Methyl m -bromo-cinnamate

A comparison of the photobehavior of two crystals, 7-methoxycoumarin (19) and methyl m-bromo-cinnamate (20), exemplifies the importance of the need for the existence of free volume close to the reaction site [133-135]. Neither of these molecules is topologically oriented for efficient reaction in the crystal, meaning that the reactive pairs need to undergo some inter-molecular realignment before they can dimerize. 

A comparison of the solid state photochemistry of two crystals, 7-methoxycoumarin and methyl m-bromo-cinnamate, further exemplifies the importance of the existence of free volume near the reaction site (Sch. 15) [127-129], In spite of the fact that the reactive double bonds are rotated by 65° with respect to each other and a center-to-center double-bond distance of 3.83 A (Fig. 16), photodimerization occurs in crystals of 7-methoxy-coumarin to give the syn head-to-tail isomer (Sch. 15). On the other hand, methyl m-bromo-cinnamate, which also has a nonideal arrangement of the... 

The action of thionyl chloride on cinnamic acid affords 3-chloro-benzothiophen-2-carbonyl chloride (207) ° phenylpropiolic acid and its methyl ester likewise yield 3-chlorobenzothiophen derivatives on treatment with sulphur dichloride, disulphur dichloride, and thionyl chloride, but not with sulphuryl chloride/ The bromo-acid (208) is obtained by the combined action of hydrogen bromide and sulphur dioxide on m-methoxyphenylpropiolic acid. °... 

---