Get In The Zone
The basics of Reading Infrared Spectrometry Graphs
What You Will Learn
This
is
a
tutorial
to
help
you
learn
to
recognize
and
read
the
peaks
in
Infrared
Spectrometry
Graphs.
A Bit About Infrared
Molecules
are
vibrating.
When
they
absorb
photons
of
the
appropriate
energy
changes
this
vibration.
What Do We Want to Know?
We
want
to
know
how
the
structure
is
related
to
the
energy
that
is
absorbed.
Why Should I care?
This
will
let
us
make
conclusions
about
the
structure.
What does an IR spectrum show us?
FUNCTIONAL
GROUPS!!!
Sooo…what are we looking at?
X
AXIS:
stretching
frequency
Y
AXIS:
number
of
photons
absorbed
More
detail
about
the
X
and
Y
axis
are
explained
in
detail
in
Dr.
Hardinger’s
lectures.
This
tutorial
is
focused
more
on
how
to
determine
the
peaks
in
the
IR
spectrum…
What are we looking for?
PEAKS!
We
are
looking
for
downward
spikes
in
the
graph.
Why are some peaks bigger than others?
Polarity
determines
the
peak’s
strength.
The
more
polar
a
molecule
is,
the
stronger
the
peak
is.
Repetition
can
also
determine
strength;
many
of
the
same
functional
group
leads
to
a
larger
peak.
How does this help us?
This
helps
us
associate
peaks
with
the
bonded
atoms.
Prep Work!!!
Calculate
the
DBE!
You
will
need
to
look
at
the
DBE
value
to
determine
the
number
of
pi
bonds.
This
will
help
you
eliminate
and
differentiate
among
functional
groups.
ZONE 1
This
zone
takes
place
between
3700‐3200
cm‐1
(on
the
x
axis)
[
citation
(a)
]
What are we looking for?
Alcohols,
terminal
alkynes,
N‐H
stretches
Tips to Note:
Peaks
may
vary
in
size.
Do
not
immediately
rule
out
peaks
because
you
think
they
are
too
small!
The
Breakdown
Alcohols (O–H)
Occur
around
3650
–
3200
cm‐1
Alcohols
have
a
very
distinct
strong
and
broad
shape.
When
we
see
this
sort
of
elongated
“U”
shape
around
this
region,
we
know
there
is
an
alcohol
group.
It
will
generally
look
like
the
portion
encircled
in
the
pink
oval
below.
[
citation
(a)
]
Terminal Alkynes (=C-H)
Occurs
around
3340
‐
3250
cm‐1
Terminal
Alkynes
are
generally
stronger
and
sharper
in
shape.
The
peak
within
the
pink
oval
below
is
a
terminal
alkyne.
Be
on
the
lookout
for
similar
shapes
in
this
region.
[
citation
(b)
]
N–H stretches
Occurs
around
3500
‐
3200
cm‐1
N
–
H
stretches
can
mean
amines
or
amides,
but
it
does
not
necessarily
have
to
indicate
either
of
these.
These
are
medium
in
intensity,
but
are
broader
in
appearance.
NOTE:
Be
sure
to
look
at
your
molecular
formula
to
make
sure
a
nitrogen
exists
in
your
molecule!
A
nitrogen
is
necessary
for
the
existence
of
an
N‐H
stretch!
All
three
of
the
following
are
N‐H
stretches.
The
first
shows
a
primary
amine,
and
the
second
shows
a
tertiary
amine.
The
last
image
shows
an
N‐H
stretch
,which
is
significantly
smaller
than
in
the
other
examples,
but
still
counts.
[
citation
(b)
]
[
citation
(b)
]
[
citation
(c)
]
ZONE 2
This
zone
takes
place
between
3200
‐
2700
cm‐1
(on
the
x
axis)
[
citation
(a)
]
What are we looking for?
Sp2
carbons,
sp3
carbons,
aldehydes,
carboxylic
acid
Tips to Note:
Look
for
C‐H
bonding
in
this
zone!
We
are
in
organic
chemistry;
nearly
every
molecule
that
we
deal
with
will
involve
C‐H
bonding.
Use
your
writing
utensil
to
map
out
areas
and
focus
in
on
these
specific
areas
to
make
sure
you
are
reading
the
graph
accurately!
The
Breakdown
Sp2
Carbon -Hydrogen (C-H)
Occurs
around
3100
‐
3000
cm‐1
Sp2
carbons
may
vary
in
size
and
shape
It
is
important
to
note
exactly
where
you
see
the
peak!
This
peak
will
occur
in
a
very
small
range,
highlight
it
and
note
it
down!
[
Professor
Steven
Hardinger’s
Thinkbook
]
Sp3
Carbon -Hydrogen / Alkyl (C-H)
Occurs
around
2960
‐
2850
cm‐1
3
Sp carbons
may
also
vary
in
size
and
shape
It
is
important
to
note
exactly
where
you
see
the
peak!
This
peak
will
occur
in
a
very
small
range,
highlight
it
and
note
it
down!
[
Professor
Steven
Hardinger’s
Thinkbook
]
Aldehyde (C-H)
One
peak
around
2900
cm‐1
and
another
around
2700
cm‐1
Aldehydes
are
of
medium
length
and
have
two
peaks.
Be
careful!!
The
first
peak
is
often
distorted
by
sp3
carbons
and
may
not
bee
seen!
Look
for
the
second
peak
around
2700
cm‐1.
[
Professor
Steven
Hardinger’s
Lecture
Supplement]
The
second
peak
is
circled
in
pink
in
the
image
above
CarboxylIc AcId (O-H)
Occurs
around
3000‐2500
cm‐1
We
can
determine
a
carboxylic
acid
by
looking
for
a
strong,
broad
peak.
BE
CAREFUL!!!
A
carboxylic
acid
has
two
components,
there
must
also
be
a
C
=
O
in
zone
4
to
have
a
carboxylic
acid!!!
Notice
that
there
is
an
OH
stretch
in
zone
2
and
a
C=O
stretch
in
zone
4!
[
citation
(d)
]
Here’s
another
example
[
citation
(a)
]
ZONE 3
This
zone
takes
place
between
2300
‐
2000
cm‐1
(on
the
x
axis)
[
citation
(a)
]
The
Breakdown
Alkyne (C≡C)
Around
2260‐2000
cm‐1
Alkynes
have
variable
and
sharp
peaks,
such
as
the
peak
circled
in
pink
below.
Note:
Look
at
your
DBE
value!
You
need
2
pi
bonds
to
form
a
triple
bond
[
citation
(e)
]
Nitrile
(C≡N)
One
around
2260‐2220
cm‐1
Alkynes
have
variable
and
sharp
peaks,
such
as
the
peak
in
the
pink
circle
below
NOTE:
REMEMBER
TO
USE
YOUR
MOLECULAR
FORMULA!!!
If
there
are
no
nitrogens
present,
you
will
not
have
a
nitrile
group!
ALSO
NOTE:
Also,
mind
the
nitrogens
in
zone
1!
DOUBLY
ALSO
NOTE:
LOOK
AT
YOUR
DBE!
You
need
2
pi
bonds
to
form
a
nitrile
group.
[
citation
(b)
]
ZONE 4
This
zone
takes
place
between
1850‐1650
cm‐1
(on
the
x
axis)
This
zone
contains
carbonyls.
REMEMBER:
Carbonyls
are
carbons
double
bonded
to
Oxygens.
PI
BONDS
ARE
NECESSARY!
LOOK
AT
YOUR
DBE
VALUE!
ALSO
REMEMBER:
Many
of
these
carbonyls
relate
to
other
peaks
in
various
other
zones
of
the
graph.
For
some
of
these
functional
groups
to
exist,
there
must
be
other
corresponding
peaks.
LOOK
FOR
THEM!
DOUBLY
ALSO
REMEMBER:
All
of
the
peaks
in
this
zone
appear
strong.
Pay
attention
to
the
number
of
photons
absorbed
(the
y
axis
value)!!!
[
citation
(a)
]
The
Breakdown
Ketone (C=O)
Around
1750‐1705
cm‐1
Ketones
will
have
a
strong
peak.
GENERALLY
Look
for
number
of
photons
in
the
low
1700s.
This
may
not
always
be
the
case,
however.
Remember
to
look
for
signs
of
conjugation!
[
citation
(d)
]
NOTE:
1715
is
a
common
value
for
a
ketone,
but
can
also
apply
to
aldehydes.
They
fall
within
similar
ranges.
How
can
I
tell
the
difference?
If
there
is
an
aldehyde,
there
will
also
be
the
double
peaked
formation
in
zone
2!
Be
on
the
lookout
and
keep
relating
what
you
already
know
to
what
you
are
finding
in
the
following
zones!
Aldehyde (C=O)
Around
1740‐1720
cm‐1
Aldehydes
will
have
a
strong
peak.
Look
in
the
low
1700s,
but
GENERALLY
closer
to
the
1720
range.
This
may
not
always
be
the
case,
however.
Remember
to
look
for
signs
of
conjugation!
Notice
the
aldehyde
peak
in
zone
2
as
well!
[
Professor
Steven
Hardinger
Lecture
Supplement
]
Esters (C=O)
Around
1750‐1735
cm‐1
Esters
will
have
a
strong
peak.
Numbers
around
the
1740s
range
are
typical.
This
may
not
always
be
the
case,
however.
Remember
to
look
for
signs
of
conjugation!
[
citation
(d)
]
CarboxylIc
AcId (C=O)
Around
1250‐1700
cm‐1
The
carbonyl
will
have
a
strong
peak.
Look
around
1710s
to
1720s.
Again,
these
numbers
may
vary,
this
is
just
a
general
guideline
for
what
would
be
considered
typical.
Notice
the
O‐H
stretch
in
zone
2!!!
This
is
necessary
for
a
carboxylic
acid!
[
citation
(d)
]
AmIde (C=O)
Around
1690
‐
1650
cm‐1
The
carbonyl
stretch
will
be
strong,
again.
Look
for
the
number
of
Nitrogens
in
your
molecule.
Also,
look
for
the
amid
group
in
zone
1!
[
citation
(b)
]
ZONE 5
This
zone
takes
place
between
1680‐1450
cm‐1
(on
the
x
axis)
NOTE:
This
zone
includes
double
bonds!
Look
at
your
DBE
values!!!
The
Breakdown
Alkene (C=C)
Around
1680
to
1620
cm‐1
This
peak
may
vary.
It
may
help
to
highlight
this
region
to
better
see
the
peak.
Check
your
DBE
value!
[
citation
(d)
]
Benzene (C=C)
One
peak
around
1600
cm‐1
and
another
around
1500‐1450
cm‐1
This
peak
may
vary.
The
peak
at
1600
may
have
2
peaks.
Look
for
both
peaks
and
a
DBE
value
of
at
least
4!
[
Professor
Steven
Hardinger’s
Lecture
Supplement
]
Additional Notes
BEWARE
OF
CONJUGATION!!!
We
remember
that
conjugation
lowers
the
energy
of
a
molecule.
This
implies
in
reading
IR
graphs
as
well.
If
functional
groups
are
conjugated,
the
pi
bond
can
will
lower
the
stretching
frequency.
More
conjugation
leads
to
A
lower
stretching
frequency.
You
can
suspect
conjugation
when
peaks
are
at
the
lower
end
of
their
range.
HIGHLIGHT
THE
ZONES!!!
When
getting
used
to
working
with
the
different
zones,
it
may
be
helpful
to
color
code
the
zones
so
you
can
zero
in
on
specific
areas
and
differentiate
peaks
that
way.
DON’T
WORRY
ABOUT
MEMORIZATION!!!
The
table
of
zones
and
stretching
frequencies
will
be
given
to
you
on
a
test
REMEMBER
YOUR
DBE
VALUES!!!
Pi
bonding
is
essential
in
determining
and
ruling
out
certain
functional
groups.
ALWAYS
REFER
BACK
TO
THE
FORMULA!!!
If
the
formula
is
given
to
you,
remember
to
refer
back
to
it.
This
formula
gives
you
ESSENTIAL
information
on
the
atoms
involved
in
the
molecule.
Work Cited
(a) Clark,
Jim.
"Interpreting
Infra‐red
Spectra."
Interpreting
Infra­red
Spectra.
2000.
Web.
11
May
2012.
<http://www.chemguide.co.uk/analysis/ir/interpret.html>.
(b) Glagovich,
Neil.
"Infrared
Spectroscopy."
CHEM
316.
2012.
Web.
11
May
2012.
<http://www.chemistry.ccsu.edu/glagovich/teaching/316/index.html>.
(c) Matt.
"Infrared
Absorbance
Spectroscopy
(IR)."
MendelSet.
Mendelset,
19
July
2011.
Web.
11
May
2012.
<http://www.mendelset.com/articles/686/infrared‐
absorbance‐spectroscopy‐ir>.
(d) "IR
Spectroscopy
Tutorial."
IR:
Carboxylic
Acids.
University
of
Colorado,
Boulder,
Chemistry
and
Biochemistry
Department,
2011.
Web.
11
May
2012.
<http://orgchem.colorado.edu/Spectroscopy/irtutor/carbacidsir.html>.
(e) "ChemWiki:
The
Dynamic
Chemistry
Textbook."
Chem
Wiki
Davis.
University
of
California,
Davis,
7
Oct.
2011.
Web.
11
May
2012.
<http://chemwiki.ucdavis.edu/>.
(f) Professor
Steven
Hardinger’s
Lecture
Supplement
(g) Professor
Steven
Hardinger’s
Thinkbook