NEET - HALOALKENES AND HALOARENES - MODEL - 2024

1. Phosgene is a common name for
(a) phosphoryl chloride
(b) Thionyl chloride
(c) Carbon dioxide and phosphine
(d) Carbonyl chloride.

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

3. Benzene reacts with n-propyl chloride in the presence of anhydrous AlCl3 to give
(a) 3 – Propyl – 1 – chlorobenzene
(b) n-Propyl benzene
(c) No reaction
(d) Isopropyl benzene.

4. Industrial preparation of chloroform employs acetone and
(a) Phosgene
(b) Calcium hypochlorite
(c) Chlorine gas
(d) Sodium chloride.

5. Chlorobenzene reacts with Mg in dry ether to give a compound which further reacts with ethanol to yield
(a) Phenol
(b) Benzene
(c) Ethylbenzene
(d) Phenyl ether.

6. When chlorine is passed through propene at 400°C, which of the following is formed ?
(a) PVC
(b) Allyl chloride
(c) Nikyl chloride
(d) 1, 2-Dichloroethane

7. Zerevitinov’s determination of active hydrogen in a compound is based upon its reaction with
(a) Na
(b) CH3MgI
(c) Zn
(d) Al.

8. The replacement of chlorine of chlorobenzene to give phenol requires drastic conditions, but the chlorine of 2,4-dinitrochlorobenzene is readily replaced since,
(a) nitro groups make the aromatic ring electron rich at ortho/para positions
(b) nitro groups withdraw electrons from the meta position of the aromatic ring
(c) nitro groups donate electrons at meta position
(d) nitro groups withdraw electrons from ortho/para positions of the aromatic ring

9. 2-Bromopentane is heated with potassium ethoxide in ethanol. The major product obtained is
(a) 2-ethoxypentane
(b) pentene-1
(c) trans-2-pentene
(d) cis-pentene-2

10. An organic compound A(C4H9Cl) on reaction with Na/diethyl ether gives a hydrocarbon which on monochlorination gives only one chloro derivative, then Ais
(a) tert-butyl chloride
(b) sec-butyl chloride
(c) isobutyl chloride
(d) n-butyl chloride

11. Compound obtained by chlorination of n-butane, will be:

(a) l-form
(b) d-form
(c) Meso form
(d) Racemic mixture

12. Reactivity order of halides for dehydrohalogenation is
(a) R– F> R– Cl > R– Br > R–I
(b) R–I> R– Br > R– Cl > R– F
(c) R–I> R– Cl > R– Br > R– F
(d) R– F> R–I> R– Br > R– Cl

Z in the above reaction sequence is
(a) CH3CH2CH2NHCOCH3
(b) CH3CH2CH2NH2
(c) CH3CH2CH2CONHCH3
(d) CH3CH2CH2CONHCOCH3

14. When CH3CH2CHCl2 is treated with NaNH2, the product formed is
(a) CH3 — CH= CH2
(b) CH3 — C=CH
(c) CHCHCH3 2 =NH2 NH2
(d) CHCHCH3 = Cl NH2

15. Which of the following is responsible for depletion of the ozone layer in the upper strata of the atmosphere?
(a) Polyhalogens
(b) Ferrocene
(c) Fullerenes
(d) Freons

16. Chloropicrin is obtained by the reaction of
(a) steam on carbon tetrachloride
(b) nitric acid on chlorobenzene
(c) chlorine on picric acid
(d) nitric acid on chloroform

17. Which of the following reactions is an
example of nucleophilic substitution reaction?
(a) 2 RX+ 2 Na -> PR+ 2 NaX
(b) RX+ H2 -> RH+ HX
(c) RX+ Mg -> RMgX
(d) RX+ KOH -> ROH+ KX

18. Benzene reacts with CH3Cl in the presence of anhydrous AlCl3 to form:
(a) chlorobenzene
(b) benzylchloride
(c) xylene
(d) toluene

19. Trichloroacetaldehyde, CCl3CHOreacts with chlorobenzene in presence of sulphuric acid and produces:

20. 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:
(a) X= Benzal chloride, Y= o – Chlorotoluene
(b) X= m – Chlorotoluene, Y= p – Chlorotoluene
(c) X= o –and p – Chlorotoluene, Y= Trichloromethyl – benzene
(d) X= Benzyl chloride, Y= m – Chlorotoluene

21. Number of isomeric alcohols of molecular formula C6H14Owhich give positive iodo form test is
(a) two
(b) three
(c) four
(d) five

22. Consider the reaction, CH₃CH₂CH₂Br + NaCN → CH₃CH₂CH₂CN + NaBr This reaction will be the fastest in

(a) ethanol

(b) water

(d) N, N’ – dimethylformamide (DMF)

23. When two halogens are attached to same carbon atom, it is known as :

(a) , – dihalide

(b) , – dihalide

(d) gem-dihalide

24. Reactivity order for HX in Lucas test.

(a) HBr > HCl < HI

(b) HCl > HBr > HI

(d) HBr > HCl > HI

25. In an S_N1 reaction on chiral centres, there is

(a) inversion more than retention leading to partial racemisation

(b) 100% retention

(d) 100% inversion

26. Predict the decreasing order of density for same Alkyl or cryle group.

(a) R / Ar – F > R / Ar – Cl < R / Ar – Br < R / Ar – I

(b) R / Ar – Br > Ar / R Cl > R / Ar – I > R /Ar > F

(d) R / Ar – I < R / Ar – Cl < R / Ar – Br > R / Ar – F

27. The correct order of increasing reactivity of C-X bond towards nucleophile in the following compounds is

(a) I < II < IV < III

(b) III < II < I < IV

(d) IV < III < I < II

28. Among the following which one can have a meso form?

(a) C₂H₅CH(OH)CH(OH)CH₃

(b) HOCH₂CH(Cl)CH₃

(d) CH₃CH(OH)CH(OH)CH₃

29. Which of the following reactions is an example of nucleophilic substitution reaction?

(a) 2RX + 2Na → R – R + 2NaX

(b) RX + KOH → ROH + KX

(d) RX + Mg → RMgX

30. If there is no rotation of plane polarised light by a compound in a specific solvent, though to be chiral, it may mean that

(a) the compound is certainly meso

(b) there is no compound in the solvent

(d) the compound is certainly a chiral.

31. Which of the following is not chiral ?

(A) 2- Hydroxypropanoic acid

(B)2- Butanol

(D) 3 – Bromopentane

32. A compound of molecular formula C₇H₁₆ shows optical isomerism, compound will be

(a) 2,3-dimethylpentane

(b) 2,2-dimethylbutane

(d) none of these.

33. Which of the following is an optically active compound?

(a)1 – Butanol

(b) 1 – Propanol

(d) 4 -Hydroxyheptane

34. Grignard reagent is prepared by the reaction between

(a) magnesium and aromatic hydrocarbon

(b) magnesium and alkane

(d) magnesium and alkyl halide

35. Reaction of t-butyl bromide with sodium methoxide produce

(A)Sodium t – butoxide

(B)t-butyl methyl ether

(C)isobutene

(D)isobutylene

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

37. Which one is formed when sodium phenoxide is heated with ethyl iodide?

(a) Ethyl phenyl alcohol

(b) Phenol

(d) None of these

38. Which is correct for aelaillic halide compounds

(a) 3, Bromo, 2-Methy, Buyt 1-ene

(b) 4-Bromo, 3-Methyl Buyt-2-ene

(d) 1-Bromo Buyt -2-ene

39. Chloroform on slow oxydation with air gives

(a) Cl₃C-COOH

(b) Formile Chloride

(d) COCl₂

40..Industrial preparation of chloroform employs acetone and

(a) Phosgene

(b) calcium hypochlorite

(d) sodium chloride

41.Rectified spirit is a mixture of

(a) 95% ethyl alcohol + 5% water

(b) 94% ethyl alcohol + 4.53 water

(d) 95.87% ethyl alcohol + 4.13% water

42. An example of a sigma bonded organometallic compound is :

(1) Grignard’s reagent

(2) Ferrocene

(3) Cobaltocene

(4) Ruthenocene

43. Identify A and predict the type of reaction

44. Identify compound X in the following sequence of reactions

45. Elimination reaction of 2-Bromo-pentane to form pent-2-ene is

(a) imination reaction

(b) Follows Zaitsev rule

(d) Dehydration reaction

(1) (b), (c), (d)

(2) (a), (b), (d)

(3) (a), (b), (c)

(4) (a), (c), (d)

46. Which of the following alkane cannot be made in good yield by Wurtz reaction?

(1) n-Heptane

(2) n-Butane

(3) n-Hexane

(4) 2,3-Dimethylbutane

Solutions :

1.Ans: (d)

Carbonyl chloride (COCl₂)

2.Ans: (a)Cl in 2,4 ,6 – trinitrochlorobenzene is activated by three NO₂ group at 0 , and p – position and hence undergoes hydrolysis most readily

3.Ans: (d)

4.Ans: (b) by distilling ethanol or acetone with a paste of bleaching power (laboratory and commercial method).

CaOCl₂ +H₂O -> Ca(OH)₂ + Cl₂

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

(a) CH₃COCH₃ + 3Cl₂ -> CCl₃. CO.CH₃+ 3HCl

(chlorination)

(b) 2CCl₃. CO.CH₃ +Ca(OH)₂ -> 2CHCl₃ +(CH₃COO)₂Ca

(Hydrolysis)

5.Ans: (b) C₆H₅Cl C₆H₅MgBr C₆H₆ +CH₃CH₂OMgBr

6.Ans: (b) At high temperature i.e. 400 substitutions occurs in preference to addition.

7.Ans: (d) Number of active hydrogen in a compound corresponds to the number of moles of CH₄ evolved per mole of the compound.

-OH , -NH₂ , -SH, – OH or – C = CH CH₄ (2CH₄ from – NH₂)

8.Ans: (b) –NO₂ group is electron attractive group, so it is able to deactivate the benzene ring. Hence withdrawal of electron from ortho & para position cause easy removal of –Cl atom due to development of +ve charge on o – and p positions.

9.Ans: (c) Potassium ethoxide is a strong base, and 2- bromopentane is a 2⁰ bromide, so elimination reaction predominates Since trans – alkene is more stable than cis. Thus trans – pentene -2 is the main product.

10.

11.Ans: (d)

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

12.Ans: (b) The order of atomic size of halogens decrease in the order I > Br >CI > F ie. On moving down a group atomic size increases. Further the bond length of C-X bond decreases in the order C- I > C –Br > C – CI > C- F and hence the bond dissociation energy decrease 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.

13.Ans: (a)

14.Ans: (b)

15.Ans: (d) Chlorofluorocarbons, E.,g CF₂Cl₂ , CHF₂Cl₂HCF₂CHCl₂These are non inflammable colour less and stable upto 550⁰ C. These are emitted as propellants in aerosol spray,cans refrigerators, fire fighting reagents etc., Thy 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.

16. Ans: (d) Chloropicrin is nitrochlorofrom. It is obtained by the nitration of chloroform with HNO₃

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

17.Ans: (d) In nucleophilic substitution, a nucleophilie 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.

22. (d) The reaction is SN₂, most suitable solvent should be polar aprotic i.e., DMF.

23 (d) gem-dihalide

24. (c) HCl < HBr < HI

25 (d) S_N1 reaction gives racemic mixture with slight predominance of that isomer which corresponds to inversion because S_N1 also depends upon the degree of ‘shielding’ of the front side of the reacting carbon.

26 (c) R / Ar I > R / Ar – Br > R / Ar Cl > R / Ar – F

27 (a) The order of reactivity, is dependent on the stability of the intermediate carbocation formed by cleavage of C-X bond. The 3° carbocation (formed from III) will be more stable than its 2° counter part (formed from IV) which in tum will be more stable than the arenium ion (formed from I). Also, the aryl halide has a double bond character in the C-X bond which makes the cleavage more difficult. However, inspite of all the stated factors, II will be more reactive than I due to the presence of the electron withdrawing -NO₂ group. C-X bond becomes weak and undergoes nucleophilic substitution reaction.

28. (a) A molecule having a plane of symmetry but having chiral carbons will have meso form .

29 (b) R−X+KOH→R−OH+K
X− replaced by OH− show nucleophilic substitution reaction

30 (c) The compounds in which asymmetric carbon atom is present, are called optically active, they rotate the plane of polarised light but the compounds which do not show optical activity inspite of the presence of chiral carbon atoms are called meso-compounds. The absence of optical activity in these compounds is due to the presence of a plane of symmetry in the molecule.

Due to absence of asymmetric carbon atom.

32(a) Organic compound exhibit the property of enantomerism (optical isomerism) only when their molecular are chiral. Most chiral compounds have a chiral centre, which an atom bonded to four different atom or groups.

2-3 , Dimenthylpantane has one chiral C-atom and do not have any symmetric element.

33 (c)

2-Chlorobutane contains a chiral carbon atom and hence is optically active compounds.

34 (d) magnesium and alkyl halide

35 (d) isobutylene is obtained

Thus, the reaction produces isobutylene.

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

37 (c) Phenetole is formed when sodium phenoxide is heated with ethyl iodide.

38 (a) 3, Bromo, 2-Methy, Buyt 1-ene

39 (d) COCl₂

40 (b) CaOCl₂ + H₂O → Ca(OH)₂ +Cl₂

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

41(d) 95.87% ethyl alcohol + 4.13% water

42 (1) Grignard’s reagent (RMgX) is a bonded organometallic compound.

43 (4) M – bromosiole gives only the respective meta substituted anline. This is a substitution reaction which reaction which goes by an elimination addition pathway.