1. INTEGRATION

2. NMR Spectrum of Phenylacetone
RECALL
Each different type of proton comes at a different place .
You can tell how many different types of hydrogen
there are in the molecule.
from last
time

3. INTEGRATION OF A PEAK Integration = determination of the area
Not only does each different type of hydrogen give a
distinct peak in the NMR spectrum, but we can also tell
the relative numbers of each type of hydrogen by a
process called integration.
Integration = determination of the area
under a peak
The area under a peak is proportional
to the number of hydrogens that
generate the peak.

4. Benzyl Acetate 55 : 22 : 33 = 5 : 2 : 3 METHOD 1 integral line
The integral line rises an amount proportional to the number of H in each peak
METHOD 1
integral line
integral
line
55 : 22 : = : 2 : 3
simplest ratio
of the heights

5. Benzyl Acetate (FT-NMR)
Actually :
/ 11.3
= 5.14
/ 11.3
= 1.90
/ 11.3
= 3.00
METHOD 2
assume CH3
/ 3 = 11.3
digital
integration
Integrals are
good to about
10% accuracy.
Modern instruments report the integral as a number.

6. DIAMAGNETIC ANISOTROPY
SHIELDING BY VALENCE ELECTRONS

7. Diamagnetic Anisotropy
The applied field
induces circulation
of the valence
electrons - this
generates a
magnetic field
that opposes the
applied field.
valence electrons
shield the nucleus
from the full effect
of the applied field
magnetic field
lines
B induced
(opposes Bo)
Bo applied
fields subtract at nucleus

8. PROTONS DIFFER IN THEIR SHIELDING
All different types of protons in a molecule
have a different amounts of shielding.
They all respond differently to the applied magnetic
field and appear at different places in the spectrum.
This is why an NMR spectrum contains useful information
(different types of protons appear in predictable places).
UPFIELD
DOWNFIELD
Highly shielded
protons appear here.
Less shielded protons
appear here.
SPECTRUM
It takes a higher field
to cause resonance.

9. CHEMICAL SHIFT

10. PEAKS ARE MEASURED RELATIVE TO TMS
Rather than measure the exact resonance position of a
peak, we measure how far downfield it is shifted from TMS.
reference compound
tetramethylsilane
“TMS”
Highly shielded
protons appear
way upfield.
TMS
Chemists originally
thought no other
compound would
come at a higher
field than TMS.
shift in Hz
downfield n

11. REMEMBER FROM OUR EARLIER DISCUSSION
Stronger magnetic fields (Bo) cause
the instrument to operate at higher
frequencies (n).
field
strength
frequency g 2p
hn = Bo
NMR Field
Strength
1H Operating
Frequency
constants
1.41 T
60 Mhz
2.35 T
100 MHz
n = ( K) Bo
7.05 T
300 MHz

12. HIGHER FREQUENCIES GIVE LARGER SHIFTS
The shift observed for a given proton
in Hz also depends on the frequency
of the instrument used.
Higher frequencies
= larger shifts in Hz.
TMS
shift in Hz
downfield n

13. THE CHEMICAL SHIFT
The shifts from TMS in Hz are bigger in higher field
instruments (300 MHz, 500 MHz) than they are in the
lower field instruments (100 MHz, 60 MHz).
We can adjust the shift to a field-independent value,
the “chemical shift” in the following way:
parts per
million
shift in Hz
chemical
shift
= d =
= ppm
spectrometer frequency in MHz
This division gives a number independent
of the instrument used.
A particular proton in a given molecule will always come
at the same chemical shift (constant value).

14. HERZ EQUIVALENCE OF 1 PPM
What does a ppm represent?
1 part per million
of n MHz is n Hz
1H Operating
Frequency
Hz Equivalent
of 1 ppm 1
n MHz = n Hz ( )
60 Mhz Hz
106
100 MHz Hz
300 MHz Hz 7 6 5 4 3 2 1
ppm
Each ppm unit represents either a 1 ppm change in
Bo (magnetic field strength, Tesla) or a 1 ppm change
in the precessional frequency (MHz).

15. NMR Correlation Chart d (ppm)
-OH
-NH
DOWNFIELD
UPFIELD
DESHIELDED
SHIELDED
CHCl3 ,
TMS
d (ppm) 12 11 10 9 8 7 6 5 4 3 2 1 H
CH2F
CH2Cl
CH2Br
CH2I
CH2O
CH2NO2
CH2Ar
CH2NR2
CH2S
C C-H
C=C-CH2
CH2-C-
C-CH-C
RCOOH
RCHO
C=C C
C-CH2-C
C-CH3 O
Ranges can be defined for different general types of protons.
This chart is general, the next slide is more definite.

16. R-CH3 0.7 - 1.3 R-N-C-H 2.2 - 2.9 R-C=C-H R-CH2-R 1.2 - 1.4 4.5 - 6.5
APPROXIMATE CHEMICAL SHIFT RANGES (ppm) FOR SELECTED TYPES OF PROTONS
R-CH
R-N-C-H
R-C=C-H
R-CH2-R
R-S-C-H
R3CH
I-C-H H
R-C=C-C-H
Br-C-H O
Cl-C-H
R-C-C-H O O
RO-C-H
R-C-N-H
RO-C-C-H
HO-C-H O O O
R-C-H
HO-C-C-H
R-C-O-C-H O
N C-C-H
O2N-C-H
R-C-O-H
R-C C-C-H
F-C-H
C-H
R-N-H Ar-N-H R-S-H
R-O-H Ar-O-H
R-C C-H

17. YOU DO NOT NEED TO MEMORIZE THE PREVIOUS CHART
IT IS USUALLY SUFFICIENT TO KNOW WHAT TYPES
OF HYDROGENS COME IN SELECTED AREAS OF
THE NMR CHART
C-H where C is attached to an
electronega-tive atom
CH on C
next to
pi bonds
acid
COOH
aldehyde
CHO
benzene CH
alkene
=C-H
aliphatic
C-H
X=C-C-H
X-C-H 12 10 9 7 6 4 3 2
MOST SPECTRA CAN BE INTERPRETED WITH
A KNOWLEDGE OF WHAT IS SHOWN HERE

18. DESHIELDING AND ANISOTROPY
Three major factors account for the resonance
positions (on the ppm scale) of most protons.
1. Deshielding by electronegative elements.
2. Anisotropic fields usually due to pi-bonded
electrons in the molecule.
3. Deshielding due to hydrogen bonding.
We will discuss these factors in the sections that
follow.

19. DESHIELDING BY
ELECTRONEGATIVE ELEMENTS

20. Cl C H d- d+ DESHIELDING BY AN ELECTRONEGATIVE ELEMENT d- d+
Chlorine “deshields” the proton,
that is, it takes valence electron
density away from carbon, which
in turn takes more density from
hydrogen deshielding the proton. Cl C H d- d+
electronegative
element
NMR CHART
“deshielded“
protons appear
at low field
highly shielded
protons appear
at high field
deshielding moves proton
resonance to lower field

21. Electronegativity Dependence of Chemical Shift
Dependence of the Chemical Shift of CH3X on the Element X
Compound CH3X
CH3F CH3OH CH3Cl CH3Br CH3I CH4 (CH3)4Si
Element X
F O Cl Br I H Si
Electronegativity of X
Chemical shift d
most
deshielded
TMS
deshielding increases with the
electronegativity of atom X

22. Substitution Effects on Chemical Shift
most
deshielded
The effect
increases with
greater numbers
of electronegative
atoms.
CHCl3 CH2Cl2 CH3Cl
ppm
most
deshielded
-CH2-Br CH2-CH2Br -CH2-CH2CH2Br
ppm
The effect decreases
with incresing distance.

23. ANISOTROPIC FIELDS DUE TO THE PRESENCE OF PI BONDS
The presence of a nearby pi bond or pi system
greatly affects the chemical shift.
Benzene rings have the greatest effect.

24. fields add together

25. H H C=C H H ANISOTROPIC FIELD IN AN ALKENE Bo protons are deshielded
shifted
downfield
fields add
C=C H H
secondary
magnetic
(anisotropic)
field lines Bo

26. H C C H ANISOTROPIC FIELD FOR AN ALKYNE Bo secondary magnetic
Shielded Bo
hydrogens
are shielded
fields subtract

27. HYDROGEN BONDING

28. HYDROGEN BONDING DESHIELDS PROTONS
The chemical shift depends
on how much hydrogen bonding
is taking place.
Alcohols vary in chemical shift
from 0.5 ppm (free OH) to about
5.0 ppm (lots of H bonding).
Hydrogen bonding lengthens the
O-H bond and reduces the valence
electron density around the proton
- it is deshielded and shifted
downfield in the NMR spectrum.

29. SOME MORE EXTREME EXAMPLES
Carboxylic acids have strong
hydrogen bonding - they
form dimers.
With carboxylic acids the O-H
absorptions are found between
10 and 12 ppm very far downfield.
In methyl salicylate, which has strong
internal hydrogen bonding, the NMR
absortion for O-H is at about 14 ppm,
way, way downfield.
Notice that a 6-membered ring is formed.