oxygen

happi A chemical element (symbol O) with an atomic number of 8 and relative atomic mass of 15.9994.
Molecular oxygen (O2), a colorless, odorless gas at room temperature.
{{quote-magazine|year=2013|month=September-October|author=http://www.americanscientist.org/authors/detail/katie-l-burke Katie L. Burke
puhekieltä A mixture of oxygen and other gases, administered to a patient to help him or her to breathe.
puhekieltä An atom of this element.
2013, Spencer L. Seager, ‎Michael R. Slabaugh, Chemistry for Today: General, Organic, and Biochemistry (page 479)

Look first at any structure to see if there is a carbon with two oxygens attached. Hemiacetals, hemiketals, acetals, and ketals are all alike in that regard.