Haloalkanes and Haloarenes Class 12 Chemistry Exam Questions

Please refer to the below Haloalkanes and Haloarenes important questions for Class 12 Chemistry. These questions and answers have been prepared as per the latest NCERT Book for Class 12 Chemistry. Students should go through chapter wise Class 12 Chemistry Important Questions designed as per the latest examination pattern issued by CBSE.

Very Short Answer Questions :

Question. Write the structure of the following compound :
1-bromo-4-sec-butyl-2-methylbenzene
Answer : 

Question. Write the major products in the following :

Answer : 

Question. Draw the structure of 2-bromopentane. 
Answer :  

Question. Write the IUPAC name of (CH₃)₂CHCH(Cl)CH₃. 
Answer : 2-Chloro-3-methyl butane

Question. Write the IUPAC name of the following compound : 

Answer :  

Question. Why does p-dichlorobenzene have a higher m.p. than its o- and m-isomers?
Answer : p-Dichlorobenzene has higher melting point than those of o-and m-isomers because it is more symmetrical and packing is better in solid form. Hence, it has stronger intermolecular force ofattraction than o-and m-isomers. 

Question. How do you convert :
Propene to 1-iodopropane ?
Answer :  

Question. Write the IUPAC name of

Answer : 4-Chloropent-1-ene

Question. Complete the following chemical equation :
CH₃CH₂CH = CH₂ + HBr →^Peroxide …
Answer : 

Question. Explain the following :
Alkyl halides, though polar, are immiscible with water.
Answer :  Alkyl halides are polar but are insoluble in water because energy required to break the intermolecular H – bond among water molecules is much higher than energy released by water halide interaction.

Question. 

which is more reactive towards SN1 reaction and why?
Answer : The S_Nl reaction proceeds through carbocation formation thus, the compound which forms more stable carbocation will be more reactive.

As, 2° carbocation is more stable than 1° carbocation thus, 2-chlorobutane is more reactive towards S_Nl reaction. 

Question. Account for the following :
Grignard’s reagents should be prepared under anhydrous conditions.
Answer : Grignard reagents react with water to form alkanes.

So, they must be prepared under anhydrous conditions. 

Question. Which halogen compound in each of the following pairs will react faster in S_N2 reaction :
(i) CH₃Br or CH₃I
(ii) (CH₃)₃CCl or CH₃Cl
Answer : (i) CH₃I will give faster S_N2 reaction.
(ii) CH₃Cl will give faster S_N2 reaction.

Question. Why are alkyl halides insoluble in water?
Answer : Alkyl halides are polar but are insoluble in water because energy required to break the intermolecular H – bond among water molecules is much higher than energy released by water halide interaction.

Question. Write the structure of an isomer of compound C₄H₉Br which is most reactive towards S_N1 reaction. 
Answer : 

Short Answer Questions :

Question. Complete the following reaction equations :

Answer : (i)

(ii) 

Question. Which would undergo S_N2 reaction faster in the following pair and why?
CH₃ — CH₂ — Br and CH₃ — CH₂ — I
Answer : Since I^– is a better leaving group than Br^–, thus, CH₃CH₂I undergoes S_N2 reaction faster than CH₃CH₂Br.

Question. Answer the following : 
Haloalkanes easily dissolve in organic solvents, why? 
Answer : Haloalkanes dissolve in organic solvents because the intermolecular attractions between  haloalkanes and organic solvent molecules have the same strength as in the separate haloalkanes and solvent molecules.

Question. Compute the following reaction equations:

Answer :(i) 

(ii)  

(iii) 

Question. Give the IUPAC names of the following compounds :

Answer : (i) 2-Bromobutane
(ii) 1,3-Dibromobenzene
(iii) 3-Chloropropene

Question. Write the IUPAC name of the following compound : 
(CH₃)₃CCH₂Br 
Answer : 

Question. Write the IUPAC name of

Answer : 4-Bromo-4-methylpent-2-ene

Question. Give reason :
n-Butyl bromide has higher boiling point than t-butyl bromide.
Answer : n-Butyl bromide, being a straight chain molecule have strong intermolecular forces whereas t-butyl bromide being a branched chain molecule have weaker intermolecular forces due to smaller surface area.
Hence, boiling point of n-butyl bromide is higher than that of t-butyl bromide.

Question. Account for the following :
Grignard’s reagents should be prepared under anhydrous conditions.
Answer : Grignard reagents react with water to form alkanes.

So, they must be prepared under anhydrous conditions. 

Question. Explain why
(i) the dipole moment of chlorobenzene is lower than that of cyclohexyl chloride?
(ii) alkyl halides, though polar, are immiscible with water? 
Answer : (i) There are two reasons :
(a) In case of chlorobenzene, carbon to which chlorine is attached is sp² hybridised and is more  electronegative than the corresponding carbon in cyclohexyl chloride which is sp³ hybridised. So the net dipole moment is lower in chlorobenzene.
(b) In chlorobenzene C—Cl bond has some double bond character so its bond length is smaller.
Hence dipole moment is smaller than cyclohexyl chloride which has a longer C—Cl single bond. 

(ii) Alkyl halides are polar but are insoluble in water because energy required to break the intermolecular H – bond among water molecules is much higher than energy released by water halide interaction.

Question. Draw the structure of major monohalo product in the following reaction :

Answer : 

Question. Why is (±)-butan-2-ol is optically inactive? 
Answer : The (±)-Butan-2-ol is optically inactive because it exist in two enantiomeric forms which are non-superimposable mirror images of each other. Both the isomers are present in equal amounts therefore, it does not rotate the plane of polarized light and is optically inactive. 

Question. Draw the structure of major monohalogen product formed in the following reaction :

Answer : 

Question. State the IUPAC name of the following compound :

Answer : 1-Bromobut-2-ene

Question. Write the mechanism of the following reaction :
CH₃CH₂OH →^HBr CH₃CH₂Br + H₂O
Answer : 

Question. Write the IUPAC name of the following compound :

Answer : 2-Bromo-4-chloropentane

Question. Write the structure of the compound 1-chloro- 4-ethylcyclohexane.
Answer : 

Question. Draw the structure of major monohalo product in each of the following reactions :

Answer : 

Question. Write the structure of the compound :
4-tert-butyl-3-iodoheptane 
Answer : 

Question. How may methyl bromide be preferentially converted to methyl isocyanide?
Answer : KCN is predominantly ionic and provides cyanide ions in solution 
         CH₃Br + KCN  →  CH₃C ≡ N + KBr
Methyl bromide           Methyl cyanide
AgCN is mainly covalent in nature and nitrogen is free to donate electron pair forming isocyanide as main product.
         CH₃Br + AgCN  → CH₃N ≡ C + AgBr
Methyl bromide             Methyl isocyanide