Ochem questions

[lilchinoboy03]

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I see this Williamson Ether synthesis problem everywhere (or something like it):

1-iodo-propane + CH3O-Na+ --> methyl propyl ether.

Ok so I get how it works. But how come you don't see elimination and get propene? There was a question on Achiever, which asks this and had both the ether and the propene as a choice, as well as both. Why does it not eliminate????

Also, another similar type of question.

(CH3)2CHCl + CH3O- (in methanol) -->

What does it favor? And the answer is E2. I understand why it's not SN2 because of steric hindrance, but why not SN1 or E1? Ethanol is said to be polar protic is favor SN1, but is methanol not also protic??? Also the explanation seems to insinuate we know it is bimolecular because it is a secondary halide...is this true? Just because it's not tertiary, it won't do SN1 or E1?

 

[feileung]

I believe you're right to rule out SN1 and E1 due to this not being a tertiary substituent. That leaves you with SN2 and E2 as your choices. CH3O- is a strong base and therefore will act as such and you will have an elimination RXN. You would have needed a weak base there to allow it to act as a nucleophile in order to go SN2.

 

[lilchinoboy03]

I believe you're right to rule out SN1 and E1 due to this not being a tertiary substituent. That leaves you with SN2 and E2 as your choices. CH3O- is a strong base and therefore will act as such and you will have an elimination RXN. You would have needed a weak base there to allow it to act as a nucleophile in order to go SN2.

but isn't it also CH3O- in williamson ether? and that is SN2 right?

 

[feileung]

Errr....I haven't covered Williamson Ether reactions yet! Sorry if I muddled it up more than I helped