Nitrogen bases, correlations between

Fig. 9 Deprotonation of cations radicals of synthetic analogs of NADH by oxygen or nitrogen bases in acetonitrile. Correlation between the intrinsic barrier and the homolytic bond dissociation energy of the cation radical (AH + —> A+ + H ).

There have been many studies on the formation of hydrogen bonds between alcohols and a wide range of bases. If the bases are of similar type (for example, all nitrogen donor atoms in amines), there is also frequently a rather good correlation between the shift of the O-H stretching band and other properties. For example, stretching frequency shifts of the OH bonds in alcohols have been correlated... 

Fig. 6.6 Schematics of hydrogen bonds between purine and pyrimidine bases with indicated trans-hydrogen bond scalar interactions and related coupling constants, which can be measured using NMR. In addition to correlations between exchangeable protons and nitrogens, also a relayed transfer to nonexchangeable aromatic protons, shown by a dashed arrow, can be employed. The...

Estimates can be made of the second term of equation (15), not usually by direct substitution, but by invoking various empirical linear correlations between AG° and AH° previously established for protonation of nitrogen and oxygen bases. 

Nitrogen was found to be of little Importance except for the female model generated from the Barley Canyon Study. In this case, female success was Inversely correlated with foliar nitrogen levels. However, these levels, based on published data (18,19), do not appear high enough to be toxic to the budworm. This observation, in view of the Inverse correlation between total nitrogen and female budworm success, leads us to... 

Nucleophilicity. A distinction is usually made between nucleophilicity and Lowry-Bronsted basicity [213]. The latter involves specifically reaction at a proton which is complexed to a Lewis base (usually H2O), while the former refers to reactivity at centers other than H. Linear correlations have been shown for gas-phase basicity (proton affinity) and nucleophilicity of nitrogen bases toward CH3I in solution [214] where the solvent is not strongly involved in charge dispersal. In each case, reaction of the base/nucleophile... 

Figure 14.25. The NOESY spectrum of CATAGCTATG in the region where correlations between the Hr protons of the deoxyri-bose sugar and the H6 and Hg protons of the nitrogenous bases are observed. (From ref. 7. Copyright 1995 by the American Association for the Advancement of Science. Excerpted with permission.)...

The simplest model of an amide bond is found in formamide, and several features of protonated formamide are highly relevant to the cleavage of protonated peptides into b and y ions. Amides are bidentate bases, and it has been demonstrated from correlations between core electron energies and proton affinities [213] and from quantum chemical calculations [214] that the carbonyl oxygen is more basic than the amide nitrogen. As demonstrated by FT-ICR, metastable ion dissociation, and RRKM and quantum chemical model calculations [214], the unimolecular dissociation of a protonated formamide molecule depends on which site the proton is attached to ... 

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