Question

In which of the following the hydrogen bond is strongest:

• A. $\mathrm{F}-\mathrm{H}-\mathrm{F}$
• B. $\mathrm{O}-\mathrm{H}-\mathrm{S}$
• C. $\mathrm{S}-\mathrm{H}-\mathrm{F}$
• D. $\mathrm{F}-\mathrm{H}-\mathrm{O}$

Answer 1

The correct option is A

$\mathrm{F}-\mathrm{H}-\mathrm{F}$

Explanation for correct answer

Correct answer: Option A

Hydrogen bonding

• Hydrogen bonding is the formation of hydrogen bonds, between the hydrogen and another atom like N, O, F.
• These are the type of weak electrostatic force of attraction caused by the dipole-dipole interaction between a hydrogen atom bound to a highly electronegative atom and another highly electronegative atom nearby.
• Hydrogen bonds can be formed between hydrogen and oxygen, hydrogen and fluorine and hydrogen and nitrogen.
• In Hydrogen bonding, there is an increase in intermolecular aggregation forces which influences the boiling point and solubility of the organic compound.

$\mathrm{F}-\mathrm{H}-\mathrm{F}$is the strongest bond

The strength of the hydrogen bond is decided by the interaction between the electronegativity of the atom bonded and hydrogen. Since, Fluorine is the most electronegative element. So the $\mathrm{F}-\mathrm{H}-\mathrm{F}$ bond will be the strongest Hydrogen bond.

Hydrogen Bonding in Hydrogen fluoride

Fluorine having the highest value of electronegativity forms the strongest hydrogen bond.

Hence, option A is correct.

Explanation for incorrect answers

(b) $\mathrm{O}-\mathrm{H}-\mathrm{S}$ have less electronegative atom (Sulphur) on one side, therefore, forms weak bond with hydrogen. Hence option (b) is incorrect.
(c)$\mathrm{S}-\mathrm{H}-\mathrm{F}$have less electronegative atom (Sulphur) on one side and more electronegative (fluorine) on the other but overall it will form weak hydrogen bonding, therefore, forms weak bond with hydrogen. Hence option (c) is incorrect.

$\left(\mathrm{d}\right)\mathrm{F}-\mathrm{H}-\mathrm{O}$ It also forms strong hydrogen bonding, but its bonding capacity is weaker compared to $\mathrm{F}-\mathrm{H}-\mathrm{F}$. Hence, option d is incorrect.