Portland State University. Department of Chemistry
Date of Publication
Master of Science (M.S.) in Chemistry
1 online resource (vii, 69 leaves, ill. 28 cm.)
Kinetics investigations of the thermal Cope rearrangement of meso-and d1-3,4-diphenylhexa-1,5-dienes were undertaken in order to gain information about the transition states for these reactions by determining the appropriate enthalpies and entropies of activation. Of particular interest were the activation parameters for the meso compounds' rearrangement as it represents the only known example in which both four-and six-centered transition states are of comparable energy.
Kinetics of the dl isomers' rearrangement in the temperature range 90-110⁰were determined using 5 X 10¯⁵M solutions of the olefin in heptane contained within sealed Pyrex ampules. Extents of reaction were determined from UV absorbance measurements at 256 nm. Product instability, becoming pronounced after 85-90% reaction, was observed. Two rate constants were calculated covering 0-85% and 0-98% reaction respectively, from each set of data. Evaluations of enthalpies of activation from the two sets of rate constants gave, respectively,
23.8 and 23.9 kcal/mole, indicating that inclusion of the increasingly erratic kinetics data collected after 85% reaction had little effect upon this activation parameter. The corresponding entropies of activation at 100⁰were -12.9 and -12.6 eu. Both activation parameters are consistent with those for other Cope rearrangements indicating that the thermal isomerization of dl-3,4-diphenylhexa-1,5-diene in the temperature range 90-110⁰is normal in every respect.
Kinetics studies of the more interesting meso-diene were precluded by the failure to locate means of controlling product decomposition, which would be expected to become more severe at the higher temperature required (140-160⁰).
Additionally, alumina-catalyzed isomerizations first observed accidently for the d1-diene, and subsequently verified for both meso--and d1-olefins, were examined. In contact with 100 times its weight of very active alumina at room temperature the d1 isomer was found to undergo conversion in the extent of 40% during a two-hour period to trans, trans-1,6-diphenylhexa-1,5-diene.meso--3,4-Diphenylhexa-1 ,5-diene underwent structural reorganization more slowly; after 70 hours over alumina a 15% conversion to a 9:1 mixture of cis-trans and trans,trans-1,6-diphenylhexa-1,5-dienes was noted. The stereo specificities observed for these unusual catalyzed rearrangements parallel those of their thermally-induced counterparts. Modifications in the syntheses of meso- and d1-1, 6--dibromo-3,4-diphenylhexanes, and meso--and dl-3,4-diphenylhexa-1,5-dienes, are also presented.
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Berg, Harlan Albert Jerome, "Kinetics of the Cope rearrangement of 3,4-diphenylhexa-1,5-diene" (1972). Dissertations and Theses. Paper 1116.