直线型l-CnH(n=5,6)自由基与氧气反应机理的理论研究

doi:10.7503/cjcu20131295

摘要/Abstract

摘要：

为了探索更长的碳链自由基l-C_nH与O₂反应的机理, 在CCSD(T)/CC-PVTZ+ZPVE//B3LYP/6-311++G(d,p)的计算水平下, 讨论了当n=5,6时, l-C_nH+O₂的各个异构化反应通道. 当n=5时, 主要反应通道为碳迁移过程, 生成主要产物为P2(CO₂+C₄H); 当n=6时, 碳-氧交换[产物为P1(CO+HC₅O)]和氧迁移过程[产物为P3(³O+HC₆O)]均为主要通道, 并具有很高的竞争性. 将所得结构与l-C_nH(n≤4)+O₂的反应机理进行了对比.

关键词: l-CnH自由基, 反应机理, 氧化, 氧迁移

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

中图分类号:

O641

TrendMD:

朱微微, 丁益宏. 直线型l-C_nH(n=5,6)自由基与氧气反应机理的理论研究. 高等学校化学学报, 2014, 35(5): 1023.

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

图/表 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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