Question

Within the list shown below, the correct pair of structures of alanine in $pH$ range $2-4$ and $9-11$ is:
I. $H_3{N}^{+}CH\left({CH}_3\right){CO}_{2}H$
II. $H_{2}NCH\left({CH}_3\right){CO}_2^{-}$
III. $H_3{N}^{+}CH\left({CH}_3\right){CO}_2^{-}$
IV. $H_{2}NCH\left({CH}_3\right){CO}_{2}H$

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

Answer 1

Answer: (A)

I, II

As the isoelectric point of Alanine is 6.1.

At $pH$ below p${}^I$ it has $N{H}_3^{⨁}$

At $pH$ above p${}^I$ it has $CO{O}^{\ominus }$

Option A is correct.