Which functional group is generally considered hydrophobic (nonpolar) in organic molecules?

• A. Hydroxyl group, $OH$
• B. Amino group, $N{H}_2$
• C. Methyl (alkyl) group, $C_{\mathrm{H}}$ (e.g., $C_{\mathrm{H}}{\_}_3$ as $C_{\mathrm{H}}{\_}_3$)
• D. Carboxylic acid group, $COOH$

Answer: (C)

Verified step by step guidance

1. Identify the polarity of each functional group by considering the electronegativity of atoms and the presence of polar bonds. Polar bonds create dipoles, making the group hydrophilic (water-attracting), while nonpolar bonds lead to hydrophobic (water-repelling) behavior.
2. Examine the hydroxyl group (\( \mathrm{OH} \)): It contains an oxygen atom bonded to hydrogen, creating a polar O-H bond due to oxygen's high electronegativity. This polarity makes the hydroxyl group hydrophilic.
3. Look at the amino group (\( \mathrm{NH_2} \)): Nitrogen is more electronegative than hydrogen, resulting in polar N-H bonds. This polarity also makes the amino group hydrophilic.
4. Consider the methyl (alkyl) group (\( \mathrm{CH_3} \)): It consists of carbon and hydrogen atoms with similar electronegativities, forming nonpolar C-H bonds. This lack of polarity makes the methyl group hydrophobic.
5. Analyze the carboxylic acid group (\( \mathrm{COOH} \)): It contains polar C=O and O-H bonds, which contribute to its hydrophilic nature due to the ability to form hydrogen bonds with water.