Unusual Boron-Carbon Compounds Containing Planar Tetracoordinate and Pentacoordinate Carbons

采用密度泛函理论(dfT),在b3lyP/6-311+g**水平上,研究了三类包含平面四配位碳原子(PTC)和平面五配位碳原子(PPC)的硼碳化合物.这三类新型化合物是由C3b2H4(包含PTC)、Cb4H2(包含PTC)和Cb5H2(包含PPC)三种稳定结构和—CHCH—单元连接起来而得到的.在理论上探讨了这些新型的硼碳化合物的成键特征,光谱性质以及芳香性.研究结果表明:包含PTC和PPC原子的能量最低的结构,在不受对称面限制的条件下,具有C2V对称性的顺式立体构型比具有反式平面构型的化合物稳定.计算的核独立化学位移(nICS)显示,这些新型化合物的三元环中心有强的芳香性.计算最稳定硼碳化合物的PTC和PPC原子的WIbErg键指数(WbIS)表明PTC和PPC的成键遵循八隅规则.Unusual boron-carbon compounds containing planar tetracoordinate carbon (ptC) and planar pentacoordinate carbon (ppC) were investigated using density functional theory (DFT) at B3LYP/6-311+G** level.These novel compounds are generally assembled with three types of stable structural units C3B2H4 with ptC, CB4H2 with ptC, and CB5H2 with ppC as well as linking elements—CHCH—.On the basis of calculation results the bonding features, spectroscopic properties, and the aromaticities of these novel boron-carbon compounds were discussed.Results show that as for the lowest-energy compounds contained ptC and ppC without being limited by symmetrical planes, stereo cis-structures of C2v symmetry are more stable than the corresponding planar trans-structures.Calculated nucleus-independent chemical shift (NICS) values show that the aromaticity of the center of the three-membered rings is the strongest.The total Wiberg bond indices (WBIs) of the ptC and ppC atoms of the most stable structures of the boron-carbon compounds indicate that the ptC and ppC obey the octal rule.supportedbytheExcellentSciencePre-researchProjectofShaanxiNormalUniversity(China)in2008---

Unusual Boron-Carbon Compounds Containing Planar Tetracoordinate and Pentacoordinate Carbons

Unusual boron-carbon compounds containing planar tetracoordinate carbon (ptC) and planar pentacoordinate carbon (ppC) were investigated using density functional theory (DFT) at B3LYP/6-311+G * * level. These novel compounds are generally assembled with three types of stable structural units C3B2H4 with ptC, CB4H2 with ptC, and CB5H2 with ppC as well as linking elements -CHCH-. On the basis of calculation results the bonding features, spectroscopic properties, and the aromaticities of these novel boron-carbon compounds were discussed. Results show that as for the lowest-energy compounds contained ptC and ppC without being limited by symmetrical planes, stereo cis-structures of C-2v symmetry are more stable than the corresponding planar trans-structures. Calculated nucleus-independent chemical shift (NICS) values show that the aromaticity of the center of the three-membered rings is the strongest. The total Wiberg bond indices (WBIs) of the ptC and ppC atoms of the most stable structures of the boron-carbon compounds indicate that the ptC and ppC obey the octal rule.Excellent Science Pre-research Project of Shaanxi Normal University (China

Effect of localized supply of nitrate on corn root morphology and NO_3~- uptake

用 PVC管进行土柱栽培试验 ,研究了限域供应 NO- 3 对玉米根重、根系密度大小和分布的影响及玉米根系形态对 NO- 3 吸收的影响 ,并讨论了限域供应 NO- 3 与侧根萌发、伸长的关系。结果表明 ,土表下灌施 NO- 3能促进根系在土壤中下层的分布 ,显著增加根系密度及其在土壤中层的分布 ;根系密度与 NO- 3 吸收量关系密切 ,相关系数 (R2 )为 0 .95 0 6。限域供应 NO- 3 能够刺激侧根萌发伸长和增加根系密度

Effect of fertigation depth on dry matter partition and water use efficiency of corn

用土柱管栽试验方法研究了不同灌溉施肥深度对夏玉米生长发育、地上地下部分同化物分配、产量和水分利用效率的影响。试验结果表明:土表下灌施抑制了玉米生育早期的地上部分生长,使根系向土壤中下层的分布加强,从而保证了作物中后期对水分养分的吸收利用,提高了水分利用效率。在本试验条件下,玉米生长的最佳灌施深度为30cm

Effect of Lateral Depth on Root and Seedling Growth and Water Use Efficiency of Winter Wheat

在试验室内 ,进行了地下滴灌埋管深度对不同生育时期冬小麦根系生长和地上部分生长影响的试验研究。结果表明 :2 0 cm和 4 0 cm埋管深度的水分分布特征 ,在生育早期抑制地上部分营养生长 ,促进冬小麦蹲苗 ;而中后期则促进生殖生长 ,产量和水分利用效率较高。不考虑犁底层影响时 ,在重壤土上 4 0 cm是冬小麦进行地下滴灌的较好埋

四川永兴汉墓出土染色绢分析

通过对四川绵阳市东郊永兴汉墓出土染色绢的现代检测分析,对其纤维属性、织物组织、染料品种进行了判定,指出其在研究四川蚕桑丝绸史及中国古代染色史上具有重要意义