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OF PHARMACOLOGY 1PowerPoint Presentation: CONTENTS: Introduction to 13 C-NMR Silent facts of 13 C-NMR Differences between 13 C-NMR and 1 H-NMR Problems in 13 C-NMR Chemical shifts Interpretation of 13 C-NMR 2INTRODUCTION TO 13C-NMR: INTRODUCTION TO 13 C-NMR Proton NMR used often for the complete elucidation of the unknown compound. Carbon NMR can used to determine the number of non-equivalent carbons and to identify the types of carbon atoms(methyl, methylene,aromatic,carbonyl ….) which may present in compound. 3Silent facts of 13C-NMR: Silent facts of 13 C-NMR 4PowerPoint Presentation: I=0 I=1/2 5DIFFERENCES BETWEEN 13C &1H NMR: DIFFERENCES BETWEEN 13 C & 1 H NMR 13 C -NMR 1 H-NMR Study of spin changes of carbon nuclei. Chemical shift ranges between 0-240 ppm. Very fast process. Pulse- fourier transform technique is used Study of spin changes of proton nuclei. Ranges 0-14ppm. Very slow process. Continuous wave method is used 6PowerPoint Presentation: 13 C -NMR 1 H-NMR valves of coupling constant ranges from 125-250HZ. Information of total number of protons carbons is obtained. By peak splitting, possible to interpret protons directly attached to carbon atom Ranges from 0-15HZ Information like total number, types of chemical environment of protons is obtained. It possible to interpret protons attached to adjacent carbon atom 7PowerPoint Presentation: 13 C-NMR 1 H-NMR Effect of substituent on adjacent carbon atom cannot varies the chemical shift. It works o frequency sweep. Substituents alters the chemical shift. It works on either field sweep or frequency sweep. 8PowerPoint Presentation: 9Problems of 13C-NMR: Problems of 13 C-NMR 13 C-NMR signal is 6000 times weaker than 1 H-NMR why??? NATURAL ABUNDANCE GYRO MAGNETIC RATIO COUPLING PHENOMENON 10PowerPoint Presentation: NATURAL ABUNDANCE: 13 C natural abundance is very low (1.08%). GYRO MAGNETIC RATIO: 13 C nucleus gyro magnetic ratio is much lesser than proton nucleus. C-1.404; H-5.585. This shows that CMR is more sensitive than PMR which is overcome by using FT-NMR technique 11PowerPoint Presentation: Coupling phenomenon: 13 C & 1 H have I=1/2 so that coupling between them probability occur. Extremely complex spectra and overlap of multiplets difficult to interprete . 13 C- 13 C coupling no! Not probable 13 C- 1 H coupling YES! Very common 12Problems of 13C-NMR can overcome by: Problems of 13 C-NMR can overcome by 13FT-NMR: FT-NMR FID 14NUCLEAR OVERHAUSER ENCHANCEMENT : NUCLEAR OVERHAUSER ENCHANCEMENT 15DECOUPLING: DECOUPLING 16PowerPoint Presentation: COUPLING TO ATTACHED PROTONSPowerPoint Presentation: The effect of attached protons on 13 C resonances n+1 = 4 n+1 = 3 n+1 = 2 n+1 = 1 C 13 3 protons 2 protons 1 proton 0 protons H H H C 13 H H C 13 H C 13 Methyl carbon Methylene carbon Methine carbon Quaternary carbon ( n+1 rule applies ) COUPLING TO ATTACHED PROTONS (J’s are large ~ 100 - 200 Hz)PowerPoint Presentation: ETHYL PHENYLACETATE 13 C coupled to the hydrogensPowerPoint Presentation: DECOUPLED SPECTRAPowerPoint Presentation: DECOUPLING THE PROTON SPINS PROTON-DECOUPLED SPECTRA A common method used in determining a carbon-13 NMR spectrum is to irradiate all of the hydrogen nuclei in the molecule at the same time the carbon resonances are being measured. This requires a second radiofrequency (RF) source (the decoupler) tuned to the frequency of the hydrogen nuclei, while the primary RF source is tuned to the 13 C frequency. 1 H- 13 C RF source 2 RF source 1 continuously saturates hydrogens pulse tuned to carbon-13 13 C signal (FID) measured “the decoupler”PowerPoint Presentation: In this method the hydrogen nuclei are “saturated”, a situation where there are as many downward as there are upward transitions, all occuring rapidly. During the time the carbon-13 spectrum is being determined, the hydrogen nuclei cycle rapidly between their two spin states (+ 1/2 and - 1/2 ) and the carbon nuclei see an average coupling (i.e., zero) to the hydrogens. The hydrogens are said to be decoupled from the carbon-13 nuclei. You no longer see multiplets for the 13 C resonances. Each carbon gives a singlet, and the spectrum is easier to interpret.PowerPoint Presentation: ETHYL PHENYLACETATE 13 C coupled to the hydrogens 13 C decoupled from the hydrogens in some cases the peaks of the multiplets will overlap this is an easier spectrum to interpretPowerPoint Presentation: q t t s s d d d SOME INSTRUMENTS SHOW THE MULTIPLICITIES OF THE PEAKS ON THE DECOUPLED SPECTRA s = singlet t = triplet d = doublet q = quartet CODE : This method gives the best of both worlds.Relaxation process: Relaxation process 25PowerPoint Presentation: 27PowerPoint Presentation: CHEMICAL SHIFTS OF 13 C ATOMSPowerPoint Presentation: R- C H 3 8 - 30 R 2 C H 2 15 - 55 R 3 C H 20 - 60 C -I 0 - 40 C -Br 25 - 65 C -N 30 - 65 C -Cl 35 - 80 C -O 40 - 80 C C C 65 - 90 C = C 100 - 150 C N N 110 - 140 110 - 175 R- C -OR O R- C -OH O 155 - 185 R- C -NH 2 O 155 - 185 R- C -H O R- C -R O 185 - 220 APPROXIMATE 13 C CHEMICAL SHIFT RANGES FOR SELECTED TYPES OF CARBON (ppm)PowerPoint Presentation: Aldehydes Ketones Acids Amides Esters Anhydrides Aromatic ring carbons Unsaturated carbon - sp 2 Alkyne carbons - sp Saturated carbon - sp 3 electronegativity effects Saturated carbon - sp 3 no electronegativity effects C=O C=O C=C C C 200 150 100 50 0 200 150 100 50 0 8 - 30 15 - 55 20 - 60 40 - 80 35 - 80 25 - 65 65 - 90 100 - 150 110 - 175 155 - 185 185 - 220 Correlation chart for 13 C Chemical Shifts (ppm) C-O C-Cl C-Br R 3 CH R 4 C R-CH 2 -R R-CH 3 RANGE /PowerPoint Presentation: SPECTRAPowerPoint Presentation: Proton-decoupled 13C spectrum of 1-propanol (22.5 MHz) 200 150 100 50 0 1-PROPANOL PROTON DECOUPLED HO-CH 2 -CH 2 -CH 3 c b aPowerPoint Presentation: 2,2-DIMETHYLBUTANEPowerPoint Presentation: BROMOCYCLOHEXANEPowerPoint Presentation: CYCLOHEXENEPowerPoint Presentation: TOLUENEPowerPoint Presentation: a a b b c c 1,2-DICHLOROBENZENEPowerPoint Presentation: 38REFERENCES: REFERENCES William Kemp: Organic spectroscopy, 3 rd edition. Robert M. Silverstein: Spectroscopic identification of Organic compounds, 6 th edition. Jagmohan : Organic spectroscopy, principles and applications, 2 nd edition. Pavia: Introduction to spectroscopy, 3 rd edition. P.S. Kalsi : Spectroscopy of organic compounds, fifth edition. Y.R. Sharma: Elementary organic spectroscopy, principle and chemical applications. 39 You do not have the permission to view this presentation. In order to view it, please contact the author of the presentation.