Question

[5] Explain the features for two of the following reactions, giving at least two example for each (a) Association (Addition). (b) Ligand exchange (c) Oxidative addition (d) Reaction of mutual ligands

Answer 1

Association Reaction OR addition reaction: In this one reactant molecule combines with other reactant molecule to form a large single molecule with other product. The term association reaction is used when the ions are present as reactant , that is when ion got reacted with other neutral species and form a single ionic product with no other products. In general addition reaction occurs when species have double and triple bonds.

Examples of association reaction

$A + B \rightarrow AB$

$A^{+} + B \rightarrow AB^{+}$

Addition of chlorine to the ethylene

$C_{2}=H_{4} + Cl-Cl \rightarrow Cl-CH_{2}-CH_{2}-Cl$

Addition of water to ethylene

$C_{2}=H_{4} + H_{2}O \rightarrow CH_{3}-CH_{2}-OH$

Ligand exchange reactions or substitution reactions:

this reaction generally occur in coordination compound where one or more ligands are replaced by one or more different ligand or species to form a new product.

Examples

In the following reaction hexa hydrated molecules were replace by 4 chlrine ion.

$[Co(H_{2}O)_{6}]^{+2} + 4Cl^{-} \rightleftharpoons [CoCl_{4}]^{-2} + 6H_{2}O$

$[Cu(H_{2}O)_{6}]^{+2} + 4Cl^{-} \rightleftharpoons [CuCl_{4}]^{-2} + 6H_{2}O$

Oxidative reaction : it is also mainly used in coordination chemistry, the reaction which increases the oxidation state of the metal in coordination compound .

Examples.

In the following reaction oxidation state of platinum got increased by addition of chlorine

^{$[PtCl_{4}]^{2-} + Cl_{2}\rightarrow [PtCl_{6}]^{+2}$}