15N NMR study of protonation position determination in 2-(6-methoxynaphthalen-2-yl)vinyl diazine chromophores

Abstract

The 1H-15N HMBC spectra were successfully used for protonation position determination in 4-[(E)-2-(6-methoxynaphthalen-2-yl)vinyl]pyrimidine (1), 2-[(E)-2-(6-methoxynaphthalen-2-yl)-vinyl]quinoxaline (2), 2-[(E)-2-(6-methoxynaphthalen-2-yl)vinyl]pyrazine (3), and 3-[(E)-2-(6-methoxynaphthalen-2-yl)vinyl]pyridazine (4). Mono protonation was proved. In three cases (compounds 1, 2 and 4) only one nitrogen was protonated while in pyrazine compound 3 the equilibrium between regioisomers was observed.