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Why include
spectroscopy in general chemistry?
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I am a physical chemist and did my
thesis research using electron spin resonance. I think that
spectroscopy is an exquisite probe, and that its application
to our everyday lives is widespread.
I teach at Bellevue Community
College, a large urban community college. Because the
chemistry department is small, I have taught every course in
our curriculum, from chemistry for non-science majors to the
year-long sophomore organic sequence, although for many
years I have been mostly teaching organic chemistry and
General Chemistry. Knowledge of spectroscopy is essential
when working with organic chemistry and when I began
teaching organic chemistry, I was surprised that most
students had not been introduced to spectroscopy at all in
their General Chemistry course. A few students had
experience with colorimetry and atomic emission spectra, but
absorption was new to almost everyone. Most had never
studied infrared, UV-visible or NMR spectroscopy and had no
experience with absorption spectra at all. The General
Chemistry courses omitted discussion of these key topics.
This is a reflection of the content of many General
Chemistry texts. Popular General Chemistry texts typically
discuss spectroscopy only associated with atomic emission
spectra and crystal field theory applied to complex ions.
This usually amounts to 10-15 pages in books that have
swollen to 1000 pages. I believe there is a mismatch here.
There is an imbalance between traditional topics and modern
ones.
General Chemistry has the largest
number of students of any of the classes in the chemistry
curriculum. It serves to introduce thousands of students to
the field of chemistry. All of the future engineers,
dentists, doctors pharmacists take General Chemistry. Many
of these professions require students to continue on with
organic chemistry. Some do not. This means that a large
number of students will only see chemistry through the view
of a General Chemistry window. Their vision of chemistry
will be forever shaped by their experience in General
Chemistry. To me this means General Chemistry students need
more than the traditional emphasis on basic atomic
structure, stoichiometry, gas laws, and equilibrium
calculations. The "spiral" approach to teaching chemistry is
used for most other topics but not for
spectroscopy.
It may sound strange to describe a
college with 17,000 students as small. The fact is that
although we have a student population of 17,000, only a
hand-full of the 17,000 students take any chemistry at all.
Even fewer take General Chemistry. Our General Chemistry
enrollment is a mere 176 students in fall quarter followed
by another cohort of 120 in winter quarter with another 24
in a summer session. The total is about 300 students each
year. The number of students who continue on and start
organic course is even smaller. We have only 48 students in
our sophomore organic chemistry. This is about 16% of the
students who started General Chemistry.
Is this an unusual situation? I
know that a similar pattern exists at the University of
Washington. In 1998-99 about 2100 students started General
Chemistry. This number dwindled to about 850 who started
sophomore organic chemistry. This means only about 40% of
the students who started General Chemistry go on to start
sophomore organic chemistry. The percentages are different
for the two colleges partly because some students from the
community college transfer to four year schools for their
sophomore year.
To me this indicates that General
Chemistry is frequently the first and, in many cases the
last, set of classes where students will be engaged in work
that uses the principles of modern chemistry. This means we
must introduce General Chemistry students to the concepts of
spectroscopy or they may never see them. Infrared,
ultraviolet-visible, NMR spectroscopy are integral parts of
modern chemistry and should be incorporated into the General
Chemistry syllabus so students get an accurate picture of
some of the tools that are used by chemists. It seems that
spectroscopy that has been around for more than 40 years or
almost three generations should have some place in the basic
General Chemistry course.
Most General Chemistry texts talk
about spectroscopy only when emission spectra of atoms and
energy levels are discussed. General Chemistry texts often
only mention spectra when discussing atomic emission
spectra. The present emphasis on stoichiometry, titrations,
redox potentials, acids and bases deals with a limited set
of information. It gives a distorted image of what is done
in chemistry.
Spectroscopy provides information
that is at the base of some very abstract ideas in General
Chemistry. In many texts students are offered little
experimental evidence for many topics about bonding. A
rudimentary experience with spectroscopy can help students
visualize current models of molecular motions, differences
in bonds, energy levels in molecules, resonance, hydrogen
bonding, color, etc.
There are a large number of
experiments that have been written for use in General
Chemistry. These are excellent experiments, but often they
require instrumentation that is unavailable to
financially-challenged departments. Even well-funded
departments may have logistical problems when huge numbers
of students are enrolled in labs. This creates a situation
where simulation software can provide students experience
without the need for additional lab space or large numbers
of instruments. A combination of simulation software and
hands-on instrument use would be ideal. If the hardware is
not available at least students should be able to gain
experience using simulations and spectra libraries.
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Reasons for including
spectroscopy in General
Chemistry
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I believe that there are at least
three significant reasons for including spectroscopy related
activities in General Chemistry.
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1. About sixty percent of General
Chemistry students do not continue with any more chemistry.
This means that they will have almost zero experience with
spectroscopy if it is omitted from the General Chemistry
syllabus. In this situation successful General Chemistry
students will not know any more about absorption spectra,
infrared spectra, NMR and ultraviolet spectra than students
who never took a chemistry course.
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2. Students who do go on to organic
often have great difficulty. One of the major tools of
organic chemistry is spectroscopy. If General Chemistry
includes a brief exposure to the concepts of IR, UV-visible
and NMR, students may have a better chance of understanding
the principles they encounter in organic
chemistry.
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3. Techniques of modern medicine
are increasingly dependent on what we chemists call
"spectroscopy" such as CAT scans, MRI's, etc.
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How can spectroscopy be
included in General
Chemistry?
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Right now you may be saying,
"General Chemistry is already overloaded with content. Where
will spectroscopy fit? What will have to be dropped from the
course? " I believe nothing need be dropped. A shift in
emphasis may be needed. The amount of time spent on
traditional topics could be altered.
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I believe that spectroscopy fits
well when discussing bonding and molecular shapes. When I
teach General Chemistry, I always introduce IR spectroscopy
during the discussion of bonding. We have a small chemistry
department with a limited budget. I know that we cannot
afford to purchase and maintain both an FTIR and FTNMR
spectrometer. Therefore, I have adopted the strategy of
introducing students to these topics using small libraries
of spectra and simulations. Specifically we have used IR
Tutor(1), IR Simulator (2), Beaker(3), and the Journal of
Chemical Education proton nuclear magnetic resonance
simulator program. Relatively inexpensive software and
spectral libraries can be used to provide
spectra.
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Spectroscopy also can be included
as part of a project during the second semester or third
quarter of the General Chemistry series. I have used a
project that is centered on an organic synthesis. Students
examine IR and NMR spectra for reactants and products in a
one step synthesis of benzil from benzoin.
Students do a microscale synthesis
and determine their melting point and percent yield. They do
an analysis of NMR and IR spectra for reactant and product.
I provide IR spectra for the reactants and products.
Students use an NMR spectrum simulator program to generate
the NMR spectra. They are asked to assign chemical shifts to
protons in the structures of reactants and products. We have
an FTIR now and students can record their own IR spectra.
This is a good experience, but not an essential one.
Students have three weeks to complete the project and submit
their project report.
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NMR simulated spectra are a great
tool for demonstrating how electronegativity influences
shielding and electron density in molecules for General
Chemistry. I introduce the class to PMR and chemical shifts.
Students then use a NMR simulator program to generate
spectra for a hydrocarbon and a series of halogenated
compounds. The effect of the halogens on the chemical shift
can be examined. Students can see the change in shielding as
the number of halogens change. They "see" the effect and are
very impressed. The students seem to feel they are dealing
with modern aspects of chemistry and enjoy the idea of
manipulating molecules while working with the simulator
program.
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Examples of
spectroscopy related activities for General
Chemistry
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4. Chemical shifts, electron
density and electronegativity
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Some
spectroscopy resources
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Infrared Pages on the
Net
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Encyclopedia of
Analytical Instrumentation
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Software and other Resources / Data
Acquisition and Electronics / Data Handling / Diffraction /
Electrochemistry / Gravimetry /Imaging / Mass Spectrometry /
Materials & Surface Analysis / Optics / Sensors /
Separations / Spectroscopy /Standards / Thermal Methods /
Titration
http://www.scimedia.com/chem-ed/analytic/ac-meths.htm#spectroscopy
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Web sources for information
regarding NMR simulation software
A Compilation of Educational NMR
Software
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Magnetic Resonance unit, Dept of
Diagnostic Radiology, Linkoping University Hospital, S-581
85 Linkoping, Sweden.
(Previous address: Dept of Physical
Chemistry, University of Umea, S-901 87 Umea,
Sweden)
Preferred email address:
PeterL@mr.us.lio.se (alternative address:
Peter.Lundberg@chem.umu.se)
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A multimedia presentation of the
basics of NMR spectroscopy. On CD-ROM with
QuickTime movies and
animation.
Four sections: Introduction (What
is the use of NMR?); The instrument room (demo of a
spectrometer); The classroom (analyzing simple spectra);
Laboratory (spectra of complex molecules) CD-ROM for
Macintosh and PCs.
Available ($60) from JCESOFT at
http:// jchemed.chem.wisc.edu/JCESoft
By CS Judd, JD Morrisett, MV Chari,
JL Browning.
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NMR concepts with
MathCad
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MathCad documents demonstrating NMR
concepts. Introduction to NMR, quadrature detection, phase
cycling, apodization.
For MathCad (PCs). Viewer
available.
Free programs from
http://science.widener.edu/svb/nmr/nmr.html
By Scott Van Bramer (
svanbram@science.widener.edu).
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Fourier transform with
MathCad
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MathCad documents showing how the
Fourier transform is used in NMR spectroscopy. Introduction,
two signals, real and imaginary spectra, and decaying
signal.
For MathCad (PCs).
Free programs from
http://science.widener.edu/svb/nmr/nmr.html
By Scott Van Bramer (
svanbram@science.widener.edu).
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A program for simulating proton NMR
spectra on a Mac. Draw the structure on screen and the
spectrum will be displayed at
60-360 MHz. Clicking on a hydrogen
in the molecular structure indicates the multiplet generated
by that hydrogen, and clicking on any peak in the spectrum
highlights the corresponding hydrogen in the molecular
structure drawing. Very easy to use.
For Macintosh.
Available ($50) from JCE Software
(Kersey Black, Proton NMR Spectrum Simulator, JCE Software,
1990 , Volume IIc, No. 1).
Email: JCESOFT@MACC.WISC.EDU
By Kersey Black.
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Program for simulation of spectra
at different field strengths ("Really Awesome Computer
Calculation Of Observed Nmr spectra"). Up to 7 spins, plus
additional singlets, and optional noise, integration,
printing on most printers, etc (in the updated version).
Easy to use.
For PCs (DOS)
Available from project Seraphim
(the old 1984 version), at $20 (disk PC4101) with a few more
programs. Email: JCESOFT@MACC.WISC.EDU. Free program Raccoon
II (the new Version 2.1, 1993) from Hans Reich (email:
REICH@chem.wisc.edu).
By Paul Schatz, and Hans
Reich.
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A spectrum simulation program
(version 1.0 for Mac) for all naturally occuring isotopes
for the first 103 elements. You can select the isotopic
abundance etc. 8 spins, dipolar coupling, etc.
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For Macintosh.
Distributed by Calleo Scientific
Software Publisher, 3951 Braidwood Dr, Fort Collins,
Colorado 80524, Ph (970) 482-9745. Price $275-375 . (www:
http://members.aol.com/calleo, Email:
calleo@aol.com)
By AK Rappe from the Colorado State
University, and CJ Casewit of Calleo.
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A partial list spectroscopy
experiments for General Chemistry
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Abney,-James-R.;
Scalettar,-Bethe-A., J. Chem. Educ. 1998, v75 n6
p757-60.
Describes absorption spectroscopy
experiments that allow students to explore the mechanisms by
which sunscreens and sunglasses provide protection from
ultraviolet radiation. Exposes students to absorption
phenomena in an engaging way.
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Ackermann,-Martin-N., J-Chem-Educ.
1970, 47, 1, 69-70.
Describes a General Chemistry
experiment which uses infrared spectroscopy to analyze
inorganic ions and thereby serves to introduce an important
instrumental method of analysis. Presents a table of eight
anions and the ammonium ion with the frequencies of their
normal modes, as well as the spectra of three sulfate
salts.
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Bosma,-Wayne-B., J. Chem. Educ.
1998, v75 n2 p214-15.
Describes a set of experiments
using a UV-VIS spectrometer to identify food colorings and
to measure the pH of soft drinks. The first laboratory
component uses locations and shapes of visible absorption
peaks as a means of identifying dyes while the second
portion uses the spectrometer for determining pH.
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Shalhoub,-George-M., J. Chem. Educ.
1980, v57 n7 p525-26.
Describes an experiment for General
Chemistry that illustrates the use of spectroscopy in the
synthesis, characterization, and nitration of
tris(acetylacetonato)cobalt (III).
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Reedijk,-J.; and-others,
Education-in-Chemistry, 1975; 12, 4, 113-114.
Describes an experiment, for the
General Chemistry laboratory, intended to introduce the
student to infrared spectroscopy. After being introduced to
the theory of molecular vibrations on an elementary level,
each student receives a list of 5-7 nickel (II) ammines to
be prepared, analyzed and characterized by infrared
spectoscopy.
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Potts,-Richard-A. J. Chem. Educ.
1974, 51, 8, 539-540.
Describes a series of experiments
designed for General Chemistry in which the students prepare
metal complexes which are then used as samples for spectral
study.
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Williams,-Gregory-M.; and-others.
J. Chem. Educ. 1989, v66 n12 p1043-45.
Described is an experiment
involving the synthesis and spectral studies of cobalt
complexes that not only give General Chemistry students an
introduction to inorganic synthesis but allows them to
conduct a systematic study on the effect of different
ligands on absorption spectra. Background information,
procedures, and experimental results are
discussed.
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Magyar,-Elaine; Magyar,-James-G. J.
Chem. Educ. 1989, v66 n3 p245-46.
Investigates the four week
chemistry program in a summer program in science and
mathematics. Identifies weekly topics for the program: (1)
color and visible spectroscopy; (2) UV spectroscopy,
fluorescence, and chemiluminescence; (3) IR and NMR
spectroscopy; and (4) lists 12 individual
projects.
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Steinert,-Roger; Hudson,-Bruce. J.
Chem. Educ. 1973, 50, 129-130.
This transition, observed with an
inexpensive ultraviolet photometer, is a potentially useful
experiment for an advanced freshman class because it
introduces several concepts of general physical
interest.
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Daines,-Terri-L.; Morse,-Karen-W.
J. Chem. Educ. 1976, 53, 2, 126-127.
Describes an experiment which
quantitatively determines glucose by a spectrophotometric
measurement of the colored complex formed between glucose
and an amine.
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