Advertisements
Advertisements
Questions
Why are aryl halides less reactive towards nucleophilic substitution reactions than alkyl halides?
Why are aryl halides less reactive than alkyl halides towards nucleophilic substitution reactions?
Why are haloarenes less reactive towards nucleophilic substitution reactions as compared to haloalkanes?
Advertisements
Solution
Aryl halides are less reactive towards nucleophilic substitution reaction due to the following reasons.
- In haloarenes, the lone pair of electron on halogen are in resonance with benzene ring. So, C – Cl bond acquires partial double bond character which strengthen C – Cl bond and difficult to be substituted by nucleophile.
Therefore, they are less reactive towards nucleophilic substitution reaction.
- In haloarenes, the carbon atom attached to halogen is sp2 hybridised. The sp2 hybridised carbon is more electronegative than sp3 hybridised carbon. This sp2-hybridised carbon in haloarenes can hold the electron pair of \[\ce{C - X}\] bond more tightly and make this \[\ce{C - Cl}\] bond shorter than \[\ce{C Cl}\] bond of haloalkanes.
Since, it is difficult to break a shorter bond than a longer bond, therefore, halorenes are less reactive than haloalkanes. - In haloarenesm the phenyl cation is not stabilised by resonance therefore SN1 mechanism cannot be followed.
- Because of the repulsion between the nucleophile and electron-rich arenas, aryl halides are less reactive than alkyl halides.
RELATED QUESTIONS
Give reasons for the following:
(CH3)3C–O–CH3 on reaction with HI gives (CH3)3C–I and CH3–OH as the main products and not (CH3)3C–OH and CH3–I.
The treatment of alkyl chlorides with aqueous KOH leads to the formation of alcohols but in the presence of alcoholic KOH, alkenes are major products. Explain.
The stability order for carbocation is _______.
(A) 2° > 3° > 1°
(B) 3° > 2° > 1°
(C) 3° > 1° > 2°
(D) 1° > 3° > 2°
Which of the following is optically inactive?
Which of the following is an example of SN2 reaction?
SN2 mechanism proceeds through intervention of ____________.
Which among MeX, RCH2X, R2CHX and R3CX is most reactive towards SN2 reaction?
Isopropyl chloride undergoes hydrolysis by:
Which of the following compounds is optically active?
Racemic compound has ____________.
An organic molecule necessarily shows optical activity if it ____________.
Which of the following compound will undergo racemisation when reacts with aq. KOH?
(i)
(ii)
CH3CH2CH2Cl
(iii)
\[\begin{array}{cc}
\ce{CH3}\phantom{..}\\
|\phantom{....}\\
\ce{CH3-CH-CH2Cl}
\end{array}\]
(iv)
\[\begin{array}{cc}
\phantom{..}\ce{H}\\
\phantom{..}|\\
\ce{CH3-C-Cl}\\
\phantom{..}|\\
\phantom{.....}\ce{C2H5}
\end{array}\]
Which of the following alkyl halides will undergo SN1 reaction most readily?
Which reagent will you use for the following reaction?
\[\ce{CH3CH2CH2CH3 -> CH3CH2CH2CH2Cl + CH3CH2CHClCH3}\]
Which of the following statements are correct about the kinetics of this reaction?
(i) The rate of reaction depends on the concentration of only (b).
(ii) The rate of reaction depends on concentration of both (a) and (b).
(iii) Molecularity of reaction is one.
(iv) Molecularity of reaction is two.
The decreasing order of reactivity of the following compounds towards nucleophilic substitution (SN2) is ______.
Racemisation occurs in ______.
HCI, Major product ______.
