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कर्नाटक बोर्ड पी.यू.सी.पीयूसी विज्ञान 2nd PUC Class 12

Assertion: KCN reacts with methyl chloride to give methyl isocyanide. Reason: CN– is an ambident nucleophile.

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प्रश्न

Assertion: KCN reacts with methyl chloride to give methyl isocyanide.

Reason: CN– is an ambident nucleophile.

विकल्प

  • Assertion and reason both are correct and reason is correct explanation of assertion.

  • Assertion and reason both are wrong statements.

  • Assertion is correct but reason is wrong statement.

  • Assertion is wrong but reason is correct statement.

  • Assertion and reason both are correct statements but reason is not correct explanation of assertion.

MCQ
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उत्तर

Assertion is wrong but reason is correct statement.

Explanation:

\[\ce{\underset{Alkyl cyanide}{R - Cl + KCN –> R - CN + KCl}}\]

Isocyanide is not obtained in this reaction. CN– is an ambident nucleophile.

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अध्याय 10: Haloalkanes and Haloarenes - Exercises [पृष्ठ १४८]

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एनसीईआरटी एक्झांप्लर Chemistry Exemplar [English] Class 12
अध्याय 10 Haloalkanes and Haloarenes
Exercises | Q V. 87. | पृष्ठ १४८

संबंधित प्रश्न

Write the structure of an isomer of compound C4H9Br which is most reactive towards SN1 reaction


How do you convert the following:

Ethanol to propanenitrile


In the following pair of halogen compounds, which compound undergoes a faster SN1 reaction?


Write the structure of the major organic product in the following reaction:

\[\ce{CH3CH(Br)CH2CH3 + NaOH ->[water]}\]


Write the structure of the major organic product in the following reaction:

\[\ce{CH3CH2CH2OH + SOCl2 ->}\]


Arrange the compounds of the following set in order of reactivity towards SN2 displacement:

2-Bromo-2-methylbutane, 1-Bromopentane, 2-Bromopentane


Which would undergo SN2 reaction faster in the following pair and why ?

CH3 – CH2 ​– Br and CH3 ​– CH2 ​– I


What is the action of the following on ethyl bromide:
moist silver oxide


The order of reactivity of the given haloalkanes towards nucleophile is:


Optically active isomers but not mirror images are called ____________.


Which of the following is the correct order of decreasing SN2 reactivity?


The process of separation of a racemic modification into d and l-enantiomers is called ____________.


Among the following, the dissociation constant is highest for:


The correct order of increasing the reactivity of C–X bond towards nucleophile in following compounds.


    (I)


     (II)

(CH3)3CCl
    (III)

(CH3)2CHCl
    (IV)


Give reason for the following:

The product formed during SN1 reaction is a racemic mixture.


In which reaction mechanism carbocation is formed?


Retention of configuration is observed in ______.


The following questions are case-based questions. Read the passage carefully and answer the questions that follow:

Nucleophilic Substitution:
Nucleophilic substitution reaction of haloalkane can be conducted according to both SN1 and SN2 mechanisms. SN1 is a two-step reaction, while SN2 is a single-step reaction. For any haloalkane, which mechanism is followed depends on factors such as the structure of haloalkane, properties of leaving group, nucleophilic reagent and solvent.

Influences of solvent polarity:
In SN1 reaction, the polarity of the system increases from the reactant to the transition state, because a polar solvent has a greater effect on the transition state than the reactant, thereby reducing activation energy and accelerating the reaction. In SN2 reaction, the polarity of the system generally does not change from the reactant to the transition state, and only charge dispersion occurs. At this time, the polar solvent has a great stabilizing effect on Nu than the transition state, thereby increasing activation energy and slow down the reaction rate. For example, the decomposition rate (SN1) of tertiary chlorobutane at 25°C in water (dielectric constant 79) is 300000 times faster than in ethanol (dielectric constant 24).

The reaction rate (SN2) of 2-bromopropane and NaOH in ethanol containing 40% water is twice slower than in absolute ethanol. Hence the level of solvent polarity has an influence on both SN1 and SN2 reactions but with different results. Generally speaking, a weak polar solvent is favourable for SN2 reaction, while a strong polar solvent is favourable for SN1. Generally speaking, the substitution reaction of tertiary haloalkane is based on SN1 mechanism in solvents with a strong polarity (for example ethanol containing water).

Answer the following questions:

(a) Why racemisation occurs in SN1? (1)

(b) Why is ethanol less polar than water? (1)

(c) Which one of, the following in each pair is more reactive towards SN2 reaction? (2)

(i) CH3 – CH2 – I or CH3CH2 – Cl

(ii)

OR

(c) Arrange the following in the increasing order of their reactivity towards SN1 reactions: (2)

(i) 2-Bromo-2-methylbutane, 1-Bromo-pentane, 2-Bromo-pentane

(ii) 1-Bromo-3-methylbutane, 2-Bromo-2-methylbutane, 2-Bromo-3- methylbutane


 Acetic anhydride from acetic acid


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