Functional Groups and Organic Classes
Quick Notes
- A functional group is a specific group of atoms that determines the chemical and physical properties of a compound.
- Organic molecules are classified based on the functional group(s) they contain.
- Important to know both names and structures of the following groups:
- Halogeno (–X): F, Cl, Br, I
- Hydroxyl (–OH): alcohols
- Carbonyl (>C=O): aldehydes and ketones
- Carboxyl (–COOH): carboxylic acids
- Alkoxy (–OR): ethers
- Amino (–NH2): amines
- Amido (–CONH2): amides
- Ester (–COOR): esters
- Phenyl (–C6H5): aromatic ring
- Saturated = only single C–C bonds
- Unsaturated = contains at least one C=C double or C≡C triple bond
Full Notes
What Are Functional Groups?
Functional groups are specific atoms or groups of atoms that give distinct chemical reactivity and physical properties to organic molecules.
They define homologous series such as alcohols, carboxylic acids, and esters.
| Name | Structure Example | Found In | Notes |
|---|---|---|---|
| Halogeno | –X (F, Cl, Br, I) | Haloalkanes | E.g. CH3Cl |
| Hydroxyl | –OH | Alcohols | Polar, allows hydrogen bonding |
| Carbonyl | >C=O | Aldehydes and Ketones | Aldehydes: end of chain, Ketones: middle |
| Carboxyl | –COOH | Carboxylic acids | Weak acids |
| Alkoxy | –OR | Ethers | R–O–R′ structure |
| Amino | –NH2 | Amines | Basic group |
| Amido | –CONH2 | Amides | Formed in peptide bonds |
| Ester | –COOR | Esters | Derived from acids and alcohols |
| Phenyl | –C6H5 | Aromatic compounds | Benzene ring attached as substituent |
Saturated vs Unsaturated Compounds
Saturated compounds contain only single bonds between carbon atoms.
Example Ethane
CH3–CH3
Unsaturated compounds contain one or more double (C=C) or triple (C≡C) bonds.
Example Ethene and Ethyne
Ethene → CH2=CH2
Ethyne → HC≡CH
Recognising Functional Groups from Structures
You should be able to:
- Identify the functional group in a skeletal, condensed, or full structural formula.
- Classify a compound based on its functional group(s).
- Recognise multiple functional groups in the same molecule (e.g. amino acids with –NH2 and –COOH).
Linked Course Questions
What is the nature of the reaction that occurs when two amino acids form a dipeptide?
When two amino acids react, the amine group (–NH2) of one reacts with the carboxyl group (–COOH) of the other in a condensation reaction. This forms a peptide bond (–CONH–) and releases a molecule of water. The resulting compound is called a dipeptide.
How can functional group reactivity be used to determine a reaction pathway between compounds?
Understanding how functional groups react allows chemists to plan a reaction pathway — a step-by-step sequence of reactions to convert one compound into another.
For example:
- Ethene → Ethanol via hydration (addition of water)
- Ethanol → Ethanoic acid via oxidation
Each step targets a specific functional group transformation (alkene → alcohol → carboxylic acid), showing how functional group reactivity guides synthetic planning.
Summary
- Functional groups determine the properties and reactivity of organic compounds
- Know the structures and names of common groups including hydroxyl, carbonyl, carboxyl, amino, ester, amide, and phenyl
- Saturated compounds have only single bonds, unsaturated compounds have double or triple bonds
- Be able to identify functional groups from any type of formula representation