What is the major difference between a cyclic hemiacetal and a cyclic acetal?

1 Answer
Nov 18, 2015

It is apparent that ketal and ketone share the same first three letters. That makes it easier to remember that:

  • acetals form from aldehydes
  • ketals form from ketones

That implies that:

  • cyclic hemiacetals form from cyclization of aldehydes
  • cyclic hemiketals form from cyclization of ketones

Let's take a look at how a cyclic hemiacetal forms.

I drew the less obvious arrows, but I'll leave the proton transfers for you to practice. The formation of a cyclic hemiketal is nearly identical; simply replace the explicit hydrogen with a methyl group.