Question

Give an example for each of the following:

(a) a $\mathbf{\beta }$-keto nitrile

(b) a $\mathbf{\beta }$-diester

(c) a-keto aldehyde

Short answer

Answer:

(a)

(b)

(c)

Step-by-step solution

Alpha carbon and its acidity

The acidity of a-hydrogens bonded to carbons flanked by two carbonyl groups increases because the electrons left behind when the proton is removed can be delocalized onto two oxygens. $\mathbf{\beta }$-Diketones have lower ${\mathbf{pK}}_{\mathbf{a}}$values than $\mathbf{\beta }$-keto esters because electrons are more readily delocalized onto the carbonyl oxygen of a ketone than they are onto the carbonyl oxygen of an ester.

Example for the given compound

(a) A $\mathrm{\beta }$- keto nitrile has a CN group (nitrile) and $>\mathrm{C}=\mathrm{O}$group at the$\mathrm{\alpha }$ position with respect to CN group. For example:

$\mathrm{\beta }$-Keto nitrile (a)

(b)A $\mathrm{\beta }$-diester has COOR (ester) group and also has another ester group at $\mathrm{\beta }$-position with respect to the first ester group. For example:

$\mathrm{\beta }$-Diester (b)

(c) A $\mathrm{\beta }$-keto aldehyde has CHO (aldehyde) group and keto group ($>\mathrm{C}=\mathrm{O}$) at position with respect to the aldehyde group. For example

$\mathrm{\beta }$-keto aldehyde (c)