Iodoform Question

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The question is from Q5 Section A of Unit 4 June 2016 Edexcel GCE Chemistry. The question is attached, and apparently the answer to part (c) is D. Can someone explain why both W and Z produce iodoform when reacting with iodine in alkaline solution? I thought the iodoform test gives a positive result when the functional group CH3COR was present, i.e. all ethyl ketones and ethanal. Surely Z should not give a positive result as it doesn't even have a C=O group, let alone the CH3COR functional group.

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tony_dolby

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I am digging in to the dim and distant past (why do exam boards expect people to know such out-dated reactions!), but seem to remember that many secondary alcohols give a positive iodoform test. This would explain why Z is positive. W is expected because it is a ketone. X is an aldehyde, but you are right, the only aldehyde that gives a positive test is ethanal. Y is a primary alcohol, so it won't give a positive test (only ethanol works).

http://www.chemguide.co.uk/organicpr.../iodoform.html

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Dennizun_win

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(Original post by tony_dolby)
I am digging in to the dim and distant past (why do exam boards expect people to know such out-dated reactions!), but seem to remember that many secondary alcohols give a positive iodoform test. This would explain why Z is positive. W is expected because it is a ketone. X is an aldehyde, but you are right, the only aldehyde that gives a positive test is ethanal. Y is a primary alcohol, so it won't give a positive test (only ethanol works).

http://www.chemguide.co.uk/organicpr.../iodoform.html

Thanks a lot!

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