Why is H-O-C-C equals O a molecule likely to exist?

Answer 1

It's not. In fact, not only is it not likely, it's not possible. There are unsatisfied valences on both carbons.

Answer 2

H-O-C-C=O is a molecule known as formic acid. It is likely to exist because it follows the octet rule, with each atom having a full outer shell of electrons. The oxygen atom can form a double bond with the carbon atom, allowing for stability and minimizing the overall energy of the molecule.