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प्रश्न
Which compound in the following pair will react faster in SN2 reaction with OH−?
CH3Br or CH3I
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उत्तर
In the SN2 mechanism, the reactivity of halides for the same alkyl group increases in the order. This happens because, as the size increases, the halide ion becomes a better leaving group.
R−F << R−Cl < R−Br < R−I
Therefore, CH3I will react faster than CH3Br in SN2 reactions with OH−.
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संबंधित प्रश्न
Out of 
, which is more reactive towards SN1 reaction and why?
Which would undergo SN2 reaction faster in the following pair and why ?
Write the structure of the major organic product in the following reaction:
\[\ce{CH3CH2Br + KCN ->[aq{.} ethanol]}\]
What happens when methyl chloride is treated with KCN?
What is the action of the following on ethyl bromide
alcoholic solution of potassium hydroxide.
Which compound in the following pair reacts faster in SN2 reaction with OH–?
- CH3Br or CH3
- CH3Cl, (CH3)3CCl
Which of the following is optically inactive?
Which of the following reactions is an example of nucleophilic substitution reaction?
The order of reactivities of the following alkyl halides for an SN2 reaction is:
Racemic compound has ____________.
The increasing order of nucleophilicity would be:
The increasing order of reactivity towards SN1 mechanism is:
(I) \[\begin{array}{cc}
\ce{CH3-CH-CH2-CH3}\\
|\phantom{........}\\
\ce{CH3}\phantom{.....}
\end{array}\]
(II) CH3CH2CH2Cl
(III) P–CH3O–C6H4–CH2Cl
Cyanide ion acts as an ambident nucleophile. From which end it acts as a stronger nucleophile in aqueous medium? Give reason for your answer.
Which one is the correct order of nucleophilic strength (pKa) of following nucleophiles?
Among the following compounds I - IV, which one forms a yellow precipitate on reacting sequentially with (i) NaOH (ii) dil. HNO3 (iii) AgNO3?
 |
 |
 |
 |
| I | II | III | IV |
Retention of configuration is observed in ______.
Convert bromoethane to propanamine.
The following questions are case-based questions. Read the passage carefully and answer the questions that follow:
|
Nucleophilic Substitution: Influences of solvent polarity: 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
Discuss SN2 mechanism of methyl bromide using aqueous KOH.
