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I attempt the synthesis of p-toluic acid using the Grignard reagent (prepared from 4-bromotoluene and Mg) and dry ice. The NMR of the raw product was recorded using $\ce{CDCl3}$ and a peak showing water is present.

NMR spectrum

According to literature, the peaks at around $\pu{8 ppm}$ (hydrogens in ortho positions with respect to the $\ce{-COOH}$ group) should have a splitting pattern of a doublet, but I got a multiplet instead. Does anyone know why?

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    $\begingroup$ Those aren’t actually supposed to be doublets; see eg chemistry.stackexchange.com/questions/84390/… and links therein. Your spectrum is entirely correct. $\endgroup$
    – orthocresol
    Commented Oct 24, 2021 at 10:08
  • $\begingroup$ If you don't have a matching splitting somewhere else, then it can't be a doublet. $\endgroup$
    – Karl
    Commented Oct 24, 2021 at 11:41
  • $\begingroup$ Beside the point these signals are AA'XX' as mentioned by @orthocresol (tangential, drawings in this question show why stating these signals as doublets lacks support by theory), be glad the experiment reveals the more complex pattern (e.g., by sample concentration, solvent, spectrometer resolution, field strength). The «water peak» in 1H NMR recorded $\ce{CDCl3}$ equally may indicate the bottle of $\ce{CDCl3}$ wasn't kept as closed as it should, and $\ce{CDCl3}$ isn't dry (anymore), too. $\endgroup$
    – Buttonwood
    Commented Oct 24, 2021 at 12:43
  • $\begingroup$ For a simulation of these pattern (even more useful for partially fluorinated compounds), see e.g. MNova's resources. $\endgroup$
    – Buttonwood
    Commented Oct 24, 2021 at 12:44

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