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प्रश्न
Elimination reactions (especially β-elimination) are as common as the nucleophilic substitution reaction in case of alkyl halides. Specify the reagents used in both cases.
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उत्तर
Alkyl halides undergo nucleophilic substitution as well as elimination (Beta-elimination) reaction. However, by proper choice of reagents and reaction conditions, a particular product can be obtained. Usually strong and bulky bases and high temperature favour elimination reactions while weaker and smaller bases and lower temperature favour substitution reactions. For example, ethyl bromide on heating with alcoholic KOH (which contain stronger base, \[\ce{C2H5O}\] ion) at about 473-523 K undergoes elimination to give ethene. But with aqueous \[\ce{KOH}\] at about 373 K, it gives ethanol.
\[\ce{CH3CH2Br ->[alc.KOH][473-523 K] CH2 = CH2 (Elimination)}\]
\[\ce{CH3CH2Br ->[aq.KOH][373 K] CH3CH2OH (Substitution)}\]
Nucleophilic substitution: Reagents used nucleophilies like \[\ce{- \overset{-}{O}H, NH3, \overset{-}{C} ≡ N;, AgCN:, O = N - O, \overset{-}{O}R}\]' etc. also, alc. \[\ce{KOH}\] at lower temperature (373 K) undergoes substitution reaction.
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संबंधित प्रश्न
How do you convert the following:
Ethanol to propanenitrile
Write the isomers of the compound having the formula C4H9Br.
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?
silver acetate
Which of the following is optically inactive?
Which one is most reactive towards SN1 reaction?
The order of reactivities of the following alkyl halides for an SN2 reaction is:
Racemic compound has ____________.
Which of the following undergoes nucleophilic substitution exclusively by SN1 mechanism?
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
Ethylene chloride and ethylidene chloride are isomers. Identify the correct statements.
(i) Both the compounds form same product on treatment with alcoholic KOH.
(ii) Both the compounds form same product on treatment with aq.NaOH.
(iii) Both the compounds form same product on reduction.
(iv) Both the compounds are optically active.
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) |
The major product formed in the following reaction is:
Convert bromoethane to propanamine.
Explain why Grignard reagents should be prepared under anhydrous conditions.
Which alkyl halide from the following pair would you expect to react more rapidly by an SN2 mechanism? Explain your answer.
\[\begin{array}{cc}\ce{CH3CH2CHCH3}\\
\phantom{.....}|\\
\phantom{......}\ce{Br}\\
\end{array}\] or \[\begin{array}{cc}\phantom{.......}\ce{CH3}\\
\phantom{...}|\\
\ce{H3C - C - Br}\\
\phantom{...}|\\
\phantom{.......}\ce{CH3}\\
\end{array}\]
Which one of the following chlorohydrocarbons readily undergoes solvolysis?
The correct order of increasing reactivity of
C-X bond towards nucleophile in the following compounds is:
The compound that will undergo SN1 reaction with the fastest rate is:
