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Thermisches Verhalten von 1,2‐Dipropenylbenzolen
Author(s) -
Heimgartner H.,
Hansen H.J.,
Schmid H.
Publication year - 1972
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19720550505
Subject(s) - conrotatory and disrotatory , chemistry , isomerization , sigmatropic reaction , cis–trans isomerism , ring (chemistry) , yield (engineering) , medicinal chemistry , stereochemistry , catalysis , organic chemistry , thermodynamics , physics
1‐ cis , 2‐ cis ‐Dipropenylbenzene ( cis , cis ‐ 1 ) isomerises thermally at 215–235° with 1st order kinetics to give trans , cis ‐ 1 and vice versa . At equilibrium 89% trans , cis ‐ and 11% cis , cis ‐ 1 are present. It is shown by thermal rearrangement of cis , cis ‐2′, 2″‐d 2 ‐ 1 that the isomerisation is attributable to aromatic [1, 7a]‐sigmatropic H‐shifts. trans , trans ‐ 1 rearranges thermally at 225–245° to yield 2, 3‐dimethyl‐1, 2‐dihydronaphthalene ( 2 ). The formation of 2 can be visualized by disrotatory ring closure followed by an aromatic [1, 5s]‐sigmatropic H‐shift. 2 is also formed when, cis , cis ‐ or trans , cis ‐ 1 are heated for 153 h at 225°. Besides 2 a small amount (3%) of 1‐ethyl‐1, 2‐dihydronaphthalene ( 5 ) is formed. The rearrangement of trans , trans ‐ 1 and trans , trans ‐2′, 2″‐d 2 ‐ 1 shows a secondary isotope effect k H / k D = 0,90.