Protonation Sites, Tandem Mass Spectrometry and Computational Calculations of o-Carbonyl Carbazolequinone Derivatives

Assessment of the Long-Range NMR C,H Coupling of a Series of Carbazolequinone Derivatives

Synthesis, the complete 1H- and 13C-NMR assignments, and the long-range C,H coupling constants (nJC,H) of some hydrogen-deficient carbazolequinones, assessed by a J-HMBC experiment, are reported. In these molecules, the protons, used as entry points for assignments, are separated by several bonds with non-protonated atom carbons. Therefore, the use of long-range NMR experiments for the assignment of the spectra is mandatory; we used HSQC and HMBC. On the other hand, the measured heteronuclear (C,H) coupling constants 2J to 5J) allow us to choose the value of the long-range delay used in the HMBC experiment less arbitrarily in order to visualize a desired correlation in the spectrum. The chemical shifts and the coupling constant values can be used as input for assignments in related chemical structures.

Hydralazine derivative of aldehyde: A new type of [M - H]+ ion formed in electrospray ionization mass spectrometry

Hydralazine has been widely employed in the development of drugs, derivatization reagents, and ligands. In the present work, we reported a new type of dehydrogenated ion [M - H]⁺ that was produced from the hydralazine derivative of hexanal in electrospray ionization mass spectrometry (ESI-MS). The formation of [M - H]⁺ ions in the ESI-MS was found to be independent on the mobile phase composition of the liquid chromatography and ESI source parameters. A series of hydralazine derivatives of aldehyde were investigated to confirm this phenomenon. The results showed that hydralazine derivatives of aldehydes that contained an sp³ hybridization carbon with a hydrogen at the α-position of aldehydes could form the unexpected [M - H]⁺ ions, whereas hydralazine derivative of acetone could only generate [M + H]⁺ ion in the ESI-MS. We proposed the possible formation mechanism of [M - H]⁺ ion for the hydralazine derivatives of aldehydes: the [M - H]⁺ ion was possibly formed by the loss a hydrogen molecule (H₂ ) from the protonated ion [M + H]⁺ . The results obtained from density functional theory (DFT) calculations supported this proposed formation mechanism of [M - H]⁺ ion.