Destroyer 2011 Ochem #90

[BMEEngineer]

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Why is choice c (primary halides react faster than tertiary halides) something that is true for SN2 reactions?

My notes (from Chad) state that tertiary halides would react with E2, E1, or SN1 not SN2. I assumed this meant that tertiary halides don't react in SN2.

Thanks!

 

[Dotoday]

No. Destroyer is correct. Chad, not so much. It is very difficult to do a Sn2, backside attack on a tertiary halide. Too much steric hindrance. Therefore, sn1 is a better option. For the primary halode, Sn2 is the best option because it is unhindered and cannot form a stable carbocation, therefore cannot do Sn1. Hope this helps.

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[BMEEngineer]

Thanks for the clarification!

 

[Slumber]

Why is choice c (primary halides react faster than tertiary halides) something that is true for SN2 reactions?

My notes (from Chad) state that tertiary halides would react with E2, E1, or SN1 not SN2. I assumed this meant that tertiary halides don't react in SN2.

Thanks!

What is the problem anyway?

For SN2 halide, it's always methyl halide > primary > secondary. It's very difficult to have initiate SN2 with tertiary halid.

 

[KyoPhan]

I'm looking at chad's notes and it also say that it's methyl>primary>secondary for SN2 reactivity. Tertiary doesn't happen for sn2.

 

[BMEEngineer]

What is the problem anyway?

For SN2 halide, it's always methyl halide > primary > secondary. It's very difficult to have initiate SN2 with tertiary halid.

I'm not sure if the book puts me under contractual obligation to not retype the question. It's one of those questions where there are about 4 things that seem to be true about SN2 and a fifth choice of "all are true", but I thought this statement was wrong (in my OP). I think what DoToday is saying is that SN2 is very energetically unfavorable and SN1 is going to happen much faster and first, so that's how Chad teaches it for ease of us remembering (it worked for me!), but that doesn't mean that SN2 will not react ever with a tertiary halide.