When comparing maximum reactivity of a compound in electrophillic addition, what factors are kept in mind while comparing propene and trans-2-butene? Why is trans-2-butene more reactive in this case than propene?
For electrophilic substitution, naturally we look for a greater electron density over the molecule. In trans-2-butene, the are two methyl groups which increase electron density over the pi bond whereas in propene there is just one methly group. In case you don't already know, alkyl groups ($R-$), increase electron density over the bonded atom. This is generally known as inductive effect.