Sn2

[DentalMan123]

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Which of the following alkyl halides will be the most suitable for a SN2 reaction? Why?

A. CH3Cl (chloromethane)

B. 1-chloropropane

C. 2-chloropropane

D. tert-Butyl chloride

E. 1-chloro-1-cyclohexene

 

[loveoforganic]

What's the mechanism look like? You have an attacking species that has to make it into that carbon orbital opposite the halide, so the less steric hinderance around that orbital, the easier the access and the more suitable the SN2 substrate. Given that, which would you choose?

 

[Rabolisk]

Very simple question. Ask yourself, what about the substrate favors SN2 over SN1?

 

[DentalMan123]

i dont understand, please elaborate

 

[Rabolisk]

Let's start from beginning. What do you know about SN2? What do those even stand for?

 

[DentalMan123]

substitution nucleophlic bimolecular reaction
would it be A? since it is the least substituted?

 

[Rabolisk]

Yes. Make sure you know why that favors SN2.

 

[DentalMan123]

So the answer is A for sure?
Why is it A? can you please give me the full explanation why
thanks

 

[Rabolisk]

The answer is A because it is least substituted. The nucleophile attacks the substrate's backside while the bond between the carbon and the leaving group (chlorine) is broken. They happen simultaneously. Review the mechanism and justify why primary halides react faster than tertiary halides for SN2.

 

[shffl]

You can kinda think of it like this (not sure if it's correct so someone correct me if I'm wrong but this was how I understood it as): SN2 reactions happen in one step. The bigger the molecule (more substituted, ,more steric hindrance), the more difficult for it to react in one step because the nucleophile has to "search" for the right spot among this giant molecule. Smaller molecule on the other hand, it is easier for the nucleophile to hit the right spot therefore reaction can proceed in one step.

 

[DentalMan123]

so why cant the answer be B? B is also a primary structure....
or E, which is a vinyl group, i believe?
Thanks

 

[Rabolisk]

Well, actually, CH3Cl is better than primary halides. In primary halides, the carbon that is attached to the halide is also bonded to one carbon group. In a methyl halide like CH3Cl, the carbon is not bonded to any carbon. Simply put, CH3Cl is even less substituted than CH3CH2CH2Cl or any vinyl halides.

 

[shffl]

chloromethane is smaller than 1-chloropropane. basically, the smaller the compound is the more likely it will be SN2 reaction

 

[Wakesc]

It's the least substituted, there's only one carbon as opposed to the others which have more alkyl parts. I too have difficulty remembering which is one step and which is two.