Question

Arrange these compounds in order of increasing acidity: 2,4-dichlorophenol, phenol, cyclohexanol.

Short answer

Question: Arrange the following compounds in order of increasing acidity: 2,4-dichlorophenol, phenol, and cyclohexanol. Answer: The order of increasing acidity for the given compounds is: cyclohexanol < phenol < 2,4-dichlorophenol.

Step-by-step solution

Identify the acidic hydrogen and the conjugate base of each compound

For each compound, the acidic hydrogen is the one that will be lost as a proton (H+) when the compound donates a proton. After losing the acidic hydrogen, the remaining molecule forms the conjugate base. - 2,4-dichlorophenol: The acidic hydrogen is attached to the oxygen atom of the hydroxyl group (-OH), and the conjugate base is the anion 2,4-dichlorophenoxide. - Phenol: The acidic hydrogen is also attached to the oxygen atom of the hydroxyl group (-OH), and the conjugate base is the anion phenoxide. - Cyclohexanol: The acidic hydrogen is attached to the oxygen atom of the hydroxyl group (-OH), and the conjugate base is the anion cyclohexoxide.

Analyze the stability of the conjugate base

The stability of the conjugate base is a key factor in determining the acidity of a compound. More stable conjugate bases tend to generate more acidic compounds because they can better accommodate the negative charge resulting from the loss of the acidic proton. - 2,4-dichlorophenoxide: The negative charge on the oxygen atom in the conjugate base is delocalized via resonance throughout the aromatic ring. The presence of two electron-withdrawing chlorine substituents further stabilizes the negative charge and increases the acidity of 2,4-dichlorophenol. - Phenoxide: The negative charge on the oxygen atom in the conjugate base is delocalized via resonance throughout the aromatic ring, which stabilizes the negative charge and contributes to the acidity of phenol. - Cyclohexoxide: There is no aromatic ring system in cyclohexanol, so the negative charge in the conjugate base is not delocalized. This makes cyclohexoxide less stable and results in lower acidity compared to the other compounds.

Arrange the compounds in order of increasing acidity

Based on the stability of their conjugate bases and substituent effects, we can arrange the compounds in the order of increasing acidity as follows: 1. Cyclohexanol (least acidic) 2. Phenol 3. 2,4-dichlorophenol (most acidic) In conclusion, the order of increasing acidity for the given compounds is: cyclohexanol < phenol < 2,4-dichlorophenol.