Introduction of Key Concepts of Nuclear Magnetic Resonance

Transcription

1 I have not yet lost that sense of wonder, and delight, that this delicate motion should reside in all ordinary things around us, revealing itself only to those who looks for it. E. M. Purcell, Nobel Lecture Introduction of Key Concepts of Nuclear Magnetic Resonance Justin Barry Group Meeting 7/4/2015

2 Outline and Concepts of the Talk Introduction Particle physics Classical representations Mechanism Interpreting spectra Proton Carbon Coupling and it s origins

3 A classical approach as a visual aid Rotating object Right hand rule to create vector Macroscopic

4 NMR is concerned with nuclear spin What is spin? Intrinsic property of nucleus Not actually from spinning What about our vector? Technically a spinor is more correct Don t worry, the classical interpretation is easier to visualize and usually still correct

5 NMR is concerned with nuclear spin What is spin? Intrinsic property of nucleus Not actually from spinning What about our vector? Technically a spinor is more correct Don t worry, the classical interpretation is easier to visualize and usually still correct

6 NMR is concerned with nuclear spin What is spin? Intrinsic property of nucleus Not actually from spinning What about our vector? Technically a spinor is more correct Don t worry, the classical interpretation is easier to visualize and usually still correct

7 Nature s smallest building blocks Elementary particle A particle in which, at the present, no structure can be observed at moderate energies -IUPAC Combinations that chemists are concerned with: Proton (2 u, 1 d) Neutron (1 u, 2 d) Electron (1 e) Photon (1 γ) u e d Charge: 2/ -1/ Spin: 1/2 1/2 γ Charge: -1 0 Spin: 1/2 1

8 Nature s smallest building blocks Elementary particle A particle in which, at the present, no structure can be observed at moderate energies -IUPAC Combinations that chemists are concerned with: u d Charge: 2/ -1/ Spin: 1/2 1/2 e γ Charge: -1 0 Spin: 1/2 1

9 Nature s smallest building blocks Elementary particle A particle in which, at the present, no structure can be observed at moderate energies -IUPAC Combinations that chemists are concerned with: proton u d neutron u d u d Charge: 2/ -1/ Spin: 1/2 1/2 u d e γ Charge: -1 0 Spin: 1/2 1

10 Nature s smallest building blocks Elementary particle A particle in which, at the present, no structure can be observed at moderate energies -IUPAC Combinations that chemists are concerned with: proton u d neutron u d u d Charge: 2/ -1/ Spin: 1/2 1/2 u d e γ Charge: 1 0 Spin: 1/2 1/2 Charge: -1 0 Spin: 1/2 1

11 Simple model using atoms Hydrogen Deuterium e - e - N + N + N 0 proton u d u neutron = 1/2 u d d = 1/2

12 Simple model using atoms Hydrogen Deuterium e - e - N + N + N 0 = 1/2 = 1 proton u d u neutron = 1/2 u d d = 1/2

13 Simple model using atoms Hydrogen Deuterium

14 Simple model using atoms Hydrogen Deuterium No net magnetic moment

15 Simple model using atoms Hydrogen Deuterium B o

16 Simple model using atoms Hydrogen Deuterium Net B o

17 Simple model using atoms Hydrogen Deuterium Net B o

18 Simple model using atoms Hydrogen Deuterium Net B o Precession Microscopic magnetism Boltzmann distribution Gyromagnetic ratio Zeeman splitting Spin states

19 The origin of the net magnetic moment Microscopic magnetism The circulation of electric currents The magnetic moments of the electrons Magnetic moments of nuclei

20 Motion in a magnetic field Consider a bar magnet at first The magnet rotates to parallel to minimize energy A nuclear spin also minimizes energy Precession

21 Precession in a magnetic field Larmor frequency Caused by angular momentum Spins will have same frequency Classical example Spinning top

22 Nuclear Zeeman splitting Nuclear spin state In the absence of B o, spins states are of same energy. Applied magnetic field splits states Spin of I can have 2I+1 states Pieter Zeeman 1902 Nobel in Physics B o LE HE Hydrogen Deuterium

23 Nuclear Zeeman splitting Nuclear spin state In the absence of B o, spins states are of same energy. Applied magnetic field splits states Spin of I can have 2I+1 states Pieter Zeeman 1902 Nobel in Physics B o LE HE m I = 1/2 m I =1 m I = -1/2 m I = -1 B o Hydrogen Deuterium

24 Nuclear Zeeman splitting Nuclear spin state In the absence of B o, spins states are of same energy. Applied magnetic field splits states Spin of I can have 2I+1 states Pieter Zeeman 1902 Nobel in Physics B o LE HE m I = 1/2 m I =1 m I = 0 m I = -1/2 m I = -1 B o Hydrogen Deuterium

25 Different degrees of magnetization Gyromagnetic ratio Ratio of the magnetic dipole moment to its angular momentum (SI unit: rad s -1 T -1 ) Magnitude difference: 1 H is more magnetic than 15 N

26 Sign difference in gyromagnetic ratio Ratio can be negative Magnetic moment stays the same B o Positive ratio Negative precession Negative ratio Positive precession

27 The population difference of spins Boltzmann distribution At 1.41 Tesla, 1 H resonate at 60 MHz N upper = e E kt = e hv kt = ,000,000 N lower 1,000,009 h = x 10-4 J sec (Plank s constant) k = 1.80 x 10-2 J/K molecule (molecular gas constant) T = absolute temperature At 14.1 Tesla, 1 H resonate at 600 MHz N upper = e E kt = e hv kt = ,000,000 N lower 1,000,106

28 Visualization summary Setting up the picture Visualize spin states Vectorize Rotating frame Net B o

29 Radiofrequency and rotating frames Radiofrequency Resonates with Larmor frequency Oscillating magnetic field component acts to tip spins

30 Measurement of signal Rotation still follows Larmor frequency

31 Chemically different nuclei Zeeman splitting Local shielding from electrons

32 Simple model using atoms Hydrogen Deuterium No net magnetic moment

33 Simple model using atoms Hydrogen Deuterium B o

34 Simple model using atoms Hydrogen Deuterium Net B o

35 Simple model using atoms Hydrogen Deuterium Net B o

36 Simple model using atoms Hydrogen Deuterium Net B o Precession Microscopic magnetism Boltzmann distribution Gyromagnetic ratio Zeeman splitting Spin states

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40 Spin-spin coupling and it s origin Spins can see each other Proton A X-type Y-type Observed NMR for proton A

41 Spin-spin coupling and it s origin Spins can see each other Proton A X-type Y-type Observed NMR for proton A deshielded more shielded

42 Splitting diagrams n+1 rule

43 Splitting diagrams n+1 rule H+1 = 4 2H+1 =

44 Splitting diagrams n+1 rule H+1 = 4 2H+1 =

45 Splitting diagrams n+1 rule H+1 = 4 2H+1 =

46 Splitting diagrams n+1 rule J H+1 = 4 2H+1 =

47 Hertz and parts per million Couplings are in units of hertz Chemical shifts are in units of ppm

48 Hertz and parts per million Couplings are in units of hertz Chemical shifts are in units of ppm

49 Hertz and parts per million Couplings are in units of hertz Chemical shifts are in units of ppm 05 Hz 100 x 10 6 Hz =.05 x 10 6 =.05 ppm

50 ppm D.R. Tyler Laboratories: Pushing Back the Forefronts of Science. Hertz and parts per million Couplings are in units of hertz Chemical shifts are in units of ppm 60 MHz 00 MHz

51 Heteronuclear coupling

52 Heteronuclear coupling

53 Heteronuclear coupling

54 Heteronuclear coupling J

55 Heteronuclear coupling J 1 J

56 Heteronuclear coupling J 1 J =1.0 integral ( 1 C, 1.1% abundance)

57 Heteronuclear coupling Hz J 1 J =1.0 integral ( 1 C, 1.1% abundance)

58 Carbon-1 NMR

59 Carbon-1 NMR

60 Carbon-1 NMR Hz Compare with previous Hz

61 Carbon-1 NMR Hz Compare with previous Hz

62 J Hz Hz Hz

63 J Hz J 2 =2.19 Hz Hz Hz

64 Increasing signal with number of scans nt=160 nt=16

65 Increasing signal with number of scans nt=160 Signal increase by x 2 Noise increases by x 2-2 nt=16

66 Carbon-1 NMR of phenol

67 Carbon-1 NMR of phenol

68 Carbon-1 NMR of phenol

69 Carbon-1 NMR of phenol δ + δ - δ - δ -

70 An example of a 2D spectrum (COSY) a b b b a a

71 Benzene-D6

72 Benzene-D6 n+1 rule? m I =1 m I = -1 m I =

73 Practical NMR demonstration Using the NMR Shimming Coupling and decoupling Exotic experiments Troubleshooting Probably another 0 mins 1hour if your interested

74 Apologies to any lefties in the audience Questions?

75 Great Resources Also the Nobel lectures of Felix Bloch, Edward M. Purcell, Richard R. Ernst, and Kurt Wüthrich are useful.