if a structural isomer has an OH attached, i don't understand why it's unlikely that it'll be a liquid at room temperature.
I think, I'm not sure, but because both O and H are gases
I can think of many alcohols that are liquid at room temperature.
You are correct that there are many alcohol molecules that are liquid at room temperature, so it's not necessarily true that a structural isomer with an OH group attached will always be a gas. The state (solid, liquid, gas) of a compound at room temperature is determined by several factors, including the strength and nature of intermolecular forces between its molecules.
For instance, in the case of alcohols, compounds like methanol (CH3OH), ethanol (C2H5OH), and propanol (C3H7OH) all possess an OH group and are liquid at room temperature. This is because they form strong intermolecular hydrogen bonds due to the presence of the OH group. These hydrogen bonds help hold the alcohol molecules together, resulting in a higher boiling point and a liquid state at room temperature.
However, some structural isomers with an OH group attached may lack the necessary characteristics to form strong hydrogen bonds or have other intermolecular forces that are too weak to keep the molecules together as a liquid at room temperature. In such cases, they may have lower boiling points and be gases at room temperature.
Therefore, while the presence of an OH group is a significant factor, it is not the sole determinant of whether a compound will be a liquid or a gas at room temperature. Other factors such as the size, shape, and other functional groups present in the molecule also play a crucial role in determining its physical state.