Carbonic acid: from polyamorphism to polymorphism

Layers of glassy methanolic (aqueous) solutions of KHCO3 and HCl were deposited sequentially at 78 K on a CsI window, and their reaction on heating in vacuo in steps from 78 to 230 K was followed by Fourier transform infrared (FTIR) spectroscopy. After removal of solvent and excess HCl, IR spectra revealed formation of two distinct states of amorphous carbonic acid (H2CO3), depending on whether KHCO3 and HCl had been dissolved in methanol or in water, and of their phase transition to either crystalline alpha- or beta-H2CO3. The main spectral features in the IR spectra of alpha- and beta-H2CO3 are observable already in those of the two amorphous H2CO3 forms. This indicates that H-bond connectivity or conformational state in the two crystalline phases is on the whole already developed in the two amorphous forms. The amorphous nature of the precursors to the two crystalline polymorphs is confirmed using powder X-ray diffraction. These diffractograms also show that alpha- and beta-amorphous H2CO3 are two distinct structural states. The variety of structural motifs found within a few kJ/mol in a computational search for possible crystal structures provides a plausible rationalization for (a) the observation of more than one amorphous form and (b) the retention of the motif observed in the amorphous form in the corresponding crystalline form. The polyamorphism inferred for carbonic acid from our FTIR spectroscopic and powder X-ray diffraction studies is special since two different crystalline states are linked to two distinct amorphous states. We surmise that the two amorphous states of H2CO3 are connected by a first-order-like phase transition.     

Vibrational spectra and rotational isomerism of ethyl trichloroacetate

The IR and Raman spectra of ethyl trichloroacetate (E-TCA) and its deuterate (E-TCA-d₅) have been measured in the liquid, glassy and crystalline states. Vibrational assignment was made by referring to isotopic wavenumber-shift, characteristic group frequencies of related esters and with the aid of a normal coordinate calculation on E-TCA and E-TCA-d₅. It is suggested that in the liquid and glassy states there exist two molecular forms (trans—trans—trans and trans—trans—gauche) with regard to the internal rotations about the ClC---C---O---CH₂CH₃ axis, and that the former persists in the crystalline state. The band pairs of E-TCA and the other ethyl esters are discussed in relation to the nature and number of rotational axes, effect of the heavy trichloromethyl group, and enhancement of band intensity by vibrational coupling.     

Conformation and vibrational spectra of 1-bromo-1,5-hexadiyne (bromobipropargyl)

The IR spectra of 1-bromo-1,5-hexadiyne (bromobipropargyl) as a vapour, liquid and crystalline solid and in several solvents have been recorded. Raman spectra were obtained for the liquid (including polarization measurements) and the crystal.The data were interpreted in terms of two conformers, trans and gauche, in the vapour and liquid states and one, trans, in the crystal. The conclusion that the trans conformer was the one present in the crystal was based on several independent pieces of evidence. Vibrational assignments were made, supported by normal coordinate calculations.     

Vibrational spectra and structure of 4-cyano-4′-pentalkoxybiphenyl in different physical states

The polymorphism, conformation mobility and structure of 4-cyano-4′-pentalkoxybiphenyl (5OCB) in different physical states are studied by IR spectroscopy. The spectra were measured in the frequency range 400–4000 cm⁻¹ at temperatures from 300 to 350 K. The IR spectra of 5OCB are modeled using the concept of conformational mobility of these molecules. An analysis of the experimental and theoretical spectra reveals absorption bands whose spectroscopic parameters are sensitive to variations of temperature (experiment) and conformation (theory); a relationship between these changes is established. It is concluded that the polymorphism of 5OCB is of conformation type. In the solid crystalline state, 5OCB molecules have conformations with a planar biphenyl fragment; the angle of orientation of the plane of the carbon framework of the alkyl radical relative to the biphenyl fragment decreases as the temperature increases from 35° in the solid crystalline state to 10° in the liquid crystalline and isotropic liquid states. In both of these states the biphenyl fragment becomes nonplanar. The angle between the phenyl rings is up to 30°. Saratov State University. Institute of Physics, Ukrainian Academy of Sciences. Samarkand State University. Translated fromZhurnal Strukturnoi Khimii, Vol. 39, No. 1, pp. 55–60, January–February, 1998. This work was supported by RFFR grant No. 97-03-32175a.     

The vibrational spectra, molecular structure and conformation of organic azides Part II. 2-Azido-1,3-butadiene

A sample of 2-azido-1,3-butadiene was synthesized from 4-bromo-1,2-butadiene and tetramethylguanidinium azide. Although the sample is highly explosive, we succeeded in making a structure determination by gaseous electron diffraction. IR spectra of the vapour, of the matrix isolated species in argon at 15 K, and of an amorphous and crystalline solid at 90 K were recorded. A Raman spectrum of the liquid, including semiquantitative polarization data, was obtained at 240 K.

The title compound was found to be planar with the CNN angle 117° oriented syn to the adjacent C=C double bond, the NNN angle was ca. 177° oriented anti to the C---N bond. The following bond distances (r_a) were obtained: N---N(N), 114.3; N---N(C), 125.3; C---N, 143.4; C=C, 135.0; and C---C, 146.7 pm.

No additional conformers were observed in the vapour, liquid, amorphous or crystalline states.     

聚甲基丙烯酸-对-甲氧基偶氮苯烷氧基酯的合成及柔性间隔基对液晶行为的影响

通过甲基丙烯酸钾盐与溴化物的反应合成了一系列柔性间隔基长度不同的甲基丙烯酸 对 甲氧基偶氮苯烷氧基酯（ＰＭＡＡＺＯｎ,ｎ＝２,３,４,５,６）,然后聚合成相应的聚合物．用１Ｈ ＮＭＲ和ＩＲ表征了聚合物的结构,ＧＰＣ测定了分子量,ＤＳＣ和偏光显微镜观测了液晶高分子的相行为和织构．研究了间隔基长度对织构、相变和热力学性质的影响,观测到聚合物的ＴＮＩ随间隔基的长度变化表现出的奇偶效应．     

The conformation and vibrational spectra of 1,5-hexadiene-3-yne (divinylacetylene) and perchloro-1,5-hexadiene-3-yne (perchlorodivinylacetylene)

Infrared spectra of 1,5-hexadiene-S-yne (divinylacetylene) have been recorded in the vapour phase, in solution and in the amorphous and crystalline solid states at 90 K in the region 4000–4020 cm^?1. Correspondingly, IR spectra ofperchloro-1,5-hexadiene-3-yne (perchlorodivinylacetylene) as a melt, as a solute in various solvents and as a solid at 90 K have been obtained. Raman spectra of the two compounds were recorded in the liquid (molten) state including polarization measurements, and as crystalline solids at 90 K.The spectral data indicate that each compound exists as one conformer only in the various states of aggregation. In divinylacetylene the molecular symmetry appears to be anti (C_2h) while for perchlorodivinylacetylene the symmetry is either C_2v (syn) or C₂ (gauche). Vibrational assignments for the spectra of both molecules are presented and the values are compared with the results of normal coordinate analyses.     

新型-meso-四(4-十四氨基甲酰苯基)卟啉及其-金属（Co）配合物的合成与液晶性能

对羧基苯甲醛和吡咯经缩合反应制得meso-四(4-羧基苯基)卟啉(1); 1与氯化亚砜反应得meso-四(4-氯甲酰基苯基)卟啉(2); 2与n-十四胺反应制得meso-四(4-十四氨基甲酰苯基)卟啉(3); 3与CoC_l2经配位反应合成了meso-四(4-十四氨基甲酰苯基)卟啉钴(4)。 3和4为新化合物,其结构经U-Vis, ¹H NMR和IR表征。偏光显微镜和DSC检测结果表明： 3和4具有液晶性能。     

Isomer populations in liquids for 1-isopropyl-3-methylimidazolium bromide and its iodide and their conformational changes accompanying the crystallizing and melting processes

Most ionic liquids (ILs) are characterized by the presence of some kind of isomer for component ions. We investigated the liquid and crystalline structures of 1-isopropyl-3-methylimidazolium halides ([i-C3mim]X, X = Br, I) by means of Raman scattering measurements backed up by density functional theory (DFT) calculations. The DFT calculations indicated that there are two stable rotational isomers of [i-C3mim](+), one of an asymmetric form (Asym) and the other a symmetric one (Sym). For both salts, it was revealed that Asym and Sym coexist in liquid states, in contrast to the presence of only Asym in crystalline states. We determined the isomer populations and showed that Asym is dominant in the liquid states of both salts (approximately 7/3). Conformational changes in [i-C 3mim](+) during the crystallizing and melting processes were observed by conducting simultaneous measurements using the techniques of Raman spectroscopy and calorimetry. We have revealed that the conformational change from Asym to Sym occurs gradually, with linking to melting in the premelting region. This is a conclusive observation of the structural changes of ILs in the premelting region and demonstrates the conformational changes between isomers during the crystallizing and melting processes.     

聚硅氧烷侧链液晶高分子的合成与表征

研究以对－烯丙氧基苯甲酸对－氰基苯酚酯为单体的聚硅氧烷侧链液晶高分子的合成方法。首先利用Williamson反应生成醚、羧酸酰化、酯化反应得到单体,然后利用硅氢化反应将单体接枝到聚甲基氢硅氧烷上得到目标产物。用IR,NMR及热台偏光显微镜等方法对单体和聚合物进行了结构表征和液晶行为分析。优化了对－烯丙氧基苯甲酸对－氰基苯酯为单体的聚硅氧烷侧链液晶高分子的合成工艺条件,提高了产率。样品表征结果证明单体和聚合物均呈现近晶液晶相,为特殊功能材料提供了原料。     

聚甲基丙烯酸4［（4＇－硝基－1＇硫酰基苯）－1－羟烷氧基本基］酯的合成

new series of sulfur-contalning side chain liquid crystalline polymers were described. Mesomorphic side chains with methylene spacer in different length have been synthesized and their structures were identified by NMR, IR and MS.The liquid crystalline nature of the polymers was characterlzed by microscopy.The Polymers have liquid crystalline nature.     

Synthesis and hydrolysis of fluoropyridinyl containing chlorosilanes

2-Fluoro-3-dimethylchlorosilylpyridine (A) and 3-fluoro-4-dimethylchlorosilylpyridine (B) were synthesized from the corresponding fluoro-lithio-pyridines and dimethyldichlorosilane at −76°C. The liquid products were unstable on standing. A and B were hydrolyzed in aqueous ammonia at room temperature to give disiloxanes which are stable crystalline solids. The new compounds were characterized by IR, ¹H NMR and MS.     

聚甲基丙烯酸4［（4＇－硝基－1＇硫酰基苯）－1－羟烷氧基本基］酯的合成

聚甲基丙烯酸４［（４＇－硝基－１＇硫酰基苯）－１－羟烷氧基本基］酯的合成张维邦，蒋，许家瑞，曾汉民（中山大学材料科学研究所广州５１０２７５）关键词含硫液晶单元，侧链液晶高分子，液晶合成与表征侧链高分子液晶是高分子液晶的重要组成部分，是当前高分子科学中...     

Peculiarities of the structure and intermolecular interactons in 4-n-ALKYL-4′-cyanobiphenyls studied by IR spectroscopy

Experimental and theoretical methods of IR spectroscopy have been used to study the peculiarities of the structure and of intermolecular interactions in the homologous series of 4-n-alkyl-4′-cyanobiphenyls (abbreviated to nCBs, where n is the number of carbon atoms in the alkyl radical). IR absorption spectra of nCBs (n = 4, 8, 9) were measured in the frequency range from 400 cm^?1 to 4000 cm^?1 and in the temperature range from 26° to 100°C, which corresponded to the crystalline, liquid crystalline and liquid states of the samples. The analysis of the measured spectra was performed with regard to available X-ray data on the structures of crystalline phases and to the theoretical modeling of IR spectra; a comparison with previously studied spectra of nCBs with n = 2 and 5 was made. Characteristic differences between the spectra of higher and lower homologues of nCBs were found. Changes in the conformation of nCB molecules with the change of temperature and the length of the alkyl radical are discussed.     

含聚碳酸酯、4-羟基苯甲酸、己二醇和1,4-苯二甲酸结构的嵌段共聚物的合成与表征

以端酰氯基团的热致液晶共聚酯ＨＴＨ ６和端酚羟基的聚碳酸酯（ＰＣ）齐聚物为原料，通过溶液缩聚法制备了含ＰＣ和ＨＴＨ ６的嵌段共聚物，并用ＩＲ、ＰＯＭ、ＤＳＣ、ＷＡＸＤ等手段对共聚物结构、热行为和结晶行为进了表征．ＤＳＣ和ＰＯＭ结果证明这些嵌段共聚物都属向列型热致性液晶．在２８０℃以下的温度范围内无相分离，而在较高温度（＞２８０℃）为两相结构．共聚物的结晶结构与ＨＴＨ ６相同，结晶度随ＨＴＨ ６含量增加而增加，结晶速度也受到ＰＣ含量的影响．     

AsCl(3): from the crystalline to the liquid state. XRD (176 < T (K) < 250) and WAXS (295 K) studies

This paper presents structural studies on crystalline and liquid AsCl(3), performed using X-ray diffraction (XRD) and wide-angle X-ray scattering (WAXS) in the 176-250 K temperature range and at 295 K for the crystalline and liquid samples, respectively. The XRD results, collected using a single-crystal diffractometer, show that AsCl(3) crystallizes in the orthorhombic system with P2(1)2(1)2(1) space group and the unit cell parameters a = 9.475(3) A, b = 11.331(2) A, and c = 4.2964(8) A at 221 K. This structure is stable in the temperature range 176-243 K. Above the melting point, at 257 K, transition to the liquid state is observed. The WAXS data were recorded up to a maximum scattering vector K(max) = 16 A(-1) and then converted to real space by the sine Fourier transform, yielding to the reduced radial distribution function (RRDF). For a series of models, based on the crystalline AsCl(3) structure, the intensity and RRDF functions have been computed and compared with the experimental data. These simulations indicate that the model consisting of six AsCl(3) molecules, arranged along the y axis, accounts satisfactorily for the experimental observation. The results of the structure analysis in both crystalline and liquid states are discussed in relation to the influence of the As lone electron pair.     

Curing of liquid crystalline epoxy resins with a biguanide

This work extends the authors' investigations on liquid crystalline epoxy resins prepared from diglycidyl ether of 4,4′-dihydroxybiphenyl (DGE-DHBP) and aliphatic dicarboxylic compounds (ADC) or difunctional aromatic compounds. Syntheses and properties of these liquid crystalline epoxy resins are described elsewhere. In this paper a study on the curing reaction of the above mentioned liquid crystalline epoxy resins is presented. Ortho-tolylbiguanide was applied as the curing agent. The curing reactions were investigated by differential scanning calorimetry, microscopic observations and IR spectroscopy. Depending upon the temperature program of curing, it was possible to obtain polymeric networks with liquid crystalline order. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 2739–2745, 1997     

Liquid crystalline nanosheet colloids with controlled particle size obtained by exfoliating single crystal of layered niobate k(4)nb(6)o(17)

Colloidally dispersed niobate nanosheets with the thickness of 1.8 nm and controlled mean lateral sizes of 0.15-7.8 mum were prepared and their liquid crystallinity was examined. The nanosheet colloids with different lateral sizes were obtained by exfoliation of single crystals of layered niobate K4Nb6O17 and subsequent ultrasonication. Naked-eye and microscope observations of the nanosheet colloids between crossed polarizers revealed liquid crystallinity of the sols characterized by birefringence as functions of the lateral sizes and concentration of the nanosheets. The nanosheet colloids with smaller lateral sizes (0.15-1.9 mum) varied from isotropic to biphasic (isotropic + liquid crystalline), and finally to fully liquid crystalline states as the colloid concentration increased. The phase transition concentrations (from isotropic to biphasic and biphasic to liquid crystalline) decreased with increasing aspect ratio (lateral-to-thickness ratio) of the nanosheets, almost in accordance with the prediction by Onsager theory, indicating that the liquid crystallinity is explained basically by excluded-volume effect between the nanosheets. On the other hand, the colloids with larger lateral sizes (6.2 and 7.8 mum) stably kept liquid crystalline state even at very low concentration (5.1 x 10-6 in volume fraction), which was much lower than that expected from the theory.     

Synthesis and characterization of liquid crystalline epoxy and co-polymerisation with a non-mesomorphic epoxy resin

A novel liquid crystalline epoxy resin based on the imine group was synthesised and structurally characterised by infrared (IR) and nuclear magnetic resonance (NMR) spectroscopy. The mesogenic behaviour of the monomer was measured by differential scanning calorimetry (DSC) and polarised optical microscopy (POM), and presented various textures in the extensive temperature range. Methyl nadic anhydride (MNA) was employed to cure the liquid crystalline epoxy resin and the curing process was investigated using POM and wide-angle X-ray diffraction (WAXD). Information about distribution of liquid crystalline epoxy resin in the blending system resulted from the FT-IR Imaging System, indicating that molecules of liquid crystalline epoxy resin can agglomerate to form anisotropic domains. The improvement in mechanical properties of diglycidyl ether of biphenol A (DGEBA) modified with liquid crystalline epoxy was achieved. Scanning electronic microscopy (SEM) showed that an extremely rough and highly deformed fracture surface can be obtained. DGEBA modified with liquid crystalline epoxy resin was characterised by dynamic mechanical analysis (DMA) for its thermal properties. The results indicate that the presence of the liquid crystal phase influences glass transition temperature (Tg).     

树枝状偶氮液晶高分子(PAMAM-MMAZO)的合成及表征

树枝状偶氮液晶高分子(PAMAM-MMAZO)的合成及表征;树枝状聚酰胺-胺;树枝状偶氮液晶;表面修饰;液晶性