I have a question about 1H NMR splitting of 3-methyl-1-butanol. enter image description here

The spectrum looks as the following.

enter image description here

The assignment of the NMR spectrum is the following.

Assign.     Shift(ppm)

  A             3.673
  B             1.66
  C             1.57
  D             1.49
  E             0.922

So based on the results, A hydrogen is splitted into triplet. Is this splitted by D hydrogen? If so, why not C hydrogen on the alcohol group?

The results are retrieved from the following link: https://www.chemicalbook.com/SpectrumEN_123-51-3_1HNMR.htm

  • $\begingroup$ The integration shows that the most upshifted signal has two hydrogens and the NMR table also agrees to show that H-C-OH shows a signal near 3.4ppm. $\endgroup$ Mar 4 '20 at 23:29
  • $\begingroup$ There is no OH signal visible here. And I´m guessing this is a fake spectrum, unless they took D2O as solvent. $\endgroup$
    – Karl
    Mar 5 '20 at 0:44
  • $\begingroup$ Well, it's possible that OH is in this multiplet if solvent is non-polar like CCl3D. If the solvent was D2O there still would be peak from HDO. $\endgroup$
    – Mithoron
    Mar 5 '20 at 0:49
  • $\begingroup$ There is no residual chloroform peak so it is not in CDCl3, the quoted reference does not say what the solvent was. $\endgroup$
    – Waylander
    Mar 5 '20 at 12:47

In this example, HA is indeed split by HD, but you have quite rightly identified that we don't see coupling to the alcohol proton, HC. This is pretty normal that we don't observe couplings to protons that are termed labile; -OH, -NH2, -SH, for example. Whenever samples contain trace amounts of an acid or base, there will be very fast exchange between the alcohol proton and that other species (water is often the culprit). In solvents like chloroform (which this spectrum was run in), the exchange is very fast, and you just observe a single peak. In other solvents, such as dmso, you might observe two broadened peaks. But, the exchange means that any coupling to that nucleus is lost

We do sometimes observe coupling to alcohol protons. If you can eliminate exchange, or slow it sufficiently, you will observe 3J couplings as you would for any other nuclear coupling pathways. 3J couplings to alcohol protons are in the order of 3-6 Hz, commonly.


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