THEORETICAL CALCULATION OF RATE CONSTANTS FOR THE THERMAL-ISOMERIZATION FROM 1,2-BUTADIENE TO 1,3-BUTADIENE

Ab initio electronic structure calculations at 6-31G* level were perf ormed to determine the mechanism of the isomerization reaction from 1, 2-butadiene to 1,3-butadiene. The MP2 method was used to improve the b arrier energies of the reaction. The calculation results show that the reaction is a stepwise process via a radical INT; the barrier energie s determined for TS1 and TS2 at UMP2/6-31G*//UHF/6-31G** + ZPE level are 64.95 x 4.184 and 64.10 x 4.184 W/mol, respectively. Based on the unified statistical theory, the thermal rate constants for the present complex reaction mechanism were computed over the termperature range 1100-1600 K. The computed thermal rate constants for the reaction are well represented by the following Arrhenius expression: k (T) = 2.4 x 10(13) exp (-62.8 kj/RT) s(-1). The theoretical investigations are fou nd to be in quantitative agreement with the experimental results.