Chemical shift representative values

Class b) represents a set of phosphane oxides, phosphane sulfides and phosphane selenides (X = PR3) where R is an alkyl or aryl group. The principal values of the 31P chemical shift tensors are shown in Table 2. The chemical shift anisotropy values Ao are large and comparable to the 31P chemical shift anisotropy variation observed in the liquid phase by change of coordination or of functionality around the phosphorus. It is noteworthy that in P(CH3)3 and PCC6H5)3 the chemical shift anisotropies are much smaller, 8 ppm and 24 ppm respectively. For a given R group, the chemical shift anisotropies range in the order Ao(0-PR3) >... 

Figure 2.43 The full optimized Leu-enkephalin structure with enlarged parts of both systems. Selected interatomic distances are indicated. (A) The plots show the correlation of experimental isotropic chemical shift values (5 so) and calculated nuclear shielding values ( 7 so). (B)The plots represent the correlation of experimental chemical shift tensor values Sii) and calculated nuclear shielding parameters of the enkephalin peptides. (C) The correlations of the experimental versus the computed parameters are shown for Leu-enkephalin. Reprinted from Ref. [96]. Copyright 2014 American Chemical Society.

Nucleus-Independent Chemical Shift (NICS) Values of SI4, SljAP, AIJSI2, SijBe, AI3P Clusters as Typical Representative of Each Series... 

Figure 6. Chart of beryllium chemical shifts. The values recorded are very solvent dependent, even though most of these species may be considered to be entirely covalent. D represents a donor molecule and P a phosphate or...

Another important component of Table 18 is substituent chemical shift (SCS) datadenvedforeachoftheSlentnes The SCS is simply thedifferencein F-NMR chemical shifts of the substituted compounds and that of unsubstituted fluoroben zene (-113 5 ppm in CDCI3) These values numerically represent the mfluence a substituent has on the shieldmg or deshieldmg of the fluorine nucleus and depend upon substituent position o, m, orp) Fluonne chemical shifts can be predicted for polysubstituted fluorobenzene systems simply by addmg the SCS value of each substituent to a base value of -113 5 ppm... 

Jones and Civcir prepared a variety of alternating oligomeric furanipyridine compounds and studied their NMR chemical shifts as well as the pKa values for the corresponding conjugate acids. All of these compounds were synthesized by Paal-Knorr reactions of 1,4-diketones with hot polyphosphoric acid. A representative example is the conversion of 24 into 25 in 82% yield. ... 

NMR Chemical Shift Values" of the Ring Carbons OF Representative 1,2-Dithietes... 

The GASPE spectrum of podophyllotoxin is shown. The signals at 8 56.0,108.6, and 152.0 each represent two carbons in identical magnetic environments, while the signal at 8 147.6 also represents two carbons that accidentally appear at the same chemical shift. Assign chemical shift values to various protonated and quaternary carbons in the structure. 

The GASPE spectrum of vasicinone is shown. The peak at 8 126.5 is a cluster of three peaks at 8 126.3 and 126.7 representing methine carbons. Similarly, the signal at 8 160 on the positive phase of the spectrum represents two close singlets at 8 160.4 and 160.5. Predict the chemical shift values of various protonated and quaternary carbons in the structure. 

Thus, if the vertical axis representing the double-quantum frequencies is defined by v, and the horizontal axis representing the chemical shifts of the two carbons A and X is defined by V2, then both pairs of C satellites of nuclei A and X will lie on the same row (at + Vx), equidistant from the diagonal. This greatly facilitates identification. The advantage is that no overlap can occur, even when fir.c values are identical, since each pair of coupled C nuclei appear on different horizontal rows. 

ACD/Labs have an extensive database which uses this approach. This approach works well except for anisotropic groups. Unlike carbon prediction this can have a massive effect on the chemical shift values and so can give rise to big errors in prediction, even for structural fragments that are well represented in... 

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