Chemical shift negative

Figure 8 Dependence of the i29Xe chemical shift (negative shielding) upon the number of xenon atoms adsorbed per gram of zeolite. Fraissard J (1996) In Grant DM and Harris RK (eds) Encyclopedia of Nuclear Magnetic Resonance Spectroscopy, Vol. 5, pp. 3058-3064. Chichester Wiley John Wiley Sons Limited. Reproduced with permission.

The negative sign indicates a chemical shift value numerically smaller than that of pyrazine itself. 

Plot para chemical shift (vertical axis) vs. para atomic charge (horizontal axis). Are the two properties correlated If they are, what is their relationship Does chemical shift increase ( C becomes deshielded) or decrease ( C becomes shielded) with increasing negative charge at carbon ... 

For illite and kaolinite with decreasing solution concentration (Figure 5) there are two important changes. The relative intensity for inner sphere complexes increases, and the chemical shifts become substantially less positive or more negative due to the reduced Cs/water ratio, especially for the outer sphere complexes. Washing with DI water removes most of the Cs in outer sphere complexes and causes spectral changes parallel to those caused by decreasing solution concentration (data not shown). 

The spin-echo experiment therefore leads to the refocusing not only of the individual nuclear resonances but also of the field inhomogeneity components lying in front or behind those resonances, a maximum negative amplitude being observed at time 2t after the initial 90° pulse. The frequency of rotation of each signal in the rotating frame will depend on its chemical shift and after the vector has been flipped by the 180° pulse, it... 

The broad-band decoupled C-NMR spectrum of ethyl acrylate shows five carbon resonances the DEPT (6 = 135°) spectrum displays only four signals i.e., only the protonated carbons appear, since the quaternary carbonyl carbon signal does not appear in the DEPT spectrum. The CH and CH3 carbons appear with positive amplitudes, and the CHj carbons appear with negative amplitudes. The DEPT (6 = 90°) spectrum displays only the methine carbons. It is therefore possible to distinguish between CH3 carbons from CH carbons. Since the broadband decoupled C spectrum contains all carbons (including quaternary carbons), whereas the DEPT spectra do not show the quaternary carbons, it is possible to differentiate between quaternary carbons from CH, CHj, and CH3 carbons by examining the additional peaks in the broad-band spectrum versus DEPT spectra. The chemical shifts assigned to the various carbons are presented around the structure. 

The chemical shifts for P—F compounds have been reviewed.The compounds differ from most other organophosphorus compounds because Sp becomes more positive as the electronegativity of the atoms attached to phosphorus increases. The effect is at a maximum for P" compounds. They behave normally with regard to an increase in shielding with increase in co-ordination number and therefore the P" compounds are the least shielded. Thus the largest negative values (— 190 to — 250) are observed for compounds of the type YPFj. With the new value of Sp of + 80 for PFg, the variation of Sp with the number of fluorine atoms in P compounds is now shown to be fairly consistent. The value of Sp has also been reported for a series of aminohalogeno P compounds. -... 

Chemical shift difference in ppm. Negative values mean upheld shifts. Source Ref 46. Copyright 1999 American Chemical Society. 

Chemical shift difference (ppm) with an uncertainty of 0.01 ppm. Negative values designate upheld shifts. 

FIG. 10 Chemical shift change of the NMR signals of EPC induced by the injection of DBC H and PRC H with a molar ratio of 1/1. Negative value means an upheld shift. 

The DD site can be ensured by the chemical shift changes of the BPA signals. The chemical shift differences of the ring proton signals of BPA on the delivery from water to bilayer phases are —0.04 and —0.11 ppm for the ortho and meta sites, respectively. Negative values mean upfield shifts recall the HCS rule. It is concluded that both benzene rings of BPA are trapped in the bilayer from the water phase and the meta site penetrates more deeply into the hydrophobic interior. 

FIG. 13 Chemical shift change of the EPC H NMR signals induced by the ring current effect of BPA. Negative value means upheld shift. (From Ref. 47. Copyright 1999 American Chemical Society.)... 

Chemical shift change (ppm) induced by the BPA delivery. Positive and negative values mean downfield and upheld shifts, respectively. 

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