Thermal unimolecular isomerization of 1,4-dimethylbicyclo[2.2.0]hexane, 1,4-dimethylbicyclo[2.1.1]hexane, and 1,4-dimethylbicyclo[2.1.0]pentane

✍ Scribed by R. Srinivasan

• Publisher: John Wiley and Sons
• Year: 1969
• Tongue: English
• Weight: 593 KB
• Volume: 1
• Category: Article
• ISSN: 0538-8066
• DOI: 10.1002/kin.550010202

✦ Synopsis

The thermal isomerization of the title compounds was studied in the vapor phase.

Over the temperature range from 445.1 to 477.5"K7 1,4-dimethylbicyclo[2.2.O]hexane underwent a homogeneous unimolecular reaction to 2,5-dimethyl-175-hexadiene, the rate constants being represented by the equation: k = 1.86 x 1011 exp (-31000 f 1800/RT) sec-l. Over the temperature range from 630.0 to 662.2"K, 174-dimethylbicyclo[2.1. I]hexane also underwent a unimolecular isomerization to the same product, the rate constants being given by the equation: k = 8.91 x 1014 exp (-56000 f 900/RT) sec-l. The pyrolysis of 1,4-dimethylbicyclo[2.1 .O]pentane gave 1,3-dimethylcyclopentene-1 and Z74-dirnethyl-l,4-pentadiene in the ratio of 9: 1. The former reaction was influenced by surface effects but the latter was not. The rate constants for the formation of Z74-dimethyl-174-pentadiene fitted the equation: k = 1.66 x 1017 exp (-57400 f 310O/RT) sec-l. The effect of the two methyl groups at the bridgehead positions in these molecules in influencing the rate of decomposition is discussed in terms of the non-bonded repulsive forces between the substituents.