Test: Haloalkanes And Haloarenes - From Past 28 Years Questions


24 Questions MCQ Test Chemistry 28 Years Past year papers for NEET/AIPMT Class 12 | Test: Haloalkanes And Haloarenes - From Past 28 Years Questions


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QUESTION: 1

Phosgene is a common name for [1988]

Solution:

Carbonyl chloride (COCl2).

QUESTION: 2

Which chloro derivative of benzene among the following would undergo hydrolysis most readily with  aqueous sodium hydroxide to furnish the corresponding hydroxy derivative? 

Solution:

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

QUESTION: 3

Benzene reacts with n-propyl chlor ide in the presence of anhydrous AlCl3 to give [1993]

Solution:


                                    
                                 Isopropyl benzene

QUESTION: 4

Industrial preparation of chloroform employs acetone and [1993]

Solution:

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) 

QUESTION: 5

Chlorobenzene reacts with Mg in dry ether to give a compound (A) which further reacts with ethanol to yield [1993]

Solution:

QUESTION: 6

When chlorine is passed through propene at 400°C, which of the following is formed ?[1993]

Solution:

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

QUESTION: 7

Zerevitinov’s determination of active hydrogen in a compound is based upon its reaction with[1994]

Solution:

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

QUESTION: 8

The replacement of chlorine of chlorobenzene to give phenol requires drastic conditions, but the chlorine of 2,4-dinitrochlorobenzene is readily replaced since, [1997]

Solution:

—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.

QUESTION: 9

2-Bromopen tane is heated with potassium ethoxide in ethanol. The major product obtained is[1998]

Solution:

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.

QUESTION: 10

 An organic compound A (C4H9Cl) on reaction with Na/diethyl ether gives a hydrocarbon which on monochlorination gives only one chloro derivative, then  A is [2001]

Solution:

QUESTION: 11

 obtained by chlorination of n-butane, will be [2001]

Solution:

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.

QUESTION: 12

Reactivity order of halides for dehydrohalogenation is [2002]

Solution:

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.

QUESTION: 13

Z in the above reaction sequence is [2002]


Solution:

QUESTION: 14

When  CH3CH2CHCl2 is treated with NaNH2, the product formed is [2002]

Solution:

QUESTION: 15

Which of the following is responsible for depletion of the ozone layer in the upper strata of the atmosphere? [2004]

Solution:

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.

QUESTION: 16

Chloropicrin is obtained by the reaction of 

Solution:

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

QUESTION: 17

In a SN2 substitution reaction of the type             [2008] which one of the following has the highest relative rate ?

Solution:

For such a reacti on the rate of S2N substitution reaction is maximum in case of CH3CH2 Br because S2N mech an ism is followed in case of primary and secondary halides i.e., S2N 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.

QUESTION: 18

Which of the following reactions is an example of nucleophilic substitution reaction? [2009]

Solution:

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 SN (S stands for substitution and N for nucleophilic) and are common in aliphatic compounds especially in alkyl halides and acyl halides.

QUESTION: 19

Benzene reacts with CH3Cl in the presence of anhydrous AlCl3 to form: [2009]

Solution:

Friedel Craft’s reaction.

QUESTION: 20

Trichloroacetaldehyde, CCl3CHO reacts with chlorobenzene in presence of  sulphuric acid and pr oduces: [2009]

Solution:

QUESTION: 21

The reaction of toluene with Cl2 in presence of FeCl3 gives ' X' and reaction in presence of light gives ‘Y’. Thus, ‘X’ and ‘Y’ are : [2010]

Solution:

QUESTION: 22

Which one is most reactive towards SN1 reaction ?

Solution:

SN1 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.

QUESTION: 23

Consider the reactions : [2011 M]


                               

                            

The mechanisms of reactions (i) and (ii) are respectively :

Solution:

A strong nucleophile favours the SN2 reaction and a weak nucleophile favours the SN1 reaction.
First reaction is SN1 reaction because C2H5OH used as solvent which is a weak nucleophile.
Second reaction is SN2 reaction because C2H5O is strong nucleophile.

QUESTION: 24

Number of isomeric alcohols of molecular formula C6H14O which give positive iodoform test is [NEET Kar. 2013]

Solution: