Compounds, NMR data

For some compounds NMR data were collected to determine the equilibrium constants for the tautomerism between the azide form such as for 30 and the tetrazole derivative 31 (Scheme 3). Similar investigations were conducted for the compounds 28 and 29 and the solvent effects and substituent effects are discussed <1996JHC747>. 

Figure 12.41 Comparison of Bohimann and Perlin effects in carbonyl compounds. (NMR data is from ref 64.)...

Dioxolane also pseudorotates essentially freely in the vapor phase. 2,2 -Bi-l,3-dioxolane (128) has been shown by X-ray crystallography to have a conformation midway between the half-chair and envelope forms. The related compound 2-oxo-l 3-dioxolane (129) shows a half-chair conformation. This result is confirmed by microwave spectroscopy and by NMR data. Analysis of the AA BB NMR spectra of the ring hydrogen atoms in some 1,3-dioxolane lerivatives is in agreement with a puckered ring. Some 2-alkoxy-l,3-dioxolanes (130) display anti and gauche forms about the exocyclic C(2)—O bond. 

Table 10 Structure and H NMR Data of Seven-membered Heterocyclic Compounds...

The NMR spectra of heterocyclic compounds with seven or more ring members are as diverse as the shape, size and degree of unsaturation of the compounds. NMR is perhaps the most important physical method to ascertain the structure, especially the conformational statics and dynamics, of large heterocycles. Proton-proton coupling constants provide a wealth of data on the shape of the molecules, while chemical shift data, heteroatom-proton coupling constants and heteronuclear spectra give information of the electronic structure. Details are found in Chapters 5.16-5.22. Some data on seven-membered rings are included in Table 10. 

An E-Z discrimination between isomeric oxaziridines (27) was made by NMR data (69JCS(C)2650). The methyl groups of the isopropyl side chains in the compounds (27) are nonequivalent due to the neighboring carbon and nitrogen centres of asymmetry and possibly due to restricted rotation around the exocyclic C—N bond in the case of the Z isomer. The chemical shift of a methyl group in (Z)-(27) appears at extraordinarily high field, an effect probably due to the anisotropic effect of the p-nitrophenyl group in the isomer believed to be Z. 

The inversion barrier between (28a) and (28c) is 114kJmoF , the invertomers having the same free energy by chance. NMR data of oxaziridine carbon and substituent groups of the ring for compounds (29) and (30), taken from the above publications, are as shown. 

Extensive secondary literature coverage of fluonne NMR data is available for articles published through 1981 Massive amounts of fluonne data were comptled in penodic reviews in Annual Reports on NMR Spectroscopy [2, 3, 4, 5, 6, 7, 8, 9] and in two volumes of Progress in NMR Spectroscopy [10, 11] Books wntten by Dungan and Van Wazer [12] and Moonev [13], both published in 1970, are still widely referenced today The majonty of %-NMR data compiled were from highly fluormated and perfluorinated compounds... 

One-carbon fluonnated compounds are used as synthetic reagents and in many theoretical inquines of structure and spectroscopy Twenty fluorohalomethanes are listed in Table 1 [56, 57, 58 59, 60, 61, 62] Fluorocarbons llBl, 22B1, and 31B1 and 12 of 15 lodofluoromethanes are not listed because of a lack of NMR data Most of the if-F values are taken from the older literature [57, 59], obtained from... 

Table 15 [S 19 56, 59 93 107 108 109, 110, 111, 112 113, 114] contams NMR data for a vanety of tnfluoromethyl compounds that do not fit into the more common categones already covered Most carbon-attached tnfluoromethyl (CF3-C) F-NMR signals fall in the 25 ppm range from -60 to -85 ppm, a notable exception being trifluoromethylacetylenes, with signals at approximately -50 ppm Trifluoromethylated compounds in which the CFj is directly bonded to an atom orlier carton are considered in Table 16 [57 59,95 109,115,116 117 118,119,120 121 122, 123 124, 125] These heteroatom contaming compounds are of interest to both organic and morganic chemists and have been studied by NMR for numerous reasons...

Analysis of Organic Fluonne Compounds Table 20. NMR Data for Fluorinated Benzenes [5tf]... 

Everett, T. S. Multinuclear NMR Spectral Identification of Organofiuor-ine Compounds unpublished data. 

H N coupling constants, often measured in H NMR using labeled compounds, are discussed together with N NMR (Section VI,D). Taking into account that H NMR data are now present in every paper dealing explicitly or implicitly with tautomerism, only a few articles are documented in this section. 

Methylisoquinolinium 2-carboxylate (230), originally prepared by Quast (70LA64), was recently identified as a defensive betaine from Photuris versicolor fireflies (99JNP378). It is a pseudo-cross-conjugated mesomeric betaine isoconjugate to the odd alternant hydrocarbon 2-isopropenyl-naphthalene anion which is an odd alternant hydrocarbon anion. This compound therefore is a member of class 13, which is very rare. The UV absorption maxima Imax (methanol) were found at 235 (4.35), 320 (shoulder, 3.97), and 326 (3.99) nm. This compound undergoes similar reactions as Homarine 19 (Scheme 75). The NMR data are presented in Table VIII. 

Pontevedrine (369) is a red compound from Papaveraceae (71TL3093). The UV-VIS absorption maxima Imax in ethanol were found at 245 (4.59), 312 (4.28), 325 (4.39), and 470 (4.01) nm. On addition of acid or alkali no changes were observable. A zwitterionic structure was proposed on the basis of the NMR data (Scheme 110). 

Propose structures for compounds that fit the following H NMR data ... 

Structure of Oxy-F Compound F is extremely unstable and is difficult to obtain at a level of purity suitable for NMR studies. However, an oxidation product, Oxy-F, formed when F is left standing at — 20° C, is considerably more stable than F and can be purified to a sufficiently high level of purity. Oxy-F is nonfluorescent and shows absorption maxima at 237 nm and 275 nm (shoulder). The high-resolution FAB mass spectrum indicated the molecular formula of Oxy-F to be C33H3809N4Na2 [m/z 703.2363 (M + Na)+ and 681.2483 (M + H)"1"]. The H and 13C NMR data allowed the assignment of structure 7 to oxy-F (Fig. 3.2.6 Nakamura et al., 1988). 

Addition of metalated, enantiomerically pure a-sulfinyl dimethylhydrazones (e.g., 9) to racemic a-chiral aldehydes 10 proceeds with good to excellent diastereo- and enantioselectivi-ty12. Diastereomeric ratios increase with increasing steric demand of the acetaldehyde substituent R1 compared to the methyl group, and each diastereomer is obtained with high enantiomeric excess. In the aldol-lype addition to 2-phenylpropanal, one of the four possible stereoisomers is formed selectively. The relative (syn) and absolute (R.R) configuration is in accord with Cram s and related rules as well as H-NMR data of closely related compounds. 

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