Short_Review

Short_Review - IR
Spectroscopy
 
 
 
 


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Unformatted text preview: IR
Spectroscopy
 
 
 
 
 Things
to
remember:
 1.

Only
bonds
with
a
dipole
moment
show
up
in
the
IR
region
 2.

Secondary
amines
(i.e.
NHR2)
show
a
“doublet”
peak
 3.

Primary
amines
(i.e.
NH2R)
show
a
“singlet”
peak
 4.

Carboxylic
acid
O‐H
stretches
are
significantly
BROAD
peaks
where
as
H‐ bonded
O‐H
stretches
show
broad
stretches
and
non‐H‐bonded
O‐H
stretches
 show
sharp
peaks
 
 Important
stretches
to
remember
 
 Bond
Type
 
 
 
 Wavenumber
(cm‐1)
 
 O‐H,
N‐H
 ~3400
 
 sp
C‐H
(alkyne)
 3100
 
 sp2
C‐H
(alkene)
 >3000
 3
C‐H
(alkane)
 
 sp <3000
 
 Aldehyde
C‐H
 2750
&
2850
 
 sp
C‐C,
C‐N
 2150
 
 sp2
C‐C
 1650
 2
C‐C
(Aromatic)
 
 sp 1650
&
1500
 
 Carbonyls
 
 
 amide
 1680
 
 carboxylic
acid
 1710
 
 ketone
 1715
 
 aldehyde
 1725
 
 ester
 1735
 
 acid
chloride
 1790
 
 anhydride
 1780
&
1810
 
 Trends:
 Conjugation:

Subtract
20
cm‐1
to
“base”
(per
dbl
bond,
excluding
aromatic
 rings)
 
 Ring
strain:
Add
20
cm‐1
to
“base”
(i.e.
per
variation
from
a
6‐mem
ring)
 
 Can
have
BOTH
in
the
same
molecule
 
 NMR
Spectroscopy
 
 
 
 
 
 
 
 Things
to
remember:
 
 1.

Downfield
=
larger
numbers
=
closer
to
an
electron
withdrawing
group
 
 





Upfield
=
smaller
numbers
=
closer
to
an
electron
donating
group
 3.

You
WILL
be
given
a
chart
with
1H
and
13C
NMR
values
 4.

Coupling
constants
(J):
 
 Vicinal
(att.
to
adjacent
C):
6‐8
Hz
 Geminal
(att.
to
same
C):
4‐10
Hz
 
 Trans
(across
alkene):
11‐18
Hz
 
 Cis
(across
alkene):
6‐15
Hz
 
 
 
 Remember:
When
assigning
peaks
in
a
spectrum,
consider
the
regions
in
which
a
 functional
group
with
NORMALLY
fall…not
just
considering
which
functional
group
 is
closest
to
the
electronegative
atom,
etc.

The
presence
of
the
EWG
(or
EDG)
will
 simply
move
the
peak
either
downfield
or
upfield
WITHIN
it’s
“normal”
range.
 
 Mass
Spectroscopy
 
 
 
 
 
 Things
to
remember:
 
 1.

Only
charged
species
show
on
the
MS
 2.

The
farthest
peak
to
the
right
(with
the
exception
of
M+1,
M+2
isotope
 peaks)
is
the
molecular
ion
peak,
or
the
Mol.
Weight
–
Mass
of
an
Electron
 3.

The
largest
peak
is
the
base
peak.

This
CAN
be
the
same
as
the
M+.
 4.

Remember
that
the
order
of
ionization
is
as
follows:
 
 lone
pairs
>
π
e‐
>
σ
e‐
 5.

When
a
neutral
fragment
is
lost
(i.e.
no
radical
or
charge),
the
peak
 appears
at
an
EVEN
m/z
 
 Consider
McLafferty
Rearr!!
 READ
IN
YOUR
BOOK
ABOUT
FRAGMENTATION!!

PRACTICE
IT!
It
only
 becomes
easy
AFTER
you
have
tried
it!
 5.

Splitting
occurs
when
there
is
an
interaction
in
the
magnetic
fields
of
 protons
on
adjacent
carbons.
 N+1
Rule:
For
a
particular
proton
(or
set
of
EQUIVALENT
protons),
 count
the
number
of
adjacent
protons
and
add
one.

That
will
be
the
 pattern
that
will
appear
for
the
particular
proton
or
set
of
protons.
 6.

Coupling
constants
will
be
the
distance
between
peaks
in
a
multiplet.
 7.

NO
SPLITTING
OR
COUPLING
FOR
13C
NMR!!

Only
singlet
peaks.
 ...
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This note was uploaded on 01/17/2011 for the course PHYS 6a taught by Professor Stanek during the Fall '07 term at UCSB.

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