Predict which member of each pair is more acidic, and explain the reasons for your predictions.
b. cyclohexanol or cyclohexanethiol

Verified step by step guidance

1. Step 1: Understand the concept of acidity. Acidity is determined by the ability of a compound to donate a proton (H⁺). The stability of the conjugate base formed after losing the proton plays a key role in determining acidity. A more stable conjugate base corresponds to a stronger acid.
2. Step 2: Compare the functional groups in cyclohexanol and cyclohexanethiol. Cyclohexanol contains an -OH group, while cyclohexanethiol contains an -SH group. Both groups can lose a proton to form their respective conjugate bases: cyclohexoxide (C₆H₁₁O⁻) and cyclohexanethiolate (C₆H₁₁S⁻).
3. Step 3: Analyze the electronegativity of oxygen and sulfur. Oxygen is more electronegative than sulfur, meaning it can better stabilize the negative charge on the conjugate base. This makes the conjugate base of cyclohexanol (C₆H₁₁O⁻) more stable than the conjugate base of cyclohexanethiol (C₆H₁₁S⁻).
4. Step 4: Consider the bond strength between the hydrogen atom and the heteroatom (O or S). The O-H bond in cyclohexanol is stronger than the S-H bond in cyclohexanethiol, making it easier for cyclohexanethiol to lose a proton compared to cyclohexanol.
5. Step 5: Conclude based on the above analysis. Cyclohexanethiol is more acidic than cyclohexanol because its conjugate base (C₆H₁₁S⁻) is less stable, and the S-H bond is weaker, allowing for easier proton donation.

Key Concepts

Acidity and pKa

Acidity in organic chemistry refers to the tendency of a compound to donate a proton (H+). The strength of an acid is often measured by its pKa value; lower pKa values indicate stronger acids. Understanding the pKa helps predict which compound in a pair is more acidic, as the one with the lower pKa will more readily donate a proton.

Functional Groups and Their Effects

Different functional groups influence the acidity of a compound due to their electronic properties. For instance, alcohols (like cyclohexanol) have a hydroxyl (-OH) group, while thiols (like cyclohexanethiol) have a sulfhydryl (-SH) group. The electronegativity and size of the atoms involved can affect the stability of the conjugate base formed after deprotonation, impacting acidity.

Inductive Effect

The inductive effect refers to the electron-withdrawing or electron-donating influence of substituents on a molecule. In the case of cyclohexanol and cyclohexanethiol, the sulfur atom in thiols is larger and less electronegative than oxygen, which can lead to a weaker stabilization of the conjugate base. This difference in stabilization can help determine which compound is more acidic.