31 Year NEET Previous Year Questions: Haloalkanes & Haloarenes - NEET MCQ

Carbonyl chloride (COCl₂).

Cl in 2, 4, 6-trinitrochlorobenzene is activated by three NO₂ groups at o, and p-positions and hence undergoes hydrolysis most readily.

                                    
                                 Isopropyl benzene

By distilling ethanol or acetone with a paste of bleaching powder (laboratory and commercial method).

Cl₂, so obtained acts as a mild oxidising as well as chlorinating agent

(a) 

(b) 

At high temp. i.e., 400°C substitution occurs in preference to addition.

Number of active hydrogen in a compound corresponds to the number of moles of CH₄ evolved per mole of the compound.

—NO₂ group is electron attractive group, so it is able to deactivate the benzene ring.

hence withdrawl of electrons from ortho & para position cause easy removal of –Cl atom due to development of +ve charge on o- and p positions.

Potassium ethoxide is a strong base, and 2-bromopentane is a 2º bromide, so elimination raction predominates

Since trans- alkene is more stable than cis.thus  trans-pentene -2 is the main product.

Chlorination of n-butane taken place via free radical formation i.e., 

Cl may attack on either side and give a racemic mixture of 2 chloro butane which contain 50% d form and 50% l-form.

The order of atomic size of h alogen s decrease in the order I > Br > Cl > F i.e  on moving down a group atomic size increases. Further the bond length of C-X bond deccreases in the order C – I > C – Br > C – Cl > C – F and hence the bond dissociation energy decreases  in the order R – F > R – Cl > R – Br > R – I hence R – I being a weakest bond break most easily. Hence R – I is most reactive.

Chlorofluorocarbons, e.g. CF₂Cl₂, CHF₂Cl₂, HCF₂CHCl₂. These are non-inflammable colour less and stable upto 550ºC. These are emitted as propellants in aerosol spray, cans refrigerators, fire fighting reagents etc. They are chemically inert and hence do not react with any substance with which they come in contact and therefore float through the atmosphere and as a result enter the stratosphere. There theyabsorb UV-rays and due to this they produce free atomic chlorine which results decomposition of ozone which cause depletion of ozone layer.

Chloropicrin is nitrochloroform. It is obtained by the nitration of chloroform with HNO₃.

Chloropicrin is a liquids, poisonous and used as an insecticide and a war gas

For such a reacti on the rate of S²_N substitution reaction is maximum in case of CH₃CH₂ Br because S²_N mech an ism is followed in case of primary and secondary halides i.e., S²_N reaction is favoured by small groups on the carbon atom attached to halogens so CH₃ CH₂ Br > CH₃ CH₂ CH₂ Br >

i.e. option (d) is correct.

In nucleophilic substitution, a nucleophile provides an electron pair to the substrate and the leaving group departs with an electron pair.

These are usually written as S_N (S stands for substitution and N for nucleophilic) and are common in aliphatic compounds especially in alkyl halides and acyl halides.

Friedel Craft’s reaction.

S_N¹ reactions involve the formation of carbocations, hence higher the stability of carbocation, more will be reactivity of the parent alkyl halide. Thus tertiary carbocation formed from (c) is stabilized by two phenyl groups and one methyl group, hence most stable.

explanation: Since rearrangement do not occur in the given nucleophilic substitution
reactions, therefore carbocations are not the intermediate in these reactions.
Thus both the reactions occur by SN2 mechanism