Question

Draw the structures of the conjugate bases of the following acids:

$$\begin{gathered} \mathit{C}\mathit{O}{\mathit{O}}^{\mathbf{-}} \\ \mathbf{\left|} \\ \mathit{C}\mathit{H} \\ \mathbf{\right|} \\ \mathit{C}\mathit{O}\mathit{O}\mathit{H} \\ \mathit{A}\mathit{c}\mathit{i}\mathit{d} \end{gathered}$$ $$\begin{gathered} \mathit{C}\mathit{O}\mathit{O}\mathit{H} \\ \mathbf{\left|} \\ \mathit{C}{\mathit{H}}_{\mathbf{2}} \\ \mathbf{\right|} \\ \mathit{N}{{\mathbf{H}}_{\mathbf{3}}}^{\mathbf{+}} \\ \mathit{A}\mathit{c}\mathit{i}\mathit{d} \end{gathered}$$

(a) (b)

Short answer

The structure of the conjugate bases are shown below.

$$\begin{gathered} {\mathrm{COO}}^{-} \\ \left| \\ \mathrm{CH} \\ \right| \\ {\mathrm{COO}}^{-} \\ \mathrm{Conjugate}\mathrm{base} \end{gathered}$$ $$\begin{gathered} {\mathrm{COO}}^{-} \\ \left| \\ {\mathrm{CH}}_2 \\ \right| \\ {{\mathrm{NH}}_2}^{+} \\ \mathrm{Conjugate}\mathrm{base} \end{gathered}$$

(a) (b)

Step-by-step solution

Introduction of conjugate acid-base pair

An acid and a base which are different only by either presence or absence of proton are referred to as conjugate acid-base pairs.

In a chemical reaction, acid donates proton and its conjugate base is formed while base accepts a proton and its conjugate acid is formed.

Explanation for (a)

The structure of the conjugate base is as follows:

$$\begin{gathered} {\mathrm{COO}}^{-}{\mathrm{COO}}^{-} \\ || \\ \mathrm{CH}\mathrm{CH} \\ \to +{\mathrm{H}}^{+} \\ \mathrm{CH}\mathrm{CH} \\ || \\ \mathrm{COOH}{\mathrm{COO}}^{-} \\ \mathrm{Acid}\mathrm{Conjugate}\mathrm{base}\mathrm{Proton} \end{gathered}$$

Explanation for (b)

The structure of the conjugate base is as follows:

$$\begin{gathered} \mathrm{COOH}{\mathrm{COO}}^{-} \\ || \\ {\mathrm{CH}}_2\to {\mathrm{CH}}_2+{\mathrm{H}}^{+} \\ || \\ {{\mathrm{NH}}_3}^{+}{{\mathrm{NH}}_3}^{+} \\ \mathrm{Acid}\mathrm{Conjugate}\mathrm{base}\mathrm{Proton} \end{gathered}$$