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#1 2008-11-20 18:01:46

orgopete
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Yahoo NMR problem

Yahoo Chemistry Answers

Organic chemistry NMR spectrum question?
The formula is C7H15ClO. The NMR spectrum has four signals.
doublet at 0.9
multiplet (maybe nine lines) at 1.6
quartet at 3.3
triplet at 3.6
no integral
What is the structure?

I have on my to do list to write an NMR tutorial. This is an example of how I go about doing them. I call it the tinker toys method. Let's start with the pieces.
C7H15ClO -- no rings or double bonds

triplet at 3.6, a HOCH2CH2; chemical shift for HO + CH2 with CH2 adjacent; cannot be HOCH(CH3)CH2 for example, wouldn't be a triplet

quartet at 3.3 gives three adjacent hydrogens, therefore ClCH(CH3)CRR'R" or CH2CHClCH

doublet at 0.9; CH3CHR

That leaves three carbons missing. I thought the peaks 0.9 could be CHC(CH3)2.

The quartet at 3.3 must contain the carbon with the chlorine on it, look it up in a table. This could be ClCCHCH3 or CH2CHClCH. If it were ClCCHCH3, this would give another CH3 doublet. Let's consider that it could be a CH2CHClCH; still a quartet with the adjacency rule.

If not ClCHCH3, then double at 0.9 not CH3CHCl. The doublet at 0.9; (CH3)2CH-.

Putting this together gives us HOCH2CH2 + CH2CHClCH(CH3)2 with a missing CH2.

If I attach them together, then I get HOCH2CH2CH2CHCl(CH3)2, 4-chloro-5-methylhexanol.

The peak at 1.6 is the missing CH2.

However, that leaves me with two missing signals, the OH and the CH of the CH(CH3)2. Below is the theoretical spectrum. Is it correct? If I had the spectrum that the data was cited from, I could really determine where the missing signals are. Oh, well.

    http://www.curvedarrow.com/chem/4chloro5methylhexan1ol_NMR.jpg

I had overlooked the comment that the spectrum had four signals. Note that my proposed structure has six signals and 6 hydrogens are contained in the one signal. It seems reasonable to expect the other reported signals to contain one and two hydrogens. That would leave 6 hydrogens at 1.6 ppm. A 9-peak multiplet does not agree with this description of 6 hydrogens. There must me more signals that were not reported.

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