Naturalproductman’s Blog

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Why is CDCl3 a Triplet?

Posted by naturalproductman on May 29, 2009

Ever wonder why when you’re taking a 13C NMR in deuterated chloroform and look at the solvent peak – there are three evenly spaced peaks with equal intensities?

The answer can be found in your good old sophmore organic chemistry textbook (*I recommend the Marc Loudon book) and/or a physical chemistry text. It turns out that 1H has a spin of 1/2 but 2H has a spin of 1. In the case of a proton (1H) the spin state will either be +1/2 or -1/2, and in the case of a deuterium (2H) the spin state will either be +1, 0 or -1. And since we’re not running the 13C NMR in a deuterium decoupled mode – we’ll see the splitting from deuterium onto the carbon. Because there are three states: +1, 0 and -1, then we’ll see the peak split into three lines.

That’s so amazing.

8 Responses to “Why is CDCl3 a Triplet?”

  1. I’m currently analysing 13C spectra and really enjoyed reading your blog entry! 🙂 quite helpful and enlightening!

  2. Sina said

    This question was asked in my organic exam last week and it’s only know that I found the answer! Thank you 🙂

  3. Loshe said

    Ive been asked that in a lab report and i looked everywhere but never found the exact clear answer!
    Thank you 🙂

  4. james said

    Could you explain why the peaks are equal intensity please?

    • naturalproductman said

      I would think that they are equal level because the three levels (-1, 0, and +1) are equally occupied. In a triplet state of a proton NMR, you usually see the middle peak higher. That is because a triplet in a proton NMR is usually really a doublet of doublets (two doublets because the proton is split by two equal neighbors). Because there is overlap in the J-value (of the two doublets) in the proton NMR triplet, the middle peak is higher.

      • Chemist said

        Hello, why is methyl isocyanide H NMR a triplet/ multiplet?

      • naturalproductman said

        Here’s a reference that explains the 14N (I =1) splitting that leads to the triplets (Figure 3 legend): McCullough CR1, Pullela PK, Im SC, Waskell L, Sem DS., J Biomol NMR. 2009 Mar; 43(3): 10.1007/s10858-009-9300-8.
        Published online 2009 Feb 6. doi: 10.1007/s10858-009-9300-8

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