stability of carbokation(?) as in SN1 Reactions

Hello,

first, I am sorry for my bad english, but however i hope that you understand my problem.

Can anyone please sort the following molecules in their stability in the transition state (don't know if that is the right word),
with the first number representing the most stabil carbokation. (Br- is thought to be splitted from the molecul and there should
stay a positive charge)

1:Ph-CH2Br
2:Ph-CHBr-CN
3:Tert-Butylbromide

I suppose that it is 1,2,3 but it could also be 1,3,2 or 2,1,3 after what i know.
Concering molecule 2, I just know that a triple bond stabilizes a neighboured carbonsextet less good than a twice bond, but this
actually has to mean that it is still better for the carbonsextet than just a proton as in molecule 1. But also the nitrilgroup
(hope thats the name of -CN group in english) withdrawes electrons, which is destabilizing the carbonsextet. So i don't know what is
more important for the stability, the two occupied pi-orbitals or the -I effect of the nitril group. If the latter, than it could
also be possible that the molecule 3 would react faster than 2, if the pi-orbitals would be more important than molecule 2 could
perhaps react faster than molecule 1.
Any help is very welcome, most welcome would be some general rule of the importance of the different effects, not just for the
nitril group.
Johannes

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