Why are aryl halides less reactive for nucleophilic substitution reactions?

CBSE 12-science - Chemistry

find the major product

Asked by mayamishra9540500880 | 04 Jul, 2022, 07:11: PM

ANSWERED BY EXPERT

CBSE 12-science - Chemistry

aadr

Asked by ap650712 | 26 Jun, 2021, 10:00: AM

ANSWERED BY EXPERT

CBSE 12-science - Chemistry

Asked by sivaveeramachaneni9 | 08 Feb, 2021, 09:47: PM

ANSWERED BY EXPERT

Answer

Verified

Hint: Aryl halides are less reactive towards nucleophilic substitution reaction as compared to alkyl halides is because of resonance stabilization in aryl halide. Due to resonance, C−Cl bond becomes shorter and stronger and cannot be easily replaced by nucleophiles.

Complete answer:

In this question, we have asked why aryl halide is less reactive towards nucleophilic substitution reactions while alkyl halide is more reactive. So, first of all, what are aryl and alkyl halides? An aryl halide is an aromatic compound in which one or more hydrogen atoms of an aromatic ring are replaced by a halide and alkyl halide means one or more hydrogen atoms of an alkane are replaced by halogen atoms and nucleophilic substitution reaction is a reaction in which a leaving group (nucleophile) is replaced by an electron-rich compound (electrophile). The alkyl halides are less reactive towards nucleophilic substitution reaction because of 1. More steric hindrance as compared to an alkyl halide, 2. The less negative charge on alkyl halide due to resonance in aryl halide and alkyl halide only have induction effect and we know that resonance effect>>> induction effect. We only have one reason in the option that is resonance stabilization in aryl halide.

So, the correct option will be B. resonance stabilization in aryl halide

Note: Inductive effect: The inductive effect is an effect regarding the transmission of unequal sharing of the bonding electron through a chain of atoms in a molecule, leading to a permanent dipole in a bond.

Resonance effect: Resonance effect is the conjugation between the ring and the substituent, which means the delocalizing of the π electrons between the ring and the substituent.

Text Solution

Solution : (i) Due to resonance, the electron pair of halogen atom are in conjugation with pi electrons of the ring. As a result C-X gets partial double bond character and bond breakage is difficult. <br> (ii) In haloarenes, halogen bonded carbon atom is `sp^(2)` hybridised. Hence breaking of C-X bond is very difficult. <br> (iii) Phenyl cation formed as a result of self-ionisation will not be stabilised by resonance. <br> (iv) Nuelcophilic substitution reaction is very less in electron rich arenes.

Explain. Aryl halides are less reactive than alkyl halides towards nucleophilic substitution reactions.

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.

Concept: Chemical Properties

Is there an error in this question or solution?

Aryl halides are less reactive towards nucleophilic substitution reaction as compared to alkyl halide due to

The formation of less stable carbene

No worries! We‘ve got your back. Try BYJU‘S free classes today!

Right on! Give the BNAT exam to get a 100% scholarship for BYJUS courses

Longer carbon halogen bond

No worries! We‘ve got your back. Try BYJU‘S free classes today!

$s p^{2}$ -hybridised carbon bonded to halogen

Right on! Give the BNAT exam to get a 100% scholarship for BYJUS courses

Open in App

Suggest Corrections