PowerPoint Presentation

1NMR Spectroscopy:Introduction History of NMRNMR Hardware and SoftwareSolution NMR Sample PreparationPresentation of Data2Important NMR Milestones1938 - NMR in molecular beams Rabi (Columbia University)1946 - NMR of Liquids and Solids Purcell, Torrey, Pound (Harvard) Bloch, Hansen, Packard (CalTech)1952 - First commercial NMR spectrometer1962 - First Superconducting Magnet for NMR1968 - First Pulse Fourier Transform NMR1969 - First Concept of MRI Scanners1971 - First 2D NMR Experiment COSY (Jean Jeener)1985 - Protein Structures2009 - First Gigahertz NMR Spectrometer

3NMR Nobel Prize Winners1944 Isador Rabi1952 Felix Bloch & Edwin Purcell

1991 Richard Ernst2002 Kurt Wthrich

2003 Paul Lauterbur & Sir Peter Mansfield

From: Bruker SpinReport, Vol 153 Laukien Prize Winners1999 Konstantin Pervushin, Roland Riek, Gerhard Wider, and Kurt Wthrich; TROSY2000 Lucio Frydman; Quadrupolar MQMAS2001 Peter Boesiger, Klaas Prmann, Markus Weiger; Sensitivity-encoded magnetic resonance imaging2002 Ad Bax, Aksel Bothner-By and James Prestegard; Residual dipolar couplings of weakly aligned molecules in solution2003 Jacob Schaefer; REDOR Technique for Solid State NMR2004 Lewis E. Kay, NMR of Biological Macromolecules2005 Stephan Grzesiek, J couplings across hydrogen bonds2006 Thomas Szyperski, Eriks Kupce, Ray Freeman, and Rafael Bruschweiler; Acceleration of Multi-dimensional NMR by novel procedures for scanning data space and efficiently processing results to obtain a conventional spectral representation2007 Robert G. Griffin; High-field dynamic nuclear polarization (DNP) for sensitivity enhancement in solid-state MAS NMR2008 Malcom H. Levitt; Optimized pulses and pulse sequences to enhance the power of liquid & solid state NMR2009 Daniel P. Weitekamp; PASADENA and BOOMERANG significantly improve NMR force detection by circumventing the problems of inhomogeneous magnetic fields2010 Paul T. Callahan; Contributions to the study of polymeric and heterogeneous materials by advanced NMR exchange, diffusion and relaxation techniques, and for his innovative q-space-diffusion-related developments that were relevant in the context of the development of diffusion-tensor imaging.2011 Daniel Rugar, John Mamin, and John Sidles; Magnetic Resonance Force Microscopy (MRFM). 2012 Klaes Golman and Jan Henrik Ardenkjaer-Larsen: Dissolution-DNP NMR4Varian Prize Winners2012Ray Freeman and Weston A. AndersonNuclear Magnetic Double Resonance2011Gareth Alun Morris, The University of Manchester, UKINEPT2010Martin Karplus, Harvard University, Cambridge, MassachusettsKarplus equations2009Albert W. Overhauser, Purdue University, West Lafayette, INNOE & Dynamic Polarization2008Alexander Pines, UC Berkeley, and Lawrence Berkeley National LaboratoryCross Polarization2007Alfred G. Redfield, Brandeis University, Waltham, MassachusettsSpin Dynamics2006John S. Waugh, MIT, Cambridge, MassachusettsAverage Hamiltonian Theory (AHT) 2005Nicolaas Bloembergen, University of Arizona, Tucson, ArizonaNuclear Magnetic Relaxation2004Erwin L. Hahn, Professor Emeritus, University of California, BerkeleySpin Echoes2002Jean Jeener, Universite Libre de Bruxelles, BelgiumTwo-dimensional NMR

56NMR SpectroscopyNUCLEAR

MAGNETIC

RESONANCE

Chapter 137The NMR Spectrometer

Sampel dilarutkan dalam pelarut yang tidak mempengaruhi proton (biasanya CCl4 atau CDCl3) dan sejumlah TMS ditambahkan sebagai referensi internal. Sample tube diletakkan di medan magnet yang dapat diatur kekuatan medan magnetnya. Sampel juga diliti dengan generator RF 60 Mhz. kawat ini sebagai sumber energy elektromagnet yang digunakan untuk merubah orientasi spin proton. Tegak lurus dari dari RF generator adalah RF coil detector. Jika tidak ada energi yang diserap, maka kawat detektor tidak tidak menangkap energy yang hilang dari RF generator. Apabila sampel menyerap energy, reoreantasi spin inti menghasilkan sinyal RF yang dapat mempengaruhi oleh RF detektor.7

Schematic NMR SpectrometerFourier transformation and the NMR spectrumFourier transform

RF PulseThe Fourier transform (FT) is a computational method for analyzing the frequencies present in an oscillating signalThe NMR spectrum9910NMR Probes

Solids Liquids

Solids

LiquidsMagic angle(54.7)11NMR Signal GenerationSpectrometer:

RF Generation:

90180 Pulse (Sequences): RD DE AQ

Receiver:FT

12

NMR Samples Types of NMR sample holdersSample preparationSpectrum quality

13Types of NMR Sample Holders

Solid State Sample RotorsSolution NMR Sample Tube Spinners NMR Sample Tubes with Caps14NMR Sample PreparationTubes and Caps:

NMR tubes are a standard length (7 and 9 inch). When chipped (and reduced in length) they should not be reused as an unbalanced tube will not spin.

Always clean the tubes thoroughly after use. First use the solvent you were using to recover your previous sample, then rinse several times with acetone and finally dry the sample tube laying flat on a layer of kimwipes or placed upside-down on a kimwipe in a beaker or Erlenmeyer flask. Choose the container so the tubes stand vertically. Dont heat the tubes above 50 C, as the glass might warp. Always store unused, clean tubes uncapped and laying on a flat surface.

Tube caps are disposable and replacements can be easily obtained in bags of 100 ($5) or 1000 ($40 at www.wilmad.com).

Degassing Samples:

NMR spectra recorded using degassed solvents usually benefit from reduced half-height line-width and thus better S/N. (O2 gas is paramagnetic!)

There are several ways of degassing your sample: the best is the freeze-pump-thaw technique, placing the sample in a ultrasonic bath works moderately well, bubbling nitrogen through or over the sample less well. 15NMR Sample PreparationQuantity:

For proton NMR spectra of small organic compounds (up to MW=500) anything between 1 and 20 mg of sample will be fine. Concentrated solutions can be viscous and may result in broad signals. Very dilute samples could be masked by impurities and solvent peaks.

Carbon-13 is present at approximately 1.1 % natural abundance. It is intrinsically less sensitive than protons (approx. six thousand times). Please provide as much sample as possible, 50 - 100 mg (or more) is fine. Preparing two samples - one dilute sample for proton NMR and one concentrated sample for carbon NMR is a useful, but unnecessary practice.

Solvent height (volume) should be uniform, 5 cm or 2 inches equal 0.5 ml. The ends of the sample distort the field homogeneity, shimming on each sample corrects this effect and takes just a minute or so. However, vastly different solvent heights (volumes) prevent complete correction and require many minutes shimming to achieve acceptable homogeneity.

Samples prepared with too much solvent waste both time and money, and provide poorer S/N. However, If you have limited amounts of sample (less than 1 mg), using less solvent is permissible. Minimum height: 1 cm, however, this requires special positioning of the sample tube and very intensive shimming.

A shim is a device used to adjust the homogeneity of a magnetic field. Originally, shims have their name from the purely mechanical shims that are used to adjust position and parallelity of the pole faces of an electromagnet. Coils that are used to adjust the homogeneity of a magnetic field by changing the current flowing through it were called "electrical current shims"[1] because of their similar function.1516NMR Sample Preparation Use clean + dry NMR tubes and caps (tubes can be re-used, caps should not!) 0.5 ml deuterated solvent (i.e. CDCl ,C D , acetone-d ,etc.) substrate requirements for routine spectra: 10 mg for proton NMR 100 mg for carbon-13 NMR min. filling height of tube: 2 inches (5 cm)

Cleaning of tubes: 1. rinse with solvent you were using 2. rinse with acetone 3. dry in (vacuum-)oven at low temperature36665 mm17NMR Sample Preparation

Clean clear solutionSuspension or opaque solutionPrecipitateNot enough solventTwo phasesConcentration gradientGOOD!B a d S a m p l e s !18NMR Sample PreparationShimmingimproves the magnetic field homogeneityIf the magnetic field is not uniform within the sample, molecules in different positions will experience different field strengths. This will produce broad, distorted, or additional signals.19Good and bad NMR Spectra are the result of:

Homogeneity of magnetic fieldSample preparationChoice of solventData acquisition parametersProcessing procedures

20Good spectrum

ppmppm21Good spectrum

IntegralsPeak pickingppm scaleppmppm22Good spectrum

ppmppm23Bad spectrum ?

24Bad spectrum !

Signal/Noise ratio badNo units specified for axis and peak picking25Bad spectrum ?

26Bad spectrum !

Tall signals are cut off27Bad spectrum ?

28Bad spectrum !

Signals too small (only allowed when trying to compare signal intensities between different spectra) 29Bad spectrum ?

30Bad spectrum !

Broad signalsPossible reasons:poor shimmingviscous samplesample too concentratedsuspended particles in sampleexcessive line broadening may have been used during processing31Bad spectrum ?

32Bad spectrum ?

33Bad spectrum ?

Areas without signals should be excluded.(If you want to print all your spectra with a default range, i.e. 0-10 ppm, dont forget to print detailed expansions.) 34

The nmr spectra included in this presentation have been taken from the SDBS database with permission.National Institute of Advanced Industrial Science and Technology (http://www.aist.go.jp/RIODB/SDBS/menu-e.html)Nuclear Magnetic Resonance (nmr)the nuclei of some atoms spin: 1H, 13C, 19F, the nuclei of many atoms do not spin: 2H, 12C, 16O, moving charged particles generate a magnetic field ()when placed between the poles of a powerful magnet, spinning nuclei will align with or against the applied field creating an energy difference. Using a fixed radio frequency, the magnetic field is changed until the E = EEM. When the energies match, the nuclei can change spin states (resonate) and give off a magnetic signal. E magnetic field = 14,092 gaussfor 1H v = 60,000,000 Hz (60 MHz)

nmr spectrumintensity10 9 8 7 6 5 4 3 2 1 0chemical shift (ppm)magnetic field 1H nuclei are shielded by the magnetic field produced by the surrounding electrons. The higher the electron density around the nucleus, the higher the magnetic field required to cause resonance.

CH3ClversusCH4lower electron higher electrondensity densityresonate at lower resonate at higherapplied field applied field

Information from 1H-nmr spectra:

Number of signals: How many different types of hydrogens in the molecule.Position of signals (chemical shift): What types of hydrogens.Relative areas under signals (integration): How many hydrogens of each type.Splitting pattern: How many neighboring hydrogens.Number of signals: How many different types of hydrogens in the molecule.

Magnetically equivalent hydrogens resonate at the same applied field.

Magnetically equivalent hydrogens are also chemically equivalent.

# of signals?CH4CH3CH3

number of signals?

Position of signals (chemical shift): what types of hydrogens.

primary0.9 ppmsecondary1.3tertiary1.5aromatic6-8.5allyl1.7benzyl2.2-3chlorides3-4H-C-Clbromides2.5-4H-C-Briodides2-4H-C-Ialcohols3.4-4H-C-Oalcohols1-5.5H-O-(variable)Note: combinations may greatly influence chemical shifts. For example, the benzyl hydrogens in benzyl chloride are shifted to lower field by the chlorine and resonate at 4.5 ppm.reference compound = tetramethylsilane (CH3)4Si @ 0.0 ppm

remember:magnetic field chemical shift

convention: let most upfield signal = a, next most upfield = b, etc.cbatms

tolueneab

chemical shifts

Integration (relative areas under each signal): how many hydrogens of each type.

a b cCH3CH2CH2Bra 3Ha : b : c = 3 : 2 : 2b 2Hc 2H

a b aCH3CHCH3a 6Ha : b = 6 : 1 Clb 1H

integration

Integration: measure the height of each step in the integration and then calculate the lowest whole number ratio: a:b:c = 24 mm : 16 mm : 32 mm = 1.5 : 1.0 : 2.0 3H : 2H : 4Habc

If the formula is known ( C8H9OF ), add up all of the steps and divide by the number of hydrogens = (24 + 16 + 32 mm) / 9H = 8.0 mm / Hydrogen. a = 24 mm / 8.0 mm/H 3 H; b = 16 mm/8.0 mm/H 2H; c = 32 mm/8.0 mm/H 4H.Splitting pattern: how many neighboring hydrogens.In general, n-equivalent neighboring hydrogens will split a 1H signal into an ( n + 1 ) Pascal pattern.neighboring no more than three bonds awaynn + 1Pascal pattern:0 11singlet1 2 1 1doublet2 3 1 2 1triplet3 4 1 3 3 1quartet4 5 1 4 6 4 1quintetnote: n must be equivalent neighboring hydrogens to give rise to a Pascal splitting pattern. If the neighbors are not equivalent, then you will see a complex pattern (aka complex multiplet).

note: the alcohol hydrogen OH usually does not split neighboring hydrogen signals nor is it split. Normally a singlet of integration 1 between 1 5.5 ppm (variable).

splitting pattern?

Information from 1H-nmr spectra:

Number of signals: How many different types of hydrogens in the molecule.Position of signals (chemical shift): What types of hydrogens.Relative areas under signals (integration): How many hydrogens of each type.Splitting pattern: How many neighboring hydrogens.

cyclohexane

a singlet 12H

2,3-dimethyl-2-butene

a singlet 12H

benzene

a singlet 6H

p-xylene

aaba singlet 6Hb singlet 4H

tert-butyl bromide

a singlet 9H

ethyl bromide a bCH3CH2-Br

a triplet 3Hb quartet 2H

1-bromopropane

a b cCH3CH2CH2-Br

a triplet 3Hb complex 2Hc triplet 2H

isopropyl chloride a b aCH3CHCH3 Cl

a doublet 6Hb septet 1H

2-bromobutane b d c aCH3CHCH2CH3 Br

a triplet 3Hb doublet 3Hc complex 2H d complex 1H

o-methylbenzyl chloride

ethanol a c bCH3CH2-OH

a triplet 3Hb singlet 1Hc quartet 2H

ethylbenzene

c b aa triplet 3Hb quartet 2Hc ~singlet 5H

p-diethylbenzene

m-diethylbenzene

o-diethylbenzene

2-bromo-2-methylbutane b CH3b CH3CCH2CH3 a Br c

a triplet 3Hb singlet 6Hc quartet 2H b & c overlap

di-n-propylether a b c c b aCH3CH2CH2-O-CH2CH2CH3

a triplet 6Hb complex 4Hc triplet 4H

1-propanol a b d cCH3CH2CH2-OH

a triplet 3Hb complex 2Hc singlet 1Hd triplet 2H

C11H165H2H9Ha 9H = 3CH3, no neighborsc 5H = monosubstituted benzeneb 2H, no neighbors

C4H8Br26H2Ha = 6H, two CH3 with no neighbors (CH3)2Cb = CH2, no neighbors & shifted downfield due to Br

C7H8O5H2H1Hc = monosubst. benzeneb = CH2c = OH

C4H9Bra doublet 1.04 ppm 6Hb complex 1.95 ppm 1Hc doublet 3.33 ppm 2Ha = two equivalent CH3s with one neighboring H (b?)c = CH2 with one neighbor H (also b) a CH3 a 6H doubletCH3CHCH2Br b 1H complex a b c c 2H doubletC10H13Cla singlet 1.57 ppm 6Hb singlet 3.07 ppm 2Hc singlet 7.27 ppm 5Ha = two-equilalent CH3s with no neighborsc = monosubstituted benzene ringb = CH2

13C nmr 13C ~ 1.1% of carbons

number of signals: how many different types of carbonssplitting: number of hydrogens on the carbonchemical shift: hybridization of carbon sp, sp2, sp3chemical shift: evironment

2-bromobutane

a c d b CH3CH2CHCH3 Br13C-nmr

mrimagnetic resonance imagingThis image is copyrighted, and used by kind permission of Joseph Hornak for use in Chem-312.http://www.cis.rit.edu/htbooks/mri/