2. Molecular Representations

In each pair, which would you expect to have the higher melting point?

(a)

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

1. CH₃CH₂OCH₂CH₂OH

2. CH₃CH₂N(CH₃)₂

3. CH₃CH₂CH₂CH₂Br

What is the smallest straight-chain alkane that is a liquid at room temperature (which is about 25 °C)?

Which has

i. the greater density: heptane or octane?

j. the higher boiling point: isopentyl alcohol or isopentylamine?

k. the higher boiling point: hexylamine or dipropylamine?

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

4. CH₃CH₂CH₂NHCH₃ 

5. CH₃CH₂CH₂COOH

6. CH₃CH₂CH₂CH₂F

Which has

a. the higher boiling point: 1-bromopentane or 1-bromohexane?

b. the higher boiling point: pentyl chloride or isopentyl chloride?

In Table 7.2, what is the smallest alkane, the smallest terminal alkene, and the smallest terminal alkyne that are liquids at room temperature, which is generally taken to be 20 °C to 25 °C?

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).

For each pair of compounds, circle the compound you expect to have the higher boiling point. Explain your reasoning.

(d) HOCH₂—(CH₂)₄—CH₂OH or (CH₃)₃CCH(OH)CH₃

(e) (CH₃CH₂CH₂)₂NH or (CH₃CH₂)₃N

(f)

Which of the following pure compounds can form hydrogen bonds? Which can form hydrogen bonds with water? Which ones do you expect to be soluble in water?

a. (CH₃CH₂)₂NH

b. (CH₃CH₂)₃N

c. CH₃CH₂CH₂OH

d. (CH₃CH₂CH₂)₂OH

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

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

(b)

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

(a)

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

(c)