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C~4~0, C~4~0^+, Nb@C~4~0^+, NbC~3~9^+, Nb@C~4~0H~4^+的 量子化学研究 总被引:1,自引:0,他引:1
用量子化学从头计算方法研究了C~4~0,C~4~0^+,Nb@C~4~0^+,NbC~3~9^+,Nb@C~4~0H~4^+的几何构型、电子结构和C~2~8一样,C~4~0(T~d)基态也为^5A~2态,笼骨架上具有四个悬挂键。计算结果表明C~4~0和C~4~0^+比NbC~3~9^+和Nb@C~4~0^+稳定,与实验结果一致。 相似文献
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异质富勒烯C~5~9Si与C~6~9Si的理论研究 总被引:4,自引:0,他引:4
利用MNDO,AM1和PM3半经验量子化学计算方法对硅杂富勒烯C~5~9Si和C~6~9Si进行了系统的理论研究.计算了稳定构型、生成热、前沿轨道能级差、电离势、电子亲和势、绝对电负性和整体硬度.结果表明,硅杂富勒烯的稳定性虽然低于全碳富勒烯,但也具有相当的稳定性.C~5~9Si的稳定性比已经合成的C~5~8X~2(X=B,N)高,C~6~9Si与C~7~0的稳定性差异也很小,因此在适宜条件下文中所讨论的硅杂富勒烯是应该能够合成的.在C~6~9Si各异构体中,取代位置在赤道的异构体具有最低的能量和最大的前沿轨道能级差,也是最稳定的异构体.与全碳勒烯C~6~0和C~7~0相比,C~5~9Si和C~6~9Si具有较小的电离势和电子亲和势,表明硅杂富勒烯容易被氧化,而被还原的难度要些,但是仍容易发生还原反应而生成负离子.因此硅原子的掺杂能够使富勒烯的氧化还原性能得以改善.C~5~9Si和C~6~9Si更容易与亲电试剂反应,而发生亲核反应的活性要相对小一些.硅杂富勒烯C~5~9Si和C~6~9Si的绝对电负性和硬度都小于相对应的全碳富勒烯,对电子的束缚力要相对小一些。 相似文献
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探讨了一类具有高位阻特征的烃基膦酸单十六烷基酯萃取剂R^1(R^2O)P(O)OH从氯化物介质中萃取Yb(III)和Lu(III)的结构与性能关系。其中,R^1分别为CH~3,C~2H~5,i-C~3H~7,cyclo-C~6H~1~1和C~6H~5,R^2为C~4H~9CH(C~2H~5)C~2H~4CH(C~6H~1~3)或C~6H~1~3CH(CH~3)CH~2CH(C~6H~1~3)。结果表明,这类萃取剂对于Yb,Lu的萃取和分离能力随着其分子中取代基空间位阻的增大而降低。 相似文献
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探讨了一类具有高位阻特征的烃基膦酸单十六烷基酯萃取剂R^1(R^2O)P(O)OH从氯化物介质中萃取Yb(III)和Lu(III)的结构与性能关系。其中,R^1分别为CH~3,C~2H~5,i-C~3H~7,cyclo-C~6H~1~1和C~6H~5,R^2为C~4H~9CH(C~2H~5)C~2H~4CH(C~6H~1~3)或C~6H~1~3CH(CH~3)CH~2CH(C~6H~1~3)。结果表明,这类萃取剂对于Yb,Lu的萃取和分离能力随着其分子中取代基空间位阻的增大而降低。 相似文献
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利用量子化学从头计算方法研究了C~nSi(n=28,29)各种可能的结构,研究结果表明:C~2~9Si为硅取代碳笼(Fullerens)中一个碳原子而形成的骨0架硅杂碳笼(Fullerenes),而且C~2~9Si最稳定结构是通过硅取代碳笼(C~3~0)最稳定结构中一个碳原子而得到.C~2~9Si比C~3~0有较低的稳定性和较高的化学活性.C~2~8Si有两种类型结构:(I)外接,(Ⅱ)缺位(hole-defect)型,即硅四连接型.计算结果表明,对C~2~8Si,外接硅型化合物更稳定,即(I)为主要成份.而且C~2~8Si最稳定结构是由C~2~8最稳定结构外接硅而形成.计算结果与实验观测一致。 相似文献
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Salicylaldehyde reacts with dimethyl acetylenedicarboxylate in benzene solution to give a mixture of dimethyl o-formylphenoxymaleate, dimethyl o-formylphenoxyfumarate, 2,3-dicarbomethoxychrom - 2 - en - 4 - ol, 2,3 - dicarbomethoxychrom - 3 - en - 2 - ol, dimethyl (2,3 - dicarbomethoxychrom - 2 - en - 4 - yl) - oxalacetate and dimethyl fumarate. 2,3 - Dicarbomethoxychrom - 3 - en - 2 - ol in this reaction is formed from 2,3 - dicarbomethoxychrom - 2 - en - 4 - ol through a benzopyrylium intermediate. The reaction of salicylaldehyde with excess of dimethyl acetylenedicarboxylate, however, gives a mixture of 2,3 - dicarbomethoxychrom - 3 - en - 2 - ol and dimethyl (2,3 - dicarbomethoxychrom - 3 - en) - 2 - oxyfumarate. 2,3 - Dicarbomethoxychrom - 3 - en - 2 - ol itself reacts further with dimethyl acetylenedicarboxylate to give 2,3,12 - tricarbomethoxychrom - 3,4 - eno[2,3 - b] pyrone. Similarly, the reaction of o-hydroxyacetophenone with dimethyl acetylendicarboxylate gives a mixture of dimethyl o-acetylphenoxymaleate, dimethyl o-acetylphenoxyfumarate, 2,3 - dicarbomethoxy - 4 - methylchrom - 2 - en - 4 - ol and 2,3 - dicarbomethoxy - 4 - methylchrom - 3 - en - 2 - ol. Both 2-hydroxychalcone and 2 - hydroxy - 4′ - methoxychalcone give mixtures of chalcone - 2 - oxymaleate and chalcone - 2 - oxyfumarate. The reaction of 2,2t?-dihydroxychalcone, however, gives 2′-hydroxyflavone, in addition to the expected maleate and fumarate. Similar reactions of 5 - chloro - 2,2′ - dihydroxychalcone and of 3,5 - dibromo - 2,2′ - dihydroxychalcone, on the other hand, give 2,3 - dicarbomethoxy - 4 - (o - hydroxyphenacyl) - 6 - chlorochrom - 2 - ene and 2,3 - dicarbomethoxy - 4 - (o - hydroxyphenacyl) 6,8 - dibromochrom - 2 - ene, respectively, together with the corresponding maleates and fumarates. 相似文献
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磺酰氨基酸钛配合物对Diels-Alder反应的对映选择性催化作用 总被引:3,自引:0,他引:3
研究了对甲苯磺酰基-L-缬氨酸、对甲苯磺酰基-L-苯丙氨酸、对甲苯磺酰基-L-亮氨酸、对甲苯磺酰基-L-异亮氨酸、对甲苯磺酰基-L-脯氨酸、1-萘磺酰基-L-缬氨酸、1-萘磺酰基-L-苯丙氨酸、1-萘磺酰基-L-亮氨酸和1-萘磺酰基-L-异亮氨酸与钛的配合物对环戊二烯与丙烯酸甲酯的环加成反应的对映选择性催化作用。萘磺酰基氨基酸钛配合物的对映选择性比对甲苯磺酰基氨基酸钛配合物好,氨基酸与钛比为2:1时比1:1要好得多。1-萘磺酰基-L-异亮氨酸与钛的2:1配合物的对映选择性最好,e.e.值为56%。 相似文献
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The incorporation of the “base-bearing amino acids”, DL - β - (uracil - 1 - yl)alanine 1 (Uala), DL - β - (thymin - 1 - yl)alanine 2 (Tala), DL - β - (cytosin - 1 - yl)alanine 3 (Cala) and DL - β - (adenin - 9 - yl 4 (Aala) into peptides has been studied. The carboxyl group of each of these compounds was protected by the formation of the ethyl ester. The t - butoxycarbonyl (t-BOC) group was suitable for the protection of the α-amino group of 1 but not that of 2, 3 and 4 because of the formation of ring substituted compounds. Peptides containing the amino acids 1–4 and L-serine were synthesised, however, by the mixed anhydride method; uracil, thymine and adenine residues needed no protection, neither did the cytosine residue provided that it was not present in the intermediate which was treated with ethyl chloroformate to produce the mixed anhydride. In this case reaction with the cytosine residue occurred. By these procedures, four protected dipeptides, namely α - N - t - BOC - L - seryl derivatives of 1–4 and three protected tetrapeptides, namely α - N - t - BOC - L - seryl - DL - β - (thymin - 1 - yl)alanyl - L - ethyl ester (t - BOC - Ser - Tala - Ser - Tala - OEt), t - BOC - Ser - Aala - Ser - Aala - OEt and t - BOC - Ser - Uala - Ser - Uala - OEt were obtained. For the protection of the α-amino group of 2 or 3 the formyl group was found to be satisfactory. 相似文献
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E. A. Maier B. Griepink J. Hinschberger T. Rymen 《Fresenius' Journal of Analytical Chemistry》1994,348(1-2):23-30
Summary A fly ash extract was prepared and studied for the homogeneity and the stability (CRM 429) with respect to five polychlorodibenzo-p-dioxins (D48, D54, D66, D67 and D70) and six polychlorodibenzofurans (F83, F94, F114, F121, F124 and F130). The certification exercise is described; the analytical techniques used for the certification and the quality control guidelines that were followed are also given. The difficulties encountered in the determination of F118 are discussed.Abbreviations CI
Confidence interval
- CV
Coefficient of variation
- D48
2,3,7,8-T4CDD
- D54
1,2,3,7,8-P5DD
- D65
1,2,3,4,6,9-H6CDD
- D66
1,2,3,4,7,8-H6CDD
- D67
1,2,3,6,7,8-H6CDD
- D70
1,2,3,7,8,9-H6CDD
- ECD
Electron capture detector
- FID
Flame ionization detector
- FT
Film thickness
- F83
2,3,7,8-T4CDF
- F89
1,2,3,4,8-P5CDF
- F94
1,2,3,7,8-P5CDF
- F114
2,3,4,7,8-P5CDF
- F118
1,2,3,4,7,8-H6CDF
- F119
1,2,3,4,7,9-H6CDF
- F121
1,2,3,6,7,8-H6CDF
- F124
1,2,3,7,8,9-H6CDF
- F127
1,2,4,6,8,9-H6CDF
- F130
2,3,4,6,7,8-H6CDF
- GC
Gas chromatography
- HR
High resolution (MS)
- H6CDD
Hexachlorodibenzo-p-dioxin
- H6CDF
Hexachlorodibenzofuran
- H7CDD
Heptachlorodibenzo-p-dioxin
- H7CDF
Heptachlorodibenzofuran
- IR
Infra Red spectroscopy
- IS
Internal standard
- LR
Low resolution (MS)
- MS
Mass spectrometry
- OCDD
Octachlorodibenzo-p-dioxin
- OCDF
Octachlorodibenzofuran
- P5CDD
Pentachlorodibenzo-p-dioxin
- P5CDF
Pentachlorodibenzofuran
- PCDD
Polychlorodibenzo-p-dioxin
- PCDF
Polychlorodibenzofuran
- RSF
Relative sensitivity factor
- SIM
Selected ion monitoring
- T4CDD
Tetrachlorodibenzo-p-dioxin
- T4CDF
Tetrachlorodibenzofuran 相似文献
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用分子动力学模拟退火找出苯并氮杂冠醚(C~1~8H~2~3O~7N)的最低能量构型后,用半经验量子化学方法AM1分别优化出了该苯并氮杂冠醚的顺、反式构型,对反式进行了前沿轨道、电荷密度计算,并作了振动分析。优化计算苯并氮杂冠醚反式构型的化合物结构数据与X射线晶体测定结果一致。对其振动分析,指认了化合物不同种类键的振动红外特征吸收峰。结构分析表明这种苯并氮杂冠醚的反式结构呈马蹄铁型,分子内有较大空腔,能够嵌入稀土金属阳离子,有较好的配位性。 相似文献
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Treatment of 2,2'-bis(bromomethyl)-1,1'-binaphthyl [(R,S)-2] with 1,1'-binaphthalene-2,2'-diol (+)-(R)-1 and cesium or potassium carbonate in refluxing acetone, gave the diastereoisomeric dioxacyclophanes (-)-(R,S)-3a and (+)-(R,R)-3b, both obtained in high yield, and the cyclic tetraether (+)-(R,R,R,S)-4 as isolated side product. Boron tribomide-promoted ether cleavage of 3a and 3b gave optically pure (-)-(S)-2 and (+)-(R)-2, respectively, and the recovered diol (+)-(R)-1. Alternatively, the same reaction sequence furnished the resolved diols (-)-(S)-1 and (+)-(R)-1 from (R,S)-1 and (+)-(R)-2, as well as optically pure 2,2'-bis(chloromethyl)-1,1'-binaphthyl (+)-(R)-5 from the racemic dibromide (R,S)-2 by using boron trichloride for ether cleavage. 相似文献
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The pentasaccharide α - Tyv - (1→3) - β - d - Man - (1→4) - α - l - Rha - (1→3) - d - Gal - (4←1) -α - d - Glc 1, the repeating unit of the O-specific polysaccharide chain of the lipopolysaccharide from S. Strasbourg, was obtained by glycosylation of benzyl - 2,6 - di - O - benzyl - 4 - O - (2,3,4 - tri - O - benzyl - 6 - O - benzoyl - α - d - glucopyranosyl) - β - d - galactopyranoside with 1,2 - methylorthoacetyl - 3 - O - acetyl - 4- O - [3 - O - (2,4 - di - O - acetyl - 3, 6 - dideoxy,- α - d - arabino - hexopyranosyl) - 2,4,6 - tri - O - acetyl - β - d - mannopyranosyl] - β - l - rhamnopyranose 3 followed by removal of protecting groups. The structure of the synthetic pentasaccharide was proved by methylation analysis and 13C NMR. 相似文献
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合成了两个新的有机晶体:反式-4-[4'-(N-羟乙基-N-甲基胺基)苯乙烯基]-N-甲基吡啶对甲苯磺酸盐trans-4-[4'-(N-hydroxyethyl-N-methylamino)styryl]-N-methylpyridiniumtoluene-p-sulfonate(简称HMASPS)和反式-4-[4'-(N-羟乙基-N-乙基胺基)苯乙烯基]-N-甲基吡啶对甲苯磺酸盐trans-4-[4'-(N-hydroxyethyl-N-ethylamino)styryl]-N-methylpyridiniumtoluene-p-sulfonate(简称HEASPS)。用X射线衍射方法对这两个单晶进行了结构测定。测试了它们频率上转换荧光及激光性质。在1064nm的ps脉冲激光的激发下,HMASPS和HEASPS在溶液中均发出~625nm的上转荧光和激光,并且有可观的激光效率。 相似文献
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Extract ofCroton humilis L. were shown to contain N - [N - (2 - methylpropanoyl) -l - glutaminoyl] - 2 - phenylethylamine, N - [N - 2R - methylbutanoyl) -l - glutaminoyl] - 2 - phenylethylamine, 2 - [N- (2 - methylpropanoyl)] - N - phenylethylglutarimide and 2 - [N- (2R - methylbutanoyl)] - N - phenylethylglutarimide. Structural proof was based on acid degradation, spectral studies as well as the synthesis of N - [N- (2- methylpropanoyl) -l - glutaminoyl] - 2 - phenylethylamine and 2 - [N - (2 - methylpropanoyl] - N - phenylethylglutarimide. 相似文献