Acetophenone

Definition

Acetophenone is an aromatic ketone compound with the chemical formula C6H5COCH3. It is a colorless liquid with a characteristic floral odor and is widely used in the production of various organic compounds and as a fragrance in personal care products.

5 Must Know Facts For Your Next Test

1. Acetophenone is a common product of the Friedel-Crafts acylation reaction, where an acyl group (such as the acetyl group) is introduced onto an aromatic ring.
2. Acetophenone can undergo a nucleophilic addition reaction with hydrogen cyanide (HCN) to form the corresponding cyanohydrin, which is a useful intermediate in organic synthesis.
3. The carbonyl group in acetophenone exhibits a characteristic absorption band in the infrared (IR) spectrum around 1680-1700 cm^-1, which can be used for identification and structural analysis.
4. In the ^1H NMR spectrum of acetophenone, the methyl group attached to the carbonyl typically appears as a singlet around 2.5-2.6 ppm, while the aromatic protons appear as a complex multiplet in the 7.4-8.0 ppm region.
5. Acetophenone is a versatile precursor in the synthesis of various organic compounds, such as in the mixed Claisen condensation reaction, where it can be used to form β-diketones.

Review Questions

• Explain the role of acetophenone in the Friedel-Crafts acylation reaction and describe the mechanism of this transformation.
  • In the Friedel-Crafts acylation reaction, acetophenone is a common product formed when an acyl group, such as the acetyl group, is introduced onto an aromatic ring. The reaction involves the use of an acyl halide (e.g., acetyl chloride) and a Lewis acid catalyst (e.g., aluminum chloride) to activate the acyl group, which then undergoes electrophilic aromatic substitution with the aromatic substrate. The mechanism proceeds through the formation of an acylium ion intermediate that subsequently attacks the aromatic ring, leading to the formation of acetophenone.
• Describe the nucleophilic addition of hydrogen cyanide (HCN) to acetophenone and explain the significance of the resulting cyanohydrin product.
  • Acetophenone can undergo a nucleophilic addition reaction with hydrogen cyanide (HCN) to form the corresponding cyanohydrin. In this reaction, the carbonyl carbon of acetophenone is attacked by the nucleophilic cyanide ion, resulting in the addition of the HCN molecule across the carbonyl group. The cyanohydrin product is a useful intermediate in organic synthesis, as it can be further transformed into other valuable compounds, such as α-hydroxy ketones or α-amino acids, through subsequent reactions.
• Discuss the spectroscopic properties of acetophenone and how they can be used for the identification and structural analysis of this compound.
  • The carbonyl group in acetophenone exhibits characteristic absorption bands in the infrared (IR) and nuclear magnetic resonance (NMR) spectra, which can be used for identification and structural analysis. In the IR spectrum, the carbonyl group of acetophenone typically shows a strong absorption band around 1680-1700 cm^-1, which is diagnostic for the presence of a ketone functionality. In the ^1H NMR spectrum, the methyl group attached to the carbonyl appears as a singlet around 2.5-2.6 ppm, while the aromatic protons appear as a complex multiplet in the 7.4-8.0 ppm region. These unique spectroscopic signatures, along with other analytical techniques, can be used to confirm the identity and structural features of acetophenone in various organic chemistry applications.

Related terms

Friedel-Crafts Reaction: The Friedel-Crafts reaction is an electrophilic aromatic substitution reaction used to alkylate or acylate aromatic rings, with acetophenone being a common product of the acylation reaction.

Cyanohydrin: Cyanohydrins are organic compounds formed by the addition of hydrogen cyanide (HCN) to the carbonyl group of aldehydes or ketones, such as acetophenone.

Carbonyl Spectroscopy: The carbonyl group in acetophenone and other aldehydes and ketones exhibits characteristic absorption bands in the infrared and nuclear magnetic resonance (NMR) spectra, which can be used for identification and structural analysis.