[Mack]

Hello everyone I am having trouble determining which benzylic halides would react faster under Sn1 and Sn2 and was hoping to get a little help.

For an Sn2 reaction how would you decide which benzylic halide would react faster if they are similar. For instance say you have (2-bromoethyl)benzene and (3-bromopropyl)benzene which would react more favorably under Sn2 conditions. They are nearly identical so I was unsure and was wondering if it would be one with the smaller chain off benzene which would be more favorable. This leads me to the follow question involving Sn1 reactions.

Say I have (2-bromoethyl)benzene and (3-bromopropyl)benzene again, but now I also have a secondary benzylic halide like (1-bromoethyl)benzene.  My thought is that the (1-bromoethyl)benzene would be considered to have better resonance and thus react better under Sn1 conditions than the other two, but again I am not entirely sure and appreciate any input.  Thanks for any help.

[Vidya]

Your first two examples are of primary halides with no resonance and this I think can give you clear picture of the type of the mechanism favored for them.
Last example is benzylic and secondary in nature so it means it is in favor of SN1 

[Mack]

Ahh, okay that helped clear everything up thank you.