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I was working the following spectroscopy problem from Clayden 2e that asks us to identify the structure of a compound from information about its carbon-13 NMR peaks.

Problem 3.5: The solvent formerly used in some correcting fluids is a single compound $\ce{C2H3Cl3}$, having 13C NMR peaks at 45.1 and 95.0 ppm. What is its structure? How would you confirm it spectroscopically?

I initially thought that the structure would be 1,1,1-trichloroethane (shown below) since there will be two different carbon chemical shifts: one bonded to three $\ce{H}$ atoms and one $\ce{C}$ atom in the 0-50ppm region (corresponding to the 45.1 ppm peak) and another peak for a carbon bonded to three $\ce{Cl}$ atoms in the 50-100ppm region (corresponding to the 95.0ppm peak).

enter image description here

Although it considers 1,1,1-trichloroethane, the solutions manual to the book concludes that the correct structure is 1,1,2-trichloroethane (shown below), the other possible structure with formula $\ce{C2H3Cl3}$.

enter image description here

However, this compound would have both peaks close to eachother in the 50-100ppm range.

Wouldn't the correct molecule be 1,1,1-trichloroethane, and wouldn't the solutions manual be incorrect? The NMR specs below that I found online corroborate my thinking.

enter image description here

enter image description here

References

Clayden, J., Greeves, N., Warren, S. Organic chemistry, 2nd ed.; Oxford University Press: New York, 2012.

https://www.chemicalbook.com/SpectrumEN_71-55-6_13CNMR.htm

https://spectrabase.com/spectrum/5WUteTf4M4u

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    $\begingroup$ I don't have a copy of the textbook so can't confirm, but the spectra predictions you post are accurate. The wikipedia (infinite in its wisdom) writes of 1,1,1-trichloroethane as a solvent, but not of 1,1,2-TCE. A blooper? $\endgroup$
    – Buck Thorn ♦
    Dec 15, 2018 at 16:09
  • $\begingroup$ Most likely was a blooper on the part of the authors. I just wanted to make sure that my explanations for the two NMRs I found online were correct. $\endgroup$
    – Ethiopius
    Dec 15, 2018 at 16:21
  • $\begingroup$ So probably you should write a very short answer so the Q can be closed $\endgroup$
    – Alchimista
    Dec 15, 2018 at 17:43
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    $\begingroup$ You can find another reliable 13C-NMR on this site: hmdb.ca/spectra/nmr_one_d/3289, which also confirms you are right about 1,1,1-trichloroethane (can find in: pubchem.ncbi.nlm.nih.gov/compound/…). $\endgroup$
    – Mathew Mahindaratne
    Dec 15, 2018 at 22:44
  • $\begingroup$ SDBS: sdbs.db.aist.go.jp/sdbs/cgi-bin/direct_frame_top.cgi confirms your conclusion. $\endgroup$
    – user55119
    Dec 16, 2018 at 2:17

1 Answer 1

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I fully agree with your assessment and assume that this is a mistake in the book. I wonder what exactly the authors suggested as spectroscopic verification. I personally would suggest using 1H-NMR as a verification method. In 1,1,1-trichloroethane, only one hydrogen peak should be observed as the three protons of a methyl group are always homotopic. In 1,1,2-trichloroethane, two signals in a $1:2$ ratio should be observed as a triplet and dublet, respectively. Depending on what the book suggests as verification, it should be easy to confirm the nomenclature error.

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  • $\begingroup$ The authors did suggest using 1H-NMR as the method to "confirm it spectroscopically". This is what they provided as the suggested method of spectroscopic confirmation: "The second structure (1,1,2-trichloroethane) looks better but it would be easily confirmed by proton NMR as the first structure (1,1,1-trichloroethane) would have one peak only but the second would have two peaks for different CHs. The solvent is indeed the second structure 1,1,2-trichloroethane." $\endgroup$
    – Ethiopius
    Dec 16, 2018 at 18:10
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    $\begingroup$ @Ethiopius Yup, that sounds like the authors were having a major derp moment. $\endgroup$
    – Jan
    Dec 17, 2018 at 3:51

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