-OH is the hydroxyl group, a functional group made of oxygen bonded to hydrogen. In Intro to Chemistry, you usually see it in alcohols, where it changes polarity, hydrogen bonding, and reactivity.
-OH is the hydroxyl group in Intro to Chemistry, and it is one of the most common oxygen-containing functional groups you will see in organic molecules. It is made of one oxygen atom bonded to one hydrogen atom, and when that group is attached to a carbon chain, the molecule is usually an alcohol.
The big idea is that oxygen pulls electrons toward itself much more strongly than hydrogen does. That makes the O-H bond polar, with oxygen carrying a partial negative charge and hydrogen carrying a partial positive charge. Because of that charge separation, molecules with -OH can interact with each other more strongly than similar-sized molecules that do not have it.
That extra attraction shows up as hydrogen bonding. An -OH group can both donate a hydrogen bond and accept one through the oxygen atom, so alcohols often have higher boiling points and better water solubility than hydrocarbons of similar size. That is why a small alcohol like ethanol mixes well with water, while a larger nonpolar molecule does not.
In chemistry class, it helps to separate the group itself from the whole molecule. The hydroxyl group is the reactive part, but the carbon skeleton attached to it affects how the compound behaves. For example, 2-propanol and propan-1-ol both contain -OH, yet their structures are arranged differently, so their physical and chemical behavior is not identical.
The -OH group also changes how a molecule reacts. Alcohols can be oxidized, dehydrated, or substituted depending on the rest of the structure and the conditions. In acid-base situations, the hydrogen on -OH can sometimes be removed, making the group part of reactions that involve proton transfer instead of just shape and bonding.
One easy mistake is confusing -OH with free hydroxide, OH-. They are not the same thing. -OH in an alcohol is covalently bonded to carbon, while OH- is an ion in water or base solutions. The bond context completely changes the chemistry.
-OH shows up whenever Intro to Chemistry moves from simple formulas into organic structure and property patterns. If you can spot a hydroxyl group, you can often predict whether a molecule will be more polar, whether it can hydrogen bond, and whether it will dissolve in water better than a nonpolar compound.
That prediction skill comes up a lot in alcohols and ethers. Alcohols have -OH bonded to carbon, so they are more reactive and usually more polar than ethers, which have an oxygen atom between two carbon groups but no O-H bond. That one difference explains a lot of the contrast in boiling point and solubility.
It also matters when you trace reactions. If a problem asks why an alcohol can be oxidized or dehydrated, the hydroxyl group is the part you track through the mechanism. In lab or homework, you may be given a structural formula and asked to identify functional groups, compare intermolecular forces, or explain why two compounds with similar formulas behave differently.
Once you recognize -OH quickly, you can move faster on structure questions and avoid mixing up molecular formulas that look similar but act differently in solution or in reactions.
Keep studying Intro to Chemistry Unit 15
Visual cheatsheet
view galleryHydroxyl Group
This is the name of the -OH functional group itself. In Intro to Chemistry, you use the term when identifying what part of an alcohol causes polarity, hydrogen bonding, and many of its reactions. If a structure has -OH attached to carbon, that is the hydroxyl group doing the work.
Alcohol
Alcohols are the main compound class built around -OH bonded to a carbon. When you see an alcohol, the hydroxyl group explains why it is more polar than a hydrocarbon and why it often boils at a higher temperature than expected for its size. The carbon chain around it still matters, though.
Hydrogen Bonding
The O-H bond in -OH makes hydrogen bonding possible. That is why alcohols tend to have higher boiling points and greater water solubility than similar molecules without -OH. In problems, this connection often shows up when you compare two liquids and explain their physical properties.
Ether
Ethers also contain oxygen, but they do not have an O-H bond. That means they cannot hydrogen bond to each other the same way alcohols can, so they are usually less polar and less reactive. This comparison is one of the easiest ways to tell alcohols and ethers apart on structure questions.
A quiz question may show you a structural formula and ask you to circle the -OH group, name the functional group, or predict whether the molecule is an alcohol. You might also compare two compounds and explain which one has the higher boiling point or greater water solubility, using the presence of -OH and hydrogen bonding as the reason.
In a problem set or lab, you may use -OH to justify reaction behavior, especially when analyzing oxidation or dehydration of alcohols. If a molecule contains -OH, you should ask what kind of intermolecular forces it can form and whether that makes it more polar than a similar molecule without it. The move is usually: identify the group, connect it to polarity, then use that to explain a property or reaction.
Alcohols contain an -OH group bonded to carbon, while ethers have an oxygen atom between two carbon groups and no O-H bond. That difference matters because alcohols can hydrogen bond more strongly and usually have higher boiling points and greater water solubility than ethers of similar size.
-OH is the hydroxyl group, and in Intro to Chemistry it usually points to an alcohol structure.
The oxygen in -OH pulls electron density toward itself, so the group is polar.
Because of its polarity, -OH lets molecules hydrogen bond and often raises boiling point and water solubility.
The group is also the site students track in reactions like oxidation and dehydration of alcohols.
Do not confuse -OH in an alcohol with OH-, which is a hydroxide ion.
-OH is the hydroxyl group, a functional group made of oxygen bonded to hydrogen. In Intro to Chemistry, it most often appears in alcohols, where it changes the molecule's polarity, intermolecular forces, and reactivity.
No. -OH in an alcohol is covalently bonded to carbon, while hydroxide is OH- as an ion. They look similar on paper, but they behave very differently in reactions and solution chemistry.
The O-H bond is polar, so molecules with -OH can hydrogen bond to each other. Those intermolecular attractions take more energy to overcome, which usually raises boiling point compared with similar nonpolar molecules.
Look for an oxygen atom directly bonded to a hydrogen atom and attached to a carbon framework. If that group is bonded to carbon, the molecule is usually an alcohol. If the oxygen is between two carbon groups instead, you are probably looking at an ether.