Yazomi
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Can someone explain how to answer this please. Yes it’s only one marker but I suck at reading infrared spectrum graphs T^T
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Hellllpppp
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The question is about the infrared spectrum of the alcohol after being (or attempting to be) oxidised. If there’s an O-H bond then it must not have been oxidised so it must be a tertiary alcohol so A.
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Yazomi
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(Original post by Hellllpppp)
The question is about the infrared spectrum of the alcohol after being (or attempting to be) oxidised. If there’s an O-H bond then it must not have been oxidised so it must be a tertiary alcohol so A.
Wait I thought tertiary alcohol couldn’t be oxidised?

The answers meant to be B

But I’m confused on how you can tell apart -OH alcohol and -OH Acid. I find the range they’re in very similar.

With this I was debating that the combination would either be -COOH so primary alcohol
Or I would probably be considering -OH as in aldehyde and C=C. Which leads to primary alcohol as well

I think they were trying to get me thinking towards ketone but the ketone range is so close to c=c as well like how do you distinguish between close curves if that makes sense
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Hellllpppp
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(Original post by Yazomi)
Wait I thought tertiary alcohol couldn’t be oxidised?

The answers meant to be B

But I’m confused on how you can tell apart -OH alcohol and -OH Acid. I find the range they’re in very similar.

With this I was debating that the combination would either be -COOH so primary alcohol
Or I would probably be considering -OH as in aldehyde and C=C. Which leads to primary alcohol as well

I think they were trying to get me thinking towards ketone but the ketone range is so close to c=c as well like how do you distinguish between close curves if that makes sense
Yeah tertiary alcohols can’t be oxidised. I was trying to say if there’s still an alcohol group in the spectra then it hasn’t been oxidised so it must be tertiary. I didn’t really look at the spectra (sorry!) so I missed the c=o bond and I think you’ve misidentified the C-H bonds as an O-H bond. If it’s got c=o as well as an o-H with these possibilities it has to be a -COOH so primary alcohol but I don’t think there’s an O-H so it must be a ketone and therefore originally a secondary alcohol. You don’t need to worry about c=c as they aren’t formed during oxidation with potassium dichromate and none of these already contain a c=c bond.
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Hellllpppp
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Sorry I’m tired and not making much sense
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gd99
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As far as I can tell, it needs you to distinguish between a possible carboxylic acid or ketone.

The reaction of an alcohol with potassium dichromate will convert a primary or secondary alcohol to a carboxylic acid or ketone, respectively.

‘A’ cannot be oxidised as it is a tertiary alcohol, so cannot be the product which the IR spectrum corresponds to, as the spectrum very clearly has a carbonyl peak present.

‘C’ and ‘D’ are both primary alcohols, so will form carboxylic acids. These will have a broad O-H peak around 300 ppm, which is not present in the spectrum (if you’re unsure, google ‘carboxylic IR spectrum’ and look at the google images results - this has some good examples which you can compare to the spectrum in the question to help you see the difference).

‘B’ is a secondary alcohol so forms a ketone. This fits the spectrum, as there is a C=O present but no O-H carboxylic acid group hence only the C-H bonds being seen in the spectrum around 3000 ppm.

Also, seeing your previous suggestion, you won’t get any C=C bonds formed in this situation, so don’t worry about that at all - it doesn’t happen.

Hope this helps - just say if any of it isn’t clear!
Last edited by gd99; 4 months ago
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Yazomi
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Ahhhh that makes sense now!! Thanks both of you! Think more visual practise is what I need
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