Hydroxyl

Definition

The hydroxyl group (OH-) is a functional group consisting of an oxygen atom covalently bonded to a hydrogen atom. It is a key component in many organic molecules and plays a vital role in their structure and reactivity.

5 Must Know Facts For Your Next Test

1. The hydroxyl group is polar, with the oxygen atom bearing a partial negative charge and the hydrogen atom bearing a partial positive charge.
2. Hydroxyl groups can participate in hydrogen bonding, which influences the physical and chemical properties of organic molecules.
3. Alcohols, phenols, and carboxylic acids are all organic compounds that contain hydroxyl groups, and these functional groups play a crucial role in their reactivity.
4. The presence of hydroxyl groups can affect the solubility, boiling point, and acidity of organic molecules.
5. Hydroxyl groups can undergo various chemical reactions, such as substitution, elimination, and oxidation, which are important in organic synthesis and biochemical pathways.

Review Questions

• Explain the role of the hydroxyl group in the structure and properties of organic molecules.
  • The hydroxyl group (OH-) is a polar functional group that is present in many organic molecules, such as alcohols, phenols, and carboxylic acids. The polarity of the hydroxyl group allows it to participate in hydrogen bonding, which can significantly influence the physical and chemical properties of the molecule, including solubility, boiling point, and reactivity. The presence of hydroxyl groups can also affect the acidity of the molecule, as the hydrogen atom can be donated to form a negatively charged hydroxide ion (OH-).
• Describe the differences in the properties and reactivity of alcohols, phenols, and carboxylic acids, all of which contain hydroxyl groups.
  • Alcohols, phenols, and carboxylic acids all contain hydroxyl groups, but the specific placement and environment of the hydroxyl group within the molecule can lead to differences in their properties and reactivity. Alcohols have the hydroxyl group attached to a saturated carbon atom, which makes them less acidic than phenols, where the hydroxyl group is directly attached to an aromatic ring. Carboxylic acids have both a hydroxyl group and a carbonyl group (C=O), making them the most acidic of the three. These differences in acidity and reactivity are important in organic synthesis and biochemical pathways, as the specific functional groups present can determine the molecule's behavior and potential for transformation.
• Evaluate the importance of the hydroxyl group in the structure and function of biomolecules, such as carbohydrates and proteins.
  • The hydroxyl group is a crucial functional group in many biomolecules, such as carbohydrates and proteins, due to its ability to participate in hydrogen bonding. In carbohydrates, the hydroxyl groups are responsible for the molecule's hydrophilicity and ability to form complex three-dimensional structures through intramolecular hydrogen bonding. In proteins, the hydroxyl groups of serine, threonine, and tyrosine amino acid residues can form hydrogen bonds with other functional groups, contributing to the stabilization of protein structure and enabling important biochemical reactions. Additionally, the hydroxyl group can undergo various chemical modifications, such as phosphorylation, which is a key regulatory mechanism in many cellular processes. The versatility and importance of the hydroxyl group in biomolecules underscores its significance in organic chemistry and biochemistry.

Related terms

Alcohol: An organic compound containing one or more hydroxyl groups (-OH) attached to a saturated carbon atom.

Phenol:

An aromatic organic compound with a hydroxyl group (-OH) directly attached to a benzene ring.

Carboxylic Acid: An organic compound with a hydroxyl group (-OH) and a carbonyl group (C=O) in the same molecule.