On Diastereotopic Carbon Atoms in Natural Abundance Carbon-13 Magnetic Resonance Spectra

Diastereotopic nuclei are intrinsically nonequivalent both chemically and magnetically.¹ Magnetic nonequivalence is either isochronous or anisochronous depending upon whether the two nuclei in question are magnetically nonequivalent in the spin-coupling sense (unequally coupled to a third nucleus) or in the chemical-shift sense (different nuclear) shieldings).² While both isochronous and anisochronous magnetic non-equivalence have been thoroughly documented in ¹H- and ¹⁹F-nuclear magnetic resonance studies,^{1, 2} reported examples from natural abundance ¹³C-magnetic resonance (cmr) spectra are conspicuously rare.³     

Dioximes of Cortisol,Stereoisomer Identification by Carbon-13 Nuclear Magnetic Resonance

Treatment of cortisol with hydroxylamine hydrochloride yields mainly two dioximes, the EE and ZE stereoisomers. In the EE isomer, the hydroxyl at C-3 oxime, is oriented towards C-2 causing a large upfield shift on this carbon which is attributed to steric compression caused by the hydroxyl. In the ZE isomer, the hydroxyl points toward C-4. Here, steric compression affects carbons C-4 to C-6 causing a diamagnetic shift. The oxime at C-20 assumes only the E-configuration because of steric hydrance.     

Carbon-13 NMR Spectrum of Bilirubin

The structure of bilirubin and of bilirubin derivatives has been studied by various physical techniques, including optical spectroscopy^(1,2), optical rotatory dispersion,⁽⁴⁾ isotope exchange⁽⁵⁾ and proton magnetic resonance spectroscopy^(2,3,5). A good deal of chemical information on bilirubin is also available^(6). The interpretation of most of the experimental results, however, have been inconclusive and different possible structures of the molecule could be shown to accommodate the experimental data.     

Carbon-13 Magnetic Resonance Spectral Studies of Quinoline Derivatives. Assignments of Bridgehead Carbons

Evidence is presented to confirm the assignments of the bridgehead carbon atoms of quinoline. The chemical shifts of C-9 and C-10 in a series of methylquinoline derivatives were determined and their respective assignments deduced from a consideration of shielding effects. The selection of suitable reference compounds is discussed.     

The Far-Infrared Laser Magnetic Resonance Spectrum of CH2F

Far-infrared laser magnetic resonance (FIR-LMR) spectra due to the CH2F radical have been recorded on seven laser lines at wavelengths between 301 and 568 μm. Observed resonances were assigned to fine and hyperfine components of pure rotational transitions of CH2F in the ground vibrational state and the first excited state of the nu4 out-of-plane bending mode. All assigned transitions obey a-dipole selection rules. The data were combined with previously reported microwave results (Y. Endo, C. Yamada, S. Saito, and E. Hirota, J. Chem. Phys. 79, 1605 (1983)) and subjected to a least-squares fit to determine the parameters of the effective Hamiltonian describing the v4 = 0 and 1 vibrational levels of the CH2F radical. Copyright 1999 Academic Press.     

The far-infrared Laser Magnetic Resonance Spectrum of the OH radical

The far-infrared Laser Magnetic Resonance (LMR) Spectrum of the OH radical in the v = 0 level of the X²Π state has been studied in detail. All transitions that are accessible with currently available laser lines have been recorded. The measurements have been analyzed and subjected to a single least-squares fit using an effective Hamiltonian. The data provide primary information on the rotational and fine-structure intervals between the lowest rotational levels and the parameter values determined in the fit are $\text{A}\text{?}{}_0\text{= ?4168.63913(78)}\text{GHz}$, $\text{γ}\text{?}{}_0\text{= ?3.57488(49)}\text{GHz}$, B₀ = 555.66097(11) GHz, D₀ = 0.0571785(86) GHz.     

二维共价有机骨架中的直接激子和间接激子

本文利用基于GW方法和Bethe-Salpeter方程的第一性原理计算,研究了两种二维共价有机骨架材料(COF)的激发态性质. 单层COF是直接带隙材料,而体相COF呈现间接带隙. 根据直接激子计算的体相COF的光学带隙和吸收光谱与实验一致,而由位于导带底的光生电子和位于价带顶的空穴形成的间接激子能量的理论计算值远低于实验荧光光谱的测量值. 研究表明,可以排除间接带隙COF材料的发光由声子主导的可能性. 研究认为体相COF的发光可能源于缺陷处直接激子的复合. 体相COF的AA堆叠结构导致其带隙是间接的. 如果将堆叠方式由AA变成AB,体相COF将转变成直接带隙材料,它的发光效率可能会增强.     

Carbon-13 Nuclear Magnetic Resonance Studies of Aspergillomarasmine A,Anhydroaspergillomarasmine B and of Aspergillomarasmine A Ca+2 Chelate

Carbon-13 NMR determinations have been carried out on aspergillomarasmine A, anhydroaspergillomarasmine B, isolated from different species of fungi and comparisons allow the attribution of the signals to all carbon atoms. Changes observed in the spectrum by forming the 1:1 che-late of aspergillomarasmine A and the fact that aspergillomarasmine B cannot give chelates, lead to a proposal for the structure of this complex.     

1H and C-13 Nuclear Magnetic Resonance of Tiaprofenic Acid

¹H-NMR spectrum of tiaprofenic acid in CDCI3 was obtained and proton chemical shifts from tetramethylsilane were assigned to each proton and set of equivalent protons of the molecule. The hydroxy proton of the carboxylic acid group was confirmed by deuterium exchange. The natural abundance C-13 nuclear magnetic resonance spectrum of the compound in CDCI3 was recorded using Fourier transorm technique. The chemical shifts of carbon resonances have been assigned on the basis of the chemical shift additivity theory and the signal multiplicity observed in the single frequency off-resonance decoupled (SFORD) spectrum. Also comparison with carbon chemical shifts of model compounds were useful.     

Carbon-13 Chemical Shift Assignment of β-Cedrene and Some Derivatives

Carbon-13 NMR spectral assignments have been obtained for β-cedrene and three derivatives: β-cedren-9-ol, its acetate and β-cedren-9-one, by combination of two-dimensional NMR techniques and shift reagent experiment.     

不同培肥土壤颗粒有机碳的13C核磁共振与红外光谱对比分析

为明确颗粒有机碳在土壤固碳中的作用机制,对比研究了不同有机培肥土壤颗粒有机碳的结构差异。以单施化肥处理为对照,选择了四种有机物料进行定位培肥试验,利用13C NMR和红外光谱技术对比分析不同有机培肥对土壤颗粒有机碳结构的影响。结果表明：颗粒有机碳以脂肪碳和含氧基团为主,脂化度高于75%,含氧官能团含量高于50%;不同有机培肥对土壤颗粒有机碳结构的影响差异性显著,树叶培肥在提高颗粒有机碳芳香度的同时,亲水性也大幅度提高,比单施化肥处理(对照)提高了0.78%;短期内,牛粪、秸秆和树叶培肥均可提高土壤颗粒有机碳的芳香度,但从长远角度分析,牛粪和秸秆培肥更利于土壤颗粒有机碳的稳定,尤其是秸秆培肥,其颗粒有机碳的芳香度分别比对照和牛粪培肥高0.35%和0.11%,而亲水性远低于二者;红外光谱与核磁分析的结果基本一致,红外光谱可用于大量样品的颗粒有机碳结构初步筛选。     

载氧环境下脉冲放电等离子体修复污染土壤体系中自由基的发射光谱

基于发射光谱检测方法的优越性以及在高级氧化降解体系中·OH和·O的重要作用,本研究采用发射光谱检测技术测定载氧环境下脉冲放电等离子体(pulsed discharge plasma, PDP)修复污染土壤体系中·OH和·O相对发射光谱强度的变化。研究建立了针-网式PDP修复污染土壤体系,利用光谱仪检测该PDP体系在载氧环境下所生成的·OH和·O的相对发射光谱强度。通过对比实验分别考察了不添加土壤、添加原土、添加有机污染土壤和添加有机-重金属复合污染土壤的PDP体系中·OH和·O的相对发射光谱强度变化,同时考察了脉冲峰值电压、电极间距和O₂体积流量变化对·OH和·O的相对发射光谱强度的影响。研究结果表明：添加土壤有利于放电的发生,进而提高了PDP体系中·OH和·O的生成;添加有机污染土壤的PDP体系中·OH和·O发射光谱强度较原土体系中低,证明了PDP体系中·OH和·O对有机物的氧化作用;重金属离子的加入对于PDP体系中有机物的降解有积极的促进作用。同时,脉冲峰值电压和O₂体积流量的增加有利于PDP体系中·OH和·O的产生,而电极间距的增加不利于PDP修复污染土壤体系中·OH和·O的生成。本研究在说明PDP用于污染土壤修复体系中·OH和·O的关键作用的基础上,分析了PDP用于污染土壤修复过程中体系主要因素变化对体系中主要自由基含量的影响规律。     

X射线光电子能谱与13C核磁共振在生物质碳表征中的应用

近年来,生物质碳(biochar)作为新型吸附剂被广泛研究。但由于制备biochar的生物质原料和热解温度的不同,使biochar的结构和组成存在差异,从而影响其对污染物的吸附。目前关于biochar的结构和组成的研究还不够全面。因此,结合了能谱与光谱分析的手段,对biochar的结构和组成进行了深入的分析。选取木质类(柳树枝条)和草类(水稻秸秆)作为原料,分别在不同热解温度(300,450和600℃)下制得biochars,并对biochars样品进行元素分析、X射线光电子能谱分析(XPS)和固态13 C核磁共振(13 C NMR)研究,以阐明不同热解温度和生物质来源的biochars的结构和组成。结果显示:biochar的H/C,O/C和(O+N)/C的比值随着热解温度的升高而降低;草类biochar比木质类biochar具有更高的灰分含量和表面极性;木质类biochar的矿物主要分布在样品颗粒内部,其表面被有机质覆盖,而草类biochar部分矿物暴露在样品颗粒表面;13 C NMR显示低温制得的biochar主要由芳香碳、脂肪碳、羧基和羰基碳组成,高温制得的biochar主要由芳香碳组成,且低温制得biochars中,木质类biochars比草类biochars含有更高的木质素的残留碳结构,这是由于木质类biochars原材料中含有更高的木质素。     

微波强场中的光谱激发现象

本文报道了元素，化合物和放电灯在微波强场产生的激发现象。介绍了一种在微波强场中产生原子发射光谱的新方法。采用作者自行改制的微波激发装置，即可使固态的元素和化合物产生光谱辐射，也可使各种放电灯和气体光谱管得以激发，用一种装置实现了几种装置的功能，对于该方法存在的问题，文中也作了一定的说明。     

单层石墨烯杨氏模量的理论模型

石墨烯力学性能的研究对其在半导体技术中的应用是十分重要的,本文基于半连续体模型并结合石墨烯纳米结构特性,通过对原子的描述构建了石墨烯形变分量和位移分量的新关系,从而给出了单层石墨烯结构形变能,并计算了不同尺寸单层石墨烯的杨氏模量值.通过对不同方向杨氏模量的分析,讨论了单层石墨烯的手性行为.结果表明:随着尺寸的增加,单层石墨烯两个方向的杨氏模量分别趋于0.746 TPa和0.743 TPa,当尺寸相同时,两方向杨氏模量的最大差值不超过0.003 TPa,此结果与文献报道结果相符.在小应变情况下,单层石墨烯薄膜呈各向同性,且薄膜尺寸变化对该特性影响不大.该计算结果对研究石墨烯的其它力学特性提供一定的参考价值.     

几种含吡啶环的双醛腙类化合物的结构与光谱性质

采用DFT/B3LYP方法在3-21+G基组下对4种含吡啶环的双醛腙类化合物进行基态(S0)构型优化, 并用单组态相互作用方法(CIS)优化四种化合物分子的激发态(S1)结构, 从理论上探讨了四种化合物的分子轨道能量、电子吸收和发射光谱等性质与结构的关系, 并与实验值进行了对比, 发现理论计算数据能够与实验结果基本一致. 通过对分子中前线轨道能量的计算, 揭示了不同取代基对材料光电活性的影响, 即分子中的共轭体系增大, 吸收光谱波长也随之红移. 根据化合物的吸收和发射光谱的计算数据推测化合物D是这四种化合物中最可选的电子传输材料及光活性材料.     

红外光谱等方法在电机易烧毁事故分析中的应用

本文应用红外光谱,气相色谱等方法对１０３２三聚氰胺醇酸绝缘漆的稀释剂“二甲苯”进行了成份分析,结论是该稀释剂根本不是二甲苯,而是以苯,甲苯,卤代烃,二甲苯,和甲醇组成的混合液,找出了电机易烧毁的原因。     

双层磁性薄膜系统中铁磁共振性质

利用能量极小原理研究了双层磁性薄膜系统中的铁磁共振特性,给出共振频率与线宽随外加磁场的变化关系.以及考虑应力各向异性、交换各向异性和单轴各向异性后,系统共振频率与线宽的变化情况.数值计算结果表明:外应力场和交换各向异性场对铁磁共振频率、频谱宽度以及磁化行为均有影响.     

几种含吡啶环的双醛腙类化合物的结构与光谱性质

采用DFT/B3LYP方法在3-21+G基组下对4种含吡啶环的双醛腙类化合物进行基态(S_0)构型优化,并用单组态相互作用方法(CIS)优化四种化合物分子的激发态(S_1)结构,从理论上探讨了四种化合物的分子轨道能量、电子吸收和发射光谱等性质与结构的关系,并与实验值进行了对比,发现理论计算数据能够与实验结果基本一致.通过对分子中前线轨道能量的计算,揭示了不同取代基对材料光电活性的影响,即分子中的共轭体系增大,吸收光谱波长也随之红移.根据化合物的吸收和发射光谱的计算数据推测化合物D是这四种化合物中最可选的电子传输材料及光活性材料.