Chemical Forums
Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: ritwik08 on October 07, 2008, 12:04:03 PM
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NC-CH2-CH2-COOH
Will the C of CN be counted in main chain????
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No. The CN group is a cyano group, and it is not counted as part of the parent chain.
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No. The CN group is a cyano group, and it is not counted as part of the parent chain.
Thats exactly what I thought. But my teacher has marked me wrong for not counting the carbon in CN. Can you supplement this argument with a reliable source please?
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What did you put as your answer that was marked wrong?
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I think it depends if the nitrile is the highest priority substituent or not. If it is, the carbon is included in the backbone and it is named as a 1-nitrile. If there is a higher priority substituent, the carbon is not included in the chain and the C-N triple bond is named as a cyano group.
In this example, I would say the acid is highest priority and the compound should be named 3-cyano-propanoic acid (ChemDraw agrees).
http://www.chem.ucalgary.ca/courses/351/orgnom/nitriles/nitriles-01.html
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What did you put as your answer that was marked wrong?
I put:
3-cyano-propan-1-oic acid
but he says it should be
4-cyano-butan-1-oic acid
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I disagree with your professor.
Go to this site:
http://www.lookchem.com/cas-160/16051-87-9.html
Give him the CAS number and tell him to double-check if he doesn't believe you.
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fyi - While not technically incorrect, the -1- before the -oic acid is redundant. Carboxylic acids, by definition, must be at the 1 position of the longest linear chain.
Even ChemSpider -- notorious for having every possible name of a compound (and some impossible names) -- says that compound is 3-cyanopropanoic acid only.
http://www.chemspider.com/Chemical-Structure.231083.html
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Carboxylic acids, by definition, must be at the 1 position of the longest linear chain.
What about...
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touche. Gotta pull out the exceptions, don't you? :)
So the acid defines the parent chain, and is by definition at position 1. That might be a more precise way to say it. Your example would be 2-ethylbutanoic acid.
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touche. Gotta pull out the exceptions, don't you? :)
That's the way my brain is wired. I don't even have to think about counterexamples, they just lie around :)
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Thanks guys for those proofs. Thanks once again. I will give him the CAS number, but there is little chance that he would pay heed to my argument.
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Your teacher is confused and wrong.
Heres why:
With only the CN group there the carbon of the CN is included in the longest chain name with the CN denoted as a nitrile.
NC-CH2-CH2-CH3 is butanenitrile
With the acid group as well the longest chain is named for the acid with the CN as a cyano group
NC-CH2-CH2-COOH is 3-cyanopropanoic acid
See this for the IUPAC proof of this:
http://www.acdlabs.com/iupac/nomenclature/93/r93_557.htm