Question

What is meant by the following term? Give an example of the reaction in the following case.

Hemiacetal

Answer 1

Gem-alkoxyalcohols are called hemiacetals. These are produced when a molecule of monohydric alcohol combines with an aldehyde in the presence of dry HCl gas.

\[\begin{array}{cc}
\ce{H3C}\phantom{.........................}\ce{CH3}\phantom{....}\ce{OH}\\
\backslash\phantom{...........................}\backslash\phantom{...}/\\
\ce{C = O + H - OCH3 <=>[Dry HCl_{(g)}] C}\\
/\phantom{...........................}/\phantom{...}\backslash\\
\phantom{....}\ce{H}\phantom{...........................}\ce{\underset{Hemiacetal}{H\phantom{....}OCH3}}\
\end{array}\]