Naming Substituted Aromatic Compounds in Organic Chemistry

Naming organic compounds is a vital component of any organic chemistry class. This is important, not only for passing your nomenclature quiz or exam, but also for molecule recognition down the line. You will often be asked to solve a reaction where a name is given in place of structure. In this article I will help you understand how to name aromatic hydrocarbons. Aromatic hydrocarbons are organic compounds that contain a benzene ring. While the simple naming structure implies that you add the substituents to benzene as you would for a regular carbon chain, youwill also be required to memorize many non-systematic names for these compounds. Systemic Naming for Benzene A single methyl substituent on bezene gets the systemic name ofmethylbenzenewith an understood number 1. If you have more than one substituent on benzene identify the one that is highest priority and assign it a number 1. Count your way clockwise or counterclockwise so that your second substituent gets thelowest possible number. For example if you have 2 methyl groups on benzene located 2 carbonsaway, you have the option of numberthem 1 and 3, or 1 and 5 (when counting in the opposite direction). You should chose 1 and 3. This gives you a final product name of 1,3-dimethyl benzene. Common Names When you recognize a common substituent on benzene you may be required to memorize their non-systemic names as follows: phenol: OH or alcohol substituent on benzene toluene: methyl substituent on benzene aniline: NH2 substituent on benzene anisole: methoxy or OCH substituent on benzene benzoic acid: carboxylic acid attached to the benzene ring benzaldehyde: aldehyde group attached to the benzene ring styrene: allylic group (-CH=CH2) attached to the ring nitrobenzene: an NO2 or nitro group attached to the ring There are many more common substituted benzene compounds, however these are the commons ones required for recognition and memorization by many organic chemistry professors. If you see a substituent on one of these compounds, assuming the above mentioned group is higher priority, it's number 1 position will beunderstood. Any additional substituents on the compound are numbered and named accordingly. For example, let's say you are given abenzene ring with a chlorine atom and OH group attached 2 carbons away from each other. OH outranks Cl making it number 1. But instead of hydroxybenzene we recognize phenol. Since Cl is 2 carbons away we get 3-chlorophenol.