N-H coupling

The steady-state free-procession (SSFP) technique was used with no NOE, and in the case of aniline the T of the 15N was reduced by addition of chromium acetylacetate as a relaxation reagent to the sample. The 15N spectrum of aniline showed a single broad line (Avi/2 = 42 Hz) in which, because of proton exchange125,126, there is no evidence of N H coupling (J = 80 Hz). 

N, H) coupling constants lie in the range of (—80 15) Hz. Some examples, including exceptions, are tabulated in Table 13. 7( N, H) coupling constants are generally less than 2 Hz in magnitude ... 

The coupling interaction between directly bonded N—H is generally dominated by the Fermi contact term, as evidenced by the dependence of 7( N—H) on the amount of s character in the bond. Table 15 lists some illustrative N—H coupling constants, determined under comparable solvent conditions, as a function of the s character in the bonding orbitals. 

Kintzinger and Lehn have uncovered a very striking effect of the orientation of the nitrogen lone-pair on N—H coupling constants in the N=C—H group. In oximes the measured N=C—H coupling constants are ca 3 Hz and ca 16 Hz for the syn and anti isomers, respectively. 

TABLE 15. Representative N—H coupling constants as a function of nitrogen hybridization ... 

The N chemical shifts and /( N— H) coupling constants of 1 -amino- and 2-aminobenzotriazole in DMSO solution have been reported and the N assignments are shown in Figure 9. There is a correlation between the chemical shifts of A -aminoazoles and A -methylazoles <90JCS(P2)237>. 

Pervushin et al.199 have measured both 2hJ(N, N) and lhJ(N, H) couplings for a DNA-protein complex and compared such values with those measured in the... 

Intramolecular lhJ(N, H) couplings were measured in the range of 195 to 302 in order to study the proton transfer equilibrium in a series of N-(R-salicylidene)-alkylamines.231... 

The reaction field theory is used96 to simulate the effect of the water environment the results on how couplings are affected by this medium effect are compatible with the known inhibition of the anomeric effect due to solvent dielectric influence. In this way, it is calculated that in methanol and methylamine only one-bond and 2J(H,H) and 2J(N,H) couplings are affected by the water environment. Changes in such couplings are dominated by the FC term. 

There are no systematic results related to J(N,H) coupling constants, so we would like to present only the result obtained for the 4-N02 derivative with an asymmetric [NHN]+ bridge. In this case, it was possible to compare the result with that obtained by using the 3J(NH,CH3) coupling constant. Both data enable an estimation of the population degrees for two N1 and N8 nitrogen atoms. The comparison is presented in Table 19.5. 

H—C—N—H coupling in several amines was observed following rigorous removal (with Na-K alloy) of traces of water. This effectively stops proton exchange on the NMR time scale. [K.L. Henold, Chem. Commun., 1340(1970).]... 

The cytosine cation has a pKa < 4 and in solution deprotonates at NH2 [5], In the solid-state Sagstuen et al. [45] assigned the primary oxidation radical observed in cytosine p(Nl) = 0.30 and p(C5) = 0.57. Furthermore there are two small exchangeable N-H couplings whose angular variations correlate well with the exocyclic N4-H s. 

Further, the change in the spectrum of 5-methoxycarbonylindole on addition of piperidine53 shows, as in the case of pyrroles,38 the elimination of the N-H coupling with the other protons of the five-membered ring. 

Moles of guanidine hydrochloride per unit mcrfe oi pepUe bond Cycoupling constant from NH qgnals. 

---