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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
from the following pair would undergo SN2 faster from the other?
a. CH3CH2CH2I b. CH3CH2CH2Cl
Complete the following reaction giving major products.
Name the reagent used to bring about the following conversion.
Chlorobenzene to biphenyl
Convert the following:
Ethanol to propane nitrile
Convert the following:
2-Chloropropane to propan-1-ol
Propane nitrile can be prepared by heating ____________
Major product of the following reaction is _______________
\[\ce{CH3-CH2-Mg-Br + NH3 ->?}\]
Write the correct order of increasing ease of dehydrohalogenation.
\[\ce{\underset{\text{(I)}}{CH3 - CH2 - CH2 - Cl}}\]
\[\ce{\underset{\text{(II)}}{CH3 - CH(Cl) - CH3}}\]
\[\begin{array}{cc}
\ce{CH3}\\
|\\
\ce{CH3-C-Cl}\phantom{...}\\
|\\
\ce{CH3}\\
\ce{(III)}
\end{array}\]
Explain primary benzylic halide shows higher reactivity by SN1 mechanism than other primary alkyl halide.
What is dehydrohalogenation? State the rule for the formation of the preferred product of dehydrohalogenation.
Which of the following is a primary halide?
Ethyl bromide undergoes the following reaction:
\[\ce{\underset{Ethyl bromide}{C2H5Br} + \underset{(aq.)}{KOH} ->[\Delta] \underset{Ethyl alcohol}{C2H5OH} + KBr}\]
Which of the following is a WRONG statement?
Which of the following is least reactive towards nucleophilic addition?
Which one is most reactive towards nucleophilic addition reaction?
Which of the following carbocation is the most stable?
Which of the following is FALSE regarding SN2 reaction mechanism?
Identify 'B' in the following reaction.
\[\ce{2-Bromobutane ->[KOH alc.][\Delta] A ->[HI] B}\]
Write the product formed when alkyl halide reacts with silver nitrite.
Convert the following.
p-Nitrochlorobenzene to p-nitrophenol
The order of reactivities of the following alkyl halides for an SN2 reaction is ______.
Which among the following statements is not correct about SN2 reaction mechanism?
Observe the following and answer the question given below:
Comment on the bond length of C-X bond in it.
Identify the chiral molecule from the following.
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 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 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 of the following reagent is used for conversion of alkyl halide into nitrile?
