Advertisements
Advertisements
Question
Explain. Aryl halides are less reactive than alkyl halides towards nucleophilic substitution reactions.
Advertisements
Solution
- 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.
RELATED QUESTIONS
Complete the following reaction giving major products.
\[\ce{CH3 - CH = CH2 ->[HBr][peroxide] A ->[alc. KOH] B}\]
Name the reagent used to bring about the following conversion.
Bromoethane to ethoxyethane
Name the reagent used to bring about the following conversion.
Ethyl bromide to ethyl isocyanide
Arrange the following in the increasing order of boiling points.
- 1-Bromopropane
- 2- Bromopropane
- 1- Bromobutane
- 1-Bromo-2-methylpropane
Convert the following:
Benzyl alcohol to benzyl cyanide
Convert the following:
2-Chloropropane to propan-1-ol
HCl is added to a hydrocarbon ‘A’ \[\ce{(C4H8)}\] to give a compound ‘B’ which on hydrolysis with aqueous alkali forms tertiary alcohol ‘C’ \[\ce{(C4H10O)}\]. Identify ‘A’ ,‘B’ and ‘C’.
Complete the following reaction sequence by writing the structural formulae of the organic compound 'A', 'B' and 'C'.
\[\ce{2-Bromobutane->[Alc.KOH]A->[][Br2]B->[][NaNH2]C}\]
The following will react faster by SN1 mechanism
What is dehydrohalogenation? State the rule for the formation of the preferred product of dehydrohalogenation.
In alkaline hydrolysis of tertiary butyl bromide, ____________.
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?
Nitroalkanes are obtained in laboratory from primary or secondary alkyl halides by the action of ______.
What type of hybridisation is present in carbocation formed during the alkaline hydrolysis of 1- bromo-1- phenyl ethane?
Which of the following is FALSE regarding SN2 reaction mechanism?
Which of the following statements is incorrect regarding the dehydrohalogenation of alkenes?
Which among the following statements is not correct about SN2 reaction mechanism?
Observe the following and answer the questions given below:
Name the type of halogen derivative.
Observe the following and answer the question given below:
Comment on the bond length of C-X bond in it.
Complete the following reaction sequences by writing the structural formulae of the organic compounds 'A', 'B' and 'C'.
\[\ce{2-Bromobutan ->[alc. KOH] A ->[][Br2] B ->[][NANH2] C}\]
What is the action of following on ethyl bromide?
alcoholic sodium hydroxide
Complete the following reaction giving major product.
\[\begin{array}{cc}
\ce{CH3}\phantom{................}\\
|\phantom{..................}\\
\ce{CH3 - C - CH2 - Cl ->[Na/dry ether]A}\\
|\phantom{..................}\\
\ce{CH3}\phantom{................}
\end{array}\]
Give a reason for the following:
Ethoxy ethane with conc. HI at 373 K gives C2H5OH and CH3I but not CH3OH and C2H5I.
Complete the following reaction giving major product.
\[\begin{array}{cc}
\ce{CH3}\phantom{.................}\\
|\phantom{...................}\\
\ce{CH3 - C - CH2 - Cl ->[Na/dry ether] A}\\
|\phantom{...................}\\
\ce{CH3}\phantom{.................}\\
\end{array}\]
Identify the substrate 'X' in the following reaction.
\[\ce{\underset{}{X + O2} ->[i) Co-naphtenate 423 K][ii) dil HClΔ] \underset{\underset{}{}}{Phenol + Acetone}}\]
