= Solution
\b[B is <2-Methylpropanoyl chloride>, $\mathrm{(CH_3)_2CHC(=O)Cl}$.] The single index of <index of hydrogen deficiency> is supplied by the <carbonyl>. Its relatively high-frequency <infrared spectroscopy> band identifies an <acyl chloride>, while two equivalent <methyl groups> explain why four <carbons> produce only three <carbon-13 NMR> resonances.
Assign $\delta_C=178.1$ to the <acyl chloride> <carbonyl>, $46.3$ to the methine and $18.9$ ppm to both <methyl groups>. Their <chemical equivalence in NMR> follows from the symmetry of the isopropyl fragment in this achiral environment.
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