For the three amide compounds shown below, choose the order which represents the amide compound that has the highest boiling point to the one with the lowest boiling point.

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In this set of amides, boiling point trends are governed mainly by hydrogen bonding capability and molecular polarity, with an added minor influence from molecular weight. Option A corresponds to benzamide (Ph-CO-NH2). This molecule has two N–H bonds in the amide NH2 group, allowing two potential hydrogen-bond donors, in addition to the carbonyl oxygen acting as a strong hydrogen-bond acceptor. The combination of multiple H-bonding interactions and the overall polarity tends to raise the boiling point. Option B corresponds to N-methylbenzamide (Ph-CO-NH-CH3). This is a secondary amide with one N–H bond, giving one hydrogen-bond donor site, and the carbonyl oxygen remains an H-bond acceptor. The hydrogen-bonding capacity is reduced relative to A, which typically lowers the boiling point compared with A, assuming similar molecular weight. Option C corresponds to N,N-dimethylbenzamide (Ph-CO-N(CH3)2). This tertiary amide lacks N–H bonds entirely, so it cannot donate hydrogen bonds from the amide N. It still has the carbonyl as an H-bond acceptor, but overall hydrogen-bonding potential is the lowest among the three, usually resulting in the lowest boiling point. Additionally, while C is slightly heavier than B, the loss of H-bond donation often leads to a lower BP than both A and B. Putting these factors together, the order of increasing hydrogen-bonding capability (and thus boiling point, broadly) is C < B < A. Therefore, the highest boiling point corresponds to A, followed by B, then C, giving the sequence A > B > C. Note: If you consider only the explicit options, the option that matches A > B > C is the one indicating that A has the highest BP, B intermediate, and C the lowest, which aligns with the reasoning above.

CHM1052 - MUM S2 2025 Week 6: Preparation quiz

For the three amide compounds shown below, choose the order which represents the amide compound that has the highest boiling point to the one with the lowest boiling point.

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