Resonancia Magnetica Nuclear y Equipo

7/31/2019 Resonancia Magnetica Nuclear y Equipo

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Hardware y Software

Crio-Magneto superconductor

Sonda superconductora RMN

Consola de Radiofrecuencia

Computadora + Software RMN

+ Impresora/Plotter

Solucin RMN

Preparacin de la muestra

Presentacin de los datos


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CRIOMAGNETOS SUPERCONDUCTORES


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alambre superconductor


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SEGURIDAD CON LOS MAGNETOS DE RMN

Los magnetos de RMN siempre estn cargados!

Los magnetos de RMN pueden interferir con dispositivos

mdicos (p. ej. marcapasos, implantes metlicos)

Los magnetos de RMN y las consolas de RF pueden interferir

con dispositivos electrnicos y mecnicos y pueden daarlos

(telfonos celulares, buscadores, relojes, llaves de autos, etc.)

Los magnetos de RMN borrarn tarjetas de crdito,, tarjetas

de identificacin, discos de 31/2, discos duros, USBs (I-pods,

mp3).

Atraen objetos ferromagnticos de cualquier tamao p. ej.

clips, monedas, llaves, ploumas, tijeras, tornillos, sillasmetlicas, cilindros de gas, etc.) y el espectrmetro y la gente

pueden sufrir graves daos o lesiones, si se manejan sin

cuidado.


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Los magnetos de RMN contener criognicos (helio y nitrgeno

lquido)

Los criognicos pueden causar quemaduras graves si no semaneja adecuadamente (use proteccin para los ojos y guantes).

Crigenos se evaporan y pueden causar asfixia si no est bien

ventilado el laboratorio.

Cuando se apaga un imn se vaporizan hasta 100 litros de heliolquido en cuestin de minutos (2600 pies cbicos, 70,000 litros de

gas) y puede causar asfixia, incluso si el laboratorio est bien

ventilado. Si un imn se apaga, salga del laboratorio

inmediatamente. No entre en pnico, el gas helio se elevar hasta

el techo. Durante una recarga, la tubera se puede romper. Los tubos

congelados de plstico se rompen como un cristal!

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CONSOLA CON COMPUTADORADE RMN


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GENERADOR DE LA SEAL DERADIOFRECUENCIA

Desacoplador (

1

H):Amplificador

Generador de Frecuencia

Transmisor: Amplificador

Generador de Frecuencia

Frequency Generators and Signal Amplifiers are required for each RF channel.Our spectrometers have 2 channels, modern spectrometers can have up to 8 channels.


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SONDAS DE RMN

Slidos

Lquidos

Slidos

Lquidos

Magic angle

(54.7)


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MUESTRAS PARA RMN

Types of NMR sample holders

Sample preparation

Spectrum quality


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TIPOS DE PORTADORES DEMUESTRA PARA RMN

Solid State

Sample Rotors

Solution NMR

Sample TubeSpinners

NMR SampleTubes with Caps


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PREPARACIN DE LA MUESTRA PARA RMNTubes and Caps:

NMR tubes are a standard length (7 and 9 inch). When chipped (and reducedin 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 layingflat on a layer of kimwipes or placed upside-down on a kimwipe in a beakeror 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 bagsof 100 ($5) or 1000 ($40 at www.wilmad.com).

Degassing Samples:

NMR spectra recorded using degassed solvents usually benefit fromreduced 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.


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Quantity:

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 oneconcentrated 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 eachsample corrects this effect and takes just a minute or so. However, vastlydifferent solvent heights (volumes) prevent complete correction andrequire many minutes shimming to achieve acceptable homogeneity.

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

PREPARACIN DE LA MUESTRA PARA RMN


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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 temperature

3 6 6 6

5 mm



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Clean

clear

solution

Suspension

or opaque

solution

PrecipitateNot

enough

solvent

Two

phases

Concentration

gradient

GOOD! B a d S a m p l e s !



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Shimming

improves the

magnetic field

homogeneity

If 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.



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are the result of:

Homogeneity of magnetic fieldSample preparation

Choice of solvent

Data acquisition parameters

Processing procedures

Espectros correctos e

incorrectos en RMN


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ppm

ppm

Espectro correcto!!


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Integrales

Peakpicking

ppm scale ppm

ppm

Espectro incorrecto?


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20ppm

ppm

Espectro correcto!!


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Signal/Noise

ratio bad

No units specified for

axis and peak picking

Espectro incorrecto!!


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Tall signals

are cut off



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Signals too small

(only allowed when trying to

compare signal intensities between

different spectra)



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Broad signals Possible reasons:poor shimming

viscous sample

sample too concentrated

suspended particles in sample

excessive line broadening may

have been used during processing



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Signals are distorted(automatic phase correction

is often insufficient)

Excessive peak picking

(low p.p. threshold,

also due to improper phasing)



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Bad spectrum ?


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Bad spectrum ?

Areas without signals should be excluded.

(If you want to print all your spectra with adefault range, i.e. 0-10 ppm, dont forget to

print detailed expansions.)


Lab Assignments


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Lab Assignments

1. 2X2 hrs Comprehensive 1H NMR and Indirect 13C Observation X00 mg2. 3 hrs Pulse Width Calibration and B1 100 mg

3. 2X2 hrs Rare spin NMR concentrated (80-90%)4. 3 hrs Decoupling 1H from 13C and B2 100 mg5. 2 hrs Spin Echo and Spin/Spin Relaxation, T2 100 mg6. 2 hrs Spin/Lattice Relaxation, T1 100 mg7. 3 hrs Nuclear Overhauser Effect 25 mg

8. 2 hrs Polarization Transfer and DEPT 100 mg9. 3 hrs 13C CP/MAS in Solids (sample provided)10. 2 hrs HETCOR (1H/13C COSY) 100 mg

11. 2 hrs 1H COSY / NOESY (optional) 25 mg

Use your own samples, if possible. Familiarize yourselves with the procedures

for each experiment, before you come to the lab. Print the manuals.

http://www.chem.binghamton.edu/NMR


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In all assignments you are expected to report on the following information:

Signal-to-noise ratio

Chemical shifts and method of reference in relation to structure

J coupling (homo and heteronuclear) in relation to structure Peak intensity and area in relation to concentration and structure/dynamics/relaxation

Effect of B0 / lab magnetic field strength, Larmor frequency and gyromagnetic ratio

Effect of B0 inhomogeneity

Pulse width and tip angle

Magnitude of B1 and B2 fields / rf field strengths used

Effect of B1 and B2 inhomogeneity

Effects of O1 and O2 / frequency offsets

Effects of sample spinning and location of spinning sidebands

Method of decoupling if used as well as effectiveness

Solvent and temperature used

Pulse sequence and instrument control programming

All critical instrument or data processing parameters

Vector and spin diagrams, as needed. Note any experimental or instrumental anomalies

The spectrometer manual to be used in this course can be downloaded from:http://www.chem.binghamton.edu/staff/schulte/CHEM585f/Chem585f-Bruker.doc
http://www.chem.binghamton.edu/staff/schulte/CHEM585f/Chem585f-Bruker.dochttp://www.chem.binghamton.edu/staff/schulte/CHEM585f/Chem585f-Bruker.dochttp://www.chem.binghamton.edu/staff/schulte/CHEM585f/Chem585f-Bruker.dochttp://www.chem.binghamton.edu/staff/schulte/CHEM585f/Chem585f-Bruker.doc

Resonancia Magnetica Nuclear y Equipo

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