仪器——课件13CNMRmainreference幻灯片.pptVIP

9 9 1 1 1 9 9 9 9 In DEPT, a second transmitter irradiates 1H during the sequence, which affects the appearanceof the 13C spectrum. some 13C signals stay the same some 13C signals disappear some 13C signals are inverted  Measuring a 13C NMR spectrum involves Chemical shift (?, ppm) 0 20 40 60 80 100 120 140 160 180 200 Proton Decoupled Spectrum O C C CH CH CH CH2 CH2 CH2 CH3 CCH2CH2CH2CH3 O Chemical shift (?, ppm) 0 20 40 60 80 100 120 140 160 180 200 DEPT Spectrum CH CH CH CH2 CH2 CH2 CH3 CCH2CH2CH2CH3 O CH and CH3 unaffected C and C=O nulled CH2 inverted 4.6 Distortionless Enhancement byPolarization Transfer (DEPT) Pulse sequence developed to determine the number of protons Directly attached to a carbon. Std H1 decoupled spectrum DEPT 135 deg. CH CH3 up, CH2 down DEPT 90 deg. CH only DEPT is a helpful to determine proton inventory, but it does not Record H’s on heteroatoms; must correlate with H1 spectrum. 13.192D NMR:COSY AND HETCOR 1D NMR = 1 frequency axis2D NMR = 2 frequency axes COSY = Correlated Spectroscopy 1H-1H COSY provides connectivity informationby allowing one to identify spin-coupled protons. x,y-coordinates of cross peaks are spin-coupledprotons 2D NMR Terminology 1H-1H COSY CH3CCH2CH2CH2CH3 O 1H 1H 1H and 13C spectra plotted separately on twofrequency axes Coordinates of cross peak connect signal of carbonto protons that are bonded to it. HETCOR 1H-13C HETCOR CH3CCH2CH2CH2CH3 O 13C 1H 1 6 6 6 1 1 3 6 6 6 6 6 6 6 6 25 25 3 1 3 9 3 9 13C NMR Spectroscopy 1H and 13C NMR compared: both give us information about the number of chemically nonequivalent nuclei (nonequivalent hydrogens or nonequivalent carbons) both give us information about the environment of the nuclei (hybridization state, attached atoms, etc.) it is convenient to use FT-NMR techniques for 1H; it is standard practice for 13C NMR 4.5 Chemical Shift Equivalence CSE = Interchangeability by a symmetry operation or by rapid mechanism. Ex. The CH3 groups of t-Buty