2. Molecular Representations

Which of the following compounds forms hydrogen bonds between its molecules?

1. CH₃CH₂OCH₂CH₂OH

2. CH₃CH₂N(CH₃)₂

3. CH₃CH₂CH₂CH₂Br

Predict which compound in each pair has the higher boiling point. Explain your prediction.

(e)

(f)

In each pair of compounds, which compound has the higher boiling point? Explain your reasoning.

a. octane or 2,2,3-trimethylpentane

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

(b)

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)

PRACTICE:Which of the following pairs of molecules would have the highest boiling point?

Rank the following isomers in order of increasing boiling point, and explain the reasons for your order of ranking.

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?

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

Despite methylcyclohexane (98.2 amu) having a higher molecular weight than toluene (92.1 amu), toluene melts at a higher temperature. Why? [Think about how the molecules can interact with each other based on their shape.]

Which has

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

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

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.

a. isopropyl bromide and n-butyl bromide