Question

In which of the following compounds do you think that intramolecular hydrogen bonding is an important factor: \((\mathrm{a}) \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{3} ;(\mathrm{b}) \mathrm{HOOCCH}_{2} \mathrm{CH}_{2}\) \(\mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{COOH} ;(\mathrm{c}) \mathrm{CH}_{3} \mathrm{COOH} ;\) (d) ortho-phthalic acid? Explain.

Short answer

Intramolecular hydrogen bonding is an important factor in compound b (\(\mathrm{HOOCCH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{COOH\)), compound c (\(\mathrm{CH}_{3} \mathrm{COOH}\)), and in ortho-phthalic acid. It is not important in compound a (\(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{3}\)) as it lacks the required highly electronegative atom

Step-by-step solution

Identify Hydrogen Bonding Capability

Intramolecular hydrogen bonding requires a hydrogen atom to be bonded to a highly electronegative atom (like N, O, F) and the presence of another electronegative atom within the same molecule. The structures need to be examined for these criteria.

Analyze Compound (a)

For compound a (\(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{3}\)), there are no highly electronegative atoms present (like N, O, F), and thus, it is not capable of hydrogen bonding.

Analyze Compound (b)

For compound b (\(\mathrm{HOOCCH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{COOH\)), there exists a hydrogen atom bonded to an oxygen atom (in -COOH) and another oxygen atom within the same molecule. Therefore, intramolecular hydrogen bonding is likely to occur here.

Analyze Compound (c)

For compound c (\(\mathrm{CH}_{3} \mathrm{COOH}\)), the hydrogen in the -COOH group can potentially form a hydrogen bond with the oxygen in the -COOH group present on the same molecule. Therefore, intramolecular hydrogen bonding is also possible.

Analyze Compound (d)

Ortho-phthalic acid has two -COOH groups very close to each other within the same molecule. Thus, a hydrogen from one -COOH can form a bond with the oxygen of the neighbouring -COOH group. Therefore, intramolecular hydrogen bonding is possible here too.

Key concepts

Hydrogen Bonding Capability

Hydrogen bonding is a type of attractive interaction between a hydrogen atom, which is covalently bonded to a more electronegative atom, and another electronegative atom. The hydrogen bond is a type of weak chemical bond that is fundamental in the properties of many compounds. For a molecule to have hydrogen bonding capability, it must contain hydrogen atoms bonded to electronegative atoms such as nitrogen, oxygen, or fluorine. In the context of intramolecular hydrogen bonding, this capability becomes crucial when the hydrogen bond occurs within the same molecule.

• Critical for hydrogen bonding: Presence of hydrogen attached to an electronegative atom.
• Occurs between two electronegative atoms if they are within a reasonable distance in the same molecule.

Understanding these features helps in assessing a molecule's potential for forming hydrogen bonds, which can affect physical properties such as boiling point and melting point.

Electronegative Atoms

Electronegative atoms are elements that have a high tendency to attract electrons towards themselves. This makes such atoms effective in forming polar covalent bonds. The most common electronegative atoms capable of forming hydrogen bonds include nitrogen (N), oxygen (O), and fluorine (F). These atoms, when bonded to hydrogen, can result in hydrogen bonding, either intermolecularly (between molecules) or intramolecularly (within the same molecule).

• Key electronegative atoms: Nitrogen, Oxygen, Fluorine.
• These atoms increase the polar character of molecules.

The role of electronegative atoms is vital in determining the strength and length of the hydrogen bonds, which in turn influences the molecular interactions within and between molecules.

Carboxylic Acid Groups

Carboxylic acids are organic acids characterized by the presence of a carboxyl group \((-COOH)\). These functional groups are known for their propensity to engage in hydrogen bonding due to the electronegative oxygen atoms present in the carbonyl \(C=O\) and hydroxyl \(OH\) portions of the group. Atoms in carboxylic acids can efficiently participate in both intramolecular and intermolecular hydrogen bonding due to the polarization of bonds caused by the oxygen atoms.

• Characteristic group: \(R-COOH\).
• Facilitates hydrogen bonding through the oxygen, leading to possible intramolecular interactions.

Carboxylic acids often have higher boiling points than other similar molecular weight compounds due to their capacity for hydrogen bonding.

Ortho-Phthalic Acid

Ortho-phthalic acid is an aromatic compound with two carboxylic acid groups positioned ortho to each other on the benzene ring. Its structure allows for a high potential for intramolecular hydrogen bonding due to the proximity of the carboxylic groups. Both groups can effectively share hydrogen atoms between their oxygen molecules, forming a stable internal interaction.

• Features two \( -COOH \) groups close together on a benzene ring.
• Strong potential for intramolecular hydrogen bonding.

This ability to form these internal bonds can affect its solubility and boiling point when compared to similar compounds with only one hydrogen bond source or a less favorable spatial arrangement.

Intramolecular Interactions

Intramolecular interactions occur within a single molecule, typically between functional groups that are positioned to allow for such interactions. These can include hydrogen bonding, van der Waals forces, and covalent bonding. Intramolecular hydrogen bonding can stabilize a molecule's structure, influencing its physical characteristics, such as solubility and reactivity.

• Occurs when groups within a single molecule interact with each other.
• Can stabilize molecular structure by reducing energy states.

Understanding intramolecular interactions is crucial for predicting how a chemical compound will behave under various conditions, ultimately affecting its practical applications in compounds like water, proteins, and even synthetic materials.