ch09 NMR 2010 mb AL2 1pp

ch09 NMR 2010 mb AL2 1pp - 1 2 3 4 5 Chapter 9 Nuclear...

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Chapter 9 Nuclear Magnetic Resonance and Mass Spectrometry: Tools for Structure Determination Part 1: NMR Order different from book: 1. Recording and using 13 C NMR spectra 2. Theory: the NMR phenomenon 3. Using proton NMR spectra 4. Theory: coupling 5. Special features of NMR spectra
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Chapter 9 2 Introduction Spectroscopy: the study of the interaction of energy with matter Energy applied to matter can be absorbed, emitted, cause a chemical change, or be transmitted Spectroscopy can be used to elucidate the structure of a molecule Examples of Spectroscopy Infrared (IR) Spectroscopy (Chapter 2) Infrared energy causes bonds to stretch and bend IR is useful for identifying functional groups in a molecule Nuclear Magnetic Resonance (NMR) Energy applied in the presence of a strong magnetic Feld causes absorption by the nuclei of some elements (most importantly, hydrogen and carbon nuclei) NMR is used to identify connectivity of atoms in a molecule Mass Spectrometry (MS) Molecules are converted to ions by one of several methods (including bombardment by a beam of electrons) The ions formed may remain intact (as molecular ions, M+), or they may fragment The resulting mixture of ions is sorted by mass/charge ( m/z ) ratio, and detected Molecular weight and chemical formula may be derived from the M+ and M+1 ions Molecular structure may be deduced from the distribution of fragment ions
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Chapter 9 3 The Electromagnetic Spectrum Electromagnetic radiation has the characteristics of both waves and particles The wave nature of electromagnetic radiation is described by wavelength ( λ ) or frequency ( ν ) The relationship between wavelength (or frequency) and energy (E) is well deFned Wavelength and frequency are inversely proportional ( ν = c/ λ ) The higher the frequency, the greater the energy of the wave The shorter the wavelength, the greater the energy of the wave
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Chapter 9 4 NMR involves absorption of energy in the radiofrequency range ν = c/ λ For IR = 3.0x10 8 m/s / 10 -4 m = 10 12 Hz; reported as Hz/c in cm -1 For NMR = 10 8 /s = 3.0x10 8 m/s / s; Radiowaves in m
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Chapter 9 5 NMR Often the single most important technique for structure determination Spectra are rich in Independent Information : Carbon NMR: number of lines = number of carbon atoms (subject to symmetry, see later) Frequency: chemical shift reveals ENVIRONMENT of carbon and hydrogen atoms Hydrogen NMR: Later, we ` ll see that the Integral: area under peak corresponds to NUMBER of hydrogen atoms in each environment Multiplicity: hydrogen atoms interact with neighbours, revealing CONNECTIVITY Coupling constant: size of this interaction reveals GEOMETRY BUT may still need more info. to solve structure…… A COMBINATION approach is most effective
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Chapter 9 6 Nuclear Magnetic Resonance (NMR) Spectroscopy The nuclei of protons ( 1 H) and carbon-13 ( 13 C), and certain other elements and isotopes, behave as if they were tiny bar magnets
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This note was uploaded on 01/30/2011 for the course CHEM 2OA3 taught by Professor Stover during the Spring '10 term at McMaster University.

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ch09 NMR 2010 mb AL2 1pp - 1 2 3 4 5 Chapter 9 Nuclear...

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