Carbon compound protonation definition

The word fluorocarbon has been used here in a generic way to indicate completely fluonnated liquids, including ethers and amines, rather than in its stricter meaning of having only carbon and fluorine atoms The definition of the word perfluori-nated is somewhat vague, because it can include compounds that retain double bonds or protons... 

Interconversion between two tautomeric structures can occur via discrete cationic or anionic intermediates (scheme 24, where T is an anion capable of reacting with a proton at a minimum of two distinct sites). Alternatively, interconversion can occur by simultaneous loss and gain of different protons (scheme 25, w here T has the same definition as in scheme 24). These mechanisms are well established for acyclic compounds, but they have been much less thoroughly investigated for heteroaromatic systems. The rate of interconversion of two tautomers is greatest when both of the alternative atoms to which the mobile proton can be attached arc hetero atoms, and isolation of the separate isomers is usually impossible in this case. If one of the alternative atoms involved in the tautomerization is carbon, the rate of interconversion is somewhat slower, but still fast. When both of the atoms in question are carbon, however, interconversion is... 

Not surprisingly, bifunctional species preceded the definition of the term distonic, both in the gas and condensed phases. For example, Hammond et al. studied the cage effect for radical pairs generated by decomposition of azo compounds. Among their targets was the doubly protonated amidine (27), whose decomposition yielded a pair of distonic radical cations (28 +).Attachment of the spin-bearing carbon in the 2-position of the diazaallyl function ensures minimal delocalization of unpaired spin into the latter. 

Fig. 2. Definition of , h as H-l -C-l -X-C-Y, where X is the interglycosidic atom and Y is the attached carbon of the aglycone, and I h as C-l -X-C-Y-H-Y. The relationship with regard to heavy atoms is as follows For P-D-glycosyl compounds, < >o is 4>h — 120, whereas for a-D-glycosyl analogues, o is h + 120 and I c is 4>h + 120. (+) stands for +60 and

It is more difficult to give a definitive list for CH2 groups as they have two substituents. In Table 15.3 we set one substituent as phenyl (Ph) just because so many compounds of this kind are available, and give the actual shifts relative to PI1CH2CH3 for protons (2.64 p.p.m.) and PI1CH2CH3 for carbon (28.9 p.p.m.), again comparing the substituent with the CH skeleton. 

Unfortunately, our carbon 13 and proton data (Table II) taken together with other data for the model compounds, do not allow an unambiguous assignment of the 3 stereoisomers which we have obtained. For the present, then, we must be content to leave the relative stereochemistry of the 5-membered ring model compounds in question. For now, we can only say that the fine structure in the copolymer spectra are certainly well within isomers shifts seen for the model compound. However, based on the fact that the relative stereochemistry of the tetrahydrofuran models are unknown and that we have only one pyran isomer, we are unable to make a definite assignment as to the relative stereochemistry of ring junctions in the original copolymer. 

The COSY, TOeSY, HETCOR. and HMQC ex periments are great aids in interpreting proton and C spectra. However, the INADEQUATE experiment is perhaps the definitive 2D NMR technique. This experiment is based on spin-spin coupling between directly bonded pairs of nuclei. It can trace out the carbon backbone of an organic compound one carbon at a time. The low sensitivity of INADEQUATE has, however, limited its practical utility. 

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