Report TWO-Dimensional NMR spectroscopy (Practical Applications and Spectral Analysis) A report submitted in (partial) fulfilment of the requirements for the completion ofChem993: Awad Nasser Albalwi Supervised by Dr.Michael Kelso & Dr.Wilford Lie School of Chemistry University of Wollongong
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Two dimensional nmr spectroscopy (practical application and spectral analysis
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Report
TWO-Dimensional NMR spectroscopy
(Practical Applications and Spectral Analysis) A report submitted in (partial) fulfilment of the requirements for the completion ofChem993:
Awad Nasser Albalwi
Supervised by
Dr.Michael Kelso & Dr.Wilford Lie
School of Chemistry
University of Wollongong
2
Table of Contents
I COVERING INFORMATION…………………..1
II CONTENTS…………………………………..……………2
1 INTRODUCTION…….………………..…………….. 3
1.1 APT………………………………………………………………...5
1.2 DEPT …………………………………..………………………. 5
1.3 COSY …………….………………………….….………….….6
1.4 NOESY.….….….………………………………..………….….6
1.5 TOCSY ……………………………………………………...…7
1.6 HMBC …………………………………………………….……8
1.7 HSQC ……………………………………...............……..9
1.8 the project Aims ……………….………………………10
2 The procedure………………………………………..…11
3 Results…………………………..…………………….….…12-18
4 Discussion……………………………………..……….…19-22
5 Conclusion …………………………………………………..22
6 Acknowledgments ………………………..……………22
7 References ……………………………………………………22
8 Index
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1. Introduction
Over the past fifty years nuclear magnetic resonance (NMR), has become the
preeminent technique for determining the structure of organic compounds. It is the
only spectroscopic method with a complete analysis and interpretation of the entire
spectrum is normally expected., nmr is non-destructive, and with modern instruments
good data may be obtained from samples weighing less than a milligram.
All nuclei that contain odd number of protons or neutrons poeeess an observable
nuclear magnetic dipole, magnetic moment (µ) and angular momentum (J). In the
presence of external static magnetic field (B) , the angular frequency (w) is linearly
dependent on (B) 12
W=
The nuclei of many elemental isotopes have a characteristic spin. Isotopes that are
useful to organic chemists are 1H, 13C, 19F and 31P, all of which have nuclear spin quantum
number (I) I = 1/2. The characteristic spin can be thought of as a small magnetic field,
and will cause the nucleus to produce an NMR signal in a static magnetic field. The
intensity of a peak observed in an NMR spectrum is related to the transition
probability between the energy level -1/2 and +1/2.
Chemical Shift
Different frequencies of peaks are observed in NMR spectra obtained from a sample
containing many nuclei in each molecule. Unlike infrared and uv-visible spectroscopy,
where absorption peaks are uniquely located by a frequency or wavelength, the location
of different NMR resonance signals is dependent on both the external magnetic field
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strength and the frequency. Since no two magnets will have exactly the same field,
resonance frequencies will vary accordingly and an alternative method for
characterizing and specifying the location of NMR signals is needed. The resulting shift
spectrum is compared with those of model compound. As the molecular complexity
increased, the 1D NMR can be improved by running the experiment at higher and higher
magnetic field strength. It thus allows interpretation of complex first order –like
spectra. Spectra obtained at highest available magnetic fields are obscured and signal
are overlapped for complex molecules
2D NMR Spectroscopy
2D NMR offer a new way to resolve even higher overlapping spectra into interpretable
multiplet and permit a chemical shift assignment to be made in a simple and direct
manner by speading resonances out into two dimensions and thereby increases the
resolutions.
There are two broad types of experiments that are commonly used in 2D NMR.
1 Correlation experiment (COSY)
2 Nuclear overhauser effect spectroscopy (NOESY)
Others are attached proton test (APT), (DEPT), (TOCSY), (HMBC), (HSQC)
In 2D NMR one dimension gives us J coupling information while the other dimension
gives chemical shift information. This type of experiment is called homonuclear J-
Resolved 2-D NMR. There is also heteronuclear J-resolved 2-D NMR which uses a spin
echo sequence and techniques similar to those described above. The tool is useful in
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well resolved spectra. 2-D measurement can be performed simultaneously for all line in
a spectrum.
1-1-(APT) The Attached Proton Test (APT) experiment is a common way to assign C-H multiplicities
in 13C NMR spectra. It provides the information on all sorts of carbons within one
experiment. Depending on the number of hydrogens bound to a carbon atom, n, CHn spin
vectors evolve differently after the initial pulse. If the delay is set to 1/J, CH and CH3
vectors have opposite phases compared to C and CH2. Therefore, the phase of CH and CH3
peaks is 180° different from C and CH2 peaks. This example demonstrates the basic
procedure of double resonance 1D NMR data acquisition and processing on spectrometers.
1-2-The DEPT: Distortionless Enhancement by Polarization Transfer
The DEPT the method has become one of the most important techniques available to the
NMR spectroscopy for determining the number of hydrogens attached to a carbon atom.
The pulse sequences involves complex program of pulses and delay times in both the 1H &
13C . The result of pulses sequences for DEPT is that carbon atoms with one ,two and three
attached hydrogens exhibit different phases as they are recorded. The phases of these
carbon signals will depend on the duration of the delays that are programmed into the
pulse sequence. In DEPT spectrum , the quaternary carbons , which have no attached
hydrogens , give no signal .
Fig.1 :The pulse sequences.2.
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1-3-COSY Correlation Spectroscopy
Cosy is one of the first 2D NMR spectra reported and It is useful for studying relatively
small molecules. COSY arise from coupled spins that in the corresponds to protons
separated by two or three bonds .The pulse sequence for the cosy is two 90◦ pulses
separated by an evolution time followed by the acquisition of the NMR signal3.
Fig.2:The pulse sequence for the cosy2.
2D COSY technique allows to walk-through the spectrum for the assignment of