This review highlights the recent advances in donor and donor–donor carbenes.

Calculations and experiments were conducted on ozonolysis of ethyl vinyl ether (EVE) and butyl vinyl ether to identify an unconventional diradical intermediate generated from the O−O bond cleavage of primary ozonide. The diradical can undergo a H atom shifting process that yields keto-hydroperoxide (KHP), the characteristic product that identifies the existence of a diradical intermediate. RRKM-ME calculation, based on the PES at the CCSD(T)/VTZ//M06-2X/6-311+ +G(2df,2p) level, disclosed branching ratios of ∼0.65% for KHP formation. Using synchrotron-generated vacuum-ultraviolet photoionization mass spectrometry measurements, the formation of KHPs (C 4 H 8 O 4 ) in ozonolysis of EVE was confirmed by ion signals of C 4 H 8 O 4 + (ionization of KHP) and C 4 H 7 O 2 + (ion fragment from the loss of HO 2 from KHP) by comparing their photoionization efficiency spectra with the calculated adiabatic ionization energies and appearance energies.