The table shows information about three carbon compounds: [table]
Compound | Structural formula | Molecular weight | Boiling point Y | | 58 | 0oC X | | 60 | 97oC Y | | 60 | 118oC Z | | 60 | ?
[/table] What is the best estimate for the boiling point of compound Z?

Question

BlackTom AI · Accepted Answer

Hydrogen-bonding ability and molecular polarity control boiling points for molecules of similar molecular weight; compare the four compounds (all ~60 g mol–1) to decide Z’s boiling point.

1) Relevant knowledge points and concepts
- Boiling point increases with stronger intermolecular forces: London dispersion < dipole–dipole < hydrogen bonding.
- Molecules with an O–H group (alcohols, carboxylic acids) can form hydrogen bonds; carboxylic acids form especially strong dimers, raising b.p.
- Esters (no O–H) cannot hydrogen-bond to themselves and therefore have much lower b.p. than isomers that do.

2) Step-by-step reasoning
- The table entries identify compounds of molecular weight ≈60 g mol–1:
  • First compound (MW 58) is butane (C4H10) with b.p. ≈0°C — nonpolar, only dispersion forces.
  • X (MW 60, b.p. 97°C) is propanol (C3H8O), an alcohol with an O–H group → strong hydrogen bonding → high b.p.
  • Y (MW 60, b.p. 118°C) is acetic acid (CH3COOH), a carboxylic acid → very strong H-bonding (dimer formation) → even higher b.p.
  • Z (MW 60) shows the structure H–C–O–C(=O)–H which corresponds to methyl formate (HCOOCH3), an ester.

3) Intermediate calculations / formula check
- Methyl formate formula: C2H4O2. Molar mass = 2×12.01 + 4×1.008 + 2×16.00 ≈ 60.05 g mol–1, consistent with the table’s MW = 60.

4) Why the correct answer is correct
- As an ester, Z cannot hydrogen-bond with itself; it has only dipole–dipole and dispersion forces. Among isomers with MW ≈60, esters have lower b.p. than the alcohol (97°C) and the carboxylic acid (118°C), but higher than the nonpolar alkane (~0°C). The known boiling point of methyl formate is about 31°C, matching this reasoning.

5) Why other choices are incorrect
- 0°C: too low — that’s for nonpolar C4H10 (butane), but Z is polar (an ester).
- 101°C or 114°C or 156°C: these are near alcohol/carboxylic-acid values or much higher; Z lacks the O–H required for those high b.p. values, so these are inconsistent.

6) Conclusion
- Based on intermolecular forces, molecular formula and known data for methyl formate, the best estimate for Z’s boiling point is 31°C, which matches the provided answer.

The table shows information about three carbon compounds: [table] Compound | Structural formula | Molecular weight | Boiling point Y | | 58 | 0oC X | | 60 | 97oC Y | | 60 | 118oC Z | | 60 | ? [/table] What is the best estimate for the boiling point of compound Z?单项选择题

类似问题

The table shows information about three carbon compounds: [table] Compound | Structural formula | Molecular weight | Boiling point Y | | 58 | 0oC X | | 60 | 97oC Y | | 60 | 118oC Z | | 60 | ? [/table] What is the best estimate for the boiling point of compound Z?

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