An investigation of the structure of salts of 1,1-dinitroalkanes and trinitromethane by spectral methods

NMR Study of CHN Hydrogen Bond and Proton Transfer in 1,1-Dinitroethane Complex with 2,4,6-Trimethylpyridine

“…The ability of a CH group to form C–H···X bonds often follows the trend C(sp)–H > C(sp 2 )–H > C(sp 3 )–H, , but introducing electronegative substituents could significantly change it. CH acidity can also be significantly changed, for example, the p K a for (CN) 3 CH is 5.13 and that for (CN) 2 CH 2 is 11.19. , After the proton transfer, complexes of the type C – ···HX + could be formed, i.e., zwitterionic pairs with carbanions. − On the one hand, the C – ···HX + hydrogen bond might be a local energy minimum along the proton transfer pathway, as, for example, it was demonstrated by calculations for the reaction of C 6 H 5 (CF 3 ) 2 CH with MeO – . On the other hand, after the proton transfer, a significant redistribution of electron density in the acid molecule can occur, decreasing the proton-accepting ability of the carbon atom and making the C – ···HX + form energetically unfavorable. − Besides, the C – /HX + ion pair might be solvent-separated or even completely dissociated in a polar solvent. , …”

“…Indeed, CC coupling should reflect the hybridization of the carbon atom involved, which changes from sp 3 for free DNE to sp 2 for DNE anion. Unfortunately, as in the experiment DNE was not 13 C enriched, we were unable to measure directly the 1 J CC couplings.…”

“…As signals of free DNE and DNE in a molecular CH•••N complex are in fast exchange, increase of 1 J CH at lower temperatures means that the coupling constant is higher in the complex than it is in the free CH acid. 13 C satellites are virtually not visible in Figure 1, but corresponding data is collected in Table S1 and Figures S3 and S4 of the Supporting Information.…”

“…1 H NMR chemical shifts of acidic CH proton and ratio of integrated intensities of NH and CH 1 H NMR signals vs temperature, table and plot of values of the 1 J CH coupling constants of DNE for spectra shown in Figure1,13 C satellites of DNE's CH group 1 H NMR signal, and magnified CH and CH 3 signals for a better showing of 3 J HH couplings. This material is available free of charge via the Internet at http://pubs.acs.org.…”