A3型Corrole中位取代基对其β位^1H-NMR的影响

采用密度泛函(DFT)方法对八个中位有不同取代基的A3型corrole进行了几何结构优化和核磁共振(NMR)理论计算.几何优化结果显示5,10,15-三苯基corrole的两个环内NH异构体的中位苯环空间排布方向不同.此外,虽然A3型corrole两个环内NH异构体A和B的能量相差不大,但A和B分子的Boltzman分布概率却有较大的不同,且受取代基影响很大. 因而在计算NMR时必须对A和B异构体的理论化学位移做Boltzman统计平均处理.NMR计算结果表明,在B3LYP/6.311+G(2d,p)//B3LYP/6-31G(d,p)水平下可以得到较为合理的corrole的1H-NMR化学位移结果.β-位氢的化学位移与取代基Hammett常数σ-p的大小成正比关系.此外,由于corrole大环的低对称性,取代基对不同位置β-位氢的NMR影响程度不同,其β-位氢化学位移的大小和顺序与中位取代基的电子效应和corrole的立体结构因素有关.     

几种B环间位取代异黄酮衍生物的核磁共振谱理论研究(英文)

在B3LYP/6-31G**水平下优化了几种B环间位取代异黄酮衍生物的几何构型,在B3LYP/6-311G**水平下计算了该类化合物的核磁共振谱。研究结果表明:在1E!1H和2E～2H中的分子内氢键,其键长为0.1668nm,使整个分子形成一个四环的交叉共轭体系。从9位羟基取代对异黄酮衍生物NMR数据的影响来看,相邻的碳和相邻的氢化学位移的减少是由于电子云密度的增加和屏蔽作用的加强。而相邻碳的化学位移增加更大。此外,从取代基对化学位移的影响进行了讨论。邻对位氢的化学位移与取代基使苯环电子云密度增大的趋势相一致。A环和C环上的氢基本不受取代基的影响。对位碳的化学位移则与取代基使苯环电子云密度增大的趋势相反,邻位碳的化学位移变化趋势不明显。     

一种天然产物Wangzaozin A的细胞毒活性

从总序香茶菜Isodon racemosa (Hemsl) Hara植物中分离得到一个对人类肿瘤细胞Bel-7402和HD-8910具有毒活性的对映-贝壳衫烷型二萜Wangzaozin A化合物(1). 应用密度泛函理论(DFT)B3LYP方法, 对该分子的几何构型进行优化, 结果表明用B3LYP/6-31G(d)优化的几何参数与它的X射线衍射结构参数基本一致. 在优化的几何构型基础上, 采用规范不变原子轨道(GIAO)法, 在B3LYP理论水平分别用6-31G(d), 6-31G(d,p), 6-31+G(d,p)和6-31++G(d,p)基组进行核磁共振(NMR)化学位移值计算, 预测的1H和13CNMR化学位移值与实验值吻合; 统计误差分析表明, 用B3LYP/6-31G(d)优化的分子构型接近实际的分子构型. 因此, DFT方法适用这一类型化合物的构型和NMR参数进行预测. 在几何优化的基础上, 在B3LYP/6-31G(d)水平上, 对Wangzaozin A分子的静电位(MEP)进行理论计算. MEP三维图表明, 在Wangzaozin A分子中α-亚甲基环戊酮的羰基和羟基附近出现富电子区域(负电位), 起着供电子作用, 与受体的正电子区域结合. 这些结果从理论上支持了α-亚甲基环戊酮结构是一种抗肿瘤活性中心的看法.     

B环对位取代异黄酮化合物的核磁共振研究

对14个合成的B环对位取代异黄酮化合物核磁共振氢谱进行了研究.利用超导核磁共振归属了B环无取代异黄酮质子的化学位移,根据取代基化学位移的变化影响规律考察了取代基对分子的影响方式.研究结果表明,2'(6'),3'(5')位质子共振迁移分别与取代基参数σ_p和S_o线性相关,说明4'位取代基主要通过电子效应影响其间位质子,其磁各向异性仅影响邻位质子,该取代基对A环质子影响不大,而对C环尤其是对2-H影响较明显.     

取代基对corrole二阶非线性光学性质的影响

在6-31G(d,p)水平上用B3LYP方法对三苯基corrole(TPC)以及氟苯基corrole系列分子进行几何构型优化.用ZINDO/SOS方法计算了这些分子的一阶超极化率.计算结果表明:TPC分子由于其结构非中心对称使其具有大小为2.46×10-50 C3·m3·J-2的一阶超极化率.引入氟苯基后,氟取代苯基corrole系列分子的一阶超极化率均有显著提高,其中5位及10,15位氟苯基取代的corrole分子具有较大的一阶超极化率(3.71×10-49 C3·m3·J-2).氟苯基corrole系列分子一阶超极化率提高主要起源于分子的二能级分量及三能级分量显著增大,且二能级分量与三能级分量大小相当、符号相同.计算表明,二能级分量的增大主要来源于第三激发态(B1)与基态之间的偶极矩的变化.跃迁通道分析表明三能级分量的增大主要通过改变与结构敏感的激发态跃迁通道,即由TPC分子B带与Q带的耦合变成了氟苯基corrole分子B带内2个不同激发态的耦合.     

电子亲和势法判断负离子聚合单体的活性

提出了利用不同取代基烯类单体的电子亲和势来判断其负离子聚合反应活性的方法.采用密度泛函理论的B3LYP/6-31G(d)方法优化了不同取代基烯类单体几何构型,在B3LYP/6-311++G(3df,2p)水平上计算了其电子亲和势.通过电子亲和势计算值与文献报道实验数据比较,表明本文采用的计算方法是比较可靠的.结合不同取代基烯类单体的电子亲和势的计算结果,通过与Q-e关系及取代基常数σ数据进行比较表明,电子亲和势可以用来判断不同单体负离子聚合反应的活性高低.     

N5H5异构体的结构与稳定性的理论研究

采用密度泛函理论的B3LYP方法在6-311++G**基组水平上对N5H5氮氢化合物异构体可能存在的构型进行了几何优化, 得到23种稳定异构体, 并研究了这些异构体间可能的互变异构情况. 为了讨论N5H5异构体作为含能材料候选物质的可能性, 还采用了G3B3方法计算了能量, 并且计算了异构体的生成热(⊿Hf,298).结果表明, 在23种异构体中链状异构体最稳定, 四元环四氮烷异构体最不稳定, 存在一个N=N双键的异构体较同类异构体能量低, 较为稳定; N5H5氮氢化合物的生成热均为正, 其中异构体E1生成热最高. 估算了N5H5的摩尔体积, 由密度公式ρ=MT/Vmol,得到E1 的密度最大.     

咪唑类化合物在乙腈溶液中负氢解离焓的理论研究

在与实验对照的基础上优化出一套计算咪唑类化合物在乙腈溶液中负氢解离焓的理论方法, 即MP2/6-311++G(d,p)//B3LYP/6-31+G(d)结合IEF-PCM溶剂模型及UA0孔穴计算法. 在此基础上, 有目的地设计了14种咪唑类负氢给体, 并计算了其在乙腈溶液中的负氢解离焓, 系统分析了影响其负氢解离焓的各种因素. 结果表明, 取代基的电子效应、体系释放负氢后的芳构化能力、咪唑环2位的苯基对前线分子轨道的贡献程度、体系电荷的分布情况及溶剂化效应等多种因素均能影响咪唑负氢给体在乙腈溶液中的负氢解离焓.     

铁屎米酮类生物碱分子化学位移的理论研究

用B3LYP/6-311+G(d,p)方法优化了6种铁屎米酮类生物碱分子的结构,并用GI-AO方法计算了这些生物碱分子中1H和13C的化学位移.计算的化学位移与实验值符合得很好.     

脂肪族酯基选择性还原模型的建立

以不同烷基取代的酯作为模型, 对其进行NaBH4还原研究. 不同取代基酯的起始反应温度和半衰期显示出了明显的差别和一定的选择性; 用B3LYP/6-31++G(d,p)//HF/6-31G(d,p)方法计算得到的过渡态能量与实验得到的活化能变化趋势一致; 实验中观察到了奇偶碳效应; 对NaBH4还原酯基的溶剂影响进行了初步研究.     

Ab initio study of 2,4-substituted azolidines. II. Amino-imino tautomerism of 2-aminothiazolidine-4-one and 4-aminothiazolidine-2-one in water solution

The relative stabilities of the tautomers of 2-aminothiazolidine-4-one and 4-aminothiazolidine-2-one were calculated at the MP2/6-31+G(d,p) level by considering their mono- and trihydrated complexes. Single-point calculations at the MP4/6-31+G(d,p)//MP2/6-31+G(d,p) level of theory were performed to obtain more accurate energies. The values of proton transfer barriers in the isolated, mono- and trihydrated tautomers of 2-aminothiazolidine-4-one (2AT) and 4-aminothiazolidine-2-one (4AT) were calculated for two different mechanisms of tautomerisation. In the absence of water, the process of proton transfer should not occur. Addition of water molecules decreases the barrier making the process faster, as the participation of two water molecules in a proton transfer reaction is more favorable than the participation of only one water molecule. To estimate the effect of the medium (water) on the relative stabilities of the tautomers of the studied compounds we applied the polarizable continuum model (PCM). (13)C NMR chemical shieldings were calculated using the GIAO approach at MP2/6-31+G(d,p) optimized geometries. HF and the DFT B3LYP functional with 6-31+G(d,p) basis set were employed. The quantum chemical results for the chemical shifts in gas phase and in polar solvents (water and DMSO) were compared with experimental data. TD DFT B3LYP/aug-cc-pVTZ calculations were performed to predict the absorption maxima of tautomers A and B of 2AT and 4AT.     

NMR spectra of salicylohydroxamic acid in DMSO-d6 solution: a DFT study

The ¹H, ¹³C and ¹H, ¹³C COSY NMR spectra of salicylohydroxamic acid (sha) were measured in DMSO-d₆ solution. The B3LYP GIAO method with the 6-311++G(d,p) basis set was chosen to reproduce the experimental spectra. All possible zusammen and entgegen conformers of monomeric sha were computed. After geometry optimisation (B3LYP/6-311++G(d,p)) only nine independent models of the molecule were shown to be stable. Additionally, the NMR chemical shifts of the Onsager model of the most stable monomer were calculated. The computed chemical shifts for the labile protons for all aforementioned geometries meaningfully underestimated experimental results suggesting the existence of the H-bonded structure of sha in DMSO solution. The most probable two dimeric structures along with two solvent-bounded aggregates were subsequently calculated at the same level of theory. The best agreement was obtained for sha H-bonded with two DMSO molecules (confirmed by the absence of concentration effect). The relative error not exceeding 10 and 4% for chemical shifts in ¹H and ¹³C NMR spectra of sha–(DMSO)₂, respectively, showed that the applied method with the B3LYP/6-311++G(d,p) basis set was efficient to predict the NMR shifts of a compound with strong H-bonds. Thus, this allows to assign properly NMR resonances to specific structure formed in DMSO solution.     

Iminopropadienones R–NCCCO and carbon suboxide, C3O2. Theoretical and experimental C NMR spectra

The ¹³C NMR data of five iminopropadienones R–NCCCO as well as carbon suboxide, C₃O₂, have been examined theoretically and experimentally. The best theoretical results were obtained using the GIAO/B3LYP/6-31+G**//MP2/6-31G* level of theory, which reproduces the chemical shifts of the iminopropadienone substituents extremely well while underestimating those of the cumulenic carbons by 5–10 ppm. The computationally faster GIAO/HF/6-31+G**//B3LYP/6-31G* level is also adequate.     

Intramolecular hydrogen bond in the push–pull CF3-aminoenones: DFT and FTIR study,NBO analysis

Postulated conformers of trifluoromethylated β-aminoenones stabilized by intramolecular NH?O and N?HO bonds were studied by IR and NMR spectroscopy and evaluated with quantum chemical calculations (B3LYP/6-311+G(d,p), MP2/6-311+G(d,p)//B3LYP/6-311+G(d,p) and MP2/6-31G(d,p)) and NBO analysis. The influence of the nature of EWG, substituents at the nitrogen atom and double bond, and of orbital interactions of heteroatoms and double bonds in these structures on the proton affinity of basic and acid centers, strength of hydrogen bonds, and the energy of tautomeric transfers is discussed. The theoretical results agree satisfactorily with the experimental observations.     

33S NMR spectroscopy 3. Substituent effects on 33S NMR parameters in 2-substituted ethanesulfonates

33S NMR parameters (chemical shifts and linewidths) in 2-substituted sodium ethanesulfonates, XCH2CH2SO3Na (X = H, CH3, OH, SH, NH2, Cl, Br, NH3+) depend upon the electronic properties of substituents. To explain experimental results and obtain additional information on the origin of the observed substituent effect (SE), sulfur isotropic absolute shielding constants have been calculated at DFT level of theory (B3LYP/6-311++G(2d,p)) by gauge-including atomic orbitals (GIAO) method. Data have been interpreted with the aid of natural bond orbital (NBO) method and natural chemical shielding (NCS) analysis. It has been demonstrated that in the class of compounds considered the diamagnetic contribution to sulfur-shielding constant is constant and the observed upfield shift of 33S resonance induced by electron-withdrawing substituents (reverse chemical shift effect) can be related to variations of the paramagnetic contribution. Substituents with different electronic properties cause variations in the polarization of S-C and S-O bonds of the -C-SO3- moiety thus determining changes of the electron density at sulfur nucleus and consequently the expansion or contraction of 3p sulfur orbitals. Also oxygen lone-pairs and sulfur core 2p electrons can play an active role in determining the paramagnetic contribution to sulfur shielding. With regard to linewidth variations, they can be ascribed primarily to changes in the nuclear quadrupole coupling constant values. B3LYP/6-311++G(2d,p) method allows obtaining a good reproducibility of SE on the electric field gradient (EFG) at sulfur, although its values tend to be underestimated significantly. Moreover, 17O shielding constants have been calculated.     

Spectroscopic characterization and single molecule structures of N,N-bis-(3-phthalimidopropyl)-N-(2-hydroxyethyl)-N-propylammonium salts and their hydrates

N,N-Bis-(3-phthalimidopropyl)-N-(2-hydroxyethyl)-N-propylammonium salts and their hydrates have been characterized by FTIR, Raman and NMR spectroscopy. Also B3LYP and PM5 calculations have been carried out. The optimized bond lengths, bond angles and torsion angles calculated by B3LYP/6-31G(d,p) approach have been compared with the spectroscopic data. The screening constants for ¹³C and ¹H atoms have been calculated by the GIAO/B3LYP/6-31G(d,p) approach and analyzed. Linear correlations between the experimental ¹H and ¹³C chemical shifts and the computed screening constants confirm the optimized geometry.     

Beta-silyl-substituted silaadamantyl,silabicyclo[2.2.2]octyl,silanorbornyl, and 1-silacyclohexyl cations. A theoretical (DFT and GIAO NMR) study

Parent 1-silaadamant-1-yl (1+) and a series of mono-beta-silyl-substituted- (2-Me+, 2-F+, 2-Cl+, 2-Br+), bis-beta-silyl-substituted- (3-Me+), and tris-beta-silyl-substituted (4-Me+)-1-silaadamant-1-yl cations were studied by the DFT method at the B3LYP/6-31G(d,p) level and by GIAO NMR at the B3LYP/ 6-31G(d,p)//B3LYP/6-31G(d,p) level. The geometries, relative energies, NMR chemical shifts, and charge distribution in the bridgehead silylium ions are discussed and compared. The magnitude of the beta-silyl effect (the Si-C-Si+ hyperconjugation) is gauged as a function of structure. Related model studies on the silabicyclo[2.2.2]octyl (5+, 6+, 5a+, and 6a+), silanorbornyl (7+ and 8+), and silacyclohexyl cations (9+ and 10+) were carried out in which the effect of beta-silyl substitution on geometry, stability, and NMR chemical shifts was probed. The acyclic model Me3Si-CH2-Si+(Me)2 (11+) was used to gauge the influence of the twist angle between the p-orbital at Si+ and the C-Si bond on relative stability and on the changes in the 29Si NMR chemical shifts. Finally, interaction of 1+ with H2O and MeOH and 2-Me+ with H2O was also examined. The resulting optimized structures (12+, 13+, and 14+) and the computed NMR chemical shifts are most compatible with the formation of silaoxonium ions.     

Quantum chemical studies on prototautomerism of 1H‐imidazo[4,5‐c]pyridine

The structural features of the 1H‐imidazo[4,5‐c]pyridine (ICPY) tautomers and homodimers of the most stable tautomers have been studied by quantum chemical methods. FTIR and Raman spectra of the ICPY were recorded in the range of 4000–60 cm^?1 and 3500–5 cm^?1. The predominant tautomer among four possible isomers of ICPY were determined. The optimized geometries and vibrational frequencies of possible ICPY tautomers and dimers were computed by B3LYP/DFT method with 6‐311++G(d,p) and 6‐31G(d) basis sets. All vibrational frequencies assigned in detail with the help of total energy distribution (TED) and isotopic shifts. ICPY dimeric forms were also characterized according to their hydrogen bonding interactions, and it has been found that the most stable ICPY homodimer establishes moderate strong N ? H …N type hydrogen bond. ¹H NMR, ¹³C NMR, and ¹⁵N NMR properties have been calculated for all tautomeric forms using the gauge independent atomic orbital (GIAO) method. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Theoretical investigation on multinuclear NMR chemical shifts of some tris(trifluoromethyl)boron complexes

Tris(trifluoromethyl)boron complexes have unusual properties and may find applications in many fields of chemistry, biology, and physics. To gain insight into their NMR properties, the isotropic ¹¹B, ¹³C, and ¹⁹F NMR chemical shifts of a series of tris(trifluoromethyl)boron complexes were systematically studied using the gauge‐included atomic orbitals (GIAO) method at the levels of B3LYP/6‐31 + G(d,p)//B3LYP/6‐31G* and B3LYP/6‐311 + G(d,p)//B3LYP/6‐311 + G(d,p). Solvent effects were taken into account by polarizable continuum models (PCM). The calculated results were compared with the experimental values. The reason that the structurally inequivalent fluorine atoms in a specific species give a same chemical shift in experimental measurements is attributed to the fast rotation of CF₃ group around the B? C(F₃) bond because of the low energy barrier. The calculated ¹¹B, ¹³C(F₃), and ¹⁹F chemical shifts are in good agreement with the experimental measurements, while the deviations of calculated ¹³C(X, X = O, N) chemical shifts are slightly large. For the latter, the average absolute deviations of the results from B3LYP/6‐311 + G(d,p)//B3LYP/6‐311 + G(d,p) are smaller than those from B3LYP/6‐31 + G(d,p)//B3LYP/6‐31G*, and the inclusion of PCM reduces the deviation values. The calculated ¹⁹F and ¹¹B chemical shieldings of (CF₃)₃BCO are greatly dependent on the optimized structures, while the influence of structural parameters on the calculated ¹³C chemical shieldings is minor. Copyright © 2009 John Wiley & Sons, Ltd.     

Imidoylketene-alpha-oxoketenimine and alpha-oxoketene-alpha-oxoketene rearrangements. 1,3-shifts of substituted phenyl groups

1,3-phenyl shifts interconvert imidoylketenes 1 and alpha-oxoketenimines 2 and, likewise, alpha-oxoketenes 3 automerize by this 1,3-shift. These rearrangements usually take place in the gas phase under conditions of flash vacuum thermolysis. Energy profiles calculated at the B3LYP/6-31G(d,p) and B3LYP/6311 + G(3df,2p)//B3LYP/6-31G(d,p) levels demonstrate that electron donating substituents (D) in the migrating phenyl group and electron withdrawing ones (W) in the non-migrating phenyl group, can stabilise the transition states TS1 and TS2 to the extent that activation barriers of ca. 100 kJ mol(-1) or less are obtained; i.e. enough to make these reactions potentially observable in solution at ordinary temperatures. The calculated transition state energies DeltaG(TS1) show an excellent correlation with the Hammett constants sigma(p)(W) and sigma(p+)(D).