carried out in the solid-state and X-ray structural studies to understand the photochemical behavior of cis-cinnamic acids by exploiting topochemical postulates. The photochemistry of excited cis-cinnamic acids can be understood from the photochemistry of corresponding trans-cinnamic acids but not from cis-cinnamic acids alone. Existence of dual reactive centers and its photoreactivity of cis-olefinic crystals are thoroughly investigated. Similar to trans-cinnamic acids, cis-cinnamic acids can also undergo direct photodimerization when the intermolecular distance of double bonds is less than 4.2 Å. Key contributing factors for the isomerization of cis-cinnamic acids are well explained. Unlike trans-cinnamic acids, polymorphic changes of cis-cinnamic acids during photoirradiation are highlighted using photochemistry and X-ray crystal structures. The role of intermolecular distance and displaced nature of reactive olefinic pairs in the photochemistry of cis-cinnamides is extensively studied. The important factors responsible for one-way isomerization of cis-cinnamides and implications of displaced nature of halogen substituted cis-cinnamides that led to multiple products are well investigated. Furthermore, uniqueness of water as a solvent is explained with the concept of “in water and on water” photoreactions of cis-cinnamic acids in an aqueous medium.