NMR SPECTROSCOPY DR. M. KANJIA Copyright reserved NMRS 2007 Application to reproduce to Dr M Kanjia • No. of Peaks Terminology Intensity Ratio One Peak Singlet n=1 Three Peaks Triplet n=2 Five Peaks Quintet 1 2 3 2 1 • n=3 Seven Peaks Septet 1 3 6 7 6 3 1 • n=4 Nine Peaks Novetet • n=0 • • • I=1 Deuterium 2H ( D ) , 14N 1 1 1 1 1 4 10 17 25 17 10 4 1 Pascal ’ s Triangle I = 1 13C NMR of CDCl 3 I = 1 2H to 13C Intensity ratio 1 : 1 : 1 Read the intensity ratio directly from Pascal Triangle. © CopyRight Reserved NMR Spectroscopy 2007 Application to reproduce to Dr M Kanjia T1 Relaxation • T1 relaxation is an enthalpic process where the energy is taken from or transferred to neighbouring spins. The surrounding of the spins is called lattice hence T1 is also known as spin lattice relaxation. In this process the Z – Component of the magnetization is return back to its equilibrium state. T1 values are useful information for NMR experiment what to set up as repetition time between each NMR scan. For 1H T1 values are from 0.5 Seconds to few seconds. Z Z Y Y X Z Z Y Y X X Return of the Z component of the magnetization to the equilibrium state © CopyRight Reserved NMR Spectroscopy 2007 Application to reproduce to Dr M Kanjia X Spin Lattice or Longitudinal Relaxation Process T1 And the Measurement of 900 & 1800 Pulse width ( PW ) 13C NMR Spectrum of Benzene in Acetone –D6 • 3600 PW • • 900 PW 2700 PW © CopyRight Reserved NMR Spectroscopy 2007 • • • • • when sample is placed in the magnetic field and radio frequency (RF) pulse is applied, the Boltzmann population of spins get upset and after a time delay T1 the Boltzmann population of spins get reestablished. This time delay T1 is called the spin lattice or longitudinal relaxation time T1 Measurement of 900 and 1800 pulses times knowledge of the 900 pulse time or pulse width ( PW ) for any spin active nucleus ( 1H, 13C, 19F, 15N ) is required to set up all multipulses FT NMR experiments. An accurate value of 900 PW is crucial for T1 value measurement. This is usually obtained using a concentrated sample to produce a strong signal after a single pulse. Record the signal intensity with various PW. All measurements must be made with the same intensity scaling and same phase corrections. The intensities should show a sinusoidal variation with pulse time or pulse with PW 900 = A maximum positive signal 2700 = A maximum negative signal 1800 = A zero signal 3600 = A zero signal It is easier to determine the position of null values at 1800 and 3600 PW The half of 1800 or quarter of 3600 values will be 900 PW Application to reproduce to Dr M Kanjia Anisotropic Field in an Alkenes ( SP2 ) • Anisotropic Field Effect Deshielded 1H Shift To Lower Field Away From TMS Field add H H C=C H H Ho Applied Field © CopyRight Reserved NMR Spectroscopy 2007 Application to reproduce to Dr M Kanjia Secondary Magnetic Field Lines Induce Anisotropic Field 13C NMR Spectrum of Cumene Aromatic 120 to 160 PPM Expansion C6H5—CH(CH3)2 CH(CH3)2 1 6 C4 126.00 PPM C 3 & 5 126.55 PPM C 2 & 6 128.53 PPM 2 5 Aromatic Benzene C1 148.79 PPM Both CH3 24.25 PPM Note :- C with H Gives taller Peak ( Relaxation T1 ) 3 Height of the peak is very important for assigning the chemical shifts 4 C 4 has 1 H C1 C3 & 5 have 2 H Height ratio 1 : 2 C 1 has no H hence smaller peak © CopyRight Reserved NMR Spectroscopy 2007 Application to reproduce to Dr M Kanjia CH 34.45 PPM 13C NMR Spectrum of 1,2-Dimethylbenzene ( O-Xylene ) CH3 1 6 C (3 ,6) General Rule :- 129.98 Carbons without H PPM Give smaller peak C (4 ,5) 126.25 PPM 2 CH3 3 5 4 C4 & C5 are equivalent ( Identical ) e.g. C1 & C2 Carbon with more 1H relaxes faster than less 1H C3 & C6 are equivalent ( Identical ) C (1 , 2) 136.52 C1 & C2 are equivalent (Identical ) PPM © CopyRight Reserved NMR Spectroscopy 2007 Both CH3 are identical hence only One peak. Application to reproduce to Dr M Kanjia CH3 19.86 PPM 1H NMR Patter of Para Disubstituted Benzene • • • • When two groups X & Y become more similar then All NMR Peaks move closer hence Outer peaks get smaller and finally disappear but Inner peaks get taller and finally merge into single peak. © CopyRight Reserved NMR Spectroscopy 2007 Application to reproduce to Dr M Kanjia 1H NMR Spectra of 4-Methyl Aniline and p-Xylene only 8.5 to 4.5 PPM Region shown H(3,5) CH3 H(2,6) 3 5 2 NH2 6 NH2 H(2,3,5,6) CH3 CH3 © CopyRight Reserved NMR Spectroscopy 2007 Aromatic Expansion Application to reproduce to Dr M Kanjia 13C NMR Spectrum of 1,4-Dimethylbenzene ( p-Xylene ) CH3 1 C2, C3, C5, & C6 129.27 PPM ( identical ) C1 & C4 6 2 5 3 4 CH3 Both CH3 21.10 PPM 134.73 PPM ( identical ) © CopyRight Reserved NMR Spectroscopy 2007 Application to reproduce to Dr M Kanjia Analysis and interpretation of 1H & 13C NMR Spectra of 2,4-Dinitromethylbenzene C6H3CH3(NO2)2 1H NMR Spectrum Integration 12.5 = 1H CH3 2.73 PPM H3 H5 CH3 H6 6 1 5 4 Expansion of aromatic region © CopyRight Reserved NMR Spectroscopy 2007 Application to reproduce to Dr M Kanjia 2 3 NO2 NO2 Analysis and interpretation of 1H & 13C NMR Spectra of 2,4-Dinitromethylbenzene C6H3CH3(NO2)2 1H NMR Spectrum CH3 H3 8.66 PPM Doublet Jmeta = 2.31 Hz H5 8.30 PPM 6 D of D 5 Jmeta = 2.31 Hz Jortho = 8.47 Hz 1 4 2 3 NO2 NO2 H6 7.63 PPM Doublet Jortho = 8.47 Hz Observation Jpara = 0.0 Hz © CopyRight Reserved NMR Spectroscopy 2007 Application to reproduce to Dr M Kanjia 13C NMR Spectra of 2,4-Dinitromethylbenzene C6H3CH3(NO2)2 CH3 C5 126.48 PPM C3 133.69 PPM C6 119.43 PPM 1 6 2 5 3 C1 140.37 PPM C2 145.69 PPM C4 148.34 PPM 4 NO2 CDCl3 © CopyRight Reserved NMR Spectroscopy 2007 Application to reproduce to Dr M Kanjia NO2 CH3 19.98 PPM Analysis and interpretation of 1H & 13C NMR Spectra of Styrene 1H NMR Spectrum C6H5-CH=CH2 Hb 5 .30 PPM Hc 5 .81 PPM Ha 6 .78 PPM Hb Integration 1H = 30 Hc Hb Hc Ha Aromatic C6H5 © CopyRight Reserved NMR Spectroscopy 2007 Ha—Hc TRANS Ha—Hb CIS Hb—Hc GEMINAL Application to reproduce to Dr M Kanjia Ha Analysis and interpretation of 1H & 13C NMR Spectra of Styrene C6H5-CH=CH2 1H NMR Spectrum Hb Ha 6 .78 PPM Hc D of Doublet Hc Jtrans = 17 .58 Hz D of Doublet Jcis Jtrans = 17 .58 Hz = 10 .90 Hz 5 .81 PPM Jgem Ha © CopyRight Reserved NMR Spectroscopy 2007 Ha = 0 .87 Hz Application to reproduce to Dr M Kanjia Hc Hb 5 .30 PPM D of Doublet Jcis = 10 .90 Hz Jgem = 0 .87 Hz Hb Analysis and interpretation of 1H & 13C NMR Spectra of Styrene 2D COSY 1H NMR Spectrum C6H5-CH=CH2 Hb Ha Hc C6H5 Ha © CopyRight Reserved NMR Spectroscopy 2007 Hc Application to reproduce to Dr M Kanjia Hb Hb Ha Hc C6H5 Ha Hc Hb Analysis and interpretation of 2D COSY 90 1H NMR Spectrum of Styrene C6H5-CH=CH2 1. Every peak in spectrum gives the diagonal footprint in cosy spectrum. 2. Non coupled 1H gives only diagonal footprint and no footprint in X & Y axes. 3. Coupled 1H will give footprint in X & Y axes. 4. Number of coupling can be seen easily just by counting the number of footprints along either X or Y axis. In the Styrene Ha gives two footprints as shown by dashed arrows hence it is coupled to two 1H ( Hb & Hc ). Where as C6H5 give s no footprint in X & Y axes hence they are not coupled to any other 1H ( Ha, Hb or Hc ). No footprint in X Application & Y axes to reproduce to Dr M Kanjia 5. Aromatic region is complex to analyse. © CopyRight Reserved NMR Spectroscopy 2007 Analysis and interpretation of 13C NMR Spectrum of Styrene C6H5-CH=CH2 Hb C4 128.11 PPM C3 & C5 126.59 PPM 137.29 PPM C1 137.91 PPM © CopyRight Reserved NMR Spectroscopy 2007 Ha 7 2 Hc C2 & C6 128.84 PPM C7 8 3 1 6 C8 113.94 PPM Application to reproduce to Dr M Kanjia 4 5 1H NMR spectrum of 2-Fluoro-6-Nitrophenol C6H3(F)(NO2)(OH) Integration 1H = 20 OH H4 F 7.43 PPM H5 7.92 PPM H 2 NO2 6 3 5 4 H H OH 10.47 PPM 1 H3 6.96 PPM Impurity © CopyRight Reserved NMR Spectroscopy 2007 Application to reproduce to Dr M Kanjia 1H NMR spectrum of 2-Fluoro-6-Nitrophenol C6H3(F)(NO2)(OH) H3 6.96 PPM OH F 2 H4 7.43 PPM H5 7.92 PPM H 6 NO 2 4 D of D of D 2x2x2 = 8 Peaks H H Jpara-F J CH-CF Jortho Jmeta Jortho Jmeta H4 © CopyRight Reserved NMR Spectroscopy 2007 Application to reproduce to Dr M Kanjia H5 H3 13C NMR spectrum of 2-Fluoro-6-Nitrophenol C6H3(F)(NO2)(OH) OH F 2 3 C4 118.47 PPM C5 119.92 PPM H 1 4 6 5 NO2 H H C3 122.98 PPM C6 135.00 PPM CDCl3 C1 144.64 PPM C2 152.17 PPM © CopyRight Reserved NMR Spectroscopy 2007 Application to reproduce to Dr M Kanjia Expansion of 13C NMR spectrum of 2-Fluoro-6-Nitrophenol C6H3(F)(NO2)(OH) OH F 19F has long range coupling which can be seen in the following example H C2 153.17 PPM 1J C2—F = 250.60 Hz 1 2 6 3 5 4 NO2 H C4 118.47 PPM 3J C4—C3—C2—F = 7.22Hz H C5 119.92 PPM C1 144.64 PPM 4J C5—C4—C3—C2—F = 3.65 Hz 2J C1—C2—F = 15.15 Hz C3 122.98 PPM 2J C3—C2—F = 15.15 Hz © CopyRight C2Reserved NMR Spectroscopy 2007 Application C1to reproduce to Dr M Kanjia C3 C5 C4 Analysis and interpretation of 1H & 13C NMR Spectra of Pyridine C5H5N 4H 7 .55 2H & 6H 8 .51 PPM 1H NMR Spectrum Integration 1H = 24 PPM 3H & 5H 7 .16 PPM 4 3 5 2 6 1 © CopyRight Reserved NMR Spectroscopy 2007 Application to reproduce to Dr M Kanjia The Electric Field Effect on Pyridine & Nitrobenzene Pyridine Nitrobenzene C5H5N C6H5NO2 Deshielded 1H © CopyRight Reserved NMR Spectroscopy 2007 Application to reproduce to Dr M Kanjia Analysis and interpretation of 1H & 13C NMR Spectra of Pyridine C5H5N 1H NMR Spectrum Expansion 4 2H & 6H 8 .51 PPM 4H 7 .55 PPM Jmeta = 1.81 Hz T of T Jortho = 4.21 HZ Jortho = 7 .65 Hz Jmeta = 1 .81 Hz 5 3 6 2 1 3H & 5H 7 .61 PPM Jortho = 7.65 Hz Jortho = 4.21 Hz Jmeta = 1.50 Hz © CopyRight Reserved NMR Spectroscopy 2007 Application to reproduce to Dr M Kanjia Analysis and interpretation of 13C NMR Spectrum of Pyridine C5H5N 4 C4 134 .59 PPM C2 & C6 C3 & C5 149 .77 PPM 122 .58 PPM 5 3 6 2 1 N1 gives no signal in 13C NMR Spectrum © CopyRight Reserved NMR Spectroscopy 2007 Application to reproduce to Dr M Kanjia
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