4.5:
Overview of Functional Groups
Functional groups are covalently bonded sets of atoms within a compound. Molecules containing the same functional groups often exhibit similar properties.
A hydroxyl group contains an oxygen atom and a hydrogen atom. This group affects the solubility of compounds, such as carbohydrates and vitamins.
A carbonyl group is a carbon atom double-bonded to an oxygen atom and is also part of other related functional groups.
Aldehydes have a variable side chain or R-group and a hydrogen atom attached to a carbonyl carbon, while ketones have two variable groups. Aldehydes and ketones are important groups in carbohydrates.
A carboxylic acid or carboxyl functional group has a carbonyl group attached to an R-group and an OH.
An amino group contains a nitrogen atom bonded to two hydrogen atoms and an R-group. Amino acids get their name from these two functional groups.
A phosphate group is a phosphorus bonded to four oxygens. It is commonly found in DNA and can also be transiently attached to other molecules to alter their function.
4.5:
Overview of Functional Groups
Functional groups are a group of atoms with characteristic properties, which when linked to the carbon skeleton of a molecule, alter the properties of that molecule. For example, certain functional groups will make a molecule hydrophilic, whereas others will make them hydrophobic. These functional groups are an indispensable part of organic chemistry and important components of biological molecules, such as carbohydrates, proteins, lipids, and nucleic acids. Each functional group is a unique arrangement of atoms and is assigned a name for the combination of atoms that make up the group.
Hydroxyl Group
The compounds containing hydroxyl groups are generally called alcohols. The hydroxyl group consists of oxygen and hydrogen, and is present in carbohydrates, proteins, and lipids. It imparts hydrophilic properties to these organic compounds, making them highly water-soluble. The hydroxyl group is involved in the hydrolysis and dehydration synthesis reaction. During hydrolysis, a larger molecule, such as polysaccharide, is split into its monomers by adding a hydroxyl group from a water molecule. In contrast, during dehydration synthesis reactions, the hydroxyl group of one monomer can combine with the hydrogen of another to synthesize a polysaccharide.
Carbonyl Group
The carbonyl group is a carbon double–bonded with oxygen found in different classes of organic compounds, such as ketones, amides, esters, and aldehydes. It imparts polarity to compounds and therefore, such compounds have higher boiling points than non-polar compounds. They are also more reactive and undergo nucleophilic addition and substitution reactions.
Carboxylic Acid Group
The carboxyl group can ionize to release hydrogen atoms from the hydroxyl group as free protons (H+), and due to this, the carbonyl-containing compounds are acidic. This group also adds polar properties to the compounds, and such compounds have higher melting and boiling points. In a human body, lactic acid— a short-chain fatty acid— is an example of a carboxyl group containing substance. It is a metabolite formed after glucose catabolism.
Amino Group
The compounds containing amino groups are called amines. In this group, nitrogen is more electronegative than hydrogen, making it polar. As a result, amines are polar compounds. This group is found in protein, vitamins, and hormones.