H and 13C NMR spectra

Interpretation of H and 13C NMR spectra has been a part of almost all synthetic work on heteropyrans. Complete assignments using 2D NMR or other more advanced techniques still seem to be exceptional [92JCS(P2)1301]. Typical values of H and 13C NMR characteristics for some 2H- and 4//-heteropyrans are given in Tables V, VI, VII, and VIII. 

Structure ofF Although F has never been obtained in a completely pure state, the FAB mass spectral data of F [m/z 687 (M + Na)+ and 665 (M+H)+], and the comparison of the H and 13C NMR spectra of F with those of Oxy-F, suggested structure 6 for this compound. To confirm this structure, F was subjected to ozonolysis, followed by diazomethane treatment. The expected diester 5 was successfully isolated, indicating that 6 is indeed the structure of compound F (Nakamura et al., 1988). The structure of the luminescence reaction product of F is considered to be 8 on the basis of comparison with the dinoflagellate luminescence system (see Chapter 8). 

The H- and 13C-NMR spectra of gelsemine (1) have been reinvestigated with 2D homonuclear NOESY and heteronuclear COSY techniques (31). As a result some of the original assignments (4,32) have been revised. Thus the <5H of values of H-14a, H-14e, H-15, and H-16 are revised from 2.37, 2.0,2.83, and 2.30 to 2.83, 2.01, 2.30, and 2.43 ppm, respectively, while the most significant corrections of <5C values involve that of C-6 from 40.2 to 50.47 ppm and 1V-CH3 from 50.4 to 40.40 ppm. These adjustments will be helpful in future studies of alkaloids in this series. 

The influences of SF5 groups upon H and 13C NMR spectra are also quite characteristic, and information about proton and carbon chemical shifts and the respective coupling constants will be included along with the 19F data where they are available. The proton and carbon NMR spectra for (pentafluorosulfanylmethylene)cyclohexane are provided in Figs. 7.3 and 7.4 as typical examples. 

The configurations of bis-aminals 68 were determined by analysis of 13C NMR data <2002T5733>. One-, and two-dimensional homo-, and heteronuclear studies ( H, 13C, H- H COSY, HMQC, and HMBC) were conducted for the first time to determine the structures of three stereoisomeric 2-methylperhydro-93-azaphenalcnc alkaloids 45 <1999MRC60>. Complete assignment of H and 13C NMR spectra of compound 86, which is a derivative of 3, has been reported <2002T5733>. The 13C NMR spectrum of compound 98 is consistent with a Cz symmetry <1996JOC4125>. 

It is well known that benzofuroxan derivatives exist as a mixture of isomers at room temperature (A and B, Equation 3). At room temperature (303 K), H and 13C NMR spectra of the benzofuroxans show benzo-protons and carbons as broad peaks, indicating fast benzofuroxan isomerization <2005RMC57>. Upon cooling, the broad signals... 

Other than classical H and 13C NMR spectra which have been reported for these compounds, no detailed studies have appeared in the literature. One X-ray crystal analysis of the TBDMS-protected alcohol analog of acid 368 has been carried out for structural proof. 

The NMR spectra of indolizidine derivatives have already been described accurately <1984CHEC(4)443 1996CHEC-II(8)237> more recently, the extensive use of mono- and bidimensional H and 13C NMR spectra allowed the structural assignment of natural compounds such as grandisine A possessing an indolizidine nucleus (Figure 3) <2005JOC1889>. 

In the study on tetrasubstituted [l,2,4]triazolo[l,5- ]pyrimidines 45, H and 13C NMR spectra of 35 different compounds have been recorded <1995JHC407>. Substituents in position 2 were various amines and sulfano groups, whereas the other substituents (Rs, R6, and R7) were alkyl, phenyl, and acetyl groups. 

Ratios were obtained by GC analysis of the crude reaction mixture. Products were separated and isolated by flash chromatography. Products were identified by comparison of their H and 13C NMR spectra with those reported in the literature. Typical isolated yields were 35-40% of 20 and 10-12% of 21... 

I3C-NMR spectroscopic data of heteroanalogs of bicyclo[4.4.0]decane, collected prior to 1983, have been summarized25 77. Therefore, only a selection of subsequent studies is noted. H- and 13C-NMR spectra of diastereomeric substituted cis- and rraw-4-hydroxy-l-oxabicyclo[4.4.0]-decanes642, as well as H-NMR spectra of isomeric perhydrooxazolo[3,4-a]quinolines 3 and 3,3a,4,5-tetrahydro-1 //-oxazolo[3,4-a]quinolines 4, have been discussed 643. The 3H data of five diastereomeric 5-methyl-3-phenyl-2,4-dioxabicyclo[4.4.0]decanes have been reported644. 

The earliest studies deal with the UV and IR spectra of the compounds under review later H- and 13C-NMR spectra became practical tools for characterizing substituted or isomeric triazolopyrimidine compounds. But many of the early rules proved to lack general validity. Now UV and 13C-NMR seem to be the most useful diagnostic tools. 

Protons attached to the C atoms of the 1,2,4-trioxolane moiety of FOZs have chemical shifts at distinctly lower field than alcohols, ethers or esters. For example, the chemical shifts of the ozonide product in equation 100 (Section VIII.C.6.a) are <5 (CDCI3) 5.7 ppm for the H atoms of the trioxolane partial structure, and 4.1 ppm for the protons at the heads of the other ether bridge639. Measurement of the rate of disappearance of these signals can be applied in kinetic studies of modifications in the ozonide structure. The course of ozonization of the methyl esters of the fatty acids of sunflower oil can be followed by observing in H and 13C NMR spectra the gradual disappearance of the olefinic peaks and the appearance of the 3,5-dialkyl-1,2,4-trioxolane peaks. Formation of a small amount of aldehyde, which at the end of the process turns into carboxylic acid, is also observed636. 

The final dehydration reaction (MTPI, DMPU, 18 h) on the alcohol 105 produced (+)-PHB (81) in 79% yield. This substance proved to be identical to the natural product by comparison of the H and 13C NMR spectra, mobility on TLC, IR spectra, mass spectra, and UV spectra. Comparison of the CD spectra of the natural (-)-PHB (6) and the synthetic (+)-PHB (81) confirmed the expected enantiomeric relationship between these two products. 

The primary cycloadduct from combination of a dipolarophile with a silyl nitronate is an isoxazolidine. The H and 13C NMR spectra are highly informative for the structural determination of these products, Tables 2.7 and 2.8 (21,25,34,35). Both the H and 13C NMR data show that HC(5) are shifted downfield relative to HC(3). An expected downfield shift is also observed with electron-withdrawing or conjugating groups. In the absence of functionalization at C(3), there is a significant upfield shift of the corresponding 13C resonance. The IR data is less reliable. The O—N—O stretch is reported to be 1055 cm-1 (Fig. 2.8), however, this stretching... 

Benzo[ >]thiophene dianion (173) has been prepared by reduction of benzo[ >J thiophene with sodium metal at - 78°C in [2H8]THF. The H and 13C NMR spectra of the purple solution obtained prove that it is the dianion and not a radical anion. This is the first example of a sulfur-containing (4n)Tr polycyclic dianion. The dianion undergoes oxidation to benzo[ ]thiophene with oxygen (85CC1033). 

Irradiation of 3,5-dihydro-3,3,5,5-tetramethyl-4//-pyrazole-4-thione S-oxide (36) in benzene-d6 solution with light of wavelengths above 320 nm affords predominantly tetramethylallene and tetramethylpyrazolinone (27) (3 2) together with small amounts of a third product characterized by a 2,4-dimethylpenta-l,3-dien-3-yl moiety as shown by H and 13C NMR spectra (92TH2). The photolysis of similar pyrazolinethione 5-oxides in solution has been investigated by Schaumann et al. (81T219), who have studied com-... 

Figure 13.23 compared the appearance of the H and 13C NMR spectra of 1-chloropentane and drew attention to the fact each carbon gave a separate peak, well separated from the others. Let s now take a closer look at the 13C NMR spectrum of 1-chloropentane with respect to assigning these peaks to individual carbons. 

A certain compound has a molecular weight of 83 and contains nitrogen. Its infrared spectrum contains a moderately strong peak at 2270 cm-1. Its H and 13C NMR spectra are shown in Figure 20.10. What is the structure of this compound ... 

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