sn2 and sn1 rxn question...

[faerielynx]

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Hi,
I know sn1 is 3>2>1 and sn2 is 1>2>3 but where does the methy fit in? is it applicable to sn1 3>2>1>methyl and sn2 methyl>1>2>3?
and which one is sp3 to sp2 hybridized? Destroyer says sn2, but i don't see that... I kinda see it for sn1 where the carbocation becomes the sp2... but not sn2. Can someone explain this...? I'm probably thinking of it at the wrong way... thanks😀

 

[TheWiredNerv]

Methly is ideal for sn2 because there are only hydrogens in the way of the nucleophile.

 

[mss255]

I also want to add that an Sn1 reaction is very, very unfavorable via a methyl carbocation. Having an empty p orbital without any hyperconjugation makes a pretty high energy lumo.

 

[ak714251]

so like some people were just saying... the way to think about it is:

sn2: one step reaction, while the leaving group needs to leave, your nucleophile needs to enter.. logically, the least sterically hindered molecule would be most accepting of this method. for that reason methyl or primary alkyl halides work best. tertiary is just too crowded

sn1: two step reaction, so here the leaving group is going to leave first. there is no issue of steric hinderance. instead you have to account for a carbocation. the more substituted your carbocation is, the more the positive charge is spread out, for that reason it is more stable. a teritary alkyl halide will become a tertiary carbocation which is significantly more stable than a primary carbocation (it cant even happen with methyl and extremely unlikely with the primary).

hope that helped, the people i tutored always seemed to get it this way