CHAPTER 2
CHLORINATED SOLVENT CHEMISTRY: STRUCTURES,
NOMENCLATURE AND PROPERTIES
David M. Cwiertny1 and Michelle M. Scherer2
1
University of California at Riverside, Riverside, CA 92521; 2The University of Iowa, Iowa
City, IA 52242
2.1 INTRODUCTION
This chapter summarizes the principles of chlorinated solvent remediation, provides over-
views of the biotic and abiotic reactions that can transform and detoxify these compounds, and
discusses the remediation challenges posed by the properties and behavior of these compounds
in the subsurface environment.
2.2 STRUCTURE AND NOMENCLATURE
Chlorinated solvents are organic compounds generally constructed of a simple hydrocar-
bon chain (typically one to three carbon atoms in length) to which at least one chlorine atom is
covalently bonded. For the current discussion, chlorinated solvents will be further divided into
three categories based upon common structural characteristics: chlorinated methanes, chlori-
nated ethanes and chlorinated ethenes. Examples from each solvent class are shown in
Figure 2.1. Additional information pertaining to the nomenclature of these chemical species
is provided in Table 2.1.
Chlorinated methanes represent the most structurally simple solvent class and consist of
a single carbon center (known as a methyl carbon) to which as many as four chlorine atoms
are covalently bonded. From the perspective of groundwater contamination, perhaps the
most well known chlorinated methane is carbon tetrachloride (CT). Also known by its
International Union of Pure and Applied Chemistry (IUPAC) name of tetrachloromethane,
CT consists of a fully chlorinated methyl carbon. By IUPAC conventions, the modifier of
“tetra” serves as an indicator of the number of chlorine atoms bound to the carbon center. For
chlorinated methanes other than CT, hydrogen atoms usually make up the remainder of the
substituents necessary to satisfy the methyl carbon’s bonding requirements. Named in a
similar fashion by IUPAC, the chlorinated methanes with a lower degree of halogenation are
trichloromethane (commonly referred to as chloroform [CF]), dichloromethane (DCM, more
commonly called methylene chloride [MC]) and chloromethane (CM, also referred to as
methyl chloride).
Chlorinated ethanes consist of two carbon centers joined by a single covalent bond.
Common groundwater pollutants from this class include 1,1,1-trichloroethane (1,1,1-TCA) and
1,2-dichloroethane. In regards to the nomenclature associated with chlorinated ethanes, a
similar convention to that used for chlorinated methanes is employed in which the prefix
attached to “chloroethane” indicates the total number of chlorine atoms on the solvent
molecule. Common acronyms for this class follow the pattern in which the first letter (or series
of letters) refers to the number of total halogen substituents (e.g., “T” for trichloro- or “Te” for
H.F. Stroo and C.H. Ward (eds.), In Situ Remediation of Chlorinated Solvent Plumes, 29
doi: 10.1007/978-1-4419-1401-9_2, # Springer Science+Business Media, LLC 2010
, 30 D.M. Cwiertny and M.M. Scherer
Cl Cl
C C
H Cl Cl Cl
H Cl
dichloromethane carbon tetrachloride
(DCM) (CT)
H Cl Cl H
H Cl
C C C C
Cl Cl
H Cl H H H Cl
1,1,1 - trichloroethane C C 1,1,2,2 - tetrachloroethane
(1,1,1-TCA) (1,1,2,2-TeCA)
Cl H
vinyl chloride
(VC)
H Cl Cl Cl
C C C C
Cl Cl Cl Cl
trichloroethene perchloroethene
(TCE) (PCE)
Figure 2.1. Chemical structures of some common chlorinated solvents.
tetrachloro-), the second letter refers to the halogen identity (e.g., “C” for chlorine) and the last
letter, in all cases “A”, refers to ethane.
In addition, the numbers preceding the name or abbreviation indicate the location of the
chlorine substituents on the two possible carbon centers. For example, 1,1,2,2-tetrachloroethane
(1,1,2,2-TeCA) possesses two chlorine atoms on each of its carbon centers, whereas the three
chlorine atoms of 1,1,1-TCA are all located on the same carbon. In certain instances, there can
be more than one way in which the same number of chlorine atoms distribute themselves on the
carbon centers, as is the case for 1,1,2-TCA and 1,1,1-TCA. These compounds, which share the
same chemical formula (C2H3Cl3) yet differ in the sequence in which their atoms are connected,
are referred to as structural isomers (Vollhardt and Schore, 1994).
Chlorinated ethenes (sometimes referred to as chlorinated ethylenes) also possess two
carbon centers, but unlike chlorinated ethanes, these carbon atoms are joined by a carbon-
carbon double bond known as a p-bond (pi-bond) system. Another important difference
between chlorinated ethanes and chlorinated ethenes is the maximum number of atoms
bound to the carbon centers in each case. The double-bonded carbon centers in chlorinated
ethenes can accommodate at most two halogen (or hydrogen) substituents, whereas the single-
bonded ethanes can accommodate three halogen (or hydrogen) substituents.
Examples of chlorinated ethenes that are important groundwater pollutants include tetra-
chloroethene, commonly referred to as perchloroethene (PCE), and trichloroethene (TCE).
Another chlorinated ethene of note is the monochlorinated species that is most commonly
referred to as vinyl chloride (VC). The nomenclature associated with the chlorinated ethenes
follows a similar convention to that used with the chlorinated methanes and ethanes
CHLORINATED SOLVENT CHEMISTRY: STRUCTURES,
NOMENCLATURE AND PROPERTIES
David M. Cwiertny1 and Michelle M. Scherer2
1
University of California at Riverside, Riverside, CA 92521; 2The University of Iowa, Iowa
City, IA 52242
2.1 INTRODUCTION
This chapter summarizes the principles of chlorinated solvent remediation, provides over-
views of the biotic and abiotic reactions that can transform and detoxify these compounds, and
discusses the remediation challenges posed by the properties and behavior of these compounds
in the subsurface environment.
2.2 STRUCTURE AND NOMENCLATURE
Chlorinated solvents are organic compounds generally constructed of a simple hydrocar-
bon chain (typically one to three carbon atoms in length) to which at least one chlorine atom is
covalently bonded. For the current discussion, chlorinated solvents will be further divided into
three categories based upon common structural characteristics: chlorinated methanes, chlori-
nated ethanes and chlorinated ethenes. Examples from each solvent class are shown in
Figure 2.1. Additional information pertaining to the nomenclature of these chemical species
is provided in Table 2.1.
Chlorinated methanes represent the most structurally simple solvent class and consist of
a single carbon center (known as a methyl carbon) to which as many as four chlorine atoms
are covalently bonded. From the perspective of groundwater contamination, perhaps the
most well known chlorinated methane is carbon tetrachloride (CT). Also known by its
International Union of Pure and Applied Chemistry (IUPAC) name of tetrachloromethane,
CT consists of a fully chlorinated methyl carbon. By IUPAC conventions, the modifier of
“tetra” serves as an indicator of the number of chlorine atoms bound to the carbon center. For
chlorinated methanes other than CT, hydrogen atoms usually make up the remainder of the
substituents necessary to satisfy the methyl carbon’s bonding requirements. Named in a
similar fashion by IUPAC, the chlorinated methanes with a lower degree of halogenation are
trichloromethane (commonly referred to as chloroform [CF]), dichloromethane (DCM, more
commonly called methylene chloride [MC]) and chloromethane (CM, also referred to as
methyl chloride).
Chlorinated ethanes consist of two carbon centers joined by a single covalent bond.
Common groundwater pollutants from this class include 1,1,1-trichloroethane (1,1,1-TCA) and
1,2-dichloroethane. In regards to the nomenclature associated with chlorinated ethanes, a
similar convention to that used for chlorinated methanes is employed in which the prefix
attached to “chloroethane” indicates the total number of chlorine atoms on the solvent
molecule. Common acronyms for this class follow the pattern in which the first letter (or series
of letters) refers to the number of total halogen substituents (e.g., “T” for trichloro- or “Te” for
H.F. Stroo and C.H. Ward (eds.), In Situ Remediation of Chlorinated Solvent Plumes, 29
doi: 10.1007/978-1-4419-1401-9_2, # Springer Science+Business Media, LLC 2010
, 30 D.M. Cwiertny and M.M. Scherer
Cl Cl
C C
H Cl Cl Cl
H Cl
dichloromethane carbon tetrachloride
(DCM) (CT)
H Cl Cl H
H Cl
C C C C
Cl Cl
H Cl H H H Cl
1,1,1 - trichloroethane C C 1,1,2,2 - tetrachloroethane
(1,1,1-TCA) (1,1,2,2-TeCA)
Cl H
vinyl chloride
(VC)
H Cl Cl Cl
C C C C
Cl Cl Cl Cl
trichloroethene perchloroethene
(TCE) (PCE)
Figure 2.1. Chemical structures of some common chlorinated solvents.
tetrachloro-), the second letter refers to the halogen identity (e.g., “C” for chlorine) and the last
letter, in all cases “A”, refers to ethane.
In addition, the numbers preceding the name or abbreviation indicate the location of the
chlorine substituents on the two possible carbon centers. For example, 1,1,2,2-tetrachloroethane
(1,1,2,2-TeCA) possesses two chlorine atoms on each of its carbon centers, whereas the three
chlorine atoms of 1,1,1-TCA are all located on the same carbon. In certain instances, there can
be more than one way in which the same number of chlorine atoms distribute themselves on the
carbon centers, as is the case for 1,1,2-TCA and 1,1,1-TCA. These compounds, which share the
same chemical formula (C2H3Cl3) yet differ in the sequence in which their atoms are connected,
are referred to as structural isomers (Vollhardt and Schore, 1994).
Chlorinated ethenes (sometimes referred to as chlorinated ethylenes) also possess two
carbon centers, but unlike chlorinated ethanes, these carbon atoms are joined by a carbon-
carbon double bond known as a p-bond (pi-bond) system. Another important difference
between chlorinated ethanes and chlorinated ethenes is the maximum number of atoms
bound to the carbon centers in each case. The double-bonded carbon centers in chlorinated
ethenes can accommodate at most two halogen (or hydrogen) substituents, whereas the single-
bonded ethanes can accommodate three halogen (or hydrogen) substituents.
Examples of chlorinated ethenes that are important groundwater pollutants include tetra-
chloroethene, commonly referred to as perchloroethene (PCE), and trichloroethene (TCE).
Another chlorinated ethene of note is the monochlorinated species that is most commonly
referred to as vinyl chloride (VC). The nomenclature associated with the chlorinated ethenes
follows a similar convention to that used with the chlorinated methanes and ethanes
