Carbon NMR - CHAPTER 13 NMR background Spectroscopy is the...

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CHAPTER 13 NMR background. Spectroscopy is the study of the interaction of electromagnetic radiation with matter. Examples of spectroscopic methods of analysis in Organic Chemistry: o IR o NMR o UV- vis MS and NMR are often used in conjunction with one another to characterize a molecule. They are very different techniques that cannot be replaced by one another. MS can be used to determine mass, formula and structure as we saw in CH 12. NMR maps out the C-H framework, and gives fine-tuned structural information such as deciphering between cis or trans double bonds. 13.1 NMR We will discuss the NMR of 13 C and 1 H. Nuclear magnetic resonance, or NMR, is a phenomenon which occurs when the nuclei of certain atoms are immersed in a magnetic field and exposed to a second oscillating electromagnetic field. Some nuclei experience this phenomenon, and others do not, dependent upon whether they possess a property called spin. Spin: - can be thought of as a small magnetic field, and - will cause the nucleus to produce an NMR signal Where does it come from? Nuclei of isotopes which possess an odd number of protons, an odd number of neutrons, or both, exhibit mechanical spin phenomena which are associated with angular momentum. This angular momentum is characterized by a nuclear spin quantum number, I such that I = 1 / 2 n, where n is an integer 0,1,2,3. ..etc. Those nuclei for which I = 0 do not possess spin angular momentum and do not exhibit magnetic resonance phenomena. The nuclei of 12 C and 16 O fall into this category. Nuclei for which I = 1 / 2 include 1 H , 13 C, 19 F, 31 P and 15 N ( 2 H and 14 N have I = 1). Since atomic nuclei are associated with charge, a spinning nucleus generates a small electric current and has a finite magnetic field associated with it. This is why I call the nuclei “tiny little magnets.”
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Deuterated solvents NMR spectra are usually taken from liquid samples, but it is important that the solvent itself doesn't contain any simple hydrogen atoms, because they would produce confusing peaks in the spectrum. There are two ways of avoiding this. You can use a solvent such as tetrachloromethane,
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This note was uploaded on 03/27/2008 for the course CHEM 228 taught by Professor Tichy during the Spring '08 term at Texas A&M.

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Carbon NMR - CHAPTER 13 NMR background Spectroscopy is the...

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