Question 36

[Guest]

I've having a problem with # 36, in the original molecule both the carbons are tertiary alcohols, and from my understanding you can't oxidize a tertiary alcohol into a carboxylic acid, but rather into a ketone, which is why i chose answer choice C, a little clarification would be greatly appreciated!!!

[admin]

Tertiary alcohols are quite difficult to oxidize.

Actually, the reaction as described can occur with certain powerful oxidizing agents. Alternatively, acidic conditions can be used to create dehydration and then the alkene can be fully oxidized. Both of which are a bit much for the MCAT.

This question has been toned down to using mild oxidizing conditions to guarantee that the oxidation cannot occur because, as you correctly noted, it is a tertiary alcohol.

[Guest]

so then why exactly is A, a carboxylic acid, the answer?

[admin]

Let's pretend you had a benzene ring (which you don't need to know about !) and there was just a lonely methyl group attached, strong oxidation turns that single methyl group into -COOH.

Now even more amazing, if the substituent was not methyl but rather propyl. Guess what strong oxidation does to C-C-C: turns it to -COOH ! Yep, just one carbon just as if it was methyl. The other carbons become carbon dioxide. In the reaction that you had, a powerful oxidation is required and literally cleaved the central bond, oxidized the now secondary alcohol up to a COOH (that is why you end up with 2 molecules).

The only redox organic chem reactions you really need to know are here, so don't worry about this one: http://www.goldstandard-mcat.com/organic-chemistry-mechanisms/

[admin]

bump

[mohsinalam5969]

Tertiary alcohols aren't oxidised by acidified sodium or potassium dichromate(VI) solution. There is no reaction whatsoever.

If you see a structure,you will look at what is happening with primary and secondary alcohols, you will see that the oxidising agent is removing the hydrogen from the -OH group, and a hydrogen from the carbon atom attached to the -OH. Tertiary alcohols don't have a hydrogen atom attached to that carbon.

So answer d is correct.