Rationalize the differences in physical properties in terms of intermolecular forces for the following organic compounds. Compare the first three substances with each other, compare the last three with each other, and then compare all six. Can you account for any anomalies? $$ \begin{array}{|lccc|} \hline & \text { bp }\left({ }^{\circ} \mathrm{C}\right) & \operatorname{mp}\left({ }^{\circ} \mathrm{C}\right) & \Delta H_{\text {vap }}(\mathbf{k J} / \text { mol }) \\ \hline \text { Benzene, } \mathrm{C}_{6} \mathrm{H}_{6} & 80 & 6 & 33.9 \\ \text { Naphthalene, } & & & \\ \mathrm{C}_{10} \mathrm{H}_{8} & 218 & 80 & 51.5 \\ \text { Carbon tetra- } & & & \\ \text { chloride } & 76 & -23 & 31.8 \\ \text { Acetone, } & & & \\ \mathrm{CH}_{3} \mathrm{COCH}_{3} & 56 & -95 & 31.8 \\ \text { Acetic acid, } & & & \\ \mathrm{CH}_{3} \mathrm{CO}_{2} \mathrm{H} & 118 & 17 & 39.7 \\ \text { Benzoic acid, } & & & \\ \mathrm{C}_{6} \mathrm{H}_{5} \mathrm{CO}_{2} \mathrm{H} & 249 & 122 & 68.2 \\\ \hline \end{array} $$

These compounds mainly have dispersion forces, which are the weakest among the intermolecular forces. The strength of these forces depends on the molecular size and shape, with larger and more extended molecules exhibiting stronger dispersion forces. - Benzene: bp = 80°C, mp = 6°C, ΔHvap = 33.9 kJ/mol - Naphthalene: bp = 218°C, mp = 80°C, ΔHvap = 51.5 kJ/mol - Carbon Tetrachloride: bp = 76°C, mp = -23°C, ΔHvap = 31.8 kJ/mol Naphthalene has the highest boiling point and melting point among the three due to its larger size and extended structure, leading to stronger dispersion forces. Carbon tetrachloride and benzene have similar boiling points, but carbon tetrachloride has a lower melting point. This could be due to the difference in molecular shapes, which affect how the molecules pack together. #Step 2: Compare the last three compounds#

These compounds have polar functional groups, leading to stronger intermolecular forces such as dipole-dipole interactions and hydrogen bonding. - Acetone: bp = 56°C, mp = -95°C, ΔHvap = 31.8 kJ/mol (dipole-dipole) - Acetic Acid: bp = 118°C, mp = 17°C, ΔHvap = 39.7 kJ/mol (dipole-dipole and hydrogen bonding) - Benzoic Acid: bp = 249°C, mp = 122°C, ΔHvap = 68.2 kJ/mol (dipole-dipole and hydrogen bonding) Acetic acid and benzoic acid have higher boiling points and melting points compared to acetone due to the presence of hydrogen bonding. Additionally, benzoic acid has higher boiling and melting points than acetic acid because of its larger molecular size, which leads to stronger dispersion forces. #Step 3: Compare all six compounds# Notice the trend of increasing boiling and melting points from nonpolar molecules to polar ones with functional groups that can form hydrogen bonding. - Nonpolar compounds (dispersion forces only): Carbon tetrachloride < Benzene < Naphthalene - Polar compounds (dipole-dipole and hydrogen bonding): Acetone < Acetic Acid < Benzoic Acid. Anomalies may be found in the comparison, such as the similar boiling points of benzene and carbon tetrachloride. This could be due to differences in molecular shapes affecting the way molecules interact and pack together. Overall, the types and strengths of intermolecular forces present have a significant impact on the physical properties of these organic compounds.