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Chapter

Cover Chemical Structure and Reactivity

Spectroscopy  

This chapter discusses mass spectrometry, infrared (IR) spectroscopy, and nuclear magnetic resonance (NMR) spectroscopy. The basic function of a mass spectrometer is to measure the mass of a molecule or, more correctly, an ion. A mass spectrometer can only separate and detect charged ions; neutral molecules cannot be detected. Both positive and negative ions can be detected, depending on the technique used. In IR spectroscopy, IR radiation is shone through a sample and certain frequencies (energies) are absorbed as molecules move to higher vibrational energy levels. Meanwhile, NMR looks at the environments of nuclei within molecules and is able to detect which nuclei are close to one another on the bonding network.

Chapter

Cover Characterisation Methods in Inorganic Chemistry

Nuclear magnetic resonance (NMR) spectroscopy  

This chapter evaluates nuclear magnetic resonance (NMR) spectroscopy. NMR is the most powerful and widely used spectroscopic method for the investigation of the molecular structures of compounds. It yields information about the shape and symmetry of molecules. For many common atom types, NMR spectroscopy defines the different environments present and their numbers. Analysis of NMR spectra often allows the full molecular configuration of a molecule to be determined. The technique also provides useful information about the rate and nature of ligand interchange in fluxional molecules and can be used to follow reactions and so determine their mechanistic pathway. While diffraction techniques usually produce accurate interatomic distances and angles, NMR studies generally yield more limited information on the separation of nuclei, such as which atoms are bonded or close neighbours in a molecule. The chapter then looks at insensitive nucleus enhancement by polarization transfer (INEPT) and COSY (Correlated Spectroscopy) NMR spectrum.

Chapter

Cover Foundations of Molecular Structure Determination

Rotational and vibrational spectroscopy  

This chapter presents a brief introduction to rotational and vibrational spectroscopy. It explains how pure rotational spectroscopy can be used in the precise determination of molecular geometry in small molecules and provide a direct means to deduce the shape of larger molecules. It also looks at how vibrational spectroscopy can be used in the measurement of geometrical parameters of gas phase molecules and in providing information about the structure and shape of molecules in the condensed phase. The chapter discusses the important role vibrational spectroscopy plays in characterization and analysis in organic chemistry where it is used typically in tandem with mass spectrometry and nuclear magnetic resonance (NMR) spectroscopy. It analyses concepts on a molecular scale by exploring how light interacts with the energy levels associated with rotational and vibrational degrees of freedom.

Chapter

Cover NMR Spectroscopy in Inorganic Chemistry

Polarization transfer and 2-D NMR spectroscopy  

This chapter evaluates polarization transfer and 2-D NMR spectroscopy. Polarization transfer, the exchange of excitation between spins, can be used to establish connectivity through scalar coupling interactions, molecular conformation through the nuclear Overhauser effect, and to study exchange. There are many 2-D experiments available, of which the most useful to the inorganic chemist are: correlation spectroscopy (COSY), heteronuclear correlation spectroscopies (HMQC, HSQC, and HMBC), and nuclear Overhauser effect spectroscopy (NOESY and HOESY). Interpretation of 2-D spectra can at first seem challenging, but with a little practice, becomes straightforward in most cases. Meanwhile, hyperpolarization refers to techniques such as DNP, OPNMR, or use of para-hydrogen, in which highly polarized spins—i.e. spins in which the population difference between NMR energy levels has been greatly increased by some physical or chemical process—are introduced into the molecule before the NMR experiment, resulting in greatly enhanced NMR signals.

Chapter

Cover Biomedical Science Practice

Spectroscopy  

Qiuyu Wang, Helen Montgomery, Nessar Ahmed, and Chris Smith

This chapter addresses spectroscopy, which is concerned with the interactions of electromagnetic radiation and matter, particularly the absorption of radiation by matter and, in some cases, its emission, and can be used to quantify molecules of interest in biomedical laboratories. Many molecules absorb light of characteristic wavelengths in the visible, UV, or IR regions of the electromagnetic spectrum. This is used as the basis for determining their concentrations using spectrophotometers and colorimeters. The absorbance of light of a specific wavelength by a solution of biological molecules depends on their concentration and the distance travelled by the light through the solution, as described by the Beer–Lambert law. The chapter then looks at infrared (IR) and Raman spectroscopy, light-scattering methods, fluorimetry, nuclear magnetic resonance (NMR) spectroscopy, and mass spectrometry.

Chapter

Cover Inorganic Spectroscopic Methods

Resonance spectroscopy  

This chapter examines resonance spectroscopy. Nuclear magnetic resonance (NMR) spectroscopy is probably the single most widely used and important physical technique available to the modern practical chemist. This is because of its wide applicability, its relative ease of use, and the amount of chemical and structural information that can be obtained from its use. The technique is frequently associated only with proton and carbon nuclei but there are many other elements to which it can potentially be applied. The chapter then looks at nuclear quadrupole resonance (NQR) spectroscopy. In NMR experiments, an external field is applied to cause a splitting of the normally degenerate nuclear spin states, but this is not necessary in NQR experiments because when there is an asymmetric charge distribution within the molecule, a molecular electric field gradient is generated. The chapter also considers electron spin resonance (ESR) spectroscopy.

Chapter

Cover Elements of Physical Chemistry

Nuclear magnetic resonance  

This chapter gives an account of the principles that govern spectroscopic transitions between spin states of nuclei in molecules. It describes simple experimental arrangements for the detection of these transitions in nuclear magnetic resonance (NMR) spectroscopy. It shows how NMR spectroscopy is used widely in chemistry and medicine. It also discusses resonant absorption which occurs when the separation of the energy levels of spins in a magnetic field matches the energy of incident photons. The chapter highlights the application of resonance which depends on the fact that many nuclei possess spin angular momentum. It highlights nuclear spin quantum number, I, of a nucleus is either a non-negative integer or half-integer.

Chapter

Cover NMR Spectroscopy in Inorganic Chemistry

Dynamic NMR spectroscopy  

This chapter focuses on dynamic NMR spectroscopy. Intra- and intermolecular dynamic processes affect the appearance of NMR spectra. When the dynamic process is slow, separate resonances are observed for each site. When the process is fast, a resonance at the weighted average chemical shift is seen. Exchange not only affects the chemical shift but also the couplings seen. If the dynamic process is intermolecular exchange, decoupling is observed due to the breaking of the bonds between the exchanging groups. If the process is intramolecular a weighted average coupling constant is seen to all the neighbouring spins involved. Dynamic processes can be studied by both variable temperature spectroscopy and by EXSY NMR, allowing the intimate mechanism of the dynamic process to be determined.

Book

Cover NMR Spectroscopy in Inorganic Chemistry

Jonathan A. Iggo and Konstantin V. Luzyanin

NMR Spectroscopy in Inorganic Chemistry offers a non-mathematical grounding in the physics of NMR spectroscopy and explores why the spectra look the way they do, providing a useful collection of NMR examples and trends in NMR parameters from inorganic chemistry. The first chapter covers the fundamentals. The second chapter looks at structure determination. The third chapter covers dynamic processes and NMR. The last chapter is about the solid state.

Chapter

Cover NMR Spectroscopy in Inorganic Chemistry

Fundamentals  

This chapter provides an overview of nuclear magnetic resonance (NMR) spectroscopy, which is commonly first encountered in organic chemistry, and attention is focused on the NMR spectroscopy of a single element, hydrogen. There are, however, many other elements that have isotopes with nuclear spin; if these elements are taken into account, NMR becomes perhaps the most important spectroscopic technique today for the characterization of inorganic compounds in solution and is of growing importance in the solid state. In solution, spin ½ nuclei give well-resolved, sharp resonances for each NMR active site in the molecule, while in the solid state, cross-polarization results in an increase in sensitivity and magic angle spinning results in an increase in resolution. The rules for interpreting NMR spectra depend only on the nuclear spins present. The chapter then presents some basic theory of NMR and a formalism for the prediction of NMR spectra in solution.

Chapter

Cover NMR Spectroscopy in Inorganic Chemistry

The solid state  

This chapter studies the solid state. Although NMR spectroscopy in solution continues to be the most widely used magnetic resonance spectroscopic technique, NMR in the solid state is rapidly growing in importance. In addition to the problems of low sensitivity and low natural abundance for many important nuclides encountered in solution, NMR in the solid state faces additional challenges due to interactions such as dipolar coupling, chemical shift anisotropy, and quadrupolar interactions that are averaged out in solution by molecular tumbling but remain in the solid state due to the restricted mobility of the molecules/ions. Cross-polarization can be used to improve the signal to noise in spectra by allowing more scans to be acquired for signal averaging in the same amount of time. Analysis of CP build-up rates also provides information about things such as internuclear distances and molecular motions.

Chapter

Cover Organic Chemistry

Review of spectroscopic methods  

This chapter presents a review of spectroscopic methods. It begins by looks at spectroscopy and carbonyl chemistry. Carbonyl compounds can be divided into two main groups: aldehydes and ketones, and acids and their derivatives. Which spectroscopic methods most reliably distinguish these two groups? Which help separate aldehydes from ketones? Which allows us to distinguish the various acid derivatives? The most consistently reliable method for doing this is 13C nuclear magnetic resonance (NMR). It does not matter much whether the compounds are cyclic or unsaturated or have aromatic substituents, they all give carbonyl 13C shifts in about the same regions. The chapter then looks at NMR spectra of alkynes and small rings.

Chapter

Cover Nuclear Magnetic Resonance

NMR experiments  

P.J Hore

This chapter explains how nuclear magnetic resonance (NMR) experiments work. Modern NMR spectroscopy is much more than simply recording a spectrum and interpreting the positions, widths, and intensities of the lines. The spins can be manipulated to tailor the information that appears in the spectrum. The chapter begins by introducing the 'vector model'. Although it has its origin in the quantum mechanics of spin angular momentum, it has the distinct advantage of being pictorial and essentially non-mathematical. The disadvantage is that it only helps us to understand the simplest NMR experiments. The chapter then uses the vector model to discuss two techniques for measuring spin relaxation times and an important method for sensitivity enhancement (Insensitive Nuclei Enhanced by Polarization Transfer or INEPT).

Chapter

Cover Making the Transition to University Chemistry

Instrumental Analysis  

This chapter expounds on the types of instrumental analysis used in chemical laboratories, especially those working with organic compounds. It also notes the fragmentation patterns that characterize a molecule. Mass spectrometry is utilized to search for a compound's molecular formula, while infrared spectroscopy involves the absorption of radiation in the electromagnetic spectrum's infrared region. The energy absorbed makes the bonds vibrate more energetically. Nuclear magnetic resonance (NMR) spectroscopy calculates nuclei's protons and neutrons that possess nuclear spins. The chapter also explains the process of spin-spin splitting or coupling in the NMR spectra as it depends on the number of adjacent protons.

Chapter

Cover Energy Levels in Atoms and Molecules

Energy levels in NMR  

This chapter looks into nuclear magnetic resonance (NMR), which is considered the most important advance in molecular spectroscopy in the second half of the twentieth century. It talks about the technique that uses NMR and electronic spin resonance (ESR) spectroscopy together, which has had an impact on all areas of molecular science from chemistry to biochemistry and medicine. It also describes an atom with angular momentum that has a rotating charge and acts as a little magnet, being governed by the microscopic rules of quantum mechanics. The chapter explains the energy of the ground state of the hydrogen atom in a magnetic field, which provides a rich pattern of energy levels. It refers to the actual magnitudes of the energies of the transitions observed in magnetic resonance experiments, which depend on the strength of the applied magnetic field.

Chapter

Cover Chemistry for the Biosciences

Chemical analysis: characterizing chemical compounds  

This chapter explores chemical analysis—the process of characterizing chemical compounds. It begins by looking at separation techniques, including solvent extraction, chromatography, electrophoresis, and centrifugation. The chapter then considers the use of mass spectrometry in determining the mass of a compound in a sample. It also outlines different spectroscopic techniques, which use the behaviour of compounds when they interact with electromagnetic radiation to help characterize them. Different spectroscopic techniques use different parts of the electromagnetic spectrum to ask different questions about chemical structure. These spectroscopic techniques include nuclear magnetic resonance (NMR) spectroscopy, infrared spectroscopy, and UV–visible spectroscopy. Finally, the chapter discusses X-ray crystallography, which reveals the three-dimensional structure of a compound in crystalline form.

Chapter

Cover Characterisation Methods in Inorganic Chemistry

Fundamental aspects of characterisation methods in inorganic chemistry  

This chapter discusses the fundamental aspects of characterization methods in inorganic chemistry. While not all of the techniques described in this book use the electromagnetic spectrum as a probe of the structures of inorganic molecules and materials, four of the main physical methods — NMR spectroscopy, vibrational spectroscopy, X-ray diffraction, and ultraviolet-visible (UV-vis) spectroscopy — all employ light of a specific range of wavelengths. Other less commonly employed techniques, such as Mössbauer spectroscopy, X-ray absorption spectroscopy (XAS), electron paramagnetic resonance (EPR), and nuclear quadrupole resonance (NQR) spectroscopy, also use portions of the electromagnetic spectrum covering the energy range from gamma rays, with wavelengths of a few picometres, to microwaves, with wavelengths of centimetres to metres. Because the full electromagnetic spectrum is employed to characterize inorganic compounds, the data obtained covers a very large wavelength and, therefore, energy range. The chapter then describes energy unit conversions and Fourier transforms in spectroscopy.

Chapter

Cover Foundations of Molecular Structure Determination

Nuclear magnetic resonance spectroscopy  

This chapter talks about the concept of nuclear spin, which focuses on nuclear magnetic moments and their study through nuclear magnetic resonance (NMR) spectroscopy. It uses the proton,1H, as the simplest example that illustrates how the phenomenon arises and describes the operation of a basic NMR spectrometer. It also describes a range of organic molecules that show how electronic effects of different substituent groups enable these to be recognized by the chemical shifts of the protons concerned, leading to the use of the technique as a diagnostic tool. The chapter analyses the occurrence of spin–spin splittings that demonstrate how neighbouring protons interact with each other. It discusses the development of Fourier transform instrumentation and its application to NMR spectroscopy and outlines the principles and uses of magnetic resonance imaging (MRI) in medically-related studies.

Chapter

Cover Tools and Techniques in Biomolecular Science

Structural analysis of proteins: X-ray crystallography1, NMR2, AFM3, and CD spectroscopy4  

Thomas Edwards1, Arwen Pearson1, Gary Thompson2, Arnout Kalverda2, Oliver Farrance3, David Brockwell3, and Gareth Morgan4

This chapter gives an overview of different techniques used to study the structure of proteins. These techniques can provide information such as size, conformation, protein-folding, interactions with other molecules, and changes in structure in response to changing environmental conditions. The chapter covers discussions on X-ray crystallography, nuclear magnetic resonance (NMR), and atomic force microscopy (AFM). It also describes circular dichroism (CD) spectroscopy, a technique used to study the secondary structure content of proteins, and how this changes when a protein unfolds or binds to another molecule. The chapter explains the basic principles behind these techniques and the types of information that each of these can provide.

Chapter

Cover f-Block Chemistry

Electronic structure, magnetism, and spectroscopy  

This chapter discusses electronic structure, magnetism, and spectroscopy. The majority of f-element atoms and ions have unpaired f-electrons, and many of the unique properties of the elements and their compounds arise from the way in which these electrons interact with each other. The chapter shows how Hund's rules can be used to work out the most stable arrangement of electrons in the atoms/ions, and how this information can be summarized in a term symbol. It then looks at magnetic properties of the ions and at the effect of paramagnetism on NMR spectra of f-element complexes. Finally, the chapter considers electronic absorption spectroscopy and lanthanoid luminescence. Magnetism and luminescence are fundamental to some of the most important applications of the lanthanoids.