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question_answer1)
Directions: (Q. 1 to 5) |
Case I: Read the passage given below and answer the following questions. |
Anucleophilic substitution reaction that occurs by an \[{{S}_{N}}1\] mechanism proceeds in two steps. In the first step, the bond between the carbon atom and the leaving group breaks to produce a carbocation and most commonly, an anionic leaving group. |
In the second step, the carbocation reacts with the nucleophile to form the subsitution product. The formation of a carbocation is the slow or rate determining step. |
The rate of \[{{S}_{N}}1\] reactions decrease in the order \[3{}^\circ >2{}^\circ >1{}^\circ \], which is the reverse order observed in \[{{S}_{N}}2\] reactions. In contrast to \[{{S}_{N}}2\] reactions at sterogenic centers, which occur with inversion of configuration, an \[{{S}_{N}}1\]reaction gives a racemic mixture of enatiomers that has no optical rotation. |
In the following questions (Q. No. 1-25), a statement of assertion followed by a statement of reason is given. Choose the correct answer out of the following choices on the basis of the above passage. |
Assertion: Rate of ethanolysis of \[1{}^\circ \] halide by \[{{S}_{N}}2\] mechanism is fast. |
Reason: Carbocation is stablised by resonance. |
A)
Assertion and reason both are correct statements and reason is correct explanation for assertion. done
clear
B)
Assertion and reason both are correct statements but reason is not correct explanation for assertion. done
clear
C)
Assertion is correct statement but reason is wrong statement. done
clear
D)
Assertion is wrong statement but reason is correct statement. done
clear
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question_answer2)
Assertion: \[{{S}_{N}}2\] reactions do not proceed with retention of configuration. |
Reason: \[{{S}_{N}}2\] reactions proceed in single step. |
A)
Assertion and reason both are correct statements and reason is correct explanation for assertion. done
clear
B)
Assertion and reason both are correct statements but reason is not correct explanation for assertion. done
clear
C)
Assertion is correct statement but reason is wrong statement. done
clear
D)
Assertion is wrong statement but reason is correct statement. done
clear
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question_answer3)
Assertion: In an optically active alkyl halide nucleophilic substitution reaction gives a mixture of enantiomers. |
Reason: Reaction occurs by \[{{S}_{N}}1\] mechanism. |
A)
Assertion and reason both are correct statements and reason is correct explanation for assertion. done
clear
B)
Assertion and reason both are correct statements but reason is not correct explanation for assertion. done
clear
C)
Assertion is correct statement but reason is wrong statement. done
clear
D)
Assertion is wrong statement but reason is correct statement. done
clear
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question_answer4)
Assertion: \[1{}^\circ \]allylic halides show higher reactivity in \[{{S}_{N}}1\] reactions than other \[1{}^\circ \] alkyl halides. |
Reason: Intermediate carbocation is stabalised by resonance. |
A)
Assertion and reason both are correct statements and reason is correct explanation for assertion. done
clear
B)
Assertion and reason both are correct statements but reason is not correct explanation for assertion. done
clear
C)
Assertion is correct statement but reason is wrong statement. done
clear
D)
Assertion is wrong statement but reason is correct statement. done
clear
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question_answer5)
Assertion: \[{{S}_{N}}1\] reaction is carried out in the presence of polar protic solvent. |
Reason: A polar protic solvent decreases the stability of carbocation due to solvation. |
A)
Assertion and reason both are correct statements and reason is correct explanation for assertion. done
clear
B)
Assertion and reason both are correct statements but reason is not correct explanation for assertion. done
clear
C)
Assertion is correct statement but reason is wrong statement. done
clear
D)
Assertion is wrong statement but reason is correct statement. done
clear
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question_answer6)
Directions: (Q. 6 to 10) |
Case II: Read the passage given below and answer the following questions. |
When haloalkanes with (\[\beta \]-hydrogen atom are boiled with alcoholic solution of KOH; they undergo elimination of hydrogen halide resulting in the formation of alkenes. These reactions are called (\[\beta \]-elimination reactions or dehydrohalogenation reactions. These reactions follow Saytzeff's rule. Substitution and therefore can engage in substitution or elimination reactions depending upon the alkyl halide and the reaction conditions. |
Among the following halides the most reactive towards alcoholic KOH is
A)
\[C{{H}_{2}}=CHBr\] done
clear
B)
\[C{{H}_{3}}COC{{H}_{2}}C{{H}_{2}}Br\] done
clear
C)
\[C{{H}_{3}}C{{H}_{2}}Br\] done
clear
D)
\[C{{H}_{3}}C{{H}_{2}}C{{H}_{2}}Br\] done
clear
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question_answer7)
The general reaction, \[R-X\xrightarrow{aq.OH-}ROH+{{X}^{-}}\] is expected to follow decreasing order of reactivity as in
A)
\[t-BuI>t-BuBr>t-BuCl>t-BuF\] done
clear
B)
\[t-BuF>t-BuCl>t-BuBr>t-BuI\] done
clear
C)
\[t-BuBr>t-BuCl>t-BuI>t-BuF\] done
clear
D)
\[t-BuF>t-BuCl>t-BuI>t-BuBr\] (t-Bu = tertiary Butyl group) done
clear
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question_answer8)
Reaction of t-butyl bromide with sodium methoxide produces
A)
sodium t-butoxide done
clear
B)
t -butyl methyl ether done
clear
C)
iso-butane done
clear
D)
iso-butylene. done
clear
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question_answer9)
In the elimination reactions, the reactivity of alkyl halides follows the sequence
A)
R-F>R-Cl>R-Br>R-I done
clear
B)
R-I>R-Br>R-Cl>R-F done
clear
C)
R-I>R-F>R-Br>R-Cl done
clear
D)
R-F>R-I>R-Br>R-Cl done
clear
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question_answer10)
The ease of dehydrohalogenation of alkyl halide with alcoholic KOH is
A)
\[3{}^\circ <2{}^\circ <\text{ }1{}^\circ \] done
clear
B)
\[3{}^\circ >2{}^\circ >\text{ }1{}^\circ \] done
clear
C)
\[3{}^\circ <2{}^\circ >\text{ }1{}^\circ \] done
clear
D)
\[3{}^\circ >2{}^\circ \text{ }<\text{ }1{}^\circ \] done
clear
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question_answer11)
Directions: (Q. 11 to 15) |
Case III: Read the passage given below and answer the following questions. |
A chlorocompound [A] on reduction with Zn-Cu and ethanol gives the hydrocarbon [B] with five carbon atoms. When [A] is dissolved in dry ether and treated with sodium metal it gave 2, 2, 5, 5-tetramethylhexane. The treatment of [A] with alcoholic KCN gives compound [C]. |
The compound [A] is
A)
1-chloro-2, 2-dimethylpropane done
clear
B)
1-chloro-2, 2-dimethylbutane done
clear
C)
1-chloro-2-methylbutane done
clear
D)
2-chloro-2-methylbutane. done
clear
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question_answer12)
The reaction of [C] with Na, \[{{C}_{2}}{{H}_{5}}OH\] is called
A)
\[{{\left( C{{H}_{3}} \right)}_{3}}CC{{H}_{2}}CON{{H}_{2}}\] done
clear
B)
\[{{\left( C{{H}_{3}} \right)}_{3}}CN{{H}_{2}}\] done
clear
C)
\[{{\left( C{{H}_{3}} \right)}_{3}}CC{{H}_{2}}C{{H}_{2}}N{{H}_{2}}\] done
clear
D)
\[{{\left( C{{H}_{3}} \right)}_{2}}CHC{{H}_{2}}N{{H}_{2}}\] done
clear
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question_answer13)
The reaction of [C] with Na, \[{{C}_{2}}{{H}_{5}}OH\]is called
A)
Gilman reaction done
clear
B)
Mendius reaction done
clear
C)
Grooves process done
clear
D)
Swart's reaction. done
clear
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question_answer14)
The reaction of [A] with aq. KOH will preferably favour
A)
\[{{S}_{N}}1\] mechanism done
clear
B)
\[{{S}_{N}}2\] mechanism done
clear
C)
E1 mechanism done
clear
D)
E2 mechanism. done
clear
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question_answer15)
Compound [B] is
A)
n-pentane done
clear
B)
2, 2-dimethylpropane done
clear
C)
2-methylbutane done
clear
D)
none of these. done
clear
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question_answer16)
Directions : (Q. 16 to 20) |
Case IV: Read the passage given below and answer the following questions. |
In haloalkanes, when a nucleophile stronger than the halide ion approaches the positively charged carbon atom of an alkyl halide, the halogen atom along with its bonding electron pair gets displaced and a new bond with the carbon and the nucleophile is formed. These reactions are called nucleophilic substitution reactions. |
|
In these reactions the atom or group of atoms which loses its bond from carbon and takes on an additional pair of electrons is called leaving group. Halide ions are good leaving groups. Some important nucleophilic substitution reactions of haloalkanes with common nucleophiles are given in the table below. |
|
| Reagent | Nucleophile | Substitution product R-Nu | Class of main product | 1. | NaOH or KOH or moist \[A{{g}_{2}}O\] | \[^{-}OH\] | ROH | Alcohol | 2. | \[{{H}_{2}}O\] | \[{{H}_{2}}O\] | ROH | Alcohol | 3. | NaI | \[{{I}^{-}}\] | R-I | Alkyl iodide | 4. | \[R'N{{H}_{2}}\] | \[R'\ddot{N}{{H}_{2}}\] | RNHR' | Sec. amine | 5. | KCN | \[\overline{C}\equiv N:\] | RCN | Nitrile (cyanide) | 6. | \[KN{{O}_{2}}\] | \[O=N-{{O}^{-}}\] | R-O-N=O | Alkyl nitrite | |
In the following questions (Q. No. 16-20), a statement of assertion followed by a statement of reason is given. Choose the correct answer out of the following choices on the basis of the above passage. |
Assertion: Alkyl halides are hydrolysed to alcohols by moist silver oxide. |
Reason: RCl is hydrolysed to ROH easily but reactions slow down on addition of KI. |
A)
Assertion and reason both are correct statements and reason is correct explanation for assertion. done
clear
B)
Assertion and reason both are correct statements but reason is not correct explanation for assertion. done
clear
C)
Assertion is correct statement but reason is wrong statement. done
clear
D)
Assertion is wrong statement but reason is correct statement. done
clear
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question_answer17)
Assertion: Alkyl halides form alkenes when heated above \[300{}^\circ C\]. |
Reason: \[C{{H}_{3}}C{{H}_{2}}CI\] reacts slowly with strong base as compared to \[C{{H}_{3}}C{{H}_{2}}I\]. |
A)
Assertion and reason both are correct statements and reason is correct explanation for assertion. done
clear
B)
Assertion and reason both are correct statements but reason is not correct explanation for assertion. done
clear
C)
Assertion is correct statement but reason is wrong statement. done
clear
D)
Assertion is wrong statement but reason is correct statement. done
clear
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question_answer18)
Assertion: RBr reacts with \[AgN{{O}_{2}}\] to give nitroalkane. |
Reason: Silver nitrite (\[AgN{{O}_{2}}\]) is an ionic compound, therefore the negative charge on nitrogen is the attacking site. |
A)
Assertion and reason both are correct statements and reason is correct explanation for assertion. done
clear
B)
Assertion and reason both are correct statements but reason is not correct explanation for assertion. done
clear
C)
Assertion is correct statement but reason is wrong statement. done
clear
D)
Assertion is wrong statement but reason is correct statement. done
clear
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question_answer19)
Assertion: The nucleophilic substitution of vinyl chloride is difficult than ethyl chloride. |
Reason: Vinyl group is electron donating group. |
A)
Assertion and reason both are correct statements and reason is correct explanation for assertion. done
clear
B)
Assertion and reason both are correct statements but reason is not correct explanation for assertion. done
clear
C)
Assertion is correct statement but reason is wrong statement. done
clear
D)
Assertion is wrong statement but reason is correct statement. done
clear
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question_answer20)
Assertion: 2-Bromobutane on reaction with sodium ethoxide in ethanol gives 1-butene as the major product. |
Reason: 1-Butene is less stable than 2-butene. |
A)
Assertion and reason both are correct statements and reason is correct explanation for assertion. done
clear
B)
Assertion and reason both are correct statements but reason is not correct explanation for assertion. done
clear
C)
Assertion is correct statement but reason is wrong statement. done
clear
D)
Assertion is wrong statement but reason is correct statement. done
clear
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question_answer21)
Directions: (Q. 21 to 25) |
Case V: Read the passage given below and answer the following questions. |
Haloarenes are less reactive than haloalkanes. |
The low reactivity ofhaloarenes can be attributed to |
- resonance effect |
- \[s{{p}^{2}}\] hybridisation of C-X bond |
- polarity of C-X bond |
- instability of phenyl cation (formed by self- ionisation of haloarene) |
- repulsion between the electron rich attacking nucleophiles and electron rich arenes. |
Reactivity of haloarenes can be increased or decreased by the presence of certain groups at certain positions for example, nitro \[\left( -N{{O}_{2}} \right)\]group at o/p positions increases the reactivity of haloarenes towards nucleophilc substitution reactions. |
Aryl halides are less reactive towards nucleophilic substitution reaction as compared to alkyl halides due to
A)
the formation of less stable carbonium ion done
clear
B)
resonance stabilization done
clear
C)
larger carbon-halogen bond done
clear
D)
inductive effect. done
clear
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question_answer22)
Which of the following aryl halides is the most reactive towards nucleophilic substitution?
A)
B)
C)
D)
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question_answer23)
Which one of the following will react fastest with aqueous NaOH?
A)
B)
C)
D)
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question_answer24)
Chlorobenzene can be converted into phenol by heating in aqueous sodium hydroxide solution at a temperature of 623 K and a pressure of 300 atm. However the rate of reaction can be increased by presence of certain groups in benzene ring. What will be the order of reactivity of following compounds towards the above substitution reaction? |
|
(i) |
(ii) |
(iii) |
A)
(iii) > (ii) > (i) done
clear
B)
(ii) > (iii) > (i) done
clear
C)
(i) > (ii) > (iii) done
clear
D)
(i) > (iii) > (ii) done
clear
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question_answer25)
The reactivity of the compounds (i) MeBr, (ii) \[PhC{{H}_{2}}Br\], (iii) MeCl, (iv) \[p-MeO{{C}_{6}}{{H}_{4}}Br\] decreases as
A)
(i) > (ii) >(iii) > (iv) done
clear
B)
(iv) > (ii) >(i) > (iii) done
clear
C)
(iv) > (iii) >(i) > (ii) done
clear
D)
(ii) > (i) >(iii) > (iv) done
clear
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