I. Ultraviolet irradiation of trans-cinnamic acid ((E)-3-phenylprop-2-enoic acid) in solution yielde — Analytical Chemistry Chemistry Question
Cinnamic acid
I. Ultraviolet irradiation of trans-cinnamic acid ((E-3-phenylprop-2-enoic acid) in solution yielded a mixture of cis-cinnamic and trans-cinnamic acids. trans-Cinnamic acid can be crystallized in two forms: α-form or β-form. Ultraviolet irradiation of crystalline trans-cinnamic acid in the α-form yielded α-truxillic acid (2,4-diphenylcyclobutane-1,3-dicarboxylic acid). Ultraviolet irradiation of crystalline trans-cinnamic acid in the β-form yielded β-truxinic acid (2,3-diphenylcyclobutane-1,4-dicarboxylic acid). α-Truxillic acid possesses a symmetric center. In β-truxinic acid, the two phenyl groups are on the same side of the cyclobutane ring, and the two carboxyl groups are on the opposite sides.
II. Hydrolysis of α-truxilline (C38H46N2O8, an alkaloid obtained from Truxillo coca) gives α-truxillic acid, methanol and an acid A (C9H15NO3). Oxidation of A with pyridinium chlorochromate (PCC) leads to B, which is readily decarboxylated to form optically inactive ketone C (C8H13NO). Oxidation of C with potassium permanganate gives N-methylsuccinimide.
Propose a reaction mechanism for the isomerization of trans-cinnamic acid.
Model Answer
Reaction mechanism for the isomerization
Draw the structure of α-truxillic acid and all its diastereoisomers.
Model Answer
[VISUAL] Ph H HOOC HH Ph H COOH α-truxillic acid
Draw the structure of β-truxinic acid and all its diastereoisomers. Show the structures which have enantiomers.
Model Answer
[VISUAL] β-truxinic acid Has an enantiomer Has an enantiomer Has an enantiomer Has an enantiomer
Suggest how the different packing arrangements of trans-cinnamic acid in the α- and β- crystal forms leads to the different structures of α-truxillic and β-truxinic acid.
Model Answer
The packing arrangement of α-type of trans-cinnamic acid which leaded to the formation of α-truxillic acid. The packing arrangement of β-type of trans-cinnamic acid which leaded to the formation of β-truxinic acid.
Why does cinnamic acid not dimerize in solution upon ultraviolet irradiation?
Model Answer
In solution all molecules of cinnamic acid were solvated and randomly arranged.
Propose the structures of A, B, C. Are A, B optically active or not? Explain. Why C is optically inactive?
Model Answer
[VISUAL] A, B, C. Optically active since A has four asymmetric carbons and has no symmetrical plane and no symmetrical center. Optically active since B has three asymmetric carbons and has no symmetrical plane and no symmetrical center. Optically inactive since C has symmetrical plane although has two asymmetric carbons.
Propose the structure of α-truxilline. Is α-truxilline optically active or not? Explain.
Model Answer
[VISUAL] Optical active since each bicyclooctane moiety has four asymmetric carbons and their configurations are exactly the same as in A thus α-truxilline has no symmetrical plane and no symmetrical center.