discussed in the section on alpha alkylations CHCH CH3 CH2- CH2CH3 3c H3c t 3C an enamine CH3cH2~伊CH2H Ketal and Acetal Formation: Ketones and aldehydes react with excess alcohol in the presence of acid to give ketals and acetals, respectively. The mechanism of acetal formation involves equilibrium protonation, attack by alcohol, and then loss of a proton to give the neutral hemiacetal (or hemiketal).The hemiacetal undergoes protonation and loss of water to give an oxocarbonium ic which undergoes attack by another mole of alcohol and loss of a proton to give the final product; note that acetal (or ketal) formation is an equilibrium process H R-OH FmalProdnct the acetalor ketal R-OH H Some examples of acetal and ketal formation are given belediscussed in the section on "alpha alkylations". Ketal and Acetal Formation: Ketones and aldehydes react with excess alcohol in the presence of acid to give ketals and acetals, respectively. The mechanism of acetal formation involves equilibrium protonation, attack by alcohol, and then loss of a proton to give the neutral hemiacetal (or hemiketal). The hemiacetal undergoes protonation and loss of water to give an oxocarbonium ion, which undergoes attack by another mole of alcohol and loss of a proton to give the final product; note that acetal (or ketal) formation is an equilibrium process. Some examples of acetal and ketal formation are given below: