which one stable

for xylenes....

i have accepted (without reason by seeing heat of formation values) that meta-xylene is most stable

The thermodynamic data for all the three xylenes has been estimated and it has been observed that the

order of thermodynamic stability is m>o>p. This has been explained on the basis that the m-isomer is the

thermodynamically controlled product, whereas the other two are kinetically controlled products. These

results are explained in terms of basicity. Rearrangement involving hydride shift ( instead of Me) can also

occur ( during isomerisation reaction).Only for the m-carbonium ion the two methyl groups ( +I) in one of

the canonical structures is capable of partially neutralising the positive charges on the ring carbon atoms. In

the other two isomers only one methyl group can act in this way. Thus the m-carbonium ion will be more

stable than the other two and so the equilibrium is shifted to the formation of m-isomer.

thx