Molecular structure, conformation, and potential to internal rotation of 2,6- and 3,5-difluoronitrobenzene studied by gas-phase electron diffraction and quantum chemical calculations.
Molecular structure, conformation, and potential to internal rotation of 2,6- and 3,5-difluoronitrobenzene studied by gas-phase electron diffraction and quantum chemical calculations.
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通过气相电子衍射和量子化学计算研究 2,6- 和 3,5-二氟硝基苯的分子结构、构象和内旋转电位。
DOI：
10.1021/jp800941z
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发表时间：
2008
期刊：
影响因子：
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通讯作者：
H. Oberhammer
中科院分区：
文献类型：
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作者：
O. V. Dorofeeva;A. V. Ferenets;N. Karasev;L. Vilkov;H. Oberhammer
用气相电子衍射(GED)、MP2从头算和密度泛函计算对3，5-二氟硝基苯(3，5-DFNB)和2，6-二氟硝基苯(2，6-DFNB)进行了研究。对两种分子的静态和动态GED模型进行了修正。通过对B3LYP/cc-pVTZ立方力场计算的核间距离(re-ra)进行非简谐振动修正，确定了平衡Re结构。3，5-DFNB具有C2v对称性的平面结构，键长和键角的re值如下：r(C-C)av=1.378(4)A，r(C-N)=1.489(6)A，r(N-O)=1.217(2)A，r(C-F)=1.347(5)A，角度C6-C1-C2=122.6(6)度，角度C1-C2-C3=117.3(3)度，角度C2-C3-C4=123.0(3)度，角度C3-C4-C5=116.9(6)度，角度C-C-N=118.7(3)度，角度C-N-O=117.3(4)度，角度O-N-O=125.5(7)度，角度C-C-F=118.6(7)度。括号中的不确定度是标准差的三倍。与硝基苯的情况一样，3，5-DFNB中硝基的内旋势垒V90=10+/-4kJ/mol，大大低于量子化学计算的结果。邻位取代基的存在迫使硝基绕C-N键旋转，离开苯环平面。对于2，6-DFNB，通过几何绕射分析确定了结构参数为r(C-C)av=1.383(5)A，r(C-N)=1.469(7)A，r(N-O)=1.212(2)A，r(C-F)=1.344(4)A，角度C6-C1-C2=1.212(5)度，扭转角为Phi(C-N)=53.8(14)度的C2对称非平面结构。角度C1-C2-C3=121.2(2)度，角度C2-C3-C4=119.0(2)度，角度C3-C4-C5=121.1(4)度，角度C-C-N=120.6(2)度，角度C-N-O=115.7(4)度，角度O-N-O=128.6(7)度，角度C-C-F=118.7(5)度。对动力学模型的修正得到势垒V0=16.5+/-1.5kJ/mol和V90=2.2+/-0.5kJ/mol，与B3LYP/6-311++G(d，p)和MP2/cc-pVTZ计算结果符合得很好。两种分子的C-F键长相近。这与2-氟硝基苯中邻位的C-F键与3-和4-氟硝基苯中间位和对位的C-F键长度相比，在早期的GED研究中观察到的急剧缩短形成了对比。
3,5-Difluoronitrobenzene (3,5-DFNB) and 2,6-difluoronitrobenzene (2,6-DFNB) have been studied by gas-phase electron diffraction (GED), MP2 ab initio, and by B3LYP density functional calculations. Refinements of r h1 and r e static and r h1 dynamic GED models were carried out for both molecules. Equilibrium r e structures were determined using anharmonic vibrational corrections to the internuclear distances ( r e - r a) calculated from B3LYP/cc-pVTZ cubic force fields. 3,5-DFNB possesses a planar structure of C 2 v symmetry with the following r e values for bond lengths and bond angles: r(C-C) av = 1.378(4) A, r(C-N) = 1.489(6) A, r(N-O) = 1.217(2) A, r(C-F) = 1.347(5) A, angleC6-C1-C2 = 122.6(6) degrees , angleC1-C2-C3 = 117.3(3) degrees , angleC2-C3-C4 = 123.0(3) degrees , angleC3-C4-C5 = 116.9(6) degrees , angleC-C-N = 118.7(3) degrees , angleC-N-O = 117.3(4) degrees , angleO-N-O = 125.5(7) degrees , angleC-C-F = 118.6(7) degrees . The uncertainties in parentheses are three times the standard deviations. As in the case of nitrobenzene, the barrier to internal rotation of the nitro group in 3,5-DFNB, V 90 = 10 +/- 4 kJ/mol, is substantially lower than that predicted by quantum chemical calculations. The presence of substituents in the ortho positions force the nitro group to rotate about the C-N bond, out of the plane of the benzene ring. For 2,6-DFNB, a nonplanar structure of C 2 symmetry with a torsional angle of phi(C-N) = 53.8(14) degrees and the following r e values for structural parameters was determined by the GED analysis: r(C-C) av = 1.383(5) A, r(C-N) = 1.469(7) A, r(N-O) = 1.212(2) A, r(C-F) = 1.344(4) A, angleC6-C1-C2 = 118.7(5) degrees , angleC1-C2-C3 = 121.2(2) degrees , angleC2-C3-C4 = 119.0(2) degrees , angleC3-C4-C5 = 121.1(4) degrees , angleC-C-N = 120.6(2) degrees , angleC-N-O = 115.7(4) degrees , angleO-N-O = 128.6(7) degrees , angleC-C-F = 118.7(5) degrees . The refinement of a dynamic model led to barriers V 0 = 16.5 +/- 1.5 kJ/mol and V 90 = 2.2 +/- 0.5 kJ/mol, which are in good agreement with values predicted by B3LYP/6-311++G(d,p) and MP2/ cc-pVTZ calculations. The values of C-F bond lengths are similar in both molecules. This is in contrast to the drastic shortening of the C-F bond in the ortho position in 2-fluoronitrobenzene compared to the C-F bond length in the meta and para position in 3- and 4-fluoronitrobenzene observed in an earlier GED study.