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CHEM A-level HEL|P

I don't get why it would be this answer instead of A and B cuz they are aldehydes.

why would it be a ketone if (C is a ketone )instead of an aldehyde or primary alcohol?

The answer is C.

Can someone explain, please?
(edited 2 years ago)
Reply 1
Hi Kittymity,

The answer can’t be A or B as oxidation with potassium dichromate and primary alcohol produces aldehydes when solution is heated gently. Not reflux. When primary alcohols are refluxed the product is a carboxylic acid. When secondary alcohols react with acidified potassium dichromate under reflux, the product is a ketone. So the answer is C. Hope that helps. :smile:
I know I'm like a year late but lets do this.
The reflux of A, would form C5H10O2 as the alcohol is tertiary, therefore cannot change, and the double O bond is an aldehyde which would turn into a carboxylic acid, making the overall formula C5H10O2

The reflux of B, would form C5H8O3 as the secondary alcohol is turned into a ketone, and the aldehyde turns to carboxylic acid, so it has 1 too many oxygen.

The reflux of C however, would create a ketone on the secondary alcohol, and the already existing ketone would remain a ketone. This brings the molecular formula to C5H8O2.

I doubt you will ever have these issues again, but in the case of struggle, try drawing out the skeletal product and counting the carbon, hydrogen and oxygen. This is how I solved it.
Kindest Regards!

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