Chemically activated 3-methyl-l-butene and 2-methyl-l-butene from photolysis of diazomethane–isobutene–neopentane–oxygen mixtures

✍ Scribed by G. W. Taylor; J. W. Simons

• Book ID: 102926287
• Publisher: John Wiley and Sons
• Year: 1971
• Tongue: English
• Weight: 565 KB
• Volume: 3
• Category: Article
• ISSN: 0538-8066
• DOI: 10.1002/kin.550030507

✦ Synopsis

An experimental study of the decomposition kinetics of chemically activated 2-methyl-I-butene and 3-methyl-I-butene produced from photolysis of diazomethane-isobuteneneopentane-oxygen mixtures is reported. The experimental rate constants for 3-methyl-I-buteone decomposition were 1.74+0.44X lo8 sec-' and 1.01 +0.25X lo8 sec-I at 3660 and 4358 A, respectively. 2-Methyl-1 -butene ezperimental decomposition rate c o n s t p s were found to be 5.94~k0.59X loi sec-' at 3660 A and 3.42 ~0 . 3 4 . X loi sec-' at 4358 A. Activated complex structures giving Arrhenius A-factors calculated from absolute rate theory of 1016.6*0.5 sec-' for 3-methyl-1-butene and 1016.2*0.4 sec-I for 2-methyl-l-butene, both calculated at 1000°K, were required to fit RRKM theory calculated rate constants to the experimental rate constants at reasonable Eo and E* values. Corrected calculations (adjusted Eo values) on previous results for 2-pentene decomposition gave an Arrhenius A-factor of 1016.45*0.35 sec-' at 1000°K. The predicted A-factors for these three alkene decompositions giving resonance-stabilized meth~~'.dyl radicals are in good internal agreement. The fact that these A-factors are only '?lightly less than those for related alkane decompositions indicates that methylallylic resonance in the decomposition products leads to only a small amount of tightening in the corresponding activated complexes. This tightening is a significantly smaller factor than the large reduction in the critical energy due to resonance stabilization.