2. Molecular Representations

Imidazole boils at 257 °C, whereas N-methylimidazole boils at 199 °C. Explain the difference in boiling points.

The high boiling points and water solubility of smaller amides are primarily due to which type of intermolecular force?

For each pair of compounds, predict the one with a higher boiling point. Which compounds have zero dipole moments?

c. cyclohexene or 1,2-dichlorocyclohexene

Which type of intermolecular force is primarily responsible for the strong association between molecules of $\mathrm{carboxylic} \mathrm{acids}$?

Which of these phenomena result from hydrogen bonding?

Hydrogen bonds are important for which of the following reasons?

Given the following molecules: ${\mathrm{CH}}_4$ (methane), ${\mathrm{NH}}_3$ (ammonia), $H_{2}O$ (water), and ${\mathrm{CO}}_2$ (carbon dioxide), arrange them in order of increasing boiling point.

For each pair of compounds, predict which compound has the higher boiling point. Check [TABLE 6-2] to see if your prediction was right; then explain why that compound has the higher boiling point.

c. 1-bromobutane and 1-chlorobutane

Which types of intermolecular forces are present in ${\mathrm{CH}}_2\mathrm{Cl}2$ (dichloromethane)?

Which intermolecular forces are present between two molecules of $C_2{H}_{6}O$ (ethanol)?

In each pair, choose the compound you would expect to have the highest boiling/melting point.

(a)

For each pair of compounds, predict the one with a higher boiling point. Which compounds have zero dipole moments?

b. cis- or trans-2,3-dichlorobut-2-ene

Contrary to expectation, the addition of more fluorines to ethane lowers the boiling point. Explain this phenomenon.

N-Methylpyrrolidine has a boiling point of 81 °C, and piperidine has a boiling point of 106 °C.

c. N,N-Dimethylformamide has a boiling point of 150 °C, and N-methylacetamide has a boiling point of 206 °C, for a difference of 56 °C. Explain why these two nitrogen-containing isomers have a much larger boiling point difference than the two amine isomers. Also explain why these two amides have higher boiling points than any of the other four compounds shown (two amines, an ether, and an alcohol).

Which of the preceding compounds forms hydrogen bonds with a solvent such as ethanol?

4. CH₃CH₂CH₂NHCH₃ 

5. CH₃CH₂CH₂COOH

6. CH₃CH₂CH₂CH₂F