Chem-805
Chem-805
Identification of organic and
Identification of organic and
inorganic compounds by
inorganic compounds by
spectroscopy
spectroscopy
Mass
Spectrometry
NMR
Infrared
Infrared
Chem-805
Chem-805
Identification of organic and
Identification of organic and
inorganic compounds by
inorganic compounds by
spectroscopy
spectroscopy
Mass
Spectrometry
NMR
Infrared
Infrared
Infrared
Infrared
10,000 cm
10,000 cm
-1
-1
to 100 cm
to 100 cm
-1
-1
Converted in Vibrational energy in molecules
Converted in Vibrational energy in molecules
Vibrational Spectra appears as bands instead of sharp
lines => as it is accompanied by a number of rotational
changes
Wave Number
=>
(cm
-1
) => proportional to energy
Depends on:
•Relative masses of atoms
•Force constant of bonds
•Geometry of atoms
Older system uses the wavelenght
(m => 10
-6
m)
cm
-1
= 10
4
/ m
The Units:
The Units:
The frequency (s
-1
) => # vibrations per second
For molecular vibrations, this number is very large (10
13
s
-1
)
=> inconvenient
More convenient : Wavenumber
=
c
(
Frequency
/
Velocity
)
e.g.
= 3 * 10
= 3 * 10
13
13
s
s
-1
-1
=
s
3 * 10
10
cm s
-1
= 1000 cm
= 1000 cm
-1
-1
Wave Length :
1
=
Intensity:
Intensity:
Transmittance (T
T
) or %T
%T
T
T
=
I
I
0
Absorbance (A
A
)
A
A
= log I
I
0
Intensity in IR
Intensity in IR
IR
IR
: Plot of %IR
%IR
that passes through a sample (transmittance
transmittance
)
vs Wavelenght
Wavelenght
Infrared
Infrared
• Position, Intensity and Shape of bands
gives clues on Structure of molecules
• Modern IR uses Michelson Interferometer
=>
involves computer, and Fourier Transform
Sampling
Sampling
=> plates, polished windows, Films …
Must be transparent in IR
NaCl, KCl : Cheap, easy to polish
NaCl, KCl : Cheap, easy to polish
NaCl
NaCl
transparent to 4000 - 650 cm
4000 - 650 cm
-1
-1
KCl
KCl
transparent to 4000 - 500 cm
4000 - 500 cm
-1
-1
KBr
KBr
transparent to 400 cm
400 cm
-1
-1
Infrared: Low frequency spectra
Infrared: Low frequency spectra
of window materials
of window materials
Bond length and strength
Bond length and strength
vs
vs
Stretching frequency
Stretching frequency
Bond
C-H
=C-H
-C-H
Length
1.08
1.10
1.12
Strenght
506 kJ
444 kJ
422 kJ
IR freq.
3300 cm
-1
3100 cm
-1
2900 cm
-1
Introduction
Introduction
IR is one of the first technique inorganic chemists used
(since 1940)
Molecular Vibration
Molecular Vibration
Newton’s law of motion is used classically to calculate
force constantr
r
e
F
F
F
F
The basic picture : atoms
(mass) are connected with
bonding electrons. R
e
is the
equilibrium distance and F
F
:
force to restore equilibrium
F(x) = -
k
x
where X is displacement from equilibrium
=
=
1
1
2
2
√
k
k
i
i
i
i
Where
Where k
k
i
i
is the force constant and
is the force constant and
i
i
is reduce mass of a particular motion
is reduce mass of a particular motion
Because the energy is quantized: E =
Because the energy is quantized: E =
h
h
i
i
Introduction
Introduction
Displacement of atoms during vibration lead to
Displacement of atoms during vibration lead to
distortion of electrival charge distribution of the
distortion of electrival charge distribution of the
molecule which can be resolve in dipole,
molecule which can be resolve in dipole,
quadrupole, octopole …. In various directions
quadrupole, octopole …. In various directions
=> Molecular vibration lead to oscillation of
=> Molecular vibration lead to oscillation of
electric charge governed by vibration frequencies
electric charge governed by vibration frequencies
of the system
of the system
Oscillating molecular dipole can interact directly
Oscillating molecular dipole can interact directly
with oscillating electric vector of electromagnetic
with oscillating electric vector of electromagnetic
radiation of the same frequency
radiation of the same frequency
h
h
=
= h
h
Vibrations are in the range
Vibrations are in the range
10
10
11
11
to 10
to 10
13
13
Hz
Hz
=>
=>
30 - 3,000 cm
30 - 3,000 cm
-1
-1
Introduction: Symmetry
Introduction: Symmetry
selection rule
selection rule
Stretching homonuclear diatomic molecule like
Stretching homonuclear diatomic molecule like N
N
2
2
does not generate oscillating dipole
does not generate oscillating dipole
Direct interaction with oscillating electronic Dipole is not
Direct interaction with oscillating electronic Dipole is not
possible
possible
inactive in IR
inactive in IR
There is no place here to treat fundamentals of symmetry
There is no place here to treat fundamentals of symmetry
In principle, the symmetry of a vibration need to be determined
In principle, the symmetry of a vibration need to be determined
Calculating stretching frequencies
Calculating stretching frequencies
Hooke’s law :
Hooke’s law :
=
=
1
1
2
2
c
c
k
k
: Frequency in cm
: Frequency in cm
-1
-1
c : Velocity of light => 3 * 10
c : Velocity of light => 3 * 10
10
10
cm/s
cm/s
k
k
: Force constant => dynes /cm
: Force constant => dynes /cm
masses of atoms in grams
masses of atoms in grams
m
m
1
1
m
m
2
2
m
m
1
1
+ m
+ m
2
2
M
M
1
1
M
M
2
2
M
M
1
1
+ M
+ M
2
2
(6.02 * 10
(6.02 * 10
23
23
)
)
=
=
4.12
4.12
k
k
C
C
-
-
C
C k
k
= 5* 10
= 5* 10
5
5
dynes/cm
dynes/cm
C
C
=C
=C k
k
= 10* 10
= 10* 10
5
5
dynes/cm
dynes/cm
C
C
C
C k
k
= 15* 10
= 15* 10
5
5
dynes/cm
dynes/cm
Calculating stretching frequencies
Calculating stretching frequencies
C
C
=C
=C K = 10* 10
K = 10* 10
5
5
dynes/cm
dynes/cm
=
=
4.12
4.12
K
K
M
M
1
1
M
M
2
2
M
M
1
1
+ M
+ M
2
2
(12)(12)
(12)(12)
12 + 12
12 + 12
=
=
4.12
4.12
10* 10
10* 10
5
5
= 1682 cm
= 1682 cm
-1
-1
Experimental
Experimental
1650 cm
1650 cm
-1
-1
C
C
—H
—H K = 5* 10
K = 5* 10
5
5
dynes/cm
dynes/cm
=
=
4.12
4.12
5* 10
5* 10
5
5
= 3032 cm
= 3032 cm
-1
-1
M
M
1
1
M
M
2
2
M
M
1
1
+ M
+ M
2
2
(12)(1)
(12)(1)
12 + 1
12 + 1
Experimental
Experimental
3000 cm
3000 cm
-1
-1
C
C
—D
—D K = 5* 10
K = 5* 10
5
5
dynes/cm
dynes/cm
=
=
4.12
4.12
5* 10
5* 10
5
5
= 2228 cm
= 2228 cm
-1
-1
M
M
1
1
M
M
2
2
M
M
1
1
+ M
+ M
2
2
(12)(2)
(12)(2)
12 + 2
12 + 2
Experimental
Experimental
2206 cm
2206 cm
-1
-1
Vibration
Vibration
s
s
www.cem.msu.edu/~reusch/Virtual/Text/Spectrpy/InfraRed/infrared.htm
Modes of vibration
Modes of vibration
C
C
—H
—H
Stretching
Stretching
Bending
Bending
C
C
O
O
H
H
H
H
Symmetrical
Symmetrical
2853 cm
2853 cm
-1
-1
H
H
Asymmetrical
Asymmetrical
2926 cm
2926 cm
-1
-1
H
H
H
H
Scissoring
Scissoring
1450 cm
1450 cm
-1
-1
Rocking
Rocking
720 cm
720 cm
-1
-1
H
H
H
H
Wagging
Wagging
1350 cm
1350 cm
-1
-1
Twisting
Twisting
1250 cm
1250 cm
-1
-1
Stretching
Stretching
frequency
frequency
Bending
Bending
frequency
frequency
Vibration
Vibration
s
s
www.cem.msu.edu/~reusch/Virtual/Text/Spectrpy/InfraRed/infrared.htm
General trends:
General trends:
•
Stretching frequencies
Stretching frequencies
are higher than
are higher than bending
bending
frequencies
frequencies
(it is easier to bend a bond than stretching or compresing them)
(it is easier to bend a bond than stretching or compresing them)
•
Bond involving Hydrogen are higher in freq. than with
Bond involving Hydrogen are higher in freq. than with
heavier atoms
heavier atoms
•
Triple bond
Triple bond
have higher freq than
have higher freq than double bond
double bond
which
which
has higher freq than
has higher freq than single bond
single bond
Structural Information from
Structural Information from
Vibration Spectra
Vibration Spectra
•
Spectrum can be treated as finger print to
Spectrum can be treated as finger print to
recognize the product of a reaction as a known
recognize the product of a reaction as a known
compound. (require access to a file of standard
compound. (require access to a file of standard
spectra)
spectra)
•
At another extreme , different bands observed can
At another extreme , different bands observed can
be used to deduce the symmetry of the molecule
be used to deduce the symmetry of the molecule
and force constants corresponding to vibrations.
and force constants corresponding to vibrations.
•
At intermediate levels, deductions may be drawn
At intermediate levels, deductions may be drawn
about the presence/absence of specific groups
about the presence/absence of specific groups
The symmetry of a molecule determines the number of bands expected
The symmetry of a molecule determines the number of bands expected
Number of bands can be used to decide on symmetry of a molecule
Number of bands can be used to decide on symmetry of a molecule
Th
Th
e
e
task of assignment is complicated by presence of low
task of assignment is complicated by presence of low
intensity bands and presence of forbidden overtone and
intensity bands and presence of forbidden overtone and
combination bands.
combination bands.
There are different levels at which information from IR can
There are different levels at which information from IR can
be analyzed to allow identification of samples:
be analyzed to allow identification of samples:
Methods of analyzing an IR
Methods of analyzing an IR
spectrum
spectrum
The effect of
The effect of isotopic substitution
isotopic substitution
on the
on the
observed spectrum
observed spectrum
Can give valuable information about the atoms
Can give valuable information about the atoms
involved in a particular vibration
involved in a particular vibration
1.
1.
Comparison with standard spectra : traditional
Comparison with standard spectra : traditional
approach
approach
2.
2.
Detection and Identification of impurities
Detection and Identification of impurities
if the compound have been characterized before, any
bands that are not found in the pure sample can be
assigned to the impurity
(provided that the 2 spectrum are recorded with identical
conditions: Phase, Temperature, Concentration)
3.
3.
Quantitative Analysis of mixture
Quantitative Analysis of mixture
Transmittance spectra = I/I
0
x 100
=> peak height
is not lineraly related to intensity of absorption
In Absorbance A=ln (I
o
/I)
=> Direct measure of
intensity
Analyzing an IR spectrum
Analyzing an IR spectrum
In practice, there are similarities between
In practice, there are similarities between
frequencies of molecules containing similar groups.
frequencies of molecules containing similar groups.
Group - frequency correlations
Group - frequency correlations
have been
have been
extensively developed for organic compounds and
extensively developed for organic compounds and
some have also been developed for inorganics
some have also been developed for inorganics
Hydrog
Hydrog
en bond
en bond
and
and
C=O
C=O
Intensity of C=O vs
Intensity of C=O vs
C=C
C=C
Band Shape: OH vs
Band Shape: OH vs
NH2 vs CH
NH2 vs CH
Free OH and Hydrogen bonded
Free OH and Hydrogen bonded
OH
OH
Symmetrical and asymmetrical stretch
Symmetrical and asymmetrical stretch
Methyl
Methyl
2872 cm
2872 cm
-1
-1
Symmetrical Stretch
Symmetrical Stretch
Asymmetrical Stretch
Asymmetrical Stretch
—
—
C
C
—
—
H
H
H
H
H
H
—
—
C
C
—
—
H
H
H
H
H
H
Anhydride
Anhydride
O
O
O
O
O
O
1760 cm
1760 cm
-1
-1
2962 cm
2962 cm
-1
-1
1800 cm
1800 cm
-1
-1
O
O
O
O
O
O
Amino
Amino
Nitro
Nitro
—
—
N
N
H
H
H
H
3300 cm
3300 cm
-1
-1
3400 cm
3400 cm
-1
-1
1350 cm
1350 cm
-1
-1
1550 cm
1550 cm
-1
-1
—
—
N
N
H
H
H
H
—
—
N
N
O
O
O
O
—
—
N
N
O
O
O
O
General IR comments
General IR comments
Precise treatment of vibrations in molecule is not feasible here
Precise treatment of vibrations in molecule is not feasible here
Some information from IR is also contained in MS and NMR
Some information from IR is also contained in MS and NMR
Certain bands occur in
Certain bands occur in narrow regions
narrow regions
:
: OH
OH
,
, CH
CH
,
, C=O
C=O
Detail of the structure is revealed by the
Detail of the structure is revealed by the exact position
exact position
of the band
of the band
e.g.
e.g. Ketones
Ketones
O
1715 cm
1715 cm
-1
-1
CH
O
CH
2
1680 cm
1680 cm
-1
-1
Region 4000 – 1300 : Functional group
Region 4000 – 1300 : Functional group
Absence of band in this region can be used to deduce absence of groups
Absence of band in this region can be used to deduce absence of groups
Caution: some bands can be very broad because of hydrogen bonding
Caution: some bands can be very broad because of hydrogen bonding
e.g.
e.g. Enols v.broad OH, C=O absent!!
Enols v.broad OH, C=O absent!!
Weak bands in high frequency are extremely useful : S-H, C
Weak bands in high frequency are extremely useful : S-H, C
C, C
C, C
N
N
Lack of strong bands in 900-650 means no aromatic
Lack of strong bands in 900-650 means no aromatic
Alkanes
Alkanes
,
,
Alkenes
Alkenes
,
,
Alkynes
Alkynes
C-H :
C-H : <3000 cm
<3000 cm
-1
-1
>3000 cm
>3000 cm
-1
-1
3300 cm
3300 cm
-1
-1
sharp
sharp
C-C
C-C
Stretch
Stretch
Not useful
Not useful
C=C
C=C
C
C
C
C
1660-1600 cm
1660-1600 cm
-1
-1
conj. Moves to lower values
conj. Moves to lower values
Symmetrical : no band
Symmetrical : no band
2150 cm
2150 cm
-1
-1
conj. Moves to lower values
conj. Moves to lower values
Weak but very useful
Weak but very useful
Symmetrical no band
Symmetrical no band
Bending
Bending
CH
CH
2
2
Rocking
Rocking
720 cm
720 cm
-1
-1
indicate
indicate
Presence of 4-CH
Presence of 4-CH
2
2
1000-700 cm
1000-700 cm
-1
-1
Indicate substitution
Indicate substitution
pattern
pattern
C-H ~630 cm
C-H ~630 cm
-1
-1
Strong and broad
Strong and broad
Confirm triple bond
Confirm triple bond
Alkane
Alkane
Alkene :
Alkene :
1-Decene
1-Decene
To give rise to absorption of IR
To give rise to absorption of IR
=> Oscillating
Oscillating
Electric Dipole
Electric Dipole
Symmetry
Symmetry
Molecules with Center of symmetry
Molecules with Center of symmetry
Symmetric vibration => inactive
Symmetric vibration => inactive
Antisymmetric vibration => active
Antisymmetric vibration => active
Alkene
Alkene
In large molecule local symmetry produce
In large molecule local symmetry produce weak or absent vibration
weak or absent vibration
C=C
C=C
R
R
R
R
trans
trans
C=C isomer -> weak in IR
C=C isomer -> weak in IR
Observable in Raman
Observable in Raman
Alkene: Factors influencing vibration
Alkene: Factors influencing vibration
frequency
frequency
1- Strain move peak to right (decrease )
1- Strain move peak to right (decrease )
C
C
C
C
C
C
angle
angle
1650
1650
1646
1646
1611
1611
1566
1566
1656 : exception
1656 : exception
2- Substitution increase
2- Substitution increase
3- conjugation decrease
3- conjugation decrease
C=C-Ph 1625 cm
C=C-Ph 1625 cm
-1
-1
1566
1566
1641
1641
1675
1675
1611
1611
1650
1650
1679
1679
1646
1646
1675
1675
1681
1681
Alkene: Out-of-Plane bending
Alkene: Out-of-Plane bending
This region can be used to deduce substitution pattern
This region can be used to deduce substitution pattern
Alkyne:
Alkyne:
1-Hexyne
1-Hexyne
Alkyne:
Alkyne:
Symmet
Symmet
ry
ry
In IR, Most important transition
In IR, Most important transition
involve :
involve :
Ground State (
Ground State (
i
i
= 0)
= 0)
to
to First Excited State (
First Excited State (
i = 1)
i = 1)
Transition
Transition (
(
i
i
= 0)
= 0)
to
to (
(
J
J
= 2)
= 2)
=> Overtone
=> Overtone
IR : Aromatic
IR : Aromatic
=C-H
=C-H
> 3000 cm
> 3000 cm
-1
-1
C=C
C=C
1600 and 1475 cm
1600 and 1475 cm
-1
-1
=C-H
=C-H
out of plane bending: great utility to assign ring substitution
out of plane bending: great utility to assign ring substitution
overtone
overtone
2000-1667: useful to assign ring substitution
2000-1667: useful to assign ring substitution
e.g. Naphthalene:
e.g. Naphthalene:
Substitution pattern
Substitution pattern
Isolated H
Isolated H
862-835
862-835
835-805
835-805
760-735
760-735
2 adjacent H
2 adjacent H
4 adjacent H
4 adjacent H
out of plane bending
out of plane bending
Aromatic substitution: Out of
Aromatic substitution: Out of
plane bending
plane bending
Aromatic substitution: Out of
Aromatic substitution: Out of
plane bending
plane bending
Aromatic and Alkene
Aromatic and Alkene
substitution
substitution
IR: Alcohols and Phenols
IR: Alcohols and Phenols
O-H Free : Sharp 3650-3600
O-H Free : Sharp 3650-3600
O-H H-Bond : Broad 3400-3300
O-H H-Bond : Broad 3400-3300
Intermolecular Hydrogen bonding Increases with concentration
=> Less “Free” OH
Less “Free” OH
IR: Alcohols and Phenols
IR: Alcohols and Phenols
C-O : 1260-1000 cm
C-O : 1260-1000 cm
-1
-1
(coupled to C-C => C-C-O)
(coupled to C-C => C-C-O)
C-O Vibration is sensitive to substitution:
C-O Vibration is sensitive to substitution:
Phenol
Phenol
1220
1220
3` Alcohols
3` Alcohols
1150
1150
2` Alcohols
2` Alcohols
1100
1100
1` Alcohols
1` Alcohols
1050
1050
More complicated than above: shift to lower Wavenumber
More complicated than above: shift to lower Wavenumber
With unsaturation (Table 3.2)
With unsaturation (Table 3.2)
Alcohol
Alcohol
C-O : 1040 cm
C-O : 1040 cm
-1
-1
indicate primary alcohol
indicate primary alcohol
Benzyl Alcohol
Benzyl Alcohol
OH
OH
sp
sp
2
2
sp
sp
3
3
Ph
Ph
overtone
overtone
C-O : 1080, 1022 cm
C-O : 1080, 1022 cm
-1
-1
: primary OH
: primary OH
Mono
Mono
Subst. Ph
Subst. Ph
735 & 697 cm
735 & 697 cm
-1
-1
Phenol
Phenol
OH
OH
sp
sp
2
2
Ph
Ph
overtone
overtone
C=C stretch
C=C stretch
Ph-O : 1224 cm
Ph-O : 1224 cm
-1
-1
Mono
Mono
Subst. Ph
Subst. Ph
out-of plane
out-of plane
810 & 752 cm
810 & 752 cm
-1
-1
Phenol
Phenol
IR: Ether
IR: Ether
C-O-C
C-O-C
=>
=>
1300-1000 cm
1300-1000 cm
-1
-1
Ph-O-C
Ph-O-C
=>
=>
1250 and 1040 cm
1250 and 1040 cm
-1
-1
Aliphatic
Aliphatic
=>
=>
1120 cm
1120 cm
-1
-1
C=C in vinyl Ether
C=C in vinyl Ether
=>
=>
1660-1610 cm
1660-1610 cm
-1
-1
appear as Doublet => rotational isomers
appear as Doublet => rotational isomers
C
H
2
CH
O
CH
3
~1620
~1620
~1640
~1640
H
2
C
CH
O
CH
3
H
2
C
CH
O
C
H
3
Ether
Ether
sp
sp
2
2
sp
sp
3
3
Ph
Ph
overtone
overtone
C=C stretch
C=C stretch
Ph-O-C : 1247 cm
Ph-O-C : 1247 cm
-1
-1
Asymmetric
Asymmetric
stretch
stretch
Ph-O-C : 1040 cm
Ph-O-C : 1040 cm
-1
-1
Symmetric
Symmetric
stretch
stretch
Mono
Mono
Subst. Ph
Subst. Ph
out-of plane
out-of plane
784, 754 & 692
784, 754 & 692
cm
cm
-1
-1
O
H
CH
C
H
3
C
H
3
CH
3
O
IR: Carbonyl
IR: Carbonyl
From 1850 – 1650 cm
From 1850 – 1650 cm
-1
-1
Ketone 1715 cm
Ketone 1715 cm
-1
-1
is used as reference point for comparisons
is used as reference point for comparisons
1715
1715
1690
1690
1725
1725
1700
1700
1710
1710
1680
1680
1810
1810
Anhydr
Anhydr
Band
Band
1800
1800
Acid
Acid
Chloride
Chloride
1760
1760
Anhydr
Anhydr
Band 2
Band 2
1735
1735
Ester
Ester
1725
1725
Aldehyde
Aldehyde
1715
1715
Ketone
Ketone
1710
1710
Acid
Acid
1690
1690
Amide
Amide
Factor influencing
Factor influencing C=O
C=O
1) conjugation
1) conjugation
C=C
C=C
C
C
O
O
C
C
+
+
—
—
C
C
C
C
O
O
-
-
Conjugation increase single bond character of
Conjugation increase single bond character of
C=O
C=O
Lower force constant
Lower force constant
lower frequency number
lower frequency number
O
OH
Ketone and Conjugation
Ketone and Conjugation
Conjugation: Lower
Conjugation: Lower
Ketone and Ring
Ketone and Ring
Strain
Strain
Ring Strain: Higher
Ring Strain: Higher
Factors influencing
Factors influencing C=O
C=O
2) Ring size
2) Ring size
O
1715 cm
1715 cm
-1
-1
Angle ~ 120
Angle ~ 120
o
o
C
H
3
C
H
3
O
O
1751 cm
1751 cm
-1
-1
< 120
< 120
o
o
O
1775 cm
1775 cm
-1
-1
<< 120
<< 120
o
o
Factors influencing carbonyl:
Factors influencing carbonyl:
C=O
C=O
3)
3)
substitution effect (Chlorine or other halogens)
substitution effect (Chlorine or other halogens)
—
—
C
C—
—
C
C
—
—
X
X
O
O
Result in stronger bound
Result in stronger bound
higher frequency
higher frequency
O
Cl
1750 cm
1750 cm
-1
-1
4) Hydrogen bonding
4) Hydrogen bonding
Decrease
Decrease
C=O
C=O
strenght
strenght
lower frequency
lower frequency
O
O
CH
3
O
H
1680 cm
1680 cm
-1
-1
Enol
Enol
Factors influencing carbonyl:
Factors influencing carbonyl:
C=O
C=O
5) Heteroatom
5) Heteroatom
Y
R
O
Inductive effect
Inductive effect
Stronger bond
Stronger bond
higher frequency
higher frequency
e.g. ester
e.g. ester
Y
R
O
Resonance effect
Resonance effect
Weaker bond
Weaker bond
Lower frequence
Lower frequence
e.g. amides
e.g. amides
Y
Y
C=O
C=O
Cl
Cl
Br
Br
OH (monomer)
OH (monomer)
OR (Ester)
OR (Ester)
1815-1785
1815-1785
1812
1812
1760
1760
1705-1735
1705-1735
NH2
NH2
SR
SR
1695-1650
1695-1650
1720-1690
1720-1690
inductive
inductive
resonance
resonance
Ester Carbonyl
Ester Carbonyl
Esters
Esters
C=O
C=O
~ 1750 – 1735 cm
~ 1750 – 1735 cm
-1
-1
O-C : 1300 – 1000 2 or more bands
O-C : 1300 – 1000 2 or more bands
Conjugation => lower freq.
R
OR
O
Inductive effect with
Inductive effect with
O
O
reinforce carbonyl =>
higher
higher
Conjugation with
Conjugation with
CO
CO
weaken carbonyl =>
Lower
Lower
Ester carbonyl:
Ester carbonyl:
C=O
C=O
Ester carbonyl:
Ester carbonyl:
C=O
C=O
C=O : 1765 cm
C=O : 1765 cm
-1
-1
C-O 1215 cm
C-O 1215 cm
-1
-1
1193 cm
1193 cm
-1
-1
sp
sp
2
2
C=O
C=O
Ester carbonyl:
Ester carbonyl:
C=O
C=O
Ester carbonyl : effect of
Ester carbonyl : effect of
conjugation
conjugation
Lactone carbonyl:
Lactone carbonyl:
C=O
C=O
Lactones
Lactones
Cyclic Ester
Cyclic Ester
O
O
1735
1735
1720
1720
1760
1760
1770
1770
1750
1750
1800
1800
O
O
O
O
O
O
O
O
O
O
Carbonyl compounds : Acids
Carbonyl compounds : Acids
Carboxylic acid
Carboxylic acid
Exist as dimer :
Exist as dimer :
C
H
3
C
OH
O
CH
3
C
O
H
O
Strong Hydrogen bond
Strong Hydrogen bond
OH : Very broad
OH : Very broad
3400 – 2400 cm
3400 – 2400 cm
-1
-1
C=O : broad
C=O : broad
1730 – 1700 cm
1730 – 1700 cm
-1
-1
C
C
—
—
O : 1320 – 1210 cm
O : 1320 – 1210 cm
-1
-1
Medium intensity
Medium intensity
Carbonyl compounds : Acids
Carbonyl compounds : Acids
C=O
C=O
OH
OH
C=O : 1711 cm
C=O : 1711 cm
-1
-1
OH : Very Broad 3300 to 2500 cm
OH : Very Broad 3300 to 2500 cm
-1
-1
C-O : 1285, 1207 cm
C-O : 1285, 1207 cm
-1
-1
Anhydride
Anhydride
s
s
C
H
3
O
O
CH
3
O
C=O always has 2 bands:
C=O always has 2 bands:
1830-1800 and 1775-1740 cm
1830-1800 and 1775-1740 cm
-1
-1
C
C
—O multiple bands 1300 – 900 cm
—O multiple bands 1300 – 900 cm
-1
-1
Carbonyl compounds : Aldehydes
Carbonyl compounds : Aldehydes
Aldehydes
Aldehydes
C=O
C=O
~ 1725 cm
~ 1725 cm
-1
-1
O=C-H : 2 weak bands 2750, 2850 cm
O=C-H : 2 weak bands 2750, 2850 cm
-1
-1
Conjugation => lower freq.
C=O : 1724 cm
C=O : 1724 cm
-1
-1
Carbonyl compounds : Aldehydes
Carbonyl compounds : Aldehydes
Aldehydes
Aldehydes
Other carbonyl
Other carbonyl
Amides
Amides
Lactams
Lactams
Acid Chlorides
Acid Chlorides
C=O ~1680-1630 cm
C=O ~1680-1630 cm
-1
-1
(band I)
(band I)
NH
NH
2
2
~ 3350 and 3180 cm
~ 3350 and 3180 cm
-1
-1
(stretch)
(stretch)
NH ~ 3300 cm
NH ~ 3300 cm
-1
-1
(stretch)
(stretch)
NH ~ 1640-1550 cm
NH ~ 1640-1550 cm
-1
-1
(bending)
(bending)
NH
O
R
R
—
—
C
C
—
—
Cl
Cl
O
O
1810-1775 cm
1810-1775 cm
-1
-1
C
C
—
—
Cl 730 – 550 cm
Cl 730 – 550 cm
-1
-1
~1660
~1660
NH
O
~1705
~1705
NH
O
~1745
~1745
Increase with strain
Increase with strain
Amides
Amides
NH
NH
2
2
: Symmetrical stretch =>3170 cm
: Symmetrical stretch =>3170 cm
-1
-1
asymmetrical stretch => 3352 cm
asymmetrical stretch => 3352 cm
-1
-1
C=O : 1640 cm
C=O : 1640 cm
-1
-1
NH Out of plane
NH Out of plane
Amides
Amides
Acid Chlorides
Acid Chlorides
Amino acid
Amino acid
Exist as zwitterions
Exist as zwitterions
C
C
CO
CO
2
2
-
-
NH
NH
3
3
+
+
NH
NH
3
3
+
+
: very broad 3330-2380
: very broad 3330-2380
(OH +
(OH + NH
NH
3
3
+
+
)
)
C
C
O
O
O
O
1600 – 1590 strong
1600 – 1590 strong
Amino acid
Amino acid
Amine
Amine
NH 3500 – 3300 cm
NH 3500 – 3300 cm
-1
-1
NH : 2 bands
NH : 2 bands
NH : 1 band
NH : 1 band
NH bending : 1650 – 1500 cm
NH bending : 1650 – 1500 cm
-1
-1
C-N : 1350 – 1000 cm
C-N : 1350 – 1000 cm
-1
-1
NH out-of-plane : ~ 800 cm
NH out-of-plane : ~ 800 cm
-1
-1
Amine salt
Amine salt
NH
NH
+
+
3500 – 3030 cm
3500 – 3030 cm
-1
-1
broad / strong
broad / strong
Ammonium
Ammonium
primary
primary
secomdary
secomdary
right
right
Left
Left
Amine
Amine
Primary Amine
Primary Amine
Secondary Amine
Secondary Amine
Tertiary Amine
Tertiary Amine
Aromatic Amine
Aromatic Amine
Other Nitrogen Compounds
Other Nitrogen Compounds
Nitriles
Nitriles
Isocyanates
Isocyanates
Isothiocyanates
Isothiocyanates
Imines / Oximes
Imines / Oximes
R-C
R-C
N :
N :
Sharp 2250 cm
Sharp 2250 cm
-1
-1
Conjugation moves to lower frequency
Conjugation moves to lower frequency
R-N=C=O
R-N=C=O
Broad ~ 2270 cm
Broad ~ 2270 cm
-1
-1
R-N=C=S
R-N=C=S
2 Broad peaks ~ 2125 cm
2 Broad peaks ~ 2125 cm
-1
-1
R
R
2
2
C=N-R
C=N-R
1690 - 1640 cm
1690 - 1640 cm
-1
-1
Nitrile
Nitrile
C
N
CH
Nitrile
Nitrile
Nitrile and Isocyanate
Nitrile and Isocyanate
Nitro
Nitro
—
—
N
N
O
O
O
O
+
+
-
-
Aliphatic :
Aliphatic :
Asymmetric : 1600-1530 cm
Asymmetric : 1600-1530 cm
-1
-1
Symmetric : 1390-1300 cm
Symmetric : 1390-1300 cm
-1
-1
Aromatic :
Aromatic :
Asymmetric : 1550-1490 cm
Asymmetric : 1550-1490 cm
-1
-1
Symmetric : 1355-1315 cm
Symmetric : 1355-1315 cm
-1
-1
Nitro
Nitro
Nitro
Nitro
Sulfur
Sulfur
Mercaptans
Mercaptans
S – H : weak 2600-2550 cm
S – H : weak 2600-2550 cm
-1
-1
Since only few absorption in that range it confirm its presence
Since only few absorption in that range it confirm its presence
Sulfides,Disulfides : no useful information
Sulfides,Disulfides : no useful information
Sulfoxides:
Sulfoxides:
R
S
R
O
Strong ~ 1050 cm
Strong ~ 1050 cm
-1
-1
Sulfones
Sulfones
:
:
Asymetrical ~ 1300 cm
Asymetrical ~ 1300 cm
-1
-1
Symetrical ~ 1150 cm
Symetrical ~ 1150 cm
-1
-1
R
S
R
O
O
2 bands :
2 bands :
Sulfur: Mercaptan R-
Sulfur: Mercaptan R-
S-H
S-H
Sulfur: Sulfonyl Chloride
Sulfur: Sulfonyl Chloride
S=O :
S=O :
Asymmetrical stretch: 1375 cm-1
Asymmetrical stretch: 1375 cm-1
Symmetrical Stretch : 1185 cm-1
Symmetrical Stretch : 1185 cm-1
Sulfur: Sulfonate
Sulfur: Sulfonate
S=O :
S=O :
Asymmetrical stretch: 1350 cm-1
Asymmetrical stretch: 1350 cm-1
Symmetrical Stretch : 1175 cm-1
Symmetrical Stretch : 1175 cm-1
S-O : several bands between 1000 – 750 cm
S-O : several bands between 1000 – 750 cm
-1
-1
Sulfur: Sulfonamide
Sulfur: Sulfonamide
S=O :
S=O :
Asymmetrical stretch: 1325 cm-1
Asymmetrical stretch: 1325 cm-1
Symmetrical Stretch : 1140 cm-1
Symmetrical Stretch : 1140 cm-1
NH
NH
2
2
stretch: 3350 and 3250 cm
stretch: 3350 and 3250 cm
-1
-1
NH Bend: 1550 cm
NH Bend: 1550 cm
-1
-1
Halogens
Halogens
C
C
—F : 1400 – 1000 cm
—F : 1400 – 1000 cm
-1
-1
C
C
—Cl : strong 785 – 540 cm
—Cl : strong 785 – 540 cm
-1
-1
C
C
—Br : 650 – 510 cm
—Br : 650 – 510 cm
-1
-1
(out of range with NaCl plates)
(out of range with NaCl plates)
C
C
—I : 600 – 485 cm
—I : 600 – 485 cm
-1
-1
(out of range)
(out of range)
Halogens
Halogens
Phosphorus
Phosphorus
Phosphines: R-PH
Phosphines: R-PH
2
2
R
R
2
2
PH
PH
P
P
—H : Sharp 2320 – 2270 cm
—H : Sharp 2320 – 2270 cm
-1
-1
P
P
H
H
2
2
bending : 1090 – 1075 and 840 - 810 cm
bending : 1090 – 1075 and 840 - 810 cm
-1
-1
P
P
H bending : 990 - 886 cm
H bending : 990 - 886 cm
-1
-1
Phosphine Oxide : R
Phosphine Oxide : R
3
3
P=O
P=O
P
P
=O very strong : 1210 - 1140 cm
=O very strong : 1210 - 1140 cm
-1
-1
Phosphate Esters : (OR)
Phosphate Esters : (OR)
3
3
P=O
P=O
P
P
=O very strong : 1300 - 1240 cm
=O very strong : 1300 - 1240 cm
-1
-1
P
P
-O very strong : 1088 – 920 cm
-O very strong : 1088 – 920 cm
-1
-1
P
P
-O : 845 - 725 cm
-O : 845 - 725 cm
-1
-1
Silicon
Silicon
Si-H :
Si-H :
2200 cm
2200 cm
-1
-1
(Stretch)
(Stretch)
950 – 800 cm
950 – 800 cm
-1
-1
(bend)
(bend)
Si-O-H :
Si-O-H :
OH: 3700 – 3200 cm
OH: 3700 – 3200 cm
-1
-1
(Stretch)
(Stretch)
Si-O : 830 – 1110 cm
Si-O : 830 – 1110 cm
-1
-1