Nitrogen compounds, chemical data

The intimate relationship between NMR parameters such as chemical shifts and spin-spin coupling constants and molecular geometry is particularly evident for derivatives with rigid frameworks. Therefore, structural and conformational effects are treated first as a separate topic and then in conjunction with specific compounds. As data on hydroxylamines, oximes and hydroxamic acids are not as extensive as those for other types of systems containing nitrogen or oxygen, comparisons with their respective parameters or effects have also been included wherever they are considered relevant. 

Similar chemical shift data are also available for the 1,3,2,4-isomeric form (compound 22) of compound 20, though the hexafluoroarsenate anion is the counterion in the example shown here (cf. chloride as counterion in compound 20). Since the ring nitrogens become chemically inequivalent, we observe an extra signal. Thus, this technique serves as an ideal tool for establishing the proportion of each isomeric form within a given sample <1988IC2749>. 

Table 10.1 Chemical data on important nitrogen compounds in the environment.

Sulphur-nitrogen compounds. 33S spectra of some sulphimides, sulphox-imides and sulphonamides29 64 65 have been reported, but the available data are not sufficient for a detailed discussion of the correlation between chemical shifts and molecular structure (Table A.6). 

Other than a detailed analysis of the N NMR spectrum of 3-phenylazo-li/-4,l,2-benzo-thiadiazine (21) (Section 6.17.7.2.2.2) no other N NMR spectral data for 1,3,4-oxadiazines or their thio-analogues appear to have been published. Nitrogen-15 chemical shift data (with respect to CH3NO2) for azo-compound (21) are appended to (21) <90MRC1027>. 

A linear relationship has been found to exist between shifts of alkanes and the shifts of isoelectronic boron-nitrogen compounds. A least-squares analysis of the available data shows that the chemical shifts may be related to those of B in the isoelectronic compounds by the expression—... 

Nitrogen-15 NMR data of quinolizinium and related compounds are useful criteria for the study of the extent of the delocalization of their n systems. For example, replacement of the central carbon atom of acenaphthylene by nitrogen leads to pyrrolo[2,l,5-chemical reactivity (for example, lack of alkenic character in the 1,2 bond) suggest a delocalized n structure (47), which is supported by the shielding of the nitrogen atom (22.3 ppm with respect to quinolizinium) in the N NMR spectrum of this compound <84JCS(P1)2553>. 

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