ether cleavage question

[jeejeejiji]

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If H-Br reacts with (CH3)3C-O-CH3
where is the Br added on to?
Does it add on to the CH3 (less hindered side)
or does it add on to the (CH3)3C (the more hindered side)?

The kaplan blue books seems to divide this into two possibilities:
the SN1 and SN2
and it seems to explain that the reaction goes through a SN1 reaction when the structure of the ether is branched and hindered,
and in this case Br adds on to the more hindered side of the ether.

But in other text books, and from what I've heard in class, and searched on line, the reaction is 'not' divided into SN1 and SN2,
and the Br is always added to the less hindered side due to its bulkiness.


Does anybody know which explanation is right??

 

[Decan]

If I had to guess, I would say H attaches to the less hindered side b/c the carbocation formed would be very stable.

 

[jeejeejiji]

that's what kaplan is saying,
but if you search on line, and read some texts,
its says the opposite; that H adds on to the more hindered side because it goes throug a SN2
I can't figure which is right??

 

[jdoc04]

that's what kaplan is saying,
but if you search on line, and read some texts,
its says the opposite; that H adds on to the more hindered side because it goes throug a SN2
I can't figure which is right??

what pg# in Kaplan?

 

[jeejeejiji]

I didn't post the page number for kaplan because it probably would change with different versions.
For mine it's p.403 and its in the chapter for alcohols and ethers.

I just asked Dr. Romano for further help on this, and will post the answer when I get a reply.

 

[potato86]

If H-Br reacts with (CH3)3C-O-CH3
where is the Br added on to?
Does it add on to the CH3 (less hindered side)
or does it add on to the (CH3)3C (the more hindered side)?

The kaplan blue books seems to divide this into two possibilities:
the SN1 and SN2
and it seems to explain that the reaction goes through a SN1 reaction when the structure of the ether is branched and hindered,
and in this case Br adds on to the more hindered side of the ether.

But in other text books, and from what I've heard in class, and searched on line, the reaction is 'not' divided into SN1 and SN2,
and the Br is always added to the less hindered side due to its bulkiness.


Does anybody know which explanation is right??

I think the oxygen gets protonated by H in HBr, and it becomes a good leaving group, which leads to a tertiatry carbocation formation. Then Br should add to the tertiary C, forming (CH3)3CBr.
I saw it in Kaplan too..under Ether section.

 

[Mstoothlady2012]

An ether with primary & secondary alkyl groups usually undergoes cleavage by SN2 attack of a nucleophile on the less hindered alkyl group. Here we have one tertiary allkyl group & one primary alkyl group, therefore it undergoes SN1 mechanism. Since SN1 involves formation of a carbocation, we want to pick the most stable carbocation, which in this case will be tertiary. Hence SN1 cleavage of the tertiary C-O bond will occur, this will give

(CH3)3CBr + HOCH3

Hope this helps! i tried my best to explain. Let me know if you dont understand anything i will be glad to explain it further🙂