Isomers distinguishing

In addition, oxidation of Cp 2NbIVCl2 by 02 in wet thf gave [Cp NbvCl2]2(//2-Cl)(//2-OI I)-(fi2-O) which existed as two isomers distinguished by the relative orientation of the Cp and bridging ligands.264 Mixed-oxidation-state trinuclear species were derived from this system. 

The term metalation was originally proposed by us about 35 years ago to denote the replacement of hydrogen bonded to carbon by metal to yield a true organometallic compound. We early observed in connection with studies of dibenzofuran types that metalation tended to yield ortho products. This direction to the ortho position, usually unmixed with para or other isomers, distinguishes the metalation reaction from the more familiar types of substitution, and makes possible the preparation of many compounds not readily available through other routes. This tendency to replace a nuclear... 

The nature of structure-R for n=l clearly suggests the existence of other n=7 isomers, distinguished from one another by the position of the second-layer atom relative to the underlying. It also suggests that analogous "stacked" or multilayer structures will occur for all larger clusters. While further studies show that both of these predictions are true, full details are not yet available. For present purposes, therefore, we... 

When the resolution of the autocorrelation vector is decreased, some signals, e.g., those for the methyl groups in m- and / -xylene, may collapse. In such a case, one cannot distinguish between these two isomers. 

Isomers are distinguished by lettering the peripheral sides of the parent beginning with a for the side 1,2, and so on, lettering every side around the periphery. If necessary for clarity, the numbers of the attached position (1,2, for example) of the substituent ring are also denoted. The prefixes are cited in alphabetical order. The numbers and letters are enclosed in square brackets and placed immediately after the designation of the attached component. Examples are... 

Indole is a heteroaromatic compound consisting of a fused benzene and pyrrole ring, specifically ben2o[ ]pyrrole. The systematic name, IJT-indole (1) distinguishes it from the less stable tautomer 3JT-indole [271-26-1] (2). Iff-Indole [120-72-9] is also more stable than the isomeric ben2o[ ] pyrrole, which is called isoindole, (2H, (3) and IH (4)). A third isomer ben2o[i ]pyrrole is a stable compound called indoli2idine [274-40-8] (5). 

Reaction with 1,3-benzenediamine-periodate (91) or with a hypochlorite—alkaline phenol (Berthelot) reagent enables the detection of both 2- and 4-aminophenol, the latter reagent giving distinguishable blue and dark green products, respectively (92). 4-Aminophenol itself has been shown to react in alkaline solution with both the 2- and 3-aminophenol isomers, a reaction exploited for their detection (93). 

Nuclear Overhauser enhancement (NOE) spectroscopy has been used to measure the through-space interaction between protons at and the protons associated with the substituents at N (20). The method is also useful for distinguishing between isomers with different groups at and C. Reference 21 contains the chemical shifts and coupling constants of a considerable number of pyrazoles with substituents at N and C. NOE difference spectroscopy ( H) has been employed to differentiate between the two regioisomers [153076 5-0] (14) and [153076 6-1] (15) (22). N-nmr spectroscopy also has some utility in the field of pyrazoles and derivatives. 

The AO AC (978.42) recognizes a similar procedure, except that the unsap onitiable material is treated with maleic anhydride to remove the trans-isomer which may possibly be present (83). The antimony trichloride colorimetric assay is performed on the trans-isomer-free material. This procedure cannot be used to distinguish certain inactive isomers, eg, isotachysterol if present, these are included in the result, giving rise to a falsely high analysis. A test must therefore be performed to check for the presence of isotachysterol. 

Physical Methods. Vitamins D2 and D exhibit uv absorption curves that have a maximum at 264 nm and an (absorbance) of 450—490 at 1% concentration (Table 8). The various isomers of vitamin D exhibit characteristically different uv absorption curves. Mixtures of the isomers are difficult to distinguish. However, when chromatographicaHy separated by hplc, the peaks can be identified by stop-flow techniques based on uv absorption scanning or by photodiodearray spectroscopy. The combination of elution time and characteristic uv absorption curves can be used to identify the isomers present in a sample of vitamin D. 

The reduction of 3,5-diphenylisoxazoline with sodium cyanoborohydride produced a mixture of isomeric 3,5-diphenylisoxazolidines. The H and NMR spectra were utilized to distinguish the isomers SOLAIOI). Sodium borohydride reductions likewise reduce isoxazolines to isoxazolidines (equation 56) (80JA4265). 

Simple oxaziridines and diaziridines do not absorb in the near UV. Lack of absorption was one argument to distinguish between true three-membered ring structures and unsaturated open chain isomers like nitrones or hydrazones. 

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