Question

Intermolecular hydrogen bonding is strongest in:
A) \[{\text{HCHO}}\]
B) \[{\text{C}}{{\text{H}}_{\text{3}}}{\text{OH}}\]
C) \[{{\text{C}}_{\text{6}}}{{\text{H}}_{\text{5}}}{\text{OH}}\]
D) \[{\text{C}}{{\text{H}}_{\text{3}}}{\text{N}}{{\text{H}}_{\text{2}}}\]

Answer 1

Hint: Hydrogen bond is found in a compound in which hydrogen bond (H-bond) is directly attached to a highly electronegative element such as Fluorine (F), Oxygen (O) and Nitrogen (N) but the strength of hydrogen bond depends on various factors.

Complete answer:
Four options are given and we need to find the strongest intermolecular hydrogen bonding among them.
First of all let us understand intermolecular hydrogen bonding.
There are different types of intermolecular force of attraction and one such is hydrogen bonding. Intermolecular hydrogen bonding occurs when hydrogen is attached to a highly electronegative atom such as fluorine (F), oxygen (O) and nitrogen (N). If we look into the order of the hydrogen bond,
Fluorine > Oxygen > Nitrogen.
Thus we can neglect the option (D) which is methylamine (\[{\text{C}}{{\text{H}}_{\text{3}}}{\text{N}}{{\text{H}}_{\text{2}}}\])
Now, in formaldehyde HCHO the hydrogen atom is not attached to an oxygen atom but with a carbon atom. Thus, will show very less H-bonding.
Comparing \[{\text{C}}{{\text{H}}_{\text{3}}}{\text{OH}}\] and \[{{\text{C}}_{\text{6}}}{{\text{H}}_{\text{5}}}{\text{OH}}\], methanol (\[{\text{C}}{{\text{H}}_{\text{3}}}{\text{OH}}\]) will show strongest H-bonding. This is because, oxygen atom in \[{\text{C}}{{\text{H}}_{\text{3}}}{\text{OH}}\] is attached to methyl (\[ - C{H_3}\] ) group while in phenol (\[{\text{C}}{{\text{H}}_{\text{3}}}{\text{OH}}\]), the hydrogen is attached to bulky phenyl (\[{C_6}{H_5} - \] ) group, which reduces hydrogen bonding.

Hence, option (B) is the correct option.

Note: Students should note that the energy of a hydrogen bond or strength can vary depending on the nature of the donor and acceptor atoms which constitute the hydrogen bond, their geometry and also environment. As a result, hydrogen bonding is stronger than Van der Waals interaction which is a type of intermolecular force of interaction.