CHED 958 |
| The supramolecular solid state offers new possibilities of studying reactions between molecules in a well-ordered environment. We have co-crystallized sorbic acid and 1, 1, 6, 6-tetraphenylhexa-2, 4-diyne-1, 6-diol (‘diol'). The asymmetric unit of the crystal contains two molecules of sorbic acid hydrogen bonded to a diol molecule. On exposure of a single crystal to 325 nm light from a He/Cd laser the sorbic acid molecules either undergo trans to cis isomerization or [2+2] photodimerization to form a cyclobutane derivative, the detailed behavior depending on the temperature. At 90K, both [2+2] photodimerization and isomerization are observed with a total yield of 6%. When a pulsed nitrogen laser (λ=337 nm) is used at 280K, 1000 pulses with an estimated total energy of 150mJ on the crystal are sufficient to induce a 5.1% yield of the dimer without isomerization. The temperature-dependent behavior is attributed to a translational motion needed to bring the sorbic acid molecules into the proper geometry for the dimerization reaction to occur, which is suppressed at the lower temperature, so that isomerization can compete with the dimerization.
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Undergraduate Research Poster Session: Physical Chemistry
2:00 PM-4:00 PM, Monday, April 7, 2008 Morial Convention Center -- Hall A, Poster
Division of Chemical Education |
