Haloalkanes and Haloarenes Test

Result

Haloalkanes and Haloarenes Test - 4

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Weekly Quiz Competition

Question 1
4 / -1

Cyanide anion has two atoms th at have lone pair of electrons. Either could act as nucleophile in the reaction. Yet in the vast majority of the cases, carbon acts as nucleophile and forms a bond to the substrate, why?

A
Nitrogen is strongly solvated in hydroxylic solvents, it will be less reactive

B
Carbon is more reactive in polar aprotic solvents, normally used for these S_N2 reactions

C
Carbon atoms are more basic than nitrogen

D
The lone pair of electrons on C is in sp hybrid orbital

Solution

Both carbon and nitrogen are capable of donating electron pair but carbon is better electron donor than nitrogen, carbon donates electron pair in most of the cases.
Question 2
4 / -1

In the following two phase reaction, catalyst works by
C₆H₅CH₂Br + KCN C₆H₅CH₂CN + KBr

A
transforming CN^- from the aqueous phase to organic containing C₆H₅CH₂Br

B
transforming C₈H₅CH₂Br from organic phase to the aqueous phase containing CN^-

C
removing Br^- from the organic base to aqueous phase

D
removing K⁺ from the organic phase to make CN^- more nucleophilic

Solution

By the following equilibrium

Cyanide ion is transferred to organic phase otherwise KCN is insoluble in organic solvents.
Question 3
4 / -1

Which of the following would react most rapidly with sodium ethoxide to produce an ether?

A
Chlorobenzene

B
2-nitrotoluene

C
p-nitrochlorobenzene

D
m-(chloromethyl)-toluene

Solution

In all other cases leaving group is on phenyl ring, not substituted, usually by nucleophiles under ordinary condition.
Question 4
4 / -1

In the given reaction,
X will be

A

B

C
1 :1 mixture of (a) and (b)

D
2 : 1 mixture of (a) and (b)

Solution
Question 5
4 / -1

In the given reaction,
X will be

A

B

C

D

Solution
Question 6
4 / -1

Consider the following reaction,
Q.
What can be correctly predicted regarding this reaction?

A
S_N1 reaction is occurring

B
S_N2 reaction is occurring

C
Neighbouring group participation and S_N2 reaction are occurring

D
Neighbouring group participation and S_N1 reaction are occurring

Solution
Question 7
4 / -1

Pick out the alkyl bromide which proceeds with retention of configuration in an S_N2 reaction with CH₃ONa (aq).

A

B

C

D

Solution

Due to inversion of configuration twice at α-carbon, there will be overall retention of configuration.
Question 8
4 / -1

For the following reaction, pick out the best term which describe its mechanism

A
S_N1

B
S_N2

C
S_N2 with neighbouring group participation

D
addition followed by substitution

Solution
Question 9
4 / -1

The reaction of tert butyl bromide with sodium methoxide produces mainly

A
isobutane

B
isobutylene

C
tert-butyl methyl ether

D
sodium tert butoxide

Solution

When the reaction of tert butyl bromide occurs with sodium methoxide, an elimination takes place. This is the E1cB elimination, wherein the Hoffman alkene is major. Then dehydro halogenation takes place. Subsequently, rather than an ether, which is typically the case, an alkene is obtained. This is why, isobutylene is formed.
Question 10
4 / -1

Which of the following undergoes nucleophilic substitution exclusively by S_N1 mechanism?

A
Benzyl Chloride

B
Ethyl chloride

C
Chlorobenzene

D
Isopropyl chloride
Question 11
4 / -1

The increasing order of nucleophilicity would be?

A
Cl^– < Br^– < I^–

B
I^– < Cl^– < Br^–

C
Br^– < Cl^–< F^–

D
I^– < Br^– < Cl^–
Question 12
4 / -1

Which of the following is most reactive towards SN1 reaction?

A
C₆H₅C(CH₃)C₆H₅Br

B
C₈H₅CH₂Br

C
C₆H₅CH(C₆H₅)Br

D
C₆H₅CH(CH₃)Br
Question 13
4 / -1

CH₃CH₂CH₂Br + NaCN → CH₃CH₂CH₂CN + NaBr, will be fastest in

A
ethanol

B
methanol

C
N, N-dimethylformamide

D
Water
Question 14
4 / -1

Comprehension Type
Direction (Q. Nos. 14-16) This section contains a paragraph, describing theory, experiments, data, etc.
Three questions related to the paragraph have been given. Each question has only one correct answer among the four given options (a), (b), (c) and (d).
Passage
Nucleophiles which have more than one type of donor atoms within the same donor group are known as ambident nucleophile e.g.
CN^- : Both carbon and nitrogen are donor.
OCN^- : Both oxygen and nitrogen are donor etc.
In case of free anionic and ambident nucleophiles, the better donor atom donate its lone pair of electron and forms bond with a-carbon after substitution reaction, in a given period, donor ability decreases from left to right. In a group, donor ability increases from top to bottom.
Q.
When CH₃CH₂Br is treated with aqueous NaCN, CH₃CH₂CN is formed while CH₃CH₂NCis formed when AgCN is used in the similar reaction. It is due to

A
negative charge on carbon atom in NaCN

B
covalent nature of Ag — C bond in AgCN

C
covalent nature of C — N bond in NaCN

D
ionic nature of Ag — C bond in AgCN

Solution

With NaCN free cyanide (CN^-) is obtained in solution, hence better donor atom carbon donate lone pair. In AgCN, due to covalent character of Ag — C bond CN^- is not free in solution hence, lone pair of ‘N’ is donated
Question 15
4 / -1

Nucleophiles which have more than one type of donor atoms within the same donor group are known as ambident nucleophile e.g.
CN^- : Both carbon and nitrogen are donor.
OCN^- : Both oxygen and nitrogen are donor etc.
In case of free anionic and ambident nucleophiles, the better donor atom donate its lone pair of electron and forms bond with a-carbon after substitution reaction, in a given period, donor ability decreases from left to right. In a group, donor ability increases from top to bottom.
Q.
Treatment of CH₃CH₂Br with either NaNO₂ or AgNO₂ gives the same nitroethane as major product because

A
negative charge on nitrogen atom in both salts

B
nitrogen lone pair is free in both salts, more easily donated than oxygen lone pair

C
NaNO₂ gives free in solution

D
AgNO₂ has Ag covalently bonded to oxygen

Solution

In both salts, lone pair on nitrogen (better donor atom than oxygen) is free for donation to alkyl halide.
Question 16
4 / -1

Nucleophiles which have more than one type of donor atoms within the same donor group are known as ambident nucleophile e.g.
CN^- : Both carbon and nitrogen are donor.
OCN^- : Both oxygen and nitrogen are donor etc.
In case of free anionic and ambident nucleophiles, the better donor atom donate its lone pair of electron and forms bond with a-carbon after substitution reaction, in a given period, donor ability decreases from left to right. In a group, donor ability increases from top to bottom.
Q.
When iodomethane is treated with sodium isocyanate (NaNCO), CH₃NCO is the major product while AgNCO gives CH₃CH₂OCN as major product because

A
negative charge on nitrogen in NaNCO and on oxygen in AgNCO

B
negative charge on oxygen atom in both salts

C
free NCO^- in case of NaNCO and covalent Ag —N bond in AgNCO

D
greater basicity of nitrogen In NaNCO and oxygen in AgNCO

Solution

With free NCO^-, better donor atom (nitrogen) donate its lone pair. If AgNCO is used, due to covalent character of Ag—N bond lone pair of oxygen is donated giving CH₃CH₂— OCN as major product.
Question 17
4 / -1

A Grignard reagent may be made by reacting magnesium with

A
Methyl amine

B
Diethyl ether

C
Ethyl iodide

D
Ethyl alcohol
Question 18
4 / -1

C-Cl bond of chlorobenzene in comparison to C-Cl bond in methyl chloride is

A
Longer and weaker

B
Shorter and weaker

C
Shorter and stronger

D
Longer and stronger
Question 19
4 / -1

Match the Column I with Column II and mark the correct option from the codes given below.

A
a

B
b

C
c

D
d

Solution

(i) Due to ‘S' at β-position, neighbouring group participation occur giving net retention (twice inversion).
(ii) S_N2 at α-carbon gives inversion and product is meso diol,
(iii) Only S_N2 hence inversion
(iv) Show neighbouring group effect