The \({ }^{13} \mathrm{C}\) NMR spectrum of ethanoic acid (acetic acid) shows a quartet centred at \(\delta=21\) with a splitting of 130 Hz. When the same spectrum is recorded using proton decoupling, the multiplet collapses to a single line. Another quartet, but with a much smaller spacing, is also seen centred at \(\delta=178\); this quartet collapses when decoupling is used. Explain these observations.

Text Transcription:

^13C

delta=21

delta=178