O chem concepts

[wifi08]

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which yeilds a more stable carbocation/radical
1)H2C=CH+ vinylic

2)H2C=CH-CH2+ allylic

3) +methylcyclohexane i.e. a primary carbon


also, which is least reactive towards SN2?
CH3CH2CH2I
CH3CH2CH2BR

 

[klutzy1987]

which yeilds a more stable carbocation/radical
1)H2C=CH+ vinylic

2)H2C=CH-CH2+ allylic

3) +methylcyclohexane i.e. a primary carbon


also, which is least reactive towards SN2?
CH3CH2CH2I
CH3CH2CH2BR

The allyl is resonance stabilized and therefore is the more stable carbocation.

I is a much better leaving group than Br and therefore will be much more reactive towards Sn2 reaction than Br.

 

[wifi08]

but what about vinylic vs the primary carbon which will yield more stable carbocation?

 

[chemtex2008]

Primary carbocations are the worst!!! You never see this happen in chemistry (except in very high energy situations such as with mass spec).

 

[doc3232]

The allyl is resonance stabilized and therefore is the more stable carbocation.

I is a much better leaving group than Br and therefore will be much more reactive towards Sn2 reaction than Br.

Not that much more reactive, but ya as he said.
Br is a very good leaving group.