Flash Photolysis of Cyclic Ethers. I. Ethylene Oxide¹

The gas-phase thermal and photochemical decomposition of heterocyclic compounds containing nitrogen, oxygen, or sulfur

“…17 The very initial act was thought to be either the formation of the -0CH20CH2CH2. biradical or of the .0CH2CH20CH2-biradical.…”

Ultrafast Photo‐ion Probing of the Ring‐Opening Process in Trans‐Stilbene Oxide

“…In cases in which the ring‐opening mechanism of oxiranes proceeds via the C−C bond, Woodward‐Hoffman (WH) rules generally describe the process well [3,4,10,16,18–20] . Interestingly, in their seminal papers describing the conservation of orbital symmetry of concerted reactions, [18,19] Woodward and Hoffman themselves explicitly discuss the thermal‐ and photo‐induced ring‐opening and closing of oxirane via the C−C bond – despite the C−O bond opening mechanism being the more common pathway for the unsubstituted oxirane molecule [2,3,7–10] . Regarding trans ‐stilbene oxide, WH rules suggest that if it was to open via the C−C bond through thermal means it would do so in a concerted conrotatory motion and produce the cis‐ carbonyl ylide (1,3‐dipole) seen in route a) of Scheme 1.…”

“…It has generally been observed that the primary oxirane molecule, alongside a number of alkyl‐substituted oxiranes, undergoes a photo‐induced ring‐opening process which involves the dissociation of one of the C−O bonds in the oxirane ring. [ 2 , 3 , 7 , 8 , 9 , 10 , 11 ] This is in contrast to cyano‐ and phenyl‐substituted oxiranes (such as trans ‐stilbene oxide) which present evidence that the ring‐opening process generally occurs through the dissociation of the C−C bond in the oxirane ring instead. [ 3 , 12 , 13 , 14 , 15 , 16 , 17 ] This discrepancy is an obvious curiosity worthy of investigation in and of itself.…”

“…[ 3 , 4 , 10 , 16 , 18 , 19 , 20 ] Interestingly, in their seminal papers describing the conservation of orbital symmetry of concerted reactions,[ 18 , 19 ] Woodward and Hoffman themselves explicitly discuss the thermal‐ and photo‐induced ring‐opening and closing of oxirane via the C−C bond – despite the C−O bond opening mechanism being the more common pathway for the unsubstituted oxirane molecule. [ 2 , 3 , 7 , 8 , 9 , 10 ] Regarding trans ‐stilbene oxide, WH rules suggest that if it was to open via the C−C bond through thermal means it would do so in a concerted conrotatory motion and produce the cis‐ carbonyl ylide (1,3‐dipole) seen in route a) of Scheme 1 . Conversely, if trans ‐stilbene oxide was to undergo a ring‐opening process via the C−C bond through a photo‐excited state, WH rules predict it would proceed through a concerted disrotatory motion, this time producing the trans‐ carbonyl ylide seen in route b) of Scheme 1 .…”

“… [15] In addition, further experiments have observed products that suggest that the ring‐opening process is occurring via the dissociation of one of the C−O bonds (as illustrated in route c of Scheme 1 ),[ 15 , 21 , 22 , 23 ] which is more in line with the process observed in the primary oxirane molecule. [ 2 , 3 , 7 , 8 , 9 , 10 , 11 ] All of this suggests that there are multiple potential pathways that stilbene oxide can follow after excitation, and the exact mechanism of these routes is still not yet fully understood.…”