The reactions of O(3P) atoms with aromatic hydrocarbons with unsaturated side chains

Formation of Stabilized Ketene Intermediates in the Reaction of O(3P) with Oligo(phenylene ethynylene) Thiolate Self-Assembled Monolayers on Au(111)

“…Therefore, it is readily apparent that the low reaction probability is a direct result of the change in accessibility of the alkyne bonds in the SAM versus the gas phase. This is also in line with the findings of Eichholtz et al, where the pre-exponential factor for addition onto the alkyne bond was measured to be nearly 2 orders of magnitude smaller than addition onto the phenyl ring . Enforcing the majority of collisions to occur with the phenyl rings naturally yields a lower probability for the addition reaction.…”

“…Typical experimental conditions yield an O( 3 P) flux of 9 × 10 13 atoms/(cm 2 s), impinging upon SAM surfaces at normal incidence with an average kinetic energy of 9 kJ/mol. The energy was chosen to discourage side reactions, namely, the addition of O( 3 P) onto the phenyl rings of oPE-SAM occurring near 18 kJ/mol . Flux is determined from monitoring the change in pressure within the reaction chamber when it is open to the incoming beam, given that the extent of O 2 dissociation is known.…”

“…This is also in line with the findings of Eichholtz et al, where the pre-exponential factor for addition onto the alkyne bond was measured to be nearly 2 orders of magnitude smaller than addition onto the phenyl ring. 15 Enforcing the majority of collisions to occur with the phenyl rings naturally yields a lower probability for the addition reaction. Thus, the ability to stereodynamically control a reaction is demonstrated herein, in this case by restricting the accessibility of a reactive group just below the immediate vacuum/film interface.…”

“…We aim to directly observe reaction products in the foundational reactions of O( 3 P) with unsaturated hydrocarbons using this technique, specifically considering addition onto phenyl-substituted alkynes. Reactions with phenylacetylene, 2-propynylbenzene, and biphenylacetylene have previously been experimentally characterized, with energetic barriers associated with O( 3 P) addition onto the side chains measured to be low (<8 kJ/mol) compared with the phenyl rings (∼20 kJ/mol). , Specifically in the case of biphenylacetylene, Eichholtz et al reported the formation of biphenyl as a main product and proposed a mechanism for its formation through, in part, decomposition of a vibrationally excited biphenylketene intermediate via phenyl ring migration to release CO . This mechanism is supported by experimental − and theoretical − studies of analogous reactions with acetylene and other substituted alkynes where CO formation results from cleavage of singlet ketenes formed from intersystem crossing of long-lived triplet ketocarbenes.…”

“…Reactions with phenylacetylene, 2propynylbenzene, and biphenylacetylene have previously been experimentally characterized, with energetic barriers associated with O( 3 P) addition onto the side chains measured to be low (<8 kJ/mol) compared with the phenyl rings (∼20 kJ/ mol). 14,15 Specifically in the case of biphenylacetylene, Eichholtz et al reported the formation of biphenyl as a main product and proposed a mechanism for its formation through, in part, decomposition of a vibrationally excited biphenylketene intermediate via phenyl ring migration to release CO. 15 mechanism is supported by experimental 16−18 and theoretical 19−23 studies of analogous reactions with acetylene and other substituted alkynes where CO formation results from cleavage of singlet ketenes formed from intersystem crossing of longlived triplet ketocarbenes. These observations are also in line with experimental studies of O( 3 P) addition onto ethylene, where intersystem crossing is observed to contribute heavily to overall product formation.…”