Which the list shown below, the correct pair of structures of alanine in pH ranges 2-4 and 9-11 is
I. `H_(3)N^(+)CH(CH_(3))CO_(2)H`
II. `H_(2)NCH(CH_(3))CO_(2)^(-)`
III. `H_(3)N^(+)CH(CH_(3))CO_(2)^(-)`
IV. `H_(2)NCH(CH_(3))CO_(2)H`

Options

A. I, II
B. I,III
C. II, III
D. III, IV

Answer

A

Explanation

In the acidic medium , alanine exists as a cation (I) and in the basic medium , it exists as anion (II).
`H_(3)overset(+)(N)-underset("Alanine")(CH)(CH_3)CO_(2)^(-)overset(H^+)toH_(3)overset(+)(N)-CH(CH_3)CO_(2)H(I)`
`H_(3)overset(+)(N)-underset("Alanine")(CH)(CH_3)CO_(2)^(-)overset(OH^-)toH_(2)N-CH(CH_3)CO_(2)^(-)(II)`