Here are a couple of examples for judging 13C chemical shifts:
Thus, in (a)
- The peak at lowest field is the caarbon with the OH attached
- The peak at highest field is the CH3 farthest from the OH
- Generally in both 13C and 1H spectra, CH2 groups fall to lower field than CH3, which assigns the remaining peaks.
- The peak at lowest field is the C=O carbon, shifted by electronegativity and "diamagnetic anisotropy"
- Assignment of the other two peaks follows from the CH2 lower than CH3 rule.
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