Chemical shifts, assignments and

Based on NMR chemical shift assignments and the use of recorded spin-spin coupling constants it was determined193 that in both 2,4-diphenyl-substituted thietane oxides (186a,b) the dominant conformers are those in which the S—O bond is equatorial and, therefore, in the trans-2,4-isomer186 one phenyl group (i.e. R1) is syn-axial to the S— O bond, whereas in the cis-2,4-diphenyl isomer 186b both phenyls are anti-equatorial to the S—O bond. 

The heteronuclear multiple-quantum coherence (HMQC) spectrum, H-NMR chemical shift assignments, and C-NMR data of podophyllo-toxin are shown. Determine the chemical shifts of various carbons and connected protons. The HMQC spectra provide information about the one-bond correlations of protons and attached carbons. These spectra are fairly straightforward to interpret The correlations are made by noting the position of each crossf)eak and identifying the corresponding 8h and 8c values. Based on this technique, interpret the following spectrum. 

The HMQC spectrum, H-NMR chemical shift assignments, and C-NMR data of vasicinone are shown. Consider the homonuclear correlations obtained from the COSY spectrum in Problem 5.14, and then determine the carbon framework of the spin systems. 

Figure 6. 31.94 MHz 13C NMR spectra for suberized cell walls from potatoes, before (bottom) and after (top) depolymerization treatment. The experimental parameters were as in Figure 4. Chemical-shift assignments and relative numbers of carbons for the untreated material are found in Table IV. Delayed-decoupling experiments left some (CH2) signal intensity in the spectrum of intact suberin, but the analogous signals were drastically attenuated in the NMR spectrum of the depolymerization residue.

Based on chemical shift assignments and coupling constants, the two methine functions at positions 2 and 2 could be correlated to the two multiplets at chemical shifts of 3.61 - 3.65 and 3.94 - 3.98 ppm. 

The present catalogue provides proton and/or carbon-13 NMR chemical shift assignments and physical constants for many of the naturally occurring diterpenoid alkaloids and their derivatives. The literature search is not intended to be exhaustive. It is hoped that the 13C NMR data bank will serve as a useful guide for determining the structures of newly isolated alkaloids. 

More recently reported chemical shift assignments and structural elucidation of the more complex carbohydrates as well as investigations of anomerization and conformation changes will form the ensuing discussion. Attention will be repeatedly drawn to the many advantages of 13C spectroscopy, the potential of which has been as yet hardly explored. 

Tugarinov V, Muhandiram R, Ayed A et al (2002) Four-dimensional NMR spectroscopy of a 723-residue protein chemical shift assignments and secondary structure of malate synthase G. J Am Chem Soc 124 10025-10035... 

Franks WT, Zhou DH, Wylie BJ et al (2005) Magic-angle spinning solid-state NMR spectroscopy of the pi immunoglobulin binding domain of protein G (GBl) N and C chemical shift assignments and conformational analysis. J Am Chem Soc 127 12291-12305... 

Table I. H and Chemical Shifts, Assignments, and T, and Tj relaxation times (sec) for celluiosic CH in I and all carbons in II - IV. Chemical shifts...

Table 2.3 MAS NMR chemical shift assignments and distribution of acid sites for various SZ and M/SZ samples loaded with TMPO probe moiecuie [26]... 

In the HETCOR experiment the peaks of an insensitive nucleus ( C. " N) are correlated with those of a sensitive nucleus ( H, F, " P). In Figure 27 the aliphatic part of the HETCOR spectrum of camphor (2) shows the specific resonances of the protons which are attached to each C nucleus. The relevant parts of the corresponding 1 D spectra are plotted along the axes. A correlation is observed as a cross-peak at the intersection of two lines drawn from a proton resonance and from a carbon peak, respectively. The three pairs of diastereotopic methylene protons H-3e do/exc H-5endo/e o and H-6c do/exo give individual cross peaks at the same carbon resonance, respectively. Correlations are not observed for quaternary carbon atoms. The technique is an important tool for chemical shift assignment and thus structure elucidation. 

The above chemical shift assignments and integrations also allow us to determine the average ethoxylate number for this surfactant. Given that the ethoxylate peak ( c ) is at 3.7 ppm ... 

Table XIO C NMR chemical shift assignments and relaxation data [48] for the methyl carbons of atactic PPO 4000 at 23 °C...

De Footer and co-workers [25] described a comprehensive C-NMR method for the analysis of composition in the most common commercial polyethylene copolymers. The method covers ethene copolymers with propene, also butene-1, hexene-1, octene-1, and 4-methyl pentene-1 in the composition range of 1-10 mol%. The chemical shift assignments and values of the resonances of the copolymers are presented... 

The chemical-shift assignments and the enrichment levels of these carbons in X-537A are presented in Table 14. 

HMBC spectra. Methyl group at 1.04 ppm has more intensive cross-peaks with these protons, and the second methyl group does more intensively with axial protons. Due to that and the value of chemical shift, the methyl group at 1.04 ppm was assigned as axial. The axial protons of the cyclohexenone ring have clear NOE cross-peaks. Discrimination of protons at C6 and C9 was based on observations of their interaction with nitrogen nuclei in HMBC and amine protons in NOESY spectra. Table 1. NMR chemical shifts, assignments and HMBC, NOESY responses in the spectra of 5a ... 

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