F324 June 2012 NMR question, please help

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F.R.A.W.A
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http://www.ocr.org.uk/Images/135165-...lysis-june.pdf

http://www.ocr.org.uk/Images/131288-...d-analysis.pdf

The final question involves identifying an ester, there is a peak at 7.3ppm for an aromatic group and the relative area is 5, for C6H5 which is fine - this I get.

However, the peak at 7.3 is split into 5 - this makes no sense to me at all. There isn't 4 Hydrogen atoms on the adjacent Carbon atom, there are two, so surely it must be a triplet??

I know this will require a lot of inconvenient link clicking and general horsing about but I'd really appreciate it if someone could help because I'm really struggling with it.

Cheers
F.R.A.W.A
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Munrot07
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(Original post by F.R.A.W.A)
http://www.ocr.org.uk/Images/135165-...lysis-june.pdf

http://www.ocr.org.uk/Images/131288-...d-analysis.pdf

The final question involves identifying an ester, there is a peak at 7.3ppm for an aromatic group and the relative area is 5, for C6H5 which is fine - this I get.

However, the peak at 7.3 is split into 5 - this makes no sense to me at all. There isn't 4 Hydrogen atoms on the adjacent Carbon atom, there are two, so surely it must be a triplet??

I know this will require a lot of inconvenient link clicking and general horsing about but I'd really appreciate it if someone could help because I'm really struggling with it.

Cheers
F.R.A.W.A
Well the problem is that you have 6 carbons in a benzene ring each with a hydrogen (or in this case only 5 carbons have a hydrogen) and some are different hydrogen environments (in this case there are 3 different environments on that ring) and you have to look at the number of hydrogens on the adjacent carbon of each different environment. Plus the splitting pattern isn't clear. I would have said a hextet but the markscheme allows for a quintet, hextet or heptet. Whats probably happened is that there were a few triplets from each environment which were so close together in terms of chemical shift that they have merged into one multiplet.

I personally choose to ignore the splitting pattern for a benzene ring. I write it down but it doesn't give you any helpful information. A benzene ring is a benzene ring so you know how many hydrogens will be on it, 6, unless there is a different group added to it, in which case it will have a different shift on the NMR spectrum (in this case a peak showing a CH2 group bonded to the benzene). Basically, don't worry about the splitting pattern for a benzene ring, it really doesn't add much information for an A level question.
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F.R.A.W.A
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Thanks, it really isn't clear which confused the hell out of me, but I probably looked into it a bit too deepy. Tah again
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Pigster
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The spec. says (page 49):

Candidates will be expected to identify aromatic protons from chemical shift values but will not be expected toanalyse theirsplitting patterns.

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