🥼organic chemistry review

key term - 2-naphthol

Definition

2-naphthol is a phenolic compound with the chemical formula C₁₀H₇OH. It is an isomer of 1-naphthol and is commonly used in organic synthesis and as a precursor for various dyes and pharmaceuticals.

5 Must Know Facts For Your Next Test

  1. 2-naphthol exhibits characteristic absorption bands in the ultraviolet (UV) and visible regions of the electromagnetic spectrum, which can be used for its identification and quantification.
  2. The hydroxyl group in 2-naphthol can participate in hydrogen bonding, affecting its solubility and reactivity.
  3. 2-naphthol can undergo electrophilic aromatic substitution reactions, such as halogenation, nitration, and sulfonation, at the 1- and 3-positions of the naphthalene ring.
  4. 2-naphthol is used as a precursor in the synthesis of various azo dyes, which are widely used in the textile industry.
  5. The presence of the hydroxyl group in 2-naphthol makes it more acidic compared to naphthalene, with a pKa value around 9.5.

Review Questions

  • Explain the significance of the hydroxyl group in the structure of 2-naphthol and how it affects the compound's properties.
    • The hydroxyl group (-OH) in the 2-position of the naphthalene ring in 2-naphthol is a key structural feature that influences its chemical and physical properties. The hydroxyl group increases the polarity of the molecule, allowing it to participate in hydrogen bonding interactions. This affects the solubility of 2-naphthol, as it becomes more soluble in polar solvents compared to the parent compound, naphthalene. Additionally, the hydroxyl group makes 2-naphthol more acidic than naphthalene, with a pKa value around 9.5, due to the stabilization of the conjugate base through resonance.
  • Describe the characteristic spectroscopic features of 2-naphthol and explain how they can be used for its identification and quantification.
    • 2-naphthol exhibits distinct absorption bands in the ultraviolet (UV) and visible regions of the electromagnetic spectrum, which can be used for its identification and quantification through spectroscopic techniques, such as UV-Vis spectroscopy. The aromatic naphthalene ring structure in 2-naphthol gives rise to characteristic $\pi \rightarrow \pi^*$ transitions, leading to strong absorption bands in the UV region, typically around 220-280 nm. The presence of the hydroxyl group can also influence the absorption spectrum, leading to additional bands or shifts in the absorption maxima. By measuring the intensity and wavelength of these absorption bands, 2-naphthol can be identified and its concentration can be determined in a sample using calibration methods.
  • Discuss the reactivity of 2-naphthol and explain how it can be utilized in the synthesis of various organic compounds, particularly azo dyes.
    • The presence of the hydroxyl group in 2-naphthol makes it a reactive compound that can undergo various electrophilic aromatic substitution reactions. The hydroxyl group can be deprotonated, forming a phenoxide ion, which can then participate in nucleophilic addition-elimination reactions. This reactivity is particularly useful in the synthesis of azo dyes, where 2-naphthol is often used as a coupling component. In the synthesis of azo dyes, the phenoxide ion of 2-naphthol can react with a diazonium salt, forming an azo linkage (-N=N-) and producing a colored, conjugated system. This ability to form azo dyes makes 2-naphthol an important precursor in the textile industry and other applications where these colorants are utilized.

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