NMR-1 Basics - NMR (Nuclear Magnetic Resonance)- NMR looks...

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Unformatted text preview: NMR (Nuclear Magnetic Resonance)- NMR looks at magnetically active nuclei that is nuclei with non-zero nuclear spin.- We will learn 1 H- and 13 C-NMR Magnetically Active Nuclei-The relative sensitivity is given at constant magnetic field and equal number of nuclei.-The absolute sensitivity is the product of relative sensitivity multiplied by natural abundance.-Another common NMR nuclei is 19 F. 100% natural abundance and its is nearly as large as 1 H. H. Friebolin: Ein und zweidimensionale NMR-Spektroskopie VCH (1988) (a) Organic molecules usually contain many hydrogens (b) More sensitive than the others (c) Historically, its done first. ~ 6000 times less sensitive than 1 H-NMR How do we proceed? Molecular structure (1) Prediction (2) Structure elucidation NMR spectra What Do We Look for in 1 H-NMR? # of unique protons Peak positions (chemical shift) Shielding by bonding electrons Magnetic anisotropy Peak splitting (spin-spin coupling) Integrals Peak area are proportional to # of protons Ethyl p-Hydroxybenzoate, 1 H-NMR A B C D(quartet) E (triplet) 2H 3H 2H 2H 1H, singlet Chemical shift scale What do we look for in 13 C-NMR? # of unique carbons Peak positions 13 C-NMR chemical shifts are spread in a much wider range than 1 H-NMR, due to the presence of p-electrons. Ethyl p-Hydroxybenzoate, 13 C-NMR A wider chemical shift range 7 6 3 1 2 4 5 symmetry Nuclear Spin and Magnetic Moment Nuclear Spin and Spin States 1 H and 13 C have a spin quantum number of 1/2....
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NMR-1 Basics - NMR (Nuclear Magnetic Resonance)- NMR looks...

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