Identifying a hydroxyl group from the molecular formula

[Shelby Y 1K]

Hi! How do we identify whether there's a hydroxyl group just from the molecular formula? For example, CH2 = CHCHO doesn't have a hydroxyl group, though the H and O are written next to each other in this specific example. Do we just have to use trial-and-error/formal charge, or is there another parameter that we go by? I've also been told that we should, for the most part, assume that there isn't a hydroxyl group.

[Kenah Angeles 2C]

Hi! Correct me if I'm wrong but to identify a hydroxyl group (-OH) from a molecular formula, consider the bonding structure implied by the formula and the typical valencies of atoms (C = 4, O = 2, H = 1). In CH₂=CHCHO, the oxygen is part of an aldehyde group (-CHO), not a hydroxyl. Structural clues and chemical logic, rather than just the sequence of atoms, guide the identification.

I'm a little confused with this as well so let me know if it may be different than what I said!