Relative acidic strength of Carboxylic acids and their derivatives
Carboxylic acids are weak acids. Mineral acids like HCl or HNO3 are very strong acids and non-edible, but many carboxylic acids are edible acids. Carboxylic acids are more acidic than phenol. The conjugate base of carboxylic acid is stabilized by two equivalent resonating structures in which the negative charge is at the more electronegative oxygen atom. Electron withdrawing group (EWG) increases the acidity of carboxylic acids while electron donating group (EDG) decreases the acidic strength of carboxylic acids. The acidic nature of carboxylic acid is also affected by direct attachment of groups such as phenyl or vinyl to the carboxylic acid. They increase the acidity of corresponding carboxylic acids.
It is due to the greater electronegativity of sp2 hybridized carbon to which carboxylic carbon is attached. This acidic character of carboxylic acid is based on its pKa values. The smaller the pka values, the stronger the acid. The effect of the following groups in increasing acidic order is
Ph < I < Br < Cl < F < CN < NO2 < CF3
What is the IUPAC name of the following acid?
CH3—CH2—CH(Br)—COOH
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → 2-Bromobutanoic acid
To name a carboxylic acid in the IUPAC system:
Choose the longest chain that includes the carbon of the –COOH group.
Replace the final “e” of the alkane name with “oic acid”.
Number the chain starting from the –COOH carbon, which is always C-1.
In \( \ce{CH3-CH2-CH(Br)-COOH} \), the chain has four carbons including the –COOH carbon, so the parent is butanoic acid. Counting from the –COOH carbon, bromine is on C-2. So the name is 2-bromobutanoic acid.