8/18/2019 Infrared and UV-Visible Spectroscopy
1/45
An Introduction to Infrared andAn Introduction to Infrared and
UV-Visible SpectroscopyUV-Visible Spectroscopy
8/18/2019 Infrared and UV-Visible Spectroscopy
2/45
LEARNING OBJE!IVES
Describe the principal regions of the electromagnetic
spectrum.
Describe the principles of infrared spectroscopy.
Describe the principles of UV-Vis spectroscopy. Describe and explain the principal factors that govern the
vibrational frequencies of bonds.
Describe and explain the principal factors that govern the
electronic absorption process in UV-Vis spectroscopy. Experimental and instrumental
8/18/2019 Infrared and UV-Visible Spectroscopy
3/45
!"E ELE!RO#AGNE!I
S$E!RU#
8/18/2019 Infrared and UV-Visible Spectroscopy
4/45
%"A! IS S$E!ROSO$&'
Atoms and molecules interact with electromagneticradiation E!"# in a wide variety of ways.
Atoms and molecules may absorb and$or emit E!". Absorption of E!" stimulates different types of
motion in atoms and$or molecules. %he patterns of absorption wavelengths absorbed and
to what extent# and$or emission wavelengths emittedand their respective intensities# are called &spectra'.
%he field of spectroscopy is concerned with theinterpretation of spectra in terms of atomic andmolecular structure and environment#.
8/18/2019 Infrared and UV-Visible Spectroscopy
5/45
IN(RARE) S$E!ROSO$&
(nfrared radiation stimulates molecular
vibrations.
(nfrared spectra are traditionally displayed as)% percent transmittance# versus wave
number *+++-*++ cm-,#.
Useful in identifying presence or absence of
functional groups.
8/18/2019 Infrared and UV-Visible Spectroscopy
6/45
IN(RARE) S$E!ROSO$&
OC
O
CH3
C
O
HO
OC
O
CH3
C
O
HO
avenumber ,$ wavelengthavenumber ,$ wavelength
8/18/2019 Infrared and UV-Visible Spectroscopy
7/45
IN(RARE) S$E!ROSO$&
(n the (" region of(n the (" region of
the electromagneticthe electromagnetic
spectrum/ thespectrum/ the
absorption ofabsorption of
radiation by a sampleradiation by a sample
is due to changes inis due to changes in
the vibrationalthe vibrational
energy states of aenergy states of a
molecule.molecule.
8/18/2019 Infrared and UV-Visible Spectroscopy
8/45
IN(RARE) S$E!ROSO$&
!ethane!ethane
"oc0ing or in
plane bending
11 11 11
2
11
1 1
1 1
1
1 1
2
1 1
2
1
1
2
11
2
11
2
1
Asymmetrical
stretching
3ymmetricalstretching
4ending or scissoring
%wisting or out-
of-plane
bending
agging or out-
of-plane
bending
8/18/2019 Infrared and UV-Visible Spectroscopy
9/45
IN(RARE) S$E!ROSO$&
Only *ibrations t+at cause a c+an,e in polarity. ,i*e rise
to bands in IR spectra / 0+ic+ of t+e *ibrations for O1
are infrared acti*e'
O C O
O C O
O C O O C O
O C O
O C O
O C O O C O
3ymmetric stretch
Asymmetric stretch
4ending doublydegenerate#
8/18/2019 Infrared and UV-Visible Spectroscopy
10/45
IN(RARE) S$E!ROSO$&
hat is a vibration in a molecule5 Any change in shape of the molecule- stretching of bonds/
bending of bonds/ or internal rotation around single bonds
hat vibrations change the dipole moment of amolecule5
Asymmetrical stretching$bending and internal rotation changethe dipole moment of a molecule. Asymmetricalstretching$bending are (" active.
3ymmetrical stretching$bending does not. 6ot (" active
8/18/2019 Infrared and UV-Visible Spectroscopy
11/45
IN(RARE) S$E!ROSO$&
1uman 4reath1uman 4reath
0
20
40
60
80
100
5001000150020002500300035004000
wavenumber/cm-1
% T
O
H HO
H H
O C O
O C O
O C O
8/18/2019 Infrared and UV-Visible Spectroscopy
12/45
IN(RARE) S$E!ROSO$&
1ow much movement occurs in the vibration of a 2-
2 bond5
10 pm
154 pmstretching vibration 7or a 2-2 bond with a
bond length of ,8*
pm/ the variation is
about ,+ pm.
bending vibration
4o 10 pm
7or 2-2-2 bond anglea change of *o is
typical. %his moves a
carbon atom about ,+
pm.
8/18/2019 Infrared and UV-Visible Spectroscopy
13/45
IN(RARE) S$E!ROSO$&
hat wavelength of electromagnetic radiation is
involved in causing vibrations in molecules5
(nfrared ("# electromagnetic radiation causes vibrations in
molecules wavelengths of 98++-,8/+++ nm or 9.8 : ,8 mm#
1ow does the mass influence the vibration5 %he greater the mass - the lower the wavenumber
H2
I2
8/18/2019 Infrared and UV-Visible Spectroscopy
14/45
IN(RARE) S$E!ROSO$&
Ethane 2hloroethane
8/18/2019 Infrared and UV-Visible Spectroscopy
15/45
IN(RARE) S$E!ROSO$&
POSITIONPOSITION RE!CE #$SSRE!CE #$SS
%ON STREN&TH%ON STREN&TH'STI((NESS)'STI((NESS)
*I&HT $TO#S HI&H*I&HT $TO#S HI&H(RE+!ENC,(RE+!ENC,
STRON& %ONSSTRON& %ONSHI&H (RE+!ENC,HI&H (RE+!ENC,
STREN&THSTREN&TH CH$N&E INCH$N&E IN
PO*$RIT,.PO*$RIT,.
STRON&*, PO*$RSTRON&*, PO*$R%ONS &I/E%ONS &I/E
INTENSE %$NSINTENSE %$NS
ITHITH H,RO&EN %ONIN&H,RO&EN %ONIN& STRON& H,RO&ENSTRON& H,RO&EN
%ONIN& &I/ES%ONIN& &I/ES%RO$ %$NS%RO$ %$NS
8/18/2019 Infrared and UV-Visible Spectroscopy
16/45
IN(RARE) S$E!ROSO$&
(n general(n general
BondBond
→→
C-HC-H C-DC-D C-OC-O C-ClC-Cl
ν ν/cm/cm-1-1
→→
30003000 22002200 11001100 700700
BondBond→→
CC≡≡OO C=OC=O C-OC-O
ν ν/cm/cm-1-1
→→
21432143 17151715 11001100
8/18/2019 Infrared and UV-Visible Spectroscopy
17/45
IN(RARE) S$E!ROSO$&
4000-30004000-3000
cmcm-1-13000-20003000-2000
cmcm-1-12000-15002000-1500
cmcm-1-11500-10001500-1000
cmcm-1-1
O-HO-HN-HN-H
C-HC-H
CC CC
CC NN
CCCCCOCO
C-OC-OC-(C-(
C-CC-C
deformationsdeformations
(ncreasing energy
(ncreasing frequency
8/18/2019 Infrared and UV-Visible Spectroscopy
18/45
IN!ER$RE!A!ION O( IN(RARE) S$E!RA An element of ;udgement is required in interpreting (" spectra but you
should find that it becomes relatively straightforward with practice. (t is often possible to assign the pea0s in the ,-1 and 6-1 stretching vibrations. %oo many bonds absorb in the region of
8/18/2019 Infrared and UV-Visible Spectroscopy
19/45
IN!ER$RE!A!ION O( IN(RARE) S$E!RA
Ethanoic acid
8/18/2019 Infrared and UV-Visible Spectroscopy
20/45
Infrared Instru2entation
3ample
compartment(" 3ourceDetector
8/18/2019 Infrared and UV-Visible Spectroscopy
21/45
Infrared Instru2entation
All modern instruments are 7ourier %ransformAll modern instruments are 7ourier %ransform
instruments.instruments.
(n all transmission experiments radiation from a(n all transmission experiments radiation from a
source is directed through the sample to a detector.source is directed through the sample to a detector. %he measurement of the type and amount of light%he measurement of the type and amount of light
transmitted by the sample gives information about thetransmitted by the sample gives information about the
structure of the molecules comprising the sample.structure of the molecules comprising the sample.
8/18/2019 Infrared and UV-Visible Spectroscopy
22/45
Infrared Instru2entation
8/18/2019 Infrared and UV-Visible Spectroscopy
23/45
Infrared E3peri2ental
!o obtain an IR spectru24 t+e sa2ple 2ust be!o obtain an IR spectru24 t+e sa2ple 2ust be
placed in a 5container6 or cell t+at is transparentplaced in a 5container6 or cell t+at is transparent
in t+e IR re,ion of t+e spectru27in t+e IR re,ion of t+e spectru27
Sodiu2 c+loride or salt plates are a co22onSodiu2 c+loride or salt plates are a co22on2eans of placin, t+e sa2ple in t+e li,+t bea2 of2eans of placin, t+e sa2ple in t+e li,+t bea2 of
t+e instru2ent7t+e instru2ent7
8/18/2019 Infrared and UV-Visible Spectroscopy
24/45
InfraredE3peri2ental
IR transparent Salt $latesIR transparent Salt $lates
8/18/2019 Infrared and UV-Visible Spectroscopy
25/45
Infrared E3peri2ental
%hese plates are made%hese plates are made
of salt and must beof salt and must be
stored in astored in a 0ater free0ater free
environment such as theenvironment such as thedessicator dessicator shown here.shown here.
8/18/2019 Infrared and UV-Visible Spectroscopy
26/45
Infrared E3peri2ental
%he plates must also be%he plates must also be
handled with gloves tohandled with gloves to
avoid contact of theavoid contact of the
plate with moisture plate with moisturefrom one's hands.from one's hands.
8/18/2019 Infrared and UV-Visible Spectroscopy
27/45
Infrared E3peri2ental
%o run an (" spectrum of a%o run an (" spectrum of a
liquid sample/ a drop or twoliquid sample/ a drop or two
of the liquid sample isof the liquid sample is
applied to a salt plate.applied to a salt plate.
A second salt plate is placedA second salt plate is placed
on top of the first one suchon top of the first one such
that the liquid forms a thinthat the liquid forms a thin
film BsandwichedC betweenfilm BsandwichedC between
the two plates.the two plates.
8/18/2019 Infrared and UV-Visible Spectroscopy
28/45
Infrared E3peri2ental
%he cell holder is then%he cell holder is then
placed in the beam of the placed in the beam of the
instrument.instrument.
%he sample is then scanned%he sample is then scanned
by the instrument utiliing by the instrument utiliing
predestinated parameters. predestinated parameters.
A satisfactory spectrum hasA satisfactory spectrum has
well defined pea0s-but notwell defined pea0s-but not
so intense as to causeso intense as to causeflattening on the bottom offlattening on the bottom of
the pea0s.the pea0s.
8/18/2019 Infrared and UV-Visible Spectroscopy
29/45
Infrared E3peri2ental
%enc ac6
8/18/2019 Infrared and UV-Visible Spectroscopy
30/45
Infrared E3peri2ental
%he salt plates are cleaned%he salt plates are cleaned by rinsing into a waste by rinsing into a wastecontainer with a suitablecontainer with a suitableorganic solvent-commonlyorganic solvent-commonly
cyclohexane -cyclohexane - 6EVE" 6EVE"A%E"A%E"
2loudy plates must be2loudy plates must be polished to return them to a polished to return them to atransparent condition.transparent condition.
%o polish cloudy windows/%o polish cloudy windows/rotate salt plate on polishingrotate salt plate on polishingcloth.cloth.
8/18/2019 Infrared and UV-Visible Spectroscopy
31/45
UV-Visible Spectroscopy
Ultraviolet radiation stimulates molecular
vibrations and electronic transitions.
Absorption spectroscopy from ,
8/18/2019 Infrared and UV-Visible Spectroscopy
32/45
UV-Visible Spectroscopy
CO
O
N C
H3C
O
H3CO
COO
N C
H3C
O
H3CO
ocaine
8/18/2019 Infrared and UV-Visible Spectroscopy
33/45
UV-Visible Spectroscopy
Electronic transitions occur when the moleculeElectronic transitions occur when the molecule
absorbs energyabsorbs energy
Electronic !ransitions inElectronic !ransitions in
(or2alde+yde(or2alde+yde
Eec7rnc 7ran87n89 :; 8; an6 n eec7rn8 6 an6 < eec7rn8 C=ar>e 7ran8
8/18/2019 Infrared and UV-Visible Spectroscopy
34/45
UV-Visible Spectroscopy
8/18/2019 Infrared and UV-Visible Spectroscopy
35/45
UV-Visible Spectroscopy
8/18/2019 Infrared and UV-Visible Spectroscopy
36/45
UV-Visible Spectroscopy
Electronic transitionsElectronic transitions !olecular >rbital %heory!olecular >rbital %heory
8/18/2019 Infrared and UV-Visible Spectroscopy
37/45
UV-Visible Spectroscopy
d-d %ransitionsd-d %ransitions =d and *d ,st and 9nd=d and *d ,st and 9nd
transitions seriestransitions series
Fartially occupied dFartially occupied dorbitalsorbitals %ransitions from lower%ransitions from lower
to higher energy levelsto higher energy levels
8/18/2019 Infrared and UV-Visible Spectroscopy
38/45
UV-Visible Spectroscopy
2harge %ransfer 2harge %ransfer
Electron donor and acceptor characteristicsElectron donor and acceptor characteristics Absorption involves e- transitions from donor to acceptor Absorption involves e- transitions from donor to acceptor
326326-- to 7e(((#to 7e(((# 7e((# and neutral 3267e((# and neutral 326
!etal is acceptor!etal is acceptor
"educed metals can be exception"educed metals can be exception
8/18/2019 Infrared and UV-Visible Spectroscopy
39/45
UV-Visible Spectroscopy
!"E BEER-
LA#BER! LA%
7or a light absorbing
medium/ the light
intensity falls
exponentially with
sample depth.
7or a light absorbing
medium/ the light
intensity falls
exponentially with
increasing sample
concentration.
100xI
IT
I
IT
o
t
o
t
==
I I7
l
cuve77e 2 5 >
= 7 5 n 7 e n 8 5 7 ? ' I )
Sam:e 6e:7=
I
I7
l
8/18/2019 Infrared and UV-Visible Spectroscopy
40/45
UV-Visible Spectroscopy
A b s o r b a n
c e
Cncen7ra7n
T Acl A ,+log−== λ ε T Acl A ,+log−== λ ε
T!e ne#ati$e lo#arit!m of T is calledt!e a%sor%ance & A' and t!is isdirectl( )ro)ortional to sam)le de)t!&called )at!len#t!* l ' and sam)leconcentration &c '+ T!e e,ation iscalled t!e Beer-.am%ert la+
ε is called t!e molara%sor)tion coefficient
and !as nits of dm3
mol-1 cm-1
8/18/2019 Infrared and UV-Visible Spectroscopy
41/45
UV-Visible Spectroscopy
Beer-La2bert La0
li2itations Folychromatic GightFolychromatic Gight
Equilibrium shiftEquilibrium shift 3olvent3olvent
p1 p1
8/18/2019 Infrared and UV-Visible Spectroscopy
42/45
UV-Visible Instru2entation
3everal types of spectrometer 3everal types of spectrometer
8/18/2019 Infrared and UV-Visible Spectroscopy
43/45
UV-Visible Instru2entation
Gight sourceGight source Deuterium and hydrogen lampsDeuterium and hydrogen lamps
filament lamp filament lamp
He arc lampsHe arc lamps 3ample containers3ample containers
2uvettes2uvettes
FlasticFlastic
IlassIlass
JuartJuart
8/18/2019 Infrared and UV-Visible Spectroscopy
44/45
UV-Visible Spectroscopy
Open-topped rectangularstandard cell (a) andapertured cell (b) for limitedsample volume
.CO.CO
8/18/2019 Infrared and UV-Visible Spectroscopy
45/45
UV-Visible Spectroscopy
Ac0nowledgementsAc0nowledgements 4ette Kreu/ "uth Dusenbery at Department of 6atural4ette Kreu/ "uth Dusenbery at Department of 6atural
3ciences U!-Dearborn.3ciences U!-Dearborn.
Dr David L !cIarvey at Keele University 1ewlett Fac0ard
Andrew Lac0son at 3taffordshire University