Hydroxyls in Alcohols, Phenols, and Carbohydrates

Hydroxyl group is majorly present in alcohol, phenol and carbohydrates. The presence of hydroxyl group decide their properties. Hence, we will learn how presence of hydroxyl in them affect their characteristics.

Alcohols

Alcohols are organic compounds containing one or more hydroxyl (-OH) functional groups attached to a carbon atom. They can be classified into primary (1°), secondary (2°), or tertiary (3°), depending on the number of carbon atoms bonded directly to the carbon atom bearing the hydroxyl group.

Reactions of Alcohols:

1. Oxidation: Alcohols can be oxidized to aldehydes, ketones, or carboxylic acids depending on the conditions and the nature of the alcohol.
   • Primary alcohols are oxidized to aldehydes first and further to carboxylic acids.
   • Secondary alcohols are oxidized to ketones.
   • Tertiary alcohols cannot be oxidized under normal conditions.
2. Esterification: Reaction with carboxylic acids to form esters and water in the presence of an acid catalyst.
3. Dehydration: Elimination of water molecule from two alcohol molecules to form an alkene. This reaction requires the presence of an acid catalyst, typically sulfuric acid or phosphoric acid.

Phenols

Phenols are aromatic compounds containing a hydroxyl group (-OH) directly bonded to an aromatic ring.

Reactions of Phenols:

1. Electrophilic Aromatic Substitution: Phenols undergo electrophilic aromatic substitution reactions more readily than benzene due to the activating effect of the hydroxyl group.
2. Acid-Base Reactions: Phenols act as weak acids due to the presence of the hydroxyl group. They can react with strong bases to form phenoxide ions.
3. Ether Formation: Phenols can react with alkyl halides in the presence of a base to form ethers through nucleophilic substitution.

Carbohydrates

Carbohydrates are polyhydroxy aldehydes or ketones or compounds that can be hydrolyzed to them. They are classified into monosaccharides, disaccharides, oligosaccharides, and polysaccharides based on the number of monosaccharide units they contain.

Reactions of Carbohydrates:

1. Monosaccharide Reactions: Monosaccharides undergo various reactions such as oxidation (e.g., Benedict’s test), reduction (e.g., Tollens’ test), and glycoside formation.
2. Glycoside Formation: Reaction of the hydroxyl group of a monosaccharide with the hemiacetal or hemiketal group of another monosaccharide, resulting in the formation of a glycosidic bond.
3. Hydrolysis: Polysaccharides can be hydrolyzed into their constituent monosaccharides by acid or enzymatic hydrolysis reactions.

Hydroxyl is an chemical group that plays a big role in organic chemistry. It is an -OH functional group with an oxygen atom bonded to a hydrogen atom, and it is usually represented as OH. These are the groups that are responsible for the framework and activity of the variety of organic compounds, and this in turn impacts their properties and reactivity. In this article, we will learn about hydroxyl group, its properties, compound containing hydroxyl group, their nomenclature rule etc.