1. Nuclear Magnetic Resonance Spectroscopy (NMR) Dr AKM Shafiqul Islam School of Bioprocess Engineering

2. X-ray UV/Visible Infrared Microwave Radio Frequency Bond-breaking Electronic Vibrational Rotational Nuclear and Electronic Spin REGIONENERGY TRANSITIONS Types of Energy Transitions in Each Region of the Electromagnetic Spectrum of the Electromagnetic Spectrum (NMR)

3. What is NMR Spectroscopy? Nuclear Magnetic Resonance Nuclear Magnetic Resonance Radio Frequency Absorption Spectra of atomic nuclei in substances subjected to magnetic fields. Radio Frequency Absorption Spectra of atomic nuclei in substances subjected to magnetic fields. Spectral Dispersion is Sensitive to the chemical environment via “coupling” to the electrons surrounding the nuclei. Spectral Dispersion is Sensitive to the chemical environment via “coupling” to the electrons surrounding the nuclei. Interactions can be interpreted in terms of structure, bonding, reactivity Interactions can be interpreted in terms of structure, bonding, reactivity

4. Do all nuclei possess spin? No. Only those with an odd atomic number or odd atomic mass: 13 C 1 H 14 N 15 N 31 P 12 C 16 O 32 S 6 8 16 NMR active NMR inactive 6 1 7 7 15

5. Two common types of NMR spectroscopy used are; 1. 1 H NMR (proton NMR) is used to determine the number of hydrogen atom in the molecule 2. 13 C NMR (carbon NMR) used to determine the number of carbon atom in the molecule.

6. The source of energy in NMR is radio waves. Radiation in the radiofrequency region of the electromagnetic spectrum are very high wavelength, so it correspond to low frequency and energy. The source of energy in NMR is radio waves. Radiation in the radiofrequency region of the electromagnetic spectrum are very high wavelength, so it correspond to low frequency and energy. When the low energy radio waves interact with the molecule, they change the nuclear spin of some elements, including 1 H and 13 C. When the low energy radio waves interact with the molecule, they change the nuclear spin of some elements, including 1 H and 13 C.

7. The Use of NMR Spectroscopy Used to determine relative location of atoms within a molecule Used to determine relative location of atoms within a molecule Most helpful spectroscopic technique in organic chemistry Most helpful spectroscopic technique in organic chemistry Maps carbon-hydrogen framework of molecules Maps carbon-hydrogen framework of molecules Depends on very strong magnetic fields Depends on very strong magnetic fields

8. 1H NMR Tells Us… The number of different absorptions implies how many different types of hydrogens are present. The number of different absorptions implies how many different types of hydrogens are present. The amount of shielding (chemical shift) is determined by each hydrogen's environment, and so we get information about the local electronic surroundings for each hydrogen. The amount of shielding (chemical shift) is determined by each hydrogen's environment, and so we get information about the local electronic surroundings for each hydrogen. The intensities of the signals tell us the number of identical hydrogens. The intensities of the signals tell us the number of identical hydrogens. The splittings of each signal tells us about the other groups proximate to the hydrogens in question. The splittings of each signal tells us about the other groups proximate to the hydrogens in question.

9. Magnetic Properties of Nuclei – Nuclear Spin 13 C and 1 H nuclei spin on their axes. 13 C and 1 H nuclei spin on their axes. Magnetic fields are produced by electric currents. Magnetic fields are produced by electric currents. The circulation of electrical charge generates a magnetic moment along the axis of spin, so that these nuclei act like tiny magnets, having a small magnetic field. The circulation of electrical charge generates a magnetic moment along the axis of spin, so that these nuclei act like tiny magnets, having a small magnetic field.

10. The 13 C and 1 H nuclei both possess spin. The 13 C and 1 H nuclei both possess spin. The nucleus can be irradiated with radio waves to cause a spin transition. The frequency of the this transition depends on the electronic environment of the nucleus. The nucleus can be irradiated with radio waves to cause a spin transition. The frequency of the this transition depends on the electronic environment of the nucleus. By measuring the frequency, we can learn about the way in which the nucleus is bonded to other atoms in the molecule. By measuring the frequency, we can learn about the way in which the nucleus is bonded to other atoms in the molecule.

11. Nuclear Spin (cont.) In the earth’s very weak magnetic field (0.000057 T), the nuclear magnetic moments of these magnetic nuclei are randomly oriented.

12. Influence of Magnetic Field

13. When an external energy source (h ) that match the energy difference (  E) between these two states is applied, energy is absorbed, causing the nucleus to “spin flip” from one orientation to another. When an external energy source (h ) that match the energy difference (  E) between these two states is applied, energy is absorbed, causing the nucleus to “spin flip” from one orientation to another. The energy difference between these two nucleus spin states corresponds to the low- frequency radiation in the RF region of the electromagnetic spectra. The energy difference between these two nucleus spin states corresponds to the low- frequency radiation in the RF region of the electromagnetic spectra.

14. 400 MHz NMR Spectrometer 400 MHz Avance System Unix computer electronic controls super- conducting magnet

15. 400 MHz Superconducting Magnet magnetic field strength 9.4 Tesla (94,000 gauss) 400 MHz is the frequency used for proton detection in this field NMR sample tube and holder descend into center of magnet Keep metal (ferromagnetic) objects, pacemakers, and credit cards several feet away!

16. NMR Sample Position (prior to release into probe) Liquid Helium -269°C (4.2 K) Liquid Nitrogen -196°C (77.4 K) NMR sample positioned at top of probe Superconducting magnets require continuous cooling. 5 mm NMR sample tube RF energy upper level of NMR solution

17. 1 H NMR spectrum An NMR Spectrum plot the intensity of a peak against its chemical shift measured in ppm. An NMR Spectrum plot the intensity of a peak against its chemical shift measured in ppm. Increasing chemical shift is plotted from right to left. Increasing chemical shift is plotted from right to left. The term upfield and downfield describe the relative location of signals. Upfield means to right. The (CH 3 ) 3 C- peak is upfield from the CH 3 O- peak. The term upfield and downfield describe the relative location of signals. Upfield means to right. The (CH 3 ) 3 C- peak is upfield from the CH 3 O- peak.

18. 1.Chemical shift - each nonequivalent hydrogen gives a unique signal along the x-axis. 2. Spin-spin coupling - neighboring NMR active nuclei split each others signal. 3. Integration - peak areas are proportional to # of equivalent nuclei giving a signal. 1 H-NMR Data: 3 components Interpretation of NMR Spectra Two signals split into multiple peaks having a ratio of areas of 2:3. “quartet”“triplet”

19. Interpretation of 1 H-NMR Data The NMR absorption are measured tetramethylsilane (TMS). TMS is a volatile and inert compound that give a single peak upfield from the typical NMR absorption The NMR absorption are measured tetramethylsilane (TMS). TMS is a volatile and inert compound that give a single peak upfield from the typical NMR absorption 10 9 8 7 6 5 4 3 2 1 0  TMS reference signal tetramethylsilane Si(CH 3 ) 4 = 0.00  increasing deshielding increasing shielding

20. What makes NMR spectroscopy so useful is the fact that the same type of magnetic nuclei ( 1 H or 13 C) in different electronic environments absorb different amounts of rf energies and have different chemical shifts, giving several different signals. What makes NMR spectroscopy so useful is the fact that the same type of magnetic nuclei ( 1 H or 13 C) in different electronic environments absorb different amounts of rf energies and have different chemical shifts, giving several different signals. The number of signals indicates the different kinds (environments) of 1 H or 13 C nuclei. The number of signals indicates the different kinds (environments) of 1 H or 13 C nuclei. The position of the signals (chemical shifts) indicate what kind of 1 H or 13 C nuclei they are (alkane, vinylic, aromatic, etc.). The position of the signals (chemical shifts) indicate what kind of 1 H or 13 C nuclei they are (alkane, vinylic, aromatic, etc.).

21. NMR SPECTROSCOPY An NMR spectrum maps the carbon-hydrogen framework of an organic molecule, since each distinct 1 H or 13 C nucleus is represented by a distinct NMR signal in the spectrum. An NMR spectrum maps the carbon-hydrogen framework of an organic molecule, since each distinct 1 H or 13 C nucleus is represented by a distinct NMR signal in the spectrum. Some important terms to understand in NMR spectroscopy are: Some important terms to understand in NMR spectroscopy are: a. Equivalent hydrogens b. Line of Integration c. Chemical Shift d. Shielding e. Spin-spin splitting

22. 1. How many absorptions are there? (indicates number of equivalent kinds of Hs.) 2. What are their intensities? (indicates the number of Hs of each type.) 3. What are their chemical shifts? (indicates the environment of each type of H.) 4. What is the splitting pattern: (indicates neighboring hydrogens.) Interpretation of NMR Spectra