Chemistry
NMR Spectroscopy
Nuclear Magnetic Resonance (NMR) spectroscopy is a powerful analytical technique used to study the structure and dynamics of molecules. It relies on the interaction between the magnetic properties of atomic nuclei and an external magnetic field. By measuring the resonance frequencies of nuclei in a sample, NMR spectroscopy provides valuable information about molecular composition, connectivity, and environment.
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eBook - PDFChemical Analysis
Modern Instrumentation Methods and Techniques
- Francis Rouessac, Annick Rouessac, John Towey(Authors)
- 2022(Publication Date)
- Wiley(Publisher)
Chemical Analysis: Modern Instrumentation Methods and Techniques , Third Edition. Francis Rouessac and Annick Rouessac, translated by John Towey. © 2022 John Wiley & Sons Ltd. Published 2022 by John Wiley & Sons Ltd. Companion Website: www.wiley.com/go/Rouessac/Analysis3e Nuclear Magnetic Resonance Spectroscopy Chapter 15 N uclear magnetic resonance (NMR) is a spectroscopic method based on the study of the nuclei of certain elements. It has become irreplaceable in a variety of areas, such as chemistry, biology, the food industry or medical imaging (MRI). It is one of the most powerful methods to obtain structural information on organic or inorganic compounds. A succession of technological advances has led to a growing number of applications for it, whether analytical or not, in industry, ranging Chapter 15: Nuclear Magnetic Resonance Spectroscopy 388 from oil exploration to the identification of food products. This chapter is limited to a simplified study of NMR in solution in the field of organic compounds. 15.1 GENERAL INTRODUCTION Nuclear magnetic resonance refers to a property of matter that has given its name to powerful method of materials investigation, in particular to identify the structure of organic or inorganic compounds. NMR spectrometers are therefore often found in research laboratories, although there are routine applications based on this property, using simpler and more robust dedicated instruments (see Figure 15.31). Organic chemists quickly understood the interest of NMR, which has accelerated its development and favoured the appearance of many technical improvements.
eBook - PDF- David R. Klein(Author)
- 2016(Publication Date)
- Wiley(Publisher)
In this chapter, we will see the role that diamag- netism plays in nuclear magnetic resonance (NMR) spectroscopy, which provides more structural information than any other form of spectroscopy. We will also learn how NMR Spectroscopy is used as a pow- erful tool for structure determination. 650 CHAPTER 15 Nuclear Magnetic Resonance Spectroscopy 15.1 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- 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 - 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- Rose Marie O. Mendoza(Author)
- 2019(Publication Date)
- Arcler Press(Publisher)
Nuclear Magnetic Resonance Spectroscopy (NMR) Chapter 5 CONTENTS 5.1. Introduction .................................................................................... 142 5.2. Magnetic Resonance ....................................................................... 143 5.3. Relaxation ...................................................................................... 149 5.4. Other NMR Parameters ................................................................... 157 References ............................................................................................. 161 Elementary Organic Spectroscopy 142 5.1. INTRODUCTION From a purely intellectual point of view, one of the interesting things about NMR (nuclear magnetic resonance) is the intricacy of the subject. However, this intricacy can cause frustration to the people who are willing to understand and utilize NMR. As with the other physical methods used in the studies of the biological systems, NMR may be utilized in the empirical mode; for instance, noting the variations in the NMR parameter with modification of an experimental variable. The better understanding of the NMR phenomenon is usually rewarded with additional clarification of the system under examination. Although there might be thresholds of the knowledge of NMR essential to read the text critically or to perform the NMR studies, there is variety of the knowledge to be achieved about the NMR which has the practical surplus of providing the greater variety of NMR experiments to be correctly utilized (Bloembergen et al., 1948) (Figure 5.1). Figure 5.1: Schematic representation of NMR. Source: https://chembam.com/techniques/nmr/ The NMR phenomenon can usually be described in the nutshell as follows. If the sample is placed in the magnetic field (MF) and is given RF radiation at a suitable frequency, nuclei in the sample are able to absorb the energy.
- 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 - 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
- Wallace Brey(Author)
- 2012(Publication Date)
- Academic Press(Publisher)
A parallel method has also been applied to infrared spectroscopy in order to increase its sensitivity and versatility. The mathematical processing of results is similar, but the beat pattern is produced optically by mixing a reference beam of light with a beam that has passed through the sample. In this section we mention a few of the ways in which N M R can be applied to biological systems. The first is the study of hydrogen bond-ing. Involvement of a hydrogen atom in a hydrogen bond leads to a substantial change in chemical shift, an unshielding or downfield shift as a result of the restrictions imposed by the electric field of the dipole, which attracts the hydrogen, on the freedom of motion of electrons about the hydrogen nucleus. Thus the hydroxyl resonance of a pure alcohol, almost completely hydrogen-bonded, appears at 6 to 7 ppm from T M S , whereas in dilute solution in an inert solvent the resonance is upfield of a methyl resonance, at about 1 ppm from T M S . The chemical shift of the hydroxyl hydrogens as observed for a solution is the concentration-weighted average of the shifts of the hydrogen-bonded protons and of the protons not involved in hydrogen bonds. If the limiting shifts can be evaluated, it is then possible to calculate the relative amounts of the monomeric species and of the hydrogen-bonded molecules in solution. If it can be assumed that only (13-8) 13-6 APPLICATIONS OF NMR 526 THIRTEEN MAGNETIC RESONANCE SPECTROSCOPY one aggregated species, say a dimer, is formed, then the equilibrium constant can be calculated, and from the temperature dependence of the equilibrium constant, the enthalpy change associated with the formation of hydrogen bonds can be determined. Of course, if the hydrogen bond in question is an intramolecular bond, it is less susceptible to changes in environment.
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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