Question

Which of the following compounds is an amino acid
(A) \[C{H_3} - C{H_2} - COO - N{H_4}\]
(B) \[C{H_3} - CH(N{H_2}) - COOH\]
(C) \[C{H_3} - C{H_2} - CO - NH_2^{}\]
(D) \[C{H_3} - CH(N{H_2})COCl\]

Answer 1

Hint: Amino acids consist of two words amino and acid. Amino refers to the amine group and acid refers to carboxylic acid. Amino acids are compounds made of nitrogen, oxygen, carbon and hydrogen. 

Complete Solution step by step:.
Amine has a chemical formula \[N{H_3}\]. 
Whereas carboxylic acid has chemical formula\[COOH\]. Amine is a base whereas carboxylic acid is an acid. They both show acid base interaction. Hence, Amine and acid interact in the form of \[N{H_2}^ + \]and \[CO{O^ - }\]having positive and negative charge interactions. This is called as zwitter ion as they exist in form of charges which are equal in magnitude. 
Amino acids are amphoteric compounds as they can act as both acid and base. Carboxylic acid reacts with bases and amine group being basic in nature, thus reacting with acids.
Option a: in \[C{H_3} - C{H_2} - COO - N{H_4}\], the interactions of \[COO\]are with $N{H_4}$. There are $5$bonds of nitrogen which are not possible.
Option b: \[C{H_3} - CH(N{H_2}) - COOH\]is an amino acid with amine and carboxylic acid both.
Option c: \[C{H_3} - C{H_2} - CO - NH_2^{}\]is an amide compound and not an amino acid because it does not have a carboxylic group.
Option d: \[C{H_3} - CH(N{H_2})COCl\] is an amino acid chloride rather than amino acid.

Thus, the correct answer is b

Note: amino acids are monomer units joined together to form protein chains. Amino acids are of two types - essential and non- essential amino acids. Those amino acids which are not present in the human body but are required from outside source are called as essential amino acids. Those amino acids which are produced in the human body and are not required from outside are called as non- essential amino acids.