6-nmr-organomet.pptVIP

Multinuclear Approach Proton NMR spectra: 3 groups of peaks integrating for 12:4:1 Resonances due to Methyl and CH2 have coupling with 31P And also shows satellites due to mercury coupling (199Hg 16.8%) While third resonance is broad In 31P, there is a single signal: Symmetrical compound: that has Mercury satellites In 199Hg NMR (with proton decoupling): quintet demonstrate the presence of 4 Phosphorus Index Heteronuclear NOE NOE enhancement can give useful gain in signal-to-noise It is most efficient when the heteronuclei is bound to proton NOEMAX = 1 + gH/2gX For nuclei having negative g, NOE is negative (for 29Si, max=-1.5) Index Exchange : DNMR – Dynamic NMR NMR is a convenient way to study rate of reactions – provided that the lifetime of participating species are comparable to NMR time scale (10-5 s) At low temperature, hydrogens form an A2B2X spin system At higher temperature germanium hop from one C to the next Index Paramagnetic compounds in NMR Usually paramegnetic compounds are too braod = give ESR In NMR, Chemical shift is greatly expanded Paramagnetic shifts are made up of 2 component: Through space Dipolar interaction between the magnetic moment of the electron and of the nucleus Contact Shift: coupling between electron and nucleus. This interaction would give a doublet in NMR but J ~ millions of Hertz!!With such large coupling, intensity of the 2 resonances are not equal = weighted mean position is not midwayWith fast relaxation, collapse of the multiplet may fall thousands Hertz away from expected position = Contact Shift Contact Shift give a measure of unpaired spin density at resonating Nucleus. Useful for studying spin distribution in organic radical or in ligands in organo metallic complexes Paramagnetic compounds in NMR 4 sets of resonances: 1 symmetrical Fac: the 3 ligand are identical 3 Asymetrical ligand in Mer occur with 3 time the probability. Index NMR-basics H-NMR NMR-Symmetry Heteronuclear-NMR Dynamic-NMR NMR and Organometallic