Table Of ContentThe Handbook of
Infrared and Raman
Characteristic Frequencies
of
Organic Molecules
Daimay Lin-Vien
Shell Development Company
Houston, Texas
Norman B. Colthup
Stamford, Connecticut
William G. Fateley
Kansas State University
Manhattan, Kansas
Jeanette G. Grasselli
Ohio University
Athens, Ohio
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Library of Congress Cataloging-in-Publication Data
The Handbook of infrared and Raman characteristic frequencies of
organic molecules / Daimay Lin-Vien . . . (et al.).
p. cm.
Includes bibliographical references and index.
ISBN 0-12-451160-0 (alk. Paper)
1. Organic compounds — Spectra. 2. Molecular spectroscopy.
3. Infrared spectroscopy 4. Raman spectroscopy I. Lin-Vien,
Daimay.
QC462.5.H343 1991
547.3O8583-dc20 91-8611
CIP
PRINTED IN THE UNITED STATES OF AMERICA
97 EB 9 8 7 6 5 4 3
Dedicated to
Lionel J. Bellamy
His monumental works on summarizing and
explaining group frequencies in vibrational
spectroscopy stand alone. His wit and his
wisdom were legendary.
and to
Tomas Β. Hirschfeld
His brilliant contributions to the theory and
practice of spectroscopy enlightened us ally
and were characterized by an unbounded
enthusiasm and delight in the field.
"If a poet at the same time be a physicist,
he might convey to others the pleasure, the
satisfaction, almost the reverence, which the
subject inspires.—Especially is its fascination
felt in the branch that deals with light.
Albert A. Michelson
Light Waves and Their Uses
PUDDLE
Our Cover
The lithograph by the artist, M. C. Escher, on our cover is
entitled, 'Tuddle." I purchased the original from Mr. Escher at
his home in Baarn, Holland, in 1968. I believe it gives us a
preview of what is to come in our interpretation of spectra. In
Puddle we find two different bicycle and human tracks (are they
different?) and two different auto and truck tracks. Likewise,
the frequency of absorption in our spectra are the tracks for the
identification of molecules. We know these frequencies provide
important data about the molecules, chemical groups, and ions.
It is the organization of this information, to be found in this
Handbook, which elucidates the molecular structure; so let the
* bracks" be your guide to molecular structure.
Bill Fateley
1991
Preface
Infrared and Raman spectroscopy are two of the most widely used tech
niques for the determination of molecular structure and for the identifica
tionofcompounds. Oneneedsonlyto glanceatthethousands ofreferences
in the Fundamental Reviews on Infrared and Raman Spectroscopy
published by Analytical Chemistry biennially to verify this statement.
Sample handling is very simple and usually non-destructive. Instrumenta
tion has improved dramatically in the last 20 years. Information can be
obtained in seconds rather than hours, and energy-limited samples (low
concentrationorsmallsize)thatwouldhavepresenteddifficultyin previous
days are now readily examined. The "FT" revolution has involved both IR
and Raman techniques, and the computer capabilities of all analytical
instrumentation today provide formidable routines for data manipulation.
The information content of the infrared and Raman spectra are
completely complementary, and both are necessary for the vibrational
analysis of a molecule. The spectroscopist, organic chemist, or physical
chemist using these techniques depends on theory, on group frequency
information on molecules that has been developed empirically over the
years, and on evaluated collections of reference spectra. The seminal texts
ofL. J. Bellamy, TheInfraredSpectraofComplexMolecules, Vols. I& II,
first publishedin 1954and 1968, arestillamongthemostwidelycitedbooks
in the world. Later books by Colthup, Daly and Wiberley, and A. Lee
Smith continued to explore and expand on our understanding of group
frequencies and how they can be used to analyze materials. The revitaliza
tion of Raman spectroscopy occurred in the 1970s with the advent of the
laser as a source. In 1974, the first book on CharacteristicRamanFrequen
ciesofOrganicCompoundswas published by Dollish, Fateleyand Bentley.
Although the Colthup et ale book is in a third edition, the Bellamy and
Dollishbooks are out ofprint. It was this fact, coupled with the continuing
rapid growth in the field of vibrational analysis, that led to this book.
xv
xvi Preface
We have attempted to integrate the discussion of the infrared and Raman
group frequencies for 16 classes of organic molecules as chapters in the text.
Literature through 1990 was searched for information on group frequen-
cies, and results of this search are evaluated and organized in the discussion.
In rigorous interpretation of spectra, it is important to understand the
origin of group frequencies and to recognize and assign them in the
spectrum. It is equally important to understand why group frequencies
shift. Our text should provide assistance, as well as references to more
thorough discussions in the literature, in the use of group frequencies. We
have also included a set of representative pairs of IR and Raman spectra in
Chapter 18 and in the Appendices, which complement the discussion in the
text by illustrating the spectral features. We gratefully acknowledge the
Aldrich Chemical Co., VCH pubHshers of the B. Schräder Raman/Infrared
Atlas, and the Sadtler Research Laboratories, Division of Bio-Rad
Laboratories, Inc., for permission to use selections from their infrared and
Raman collections in order to present the pairs of spectra for each com-
pound. A summary of characteristic Raman frequencies from DoUish et al.,
and the Colthup correlation charts for infrared frequencies are presented in
Appendix Three.
The purpose of this book is to provide a reference to aid in the interpreta-
tion of the infrared and Raman spectra of organic compounds. We hope it
accomplishes that. Although excellent instrumentation and software are
now readily available to chemists everywhere, it is perhaps more important
than ever that the interpretations of the data are based on sound
spectroscopic principles. There is still no better way to do this than to use
and understand the group frequencies of organic molecules.
D. Lin-Vien
N. B. Colthup
W. G. Fateley
J.G. GrasseUi
Acknowledgment
The authors wish to thank Mr. Dick Nyquist for the wonderful help and
guidance he has provided us in the preparation of this book. For many years
he has published outstanding papers on the relationship between vibrational
group frequencies and structure in molecules. It is work such as this that
made this book possible
Many thanks to you, Dick!
All of us
CHAPTER 1
Introduction
Infrared (IR) and Raman spectroscopies provide information on molecular
vibrations. These methods cause molecules to undergo changes in vibra-
tional energy state by subjecting them to excitation radiation in selected
spectral regions. IR and Raman spectroscopy differ in the means by which
photon energy is transferred to the molecule and in the instrumentation
used. Thus, the information extracted exhibits different characteristics.
Infrared and Raman spectroscopy are complementary rather than com-
peting techniques. The molecular vibrational frequencies observed by both
techniques are nearly the same, but the vibrational band intensities differ
(sometimes markedly so) because of the different excitation mechanisms
and therefore different selection rules.
1-1.
PRINCIPLES AND SELECTION RULES
The theory and selection rules of IR and Raman transitions have been
discussed by Herzberg [1] and Steinfeld [2] in detail. Fateley et al. [19] have
discussed the infrared and Raman selection rules for molecular and lattice
vibrations by the correlation method. Considerations on the selection rules
from the view of molecular symmetry are given by Cotton [3] and Drago [4].
Only qualitative descriptions of the principles and selection rules of IR
Raman spectroscopies are given here.
2 Chapter 1 : Introduction
1 -1 · 1 · I nfrared Spectroscopy
In IR spectroscopy, the vibrational excitation is achieved by radiating the
sample with a broad-band source of radiation in the infrared region, which
is generally 4000-200 cm~^ (2.5-50/im). The wavenumber, ν in cm"\ is the
number of waves per centimeter. It is equal to the reciprocal of the wave-
length λ in cm, and is equal to the frequency ν divided by c, the velocity of
light (cm sec"^). In the IR region, the wavelength λ is given in micrometers
μνα or 10"^ m. As illustrated in Fig. 1-1, the molecule is excited to a higher
vibrational state by directly absorbing the infrared radiation. The transmit-
tance at a given wavenumber can be calculated according to Eq. 1. The
transmission spectrum is then obtained by plotting the transmittance versus
the IR wavenumber. Similarly, the absorbance at a given wavenumber can
be obtained by using the Beer-Lambert equation (Eq. 2). A plot of absor-
bance versus wavenumber yields an absorption spectrum.
Τ ^ γ. (1)
Λ = log(^
= abc, (2)
where Τ is transmittance, A is absorbance, /q is the intensity of the entering
radiation (before sample absorption), / is the intensity of the transmitted
Hght (after sample absorption), a is absorptivity, b is cell thickness, and c is
concentration.
1-1.2. Raman Spectroscopy
The origin of Raman spectroscopy is an inelastic scattering effect. In this
case, the excitation radiation source is monochromatic and is much more
energetic than infrared radiation. Elastic and inelastic scattering of radia-
tion by the sample is observed in a Raman experiment. In elastic scattering
(Rayleigh scattering), the molecule is excited to a virtual state, and then
relaxes to the original vibrational state by re-emitting a photon at the same
frequency as the incident light. The molecule **absorbs" no energy from the
incident radiation in this case. See Fig. 1-1.
Only a very small fraction of molecules undergo inelastic scattering
(Raman scattering). When Raman scattering occurs, the excited molecule
relaxes to a different vibrational level, rather than to the original state. The
energy carried by an inelastically scattered photon is different from that of
1 -1. Principles and Selection Rules
VIRTUAL
STATES
VIBRATIONAL
STATES
V= 4 -
V= 3 —
V= 2-
v=i-
—I v = o -
STOKES RAYLEIGH ΑΝΤΙ -
STOKES
IR RAMAN
Fig. 1-1. Energy states involved in IR and Raman spectroscopies.
the incident Hght. In a Raman spectrum, the energy difference between the
incident and scattered Hghts appears as a frequency shift between the scat-
tered Hght v' and the excitation frequency v. These two frequencies, ν and
v', are related to the vibrational energy by the following equation (see also
Fig. 1-1):
hv = hv' + ģ,ibration (3)
It should be noted that in Raman experiments, the final vibrational state
of the molecule can be either higher or lower in energy than the original
state. In the case where the final vibrational state is lower in energy than the
original one, the scattered photon will exhibit a higher frequency than the
incident radiation. Thus, a blue shift from the excitation frequency is
observed. Raman bands of this type are called anti-Stokes lines. Similarly,
a red shift from the incident radiation is observed when the final state
exhibits higher energy than the original state; these Raman bands are
referred to as Stokes lines. Since most of the molecules are at ground vibra-
tional state (υ = 0) at room temperature, the Stokes lines exhibit higher
Raman intensity than the corresponding anti-Stokes lines, which originate
from an elevated vibrational state {υ = 1). Therefore, the Stokes lines are
more commonly used for molecular characterization.
