Ncert Solutions Chemistry Class 12th

This is a long answer type question as classified in NCERT Exemplar

Because of the following reasons, aryl halides are less reactive towards nucleophilic substitution processes than alkyl halides:

(i) The halogen atom's electrons are conjugated to the aryl ring's -electrons, giving the C-X bond a partial double bond character. The whole molecule is then resonance stabilised, allowing for the formation of the following configurations. C-X bond cleavage in haloarenes is more difficult than in haloalkanes due to this bond creation.

ii) The carbon linked to the halogen in haloalkanes is sp³ hybridised, whereas the carbon coupled to the halogen in haloarene is sp² In haloalkanes, the sp² hybridised carbon atom binds the halogen atom more firmly than a connection between sp³ carbon atom and halogen atom. Haloarenes have a shorter C-X bond than haloalkanes, making them more difficult to break.

(iii) Because the phenyl cation is not resonance stabilised, the S_N¹ mechanism of substitution cannot be used.

(iv) Because of the potential for repulsion between electron-rich arenes and approaching electron-rich nucleophiles, aryl halides are less reactive than alkyl halides.

The inclusion of an electron withdrawing group at the ortho- and para-positions can enhance the reactivity of aryl halides. At the meta-position, there is no impact. The presence of an electron withdrawing group, such as the nitro group, at ortho- and para- locations pulls electrons away from the benzene ring, making it easier for the nucleophile to attack haloarene. The carbanion is stabilised as a result of resonance. The -NO₂ group stabilises the negative charge at ortho- and para-positions with regard to the halogen substituent, but none of the resonant structures in meta-nitrobenzene contain the negative charge on the carbon atom bearing the -NO₂ group. As a result, the inclusion of a meta-position electron withdrawing group has no influence on the aryl halide's reactivity.

This is a long answer type question as classified in NCERT Exemplar

Multiple halogen groups are present in these carbon compounds, which have a wide range of applications in industry. Polyhalogen compounds are what they're called. The following are the different chemicals and their impact on life:

1. Dichloromethane, commonly known as methylene chloride, is a solvent that is used as a paint remover, an aerosol propellant, a process solvent in drug manufacturing, and a metal cleaning and finishing solvent. The central nervous system has been documented to be harmed by dichloromethane. Low amounts of this chemical might cause mild hearing and visual impairment, while larger levels in the air can induce dizziness, nausea, tingling, and numbness in the fingers and toes. Methylene chloride produces severe burning and moderate skin redness in humans when it comes into close contact with the skin. The cornea can be burned by direct contact with the eyes.

2. Trichloromethane or Chloroform: This is mostly utilised as a solvent for lipids, alkaloids, iodides, and other compounds, and it is also used to make Freon R-22. It used to be used as an anaesthetic in medicine, but now it's replaced with less harmful alternatives like ether. Chronic exposure to chloroform, which is transformed to phosgene and causes liver and kidney damage as well as skin ulcers, is deadly.

3. Tetrachloromethane, also known as carbon tetrachloride, was commonly utilised to make cleaning solutions, chlorofluorocarbons, and aerosol propellants. The use of CCl₄ has resulted in the loss of the ozone layer, which shields the planet from UV radiation, leading to an increase in skin cancer and other diseases.

4. DDT, or p, p'-dichlorodiphenyltrichloroethane, was a commonly used pesticide. They're chlorinated organic pesticides that became popular after WWII due to their excellent effectiveness against malaria-causing mosquitoes and typhus-carrying lice. The major consequences began with insects developing resistance to DDT and a high toxicity to fish. The issue was exacerbated by DDT's chemical persistence and fat solubility. In terms of chemistry, DDT is not metabolised or solubilized well by mammals. The fatty tissues are where it is deposited and kept. DDT builds up within the animal over time if it is consumed at a constant pace, harming the ecosystem.

This is a long answer type question as classified in NCERT Exemplar

The structure of the alkyl halide as well as the chemicals used in the reaction dictate whether it undergoes substitution or elimination. The reactivity of alkyl halides to substitution processes can be examined to better understand their structural characteristics. The S_N² mechanism, which involves cleavage of the halide from the carbon atom and simultaneous attachment of the attacking nucleophile, is preferred by primary alkyl halides for substitution reactions.

Tertiary halides, on the other hand, go through an elimination process due to the production of stable carbocation. Tertiary halides also prefer to go through the S_N¹ reaction, which is a two-step reaction including the creation of a stable carbocation once the halide atom is cleaved. Depending on the solvent and temperature circumstances, secondary halides exhibit intermediate reactivity in both elimination and substitution processes.

The given reaction is for a primary alkyl halide undergoing S_N² substitution.

The provided reaction is for an S_N² substitution of a tertiary alkyl