Explain SN 2 reaction with an example.

Consider the alkaline hydrolysis of methyl bromide to give methanol CH 3 - Br + NaOH → ∆ CH 3 - OH + NaBr The rate of the reaction is proportional to the concentration of methyl bromide as well as the concentration of hydroxide ion. Rate = K × CH 3 - Br × OH - The order of the reaction is 2. In the rate determining step, the carbon to hydroxide ion bond formation and carbon to bromine bond breaking are simultaneous processes. Hence, the reaction is bimolecular as both methyl bromide and sodium hydroxide are involved in the rate determining step. Thus, the above reaction is bimolecular nucleophilic substitution reaction.

Write only equation of Friedel-Craft reaction.

Friedel–Crafts alkylation involves the alkylation to an aromatic ring with an alkyl halide using a strong acid, such as aluminium chloride, ferric chloride as solvent. The equation for the chemical reaction is C 6 H 6 + CH 3 Cl → C 6 H 5 - CH 3 + HCl

Write only equation for Fittig reaction.

When aryl halide is heated with another aryl halide in the presence of sodium in dry ether, halogen atom is replaced by aryl group. This reaction is called Fittig reaction. Chlorobenzene is heated with another molecule of chlorobenzene in the presence of sodium in dry ether to give biphenyl.

Explain Markovnikov's rule with example.

Markovnikov's rule states that during the addition across unsymmetrical multiple bond, the negative part of the addendum gets attached to the carbon atom which posses lesser number of hydrogen atoms while the positive part goes to the carbon atom with more hydrogen atoms. Addition of hydrogen bromide to propene takes place in accordance with Markovnikov's rule. Thus, bromide ion is added to middle carbon which is having less number of hydrogen atoms and proton is attached to terminal carbon atom.

Explain S N 1 unimolecular nucleophilic substitution reaction. Give one example.

These are basically unimolecular nucleophilic substitution reactions and follow first order kinetics. These reactions are carried out in polar protic solvents such as water, alcohol, acetic acid, etc. solvents of low polarity favour S N 1 reactions. Therefore, rate increases with the increase in ionising power of solvent. They can occur with weak nucleophiles in low concentrations. It is a two-step process. The species formed in the slow step contains a positively charged, electron deficient carbon called a carbocation. These are unstable and react rapidly with nucleophile that have unpaired electrons available for bond formation. The rate of reaction depends on the concentration of the substrate only not on the concentration of nucleophile. The order of reactivity for different alkyl halides of the series is 3 ∘ > 2 ∘ > 1 ∘ > CH 3 X . Example : The alkaline hydrolysis of tertiary butyl bromide involves S N 1 nucleophilic substitution.

Write only chemical equation of Wurtz reaction.

Two molecules of alkyl halides (same or different) react with metallic sodium in the presence of ether to form alkanes. This reaction is called Wurtz reaction, and it is used to prepare symmetrical alkanes. Two molecules of bromomethane reacts with metallic sodium in presence of ether to form ethane. CH 3 - Br + 2 Na + Br - CH 3 → Dry ether CH 3 - CH 3 + 2 NaBr

Explain Hunsdieckers reaction by giving a chemical equation.

It is a chemical reaction in which the silver salts of carboxylic acid reacts with halogens to form an unstable intermediate which further undergoes thermal decarboxylation to form an alkyl halide as a final product. This reaction is called Hunsdieckers reaction. Silver propanoate reacts with bromine in the presence of CCl 4 to form bromomethane. CH 3 CH 2 COOAg Silver propanoate + Br 2 → CCl 4 CH 3 CH 2 Br Bromomethane + CO 2 + AgBr

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Write the structure, IUPAC name and one use of DDT.

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