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19%20Ch13 - CHAPTER 13 NMR Spectroscopy Important Terms...

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382 CHAPTER 13 NMR Spectroscopy Important Terms applied magnetic field the externally applied magnetic field. chemically equivalent protons with the same connectivity relationship to the rest of the molecule. protons chemical shift location of a signal occurring in an NMR spectrum. It is measured downfield from a reference compound (most often TMS). 13 C NMR nuclear magnetic resonance that shows carbon ( 13 C) nuclei. COSY spectrum a 2-D NMR spectrum showing 1 H- 1 H correlations. coupled protons protons that split each other. Coupled protons have the same coupling constant. coupling constant the distance (in hertz) between two adjacent peaks of a split NMR signal. DEPT 13 C NMR spectrum a group of four 13 C NMR spectra that distinguish CH 3 , CH 2 , and CH groups. diamagnetic anisotropy the term used to describe the greater freedom of π electrons to move in response to a magnetic field as a consequence of their greater polarizability compared with σ electrons. diamagnetic shielding shielding by the local magnetic field that opposes the applied magnetic field. diastereotopic hydrogens two hydrogens bonded to the same carbon that will result in a pair of diastereomers when each of them is replaced in turn with deuterium. 2-D NMR two-dimensional nuclear magnetic resonance. doublet an NMR signal that is split into two peaks. doublet of doublets an NMR signal that is split into four peaks of approximately equal height. A doublet of doublets is caused by splitting a signal into a doublet by one hydrogen and into another doublet by another (nonequivalent) hydrogen. downfield farther to the left-hand side of the spectrum. effective magnetic field the magnetic field that a nucleus "senses" through the surrounding cloud of electrons. enantiotopic hydrogens two hydrogens bonded to a carbon that is bonded to two other groups that are nonidentical.
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Chapter 13 383 Fourier transform NMR a technique in which all the nuclei are excited simultaneously by an rf (FT-NMR) pulse, their relaxation monitored, and the data mathematically converted to a frequency spectrum. geminal coupling the mutual splitting of two nonidentical protons bonded to the same carbon. gyromagnetic ratio the ratio of the magnetic moment of a rotating charged particle to its angular momentum. HETCOR spectrum a 2-D NMR spectrum showing 13 C- 1 H correlations. 1 H NMR nuclear magnetic resonance that shows hydrogen nuclei. high-resolution NMR NMR spectroscopy that uses a spectrometer with a high operating frequency. spectroscopy long-range coupling splitting of a proton by a proton more than 3 σ bonds away. magnetic resonance NMR used in medicine. The difference in the way water is bound in imaging (MRI) different tissues produces the signal variation between organs as well as between healthy and diseased states.
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