Introduction to Stereochemistry

• Stereochemistry is the study of the spatial arrangement of atoms and molecules and their effects on the chemical and physical properties of substances.
• The term 'stereo' derives from the Greek word for 'three-dimension' and stereochemistry refers to the three-dimensional structure of molecules.
• It explores how the arrangement of atoms within molecules impacts reactivity and behaviour.
• Two main aspects are geometric isomerism and optical isomerism.

Geometric Isomerism in Coordination Complexes

• Geometric isomerism occurs in coordination complexes where the same atoms are connected in the same order but have a different spatial arrangement.
• In coordination chemistry, two types are prevalent: cis-trans (or E-Z) isomerism and fac-mer isomerism.
• Cis and trans isomers refer to complexes where two identical ligands are either next to each other (cis) or opposite each other (trans).
• Fac and mer isomers are specific to octahedral complexes where the three identical ligands are either in one face (fac) or around one meridian (mer).

Optical Isomerism in Coordination Complexes

• Optical isomerism is a form of stereochemistry that describes compounds which are mirror images of each other, much like left and right hands.
• These mirror image compounds are called enantiomers and they cannot be superimposed on each other.
• Optical isomers affect plane-polarized light differently. One isomer will rotate the plane of polarized light to the right (dextrorotatory) and the other to the left (levorotatory).
• This can be important in drug design as some drugs may have different pharmacological effects depending on their stereochemistry.

Coordination Complexes and Chirality

• Chirality is the property of a molecule that makes it non-superimposable on its mirror image.
• A molecule is chiral if it has an asymmetric center - a central metal atom in a complex that's bonded to a set of ligands in a non-identical but mirrored arrangement.
• Chirality, like isomerism, has a substantial effect on the chemical behaviour and properties of the molecule, including reactivity, solubility and boiling point.

Role of Stereochemistry in Real-World Applications

• Understanding stereochemistry is essential in numerous fields including drug design, materials science, and molecular biology.
• For example, the stereochemistry of a drug molecule can influence its effectiveness and cause side effects.
• In materials science, the stereochemistry of polymers can affect their properties like strength, flexibility, and resistance to heat and chemicals.