4. Out of the following hydrogen bonding schemes shown by … which one corresponds to the weakest hydrogen bond in a given solvent condition?

   (1) O-H …O<
   (2) N-H…H<
   (3) O-H…N<
   (4) N-H…N<

   Understanding Hydrogen Bond Strength in Different Schemes

   In order to stabilise molecular interactions and structures in various solvents, hydrogen bonding is essential. However, because of the characteristics of the donor and acceptor atoms involved, some hydrogen bonds are much weaker than others.

   Hydrogen Bond Strength-Related Factors

   A hydrogen bond’s strength is determined by:

   The donor and acceptor atoms’ electronegativity Stronger hydrogen bonds are formed by more electronegative atoms (O > N).

   Atomic size: Stronger interactions result from smaller atoms.

   Bond polarity: Stronger hydrogen bonds are a result of highly polar bonds.

   Hydrogen Bonding Scheme Comparison

   Let’s examine the hydrogen bonding interactions that are provided:

   O-H… O → Strongest because oxygen is a highly electronegative donor and acceptor.

   N-H … H → This is a very weak interaction because hydrogen is not an electronegative atom and lacks strong bonding ability.

   O-H … N → Moderately strong, as oxygen is a better donor, and nitrogen is a good acceptor.

   N-H…N → This is the weakest hydrogen bond because:

   • Nitrogen is less electronegative than oxygen, meaning it is a weaker hydrogen bond acceptor.
   • N-H donors are weaker than O-H donors, leading to weaker bonding.
   • Solvent conditions can further weaken this bond, especially in polar solvents where competition from water molecules can disrupt the interaction

Conclusion: The Weakest Hydrogen Bond

Among the given options, N-H…N (Option 4) forms the weakest hydrogen bond in a given solvent condition. This is due to the lower electronegativity of nitrogen compared to oxygen, resulting in a less stable and weaker interaction.