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प्रश्न
Explain. Aryl halides are less reactive than alkyl halides towards nucleophilic substitution reactions.
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उत्तर
- The low reactivity of aryl halides is due to the resonance effect and sp2 hybrid state of carbon to which halogen atom is attached.
- In aryl halides, one of the lone pairs of electrons on the halogen atom is in conjugation with π-electrons of the ring. Due to resonance, the C–X bond acquires partial double bond character. Thus, the C–X bond in aryl halides is stronger and shorter than alkyl halides. Hence, it is difficult to break C–X bond in aryl halides.
- Further, the phenyl cation produced due to the self-ionization of aryl halide will not be stabilised by resonance. This rules out the possibility of SN1 mechanism. Also, the backside attack of nucleophiles is blocked by the aromatic ring. This rules out the possibility of SN2 mechanism. As a result, nucleophilic substitution reaction involving cleavage of C–X bond in haloarenes proceeds with difficulty.
- Therefore, aryl halides are less reactive than alkyl halides towards nucleophilic substitution reactions.
संबंधित प्रश्न
Complete the following reaction giving major product.
\[\begin{array}{cc}\ce{CH3\phantom{................}}\\
|\phantom{...................}\\
\ce{CH3 - C - CH2 - Cl ->[Na/dry ether] A}\\
|\phantom{...................}\\
\ce{CH3\phantom{................}}
\end{array}\]
Convert the following:
Benzyl alcohol to benzyl cyanide
Convert the following:
Ethanol to propane nitrile
Complete the following reaction sequence by writing the structural formulae of the organic compound 'A', 'B' and 'C'.
\[\ce{2-Bromobutane->[Alc.KOH]A->[][Br2]B->[][NaNH2]C}\]
Observe the following and answer the question given below.
Comment on the bond length of C–X bond in it.
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Major product of the following reaction is _______________
\[\ce{CH3-CH2-Mg-Br + NH3 ->?}\]
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\[\ce{\underset{Ethyl bromide}{C2H5Br} + \underset{(aq.)}{KOH} ->[\Delta] \underset{Ethyl alcohol}{C2H5OH} + KBr}\]
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Which one is most reactive towards nucleophilic addition reaction?
Identify major product 'B' in the following reaction.
\[\ce{But-1-ene ->[HBr][Peroxide] A ->[AgCN][\Delta] B}\]
Convert the following.
p-Nitrochlorobenzene to p-nitrophenol
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The order of reactivity of the given haloalkanes towards nucleophiles is:
Which among the following statements is not correct about SN2 reaction mechanism?
With which halogen the reactions, of alkanes are explosive?
Observe the following and answer the question given below:
Comment on the bond length of C-X bond in it.
Observe the following and answer the question given below:
Can react by SN1 mechanism? Justify your answer.
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Complete the following reaction sequences by writing the structural formulae of the organic compounds 'A', 'B' and 'C'.
\[\ce{2-Bromobutan ->[alc. KOH] A ->[][Br2] B ->[][NANH2] C}\]
Complete the following reaction giving major product.
\[\begin{array}{cc}
\ce{CH3}\phantom{...............}\\
|\phantom{..................}\\
\ce{CH3 - C - CH2 - Cl->[Na/dry ether]A}\\
|\phantom{..................}\\
\ce{CH3}\phantom{...............}\\
\end{array}\]
Complete the reaction:
\[\ce{CH3CH2Cl ->[AgCN][alc.\Delta]}\] ?
Complete the following reaction giving major product.
\[\begin{array}{cc}
\ce{CH3}\phantom{...............}\\
|\phantom{..................}\\
\ce{CH3 - C - CH2 - Cl ->[Na/dry ether]A}\\
|\phantom{...................}\\
\ce{CH3}\phantom{.................}
\end{array}\]
Which among the following is NOT benzylic halide?
Which of the following reagent is used for conversion of alkyl halide into nitrile?
