How does nucleophilic substitution reaction occur in alkyl halide? Give its reaction mechanism.

Nucleophilic substitution of alkyl halides is the substitution of the halogen by another group called a nucleophile. The alkyl halide substrate contains a polarised carbon halogen bond. The SN 2 mechanism begins when an electron pair of the nucleophile attacks the back lobe of the leaving group. Carbon in the resulting complex is trigonal bipyramidal in shape. With the loss of the leaving group, the carbon atom again assumes a pyramidal shape; however, its configuration is inverted. The intermediate shows both the nucleophile and the substrate. Also notice that the nucleophile must always attack from the side opposite the side that contains the leaving group. This occurs because the nucleophilic attack is always on the back lobe (anti bonding orbital) of the carbon atom acting as the nucleus. SN 2 mechanisms always proceed via rearward attack of the nucleophile on the substrate. This process results in the inversion of the relative configuration, going from starting material to product. This inversion is often called the Walden inversion.

Write short notes on following: D.D.T

Dichlorodiphenyl-trichloroethane is commonly known as DDT. It is a colourless, tasteless, and almost odourless crystalline chemical compound. Originally developed as an insecticide, it became infamous for its environmental impacts. It is prepared by heating the mixture of chlorobenzene and chloral in the presence of sulphuric acid.

Write short notes on following: freons

Freon is a chlorofluorocarbon (CFC) that has been linked to ozone depletion, so it is quickly being phased out of use. Freon is not only used in air conditioning units, but it has also been used in upright and chest freezers. Chlorofluoro derivatives of methane and ethane are prepared by the reaction of carbon tetrachloride and hexachloroethane, respectively with HF in presence of SbCl 5 •

Write the IUPAC name of CHCl 3 and CHI 3 .

The common names of the given compounds are chloroform and Iodoform are formed by the reaction of an alkane in the presence of excess sunlight by replacing the hydrogen atoms. Since, the number of carbon atoms in the compound is one and three atoms of chlorine and iodine are present. Hence, the IUPAC name of the given compounds are trichloromethane and triiodomethane.

How chloroform is stored for safe storage?

Chloroform is slowly oxidised by air in the presence of light to an extremely poisonous gas phosgene. Thus, it is stored in closed dark coloured bottles safely and completely filled so that air is kept out. The equation for the formation of phosgene is: 2 CHCl 3 + O 2 → sunlight 2 HCl + 2 COCl 2

Explain the following reactions of chlorobenzene : Reaction with chlorine in the presence of FeCl 3 in dark

Chlorobenzene reacts with chlorine in the presence of a Lewis acid, anhydrous FeCl 3 in the absence of sunlight to form ortho and para dichlorobenzene. The major product formed in this reaction is para dichlorobenzene and ortho dichlorobenzene is the minor product. This reaction is called halogenation.

Explain the following reaction of chlorobenzene : Fitting 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 the following reactions of chloroform : Effect of air and sunlight

Chloroform undergoes oxidation in the presence of air and sunlight to form a toxic gas, phosgene and hydrochloric acid. In order to avoid this, chloroform is kept in dark bottles to prevent any oxidation process. 2 CHCl 3 + O 2 → sunlight air 2 COCl 2 + 2 HCl

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EMBIBE CHAPTER WISE PREVIOUS YEAR PAPERS FOR CHEMISTRY>Chapter -1 - Haloalkanes and Haloarenes>Madhya Pradesh Board-2019>Q 5

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What is elimination reaction? Mention Saytzeff's rule associated with it.

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