3 Compounds with four groups attached to nitrogen are also known, but the nitrogen atom must carry a positive Er charge. Such compounds are called quaternary ammonium salts R + R一N-RX 季铵 R A quaternary ammonium saltOrganic Chemistry Organic Chemistry Xiamen Xiamen University University „ Compounds with four groups attached to nitrogen are also known, but the nitrogen atom must carry a positive charge. Such compounds are called quaternary ammonium salts. R N R R R X A q uaternary am m onium salt 季铵盐