HALIDES
CH Out -of-Plane Bending
Making Decisions on a Functional Group
/ What you need to know
SURVEY OF SPECTRA
Typical Infrared Absorption
Regions
WAVELENGTH (mm) C-Cl
2.5 4 5 5.5 6.1 6.5 15.4
O-H C-H C N C=O C=N C-Cl
Very C-O
N-H C C few C=C
C-N
X=C=Y bands C-C
(C,O,N,S) N=O N=O *
4000 2500 2000 1800 1650 1550 650
FREQUENCY (cm-1)
The C-X stretching region
• C-Cl 785 to 540 cm-1,
often hard to find amongst the
fingerprint bands!!
• C-Br and C-I
appear outside the useful range of
infrared spectroscopy.
• C-F bonds can be found easily, but are not
that common.
Often used as a solvent for IR spectra.
When it is used, spectra show C-Cl absorptions.
Carbon Tetrachloride
Cl
Cl C Cl C-Cl
Cl
Chlorobenzene benzene ring
combination
bands
Cl
oops
benzene
C=C C-Cl
=C-H OUT OF PLANE BENDING
OUT-OF-PLANE BENDING
(OOPS)
PLANE
above
H
ALKENES H
H
below
H also with
BENZENES
10 11 12 13 14 15 m
ALKENES
R H
Monosubstituted C C s s
H H
Disubstituted
R R
cis-1,2- C C s
H H
H R
trans-1,2- C C s
R H
R H
1,1- C C s
R H
R R
Trisubstituted C C m
R H
R R
Tetrasubstituted C C =C-H OUT OF PLANE BENDING
R R
1000 900 800 700 cm-1
BENZENES 10 11 12 13 14 15 m
Monosubstituted s s
Disubstituted
ortho s
meta m s s
para s
RING H’s
Trisubstituted OOPS
1,2,4 m s
1,2,3 s m
1,3,5 s m
combination bands
1000 900 800 700 cm-1
YOU DO NOT NEED TO MEMORIZE
THE ALKENE AND AROMATIC OOP
ABSORPTION CHARTS !
If they are needed to solve a problem on an
exam, I will provide them.
BACKGROUND
SPECTRUM
MODERN FT-IR INSTRUMENTS SUBTRACT
THE “BACKGROUND”
“BACKGROUND”
Carbon Dioxide and Water
H-O-H
H-O-H
O=C=O
MAKING DECISIONS
DECISION FLOW CHART
Tables 11-8 and 11-9
YES C=O present ?
YES
anhydride 2 C=O Peaks
acid OH present ?
amide NH present ?
ester C-O present ?
aldehyde CHO present ?
ketone
NO
C=O present ? NO
YES
OH present ? alcohol
NH present ? amine
C-O present ? ether
= present ?
C=N nitrile
= present ?
C=C alkyne
C=C present ? alkene
(benzene ?) aromatic
NO2 present ? nitro cpds
C-X present ? halides
YES C=O present ? NO
YES YES
anhydride 2 C=O Peaks OH present ? alcohol
acid OH present ? NH present ? amine
amide NH present ? C-O present ? ether
ester C-O present ? = present ?
C=N nitrile
aldehyde CHO present ? = present ?
C=C alkyne
ketone C=C present ? alkene
NO (benzene ?) aromatic
NO2 present ? nitro cpds
C-X present ? halides
GUIDELINES
DECISION FLOW CHART
Tables 11-8 and 11-9
How to Use an Infrared Spectrum
1) Molecular formula:
calculate index of hydrogen deficiency
2)
Check for carbonyl:
note any shift from 1715 cm-1
3) Check for O-H, N-H
4) Check for triple bonds
5) Check for C=C, benzene rings
How to Use an Infrared Spectrum
CONTINUED
6) Look below 1550 cm-1; check for C-O and
nitro
7) Go back over spectrum for refinements;
check the C-H region for aldehydes
and for peaks above 3000 cm-1
(alkenes and terminal alkynes)
FINAL SUMMARY
WHERE YOU SHOULD HAVE A SECURE GRASP
WHEN READING INFRARED SPECTRA
THE MINIMUM YOU NEED TO KNOW
EXPANDED CH
BASE VALUES 3000
OH 3600 3300 3100 2900 2850
NH 3400 C-H =C-H -C-H 2750
-CHO
CH 3000
CH2 and CH3 bend : 1465 and 1365
C N 2250
C C 2150 1800 1735 1725 1715 1710 1690
aldehyde acid
acid ester ketone amide
C=O 1715 chloride
C=C 1650 anhydride : 1810 and 1760
EXPANDED C=O
C-O 1100 benzene C=C : between 1400 and 1600
Know also the effects of H-bonding, conjugation and ring size.
WHERE CAN I GET
MORE SPECTRA
FOR PRACTICE?
ADDITIONAL SOURCES OF INFRARED SPECTRA
1) In the back of your laboratory book
is an index of all the infrared spectra in the book.
Pavia, Lampman, Kriz and Engel,
Introduction to Organic Laboratory Techniques,
Saunders College Publishing
2) In the Chemistry Department computer lab in the
ChemApps/Spectroscopy folder are two programs
called “Spectrabook I” and “Spectrabook II”.
These programs can display the IR spectra of many
compounds and the selection lists can be grouped
by functional group. When you click on a peak with
the mouse the group of atoms resposible for the
absorption is shown.
3) There are several web sites that have spectra,
including:
http://www.dq.fct.unl.pt/qoa/jas/ir.html
http://www.aist.go.jp/RIODB/SDBS/menu-e.html
http://webbook.nist.gov/chemistry/
http://www.chem.ucla.edu/~webnmr/index.html
http://www.nd.edu/~smithgrp/structure/workbook.html
4) Books on the subject of spectroscopy, such as:
D.L.Pavia, G.M.Lampman, and G.S.Kriz,
Introduction to Spectroscopy, 3rd ed., Harcourt.
You will probably be able to find some local WWU students
who have this book (it is used in Chem 454 and 455)
- but it is more advanced than you probably need.
5) The program “IR Tutor” can be found in the
ChemApps folder in the Chemistry Department
computer lab.
This program contains a number of sample spectra and
the vibrations responsible for each peak can be viewed
as an animation.
