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#1 2009-03-16 16:54:32

orgopete
Administrator

Identify 7-bromohept-4-ynal from IR and NMR spectra

Yahoo!Answers in chemistry 3/14/09 wrote:

Open Question: Organic Chemistry Synthesis Products and IR help please!!!! Check my work?
http://www.curvedarrow.com/chem/ZZ3324EE9A.jpg
Which functional groups do you see?
ketone, ester, ether, terminal alkyne (-CCH), internal alkyne (-CC-), benzene, alkene, nitrile, cycloalkane, alcohol, aldehyde

I see: nitrile, alcohol, terminal alkyne
http://www.curvedarrow.com/chem/ZZ411C6864.jpg
I see: B?

I suppose I should stop picking on this guy. He has provided fodder for my jibes and problems to post.

Let's analyze what we have. The IR shows a CΞC at 2200 cm-1 and a C=O at 1700 cm-1.

The MF C7H9BrO means we have 3 rings and/or double bonds. With the C=O, that leaves us with 2 rings or double bonds. The CΞC means no other rings or double bonds.

The NMR shows a peak near 10 ppm, 1H, 2 adjacent hydrogens. If you look in a table, you will find this shift is consistent with an aldehyde. Therefore we have a CHOCH2-

The rest of the NMR shows several CH2 groups by the integral. None has more than a single CH2 adjacent as they are all triplets. The highest field almost looks like a quartet, but I am guessing that since these are hand drawn, it is in error. This means all of the CH2 hydrogens are in isolated units of CH2CH2.

Let's try to put this together. A CHO + CH2CH2 + CΞC + CH2CH2 + Br. That gives us D.

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