Theoretical Studies on the Reaction Pathways of l-CnH(n=5,6)+O2†

doi:10.7503/cjcu20131295

Abstract

Abstract:

The C_nH free radicals were reported to play an important role in interstellar chemistry. The oxidation processes of C_nH radicals with n=1—4 had been explored by means of the theoretical and experimental methods. To further understand the reaction properties of the long carbon chain radicals, we report the first theoretical survey of the l-C₅H+O₂ and l-C₆H+O₂ reactions at the CCSD(T)/CC-PVTZ+ZPVE//B3LYP/6-311++G(d,p) level. The carbon transfer was found to be the main pathway in the l-C₅H+O₂ reaction, giving the main product P₂(CO₂+C₄H). Yet, the case is a little different for l-C₆H+O₂. The energy barrier between the C,O-exchange[resulting in P1(CO+HC₅O)] and the oxygen transfer[resulting in P3(³O+HC₆O)] is only 0.4 kJ/mol, indicative of their co-predominance. The present results were compared with the shorter l-C_nH radicals with O₂.

Key words: l-CnH radical, Reaction mechanics, Oxidation, Oxygen transfer

CLC Number:

O641

TrendMD:

ZHU Weiwei, DING Yihong. Theoretical Studies on the Reaction Pathways of l-C_nH(n=5,6)+ $O 2 †$ [J]. Chem. J. Chinese Universities, 2014, 35(5): 1023.

Figures/Tables 6

Table 1 Relative energies of reactant, intermediates, transition states and products for the l-C5H+O2 reaction at the B3LYP/6-311++G(d,p) level and CCSD(T)/CC-PVTZ//B3LYP/6-311++G(d,p)+ ZPVE level

l-C₅H+O₂	ΔE/(kJ·mol^-1)			l-C₅H+O₂	ΔE/(kJ·mol^-1)
l-C₅H+O₂	B3LYP/6-311++ G(d,p)		CCSD(T)/ CC-PVTZ	CCSD(T)/CC- PVTZ+ZPVE	B3LYP/6-311++ G(d,p)	CCSD(T)/ CC-PVTZ	CCSD(T)/CC- PVTZ+ZPVE
R	0	0	0	QTS1/2	-43.9
1	-118.4	-85.0	-77.8	TS1/3	-112.6	-88.3	-82.5
Q1	-49.4			TS3/P2	-466.6	-484.6	-473.3
2	-196.3	-159.0	-151.5	TS3/4	-465.4	-475.4	-465.4
Q2	-183.3			TS4/5	-490.5	-497.6	-491.3
3	-552.4	-581.3	-565.0	P1(CO+HC₄O)	-632.8	-614.4	-608.5
4	-492.6	-506.8	-498.4	P2(CO₂+C₄H)	-498.4	-523.1	-508.9
5	-633.2	-660.8	-653.3	P3(³O+HC₅O)	-182.0	-183.3	-178.3

Table 2 Relative energies of reactant, intermediates, transition states and products for the l-C6H+O2 reaction at the B3LYP/6-311++G(d,p) level and CCSD(T)/ CC-PVTZ//B3LYP/6-311++G(d,p)+ ZPVE level

l-C₆H+O₂	ΔE/(kJ·mol^-1)			l-C₆H+O₂	ΔE/(kJ·mol^-1)
l-C₆H+O₂	B3LYP/6-311++ G(d,p)		CCSD(T)/ CC-PVTZ	CCSD(T)/CC- PVTZ+ZPVE	B3LYP/6-311++ G(d,p)	CCSD(T)/ CC-PVTZ	CCSD(T)/CC- PVTZ+ZPVE
R	0	0	0	TS2/3	-190.8	-225.2	-218.0
1	-179.1	-209.3	-193.3	TS3/4	-506.8	-540.3	-527.7
2	-198.8	-230.2	-219.3	TS3/P2	-425.2	-434.8	-426.9
3	-508.5	-543.2	-529.4	TS4/P1	-545.7	-587.6	-579.6
4	-583.8	-620.6	-604.7	P1(³O+HC₆O)	-604.7	-584.2	-581.3
TS1/2	-114.3	-126.8	-117.6	P2(CO₂+C₅H)	-467.9	-490.1	-488.0
TS1/P3	-126.8	-124.7	-117.2	P3(CO+HC₅O)	-181.6	-185.1	-178.7

Fig.1 Potential energy surface of l-C5H+O2 reaction at B3LYP/6-311++G(d,p) level and CCSD(T)/CC-PVTZ//B3LYP/6-311++G(d,p)+ZPVE level(square bracket)^Broken line(---) refer to the pathway in doublet state, real line(—) refer to quartet state.

Fig.2 Potential energy surface of l-C6H+O2 reaction at B3LYP/6-311++G(d,p) level and CCSD(T)/CC-PVTZ//B3LYP/6-311++G(d,p)+ ZPVE level(square bracket)

Fig.3 Optimized structures of the reactant, intermediates, transition states and products in the l-C5H+O2 reaction at B3LYP/6-311++G(d,p) level[Bond lengths are in nm; bond angles are in degree]

Fig.4 Optimized structures of the reactant, intermediates, transition states and products in the l-C6H+O2 reaction at B3LYP/6-311++G(d,p) level[Bond lengths are in nm; bond angles are in degree]

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