Chemistry
Nuclear Magnetic Resonance spectrometer
A Nuclear Magnetic Resonance (NMR) spectrometer is a powerful analytical instrument used to study the structure and dynamics of molecules. It works by subjecting a sample to a strong magnetic field and radiofrequency radiation, causing the nuclei of atoms to resonate at characteristic frequencies. By analyzing the resulting NMR spectra, chemists can determine the connectivity and environment of atoms within a molecule.
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11 Key excerpts on "Nuclear Magnetic Resonance spectrometer"
eBook - ePub- Simonpietro Agnello(Author)
- 2021(Publication Date)
- Wiley(Publisher)
10 Nuclear Magnetic Resonance Spectroscopy Alberto Spinella1 and Pellegrino Conte2 1 Advanced Technologies Network Center (ATeN Center), University of Palermo, Palermo, Italy 2 Department of Agriculture, Food and Forestry Sciences, University of Palermo, Palermo, Italy10.1 Introduction
Nuclear magnetic resonance (NMR) spectroscopy is a powerful technique used in many fields from basic to applied sciences in order to characterize both molecular and supramolecular structures of organic and inorganic compounds. Among the various spectroscopic techniques, NMR is one of the most versatile due to its ability to unveil three‐dimensionality of molecular systems in each of the three different physical states (liquid, solid, and gas) and regardless of sample crystallinity.Purcell, Torrey, and Pound at Harvard University [1] and Bloch, Hansen, and Packard at Stanford University [2] performed the first NMR experiments in condensed matter independently of each other in 1945. In particular, they obtained NMR signals from protons of paraffin wax and liquid water, respectively. However, since those pioneering days, NMR has become a well‐established spectroscopic technique. In particular, both liquid and solid‐state NMR spectroscopies are largely exploited for molecular structure determination and dynamics in several chemistry fields (e.g. protein chemistry, materials science, cultural heritage, food science, and so on), while NMR imaging is recognized as a very powerful tool in modern medicine in order to monitor biological tissues and living functions.In the following, an overview of the basic principles of NMR spectroscopy and the main topics that may be useful to researches of different areas will be given. A detailed and in‐depth introduction to NMR spectroscopy can be found in several textbooks [3 –5 ].10.2 NMR General Concepts
10.2.1 Nuclear Spin and Magnetic Moment
All elementary particles have an intrinsic property referred to as spin. This property has been introduced to explain the deflection of the elementary particles when they pass through an inhomogeneous magnetic field. In fact, according to the experiment by Stern and Gerlach, an elementary particle, such as an electron, being a moving electric charge, should behave like a small linear magnet when crossing a magnetic field gradient. Therefore, a continuous distribution should be revealed on the surface of a detector. Conversely, the image obtained by elementary particles crossing the magnetic field gradient is an ensemble of discrete points of accumulation. This suggests that all the elementary particles have an intrinsic spin angular momentum which can have only discrete values given by:
eBook - PDF- Satinder Ahuja, Neil Jespersen(Authors)
- 2006(Publication Date)
- Elsevier Science(Publisher)
Chapter 10 Nuclear magnetic resonance spectroscopy Linda Lohr, Brian Marquez and Gary Martin 10.1 INTRODUCTION Nuclear magnetic resonance (NMR) is amenable to a broad range of applications. It has found wide utility in the pharmaceutical, medical and petrochemical industries as well as across the polymer, materials science, cellulose, pigment, and catalysis fields to name just as a few examples. The vast diversity of NMR applications may be in part due to its profound ability to probe both chemical and physical properties in-cluding chemical structure as well as molecular dynamics. This gives NMR the potential to have a great breadth of impact compared with other analytical techniques. Furthermore, it can be applied to liquids, solids or gases. In some ways, it is a ‘‘universal detector’’ in that it detects all irradiated nuclei in a sample regardless of the source. Signals appear from all components in a mixture, proportional to their concentration. NMR is therefore a natural compliment to separation techniques such as chromatography, which provide a high degree of component selectivity in a mixture. NMR is also a logical compliment to mass spectrometry, since it can provide critical structural information. Compared to other solid-state techniques, NMR is exquisitely sensitive to small changes in local electronic environments, such as discerning individual polymorphs in a crystalline mixture. Beyond the qualitative molecular information afforded by NMR, one can also obtain quantitative information. Depending on the sample, NMR can measure relative quantities of components in a mixture as low as 0.1–1% in the solid state. NMR limits of detection are much lower in the liquid state, often as low as 1000:1 down to 10,000:1. In-ternal standards can be used to translate these values into absolute quantities. Of course, the limit of quantitation is not only dependent on Comprehensive Analytical Chemistry 47 S.
- SachchidaNand Shukla(Author)
- 2019(Publication Date)
- Arcler Press(Publisher)
Nuclear Magnetic Resonance Spectroscopy (NMR) 5 CONTENTS 5.1. Introduction ................................................................................... 134 5.2. Overview of Concepts ................................................................... 134 5.3. Quantum Mechanical Description ................................................. 137 5.4. Description of The Nuclear Quantum Number ............................... 138 5.5. The Population of The Energy Levels .............................................. 139 5.6. Nmr Spectra of Several Nuclei ....................................................... 142 5.7. Fine Structure of NMR Spectrum .................................................... 147 5.8. Nuclear Relaxation ........................................................................ 151 5.9. The Noe Phenomenon ................................................................... 153 5.10. Use Of Nuclear Magnetic Resonance To Monitor the Rate Processes ....................................................................... 156 5.11. Miscellaneous Uses ..................................................................... 158 References ............................................................................................. 163 Introduction to Modern Instrumentation Methods and Techniques 134 5.1. INTRODUCTION Nuclear magnetic resonance (NMR) spectroscopy was discovered after World War II and from then the applications of NMR spectroscopy to chemistry have been expanding continuously. It was quite natural then that Nuclear magnetic resonance took a vital part in undergraduate chemistry education. In recent years, applications of Nuclear magnetic resonance have been stretched to medicine and biology (Tompa et al., 1996; Bilgic et al., 2015). The fundamental principles are normally covered in physical chemistry course and every undergraduate physical chemistry course textbook includes a chapter on it.
eBook - ePubProblems of Instrumental Analytical Chemistry
A Hands-On Guide
- JM Andrade-Garda, A Carlosena-Zubieta;MP Gómez-Carracedo;MA Maestro-Saavedra;MC Prieto-BlancoRM Soto-Ferreiro(Authors)
- 2017(Publication Date)
- WSPC (EUROPE)(Publisher)
CHAPTER 7
NUCLEAR MAGNETIC RESONANCE AND MASS SPECTROMETRIES
Miguel Angel Maestro-Saavedra
OBJECTIVES AND SCOPE
The main objective of this chapter is to present students a concise, basic and practical overview of two powerful techniques for the structural characterization of organic and inorganic chemical structures; namely, nuclear magnetic resonance (NMR) spectrometry and mass spectrometry (MS). Explanations range from essential background to descriptions of key concepts to some practical applications. A selected collection of exercises show how these key concepts are applied and how a structural elucidation from the NMR and MS spectra can be obtained.To explain how to interpret a mass spectrum is anything but simple because there are no fixed rules which can be followed. Therefore, in this chapter, it is attempted to present the very basics of the MS technique and give some general guidances, along with some examples.PART A: NUCLEAR MAGNETIC RESONANCE SPECTROMETRY
1.INTRODUCTION TO NUCLEAR MAGNETIC RESONANCE
Nuclear magnetic resonance (NMR) spectrometry is a fundamental tool for the structural determination of organic and inorganic molecules. It employs low-energy radiation, in the radio frequencies (RF) region, in order to gather information on the structure of alkyl groups and other hydrogen-containing elements. Then, the presence of functional groups in the molecule is deduced.1.1.Basic principles
Many atomic nuclei behave as if they were spinning around themselves (nuclear spin) . When a charged particle (nucleus) moves or rotates, it creates a magnetic field. The orientation of H is random in the space until the nuclei is inserted in an external magnetic field Ho, which causes H to get aligned with H 0 . This can occur in two forms: aligning the magnetic moment H in the direction of the H 0 field (energetically favorable) or otherwise, counterclockwise to H 0 (it requires the input of energy as it is energetically unfavorable). The two possibilities are referred to as the nuclear spin states α and β
eBook - PDF- David R. Klein(Author)
- 2020(Publication Date)
- Wiley(Publisher)
In this chapter, we will see the role that diamagnetism plays in nuclear magnetic reso- nance (NMR) spectroscopy, which provides more structural information than any other form of spectroscopy. We will also learn how NMR spectroscopy is used as a power- ful tool for structure determination. 696 CHAPTER 16 Nuclear Magnetic Resonance Spectroscopy 16.1 INTRODUCTION TO NMR SPECTROSCOPY Nuclear magnetic resonance (NMR) spectroscopy is arguably the most powerful and broadly appli- cable technique for structure determination available to organic chemists. Indeed, the structure of a compound can often be determined using NMR spectroscopy alone, although in practice, structural determination is generally accomplished through a combination of techniques that includes NMR and IR spectroscopy and mass spectrometry. NMR spectroscopy involves the study of the interaction between electromagnetic radiation and the nuclei of atoms. A wide variety of nuclei can be studied using NMR spectroscopy, including 1 H, 13 C, 15 N, 19 F, and 31 P. In practice, 1 H NMR spectroscopy and 13 C NMR spectroscopy are used most often by organic chemists, because hydrogen and carbon are the primary constituents of organic compounds. Analysis of an NMR spectrum provides information about how the individual carbon and hydrogen atoms are connected to each other in a molecule. This information enables us to determine the carbon- hydrogen framework of a compound, much the way puzzle pieces can be assembled to form a picture. A nucleus with an odd number of protons and/or an odd number of neutrons possesses a quantum mechanical property called nuclear spin, and it can be probed by an NMR spectrometer. Consider the nucleus of a hydrogen atom, which consists of just one proton and therefore has a nuclear spin. Note that this property of spin does not refer to the actual rotation of the proton.
eBook - PDF- David R. Klein(Author)
- 2021(Publication Date)
- Wiley(Publisher)
NMR spectroscopy involves the study of the interaction between electromagnetic radiation and the nuclei of atoms. A wide variety of nuclei can be studied using NMR spectroscopy, including 1 H, 13 C, 15 N, 19 F, and 31 P. In practice, 1 H NMR spectroscopy and 13 C NMR spectroscopy are used most often by organic chemists, because hydrogen and carbon are the primary constituents of organic compounds. Analysis of an NMR spectrum provides information about how the individual carbon and hydrogen atoms are connected to each other in a molecule. This information enables us to determine the carbon- hydrogen framework of a compound, much the way puzzle pieces can be assembled to form a picture. A nucleus with an odd number of protons and/or an odd number of neutrons possesses a quan- tum mechanical property called nuclear spin, and it can be probed by an NMR spectrometer. Con- sider the nucleus of a hydrogen atom, which consists of just one proton and therefore has a nuclear spin. Note that this property of spin does not refer to the actual rotation of the proton. Nevertheless, it is a useful analogy to consider. A spinning proton can be viewed as a rotating sphere of charge, which generates a magnetic field, called a magnetic moment. The magnetic moment of a spinning proton is similar to the magnetic field produced by a bar magnet (Figure 15.1). FIGURE 15.1 (a) The magnetic moment of a spinning proton. (b) The magnetic field of a bar magnet. Direction of rotation N S Axis of spin and of the magnetic moment Magnetic lines of force N S (a) (b) DO YOU REMEMBER? Before you go on, be sure you understand the following topics.
eBook - PDF- J.R.J. Paré, J.M.R. Bélanger(Authors)
- 1997(Publication Date)
- Elsevier Science(Publisher)
J.R.J. Par~ and J.M.R. B~langer (Editors) Instrumental Methods in Food Analysis 9 1997 Elsevier Science B.V. All rights reserved. Chapter 6 Nuclear Magnetic Resonance Spectroscopy (NMR): Principles and Applications Calin Deleanu (1) and J. R. Jocelyn Par~ (2) 1) Costin D. Nenitescu Institute of Organic Chemistry, NMR Department, Spl. Independentei 202 B, P. O. Box 15-258, Bucharest, Romania and 2) Environment Canada, Environmental Technology Centre Ottawa, ON, Canada KIA 0H3 6.1 INTRODUCTION The Nuclear Magnetic Resonance (NMR) technique is now half a century old [1,2]. One might consider this as a long time, or at least as a time sufficiently long to justify the fact that NMR is by now a technique present in both advanced research and basic undergraduate courses in so many fields like chemistry, physics, biology, food sciences, medicine, material sciences, and so on. But if we consider the formidable progress that took place in these years, with NMR opening several stand-alone research fields (to mention only liquid-, solid-, localized-, low resolution-NMR, NMR Imaging and Microscopy) and the explosion of new techniques and instrumentation, then 50 years is a rather short time. By now, high resolution NMR is the most powerful technique for structure elucidation of chemical compounds in solution. It is also one of the most expensive techniques in terms of equipment, but meanwhile, very significantly, a technique which is already part of almost all research and teaching establishments. While the manufacturers are continuously pushing the limits of the instrumentation, trying to cope with every day developments in theoretical knowledge, the research, teaching and health establishments keep buying equipment costing roughly a million US
- L. M. Jackman, S. Sternhell, D. H. R. Barton, W. Doering(Authors)
- 2013(Publication Date)
- Pergamon(Publisher)
D. CHEMICAL EFFECTS IN N. M. R. The purpose of this section is to introduce, in the simplest terms, the effects which make n.m.r. spectroscopy important in chemistry. It is necessary to be acquainted with the phenomena described in this section in order to follow the detailed and separate accounts of each, given in subsequent Parts. (i) C H E M I C A L S H I F T So far in our discussion of nuclear magnetic resonance we have more or less assumed that the resonance frequency of a nucleus is simply a function of the applied field and the gyromagnetic ratio of the nucleus. If this were indeed the case nuclear magnetic resonance would be of little value to the organic chemist. It turns out, however, that the observed resonance fre-quency is to a small degree dependent on its molecular environment. This is because the extranuclear electrons magnetically screen the nucleus so that the magnetic field felt by the nucleus is not quite the same as the applied field. Naturally, we might expect the efficiency of this shielding by the extra-nuclear electrons to bear some sort of relationship to the type of chemical bonding involved. Thus, naively, we might predict that electron withdrawal from a given nucleus would decrease the shielding of that nucleus. To the extent to which this is true we can regard the magnetic nucleus as a tiny probe with which we may examine the surrounding electron distribution. Although the nuclear resonance picture of electron distribution is not nearly as simple as the one 12 An Introduction to NMR Spectroscopy drawn above, it has been found that nuclear resonance frequencies, when properly determined, are remarkably characteristic of molecular structure. We shall be concerned almost exclusively with the nuclear magnetic resonance of the hydrogen nucleus, that is with proton magnetic resonance, and a preliminary idea of the effect of structure on proton resonance fre-quencies can be gained by reference to Fig.
eBook - PDFBioactive Natural Products
Detection, Isolation, and Structural Determination, Second Edition
- Steven M. Colegate, Russell J. Molyneux, Steven M. Colegate, Russell J. Molyneux(Authors)
- 2007(Publication Date)
- CRC Press(Publisher)
17. Field, L.R., Fundamental aspects of NMR spectroscopy, in Analytical NMR , Field, L.R. and Sternhell, S., Eds., John Wiley, Chichester, 1989. 18. Friebolin, H., Basic One and Two Dimensional NMR Spectroscopy, 4th Edition , VCH, Weinheim, 2005. 19. Macomber, R.S., A Complete Introduction to Modern NMR Spectroscopy , Wiley, New York, 1997. 20. Becker, E.D., High Resolution NMR: Theory and Chemical Application, 3rd Edition , Academic Press, San Diego, CA, 1999. 21. Gunther, H., NMR Spectroscopy, 2nd Edition , Wiley, Sussex, 1994. 22. Abraham, R.J. and Loftus, P., Proton and Carbon-13 NMR Spectroscopy—An Integrated Approach , Heyden, London, 1980. Nuclear Magnetic Resonance Spectroscopy 105 23. Ernst, R.R., Bodenhausen, G., and Wokaun, A., Principles of Nuclear Magnetic Resonance in One and Two Dimensions , Oxford University Press, Oxford, 1987. 24. Levitt, M.H., Spin Dynamics—Basics of Nuclear Magnetic Resonance , Wiley, Sussex, 2001. 25. Hore, P.J., Jones, J.A., and Wimperis, S., NMR: The Toolkit , Oxford, New York, 2000. 26. Freeman, R., Spin Choreography- Basic Steps in High Resolution NMR , Spektrum Academic, Oxford, 1996. 27. Keeler, J., Understanding NMR Spectroscopy , Wiley, 2006. 28. Andrew, E.R., in Nuclear Magnetic Resonance , Cambridge University Press, London, 1955, p 141. 29. Recommendations for the presentation of NMR data for publication in chemical journals, Pure Appl. Chem ., 29, 627, 1972. 30. Presentation of NMR data for publication in chemical journals—B. Conventions relating to spectra from nuclei other than protons, Pure Appl. Chem ., 45, 217, 1976. 31. Karplus, M., Contact electron-spin coupling of nuclear magnetic moments, J. Chem. Phys ., 30, 11, 1959. 32. Haasnoot, C.A.G., De Leeuw, F.A.A.M., and Altona, C., The relationship between proton-proton NMR coupling constants and substituent electronegativities—I. An empirical generalization of the Karplus equation, Tetrahedron , 36, 2783, 1980.
eBook - PDF- T. W. Graham Solomons, Craig B. Fryhle, Scott A. Snyder(Authors)
- 2022(Publication Date)
- Wiley(Publisher)
442 CHAPTER 9 Nuclear Magnetic Resonance and Mass Spectrometry To learn more about these topics, see: 1. Sheehan, J. C. The Enchanted Ring: The Untold Story of Penicillin. MIT Press: Cambridge, 1984, p. 224. 2. Nicolaou, K. C.; Montagnon, T. Molecules that Changed the World. Wiley-VCH: Weinheim, 2008, p. 366. Summary and Review Tools The study aids for this chapter include key terms and concepts and NMR chemical shift correlation charts. See the online course materials in for additional examples, videos, and practice. Problems Note to Instructors: Many of the homework problems are available for assignment in your online course. NMR Spectroscopy The following are some abbreviations used to report spectroscopic data: 1 H NMR: s = singlet, d = doublet, t = triplet, q = quartet, bs = broad singlet, m = multiplet IR absorptions: s = strong, m = moderate, br = broad 9.20 How many 1 H NMR signals (not peaks) would you predict for each of the following compounds? (Consider all protons that would be chemical shift nonequivalent.) (a) (c) (e) Br (g) (i) (b) (d) (f) O (h) OH OH 9.21 How many 13 C NMR signals would you predict for each of the compounds shown in Problem 9.20? 9.22 Propose a structure for an alcohol with molecular formula C 5 H 12 O that has the 1 H NMR spectrum given in Figure 9.34. Assign the chemical shifts and splitting patterns to specific aspects of the structure you propose. δ H (ppm) 1 2 0 1H 2H 3H C 5 H 12 O 6H FIGURE 9.34 The 1 H NMR spectrum (simulated) of alcohol C 5 H 12 O, Problem 9.22. Problems 443 9.23 Propose structures for the compounds G and H whose 1 H NMR spectra are shown in Figures 9.35 and 9.36. 1.0 1.5 2.0 4.0 4.2 TMS G, C 4 H 9 Br δ H (ppm) 0 1 2 3 4 5 6 7 8 FIGURE 9.35 The 1 H NMR spectrum of compound G, Problem 9.23. Expansions of the signals are shown in the offset plots. 4.0 4.2 4.4 5.6 5.8 6.0 δ H (ppm) 0 1 2 3 4 5 6 7 8 TMS H, C 3 H 4 Br 2 FIGURE 9.36 The 1 H NMR spectrum of compound H, Problem 9.23.
eBook - PDF- James W. Robinson, Eileen Skelly Frame, George M. Frame II(Authors)
- 2014(Publication Date)
- CRC Press(Publisher)
using.the.picoSpin-45.shows.small.peaks.in.the.spectrum.of.the.lemon.oil.that.are.due.to.other.trace. compounds.extracted.from.the.raw.material.( Figure.3 .75 ). Another.example.of.the.use.of.NMR.for.pharmaceutical.QC.is.the.screening.of.final.products. for.active.pharmaceutical.ingredients.(APIs).as.well.as.binders,.excipients,.and.contaminants . .In. softgel.tablets,.a.major.component.is.polyethylene.glycol.(PEG),.seen.in.the.NMR.spectrum.of.an. over-the-counter.ibuprofen.softgel.product.( Figure.3 .76a ). 3.11 LIMITATIONS OF NMR There.are.two.major.limitations.to.NMR:.(1).It.is.limited.to.the.measurement.of.nuclei.with. magnetic.moments.and.(2).it.may.be.less.sensitive.than.other.spectroscopic.and.chromatographic. methods. of. analysis . . As. we. have. seen,. although. most. elements. have. at. least. one. nucleus. that. responds.in.NMR,.that.nucleus.is.often.of.low.natural.abundance.and.may.have.a.small.magne-togyric.ratio,.reducing.sensitivity . .The.proton,. 1 H,.and.fluorine,. 19 F,.are.the.two.most.sensitive. elements. Elements.in.the.ionic.state.do.not.respond.in.NMR,.but.the.presence.of.ions.in.a.sample.contrib-utes.to.unacceptable.line.broadening . .Paramagnetic.contaminants.such.as.iron.and.dissolved.oxygen. also.broaden.NMR.lines . .Nuclei.with.quadrupole.moments,.such.as. 81 Br,.broaden.the.NMR.signal . . Line.broadening.in.general.reduces.the.NMR.signal.and.hence.the.sensitivity . 3.12 ELECTRON SPIN RESONANCE SPECTROSCOPY Electron. spin. resonance. (ESR). spectroscopy,. also. called. electron. paramagnetic. resonance. (EPR).spectroscopy.and.electron.magnetic.resonance.(EMR).spectroscopy,.is.an.MR.technique. for. studying. species. with. one. or. more. unpaired. electrons . . These. species. include. organic. and. inorganic.free.radicals.and.transition.metals.ions . .Unpaired.electrons.can.also.exist.as.defects.in. materials. .Unpaired.electrons.possess.spin,.with.a.spin.quantum.number. S .=.1/2,.and.therefore. also.possess.a.spin.magnetic.moment .
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