Carbanions are defined as

• A. A positively charged carbon atom
• B. A neutral carbon with a lone pair
• C. Negatively charged species with a negative formal charge on carbon
• D. A carbon radical

Answer: (C)

Think of carbanions as carbon-centered anions: the carbon atom carries the extra electron pair, giving it a negative formal charge. This situation commonly arises when a hydrocarbon is deprotonated, and the electrons from the C–H bond remain with carbon, producing a negative charge on carbon. A positively charged carbon would be a carbocation, not a carbanion; a neutral carbon with a lone pair describes a carbene; and a carbon radical has an unpaired electron, which is different from carrying a negative charge. So carbanions are best described as negatively charged species with a negative formal charge on carbon.