Nitriles of the type \(\mathrm{RCH}_{2} \mathrm{CN}\) undergo an addition reaction analogous to the aldol addition in the presence of strong bases such as lithium amide. Hydrolysis of the initial reaction product with dilute acid yields a cyanoketone, Show the steps that are involved in the mechanism of the over-all reaction and outline a scheme for its use to synthesize large-ring ketones of the type \(\left(\mathrm{CH}_{2}\right)_{n} \mathrm{C}=O\) from dinitriles of the type \(\mathrm{NC}\left(\mathrm{CH}_{2}\right)_{n} \mathrm{CN}\).

In the presence of a strong base such as lithium amide (\(\mathrm{LiNH}_{2}\)), the base abstracts the acidic α-hydrogen from the nitrile to generate the nitrile anion, as follows: \[\mathrm{RCH}_{2}\mathrm{CN} + \mathrm{LiNH}_{2} \rightarrow \mathrm{Li}^{+}\mathrm{RCHCN}^{-} + \mathrm{NH}_{3}\] Step 2: Nucleophilic Addition

The resulting nitrile anion acts as a nucleophile and attacks another nitrile molecule at the electrophilic carbon of the nitrile group (C≡N). This reaction forms an intermediate, as shown below: \[\mathrm{Li}^{+}\mathrm{RCHCN}^{-} + \mathrm{RCH}_{2}\mathrm{CN} \rightarrow \mathrm{Li}^{+}\mathrm{RCH(CN)CH}_{2}\mathrm{CN}\] Step 3: Hydrolysis

Next, the intermediate from step 2 undergoes hydrolysis in the presence of dilute acid. The nitrile group is hydrolyzed to form a ketone, yielding the cyanoketone product: \[\mathrm{Li}^{+}\mathrm{RCH(CN)CH}_{2}\mathrm{CN} + 2\mathrm{H}_{2}\mathrm{O} \rightarrow \mathrm{RCH(CN)COCH}_{2}\mathrm{CN} + \mathrm{Li}^{+}\mathrm{OH}^{-}\] Step 4: Synthesis of Large-Ring Ketones

To synthesize large-ring ketones of the type \(\left(\mathrm{CH}_{2}\right)_{n} \mathrm{C}=O\) from dinitriles of the type \(\mathrm{NC}\left(\mathrm{CH}_{2}\right)_{n} \mathrm{CN}\), we can follow a similar reaction mechanism. Initially, we would perform the similar reaction steps as discussed above (deprotonation of an α-hydrogen, nucleophilic addition, and hydrolysis). After obtaining the cyanoketone from the dinitrile, we would perform an intramolecular reaction to form the large ring ketone. A suitable reagent could then be used to close the cycle and form the large-ring ketone, such as a strong base followed by acid work-up. In summary, the overall process would involve the deprotonation, nucleophilic addition, and hydrolysis steps for the given dinitrile compound, followed by an intramolecular cyclization reaction to form the large-ring ketone.