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Alkyl halides-Mechanism of nucleophilic substitution Level 1

Exercise 1

1. Which of the following molecules is an alkyl halide?
  a) H2C=CHCl b) C6H5Br c) C6H5CH2Cl d) CH3CH2Br
2. 2-chloro-2-butene is not an alkyl halide because:
  a) It does not have an alkyl group.
b) It has a double bond. c) It is an alkene. d) The halogen is bonded to a sp2 C.
3. The general formula of an alkyl halide is:
  a) CnH2n+2X b) CnH2nX c) CnH2n+1X d) CnH2n-1X
4. Which of the following is a secondary alkyl halide?
  a)1-Chloropropane b) 2-Chloropropane c) 2-Chloro-2-methylpropane d) Iodoethane.
5. An alkyl halide may be prepared by which one of the following methods?
  a) From an alkane using sunlight.
b) From an alkene by addition.
c) From an alcohol withPCl5 or SOCl2 d) Any one of the above.
6. Which of the following concerning the carbon-halogen bond in alkyl halide is true?
 

a) it is non polar.

b) Cl atom has ö- and C ö+ charge.

c) Cl atom has ö+ and C ö- charge. d) the alkyl group exhibits -I effect.
7. The characteristic reactions of alkyl halides are:
 

a) Electrophilic substitution reactions.

b) Addition reactions c) Nucleophilic substitution reactions d) Rearrangements.
8. When an alkyl halide is heated with aqueous base (NaOH, or KOH) the major reaction that takes place is:
 

a) nucleophilic substitution

b) dehydrohalogenation
c) elimination d) both b) and c).
9. When an alkyl halide is heated with alcoholic base (NaOH, or KOH) the major reaction that takes place is:
 

a) nucleophilic substitution

b) dehydrohalogenation
c) elimination . d) both b) and c)
10. Ethyl bromide on heating with aqueous NaOH gives:
  a) Ethanol b) Ethane c) Ethene d) Diethylether
11. On heating Isopropyl chloride with alcoholic KOH propene is obtained which of the following statements concerning this reaction is true?
  a) It is an elimination reaction b) It is dehydohalogenation
c) It is the reverse of an addition rexn. d) All of them are true.
12. An ether cannot be prepared by which of the following reactions?
  a) Williamson reaction b) Heating C2H5Br with dry Ag2O
c) Heating alkyl halide with Na. d) none of the above.
13. Which of the following is not a true statement?
  a) Isopropyl chloride reacts with Mg in dry ether forming a Grignard reagent.
b) Ethyl bromide with silver acetate gives an ester.
c) In Wurtz-Fittig reaction two alkyl halides combine in the presence of Na.
d) Williamsons ether synthesis involves the use of an alkoxide.
14. The product of Wurtz reaction involving isopropyl chloride is:
 

a) 2,2-dimethyl propane

b) 2,2-dimethyl butane c) 2,3-dimethyl propane d) 2,3-dimethylbutane
15. In alkyl halides the C-Cl bond has a larger dipole moment than C-F bond even though F is more electronegative than Cl. This is because:
 

a) The nuclear charge of F > Cl.

b) The affinity energy of F > Cl. c) C -Cl distance > C-F. d) Cl has a larger atomic number.
16. Which of the following reactions of an alkyl halide is not nucleophilic substitution.
 

a) Heating with NaOEt.

b) Heating with NH3.

c) Ester formation

d) Dehydrohalogenation.
17. Which of the following statements is not true with respect to SN1 mechanism?
  a) It is a two-step reaction. b) The rate depends on the concentration of alkyl halide.
c) The rate does not depend on the concentration of the nucleophile.
d) A non polar solvent will enhance the rate of the reaction.
18. Which of the following statements is not true with respect to SN2 mechanism?
 

a) The rate depends on concentration of both nucleophile and base.

b) A good leaving group favours the reaction.
c) Generally primary halides substitute by this mechanism.
d) Secondary halides substitute exclusively by this mechanism.
19. Which of the following solvent systems is most suited for a SN1 reaction:

a) Ethanol

b) Hexane c) Benzene d) Ethanol / water
20. Which one of the following undergo substitution mainly by SN1 mechanism?

a) 1-Chloropropane

b) 2-Chloropropane c) 1-Chlorobutane d) 3-Chloropropene
21. On heating with a strong base which one of the following undergo only substitution and only by SN2 mechanism?

a) CH3Br

b) 2-Chloropropane c) 1-Chlorobutane . d) 3-Chloropropene
22. When (R)-2-Chlorobutane undergoes substitution (heating with NaOH) by SN2 mechanism the product formed is:
a) (+)-2-Butanol b) (-)-2-Butanol c) (±)-2-Butanol d) (S)-2-Butanol
23. In a SN1 reaction the first step is the rate-determining step because:

a) it is the slow step

b) it involves bond breaking c) the Ea of the first step is high d) of all of them.
24. In a SN2 reaction the rate depends on both the alkyl halide and the base because:
 

a) there is only one step

b) both are part of the slow step c) both a) and b) d)none of the above