Draw the conjugate base for each compound below (the acidic hydrogen in each case is marked with an *).

(a)

Bronsted-Lowry has given the acid-base theory to describe conjugate acid and conjugate base. When in a chemical reaction, an acid donates its proton, i.e., hydrogen ion, the compound formed is a conjugate base of that acid.

We can define this by a chemical reaction:

$\mathbf{Acid}\mathbf{}\mathbf{+}\mathbf{}\mathbf{Base}\mathbf{}\mathbf{\rightleftharpoons }\mathbf{conjugate}\mathbf{}\mathbf{base}\mathbf{}\mathbf{+}\mathbf{}\mathbf{conjugate}\mathbf{}\mathbf{acid}$

For example, when we put an acid into water, it will lose its ${\mathrm{H}}^{+}$and the remaining compound will be the conjugate base of that acid. Let us take HCl as an acid. When it is put in water, it will release its hydrogen ion and ${\mathrm{Cl}}^{-}$will be the conjugate base of HCl.

When any oxygen cation is attached to the three bonds, that cation is known as an oxonium ion. If Oxygen cation $\left({\mathrm{O}}^{+}\right)$is attached with three hydrogen atoms, then ${\mathrm{H}}_3{\mathrm{O}}^{+}$will be known as a hydronium ion. In our case, the oxygen cation is attached with two alkyl (ethyl) groups and one hydrogen atom; therefore, according to IUPAC naming, the compound is called diethyl oxonium ion.

Diethyl oxonium ion

In our compound, there are many hydrogen atoms, but the hydrogen atom marked with (*) is acidic hydrogen. Acidic hydrogen is the hydrogen atom that dissociates easily as a hydrogen $\left({\mathrm{H}}^{+}\right)$ion when acid is dissolved in water.

Therefore, the conjugate base of diethyl oxonium ion is:

Conjugate base of Diethyl oxonium ion