# Topochemical solid state photodimerization of nonideally oriented monomers: 7-chlorocoumarin and 7-methoxycoumarin

Gnanaguru, K and Ramasubbu, N and Venkatesan, K and Ramamurthy, V (1984) Topochemical solid state photodimerization of nonideally oriented monomers: 7-chlorocoumarin and 7-methoxycoumarin. In: Journal of Photochemistry, 27 (3). pp. 355-362.

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## Abstract

Photodimerizations of 7-chlorocoumarin and 7-methoxycoumarin in the solid state were studied; syn head-to-head and syn head-to-tail dimers are the respective products of irradiation in the solid state. X-ray crystal structure analyses of 7-chlorocoumarin and 7-methoxycoumarin reveal unusual features. 7-Chlorocoumarin is arranged in a $\beta$-type packing, the centre-to-centre distance between the reactive double bonds being $4.454 \AA$, which lies outside the limit accepted at present of $3.5-4.2 \AA$. In contrast, the reactive double bonds of 7-methoxycoumarin are rotated by about 65° with respect to each other with the centre-to-centre distance between the double bonds being $3.83 \AA$. In spite of these unfavourable arrangements photodimerization of these two coumarins in the solid state occurs through a topochemical process with large dimer yields.

Item Type: Journal Article Copyright of this article belongs to Elsevier Science B.V. Division of Chemical Sciences > Organic Chemistry 24 Mar 2008 19 Sep 2010 04:43 http://eprints.iisc.ernet.in/id/eprint/13406