Abstract: The mechanism of the reaction of 2-methyl-1-butene and 2-methyl-2-butene with methanol to yield TAME was theoretically studied by ab-initio H-F/6-31G*. The results show that the reaction includes two elementary reactions. First, isoamylene reacts with proton to produce tert-carbonium intermediate, then the intermediate reacts with methanol to produce the final product TAME. The activation energy of the resulting tert-carbonium from 2-methyl-1-butene and 2-methyl-2-butene are E₁=2.26 kJ/mol, E₂=7.72 kJ/mol respectively. The activation energy of the resulting TAME from methanol and tert-carbonium is E₃=1.29 kJ/mol, so the formation of tert-carbonium is the rate-determining step, and the rate of etherification of 2-methyl-1-butene is quicker. For both 2-methyl-1-butene and 2-methyl-2-butene translate into tert-carbonium intermediate under the acidic condition, and the intermediate need to overcome E'₁=4.40 kJ/mol, E'₂=63.11 kJ/mol when it translate into 2-methyl-1-butene and 2-methyl-2-butene again, so it is very hard for it to translate into alkenes again. The isomerization of different alkenes didn't exist in this reaction.

Key words: TAME, Transition state, Ab-initio, IRC