CCL: How to evaluate the difficulty of synthesize?

 Sent to CCL by: "Li  Qiang" [chem_liqiang#sohu.com]
 Dear all,
        I are finding a computational method to evaluate(or predict) the
 difficulty of synthesize. I have known that SYBYL(Tripos) has a very general
 method to evaluate it according to the complexity of molecular structure. But it
 is less physical meaning in real organic reaction.
        By the way, I hope to know the stability of compound from its structure,
 how to evaluate this property?
        Thank you for advance!
 Best regards,
 Li Qiang