DAT Achiever SNS 1 Ques. 75?

[DelToro06]

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I dont understand how the answer is C. There are no hydrogens to spare to make the most stable alkene. Im just confused as to it. If someone could explain it better than achiever it would be much appreciated.

 

[potbelly]

I dont understand how the answer is C. There are no hydrogens to spare to make the most stable alkene. Im just confused as to it. If someone could explain it better than achiever it would be much appreciated.

Okay.. First OH gets protonated and become water, which is a good leaving group. After water leaves, it becomes a secondary carbocation.

Then, methyl shift occurs here to make more stable carbocation. (becomes tertiary carbocation in this case.) Fianlly, a double bond is formed.

Hope this helps.

 

[nze82]

Post the question!

 

[DelToro06]

What major alkene product will be formed through the following dehydration of alcohol?

(CH3)3-C-CHOH-CH3 ---(H+,heat)----> the answer is:

(CH3)2-C(double bond)-C-(CH3)2

 

[nze82]

What major alkene product will be formed through the following dehydration of alcohol?

(CH3)3-C-CHOH-CH3 ---(H+,heat)----> the answer is:

(CH3)2-C(double bond)-C-(CH3)2

Acid catalyzed reaction + Heat = E1 reaction
So, the first thing that happens is that the -OH group, which is a poor leaving group, gets protonated to become a better leaving group.

(CH3)3-C-CH(HOH+)-CH3

Then the -HOH+ leaves resulting in:

(CH3)3-C-CH+-CH3

At this point, we have a secondary carbocation. But this can undergo rearrangement (Methyl Shift: Remember to look for rearrangements in case of SN1 and E1 reactions) to produce a more stable tertiary carbocation as follows:

(CH3)2-C+-CH(CH3)-CH3

Then the green proton is abstracted, resulting in the final product that looks like:

(CH3)2-C=C-(CH3)2

Hope this helps!