Which of the following can form hydrogen bonds? CHA CH3OH CH3F HBr and CH3F CH3OH and CH3F NHBr2 and CH3OH HBr and CH3OH HBr NHBr2
The Correct Answer and Explanation is:
Correct Answer: NHBr₂ and CH₃OH
Explanation
A hydrogen bond is a special, strong type of intermolecular dipole-dipole interaction. For a hydrogen bond to form, specific conditions must be met. First, a molecule must contain a hydrogen atom covalently bonded to a highly electronegative atom, namely nitrogen (N), oxygen (O), or fluorine (F). This creates a hydrogen bond donor, as the large electronegativity difference results in a highly polarized bond and a significant partial positive charge (δ+) on the hydrogen atom. Second, another nearby electronegative atom (N, O, or F) with at least one lone pair of electrons must be present to act as a hydrogen bond acceptor. This lone pair is attracted to the partially positive hydrogen atom of the donor molecule.
Analyzing the given options based on these criteria:
- CH₃OH (Methanol): This molecule contains a hydrogen atom directly bonded to an oxygen atom in its hydroxyl (-OH) group. This H atom can act as a hydrogen bond donor. The oxygen atom also possesses lone pairs, allowing it to act as a hydrogen bond acceptor. Therefore, methanol can form hydrogen bonds with itself.
- NHBr₂ (Dibromoamine): This molecule features a hydrogen atom covalently bonded to a nitrogen atom (N-H). This H atom serves as a hydrogen bond donor. The nitrogen atom also has a lone pair, enabling it to be a hydrogen bond acceptor. Consequently, dibromoamine is capable of forming hydrogen bonds.
Since both methanol (CH₃OH) and dibromoamine (NHBr₂) individually possess the necessary components for hydrogen bonding (both a donor and an acceptor), a mixture of the two can readily form hydrogen bonds with each other. For example, the hydrogen from methanol’s -OH group can form a hydrogen bond with the nitrogen atom of NHBr₂.
Other molecules listed do not meet the criteria:
- CH₄ (Methane): Hydrogen is bonded to carbon, which is not sufficiently electronegative.
- HBr (Hydrogen Bromide): Although the H-Br bond is polar, bromine is not one of the three highly electronegative atoms (N, O, F) required for this specific interaction.
- CH₃F (Fluoromethylane): While it has an electronegative fluorine atom with lone pairs (an acceptor), all of its hydrogen atoms are bonded to carbon. It lacks a hydrogen bond donor and thus cannot form hydrogen bonds with itself.
