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It is a $\ce{^1H}$-NMR spectrum and I think the signal near 3,61 ppm is the CH2 group next to the hydroxy group. But which signal is the hydroxy group and which protons are in the multiplet?


Welcome to ChemistrySE.

In short: is the spectrum consistent with 3-methyl-1-butanol? No. The triplet splitting and integral of the signal at 0.86ppm is inconsistent with an isopropyl sidechain. This suggests a methyl group attached to a methylene, $\ce{-CH2-CH3}$.

The signal at $\pu{3.6 ppm}$ has a chemical shift symptomatic of an alcohol, as you suggest. It has diagnostic splitting of $\pu{4.2 Hz}$, also consistent with coupling to the alcohol peak. So, this peak is a doublet of triplets..... which makes it look a bit like a quartet. To see this coupling, the sample needs to very dry to eliminate exchange decoupling. So where is the alcohol peak? In the absence of any exchange, and in chloroform (most likely solvent used given the spectrum shown), alcohol peaks usually come in the region of about $1.2$-$\pu{1.5 ppm}$. So possibly under the multiplet. Which would then leave you with 6 protons to account for......or $3 \times \ce{CH2}$ groups. The peak at $\pu{1.5 ppm}$ has coupling that suggests it is attached to the $\ce{-CH2OH}$, giving a $\ce{-CH2CH2OH}$ group. There are 14 protons in all. You've got a $\ce{-CH2-CH3}$, a $\ce{-CH2CH2OH}$ and the rest are probably $\ce{-CH2\!-}$. How might you put them together?

In the real world, identification of complete unknowns are rarely done using $\mathrm{^1H \ NMR}$ alone. Mass Spec, $\mathrm{^{13}C}$, and a range of $\mathrm{2D}$ options are very useful.

And to answer a follow-up question below, the splitting at 1.54 is from the protons on the beta carbon, and is a triplet of triplets. When coupling constants are close (6.5 and 6.8) this will appear as a pseudo-pentet, as shown below:

enter image description here

  • $\begingroup$ Do you also know which solvent is used? $\endgroup$ Apr 15 at 11:39
  • $\begingroup$ Not conclusively. CDCl3 is the most common solvent used for small organics - its residual peak comes at 7.26ppm, and so not visible in this spectrum. Other common possible solvents (dmso, methanol, acetone) are not visible in this spectrum. $\endgroup$
    – long
    Apr 18 at 7:07
  • $\begingroup$ Thanks for your answer! One last thing I want to know.... Can you explain the splitting at 1,54Hz? $\endgroup$ Apr 29 at 8:21
  • $\begingroup$ This is due to the protons on the beta carbon (the middle ones in this group) -CH2-CH2-CH2OH. They are coupled to the terminal CH2 and also the gamma CH2, so will be a triplet of triplets. When the coupling is very close, (6.8 and 6.5), this pattern will look like a pseudo-pentet. I'll put the splitting pattern in the answer above. Feel free to accept the answer to close it off if it addresses what you were after. $\endgroup$
    – long
    Apr 29 at 22:13

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