Molecular Structure, Functional Groups and Isomerism

Molecular Structure, Functional Groups and Isomerism

Molecular Structure

• Atoms are the building blocks of every substance and they combine to form molecules.
• A molecule is a group of two or more atoms bonded together.
• Covalent bonds are strong bonds formed between atoms resulting in the formation of a molecule.
• Remember that each kind of atom has a specific number of valence electrons, which determine how it can bond with other atoms.
• The number of covalent bonds an atom can form depends upon its number of unpaired electrons.
• Visualise molecules in 3D using ball and stick models or space-filling models to understand the molecular structure better.

Functional Groups

• Functional groups are specific groupings of atoms within molecules that have their own characteristic properties, regardless of the other atoms present in a molecule.
• Some important functional groups include the hydroxyl group (-OH), carboxyl group (-COOH), amino group (-NH2), and alkyl group (R).
• Functional groups determine how organic compounds react - as the same functional group in different molecules will react in the same way.
• Remember to identify functional groups when analysing organic compounds to predict how they will react.

Introducing Isomerism

• Isomerism is a phenomenon where two or more compounds have the same molecular formula but different structures or arrangements of atoms.
• Isomers have the same number of atoms of each element but have different arrangements of their atoms.
• There are two main types of isomerism: Structural (or constitutional) isomerism and Stereoisomerism.

Structural Isomerism

• Structural isomers have the same formula but different structural arrangements.
• Types of structural isomerism include chain isomerism, functional group isomerism, position isomerism and tautomeric isomerism.
• Chain isomerism occurs when the carbon chain is arranged differently.
• Functional group isomerism occurs when the functional group changes.
• Positional isomerism occurs when the functional group is located at different positions on the carbon chain.
• Tautomeric isomerism is a special kind of functional group isomerism that involves the movement of a hydrogen atom.

Stereoisomerism

• Stereoisomers have the same formula and structural backbone but differ in the spatial arrangement of atoms.
• The two main types of stereoisomerism are geometric isomerism (also called cis-trans isomerism) and optical isomerism.
• Geometric isomerism occurs due to restricted rotation about double bonds or cycles, causing different spatial arrangements of atoms.
• Optical isomerism occurs when there is an asymmetric carbon atom, which causes the molecule to rotate the plane of polarized light.

Remember that understanding the molecular structure, functional groups, and types of isomerism are foundational to organic chemistry. Knowing this will significantly help to predict the chemical behaviour of different organic compounds.