Racemic mixture are optically inactive. Give reason.

An equimolar mixture of the enantiomers (dextro and laevo isomers) is called racemic mixture. In racemic mixture dextro + and laevo - isomer will rotate light in the direction opposite to another. Hence, the rotation due one isomer will be cancelled by rotation due to others. Therefore, racemic mixture are optically inactive.

Which conformer has higher energy in the Sawhorse projection formula of ethane and why?

Ethane CH 3 - CH 3 shows two conformation, i.e. eclipsed conformation and staggered conformation. The eclipsed conformation has higher energy in the Sawhorse projection formula of ethane. Because, the repulsion between the electron clouds of σ - bond of non-bonded hydrogen atoms is maximum as hydrogen atoms on the back carbon are exactly placed behind each of the hydrogen atoms on the front carbon.

Complete the following chemical reactions and write the products. i) CH 3 – CH 2 - Cl + KOH Alc . → ii) R - CH = CH 2 + HBr → Peroxide

i) It is an elimination reaction. Haloalkane when boiled with alcoholic potassium hydroxide form alkenes by elimination of one molecule of HX . Chloroethane on boiling with alcoholic potassium hydroxide, gives ethene. CH 3 – CH 2 - Cl + KOH Alc . → CH 2 = CH 2 + KCl + H 2 O ii) In the presence of peroxide addition of hydrogen halide to an unsymmetrical alkene takes place according to the anti-Markowniff's rule. This is called peroxide effect or Kharasch effect. According anti-Markowniff's rule, in the presence of peroxide, the negative part of the molecule to be added goes to the carbon atom containing larger number of hydrogen atom. R - CH = CH 2 + HBr → Peroxide R - CH 2 - CH 2 - Br

Arrange the following alkyl halides in ascending order of their reactivity towards S N 1 reaction. CH 3 - X , CH 3 - CH 2 - X , CH 3 - CH X - CH 3 , CH 3 - C CH 3 2 - X . X = Same

The S N 1 reaction proceeds through the heterolytic fission of C - X bond leading to the formation of a carbocation and a halide ion. The greater the stability of carbocation, greater will be its ease of its formation from alkyl halide (haloalkane) and faster will be the rate of reaction. In the case of alkyl halide, the tertiary alkyl halide undergo S N 1 reaction very fast because the high stability of tertiary carbocations. The ascending order of the reactivity of the given compounds are as follows: CH 3 - X < CH 3 - CH 2 - X < CH 3 - CH X - CH 3 < CH 3 - C CH 3 2 - X .

Complete the following reaction. C 2 H 5 OH + PCl 5 →

When ethyl alcohol reacts with Phosphorus pentachloride, it forms chloroethane. This reaction can be written as, C 2 H 5 OH + PCl 5 → C 2 H 5 Cl + POCl 3 + HCl

Explain the mechanism of the uni-molecular nucleophilic substitution reaction.

Uni-molecular nucleophilic substitution reactions are generally completed in two steps. The first step of the reaction is the slowest step and is also called the rate-determining step. Thus, the rate of the reaction of uni-molecular nucleophilic substitution reaction is 1 . In the first step of the reaction, carbocation is formed which further reacts with nucleophiles to form products in the second step. The mechanism of the reaction is the following;

Write hybridized state of carbon bonded to halogen atom in allyl chloride.

The chemical formula of allyl chloride is CH 2 = CH - CH 2 - Cl . The carbon bonded to halogen atom in allyl chloride forms four sigma bonds with two hydrogen atoms, one chloride atom, and one carbon atom, and it has no lone pair of electrons. Therefore, the hybridized state of the carbon bonded to the halogen atom is sp 3 .

Explain the mechanism of the bimolecular nucleophilic substitution reaction.

The reaction rate of the bimolecular nucleophilic substitution reaction depends on the concentration of alkyl halide and nucleophile. So, the order of this reaction is 2 . Therefore, it is called bimolecular substitution reaction and is represented as S N 2 . Mechanism- The mechanism of the reaction is following:

E M B I B E

EMBIBE CHAPTER WISE PREVIOUS YEAR PAPERS FOR CHEMISTRY>Chapter -1 - Haloalkanes and Haloarenes>Rajasthan Board-2019>Q 8

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Differentiate between configurational and conformational isomers.

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