CHEM 222 Lecture Notes - Lecture 9: Ionization Chamber, Isotope Analysis, Benzene
17 Mar 2017
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Nmr spectrum collection: compound dissolved in nmr solvent (usually deuterated so solvent 1-h signals do not drown out spectrum) --place in tube i. e. d-chloroform (99% deuterated) mostly used, 99% no 1-h signals, 1% 1-h signal 7. 26 ppm. Integration and intensity of 13-c signals not necessarily representative of # of. 13-cs: for hydrogen, spectrum can tell us about how many there are, but not for 13-c, no multiplicity (splitting, 13-c - 13-c splitting does not occur due to low natural abundance of 13-c vs. 12-c: 1-h - 13-c splitting removed by proton decoupling to simplify spectra. Practice 13-c chemical shifts: a sample has one 13-c resonance detected, 750 hz higher frequency than tms, at a carrier frequency of 75 mhz. What is the chemical shift in ppm: 750 hz / 75mhz = 10 ppm. Electronic effects on chemical shift: sigma electrons: nearby electronegative groups deshield nuclei, reduces sigma-bond electron density at nucleus.
