1. Which ion acts as the electrophile in Friedel-Crafts acylation?
A.
Acylium ion
B.
Hydroxide ion
C.
Hydride ion
D.
Chloride ion
Correct Answer:
Acylium ion
Explanation:
The acylium ion is the electrophile that attacks the benzene ring during Friedel-Crafts acylation.
2. What is the general formula of an acylium ion?
A.
RCO+
B.
RCH2+
C.
RCOO−
D.
RNH2+
Correct Answer:
RCO+
Explanation:
An acylium ion contains an acyl group, RCO, carrying a positive charge, so its general formula is RCO+.
3. Which reagent helps generate an acylium ion from an acyl chloride in Friedel-Crafts acylation?
A.
Anhydrous AlCl3
B.
Aqueous NaOH
C.
Dilute HCl
D.
Sodium metal
Correct Answer:
Anhydrous AlCl3
Explanation:
Anhydrous aluminium chloride acts as a Lewis acid and helps the acyl chloride form the acylium ion.
4. Which acylium ion is formed from ethanoyl chloride, CH3COCl?
A.
CH3CO+
B.
CH3CH2+
C.
CH3O+
D.
COCl+
Correct Answer:
CH3CO+
Explanation:
Removal of chloride from CH3COCl in the presence of AlCl3 produces the ethanoyl acylium ion, CH3CO+.
5. In an acylium ion, which atom is the main electron-deficient center?
A.
The carbonyl carbon
B.
The oxygen atom only
C.
The alkyl carbon farthest from the carbonyl group
D.
The chlorine atom
Correct Answer:
The carbonyl carbon
Explanation:
The carbonyl carbon of the acylium ion is electron-deficient and is attacked by the benzene ring.
6. Which pair represents resonance forms of an acylium ion?
A.
R-C≡O+ and R-C+=O
B.
R-C−=O and R-C≡O−
C.
R-CH2-OH and R-CH2-O−
D.
R-CCl3 and R-CCl2+
Correct Answer:
R-C≡O+ and R-C+=O
Explanation:
The acylium ion is commonly represented by the resonance forms R-C≡O+ and R-C+=O.
7. What type of species is an acylium ion in Friedel-Crafts acylation?
A.
Electrophile
B.
Nucleophile
C.
Free radical
D.
Neutral solvent
Correct Answer:
Electrophile
Explanation:
The acylium ion is electron-deficient and accepts electrons from the benzene ring, so it behaves as an electrophile.
8. Which bond is broken when an acyl chloride interacts with AlCl3 to produce an acylium ion?
A.
The carbon-chlorine bond
B.
The carbon-hydrogen bond
C.
The carbon-carbon bond
D.
The oxygen-hydrogen bond
Correct Answer:
The carbon-chlorine bond
Explanation:
Coordination with AlCl3 facilitates cleavage of the acyl chloride carbon-chlorine bond, leading to formation of the acylium ion.
9. What is the formula of the acylium ion formed from propanoyl chloride, CH3CH2COCl?
A.
CH3CH2CO+
B.
CH3CH2+
C.
CH3CO+
D.
CH3CH2O+
Correct Answer:
CH3CH2CO+
Explanation:
Propanoyl chloride loses chloride during acylium ion formation, giving the propanoyl ion CH3CH2CO+.
10. Why does the acylium ion readily react with benzene in Friedel-Crafts acylation?
A.
It is electron-deficient and attracts the benzene pi electrons
B.
It is negatively charged and repels pi electrons
C.
It is a neutral molecule with no reactive center
D.
It supplies hydrogen ions to benzene
Correct Answer:
It is electron-deficient and attracts the benzene pi electrons
Explanation:
The positive charge makes the acylium ion electron-deficient, allowing it to attract the pi electrons of benzene.
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