Physics, Chemistry & Maths Glossary

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A

Alcohol Oxidation with Potassium Dichromate

Potassium dichromate oxidises 1^o and 2^o alcohols and gets reduced to green Cr³⁺ ion.

In case of 3^o alcohols the bright orange colour of dichromate ion remains as it is indicating no reaction.

The colour change can be used to indicate a reaction. If the orange colour changes to green or blue green a reaction has occurred.

fig.

Alkyl Halide Nucleophilic Substitution/Elimination

Primary: Generally S_N2 is better than E2. E2 is favoured by strong bulky base with heating as bulky base finds is harder to reach C than H due to steric hindrance

Secondary: S_N2 is favoured over E2 if nucleophile is weak base and the solvent is polar and aprotic. E2 is favoured over S_N2 if strong base is used in protic solvent. Heating further favours E2 over S_N2. Reactions can go via S_N1 and E1 mechanisms in protic solvents.

Tertiary: E2 is almost exclusive in the presence of strong base and protic solvent.