Nitrogen-Proton Couplings

One-bond couplings have been proposed as indicators of the 

The values of Jisn-ih can be up to 2 Hz and are in general negative. Model compounds have suggested a dihedral angle dependence of the form (Bystrov et al, 1975) 

Three-bond couplings in lysine have been measured. These are expected to be dependent on the dihedral angles x and ij/ of the side chains and peptide backbone, respectively (Blomberg et al, 1976). 

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Crepaux, D., Lehn, J. M., Dean, R. R. Nuclear Spin-Spin Interactions. X. Signs of Geminal and Vicinal Nitrogen-Proton Coupling Constants. Stereochemistry and Medium Effects on NH Couplings. Mol. Phys. 16, 225 (1969). 

The nitrogen—proton coupling constants for the separately observable cis and trans isomers of N -n-butylformamide and N-n-propyl-acetamide are shown in (15)-(17). The value of the coupling across the C-N bond relative to that observed in A -formamide (7i sjsi c-h =... 

Two-bond nitrogen-proton coupling 441, Three-bond nitrogen-proton coupling 441,... 

The pristine one electron reduced radical (1), which has zero charge, is characterized by a single a-proton coupling. On annealing, its resonance lines disappear in the temperature range 100 K - 150 K. The second electron gain product observed (2) is protonated at the exocyclic nitrogen its spectral lines disappear at temperatures above 250 K. 

Purines. - A study of anhydrous deoxyadenosine (compound iv) single crystals x-irradiated (70 kGy) and investigated at 10 K found four base radicals (21-24) and one deoxyribose radical (25) (see p. 251).20 Radical 21, a de-protonated electron loss product, was stable to 100 K and readily photobleached at 10 K. Its nitrogen hyperfine coupling tensors were estimated by using values that resulted in acceptable EPR spectral simulations these were A(N10) = (1.76, 0, 0) mT, A(N3) = (0.99, 0, 0) mT and A(N1) = (0.34, 0, 0) mT. 

This explains why only one nitrogen atom was detected and there is no proton coupling. It also provides some explanation why the crystal... 

To complete this section, mention will be made of the interesting radical H2CN-, recently identified in an argon matrix at 4-2°K (Cochran et al., 1962). This was formed by photolysing HI in the presence of HCN. The two protons have an isotropic hyperfine coupling of 87-4 G. The nitrogen hyperfine coupling was not completely documented. 

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