1. 1. What is an NMR Spectrum ? 2. What are the Spectral Features? 3. What are the Spectral Parameters? 4. How much should be known about the NMR Phenomena and the NMR detection methods for a Chemist to interpret the NMR spectra of molecules ? 5. Some aspects of the recent advances in NMR spectroscopy and the utility of NMR as a tool in structure determination.

2. Moderate Resolution HR PMR Spectrum CH3CH3 CH2CH2 OHOH δ= 1.13 ppm TMS δ= 0 ppm Acidic medium: spin coupling for OH protons do not show up This calculated and simulated [60 MHz] spectrum has the chemical shift and frequency values as obtained from a real NMR spectrum of alcohol. The above figure plotted using MS Excel application and line drawing from MS WORD drawing tools. High Resolution spectrum as shown above would be possible with good homogeneity of the magnetic field. 5.24 ppm 3.61 ppm 1.13 ppm 0 OH-CH 2 -CH 3 An NMR Spectrum

3. Single NMR line This NMR spectral line can be attributed with a characteristic shape and is describable by a mathematical equation. There are in general two distinct kind of shapes known for the spectral lines 1. Gaussian line shape 2. The Lorentzian shape. Line position δ ppm 0 ppm Reference line Both are typically symmetric line shapes:: symmetric about the line centre δ0δ0 Amplitude Full Width at Half Height Δ =FWHH Spectral features Besides these individual line features, it is the characteristic groups and patterns of lines in a spectrum which is useful for structure elucidation and the INTEGRATED INTENSTIEIS

4. Moderate Resolution HR PMR Spectrum CH3CH3 CH2CH2 OHOH δ= 1.13 ppm TMS δ= 0 ppm Acidic medium: spin coupling for OH protons do not show up 5.24 ppm 3.61 ppm 1.13 ppm 0 OH-CH 2 -CH 3 Spectral Parameters Each line in the spectrum must have the central line position and line amplitude/intensity and line width Groups of lines as multiplet pattern can be recognized quartet triplet Chemical shift δ 1 (q) Chemical shift δ 2 (t) J 12 J 21 J ij ’ s are spin spin coupling constants Individual line characteristics Characteristic groups and patterns of lines

6. Z-direction 100 MHz Electro- magnet/Permanent magnet Systems Supercon magnet systems above 100MHz up to 900MHz as known currently Magnet Current source Superconduc ting current carrying coils Pulse widths could be 10-2 μs Detection of the Phenomenon-I ; PROBE

7. Free Induction Digitized FID analog signal FID digitized points Received Analog Signal Analog to Digital Converter A D C Digitized Signal Detection –II Spectrometer principles

8. dimension A(50),B(50),Y(50),X(50) K=32 open (unit=1, file="output") Print 10,K DO 11 N=1,K X(N)=(N-1)*3.5/K X(N)=EXP(-1.0*X(N)) Y(N)=X(N)*(COS(2*3.14*(N-1)*10.0/K)+ 1 COS(2*3.14*(N-1)*4.0/K)) 11 write (1,20) N,Y(N) DO 12 M=1,K A(M)=0 B(M)=0 DO 13 N=1,K-1 A(M)=A(M)+Y(N)*COS(2*3.14*(M-1)*(N-1)/K) 13 B(M)=B(M)+Y(N)*SIN(2*3.14*(M-1)*(N-1)/K) A(M)=A(M)/K B(M)=B(M)/K M2=M/2 12 write (1,30) M2,A(M2),B(M2) 10 FORMAT(1x,I2) 20 FORMAT(1x,I2,2x,F10.5) 30 FORMAT(1x,I2,2x,F10.5,2x,F10.5) close (unit=1) STOP END A program in Fortran for “Fast Fourier Transform” Digitized FID Signal Digital Computer ----------------------- ----------------------- ----------------------- - ---------------------- ------------ - FFT Program run OUTPUT Spectrum !!

9. FID FT Real FT Imag. Integration All the signal shapes have been calculated in MS EXCEL In practice FFT program calculates Frequency domain spectra from the time domain signal Time Domain Signal Frequency Domain Spectra after FT Similar to the CW mode Spectra Pulsed detection mode Detection-II ; Recording of Spectra

10. ADC CW RF Source Gate Pulse Programmer DC Pulse Power Amplifier Rectangular RF Pulse Sample coil in the Probe with sample Low noise RF Preamplifier FID High Gain Signal Amplifier Phase Sensitive Detector Reference Signal computer [FFT] Spectrum to display monitor/Plotter High Power RF Pulses to Probe HR NMR in Liquids 100W NMR of Solids 3KW PP Matched 50 Ω Time Domain signal Transmitter Receiver

11. Transmitter ON time Probe & sample Crossed Diodes Receiver Receiver OFF time Receiver Silent or dead time DATA acquisition starts at this time 1 23 4 5 After the RF pulse, the FID is the impulse response from the sample spin system. The pulsing and FID can be repeated and added to acquire the averaged signal for better signal to noise ratio Detection-III ; Spectral data acquisition

12. Long T 2 Short T 2 Achieving a Sharp signal depends on the homogeneity of the magnetic filed: Shimmimng the magnetic field using gradient correction coils and sample spinning are the provisions in the spectrometer system for improving the homogeneity Signal level Noise Level Data Processing