Importance of water and intramolecular interaction governs substantial blue shift of Csp2–H stretching frequency in complexes between chalcogenoaldehydes and water

Geometrical structure, stability and cooperativity, and contribution of hydrogen bonds to the stability of complexes between chalcogenoaldehydes and water were thoroughly investigated using quantum chemical methods. The stability of the complexes increases significantly when one or more H₂O molecules are added to the binary system, whereas it decreases sharply going from O to S, Se, or Te substitution. The O–H⋯O H-bond is twice as stable as C_sp²–H⋯O and O–H⋯S/Se/Te H-bonds. It is found that a considerable blue-shift of C_sp²–H stretching frequency in the C_sp²–H⋯O H-bond is mainly determined by an addition of water into the complexes along with the low polarity of the C_sp²–H covalent bond in formaldehyde and acetaldehyde. The C_sp²–H stretching frequency shift as a function of net second hyperconjugative energy for the σ*(C_sp²–H) antibonding orbital is observed. Remarkably, a considerable C_sp²–H blue shift of 109 cm⁻¹ has been reported for the first time. Upon the addition of H₂O into the binary systems, halogenated complexes witness a decreasing magnitude of the C_sp²–H stretching frequency blue-shift in the C_sp²–H⋯O H-bond, whereas CH₃-substituted complexes experience the opposite trend.

The considerable blue shift of C_sp²–H stretching frequency.

Dioxiranes: A Half-Century Journey

Dioxiranes are multi-tasking reagents inheriting mild and selective oxygen transfer attributes. These oxidants are accessed from the reaction of ketones with an oxidant and are employed stoichiometrically or catalytically (in...

Continued Progress towards Efficient Functionalization of Natural and Non-natural Targets under Mild Conditions: Oxygenation by C-H Bond Activation with Dioxirane

The successful isolation and characterization of a dioxirane species in 1988 opened up one of the most attractive methods for the efficient oxidation of simple and/or structurally complex molecules. Dioxirane today rank among the most powerful tools in organic chemistry, with numerous applications in commercially important processes. They were quickly recognized as efficient oxygen transfer agents, especially for epoxidations and for a wide range of O-insertion reactions into C-H bonds. Dioxirane possess catalytic activity and appear as highly (chemo-, regio-, and stereo-) selective oxidants, despite their reactivity under mild and strictly neutral conditions being controlled by a combination of steric and electronic factors. In this review, we discuss some of the most recent and significant developments in the selective homogeneous and heterogeneous oxyfunctionalization of non-activated C-H bonds in hydrocarbons of natural and non-natural targets by using isolated dioxirane or, more generally, by using the ketones (i.e., the dioxirane precursors) as organocatalysts.