Abstract: Novel compounds of 1,2-di(isobutylphenyl)ethane and 1,2-di(isobutylphenyl)ethylene, method for producing the same and method for preparing 4-isobutylstyrene and .alpha.-(4-isobutylphenyl)propionic acid from any of these compounds. In the preparation of 4-isobutylstyrene from the former two compounds by cracking or disproportionation, the components in the resultant reaction mixture can be separated without difficulty, the formation of by-product isobutylbenzene can be avoided, and the remaining unreacted starting material can be reused for the same reaction without causing any adverse effect on a catalyst.