Which is the correct decreasing order of boiling point

A. 1-Bromoethane

B. 1-Bromopentane

C. 1-Bromobenzene

D. 1-Bromopropane

Choose the correct answer from the options given below:

C > B > D > A

The correct answer is option 2. C > B > D > A.

To determine the correct decreasing order of boiling points for the given brominated compounds, we need to analyze each compound based on the principles of molecular structure, molecular weight, and intermolecular forces.

A. 1-Bromoethane

Formula: \(C_2H_5Br\)

Boiling Point: 38.4°C

1-Bromoethane is the smallest molecule among the compounds listed. Its boiling point is relatively low because:

It has the smallest molecular size and weight.

The intermolecular forces in 1-Bromoethane are primarily dipole-dipole interactions and van der Waals forces, which are weaker compared to the larger molecules and those with aromatic rings.

D. 1-Bromopropane

Formula: \(C_3H_7Br\)

Boiling Point: 71°C

1-Bromopropane has a higher boiling point than 1-Bromoethane due to:

Increased molecular weight and size, which lead to stronger van der Waals forces.

The increase in molecular size leads to greater dispersion forces, thus requiring more energy to overcome these forces and boil the substance.

B. 1-Bromopentane

Formula: \(C_5H_{11}Br\)

Boiling Point: 129°C

1-Bromopentane has the highest boiling point among the aliphatic bromides because:

It has the largest molecular size and weight of the aliphatic bromides listed.

Greater molecular size leads to stronger van der Waals forces.

More substantial dispersion forces in 1-Bromopentane mean more energy is required to break these forces, resulting in a higher boiling point.

C. 1-Bromobenzene

Formula: \(C_6H_5Br\)

Boiling Point: 156.2°C

1-Bromobenzene has a significantly higher boiling point due to:

The presence of the aromatic benzene ring, which increases the molecular weight and surface area.

Stronger van der Waals forces due to the large, planar, and aromatic nature of the molecule, which contribute to a higher boiling point.

The dipole-dipole interactions are enhanced in the presence of the aromatic system, further increasing the boiling point.

Correct Decreasing Order of Boiling Points: 1-Bromobenzene (C) >1-Bromopentane (B) >  1-Bromopropane (D) > 1-Bromoethane (A)

Thus, the correct answer is: 2. C > B > D > A