Alcohols are organic molecules containing the hydroxyl functional group, where the OH is directly bonded to carbon. The carbon directly attached to OH is technically called the carbinol carbon. The carbinol carbon (carbon attached to OH), however, is the key to understanding the most common classifications we use for alcohols, that being “primary”, “secondary”, and “tertiary” alcohols. If the carbon attached to the hydroxyl is primary, it is attached to one other carbon. If it is a secondary alcohol, the carbon is attached to two other carbons. If the hydroxyl is attached to a carbon attached to three other carbons, it is a tertiary carbon. It is methanol if the hydroxyl is attached to only one carbon. Hydroxyl groups attached to aromatic rings are called, phenols. Not all functional groups containing OH are alcohols. If the OH is attached to a carbonyl (C=O), that functional group is called a “carboxylic acid”. The OH attached to an alkene is called an enol (ene + ol).

Ethers are a class of organic compounds that possess an ether group where an oxygen is connected to two carbons either alkyl or aryl groups. They have the general formula R–O–R′, where R and R′ represent the alkyl or aryl groups. There are two varieties of ethers: if the alkyl groups are the same on both sides of the oxygen atom, then it is a simple or symmetrical ether. However, if they are different, the ethers are called mixed or unsymmetrical ethers. A typical example of the first group is usually a solvent such as diethyl ether also and anesthesia commonly referred to simply as “ether” (CH₃–CH₂–O–CH₂–CH₃). Ethers are common in biochemistry, pervasive linkages in carbohydrates and lignin.

Similar to oxygen, sulfur is also a nonmetal found in organic compounds. The two amino acids containing sulfur are nonpolar and hydrophobic. The amino acid methionine is one of the most hydrophobic amino acids and often found on the interior of proteins. The amino acid Cysteine does ionize to yield the thiolate anion. Cysteines are also rare to find on the surface of a protein for several reasons. First, sulfur has a low propensity to hydrogen bond, unlike oxygen. As a result of this H₂S is a gas under conditions that H₂O is a liquid. Second, the thiol group of cysteine reacts with other thiol groups in an oxidation reaction that yields a disulfide bond. As a consequence, cysteine residues are most frequently buried inside proteins.