If the boiling points of methoxyethane and propanol are 281 K and 370 K respectively, predict the boiling point of propanal.

322 K

The correct answer is option 3. 322 K.

Boiling points are significantly influenced by the types and strengths of intermolecular forces present in a compound. The main types of intermolecular forces are:

Van der Waals forces (London dispersion forces): Present in all molecules, but particularly dominant in non-polar compounds.

Dipole-dipole interactions: Present in polar molecules with permanent dipoles.

Hydrogen bonding: A strong type of dipole-dipole interaction occurring in molecules where hydrogen is directly bonded to highly electronegative atoms like nitrogen, oxygen, or fluorine.

Compounds and Their Boiling Points

Methoxyethane (ethyl methyl ether)

Structure: \(CH_3-O-CH_2CH_3\)

Boiling Point: 281 K

Intermolecular Forces: Dipole-dipole interactions and van der Waals forces.

The ether group creates a dipole, but the interactions are not as strong as hydrogen bonds.

Propanol (1-propanol)

Structure: \(CH_3CH_2CH_2OH\)

Boiling Point: 370 K

Intermolecular Forces: Hydrogen bonding and van der Waals forces.

The hydroxyl group \((-OH)\) allows for strong hydrogen bonding, significantly increasing the boiling point.

Propanal

Structure: \(CH_3CH_2CHO\)

Intermolecular Forces: Dipole-dipole interactions and van der Waals forces.

The carbonyl group \((C=O)\) creates a strong dipole, leading to dipole-dipole interactions. However, there are no hydrogen bonds.

Predicting the Boiling Point of Propanal

Methoxyethane (281 K) has weaker dipole-dipole interactions compared to propanal because the ether linkage is less polar than a carbonyl group. Propanol (370 K) has hydrogen bonding, which is much stronger than the dipole-dipole interactions in propanal, leading to a significantly higher boiling point.

Given that:

Propanal’s carbonyl group provides stronger dipole-dipole interactions than the ether group in methoxyethane. Propanal lacks hydrogen bonding, which makes its boiling point lower than that of propanol.

We can conclude that the boiling point of propanal will be higher than methoxyethane's 281 K but much lower than propanol's 370 K. The most reasonable value among the options provided is: 322 K.

This value is logical given that it is higher than 281 K (methoxyethane) due to stronger dipole-dipole interactions but lower than 370 K (propanol) due to the absence of hydrogen bonding.