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प्रश्न
How do polar solvents help in the first step in SN1 mechanism?
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उत्तर
The SN1 mechanism proceeds through the formation of carbocation. It involves breaking of C-halogen bond for which energy is obtained through the salvation of halide ion with the proton of the protic solvent. Thus, polar solvents help in ionisations step by stabilizing the ions by solvation.
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संबंधित प्रश्न
Write the structure of an isomer of compound C4H9Br which is most reactive towards SN1 reaction
Write the structures of A, B and C in the following:
In the following pair of halogen compounds, which compound undergoes a faster SN1 reaction?
Write the mechanism of the following reaction:
\[\ce{{n}BuBr + KCN ->[EtOH-H2O] {n}BuCN}\]
Arrange the compounds of the following set in order of reactivity towards SN2 displacement:
2-Bromo-2-methylbutane, 1-Bromopentane, 2-Bromopentane
The stability order for carbocation is _______.
(A) 2° > 3° > 1°
(B) 3° > 2° > 1°
(C) 3° > 1° > 2°
(D) 1° > 3° > 2°
What is the action of the following on ethyl bromide
alcoholic solution of potassium hydroxide.
What is the action of the following on ethyl bromide?
silver acetate
In the reaction, \[\ce{R - X + NaOR' -> ROR’ + X}\] ( – ve ion). The main product formed is:
Halogenation of alkanes is ____________.
The order of reactivity of the given haloalkanes towards nucleophile is:
In the SN1 reaction, racemization takes place. It is due to:
Which of the following is an optically active compound?
Match the reactions given in Column I with the types of reactions given in Column II.
| Column I | Column II | |
| (i) |  |
(a) Nucleophilic aromatic substitution |
| (ii) | \[\begin{array}{cc} \ce{CH3 - CH = CH2 + HBr -> CH3 - CH - CH3}\\ \phantom{............................}|\phantom{}\\ \phantom{.............................}\ce{Br}\phantom{} \end{array}\] |
(b) Electrophilic aromatic substitution |
| (iii) |  |
(c) Saytzeff elimination |
| (iv) |  |
(d) Electrophilic addition |
| (v) | \[\begin{array}{cc} \ce{CH3 CH2 CH CH3 ->[alc.KOH] CH3 CH = CH CH3}\\ \phantom{}|\phantom{..........................}\\ \phantom{}\ce{Br}\phantom{........................} \end{array}\] |
(e) Nucleophilic substitution (SN1) |
Which of the following is the definition of chirality?
CCl4 is insoluble in water because:-
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: 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
Identify the product in the following reaction: 
Discuss SN2 mechanism of methyl bromide using aqueous KOH.
