Transcript Metal Contaminants - environmentalgeochemistry

ENVIRONMENTAL GEOCHEMISTRY AT TEXAS A&M UNIVERSITY
Chemistry of Metals and Organics
Atoms & Molecules
Bruce Herbert
Geology & Geophysics
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Contaminant Chemistry
■ The dominant geochemical factor that determines the fate and transport of
contaminants is contaminant chemistry.
■ In this section we will describe the chemistry of metal and organic
contaminants in terms of their basic properties which control their reactivity,
toxicity, transport, and biodegradability.
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Which Chemicals are Important Contaminants?
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Contaminant Chemistry
In 1978 the Environmental Protection Agency (EPA) created a list of toxic pollutants
with wastewater effluent concentration limits and guidelines in 1978 as a result of a
lawsuit brought against the EPA by a number of environmental groups. This list
was called the priority pollutant list.
■ The pollutants on the list were the most common toxic compounds released
from point sources by industry in 21 categories.
■ The list contained 129 compounds
■ The 13 metals are defined as total metals, since metals can combine with
ligands to form thousands of different compounds in a typical
environmental sample.
Under the legislative authority granted to the U.S. Environmental Protection Agency (EPA)
under the Comprehensive Environmental Response, Compensation, and Liability Act of 1980
(CERCLA) and the Superfund Amendments and Reauthorization Act of 1986 (SARA), EPA
develops standardized analytical methods for the measurement of various pollutants in
environmental samples from known or suspected hazardous waste sites.
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Contaminant Chemistry
The Contract Laboratory Program (CLP) Target Compound and Target Analyte
Lists (TCL/TALs) were originally derived from the EPA Priority Pollutant List.
■ The list contains:
■ Volatile organics
■ Semivolatile organics
■ Pesticides/aroclors
■ Chlorinated Dibenzo-p-dioxins / Chlorinated Dibenzofurans (CDDs /
CDFs)
■ Metals and Cyanide
■ The list is based on advances in analytical methods, evaluation of method
performance data, and the needs of the Superfund program.
See http://www.epa.gov/superfund/programs/clp/target.htm
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The Chemistry of Metals and other Inorganic
Contaminants
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Which metals are the most toxic - make a list.
Why?
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Contaminant Chemistry and Electronic Configuration
■ Classification of contaminants are based on measures of their reactivity. In
general, reactivity is controlled by an atom's electronic configuration
■ Electronic configuration: distribution of electrons in an atom's orbitals.
■ Electronic orbitals: probability functions of the electron density around a
nucleus.
Figure 2.1 The electron density around a
positive nucleus. Circle shows 90%-99%
probability region for a 1s orbital.
Taken from Gray. 1973. Chemical Bonds: An Introduction to Atomic and
Molecular Structure. Benjamin/Cummings Publ., Menlo Park. p. 21.
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Contaminant Chemistry and Electronic Configuration
■ The distribution of electrons, and the type of orbital, around a nucleus is
describe with quantum numbers.
■ Electrons have energy levels or shells designated by "n", the principle quantum
number. The energy levels determine the effective volume of an electron
orbital, the volume increases as n increases.
■ The orbital shape quantum number, "l" describes the type of orbital.
There are (n-1) orbital-shape quantum numbers.
■ The 0, 1, 2, and 3 values of l are often designated as s, p, d, and f orbitals
■ The orbital-orientation quantum number, ml, describes the shape of the s,
p, d, or f orbitals. It can have values equal to -l, -l+1,..0,..l-1, l.
■ The spin quantum number, ms, describes the electron spin, which can be
one of two directions.
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Contaminant Chemistry and Electronic Configuration
Table 2.2 Number of electrons needed to fill different orbitals described by
different quantum numbers.
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Contaminant Chemistry and Electronic Configuration
Electron orbitals for different quantum
numbers.
Taken from Gray. 1973. Chemical
Bonds: An Introduction to Atomic
and Molecular Structure.
Benjamin/Cummings Publ., Menlo
Park. p. 22.
l = 0
n = 1
n = 2
n = 3
l = 1
l = 2
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Contaminant Chemistry and Electronic
Configuration
■ Electrons are filled in sequence of increasing relative energies of the
orbitals (Figure 2.3). No two electrons can have the same quantum
numbers. This is the Pauli Exclusion Principle.
d
Increasing
Energy
p
s
f
d
f
d
p
s
d
p
s
p
s
p
s
s
n=
1
2
3
4
5
6
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Contaminant Chemistry and Electronic
Configuration
Pr incip al
Quantum
Number
n
1
The
ns
1
Base
2
3
4
5
6
7
3
Table
Subshells being complet ed
2
H
Periodic
Nonmet als
np
He
Cat ions
He
4
Li
11
Na
19
K
37
Rb
55
Cs
87
Fr
6
5
Be
Mg
Ca
38
Sr
56
Ba
88
Ra
B
Transit ion Met als
( n- 1 ) d
12
20
21
Sc
39
Y
57
La
89
Ac
2
22
Ti
40
Zr
72
23
V
41
Nb
73
Hf
Ta
104
105
Rf
24
Cr
42
Mo
25
Mn
43
26
Fe
44
27
Co
45
13
Al
28
Ni
46
29
Cu
47
30
Zn
48
Tc
Ru
Rh
Pd
Ag
Cd
Re
Os
Ir
Pt
Au
Hg
74
W
31
Ga
49
In
81
106
Tl
7
C
14
Si
32
Ge
50
Sn
82
Pb
8
15
As
51
Sb
83
Bi
Post t ransit ion
Ha
16
F
17
S
P
33
10
9
O
N
34
Se
52
Cl
35
84
Po
Ar
36
Br
53
Kr
54
I
Te
Ne
18
85
At
Xe
86
Rn
Met als
( n- 2 ) f
Lant hanide
Series
Act nides
Series
58
Ce
90
Th
59
Pr
91
Pa
60
Nd
92
U
61
Pm
93
Np
62
Sm
94
Pu
63
Eu
95
Am
64
Gd
96
Cm
65
Tb
97
Bk
66
Dy
98
Cf
67
Ho
99
Es
68
Er
100
Fm
69
Tm
101
Md
70
Yb
102
No
71
Lu
103
Lr
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Electronic Configuration and Metal Chemistry
The electronic configuration, especially that of the valence electrons,
determines chemical properties and reactivity.
■ The base cations have valence electrons in s and p orbitals. These
elements lose electrons to achieve a noble gas configuration.
■ The transition metals, either as a neutral atom or an ion, have valence
electrons in the d and f orbitals. These elements lose electrons.
■ The nonmetals have valence electrons in s and p orbitals. These
elements gain electrons to achieve a noble gas configuration.
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Atomic Properties
■ The effective atomic radii, R, of an atom is defined as one half of the distance
between two nuclei of the element that are held together by covalent bonds.
■ The atomic radii increases as you move down the periodic table and
decreases across a row of the periodic table
■ The radii is used to calculate the charge-to-radius ratio (Z/R) or ionic
potential (IP), which is an important factor in determining the polarizability
of an atom.
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Atomic Properties
■ The first ionization energy, I1, of an atom is defined as the energy required to
remove an electron from a gaseous atom.
■ The ionization potential decreases as you move down the periodic table
and increases across a row.
■ The electron affinity (ea) of an atom is defined as the energy change
accompanying the addition of one electron to a neutral gaseous atom.
■ The electron affinity decreases as you move down the periodic table and
increases across a row.
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Atomic Properties
■ The electronegativity (EN) of an atom is the relative ability of an atom to
attract electrons to itself in a chemical bond
■ Electronegativity qualitatively describes the sharing (covalent character)
of electrons between 2 different atoms.
■ High electronegativities indicates electrons will be transferred in a
chemical bond (ionic).
■ Polarization: the ease to which an electron cloud is deformable
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Atomic Properties
Increasing
Radii
Decreasing IP
and EA1
The Periodic Table
Effective Atomic Radii
and Ionization Energies
2
H
He
Base Cations
3
4
Li
11
2
Nonmetals
6
5
Be
12
7
C
B
8
He
10
9
O
N
F
13
14
15
16
17
81
82
83
84
85
Ne
18
Transition Metals
Increasing
Cl
Al
Si
P
S
Ar
Increasing
Electronegativity
20
27
29
30
34
35
36
19
21
22
23
24
25
26
28
31
32
33
IP and EA
Ca Sc
Ti
Cu Zn
Kr
K
V
Cr Mn Fe Co Ni
Ga Ge As Se Br
Decreasing
37
38
39
44
46
52
40
41
42
43
45
47
48
49
50
51
53
54
Atomic RAdii
I
Rb
Zr
Nb Mo Tc Ru Rh Pd Ag Cd In
Sn Sb Te
Xe
Sr
Y
Na
55
Cs
87
Fr
Mg
56
Ba
88
Ra
Lanthanide Series
Actnides Series
57
La
89
Ac
72
73
74
Hf
Ta
104
105
Rf
58
Ce
90
Th
W
Re
Os
Ir
Pt
Au
Hg
106
Pr
91
Pa
60
Nd
92
U
Pb
Bi
Po
86
At
Rn
Posttransition Metals
Ha
59
Tl
61
Pm
93
Np
62
Sm
94
Pu
63
Eu
95
64
Gd
96
Am Cm
65
Tb
97
Bk
66
Dy
98
Cf
67
Ho
99
Es
68
Er
100
Fm
69
Tm
101
Md
70
Yb
102
No
71
Lu
103
Lr
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Hard and Soft Acids and Bases
■ Atoms can be classified as either "hard" or "soft" Lewis acids or bases (HSAB)
based on their properties. These are relative terms.
■ Lewis acids and bases
■ Lewis acids are any species that employs an empty electronic orbital to
initiate a complexation reaction. Lewis acids accept electrons.
■ Lewis bases are species that employs a doubly occupied electronic orbital
to initiate a complexation reaction. Lewis bases donate electrons.
■ Lewis acids and bases can be neutral molecules, ions, or neutral or charged
macromolecules.
■ Complexation is the reaction between Lewis acids and bases. It is one of
the basic chemical reactions in solution and during sorption.
■ Compare the definition of a Lewis acid or base to that of a Bronsted acid or
base. A Bronsted acid donates protons (H+). A Bronsted base accepts protons
(H+)
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Hard and Soft Acids and Bases
■ Hard Lewis acids and bases are species, respectively, that are small, high
oxidation state, slightly polarizable species with high electronegativities. Ions
typically have electron configurations of an inert gas. Hard Lewis bases tend
not to undergo oxidization.
■ Examples: cations of H, Na, K, Ca, Mg, Al3+, and Fe3+.
■ Soft Lewis acids and bases are species that are large, more polarizable species
with low electronegativities. Ions typically have electron configurations with 10
or 12 valence electrons (filled d orbitals). Soft Lewis bases tend to undergo
oxidization easily.
■ Examples: Cd2+, Cu+, Hg2+.
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Hard and Soft Acids and Bases
■ HSAB can be used to organize complexation reactions because hard acids
typically complex with hard bases, and vice-versa under similar conditions of
acidity.
■ Many of the bivalent trace metals (transition metals) are borderline.
■ Generally, those ionic species with high electronegativities are hard and
those with low electronegativities are soft.
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Hard and Soft Acids and Bases
Several parameters have been used to help classify atoms as either
"hard" or "soft" acids or bases (HSAB).
The ionic potential is the charge to radius ratio.
valence
IP 
radius(nm)
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Hard and Soft Acids and Bases
The Misono softness parameter is an indication of covalent bonding
potential, and is defined as:
IzR
Y  10
Z  Iz1
■ R is the ionic radius (nm), Z is the valence, and Iz is the ionization potential of
the ion with a valence of Z.
■ For Y < 0.25 nm, metal ions form ionic bonds and are hard acids
■ For Y > 0.32 nm, metal ions form covalent bonds and are soft acids
■ For 0.25<Y<0.32, metal ions are borderline whose tendency to form
covalent bonds depends on solvent, stereochemical, and electronic
configurational factors
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Significance of the HSAB Concept
HSAB concept can be used to predict complexation
■ Complexes form when an ions acts as a central group to
attract and form a close association with other atoms or
molecules
■ The associated ions or molecules are ligands
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Significance of the HSAB Concept
■ The principles of HSAB can be used to predict the speciation of transition
metals in subsurface systems as well as their relative toxicity.
■ The speciation of transition metals is more affect by the presence of natural
organic matter than the speciation of the base cations.
■ Likewise, changes in the concentrations of Cl-, and S2- in subsurface waters will
also strongly affect the speciation of trace metals.
■ Finally, metal toxicity is often due to the complexation of a trace metal with a
biologically important molecule in an organisms. Because these organic
molecules are soft, the HSAB would predict that toxicity is directly related to
the softness of a trace metal.
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Representative Metal Toxicity Sequences
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Organic Molecules
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Aflatoxin
http://www.niehs.nih.gov/health/impacts/aflatoxin/index.cfm
http://www.icrisat.org/aflatoxin/aflatoxin.asp
http://www.ces.ncsu.edu/depts/pp/notes/Corn/corn001.htm
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Aflatoxin b1 3d structure
http://en.wikipedia.org/wiki/File:Aflatoxin_b1_3d_structure.png
Aflatoxin Sorption to Clays: Why?
http://en.engormix.com/MAmycotoxins/articles/understanding-adsorptioncharacteristics-yeast-t218/p0.htm
http://wgharris.ifas.ufl.edu/SEED/COMPONENTS.HTM
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Structure-Activity Relationships
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Quantitative Structure-Activity Relationships (QSARs)
■ We are interested in the environmental fate, toxicity, and contaminating potential of
over 70,000 natural and man-made organics chemicals.
■ Obviously, we can not memorize the chemical properties of such a large number of
organics, therefore structure-activity relationships have been developed.
■ Structure-activity relationships are quantitative relationships between the chemical
structure of an organic and its chemical and physical properties.
■ ECOSAR (Ecological Structure Activity Relationships) is a personal computer software
program that is used to estimate the toxicity of chemicals used in industry and
discharged into water. The program predicts the toxicity of industrial chemicals to
aquatic organisms such as fish, invertebrates, and algae by using Structure Activity
Relationships (SARs). The program estimates a chemical's acute (short-term) toxicity
and, when available, chronic (long-term or delayed) toxicity.
http://www.epa.gov/opptintr/newchems/21ecosar.htm
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Structure-Activity Relationships
■ We can predict the properties of organic contaminants based on
their structure.
■ The two complex structures shown below are pesticides.
Aldicarb is on the left and aldrin is on the right.
CH3
CH3
S
C
CH3
Cl
O
CH
NOCNHCH 3
Cl
CCl 2
CH2
Cl
Cl
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Chemical Bonds and Organic Contaminant Structure
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Chemical Bonds
■ There are several types of bonds which can form between
atoms, or between molecules.
■ Chemical bonds are forces of attraction between two atoms
or molecules.
■ Bonds hold molecules together, control the interaction of
metals with ligands, or control the interaction between
solutes and solvents.
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Covalent Bonds
■ Reactivity of organic compounds is related to the strength of chemical bonds
between the atoms in an organic molecule.
■ Almost all atoms within an organic molecule are bound together with
covalent bonds.
■ Covalent bonds form when two atoms share electrons that exist in similar
orbitals.
■ Pure covalent bonds: electrons are shared equally in the bond
■ Molecules such as Cl2, H2, and O2
■ Polar covalent bonds form when electrons are share unequally
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Chemical Bonds and Organic Contaminant Structure
The overall structure of organic contaminants, or their spatial arrangement
of atoms, is determined by their structural backbone.
■ The structural backbone is generally composed of carbon atoms
(though N, S, and O can also compose part of the backbone)
covalently bonded together to give the overall shape to the molecule.
■ Covalent bonds are formed when electrons are shared between
atoms in order to fill their valence shell. Each covalent bond shares
two electrons.
CH3
CH3
S
C
O
CH
NOCNHCH 3
CH3
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Organic Contaminant Structure
■ Single, double, and triple covalent carbon bonds are possible in the
structural backbone.
■ Saturated hydrocarbons are compounds formed with single bonds in
their structure.
■ Unsaturated hydrocarbons are compounds with double and triple bonds .
■
Single carbon bonds:
Alkanes(CnH2n+2)
■
Double carbon bonds:
Alkenes(CnH2n)
■
Triple carbon bonds:
Alkynes(CnH2n-2)
CH3  (CH2 )6  CH3
n  octane
CH2  (CH2 )6  CH3
1 octene
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Organic Contaminant Structure
■ Unsaturated organics
backbones:
CH3
CH3 - (CH2)6 - CH3
■ straight chain
■ branched chain
■ cyclic compounds
■ Saturated organics
backbones:
Octane
CH2 = (CH2)6 -CH3
1-Octene
CH3
CH3
CH3 - C - CH2 - CH
CH3
Isooctance
CH3
CH2 = (CH2)6 = CH2
1,7 Octadiene
CH3
■ aromatic compounds.
Cyclopentane
Methyl-cyclohexane
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Covalent Bond Energies and Bond Lengths
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Electronegativity and Bond Polarity
■ Differences in electronegativity: electron cloud around a bond is not shared
equally.
■ The bond then has a partial ionic character, and is termed a polar covalent
bond. Polarization is important in determining the organic compound's
■ Solubility in polar solvents
■ Directing the course of chemical reactions
■ Polarity:
■ A molecule is polar if its electron cloud is not evenly distributed around
the nuclei.
■ This imparts a net charge to different parts of the molecule.
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Polarity of Water
■ Electronegativity differences between O and H create polar O-H
bonds
■ Water is one of the most polar solvents known.
Solvent
Hexane
Toluene
Methy lene
Chloride
Methano l
Wate r
Polari ty Index
0.1
2.4
3.1
5.1
10.2
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Electronegativity and Dipole Moment
■ Dipole moment: sum of all
bond dipoles.
■ Dipole moments are
given in arbitrary units
called Debye units.
■ The arrow points to the
negative part of the
molecule.
CH3
CH3
F
NO2
NO2
0.43D
3.93D
4.39D
O OH
C
O OH
C
O OH
C
H
CH3
F
4.14
4.20
4.38
Debye Units
pK a at 25C
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Electronegativity of Functional Groups and Bond Polarity
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Ionic Bonds
■ Ionic bonds: electrons are transferred between two atoms and the
atoms are then attracted by electrostatic forces.
■ Ionic bonds are found in the alkali metal-halides such as NaCl.
■ The electrostatic energy of an ion pair, Mz+Xz-, is described by
Coulomb's Law
q q
E
4r
Z  Z  e2
E
4r
E:
Q:
R:
Z:
E:
E:
energy (Jmol-1)
charge (Coulombs (C))
distance of separation (m)
ionic charge (none)
electronic charge (1.6 x 10-19 C)
permittivity (dielectric constant) (C2m-1J-1
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Other Intermolecular Forces
■ Intramolecular forces are bonds that hold a molecule together.
■ Intramolecular forces are dominated by strong covalent and ionic
interactions
■ Other, weaker bonds may be important in different situations
■ There are several types of weaker, intermolecular bonds which form between
molecules.
■ These bonds are the forces which
■ hold some solids together,
■ allow a molecule to sorb to a mineral surface
■ determine the interaction between a solute and a solvent
■ may be important in giving macromolecules shape.
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Other Intermolecular Forces
■ Intramolecular forces are bonds that hold a molecule together.
■ Intramolecular forces are dominated by strong covalent and ionic
interactions
■ Other, weaker bonds may be important in different situations
■ There are several types of weaker, intermolecular bonds which form between
molecules.
■ These bonds are the forces which
■ hold some solids together,
■ allow a molecule to sorb to a mineral surface
■ determine the interaction between a solute and a solvent
■ may be important in giving macromolecules shape.
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Hydrogen Bonding and Other Dipole Interactions
■ Weak, intermolecular bonds include van der Walls forces, dipole-dipole interactions
including hydrogen bonds, ion-dipole bonds, and pi () bonding.
■ H bonding is the result of the polarization of a bond formed between H and O, F, or N.
■ H bonding between solvent and solute greatly increases solubility
■ H bonding causes lack of ideality in ideal gas and solution laws
■ Intramolecular H bonding changes reactivity compared to compound without
intramolecular bonding
■ H bonding plays a significant role in the 3-D conformation of large macromolecules
such as proteins and other biomolecules
Bond
van der Waals
dipole-dipole
H-bond ing
ion-dipole
pi bonds
Bond Energy
1-2 kca l mole-1
<2 kca l mole-1
2-10 kca l mole-1
~5 kca l mole-1
~5 kca l mole-1
O  H     : X 
       
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Organic Contaminant Structure
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Organic Contaminant Structure: Structural Backbone
■ Aliphatic compounds do not have delocalized electrons, though they can
have double bonds.
■ Compounds that have delocalized electrons form aromatic molecules,
■ Delocalization occurs in ring structures where pi bonds can form
between electrons in adjacent p orbitals.
■ Multiple aromatic rings for polycyclic aromatic hydrocarbons.
■ Because of delocalization, benzene and other aromatics experience
increased resonance energy (stabilization) which leads to stability and
long term persistence.
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Aliphatic and Aromatic Organics
ALIPHATICS
CH3 - (CH2)6 - CH3
Octane
CH2 = (CH2)6 -CH3
1-Octene
Cyclopentane
AROMATICS
CH3
Biphenyl
Methylbenzene (toluene)
Pyrene
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Isomers
■ If two compounds have the same molecular formula but different
structures, they are called isomers.
■ Structure determines reactivity: half-life of hydrolysis at 25° C is 1 yr for
isomer I and III, 1 month for compound II, and 30 s for compound IV.
Butyl chloride isomers
CH3(CH2)3Cl CH3CH2CH(Cl)CH3 (CH3)2CHCH2Cl (CH3)3CCl
Cl
Cl
Cl
I
II
Cl
III
IV
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Organic Contaminant Structure: Functional Groups
■ To the structural backbone are attached various atoms or groups of atoms,
these are called functional groups .
■ Position of functional groups on structural backbone are designated by
number.
■ Position for two functional groups on aromatics can also be designated
using ortho, meta, or para designations.
A
B
6
5
3
A
A
6
2
B
5
4
4
ort ho
or 1 ,2
m et a
or 1 ,3
6
2
5
3
B
para
or 1 ,4
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Chemistry of Functional Groups: Alkyl Halides
■ Properties (R-X where X is F, Cl, or Br)
■ dipole moment, higher e- density around the halide
■ generally compounds are insoluble in water
■ Some compounds have high vapor pressure [inversely correlated
with molecular weight]
Cl
Cl
Cl
C
Cl
C
Cl
H
p,p' DDT
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Chemistry of Functional Groups: Alcohols and Ethers
■ Properties (R-OH and R-O-R’)
■ dipole moment: higher e- density around the oxygen
■ generally compounds are soluble in water, solubility is
inversely correlated with molecular weight
■ low vapor pressure
■ H bonding potential, electrostatic bonding at high pH when
alcohol dissociates
■ Alcohols are weak acids with pKa’s above 8.
H H
H C C OH
H H
Et hanol
CH3
CH3 O C CH3
CH3
Met hyl-t ert
But yl Et her
OH
Phenol
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Chemistry of Functional Groups: Acids & Esters
■ Properties (R-COOH, R-(C=O)-O-R’)
■ dipole moment, higher e- density around the oxygen
■ generally compounds are soluble in water, solubility is inversely
correlated with molecular weight
■ H bonding potential; can form dipole-dipole bonds; electrostatic
interactions if COOH is deprotonated (anion exchange, ligand bonding
with metals
■ Weak Bronstead acid (H+ donating) and weak Lewis acid (e- accepting
group) in acid solution
OCH 2 COOH
Cl
COOCH 3
COOCH 3
Dimethyl phthalate
Cl
2,4-(Dichlorophenoxy) acetic acid
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Chemistry of Functional Groups: Aldehydes & Ketones
■ Properties (R-(C=O)-R’)
■ dipole moment, higher e- density around the oxygen
■ generally compounds are soluble in water, solubility is
inversely correlated with molecular weight
■ H bonding potential
■ weak lewis base (e- donating group) in acid solution
H
H
C
H
O
C
H
Acetylaldehyde
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Chemistry of Functional Groups: Amides
■ Properties R-(C=O)-NH2
■ dipole moment, higher e- density around the oxygen and
nitrogen
■ generally compounds are soluble in water, solubility is
inversely correlated with molecular weight
■ H bonding potential, may also form electrostatic bonds if
amide group protonates.
H2 C
H
O
C
C
NH2
Acrylamide
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Chemistry of Functional Groups: Nitriles
■ Properties (R-CN)
■ dipole moment, higher e- density around the nitrogen
■ generally compounds are soluble in water, solubility is
inversely correlated with molecular weight
■ H bonding potential
H
H2 C
C
C
N
Acrylonitrile
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Chemistry of Functional Groups: Amines
■ Properties (R-NH2; R2NH; R3N)
■ dipole moment, higher e- density around the nitrogen
■ generally compounds are soluble in water, solubility is
inversely correlated with molecular weight
■ H bonding potential, may also form electrostatic bonds if
amine group protonates.
■ Amines are weak bases, the amine group will protonate at
low pH
NH 2
Aniline
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Chemistry of Functional Groups: Nitro
■ Properties (R-NO2)
■ dipole moment, higher e- density around the oxygens
■ generally compounds are soluble in water, solubility is
inversely correlated with molecular weight
■ H bonding potential
OH
NO 2
NO 2
2,4 Dinitrophenol
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Structure-Activity Relationships of Pesticides
Notes: aqueous solubility is in umoles/L; Units for Kd are (umoles/kg adsorbed)/(umoles/L)
Low pH refers to pH=4, high pH>6.
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