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Which of the following alkyl halides will undergo SN1 reaction most readily? - Chemistry

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प्रश्न

Which of the following alkyl halides will undergo SN1 reaction most readily?

पर्याय

  • \[\ce{(CH3)3C-F}\]

  • \[\ce{(CH3)3C-Cl}\]

  • \[\ce{(CH3)3C-Br}\]

  • \[\ce{(CH3)3C-I}\]

MCQ

उत्तर

\[\ce{(CH3)3C-I}\]

Explanation:

\[\ce{(CH3)3C-I}\] will undergo SN1 reaction most readily as C-I bond is weakest, due to the large difference in the size of carbon and iodine.

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पाठ 10: Haloalkanes and Haloarenes - Exercises [पृष्ठ १३७]

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एनसीईआरटी एक्झांप्लर Chemistry [English] Class 12
पाठ 10 Haloalkanes and Haloarenes
Exercises | Q I. 17. | पृष्ठ १३७

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संबंधित प्रश्‍न

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    (I)


     (II)

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(iv) Molecularity of reaction is two.


Which one is the correct order of nucleophilic strength (pKa) of following nucleophiles?


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Arrange the following compounds in increasing order of reactivity towards SN2 reaction.

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


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


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