In lab I combined 1-propanol with acetic acid to make propyl ethanoate. I obtained an HNMR and an IR of the product. The HNMR suggests that the product was successfully synthesized. The IR has the correct bands for the expected product, but it also has an OH peak. What would this band be?


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  • $\begingroup$ Any extra peaks in your HNMR, maybe something near 1.5 ppm? $\endgroup$ – orthocresol Mar 26 '17 at 0:34
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    $\begingroup$ What is the shape of this "OH" peak? Is it the typical broad hump or is it more like a small spike with a broad shoulder? That second one is the overtone for the carbonyl peak. $\endgroup$ – Ben Norris Mar 26 '17 at 0:50
  • $\begingroup$ How did you purify the compound and have you been careful about making sure that the sample is dry? $\endgroup$ – Zhe Mar 26 '17 at 13:42

The Spectral Database for Organic Compounds maintained by AIST includes an IR spectrum recorded for the neat film of this compound equally known as propyl acetate (CAS registry number 109-60-4):

enter image description here

If you superimpose an IR spectrum of your isolated product, and see the absorption band by OH and others by your starting material, the pure 1-propanol (CAS registry number 71-23-8), than your sample likely still contains 1-propanol. This were an indication that, for example, your purification by distillation was insufficient, and a better distillation column should be used for a subsequent second distillation.

enter image description here

The presence of remaining propanol may be confirmed by 1H NMR, too (remember that solvents like $\ce{CDCl3}$ more likely provide an OH signal that is broad, while d6-DMSO with slow H-D exchange rates a multiplet signal; and a droplet of $\ce{D2O}$ may mute the OH-signal completely).

For a purity check, especially if you are not allowed to alter how the H NMR data is recorded (in particular, increase of t2 time to account for different relaxation times, cf. DOI 10.1021/ed085p294), search for a complementary confirmations of purity like refractive index, and -- provided enough sample is available -- boiling temperature at known pressure, for example.


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