Allo-cinnamic acid

Stobbe, H. and Lehfeldt, A. (1925). Polymerization and depolymerization by light of different wavelengths. II. a and p-trans cinnamic acids, allo-cinnamic acids and their dimers. Berichte, 58B, 2415-27. [234]... 

Which of the two is the cis form and which the trans form has not been determined. A third cinnamic acid, viz., iso-cinnamic acid, is also known, but the constitution of it has not been established. Cinnamic acid is found in nature in the resin storax both as the free acid and as the cinnamic alcohol ester, styrin. It is also found in Peru and Tolu balsams as the free acid and as the benzyl alcohol ester, the benzoic acid ester of benzyl alcohol being present also. Thus benzyl alcohol, benzoic acid, cinnamic alcohol and cinnamic acid are all constituents of esters present in these plant resins. Allo-cinnamic acid, the geometric isomer, is obtained from coca leaves from which the alkaloid cocaine is also obtained (p. 896). When cinnamic acid is heated with lime it loses carbon dioxide and yields the unsaturated side-chain hydrocarbon st3rrene, or phenyl ethylene, CeHs—CH = CH2. On reduction it yields first cinnamic aldehyde, found in oil of cinnamon (p. 842) and then cinnamic alcohol. Both cinnamic acid and allo-cinnamic acid yield anhydrides. 

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