Which general formula represents an alcohol?

• A. R-OH
• B. R-O-R
• C. R-CO-R
• D. R-CHO

Answer: (A)

Alcohols are organic compounds that contain a hydroxyl group (-OH) bonded to a carbon atom. The simplest way to represent this family is with the general formula R-OH, where R stands for any carbon-containing group (an alkyl or aryl group). This -OH group is what defines an alcohol and sets it apart from other oxygen-containing classes. The other structures correspond to different functional groups: an ether has oxygen bonded to two carbon groups (R-O-R), a ketone has a carbonyl group between two carbons (R-CO-R), and an aldehyde has a carbonyl attached to at least one hydrogen (R-CHO). Because the defining feature of alcohols is the hydroxyl group, the formula R-OH best represents an alcohol. For example, methanol is CH3OH and ethanol is C2H5OH, showing how the same -OH group attaches to different carbon chains.