Aryl halides are extremely less reactive towards Nucleophilic Substitution reactions. Answer: Aryl halides are extremely less reactive towards Nucleophilic Substitution reactions. because C—X bond

acquires a partial double bond character due to resonance. As a result, the bond cleavage in

haloarene is difficult than haloalkane and therefore, they are less reactive towards nucleophilic

substitution reaction.(draw the resonating structures of chlorobenzene)

2. 3. Haloarenes are less reactive than haloalkanes and haloalkenes.

C-X bond length in halobenzene is smaller than C-X bond length in CH3-X Answer: because C—X

bond in halobenzene acquires a partial double bond character due to resonance

4. Haloalkanes react with KCN to form alkyl cyanides as main product while AgCN forms isocyanides

as main product. Answer: Haloalkanes react with KCN to form alkyl cyanides as main product while

AgCN forms isocyanides as main product.since KCN is predominantly ionic and provides cyanide ions

in solution. Although both carbon and Nitrogen can donate electron pair but carbon donates electron

pair instead of Nitrogen to form more stable C-C bond. How ever, AgCN is mainly covalent in nature

and Nitrogen is free to donate electron pair forming isocyanide as the main product.

5. Allyl chloride is more reactive than n - propyl chloride towards nucleophilic substitution reaction.

Answer: Allyl chloride is more reactive than n - propyl chloride towards nucleophilic substitution

reaction.because allyl carbocation is stabilized by resonance whereas n propyl carbocation is

stabilized by +I effect only.

6. 7. Allyl chloride is hydrolysed more readily than n-propyl chloride.

Tert-Butylbromide reacts with aq. NaOH by SN1 mechanism while n-butylbromide reacts by SN2

mechanism

8. Ethyl iodide undergoes SN2 undergoes reaction faster than ethyl bromide. Answer:Since I- ion is

better leaving group than Br- ion, Ethyl iodide reacts faster than ethyl bromide in SN2.

9. Benzyl chloride undergoes SN1 reaction faster than cyclohexyl methyl chloride. Answer: because in

case of benzyl chloride the carbocation formed is stablised by resonance.

10. p - nitro chlorobenzene undergoes nucleophilic substitution faster than chlorobenzene Answer: p -

nitro chlorobenzene undergoes nucleophilic substitution faster than chlorobenzene,due to presence

of electron withdrawing groups such as nitro group in p - nitro chlorobenzene.,it forms more stable

carbanion

11. The presence of nitro group (–NO2 ) at ortho and para postions in haloarenes increases the

reactivity of haloarenes towards Nucleophilic substitution reaction. Answer: The presence of nitro

group (–NO2 ) at ortho and para postions in haloarenes helps in stabilization of resulting carbanion by

–R and –I effects and hence increases the reactivity of haloarenes towards Nucleophilic substitution

reaction.

12. Electrophilic aromatic substitution reactions in haloarenes occur slowly. Answer:Chlorine

withdraws electrons through inductive effect and releases electrons through resonance. The

inductive effect is stronger than resonance and causes net electron withdrawal as a result

Electrophilic aromatic substitution reactions in haloarenes occur slowly

13. Although chlorine is an electron withdrawing group, yet it is ortho-

, para- directing in electrophilic

aromatic substitution reactions. Answer: As the weaker resonance (+R) effect of Chlorine which

stabilize the carbocation formed tends to oppose the inductive effect of Chlorine which destabilize

the carbocation at ortho and para postions and makes deactivation less for ortho and para postion.

14. The dipole moment of chlorobenzene is lower than that of cyclohexyl chloride. Answer: The dipole

moment of chlorobenzene is lower than that of cyclohexyl chloride.because in chlorobenzene

electron withdrawing inductive effect is opposed by electron releasing resonance effect there fore it

is relatively less polar. On the other hand in cyclohexyl chloride there is only electron with drawing is

inductive effect of -Cl atom due to which more polar.CBSE 2021

15. Grignard reagents should be prepared under anhydrous conditions. Answer: Grignard reagents

should be prepared under anhydrous conditions.because Grignard reagent reacts with water and get

decomposed and form alkanes RMgX + H2O R-H + Mg (OH) X.

16. The treatment of alkyl chlorides with aq.KOH leads to the formation of alcohols but in the presence

of alc.KOH alkenes are major products. Answer: The treatment of alkyl chlorides with aq.KOH leads

to the formation of alcohols but in the presence of alc.KOH alkenes are major products.because in

presence of aq.KOH(more polar), nucleophilic substitution reaction takes place ,thus alcohols are

formed while in presence alc.KOH(less polar),elimination reaction takes place.thus alkenes are major

products.

16. Alkyl halides, though polar, are immiscible with water. Answer: Alkyl halides, though polar, are

immiscible with water.because alkyl haides are unable to form H-bond with water as well as unable to

break the existing H-bonds among water molecules.

17. The solubility of haloalkanes in water very low.

18. Haloalkanes easily dissolve in organic solvents. Answer: because the new intermolecular attractions

between haloalkanes and organic solvents have much the same strength as ones being broken in the

separate haloalkanes and solvent molecules.

19. Halogen compounds used in industry as solvents are alkyl chlorides rather than bromides and

iodides. Answer: because alkyl chlorides are more stable and more volatile than bromides and

iodides.

20. Haloalkanes have higher boiling points as compared to those of corresponding alkanes.

Answer:Haloalkanes have higher boiling points as compared to those of corresponding alkanes.Due

to greater polarity as well as higher molecular mass as compared to the parent hydrocarbon,

21. n- butyl bromide has higher point than tert.- butyl bromide. Answer: n- butyl bromide being a

straight chain alkyl halide has larger surface area than tert. butyl bromide. Larger the surface area

,larger the magnitude of the vanderwaal’s forces and higher is the boiling point.

22. The boiling points of alkyl halides decrease in the order: RI > RBr > RCl > RF. Answer: The boiling

points of alkyl halides decrease in the order: RI > RBr > RCl > RF.This is because with the increase in

size and mass of halogen atom, the magnitude of van der Waal forces increases

23. .P-Dichlorobenzene has higher m.p and solubility than those of o- and m- isomers. Answer: P-

Dichlorobenzene has higher m.p and solubility than those of o- and m- isomers. Since p-

dichlorobenzene has more symmetrical structure than other two isomers, hence its molecules fit

more closely in the crystal lattice and consequently stronger intermolecular attractive forces.

24. Racemic mixture is optically inactive. Answer: A Racemic mixture contains two enantiomers in d & l

equal proportions. As the rotation due to one enatiomer is cancelled by equal and opposite rotation

of another isomer. Therefore it is optically inactive..

25. 1-Bromobutane optically inactive but 2-Bromobutane is optically active. Answer: 2-Bromobutane

has four different groups attached to the tetrahedral carbon and has chiral carbon, therefore it is

optically active

22. Preparation of alkyl chloride from alcohols by treating it with Thionyl chloride SOCl2 is the best

method. Answer: Because it gives almost pure alkyl chloride since the by products of the reaction i.e.

SO2 and HCl are in gaseous phase.

23. Alkyl halides are generally not prepared in laboratory by free radical halogenations of alkanes.

Answer: Alkyl halides are generally not prepared in laboratory by free radical halogenations of

alkanes.since Free radical chlorination or bromination of alkanes gives a complex mixture of isomeric

mono- and polyhaloalkanes, which is difficult to separate as pure compounds. Consequently, the yield

of any one compound is low.

24. Sulphuric acid is not used during the reaction of alcohols with KI. Answer: H2SO4 cannot be used

along with KI in the conversion of an alcohol to an alkyl iodide as it converts KI to corresponding HI

and then oxidizes it to I2