Melting Points of Derivatives of Some Aldehydes and Ketones Melting Points (°C) Compound Formula MW Acetone CH3COCH3 58.08 0.79 Butanal CH3CH2CH2CHO 72.10 0.82 Dichloroacetone CH3COCHCl2 86.13 0.81 Furfural C5H4OCHO 96.08 Benzaldehyde C6H5CHO 106.12 1.05 Heptane-2,6-dione CH3COCH2CH2COCH3 114.18 0.97 Heptanone CH3CH2CH2COCH3 104.18 0.88 3-Heptanone CH3COCH2CH2CH2COCH3 118.18 0.82 Heptanal CH3CH2CH2CH2CHO 114.18 0.82 Acetophenone C6H5COCH3 120.66 1.03 2-Octanone CH3CH2CH2CH2COCH2CH3 128.21 0.82 Cinnamaldehyde C6H5CH=CHCHO 132.15 Propiophenone C6H5COCH2CH3 134.17 1.01
The Correct Answer and Explanation is:
To analyze the melting points of derivatives of some aldehydes and ketones, we need to clarify a point first: the table provided lists molecular weights and density values, not melting points. In fact, many of these values (like “0.79”, “0.82”, etc.) are in the range of densities in g/cm³, not melting points in °C.
So let’s correct the interpretation:
Correct Interpretation of the Table:
| Compound | Formula | MW (g/mol) | Density (g/cm³) |
|---|---|---|---|
| Acetone | CH₃COCH₃ | 58.08 | 0.79 |
| Butanal | CH₃CH₂CH₂CHO | 72.10 | 0.82 |
| Dichloroacetone | CH₃COCHCl₂ | 86.13 | 0.81 |
| Furfural | C₅H₄OCHO | 96.08 | — |
| Benzaldehyde | C₆H₅CHO | 106.12 | 1.05 |
| Heptane-2,6-dione | CH₃COCH₂CH₂COCH₃ | 114.18 | 0.97 |
| Heptanone | CH₃CH₂CH₂COCH₃ | 104.18 | 0.88 |
| 3-Heptanone | CH₃COCH₂CH₂CH₂COCH₃ | 118.18 | 0.82 |
| Heptanal | CH₃CH₂CH₂CH₂CHO | 114.18 | 0.82 |
| Acetophenone | C₆H₅COCH₃ | 120.66 | 1.03 |
| 2-Octanone | CH₃CH₂CH₂CH₂COCH₂CH₃ | 128.21 | 0.82 |
| Cinnamaldehyde | C₆H₅CH=CHCHO | 132.15 | — |
| Propiophenone | C₆H₅COCH₂CH₃ | 134.17 | 1.01 |
Explanation:
This table includes aldehydes and ketones of varying structures, molecular weights, and densities. While melting points are not provided, one can infer trends based on molecular weight, branching, and functional group effects. In general:
- Aromatic compounds like benzaldehyde, acetophenone, cinnamaldehyde, and propiophenone have higher molecular weights and higher densities. These compounds typically also have higher melting and boiling points due to stronger intermolecular interactions, particularly π–π stacking and dipole forces.
- Straight-chain aliphatic ketones and aldehydes (e.g., butanal, heptanal, heptanone) have lower densities and usually lower melting points. Their intermolecular forces are mostly dipole-dipole and van der Waals.
- Halogenated ketones like dichloroacetone have intermediate density. The electronegative chlorine atoms increase polarity, possibly raising boiling/melting points relative to similarly sized unhalogenated ketones.
- Furfural, a heterocyclic aldehyde, and cinnamaldehyde, a conjugated aldehyde, are special cases. Their ring structures and conjugation often influence both melting and boiling points significantly.
If the question intends for us to predict melting point trends, the aromatic and heavier compounds generally melt at higher temperatures, although branching and symmetry also play roles. More data would be needed for exact melting points.
