Nmr spectroscopy:- An overview and its principle
- 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
- 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