Proton H Chemical Shifts

Nuclear Magnetic Resonance Spectroscopy Table 4.2 Proton ( H) chemical shifts (ppm) of some methyl, silyl and germyl compounds. 

Section 13 19 2D NMR techniques are enhancements that are sometimes useful m gam mg additional structural information A H H COSY spectrum reveals which protons are spin coupled to other protons which helps m deter mining connectivity A HETCOR spectrum shows the C—H connections by correlating C and H chemical shifts... 

HETCOR (Section 13 19) A 2D NMR technique that correlates the H chemical shift of a proton to the chemical shift of the carbon to which it is attached HETCOR stands for heteronuclear chemical shift correlation Heteroatom (Section 1 7) An atom in an organic molecule that IS neither carbon nor hydrogen Heterocyclic compound (Section 3 15) Cyclic compound in which one or more of the atoms in the nng are elements other than carbon Heterocyclic compounds may or may not be aromatic... 

Table 2 H Chemical Shifts of Protons on the Heterocyclic Rings of Simple Benzazines cf. naphthalene, column 1)...

HETCOR (Section 13.19) A 2D NMR technique that correlates the H chemical shift of a proton to the C chemical shift of the carbon to which it is attached. HETCOR stands for heteronuclear chemical shift correlation. 

Table 13.3 shows the correlation of H chemical shift with electronic environment in more detail. In general, protons bonded to saturated, sp3-hybridized carbons absorb at higher fields, whereas protons bonded to s/ 2-hybridized carbons absorb at lower fields. Protons on carbons that are bonded to electronegative atoms, such as N, O, or halogen, also absorb at lower fields. 

The chemical shifts of the P—H group have been tabulated for 150 compounds. Like many other heteroatom-bound protons, the chemical shift range is large (r 0 —12 p.p.m.). In this case shielding of the proton increases with decrease in co-ordination number at phosphorus. The... 

Figure 3. (a) The computer-simulated spectrum of the olefinic protons using chemical shifts of 6.3 and 6.1 ppm and a coupling constant (J) of 15 Hz. (b) The olefinic region of the 100 MHz H-NMR spectrum of the originally isolated xenognosin A. The marked resonances correspond exactly with the resonances of the simulated spectrum. 

H and 13C NMR Data. The H chemical shifts of CF2H protons of difluoromethyl ethers lie between 6.00 and 6.3 ppm, with a significantly enhanced F—H two-bond coupling constant of around... 

Table 10. Vinylic C-H proton and a-C-H chemical shift in monosubstituted cyclopropenones and triafulvenes...

Nicolet TT-7 Fourier transform accessory. Chemical shifts are reported in ppm downfield from internal TMS. Multiplicities are indicated as s = singlet, d = doublet, and m = multiplet. bThis multiplet represents one of the H-5 protons. The chemical shift of the other one was not assigned. 

Table 5.5 Approximate H Chemical Shifts (5) for Olefinic Protons C=C-H...

Figure 5.3 GHMBC spectrum of a colored impurity formed during the synthesis of Tipranavir. The long-range delay in the experiment was optimized for 10 Hz the data were acquired in 12.5 h. Chemical shift labels show the chemical shift of the carbon to which a given proton is long-range coupled. As can be seen by simple inspection, there was considerable degradation of the sample during the course of the data acquisition as there are peaks in the contour plot corresponding to responses that were not observed in the proton spectrum taken at the outset of data acquisition, which is plotted above the contour plot.

In the framework of H NMR spectroscopy, the formation of dihydrogen bonds is connected with changes in electron environments of H nnclei that participate in dihydrogen bonding. In other words, dihydrogen bonding can be seen from the H chemical shifts of both proton donors and proton acceptors. 

H Chemical Shift Data (ppm) for -Chloroallyl Thiocarbamates and Thiocarbamate Sulfoxides (2, 8). Solutions in CDCl at 20 -40°C with tetramethylsilane as the internal standard. Proton coupling in Hz ... 

The aromatic protons of isopavine alkaloids generally appear between 8 6.45 and 6.80 in CDCI3 solutions as either four or three singlets. In case of the latter, it is always the most downfield absorption peak that integrates for two protons. The chemical shifts of aromatic protons are mostly reported without specific assignment to positions, because no set of rules have yet been formulated for the chemical shifts of these protons due to the asymmetrical nature of the isopavine ring system (112). Similarly, methine and methylene protons are usually reported as an unresolved complex pattern between 8 2.2 and 3.9. It has been reported, however, that the H-12 absorption appeared as a triplet at 8 3.8-3.9 (67), moving downfield by about 1 ppm in quaternary species to display a triplet at 8 4.8 (7 = 6 Hz) (81). 

The H chemical shifts of the methyl groups of pulegone demonstrate the use of this experiment the protons of methyls a and c show a positive shift while b displays a negative shift. 

The chemical shifts of a-protons in some conformationally rigid enol ethers, e.g., 1, have been studied. It was found that they depend not only on their relative position with respect to the alkoxy group, but also on the torsional angle between the C —H and the C—C bonds it is claimed that electric-field effects of the alkoxy groups are responsible267. H Chemical shifts have also been used for the stereochemical assignment of eyclohexylidenecyanoacetates 2. 

Early work on H chemical shifts of oximes, hydrazones, aldimines and ketimines has been collected286. It was shown that an oc-proton is always deshielded (increased 6 value) when it is cis relative to the group X at the nitrogen 1, compared to the trans orientation 2, with chemical shift differences varying between 0.2 and 1.35 ppm. The same is valid for R1 = H, where Ad is 0.3 to 1.0 ppm. 

In l-chloro-l,2-dimethylcyclobutane and l-bromo-l,2-dimethylcyclobutane the H-2 and 2-methyl protons absorb at higher frequencies (larger <) values) if they are cis to the halogen atom. Analogous trends have been observed for H-3 and the 3-methyl protons in l-chloro-1,3-dimethylcyclobutane and l-bromo-l,3-dimethylcyclobutane but here the differential shifts are smaller464. Overall, H chemical shifts are not very reliable parameters for the differentiation of diastereomers. 

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