Quaternary ammonium: formal charge

Compounds containing a nitrogen atom with four attached groups also exist, but the nitrogen atom must carry a formal positive charge. Such compounds are called quaternary ammonium salts. 

Nitrogen compounds with four alkyl groups bonded to the nitrogen—thereby giving the nitrogen a positive formal charge—are called quaternary ammonium salts. Their names consist of the names of the alkyl groups in alphabetical order, followed by anunonium (all in one word), and then the name of the counterion as a separate word. 

Important derivatives of ammonia are the tetraalkyl ammonium salts. The cation in these salts has four organic groups attached to the nitrogen atom and is called a quaternary ammonium ion. In a quaternary ammonium ion, the nitrogen atom has a formal charge of -l-l. Two examples of such cations are shown in the margin. 

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