2.Which compound has the highest melting point?
1-Butyne, trans-2-Butene, cis-2-Butene, 1-butanol, diethyl ether
The correct answer and explanation is :
The compound with the highest melting point in the given list is 1-butanol.
Explanation:
To determine the compound with the highest melting point, we need to consider several factors that influence melting point, such as molecular weight, intermolecular forces (hydrogen bonding, van der Waals forces, dipole-dipole interactions), and the symmetry of the molecule.
1. 1-Butyne (C₄H₆):
- 1-Butyne is an alkyne, which has a linear structure and relatively weak dispersion forces between the molecules.
- Alkynes typically have lower melting points compared to compounds capable of forming hydrogen bonds because their intermolecular forces are weaker.
- Melting point: -139.5°C
2. trans-2-Butene (C₄H₈):
- This is an alkene with a trans configuration. Alkenes have a nonpolar nature, and the trans-isomer has a more symmetrical shape than the cis-isomer.
- Alkenes have weak dispersion forces, but symmetry allows for efficient packing in the solid state, leading to a moderately higher melting point than alkynes.
- Melting point: -105°C
3. cis-2-Butene (C₄H₈):
- Similar to trans-2-butene, but with a cis configuration, meaning it has a more “bent” structure.
- The bent shape reduces the packing efficiency, leading to weaker intermolecular interactions than the trans-isomer. Thus, the melting point of cis-2-butene is lower than that of trans-2-butene.
- Melting point: -185°C
4. 1-Butanol (C₄H₁₀O):
- 1-Butanol is an alcohol, and alcohols can form hydrogen bonds due to the presence of an -OH group. These hydrogen bonds are much stronger than the van der Waals forces found in alkanes, alkenes, and alkynes, which results in a higher melting point.
- Alcohols generally have significantly higher melting points due to these intermolecular hydrogen bonds.
- Melting point: -89°C
5. Diethyl ether (C₄H₁₀O):
- Diethyl ether has an oxygen atom, which could participate in dipole-dipole interactions. However, it cannot form hydrogen bonds as efficiently as alcohols because it lacks an -OH group.
- Ethers typically have relatively low melting points compared to alcohols due to weaker interactions between molecules.
- Melting point: -116°C
Conclusion:
1-Butanol has the highest melting point among the compounds listed. This is primarily due to its ability to form hydrogen bonds, which are strong intermolecular forces that require more energy to overcome, thus resulting in a higher melting point.