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This page explains the chemical structures of quaternary ammonium compounds (quats). For information on the health effects and uses of quats, see the Quaternary Ammonium Compounds (ADBAC/DDAC) Fact Sheet.

Quaternary ammonium compounds, also called quats, are chemicals made of two basic parts. The first part is a central nitrogen atom.1 The second part is made up of four clusters of atoms2 that are attached to the nitrogen atom (Figure 1). The U.S. Environmental Protection Agency (EPA) currently classifies quats into four different groups based on the structure of the four clusters attached to the central atom. The physical and chemical properties of the quats contribute to the behavior of the quat and how toxic it is. The EPA has identified specific compounds in each group to represent the rest of them when they do toxicity testing.

Some quats may have chlorine atoms attached to them. These are called chlorides, which means the chlorine atom borrows an electron from the nitrogen atom. The chlorine atom, with its borrowed electron, has a negative electrical charge. When the nitrogen atom gives up one of its electrons, it is called an ammonium ion. It has a positive electrical charge. Overall, the compound has no electrical charge because the positive and negative charges balance out. Compounds like these are salts.

Figure 1. Quaternary ammonium cation general structure. "R" is any cluster of atoms.

Group I Quats

Group I quats are called "didecyl dimethyl ammonium chloride", or DDAC for short. These are the simplest quats that have straight chains of carbon atoms attached to the nitrogen (Figure 2). "Didecyl" means that two of the clusters are chains of carbon atoms that are at least 10 atoms long. "Dimethyl" means that the other two clusters attached to the nitrogen atom are just a single carbon atom with hydrogen atoms attached.

Figure 2. General structure of Group I Quats: DDAC

Group II Quats

Group II quats are called "alkyl dimethyl benzyl ammonium chloride", or ADBAC for short. These have two clusters made up of a single carbon atom each. The third cluster is a long chain of carbon atoms attached to the nitrogen atom. The fourth cluster is in the form of a ring. The carbon atoms that make up the ring have only hydrogen atoms attached to them. That ring is called a "benzyl" ring3 (Figure 3). Another name for this basic structure is benzalkonium chloride. This is sometimes written as BAC for short. The EPA has combined 24 compounds with this basic structure under Group II quats.

  1. The atom is the smallest unit of matter that is composed of three subatomic particles: the proton, the neutron, and the electron. Protons and neutrons make up the nucleus of the atom, a dense and positively charged core, whereas the negatively charged electrons can be found around the nucleus in an electron cloud.
  2. Clusters are a group of atoms, molecules, or ions that adhere together under forces like those that bind the atoms.
  3. Benzyl features a benzene ring (C6H6) attached to a methylene group (βˆ’CH2βˆ’) group.

Figure 3. General structure of Group II Quats: ADBAC

Group III Quats

Group III quats are more complicated. They have two chlorine atoms stuck to the benzyl ring instead of just hydrogen atoms. These chlorine atoms are always in the same position on the ring. The EPA has allowed one particular chemical in the group to be used for all of the required toxicity testing for Group III quats.

Group IV Quats

The last group, Group IV quats, are even more complicated than Group III. Each compound in this group must undergo separate toxicity testing because these quats do not all behave in the same way. One Group IV quat's toxicity cannot predict another's.

How to Identify Quats

The names of chemicals give us hints about how they are built by describing their parts. However, there are variations in how chemists describe or name chemical compounds. There may be more than one name that describes the same compound. That's why chemists use tools like a Chemical Abstracts Service (CAS) Registry Number to identify compounds. CAS numbers are listed on Safety Data Sheets and sometimes pesticide labels. When the chemical name is long or complex, you can look up the CAS number to make sure you have the right compound. Table 1 below lists all the unique chemicals in Group 1 (DDAC) and Group II (ADBAC).

Table 1. List of chemicals included in Group I (DDAC) and Group II (ADBAC) quaternary ammonium compounds.* The U.S. EPA assigns a pesticide code number (PC Number) to pesticide active ingredients or mixes of active ingredients.
Group I Cluster - Didecyl dimethyl ammonium chloride (DDAC)
Chemical Name CAS Number(s) PC Number(s)
Didecyl dimethyl ammonium chloride 7173-51-5 69149
Dioctyl dimethyl ammonium chloride 5538-94-3 69166
Octyl decyl dimethyl ammonium chloride 32426-11-2 69165
Alkyl dimethyl ethyl ammonium bromide 84540-07-8 69146
Oxydiethylenebis (alkyl*) dimethyl ammonium chloride 68607-28-3 69173
Group II Cluster – Alkyl dimethyl benzyl ammonium chloride (ADBAC)
Chemical Name CAS Number(s) PC Number(s)
Alkyl dimethyl benzyl ammonium chloride 53516-76-0
Dialkyl methyl benzyl ammonium chloride 73049-75-9 69119
Alykyl dimethyl benzyl ammonium saccharinate 68989-01-5 69171
Alkyl dimethyl ethylbenzyl ammonium chloride 85409-23-0
n-alkyl dimethyl 1-naphtylmethyl ammonium chloride 53516-75-9 69112
Dodecyl benzyl trimethyl ammonium chloride 1330-85-4 69125
n-alkyl dimethyl dimethyl ammonium chloride N/A 169159
Diisobutylphenoxy ethyoxyethyl dimethyl benzyl ammonium chloride [Benzethonium Chloride] 121-54-0 69122
Methyl dodecyl benzyl tri methyl ammonium chloride - 80%
Methyl dodecyl xylene bis tri methyl ammonium chloride – 20%
1399-80-0 69129


  • Reregistration Eligibility Decision for Alkyl Dimethyl Benzyl Ammonium Chloride (ADBAC). August 2006. U.S Environmental Protection Agency.
  • Reregistration Eligibility Decision for Aliphatic Alkyl Quaternaries (DDAC) August 2006. U.S. Environmental Protection Agency.

Additional Resources:

If you have questions about this, or any pesticide-related topic, please call NPIC at 800-858-7378 (8:00am - 12:00pm PST), or email us at npic@ace.orst.edu.

Last updated May 04, 2023

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NPIC provides objective, science-based information about pesticides and pesticide-related topics to enable people to make informed decisions. NPIC is a cooperative agreement between Oregon State University and the U.S. Environmental Protection Agency (cooperative agreement #X8-83947901). The information in this publication does not in any way replace or supersede the restrictions, precautions, directions, or other information on the pesticide label or any other regulatory requirements, nor does it necessarily reflect the position of the U.S. EPA.