Basic principles and how nmr spectra works Its Application and its forensic uses

1. NMR- SPECTROSCOPY : AN OVERVIEW
Submitted By:-
S.M.G.Jafar
M.Sc 1st Semester
BUNDELKHAND UNIVERSITY, JHANSI
Submitted To:-
Dr. A.P.J. Abdul Kalam Institute Of
Forensic Science and Criminology
Dr. A.P.J. ABDUL KALAM
INSTITUTE OF FORENSIC SCIENCE AND CRIMINOLOGY

2. • CONTENTS
1. INTRODUCTION
2. HISTORY
3. PRINCIPLE
4. HOW NMR-SPECTA WORKS
5. INSTRUMENTATION
6. APPLICATIONS OF NMR-SPECTROSCOPY
7. FORENSIC USE OF NMR-SPECTROSCOPY

3. • INTRODUCTION
What is Spectroscopy?
Spectroscopy is the analysis of the interaction between matter and
any portion of the Electromagnetic Spectrum.
OR
Spectroscopy is the interaction of Electromagnetic Radiation with
matter, which may result in Absorption , Emission , Reflection , Rotation
of EMR.

4. INTRODUCTION
NMR-SPECTROSCOPY?
• Nuclear magnetic resonance Spectroscopy is an analytic chemistry
technique used in quality control and research for detecting the content
and purity of the sample as well as its molecular structure.
• NMR is based on the absorption of EMR in the radio frequency region 4 to
900 Mhz by nuclei of atoms.
• In NMR- Spectroscopy Radio frequency is used because of its long
wavelength .
• Two types of Spectroscopy is used
1:- ¹H NMR
2:- ¹³C NMR

5. • HISTORY OF NMR-SPECTROSCOPY.
• 1938:- l.l.Rabi Columbia University made measurement
for nuclear magnetic moments. 1944 got Noble Prize
for his work.
• 1946:- F. Block & E.M. Purcell demonstrated NMR for
condensed matter. In 1952 they got Noble prize for that.
• 1950:- It was observed that there was slight change in
the atomic nucleus larmor frequencies due to the
chemical bonding state of the atoms.

6. PRINCIPLE
Proton is present in the nuclei of atom & proton shows spin moment ,
due to this spin proton acts as a small magnet . When this proton is
subjected to Electromagnetic Radiation resonance takes place and this
process is called NMR-Spectroscopy.
Spin quantum number should be more than 0 then only the NMR takes
place .
Eg:- ¹H , ¹³C , ¹⁴N
Non – active NMR
Eg:- ¹²C

7. Nuclei shows two type of spins
1:- +½ or alpha spin
2:- -½ or beta spin
Alpha spin is obtained When the
Proton is subjected to Magnetic field
Beta spin is obtained whem the proton
Is subjected to the EMR (Radio waves)

8. • How NMR-Spectra Works.
4 steps are used :-
1. No. of signal
2. Position of signal
3. Splitting of signal
4. Intensity of signal
1. Number of signal
Two types of compounds
a) Chemically Equivalent protons

9. These are those protons which gives only one type of signal and hence
result in the formation of 1nmr signal
Eg:- CH3CH3
b) Chemically Non Equivalent protons
These are thise protons which gives different types of signal it may be
2,3 but not one
It forms 2 nmr signal , 3 nmr signal etc.
Eg:- CH₃–CH₂–Br

10. 2. Position of signal
In position of the signal we study Chemical Shift .
Chemical shift is the position of signal from the reference.
Shielding and Deshielding also occurs in signals
The proton which has deficiency of electron gives the spectra in down
field or Deshielding
The proton which has no deficiency of electron gives the spectra in up
field or Shielding

11. Chemical shift is measured in ppm i.e. parts per million
And is given by
Chemical shift = frequency of sample – frequency of reference. ×10^6
operating frequency of spectrometer. Ppm
*Tetramethyl silane is used as refrence due to its stable state , low
Deshielding and non reactive or its inert nature
*In TMS 12 chemical equivalent protons are present

12. 3. Splitting of Signal
Splitting of signal is caused by the neighbouring protons .
The relation is given by 2nI+1
Where,
N= number of neighbouring proton
I = spin angle of quantum number
For H atom l= ½
Then, 2×n×½+1
= n+1. Eg. In CH₃–CH₂–Br for first CH₃
its neighbouring proton is 2 so
2+1=3
Which give triplet peak for nmr

13. 4. Intensity of signal
• Intesity of signal tells us about the peak area of signal.

14. Eg:- CH₃–CH₂–Br intensity , it gives two tyoes of peak 1st one is triplet and
the 2nd one is quadrate then the peak spectra is
Difference of peak area between two peaks is called COUPLING
CONSTANT

15. • INSTRUMENTATION

16. 1. Sample tube :- Sample is placed 8.5cm long and 0.3 cm in diameter
2. Sample Holder:- A device that hold sample tube in position
3. Permanent magnet:- Provide magnetic field of 60-100 Mhz
4. Magnetic coil:- It induce magnetic field when current flow through
them
5. Sweep Generator:- Produces equal amount of magnetic field pass
through the sample
6. RF transmitter:- Produce short powerful pulse of radio waves
7. RF Detector:- It is used to measure the intensity of the unabsorbed
radio frequency emits
8. Recorder :- Record NMR signal obtaine from detector

17. • APPLICATIONS
1. To identify the molecular structure and its nature
2. To identify the purity and composition of sample
3. To identify the Proton environment
4. To identify the moisture analysis
5. The percentage of hydrogen in the Compound can be determined
6. Type and number of proton and carbon
7. In medical field ; MRI , Tumors etc.

18. • FORENSIC APPLICATIONS
• Used in examination of microscopic trace evidences
• Analysis of controlled drugs
• For detecting poisons specially Organophosphorous pesticides
• Used in forensic toxicology
• ¹H-NMR is used to characterize the cocaine , disterio isomers and
other types of drugs
• Used in the study of metabolites in human saliva