Which compound will not take part in the Friedel-Crafts acylation?
ii and iii
only ii
i and ii
only ii
only i
The Correct Option is D
Approach Solution - 1
Friedel-Crafts Acylation
Friedel-Crafts acylation is an electrophilic aromatic substitution reaction where an acyl group (R-C=O) is added to an aromatic ring. The reaction requires a Lewis acid catalyst, such as AlCl3.
Factors Affecting Friedel-Crafts Reactions:
Activating and Deactivating Groups: Electron-donating groups (activating groups) on the aromatic ring increase the reactivity of the ring towards electrophilic attack. Electron-withdrawing groups (deactivating groups) decrease the reactivity.
Strongly Deactivating Groups: Aromatic rings with strongly deactivating groups do not undergo Friedel-Crafts reactions. The deactivating group reduces the electron density of the ring, making it less susceptible to electrophilic attack. Also, the Lewis acid catalyst can complex with the deactivating group, further deactivating the ring.
Analyzing the Compounds:
Compound i (Benzene): Benzene readily undergoes Friedel-Crafts acylation.
Compound ii (Nitrobenzene): The nitro group (-NO2) is a strongly deactivating group. Nitrobenzene does not undergo Friedel-Crafts reactions.
Compound iii (Toluene): The methyl group (-CH3) is an activating and ortho/para directing group. Toluene undergoes Friedel-Crafts acylation.
Therefore, the correct answer is (D) only ii
Approach Solution -2
1. Friedel-Crafts acylation reaction:
The Friedel-Crafts acylation reaction is an electrophilic aromatic substitution reaction used to introduce an acyl group (\(-CO-\)) onto an aromatic ring. For this reaction to occur, the aromatic ring must be activated toward electrophilic substitution. Activating groups are electron-donating substituents that increase the electron density on the aromatic ring, making it more reactive toward electrophiles. Conversely, deactivating groups (electron-withdrawing substituents) decrease the electron density on the aromatic ring, making it less reactive toward electrophilic substitution.
2. Analyze the given compounds:
- (i) Benzene (\(C_6H_6\)): Benzene is a simple aromatic compound with no substituents. It is activated toward electrophilic substitution because it has no deactivating groups. Therefore, benzene will participate in Friedel-Crafts acylation.
- (ii) Nitrobenzene (\(C_6H_5NO_2\)): The nitro group (\(-NO_2\)) is a strong electron-withdrawing group (deactivating). It decreases the electron density on the benzene ring, making it less reactive toward electrophilic substitution. Therefore, nitrobenzene will not participate in Friedel-Crafts acylation.
- (iii) Toluene (\(C_6H_5CH_3\)): The methyl group (\(-CH_3\)) is an electron-donating group (activating). It increases the electron density on the benzene ring, making it more reactive toward electrophilic substitution. Therefore, toluene will participate in Friedel-Crafts acylation.
3. Key conclusion:
The only compound that will not take part in the Friedel-Crafts acylation is nitrobenzene (ii).
4. Final answer:
The correct option is (D).
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Concepts Used:
Aromatic hydrocarbon
Aromatic hydrocarbons, sometimes known as arenes, are aromatic organic molecules made up entirely of carbon and hydrogen. In aromatic compounds a benzene ring which is named after the simple aromatic chemical benzene, or a phenyl group when part of a larger structure, is the configuration of six carbon atoms.
Read More: Aromaticity
Reactions of Aromatic Hydrocarbons:
1. Aromatic Substitution Reactions
This reaction involves the replacement of one substituent on the ring of an aromatic hydrocarbon, commonly a hydrogen atom, by a different substituent group.
The common types of aromatic substitution reactions are:
- Nucleophilic aromatic substitution reactions
- Electrophilic aromatic substitution reactions
- Radical nucleophilic aromatic substitution reactions
2. Coupling Reactions
In these types of reactions, the coupling of two fragments that have a radical nature is achieved with the help of a metal catalyst