Arrange the following sets of compounds in order of increasing acid strength. Briefly explain your answer.
i) Acetic acid, monochloracetic acid, dichloracetic acid, trichloracetic acid
ii) Acetic acid, succinic acid, malonic acid (compare first dissociation only)
Answer: i) Chlorine is acceptor of electrons and it stabilizes the carboxylate anion. The more chlorine atoms in alpha-position of acetic acid - the more acidity. Therefore: Acetic acid Monochloracetic acid Dichloracetic acid Trichloracetic acid ii) The similar situation. Malonic acid can be described as -COOH substituted acetic acid. -COOH group is strong acceptor of electons. Succinic acid can be described as -CH2COOH substituted acetic acid. -CH2COOH is weak acceptor of electrons. Therefore: Acetic acid Succinic acid Malonic acid