Abstract:The reaction of ground-state Y (a 2 D) atoms with ketene (H 2 CCO) was studied at two collision energies, 22.7 and 10.4 kcal/mol. At both collision energies, four competing processes were observed corresponding to formation of YCH 2 , YCCO, YCHCO (with elimination of CO, H 2 , and H, respectively), and nonreactive scattering. The endoergicity of the YCHCO + H product channel was 10.5 ( 2.0 kcal/mol, leading to D 0 (Y-CHCO) ) 93.4 ( 2.0 kcal/mol. Product branching ratios measured at both collision energies show… Show more
“…At wider lab angles, the slower peak (∼175 μs) becomes more intense than the fast peak. This behavior is very similar to that seen previously in our studies of reactions of transition metal atoms with C 2 H 4 , C 2 H 2 , and carbonyl-containing species such as H 2 CO, and clearly results from decay of π-complexes back to reactants. As in the previous studies, data was simulated using two separate P ( E ) and T (θ) combinations (Figure ).…”
Section: Results and Analysissupporting
confidence: 89%
“…Alternatively, β-H migration to the metal (rather than to the H atom bound to the metal) can lead to production of a Y allyl dihydride complex, which can subsequently eliminate allene. This is analogous to mechanisms believed to play important roles in formation of YH 2 in reactions of Y with ethane 12 and formaldehyde. , 16 Proposed reaction mechanism (top) for Y + propene. Addition to the CC bond leads to formation of a π-complex, followed by intramolecular insertion into a methyl C−H bond.…”
Branching ratios between C−C and C−H bond activation were measured for reactions of ground-state Y
(a2D, s2d) atoms with two C3H6 isomers (cyclopropane and propene) in crossed molecular beams. For both
isomers, C−C bond activation led to formation of YCH2 + C2H4, whereas C−H activation led to YC3H4 +
H2 and YH2 + C3H4. The angular and velocity distributions for all three product channels and for nonreactive
collisions were measured at several collision energies (E
coll). For Y + cyclopropane, the branching ratio for
YCH2 + C2H4 increased relative to YC3H4 + H2 with increasing E
coll, this C−C activation channel becoming
dominant at E
coll ≥ 19 kcal/mol. For the propene reaction, φYCH
2
/φYC
3
H
4
also increased with E
coll, reaching
0.75:1.00 at E
c
oll = 28.8 kcal/mol. For both C3H6 reactants, formation of YH2 + C3H4 was observed as a
minor channel at the highest collision energies. Experimental results and Rice−Ramsperger−Kassel−Marcus
(RRKM) modeling indicate that for propene reactions all three channels involve initial formation of
π-association complexes that undergo insertion into one of the sp3-hybridized β-C−H bonds in the methyl
substituent. Decay of the yttrium allyl hydride intermediate by β-H migration leads to the two C−H activation
products, YC3H4 + H2 and YH2 + C3H4. We propose that the YCH2 + C2H4 channel involves reverse β-H
migration forming the same strongly bound metallacyclobutane intermediate formed in the Y + cyclopropane
reaction.
“…At wider lab angles, the slower peak (∼175 μs) becomes more intense than the fast peak. This behavior is very similar to that seen previously in our studies of reactions of transition metal atoms with C 2 H 4 , C 2 H 2 , and carbonyl-containing species such as H 2 CO, and clearly results from decay of π-complexes back to reactants. As in the previous studies, data was simulated using two separate P ( E ) and T (θ) combinations (Figure ).…”
Section: Results and Analysissupporting
confidence: 89%
“…Alternatively, β-H migration to the metal (rather than to the H atom bound to the metal) can lead to production of a Y allyl dihydride complex, which can subsequently eliminate allene. This is analogous to mechanisms believed to play important roles in formation of YH 2 in reactions of Y with ethane 12 and formaldehyde. , 16 Proposed reaction mechanism (top) for Y + propene. Addition to the CC bond leads to formation of a π-complex, followed by intramolecular insertion into a methyl C−H bond.…”
Branching ratios between C−C and C−H bond activation were measured for reactions of ground-state Y
(a2D, s2d) atoms with two C3H6 isomers (cyclopropane and propene) in crossed molecular beams. For both
isomers, C−C bond activation led to formation of YCH2 + C2H4, whereas C−H activation led to YC3H4 +
H2 and YH2 + C3H4. The angular and velocity distributions for all three product channels and for nonreactive
collisions were measured at several collision energies (E
coll). For Y + cyclopropane, the branching ratio for
YCH2 + C2H4 increased relative to YC3H4 + H2 with increasing E
coll, this C−C activation channel becoming
dominant at E
coll ≥ 19 kcal/mol. For the propene reaction, φYCH
2
/φYC
3
H
4
also increased with E
coll, reaching
0.75:1.00 at E
c
oll = 28.8 kcal/mol. For both C3H6 reactants, formation of YH2 + C3H4 was observed as a
minor channel at the highest collision energies. Experimental results and Rice−Ramsperger−Kassel−Marcus
(RRKM) modeling indicate that for propene reactions all three channels involve initial formation of
π-association complexes that undergo insertion into one of the sp3-hybridized β-C−H bonds in the methyl
substituent. Decay of the yttrium allyl hydride intermediate by β-H migration leads to the two C−H activation
products, YC3H4 + H2 and YH2 + C3H4. We propose that the YCH2 + C2H4 channel involves reverse β-H
migration forming the same strongly bound metallacyclobutane intermediate formed in the Y + cyclopropane
reaction.
“…31 For Y, the P(E) values for the elimination of H 2 and CH 4 show that a greater fraction of the available energy was partitioned into translational energy than for the Zr reactions, suggesting a potential energy barrier in the exit channel for both H 2 and CH 4 elimination in the Y reaction. 9,18,21,43 As shown in Figure 15, the P(f T ) distribution for CH 4 elimination from Y + 2-butyne peaks further away from the zero of translational energy than those for H 2 elimination from Y + propyne. Thus, a larger amount of translational energy is observed in the system with more product vibrational degrees of freedom.…”
The reactions of Y (a2D), Zr (a3F), Nb (a6D), Mo (a7S), and electronically excited-state Mo* (a5S) with propyne (methylacetylene) and 2-butyne (1,2-dimethylacetylene) were investigated using crossed molecular beams. For all of the metals studied, reactions with propyne led to H2 elimination, forming MC3H2. For Y + propyne, C-C bond cleavage forming YCCH + CH3 also was observed, with an energetic threshold in good agreement with an earlier determination of D0(Y-CCH). For Y + 2-butyne, three reactive channels were observed: YC4H4 + H2, YC3H3 + CH3, and YC3H2 + CH4. The C-C bond cleavage products accounted for 21 and 27% of the total products at Ecoll = 69 and 116 kJ/mol, respectively. For Zr and Nb reactions with 2-butyne, competition between H2 and CH4 elimination was observed, with C-C bond cleavage accounting for 12 and 4% of the total product signal at Ecoll = 71 kJ/mol, respectively. For reactions of Mo and Mo* with 2-butyne, only H2 elimination was observed. The similarity between reactions involving two isomeric species, propyne and allene, suggests that H atom migration is facile in these systems.
“…To better understand the fundamental aspects of this reaction, several studies have been reported on the investigation of the relevant mechanism [7][8][9][10][11][12][13][14][15][16][17][18][19][20]. As one of the sim ple carbonyl containing organic molecules, acetalde hyde is used in many practical application fields such as organic synthesis, catalysis, etc.…”
The mechanism of the reaction of osmium atom with acetaldehyde has been investigated with a DFT approach. All the stationary points are determined at the UB3LYP/sdd/6 311++G** level of the the ory. Both ground and excited state potential energy surfaces are investigated in detail. The present results show that the title reaction start with the formation of a CH 3 CHO-metal complex followed by C-C, aldehyde C-H, C-O, and methyl C-H activation. These reactions can lead to four different products (HOsCH 3 + CO, OsCO + CH 4 , OsCOCH 3 + H, and OsO + C 2 H 4 ). The minimum energy reaction path is found to involve the spin inversion in the initial reaction step. This potential energy curve crossing dramatically affects reaction exothermic. The present results may be helpful in understanding the mechanism of the title reaction and further experimental investigation of the reaction.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
