Complexes of Formaldehyde and α-Dicarbonyls with Hydroxylamine: FTIR Matrix Isolation and Theoretical Study

Profound importance of the conventional O-H⋯O hydrogen bond versus a considerable blue shift of the Csp2-H bond in complexes of substituted carbonyls and carboxyls

Using quantum chemical approaches, we investigated the conventional O-H⋯O and nonconventional Csp2-H⋯O hydrogen bonds between carboxylic acids and aldehydes in 21 stable complexes. The strength of complexes is determined by the conventional O-H⋯O bond together with the nonconventional Csp2-H⋯O hydrogen bond, in which the former one is 4-5 times as strong as the latter one. Proportional linear correlations of the interaction energy with both individual energies of the O-H⋯O and Csp2-H⋯O hydrogen bonds are proposed. Different impacts of electron-donating and electron-withdrawing groups in substituted formaldehyde and formic acid on characteristics of conventional and nonconventional hydrogen bonds, as well as the strength of both hydrogen bond types and complexes, are also evaluated. Following complexation, it is noteworthy that the largest blue shift of the Csp2-H stretching frequency in the Csp2-H⋯O bond up to 105.3 cm-1 in CH3CHO⋯FCOOH is due to a decisive role of the O-H⋯O hydrogen bond, which has been rarely reported in the literature. The obtained results show that the conventional O-H⋯O hydrogen bond plays a pivotal role in the significant blue shift of the Csp2-H stretching frequency in the nonconventional Csp2-H⋯O hydrogen bond. Remarkably, the considerable blue shift of the Csp2-H stretching frequency is found to be one H of C-H in formic acid substituted by the electron-withdrawing group and one H in formaldehyde substituted by the electron-donating group. In addition, the change in the Csp2-H stretching frequency following complexation is proportional to both changes of electron density in σ*(Csp2-H) and σ*(O-H) orbitals, in which a dominant role of σ*(O-H) versus σ*(Csp2-H) is observed.

Photo-Induced Reactions between Glyoxal and Hydroxylamine in Cryogenic Matrices

In this paper, the photochemistry of glyoxal−hydroxylamine (Gly−HA) complexes is studied using FTIR matrix isolation spectroscopy and ab initio calculations. The irradiation of the Gly−HA complexes with the filtered output of a mercury lamp (λ > 370 nm) leads to their photoconversion to hydroxyketene−hydroxylamine complexes and the formation of hydroxy(hydroxyamino)acetaldehyde with a hemiaminal structure. The first product is the result of a double hydrogen exchange reaction between the aldehyde group of Gly and the amino or hydroxyl group of HA. The second product is formed as a result of the addition of the nitrogen atom of HA to the carbon atom of one aldehyde group of Gly, followed by the migration of the hydrogen atom from the amino group of hydroxylamine to the oxygen atom of the carbonyl group of glyoxal. The identification of the products is confirmed by deuterium substitution and by MP2 calculations of the structures and vibrational spectra of the identified species.