Solids Techniques - NMR Spectroscopy
Solids Techniques - NMR SpectroscopyJürgen Schulte Science 2S2 – G-14 Smart EnergySN – 10241
Topics: Part I – Introduction History of NMR NMR Hardware2
Books for NMR Spectroscopygeneral:specialized:3
Journals for NMR SpectroscopyJournal of Magnetic ResonanceAugust 2, 2019 issue:JMR’s Golden Jubilee: Magnetic Resonance in the 21st 4
NMR Milestones 1938 – NMR of LiCl molecular beams.Rabi (Columbia University)1952 – First commercial NMR spectrometer7LiNMR resonance:0.21 Tesla @ 3.518 MHz1962 – First Superconducting Magnet for NMR1968 – First Pulse Fourier Transform NMR1969 – First Concept of MRI Scanners1971 – First two-dimensional NMR Experiment 1946 – NMR of Liquids and Solids.Purcell, Torrey, Pound (Harvard)Bloch, Hansen, Packard (CalTech)1985 – First Protein Structure solved by NMR2009 – First 1 Gigahertz NMR Spectrometer (23.5 T)2019 – High Temperature Superconducting Magnets1.1 GHz NMR, St. Jude, Memphis TN1.2 GHz NMR, Florence, Italy(Packard, 1951)5
NMR Nobel Prize Winners 1944 (P) Isador Rabi 1952 (P) Felix BlochEdward Purcell 1991 (C) Richard Ernst 2002 (C) Kurt Wüthrich 2003 (M) Paul LauterburPeter Mansfield 2013 (C) Martin Karplus(computational chemistry)Martin KarplusFrom: Bruker SpinReport, Vol 1536
NMR Spectroscopy NUCLEAR MAGNETIC RESONANCE7
NMR MagnetsMagnet Types: Permanent Magnets:low fields ( 2.5 Tesla) Electromagnets: high fieldspoor stability and homogeneity8
NMR MagnetsMagnet Types: Superconducting Magnets (aka. Cryomagnets): high, stable, and homogeneous fields Expensive to purchase, operate, and maintain.Weekly Nitrogen refills (left) and monthly Helium refills (right) are required.9
NMR MagnetsCross section of asuperconducting magnet:The superconducting coil is cooled to4 Kelvin in a bath of liquid Helium.The Helium vessel is surrounded by acontainer of liquid Nitrogen (77K).Helium and Nitrogen containers areseparated and surrounded byvacuum.A probe is installed in the bottom ofthe magnet bore and samples can beinserted from the top of the magnet.10
NMR MagnetsInside a superconducting magnetBundled wires withsuperconducting filamentsManufacturingsuperconducting wires11
NMR Magnets12
NMR MagnetsBU presently has five NMR Spectrometers:Magnet Field:1H Frequency:Location:liquid/solid:B0 ν0 2.35 T100 MHzS2Liquids7.05 T9.4 T14.1 T300 MHz 400 MHz 600 MHzS2SNSNL&SL&SL&SPharm.:9.4 T400 MHzCELiquidsAll our instruments have superconducting magnets.Dangers: High magnetic fields may cause pacemakers, insulin pumps, and other electronic medical devices to fail, may erase hard disks, credit cards, and your BU ID, will attract ferromagnetic objects and turn them into dangerous projectiles. Cryogens (liquid Nitrogen and Helium) will cause burns when contacting eyes or skin,will displace breathable air in case of a magnet quench.https://www.youtube.com/watch?v d-G3Kg-7n Mhttps://www.youtube.com/watch?v 6-sxe79Y5Nchttps://www.youtube.com/watch?v Pu7eY8tRE c13
NMR MagnetsMagnet quench:An energized magnet can fail when a segmentof the superconducting wire becomes resistivedue to localized heating.The entire energy (Mega Joules) stored in themagnet coil is released instantaneously andvaporizes the entire volume of liquid Heliumwithin minutes.14.1 Tesla magnet quenchCoil current: 183 AmperesEnergy: 774 kJ14
NMR MagnetsAccidents:15
NMR ConsolesNMR Manufacturers:(DE,CH)(US)(Japan)16
Modern NMR Spectrometer.Chemistry’s 600 MHz NMR inthe Smart Energy Building. soon to be joined by a400 MHz NMR spectrometer 17
Modern NMR ConsoleMultiple RF channels,high sensitivity,high resolution.18
Benchtop NMR Systems1Htypically 60-100 MHz(1.4 – 2.3 T permanent magnet)Nuclei: 1H ( 1 option: C, P, or F)Low resolution,Low sensitivity,Low power. can use existing magnets.Suitable for teaching labs.Limited usefulness for research.19
NMR Probes LiquidsSolids andSamples20
Recent NMR Progress2016: First 23.5 Tesla magnet (1 GHz)Bayreuth University, Germany.2019: First 1.1 GHz NMRSt. Jude Hospital, Memphis TN.2020: First 1.2 GHz NMRFlorence University, ItalyNine 1.2 GHz NMRs have currently been ordered (in Europe).21
Topics: Part II – NMR Theory Nuclei – Spin – Magnetic Moments Shielding – Chemical Shifts Coupling – Molecular Structure Relaxation – Linewidth22
Nuclear Spin Quantum Number (I) Nuclei must possess a “non-zero spin” to be NMR active. Can we calculate I? Nucleus Protons NeutronsMass m p n1H2H Even p even n I 0 no NMR signals ( 12C, 16O) Odd p odd n integer IRecap:(mass) m(atomic #) pz (charge)a (# of atoms)XI 1: 2H, 14NI 3: 10BI 6: 50V All other nuclei: half-integer I (1/2, 3/2, 5/2, )I 7/2: 51VI 5/2: 17O, 27AlI 3/2: 11B, 23NaI 1/2: 1H, 13C, 15N, 19F, 29Si, 31P, 119SnIsotopes withnear 100 %natural abundance Nuclei with I ½ will produce the sharpest signals (high resolution NMR).Nuclei with I ½ are called quadrupolar nuclei, as they possess an electrical quadrupole. broad signals23
Periodic Table of the NMR IsotopesIIIIIIVVIVIIH3H alf-Integer Quadrupolar SpinNaXVIII310Integer Quadrupolar Spin9Li23XVIISpin ½ Nuclei6LiVIIIAlmost all elements have NMR active isotopes.12IV352527MgAl29Si31PCl33S37ArCl39K40K 1YbEsFmMdNoElements without naturally occurring NMR-active isotopes are left uncolored.Most Spin-½ isotopes are preferred over quadrupolar (I ½) isotopes.In Solid State NMR, half-integer spins are preferred over integer spins.Adapted from: Harris RK, Becker ED, Cabral de Menezes SM, Goodfellow R, Granger P: NMR Nomenclature. Nuclear Spin Properties and Conventions for Chemical Shifts (IUPAC Recommendations 2001). Pure Appl Chem 2001; 73:1795-1818.24
Nuclear Spin Quantum Number (I) High natural abundance is desirable, but “Spin-½” nuclei are preferred because they produce the sharpest signals. (Linewidth: few Hz in liquids) Quadrupolar Nuclei ( I ½ ) have extremely broad signals. (Linewidth: kHz/MHz) Elements with less abundant isotopes may be chemically or biologically important, i.e. 13C, 15N, 17O.IsotopeSpin INat. 98 %5700Direct Observation12C098.89 %0No Signal13C½1.11 %1Direct & Indirect Observation14N199.63 %2.1Direct Observation (large molecules are “invisible”)15N½0.37 %0.02Isotopic Labeling, Indirect ObservationThe sensitivity of “Spin-½” nuclei can be increased either chemically (isotopic enrichment) or by special NMR techniques,i.e. Polarization Transfer (Cross Polarization, DEPT, INEPT, HETCOR), indirect detection through 1H (HSQC, HMBC). Solids NMR spectra of “Spin-½” nuclei can produce sharp peaks. (tens/hundreds of Hz) Solids NMR spectra of half-integer-spin quadrupolar nuclei havea moderately broad central transition (kHz) and extremely broad satellite transitions (MHz). Solids NMR spectra of integer-spin quadrupolar nuclei have broad satellite transitions (MHz) and no central transition. In Solid State NMR “broad” does not equal “bad”!Line width and signal shape can contain a wealth of structural and dynamic information about the molecule or material.25
Magnetic Spin Quantum Number (M) General condition: 2I 1 spin statesMI I, I-1, I-2, , -Ii.e.: I 2, M 2,1,0,-1,-2 “Spin ½” case 1H: MI ½ (α) andMI – ½ (β) Magnetic Moments (Z components) are quantized:μZ γħMI γħI ½ γħB0(Z)26
Spins in a Magnetic Field The α and β states possess the same energies(are degenerate) unless placed into a magnetic field:βEΔE hν0 2 μzB0α, βν0 (γ/2π) B0Zeeman Effect2.35T7.05T100 MHz 300 MHzα14.1T600 MHzB0ν0{1H}27
Magnetic Spin Quantum Number (M) General condition: 2I 1 spin statesMI I, I-1, I-2, , -I “Spin 3/2” case 11B: MI 3/2, 1/2, – 1/2, – 3/2. Magnetic Moment (Z component):μZ γħMI γħI ½ γħ , 3/2 γħB0Satellite Transition(Z)Central TransitionSatellite Transition28
Boltzmann factor:𝑁α𝑁β 𝑒𝑥𝑝 Δ𝐸𝑘𝑇Only 0.001% of all spins are detected. 1.00002(at 100 MHz)NMR has a very low sensitivitycompared to other techniques!29
EM Spectrum NMR Frequency Range Resonance Frequencies of Selected Nuclei at B0 14.1 Teslalow band13C15N010031P200205/203Tl300high band19F1H3H3He400500600MHzX-Nuclei ( BB Nuclei)Our 600 MHz Solids probe is a Triple-Nucleus probe (H,X,Y)with selectable tuning ranges for various nucleus combinations.30
EM Spectrum31
NMR ExperimentsNMR Experiment FlowchartSampleMagnetMagnetizationSolution NMR:All adjustmentsand calibrations are donewith the test sample.Solid State NMR:RFResponseDetectionDataRepeat all steps with:Adamantane – adjust shimsKBr – adjust magic angleReference – adjust RF matchTest sample – finally ProcessingSpectrumStorage32
NMR Experiments – Continuous Wave NMRCW SpectrometerFrequency or field sweeps can be very time consuming.(several minutes per scan for high resolution)33
NMR Experiments – Pulse-Fourier TransformPulse Fourier Transform Spectrometer(records time domain data after a radiofrequency pulse)5 µsFTThe FID (Free Induction Decay) is Fourier-Transformed into the spectrum.A single RF pulse at the frequency ν0 excites a band of frequencies around ν0.The RF power is adjusted to excite a 50 kHz range with a 5 µs 90o pulse.This is also called a “50 kHz B1 field ”.MHzν034
Spins – Calculation/VisualizationNMR HamiltoniansProduct OperatorsPulse:Zeeman InteractionRF FieldChemical ShiftsQuadrupolar InteractionSpin RotationChemical Shift:Dipolar InteractionSpin CouplingJ-Couplings:Is this much detail needed?What are we using NMR for?35
Spins – The Vector ModelCoherenceMost NMR Experiments use combinations of90º and 180º pulses(π/2 and π pulses)along the x or y axis.36
NMR Pulses / Pulse SequencesPulses are described by the angle (degree or radian) by which they turn the magnetization:zzz180ºyx90ºyxπy(π/2)yxOnly the magnetization in the X,Y plane is observable, Z magnetization is not.Pulse Sequences consist of a series of pulses separated by delays:πRDπ/2τAQInversion Recovery Experiment37
NMR Pulses / Pulse Sequences"p2 p1*2""d11 30m""acqt0 -p1*2/3.1416"1 ze2 d1p2 ph1d8p1 ph23 go 2 ph31d11 wr #0exit;t1ir;avance-version (07/04/03);T1 measurement using inversion recovery;pl1 : f1 channel - power level for pulse (default);p1 : f1 channel - 90 degree high power pulse;p2 : f1 channel - 180 degree high power pulse;d1 : relaxation delay; 1-5 * T1;d11: delay for disk I/O[30 msec];d8 : recovery delay;NS: 8 * n;DS: 4;td1: number of experimentsRelaxation DelayInversion PulseRecovery DelayDetection PulseDetection Loopif #0ph1 0 2ph2 0 0 2 2 1 1 3 3ph31 0 0 2 2 1 1 3 3πRDd1π/2AQτp2d8p1Inversion Recovery Experiment38
Pulse Sequences can be very complicated39
NMR Parameters - ShieldingThe general resonance condition:An increased electron density willshield the nucleus and it will requirea higher value of B0 to achieve resonance:lowerelectrondensityν0 (γ/2π) B0In reality we observeseparate signals for different protons.Beff B0 – σ B0higherelectrondensityThe resonance condition becomes:This would mean that every protonspectrum would only have one signal.(more shielded)ν (γ/2π) B0 (1 – σ)increasing field B0increasing shieldingdownfield (less shielded)upfield (more shielded)These terms originate from the early days of NMR when the magnetic field was swept while transmitting a constant frequency.Today’s NMR spectrometers usually have a fixed magnetic field and record frequencies. The direction of the frequency axis is inverted.increasing frequencydecreasing shielding40
NMR Parameters - Chemical ShiftThe resonance condition:ν (γ/2π) B0 (1 – σ)The problem:The absolute frequency ν is very large (MHz - GHz) and is B0 dependent.The range Δν for most nuclei is very small (Hz - kHz).i.e. a spectrum may have two proton signals at 60.000000 MHz and 60.000120 MHz.The solution:Chemical Shift (δ)Report a signal’s position relative to a reference signal, i.e. tetramethylsilane (TMS),and normalize it to the reference frequency:δ(X) 106 [ν(X)–ν(TMS) ] / ν(TMS)δ(X) 106 [60,000,120 – 60,000,000] / 60,000,000 2 (ppm)Chemical shifts are field independent and are reported in ppm unitswith typical ranges of 15 ppm for 1H and 250 ppm for 13C.Chemical shifts increase from right to left.100 ppm41
NMR Parameters - Chemical Shift Example: 1H spectrum of Ethylbenzene at 7.05 T and 2.35 T- Chemical shifts (measured in ppm) are identical at different magnetic fields.- Couplings (Signal splittings, measured in Hertz) are also identicalat different fields, but take up less space at higher fields/frequencies.Better chemical shift dispersion at higher fields.42
NMR Parameters - Chemical Shift Example: 1H spectrum of Cellobiose Octaacetate at 14.1 T, 7.05 T, and 2.35 T(cellobiose)600 MHz(14.1 T)300 MHz(7.05 T)100 MHz(2.35 T)Large molecules will benefit most from a higher magnetic field strength.43
NMR Parameters - Chemical Shift1H13CChemical shifts of 1H and 13C relative to TMS (0 ppm)44
NMR Parameters - Chemical ShiftChemical shift ranges for common inorganic nuclei.45
NMR Parameters - CSAChemical Shift Anisotropy:The chemical shift depends on the relative orientationof a molecule or a crystal to the B0 field.B0θ 90ºCNB0θ 30ºNCB0 θ 0ºNCδ / ppm90º45º0ºA single crystal will have a sharp NMR signal at achemical shift that depends on the angle θbetween B0 and the principal axis of the crystal:ν (3 cos2 θ - 1)A powder sample consists of a large number of microscopic crystals at random orientations.A powder spectrum represents a superimposition of all individual crystal orientations in the sample.46
NMR Parameters - CSAChemical Shift Anisotropy:A powder sample consists of a large number ofmicroscopic crystals at random orientations.This leads to a superimposition of the signals of allindividual crystals, resulting in a powder pattern spectrum.axiallyasymmetricν (3 cos2 θ - 1)The lineshape is determined by the axial asymmetryof the electronic and molecular surrounding.axiallysymmetricIn solution the Brownian motion will average all orientations,leading to a single sharp signal. In solid samples we need tosimulate rapid re-orientation of the molecules:Spinning a powder sample around the “magic angle” (54.7º)will sharpen the signal around the isotropic chemical shift.(3 cos2 θ - 1) 0 for θ 54.7º47
NMR Parameters - Couplings- Spin, Spin Coupling (scalar coupling, J-coupling)Interaction between spins through valence electrons.B0JAXAXν0{X}AXν0{A}ΔE JAX · I(A) · I(X)The magnetic field at nucleus X will be enhanced orattenuated depending on the orientation of spin A.48
NMR Parameters - Couplings- Doublets, Triplets, MultipletsCouplings to more than one nucleus increase multiplicity. – CH CH2– CH3Multiplicity: n 1for n : 2·I·n 1for other spins I.Couplings to chemically and magnetically different spins can lead tocomplex multiplicity patterns ( dd, ddd, dt, . , m)49
NMR Parameters - Couplings- Doublets, Triplets, MultipletsSimulate spectra with measured or calculated couplings to determine multiplicity. J. Schulte, J. Lauterwein, M. Klessinger, and J. Thiem, Magnetic Resonance in Chemistry 41, 123-130 (2003),"Configurational Assignment in Alkyl-Branched Sugars via the Geminal C,H Coupling Constants."Couplings to chemically and magnetically different spins can lead tocomplex multiplicity patterns ( dd, ddd, dt, . , m)50
NMR Parameters - Couplings- single-bond vs. multi-bond coupling constantsC-H1JCH:100 to 200 HzC-C-H2JCH:-10 to 10 HzC-C-C-H3JCH:0 to 10 HzH-C-H2JCH:-5 to -15 HzH-C-C-H3JCH:0 to 10 HzCouplings arealways quotedin Hertz units(also: cps)Couplings areindependent ofthe magneticfield.Longer range couplings are only visible, if all nucleiin the coupling pathway are in the same plane.(W configuration – zig-zag arrangement)51
NMR Parameters - Couplings- Structural dependence of vicinal J couplingsKarplus Equation forH-C-C-H, C-C-C-H and C-O-C-Hdihedral angles:3J(Φ) A B cos Φ C cos2 Φ(A, B and C can be tuned to fitdifferent classes of compounds)52
NMR Parameters - Couplings- Dipolar Coupling (d)Interaction between spins through space. No bonds are necessary.Dipolar couplings can span thousands of hertz.B0θμ1Δν12μ2rΔν12 3d12/2 (3 cos2 θ - 1) / r3 In liquids the Brownian motion averages all orientations.(3 cos2 θ - 1) 0, no dipolar splitting. Solids and molecules dissolved in liquid crystals are aligned.(3 cos2 θ - 1) 0, dipolar splitting / broadening. Sample spinning around θ 54.7 can remove broadening.Magic Angle Spinning (MAS)53
NMR Parameters - Relaxation What is relaxation? Loss of magnetization through interaction of a spin with other spins or with the sample (“lattice”)will allow the spins to return to a thermal equilibrium. Some mechanisms for relaxation: Paramagnetic relaxation(proximity of free electrons: paramagnetic metals, radicals) Quadrupolar relaxation(nuclei with I 1/2) Dipolar relaxation(proximity of other spins, typ. 1H) Spin rotation relaxation(i.e. rotating methyl groups) Chemical shift anisotropy (CSA) relaxation Relaxation rates are additive:R2 1/T2 1/T2para 1/T2quad 1/T2dipol 1/T2SR 1/T2CSA 1 10610354
NMR Parameters - Relaxation T1 relaxation (spin-lattice relaxation, longitudinal relaxation)Heat is released to the lattice (sample) when the spin reverts to the lower energy level.T1 Measurement by “Inversion Recovery” technique:ππ/2IττT1 1.44 · τnullMeasure Intensities for various τ values and fit with: I 2I0 exp (- τ / T1)Typical T1’s: - seconds to minutes for Spin-½ nuclei (i.e. 1H: 2 sec., 13C: 20 sec., 15N: 200 sec)- milliseconds for quadrupolar nuclei (i.e. 17O: 20 ms for H2O, 1 ms for organic molecules)- microseconds for paramagnetic nuclei, signal decays too fast to be observed.55
NMR Parameters - Relaxation T2 relaxation (spin-spin relaxation, transverse relaxation)Energy dissipation by interactions between spins.T2 is always shorter than T1 (because of field inhomogeneity).T2 can be estimated from the width of the signal at half height:Intrinsic T2 relaxation:ν½T2* 1/π·ν½with1/T2* 1/T2 1/T2inh.T2 can be measured more accurately by the “Spin-Echo” technique:π/2πIττI I · exp(2 τ / T )02τ56
NMR Parameters - Relaxation Recap: T2 determines the linewidth of the NMR signal.“Short T2 lead to broader signals.” T1 determines the repetition rate of the NMR experiments.“Most of the experimental time is spent waiting forthe magnetization to recover between scans.” After a 90 degree pulse:Wait 5 T1 for 99% magnetization recovery.Wait 2 T1 for 88% magnetization recovery. Better: Use a smaller pulse angle, i.e. 60 :cosθ exp (-tr/T1)(θ: pulse angle, tr: repetition time)Examples: 1H90 , T1 2 s 5 T1 10 s 100 s for 10 scans @ 100% signal: Int. 3.160 , T1 2 s 1 T1 2 s 100 s for 50 scans @ 60% signal: Int. 4.213C90 , T1 10 s 5 T1 50 s 100 s for 2 scans @ 100% signal: Int. 1.430 , T1 10 s tr 2 s 100 s for 50 scans @ 50% signal: Int. 3.530 , T1 60 s tr 2 s 100 s for 50 scans @ 10% signal: Int. 0.757
Key Techniques for Solid State NMR:1. DecouplingIrradiating a nucleus (typically 1H) will lead to an equal distribution of its α and β populations.1H will become “invisible” to oth
1985 –First Protein Structure solved by NMR 2009 –First 1 Gigahertz NMR Spectrometer (23.5 T) 2019 –High Temperature Superconducting Magnets 1.1 GHz NMR, St. Jude, Memphis TN 1.2 GHz NMR, Florence, Italy 1938 –NMR of LiCl molecular beams. Rabi (Columbia University) 1946 –NMR
5 nuclear magnetic resonance (nmr) spectroscopy 33 5.1 the physics of nuclear spins and nmr instruments 33 5.2 continuous wave (cw) nmr spectroscopy 37 5.3 fourier-transform (ft) nmr spectroscopy 39 5.4 chemical shift in 1h nmr spectroscopy 40 5.5 spin-spin coupling in 1h nmr spectroscopy 50
14.1 An Introduction to NMR Spectroscopy A. The Basics of Nuclear Magnetic Resonance (NMR) Spectroscopy nuclei with odd atomic number have a S ½ with two spin states ( 1/2 and -1/2) 1H NMR (proton NMR): determines number and type of H atoms 13C NMR (proton
Experiment 13 - NMR Spectroscopy Page 1 of 10 13. Nuclear Magnetic Resonance (NMR) Spectroscopy A. Basic Principles Nuclear magnetic resonance (NMR) spectroscopy is one of the most important and widely used methods for determining the structure of organic molecules. NMR allows one to deduce the carbon-hydrogen connectivity in a molecule.
Aug 01, 2018 · 1H NMR, 19F NMR, 31P NMR experiments -about 3 5 mg 13C NMR short run experiment (0.5 -1 hr) about 20 50 mg; long run experiment about 5 10 mg 0.6-0.7 ml of NMR solvent is appropriate for the right solvent level in NMR tube. Unsuitable solvent level can lea
NMR SOLVENTS Deuterated Solvents for NMR NMR Solvents NMR Reference Standards NMR Tubes. Cambridge Isotope Laboratories, Inc. www.isotope.com s tel: 978-749-8000 800-322-1174 (USA) fax: 978-749-2768 cilsales@isotope.com TABLE OF CONTENTS
1. Introduction to Spectroscopy, 3rd Edn, Pavia & Lampman 2. Organic Spectroscopy – P S Kalsi Department of Chemistry, IIT(ISM) Dhanbad Common types? Fluorescence Spectroscopy. X-ray spectroscopy and crystallography Flame spectroscopy a) Atomic emission spectroscopy b) Atomic absorption spectroscopy c) Atomic fluorescence spectroscopy
5 Experiment 8.16 - Quantitative 13C NMR Spectroscopy with Inverse Gated 1H-Decoupling 68 Experiment 8.17 - NMR Using Liquid-Crystal Solvents 68 CHAPTER 9 - HETERONUCLEAR NMR SPECROSCOPY 70 SUMMARY 70 Experiment 9.1 - 1H-Decoupled 15N NMR Spectra with DEPT 70 Experiment 9.2 - 1H-Coupled 15N NMR Spectra
5 SIMULIA To be published by ASM: www.asminternational.org ASM Handbook Volume 22B Application of Metal Processing Simulations, 2010 The Deterministic Single Objective Problem In the case of a single objective problem, we are maximizing or minimizing a single output and/ or constraining a set of outputs to stay within a certain range.
