ESSENTIAL NMR EXPERIMENTS FOR EVERY ORGANIC CHEMIST

1
ESSENTIAL NMR EXPERIMENTS FOR EVERY ORGANIC
CHEMIST
A presentation by Dr. M. Sales in the
Laboratories of Prof. A. B. Charette 10 January
2005
2
General Outline
1. Introduction to information that can be
obtained from NMR spectroscopy
2. A Diels-Alder adduct is used as an example to
illustrate The various NMR experiments that can
be obtained
2.1-2.3 Examples of C,H (heteronuclear)
correlation experiments
2.4, 2.5 and 2.10 Examples of H,H (homonuclear)
correlation experiments
2.6-2.9 Examples of NOE and chemical exchange
experiments
3. A brief application of experiments on a
precursor substrate
4. Recommended resources for a detailed
INTRODUCTION to NMR Theory and Application
3
Problems, problems
4
1. What information can NMR spectroscopy provide
Structural Theory NMR equivalent
Qualitative composition Choice of nucleus / isotope
Quantitative composition Signal intensities / integration
Functional groups Chemical shifts
Connectivity J (scalar) couplings
Spatial relationship of atoms NOE (distance) J couplings (dihedral angle)
Dynamics Chemical exchange, lineshape broadening
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1.1 Functional group information from Chemical
Shift
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1.2 Connectivity information from scalar coupling
1JHC HMQC (Heteronuclear Multiple Quantum Coherence)
2JHC, 3JHC HMBC (Heteronuclear Multiple Bond Correlation)
2JHH and 3JHH 2D COSY (Correlation SpectroscopY) Homodecoupling, 1D selective COSY
2JHH ,3JHH, 4JHH, 5JHH 2D TOCSY (TOtal Correlation SpectroscopY) 1D selective TOCSY
7
1.3 Spatial Relationships of atoms from scalar
couplings
The Karplus equation relates 3JHH with the
dihedral angle. 3JHH values are obtained from
routine H NMR spectra and homodecoupling
experiments.
C. Altona et al Magn. Res. Chem. 1994, 32, 670
Coupling constant analysis assigns the
4,4a-syn/anti relationship
8
1.4 Spatial Relationships of atoms from NOE
Typical usage of NOE relationships in literature
to assign relative stereochemistry
Arakawa, Y. et al Chem. Pharm. Bull. 2003, 51,
1015-1020
1.5 Investigation of Dynamic processes by
observation of Chemical Exchange
Line-broadening and coalescence of signals are
routine methods to investigate Dynamics in
moleculer systems. However, 1D and 2D EXSY
(EXchange SpectroscopY) methods can indicate
chemical exchange before line broadening occurs
Perrin, C. L. and Dwyer T. J. Chem. Rev. 1990,
90, 935-967
2D EXSY of N,N-dimethylformamide
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2. DA derivative used in NMR study
Examples of the following NMR experiments of the
DA derivative will be presented
13C NMR DEPT HMQC HMBC
1H NMR 2D COSY 2D TOCSY 2D NOESY 1D NOE 2D ROESY
homodecoupling 1D selective COSY 1D EXSY
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2.1 C-13 and DEPT
7
CO
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2.1 C-13 and DEPT
4xAr d
Ar one aromatic carbon
2xAr d


Ar d


4 d
3 d

2 x Ar s
Ar s


2 x Ar d
12
2.1 C-13 and DEPT
1
6
2
5
7
2
2
1
2 x CH2Ph
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2.2 HMQC
4
3
2
5
1 2
1
2
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2.2 HMQC
1
2
o-Ar
1
5
3
2
4
2
6
15
2.3 HMBC
D
A
C
Regions A, B, C and D are expanded on next slide.
B
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2.3 HMBC
o-Ar (Bn)
Unambiguous assignment of ortho-Ar to the
benzylic moeity attached to C-1.
2
6
CO
CH2Ph (1)
CH2Ph (2)
Region B
Region A
C-2
CH2Ph (1)
C-1
2
2
C-5
C-2
CH2Ph (2)
C-1
1
1
CH2Ph (1)
C-2
1
1
CH2Ph (2)
C-6
2
2
Region C
Region D
Unambiguous assignment of both CH2Ph is achieved
from analysis of HMBC spectrum
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2.4 COSY
7
5
6
2
3
4
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2.4 COSY
6
2
5
1
1
5
6
2
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2.4 COSY
2
1
1
2
2
1
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2.4.1 Spin system deduced from COSY
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2.5 Homodecoupling
Reference (Irradiate 9 ppm)
2 (4.56 ppm) 2.6, 5.5 Hz
4 (6.37 ppm)
decoupled (Irradiate 6.37 ppm)
reference
J 2-4 0.5 Hz
J 2-3 5.5 Hz J 2-1 2.6 Hz
decoupled
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2.5 Homodecoupling
Reference (Irradiate 9 ppm)
2 (4.56 ppm)
3 (6.28 ppm) 1.5, 7 Hz
1 (2.56 pm) 4.7, 9.5, 10 Hz
Decoupled (Irradiate 4.56 ppm)
reference
J 1-2 2.6 Hz
J 2-3 5.5 Hz
J 1-1 4.7 Hz J 1-1 9.5 Hz J 1-2 10 Hz
J 3-5 1.5 Hz J 3-4 7 Hz
decoupled
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2.5.1 Analysis of coupling constants
4 possible relative configurations where dihedral
angle between HC-1 and HC-2 is 0 º. (J 1-2
10 Hz)
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2.6 2D NOESY
1 2
7
3
4
5
6
1 2
Integration of NOE crosspeaks Reference
Diagonal of protons 1 and 2 Integrate for 2.00
4
3
6
5
7
-1 NOE
-4 NOE
-3 NOE
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2.6.1 Assignment of benzylic protons with the
aid of NOE crosspeaks
CH2Ph
CH2Ph
Note No scalar couplings between 1 or 2 to any
of the benzylic were observed in the COSY or
homodecoupling experiments. Therefore
NOE/dipolar interactions are used to assign
benzylic protons
1
2
1 2
5
1 2
6
2
1/2-6 -7
1/2-2 -4
1-CH2Ph -3
1-CH2Ph -2
5-6 -5
CH2Ph (1)
CH2Ph (2)
2-CH2Ph -3
2-CH2Ph -3
1-2 -2
Note The combined NOE between 1,2-6 of -7
offers further support for assigned relative
configuration
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2.6.2 Chemical exchange crosspeaks observed in
2-D NOESY
E/Z isomerism of 3o amide
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2.6.2 Chemical exchange crosspeaks observed in
2-D NOESY
2 (E)
2 (Z)
These expansions of the 2-D NOESY spectrum
clearly indicate that the crosspeaks correlate
the proton resonances of the major conformer (E)
to those of the minor conformer (Z). This
establsihes the identity of the minor species in
the H NMR spectrum as a conformer of the major
compound and not a contaminant.
2 (E)
2 (Z)
7 (E)
7 (Z)
2 (E)
2 (Z)
6 (Z)
6 (E)
7 (Z)
2 (E)
2 (Z)
6 (Z)
7 (E)
6 (E)
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2.6.3 Further support for the assigment of o-Ar
(Bn) via analysis of NOE crosspeaks
CH2Ph (1)
2
o-Ar (PhCON)
-0.5
-1
-1.5
region expanded
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2.7 1D NOE
7
5 3
6 4
4 1.5
3 0.5
7 (Z)
4
5 8
2 3
3 40
Irradiation Frequency
3
4 34
2 9
5 5
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2.8 2D ROESY
n0 Larmor frequency of precessing proton
nucleus tc correlation time which is dependant
on solvent viscosity and moleculer weight
Imax/Io represents relative maximum crosspeak
signal intensity
2D NOESY ?c ? ? maximum 20, the case for small
molecules ?c ? 0 maximum 50, the case for
proteins ?o x ?c 0 the crosspeak intensitiy
0
2D ROESY ?c ? 0 maximum 20 ?c ? ? maximum
34 Useful for molecules of intermediate molecule
weight
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2.8 2D ROESY
Chemical exchange crosspeaks observed in 2D ROESY
ROE crosspeaks detected between methyl proton 7
to protons 4 and 3 support assigned relative
configuration
4
3
7 E
7 Z
7 Z
7
0.15 ROE
7 E
0.3 ROE
Integration of NOE crosspeaks Reference
Diagonal of protons 1 and 2 Integrate for 2.00
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2.9 TOCSY
5
2
1 2
1
1 2
B
A
regions A and B are expanded on next slide
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2.9 TOCSY
3
1
2
1 2
4
1 2
5
7
1
2
1 2
5
1
1 5
2
2
1 2
1
2
2
Region A
Region B
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2.10 1D EXSY experiment
1D EXSY (EXchange SpectroscopY) uses the same
pulse sequence as the 1D NOESY except that the
mixing time has been optimised to observe
chemical exchange.
Reference (1H NMR)
Expt 1 (1D EXSY)
2 (Z)
2 (E)
Irradiation Frequency
Expt 2 (1D EXSY)
7 (E)
7 (Z)
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3.1 Chemical exchange
7 (E)
4 (E), 4 (Z)
7 (Z)
2 (E)
2 (Z)
3 (E)
3 (Z)
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3.2 1D selective COSY used for assignment of
proton resonances
7 (E)
4 (E), 4 (Z)
2 (E)
7 (Z)
2 (Z)
3 (E)
3 (Z)
2 (Z)
3 (Z)
Irradiation Frequency
2 (E)
3 (E)
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3.3 1D EXSY experiment
These 1D EXSY experiments provide evidence that
the two species observed in the H NMR spectrum
are conformers.
3 (E)
3 (Z)
3 (E)
3 (Z)
Irradiation Frequency
2 (E)
2 (Z)
7 (E)
7 (Z)
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4. Recommended resources for a detailed
INTRODUCTION to NMR Theory and Application
H. Friebolin Basic One- and Two-Dimensional NMR
Sectroscopy 3rd Edition 1998 Wiley-VCH
Croasmun W. R., Carlson R. M. K. Two-Dimensional
NMR Spectroscopy Applications for Chemists and
Biochemists 2nd Edition 1994 VCH Publishers
Sanders J. K. M. and Hunter B. K. Modern NMR
spectroscopy A Guide for Chemists 2nd Edition
1993 Oxford University Press
Derome A. E. Modern NMR techniques for chemistry
research 1st Edition 1987 Pergamon press
Braun S., Kalinowski H.-O., Berger S. 150 and
More Basc NMR Experiments A Practical
Course 2nd Edition 1998 Wiley VCH Publishers