tailieunhanh - Ebook Atkins’ physical chemistry (8th edition): Part 2

(BQ) Part 2 book "Atkins’ physical chemistry" has contents: Molecular spectroscopy 3 - Magnetic resonance, molecular interactions, molecules in motion, the rates of chemical reactions, the kinetics of complex reactions, molecular reaction dynamics, processes at solid other contents. | Molecular spectroscopy 3: magnetic resonance One of the most widely used spectroscopic procedures in chemistry makes use of the classical concept of resonance. The chapter begins with an account of conventional nuclear magnetic resonance, which shows how the resonance frequency of a magnetic nucleus is affected by its electronic environment and the presence of magnetic nuclei in its vicinity. Then we turn to the modern versions of NMR, which are based on the use of pulses of electromagnetic radiation and the processing of the resulting signal by Fourier transform techniques. The experimental techniques for electron paramagnetic resonance resemble those used in the early days of NMR. The information obtained is very useful for the determination of the properties of species with unpaired electrons. 15 The effect of magnetic fields on electrons and nuclei The energies of electrons in magnetic fields The energies of nuclei in magnetic fields Magnetic resonance spectroscopy Nuclear magnetic resonance The NMR spectrometer The chemical shift The fine structure Conformational conversion and exchange processes When two pendulums share a slightly flexible support and one is set in motion, the other is forced into oscillation by the motion of the common axle. As a result, energy flows between the two pendulums. The energy transfer occurs most efficiently when the frequencies of the two pendulums are identical. The condition of strong effective coupling when the frequencies of two oscillators are identical is called resonance. Resonance is the basis of a number of everyday phenomena, including the response of radios to the weak oscillations of the electromagnetic field generated by a distant transmitter. In this chapter we explore some spectroscopic applications that, as originally developed (and in some cases still), depend on matching a set of energy levels to a source of monochromatic radiation and observing the strong absorption that occurs at