Embed Size (px)
Citation preview
1 The world leader in serving science
Making NMR Accessible: Benchtop NMR Spectroscopy in the Classroom
Dean Antic, Ph.D. Senior Applications Scientist
Thermo Scientific picoSpin 45 NMR Spectrometer
2
Agenda
•Why NMR spectroscopy?
•picoSpin 45 NMR Spectrometer
•Application Examples • Fischer Esterification • Solvent Effects • Enol-Keto Tautomerism • Reaction Monitoring
3 3
Why NMR Spectroscopy?
• Most powerful analytical method in organic chemistry • Identifies chemical groups • Yields quantitative concentration ratios • Reveals structure
picoSpin 45 Ethyl Acetate spectrum
4
What NMR Signals Tell Us
• The number of signals shows how many different kinds of protons are present.
• The location of the signals shows how shielded or deshielded the proton is.
• The intensity of the signal shows the number of protons of that type.
• Signal splitting shows the number of protons on adjacent atoms.
5
picoSpin 45 Spectrometer Features • 45 MHz pulsed FT NMR spectrometer
• 1H only ; 19F & High Temperature option
• High Resolution: <60 ppb resolution
• High Performance: SNR for water of >500
• Compact: 10.5 lbs total weight
• Replaceable capillary micro-coil cartridge
• 30 µL sample volume
• No cryogens or compressed gas needed
• No special environment
• Solid-state technology, no moving parts
• Ethernet interface; controlled by web browser
• 12 month license to Mnova
6
NMR Spectrometer Alternatives
Anasazi 60 MHz
Bruker 400 MHz
picoSpin 45 MHz
Varian 900 MHz
7
The miniaturization of NMR
RF preamplifiers
Permanent magnet
Magnet temperature controller
Fluid cartridge and sub-panel
Embedded web server
Data converters, DSP
Pulse sequencer
Rx and Tx amplifiers
Shim coil controller
8
Inside the Cartridge
Tx/Rx Microcoil
0.3 mm ID quartz capillary
PTFE transition
9
picoSpin 45 spectrometer in the field Chemistry Lab Fume hood
10
Is it Robust?
NASA Zero-G Experiments
picoSpin 45
11
Is it Mobile?
Grays Peak • Continental Divide • Summit County, CO • Elevation ~14,278 ft
12
Chemical Education
Dr. Kevin Blair with students Western Michigan University
13
Teaching Applications
• Chemistry education – organic, physical, inorganic, instrumental • Structure elucidation • Reaction monitoring • Chemical kinetics • Chemical environment • Chemical thermodynamics • Learn NMR concepts
• In the lab • In the classroom
14
The Organic Curriculum
• Fischer Esterification – Synthesis of Banana Oil • Demonstrates the use of bench-top NMR in a traditional Organic Chemistry
Teaching Lab • Adaptation of a traditional Organic 200-Level lab experiment
• Solvent Effects – Acetone/Methanol solutions • Demonstrates the use of bench-top NMR in an Advanced Organic Chemistry Lab • Study solvent effects and the impact on NMR spectra
• Chemical Thermodynamics – Enol-Keto Tautomerism • Demonstrates the use of bench-top NMR in a traditional Physical Chemistry
Teaching Lab • Explore concepts in chemical thermodynamics by measuring & quantifying
intramolecular enol-keto tautomerism • Reaction monitoring: A Transesterification
Reaction • Demonstrates the use of bench-top NMR in a traditional Organic Chemistry
Teaching Lab • Utilize a traditional Organic 200-Level lab experiment
15 The world leader in serving science
Synthesis of 3-Methylbutyl Acetate
Fischer Esterification
16
Experimental Procedure
Acetic acid 3-Methylbutanol H2SO4 3-Methylbutyl acetate
25 mL 20 mL 5 mL
0.42 mol 0.18 mol Conc. 80-90% yield
• Acquire spectrum of reactants;
• Set up reflux apparatus;
• Charge 250 mL RBF with reactants & acid catalyst - acquire spectrum;
• Reflux for 1 hr - acquire spectrum;
• Wash: 2×50 mL H2O, 3×25 mL 5% NaHCO3 - acquire spectrum;
• Salt extraction: 2×50 mL sat. NaCl, dry over MgSO4 - acquire spectrum;
• Set up simple distillation apparatus – collect fraction 135-143 ºC;
• Acquire spectrum of product;
Reference: Gokel, H. D.; Durst, G. W. Experimental Organic Chemistry; McGraw-Hill, New York, 1980; pp 342-347.
17
Reactant: Acetic Acid (anhyd.)
10 scans T1 = 6s O
H
O
CH 3
TMS
18
Reactant: 3-Methylbutanol
-OH
-CH2- -CH-
-(CH3)2
-CH2-
CH
C H 3
CH 2
O HCH 2
CH 3
16 scans T1 = 8s
TMS
19
Product: 3-Methylbutyl acetate
O=CCH3
-CH2- -CH-
-(CH3)2
-CH2-
O
C H 3O
CH
C H 3
CH 2
CH 2
CH 3
16 scans T1 = 8s
TMS
20
Typical Spectral Set
21
Expanded Spectral Set
22 The world leader in serving science
Acetone in Methanol
Solution Effects
23
24 The world leader in serving science
Keto-Enol Tautomerism of an Acyclic β-Diketone
Chemical Thermodynamics
Acetylacetone
25
• Acquire: 1H spectrum of acetylacetone (AcAc) as a function of temperature
• Quantify: integrate enol & keto proton signals to determine equilibrium constant Keq
• Determine: ∆𝑯, ∆𝑺, and ∆𝑮 • ∆𝐺𝐺 = ∆𝐻𝐺 − 𝑇∆𝑆𝐺
• ∆𝐺𝐺 = −𝑅𝑇 ln𝐾𝑒𝑒 = ∆𝐻𝐺 − 𝑇∆𝑆𝐺; ln𝐾𝑒𝑒 = − ∆𝐻𝐺𝑅𝑅
+ ∆𝑆𝐺𝑅
• Plot: ln𝐾𝑒𝑒 vs. 1𝑅(K)
; slope = - ∆𝐻𝐺𝑅
, intercept = ∆𝑆𝐺𝑅
• Determine: Temperature dependence of Enol concentration
Goals & Procedure
Reference: Drexler, E. J.; Field, K. W. J. Chem. Ed. 1976, 53(6), 393.
• Set magnet temperature = 34 ºC
• Adjust Tx frequency (Larmor slope ≈ -37 kHz/ºC)
• Inject sample – acquire spectrum • Repeat every 2 ºC up to 58 ºC, shim on AcAc at each step
Goals
Procedure
26
27
28
Temperature Dependence of Enol Concentration
T(ºC) %Enol Keq
34 80 4.94
58 66 2.97
Literature1
33 81 4.3
Reference: 1Burdett, J. L.; Rodgers, M. T. J. Amer. Chem. Soc. 1964, 86, 2108.
%Enol =𝑒 𝑡 − 0.5 𝑘 𝑡
𝑒 𝑡 ∗ 100
29
Temperature Dependence of Keq
𝐾𝑒𝑒 =𝑒 𝑡
0.5 𝑘 𝑡
30 The world leader in serving science
Transesterification Synthesis of Methyl Acetate
Reaction Monitoring
31
Experimental Procedure
Ethyl Acetate Methanol H2SO4 Δ Methyl acetate Ethanol
2 mL 5 mL 0.3 mL RT - -
1 mol 6 mol Conc. 42-52ºC
Reference: http://www.picospin.com/applications/education/transesterification/
Procedure 1 • Charge test tube with a MeOH and EtOAc
• Add acid catalyst; mix
• Draw 40 µL aliquot, inject sample
• Acquire continuously for ~90-120 min:
• 600-700 scans • T1 = 10 s • Save individual scans • Process 12 scan averages
Procedure 2 – in situ • Charge test tube with a MeOH and EtOAc
• Add acid catalyst; heat in hot water bath
• Draw 40 µL aliquot & inject every 5 min
• Acquire individual spectra ~90-120 min:
• 12 Scans per sample • T1 = 10 s • Save averaged scans
32
Initial Reaction Mixture - Before
33
Reaction Mixture - During
34
Reaction Mixture – After
35
Summary We explored:
• The picoSpin 45 NMR spectrometer and its capabilities;
• How to use bench-top NMR in the teaching laboratory by exploring different applications in organic, physical and analytical chemistry teaching labs;
• Adapting your curriculum to bench-top NMR applications.
36
Contact Information
• Website resources: www.thermoscientific.com/picospin • Video tutorials: www.youtube.com/picoSpinNMR • Information: [email protected] • Application support: [email protected] • Technical support: [email protected]
37
Thank you very much!
Questions?
