JEE Main Previous Year Papers Questions With Solutions Chemistry Haloalkanes and Haloarenes

JEE Main Previous Year Papers Questions With Solutions Chemistry Haloalkanes and Haloarenes

Ans.(2) The reaction is nucleophilic sustitution reaction.

2.On mixing a certain alkane with chlorine and irradiating it with ultraviolet light, it forms only one monochloroalkane. This alkane could  be  (2003)
1) pentane                    2) isopentane
3) neopentane             4) propane
Ans.

Ans.(1) Rate of reaction will be fastest when Z is Cl because it is a weakest base.

4.The compound  formed on heating chlorobenzene with chloral in the presence concentrated sulphuric   acid  is    (2004)
1) gammexene              2)  hexachloroethane
3) Freon                        4) DDT
Ans.(4) Dicholodiphenyl trichloroethene.

Ans.(4) Due to steric hindrance.

6.Reaction of one molecule of HBr with one molecule of 1,3-butadiene at 40°C gives predominantly         (2005)
1)3-bromobutene under kinetically controlled conditions
2)l-bromo-2-butene under thermodymically controlled conditions
3)3-bromobutene under thermodynamically controlled conditions
4)l-bromo-2-butene under kinetically controlled conditions
Ans.(2)CH₃ – CH = CH₂

7. Alkyl halides react with dialkyl copper reagents to give          (2005)
1)alkenes
2)alkyl copper halides
3)alkanes
4)alkenyl halides
Ans.(3)R₂CuLi + R’X—>R-R +R-Cu + LiX

Ans.CH₃0^– is more reactive and PhO- is least reactive.

9.Reaction of trans-2-phenyl-l bromo cyclopentane on reaction with alcoholic KOH produces.     (2006)
1)4-phenylcyclopentene
2)2-phenylcyclopentene
3)1-phenylcyclopentene
4)3-phenylcyclopentene
Ans.(4) Nucleophilic substitution of Cl^– by CN^–.

10. The structure of the major product formed in the following reaction is   (2006)

Ans.(4) According to E₂ elimination mechanism.

11.Which of the following is the correct order of decreasing SN₂ reactivity ?  (2007)
1)RCH₂x > R₃CX > R₂CHX
2)RCH₂X>R₂CHX>R₃CX
3)R₃CX >R₂CHX > RCH₂X
4)R₂CHX>R₃CX>RCH₂X
Ans.(2)More is the steric hindrance at the carbon bearing the halogen, lesser is the S_N2 reactivity.

12.The organic chloro compound, which shows complete stereochemical inversion during a S_n2 reaction, is    (2008)
1)(C₂H₅)₂CHCl            2) (CH₃)₃CCl
3) (CH₃)₂CHCl             4) CH₃Cl
Ans.(4) For S_n2 reaction, the C atom is least hindered towards the attack of nucleophile in the case of CH3Cl.

13.Consider the following bromides :

Ans.(1) S_N1 proceeds via carbocation intermediate, the most stable one forming the product faster. Hence reactivity order for A, B, C depends on stability of carbocation created

14.Phenol is heated with a solution of mixture of KBr and KBr0₃. The major product obtained in the reaction is  (2011)
1)4-Bromophenol
2)2, 4, 6-Tribromophenol
3)2-Bromophenol
4)3-Bromophenol
Ans.

15.Which branched chain isomer of the hydrocarbon with molecular mas 72u gives only one isomer of mono substituted alkyl halide ?  (2012)
1) Tertiarybutylchloride
2) Neopentane
3) Isohexane
4) Neohexane
Ans.(2) Neopentane, (CH₃)₄C, on monochlorination gives only one isomer.

16.In S_n2 reactions, the correct order of reactivity for the following compounds :

Ans.(3) Order of required reactivity :
CH₃C1 > CH₃CH₂C1 > (CH₃)₂CHC1 > (CH₃)₃CC1

17.The synthesis of alkyl fluorides is best accom­plished by (2015)
1)Free radical fluorination
2)Sandmeyer’s reaction
3)Finkelstein reaction
4)Swarts reaction
Ans.(4) R -X + AgF —> R – F + AgX.