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1.
Preparation and Spectroscopic Investigations of Highly Branched Functional Siloxanes The preparation of the siloxanes [(Me3SiO)3SiO]n(Me3SiO)3?nSiX and (Me3SiO)3Si[OSi(OSiMe3)2]2X (n = 1?3, X = H, Cl, OC2H5, OH) is described. The hydride-siloxanes and the siloxanoles have been investigated by i.r. and 29Si-n.m.r. spectroscopy. The frequencies of the Si? H stretching vibration, the 29Si? 1H coupling constants and the 29Si-chemical shifts of the Si(H) signal for the hydride-siloxanes as well as the frequencies of the (Si)O? H stretching vibration, the relative (Si)O? H acidity, and the 29Si-chemical shifts of the Si(OH) signal for the siloxanoles show a dependence on the number of the (Me3SiO)3SiO groups. The spectroscopic data are discussed with respect to the silicate environment of the Si(H) and Si(OH) atom, respectively. In the siloxanoles intramolecular hydrogen bondings were observed. 相似文献
2.
Polymerization behavior of hexamethylcyclotrisiloxane (D3) in toluene solution with the use of benzyltrimethylammonium bis(o-p;henylenedioxy)phenylsiliconate as a catalyst, dimethyl sulfoxide as promoter, and adventitious moisture as initiator was investigated. The polymerization system gives a linear difunctional polymer, HO(Me2SiO)xH, with a molecular weight which is inversely proportional to the amount of water reacted rather than to the amount of catalyst employed. The polymerization in the presence of H2O gives rise to molecular weight distributions very close to Poisson distributions. The normalized experimental GPC curve agrees very well with the theoretical GPC curve calculated from the polymerization scheme: \documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{*{20}c} {{\rm H}_2 {\rm O} + ({\rm Me}_2 {\rm SiO})_3 \to {\rm HO}({\rm Me}_2 {\rm SiO})_3 {\rm H}} \\ {{\rm HO(Me}_{\rm 2} {\rm SiO)}_{\rm 3} {\rm H} + {\rm N(Me}_{\rm 2} {\rm SiO)}_{\rm 3} \to {\rm HO}({\rm Me}_2 {\rm SiO})_{3(n + 1)} {\rm H}} \\ \end{array} $$\end{document} Polymerization carried out in the combined presence of H2O and ROH, where R is Me or Me3Si, gives rise to bimodal molecular weight distributions. The resulting polymers consist of HO(Me2SiO)2xH and RO(Me2SiO)xH. The molecular weight of the former is twice that of the latter, and their proportion depends on the ratio of H2O to ROH. The system is a special type of “living” polymer. 相似文献
3.
The structural parameters of the completely relaxed 4–21G ab initio geometries of more than 30 basic organic compounds are compared to experimental results. Some ranges for systematic empirical corrections, which relate 4–21G bond distances to experimental parameters, are associated with total energy increments. In general, for the currently feasible comparisons, the following corrections can be given which relate calculated distances to experimental rg parameters and calculated angles to rs-structures For CC single bond distances, deviations between calculated and observed parameters (rg) are in the ranges of ?0.006(2) to ?0.010(2) Å for normal or unstrained hydrocarbons; ?0.011(3) to ?0.016(3) Å for cyclobutane type compounds; and +0.001(5) to +0.004(4) Å for CH3 conjugated with CO. For CO single bonds the ranges are ?0.006(9) to +0.002(3) Å for CO conjugated with CO; and ?0.019(3) to ?0.027(9) Å for aliphatic and ether compounds. A very large and exceptional discrepancy exists for the highly strained ethylene oxide, rs — re = ?0.049(5) Å and in CH3OCH3 and C2H5OCH3 the rs — re differences are ?0.029(5), ?0.040(10) and ?0.025(10) Å. Some of these discrepancies may also be due to deficiencies of the microwave substitution method caused by atomic coordinates close to inertial planes. For CN bonds, two types of NCH3 corrections are from +0.005(6) to ?0.006(6) and from ?0.009(2) to ?0.014(6) Å; and the range for NCO is +0.012(3) to +0.028(4) Å. For isolated CC double bonds the range is + 0.025(2) to +0.028(2) Å. For conjugated CC double bonds the correction is less positive (+0.014(1) Å for benzene). For CO double bonds the corrections are ?0.004(3) to +0.003(3) Å. For bond angles of type HCH, CCH, CCC, CCO, CCO, OCO, NCO and CCC the corrections are of the order of magnitude about 1–2° (or better). Angles centered at heteroatoms are less accurate than that, when hydrogen atoms are involved. Differences in HOC and NHC angles were found in a range of ?2.3(5)° to ?6.2(4)°. 相似文献
4.
Stanislav Bhm Diana Antipova Josef Kuthan 《International journal of quantum chemistry》1997,62(3):315-322
Two alternative dehydration reactions C(OH)4 → (HO)2CO + H2O and C(OH)4 + H2O → (HO)2CO + 2H2O are studied by ab initio Becke3LYP/6–311 + G** and MP2/6–31G** methods. Calculated energy and geometry characteristics of intermediates and transition states predict a catalytic effect of one water molecule and the exothermism of the transformations. Relevant HF/6–311 + G**, HF/6–31G**, HF/6–31G, and HF/3–21G calculations were performed for comparison. © 1997 John Wiley & Sons, Inc. 相似文献
5.
The etherate of (Ph2SiO)8[Al(O)OH]4 can be transformed into the pyrazine adduct (Ph2SiO)8[Al(O)OH]4 · 3N(C2H2)2N ( 1 ), the ethyl acetate adduct (Ph2SiO)8[Al(O)OH]4 · 3H3C-C(O)OC2H5 ( 2 ), the 1,6-hexane diol adduct (Ph2SiO)8[Al(O)OH]4 · 2HO–CH2(CH2)4CH2–OH ( 3 ) and the 1,4-cyclohexane diol adduct (Ph2SiO)8[Al(O)OH]4 · 4HO–CH(CH2CH2)2CH–OH ( 4 ). In all compounds the OH groups of the starting material bind to the bases through O–H ··· N ( 1 ) or O–H ··· O hydrogen bonds ( 2 , 3 , 4 ) as found from single-crystal X-ray diffraction analyses. Whereas in 1 only three of the central OH groups bind to the pyrazines, in 2 two of them bind to the same carbonyl oxygen atom of the ethyl acetate resulting in an unprecedented O–H ··· O ··· H–O double hydrogen bridge. The hexane diol adduct 3 in the crystal forms a one-dimensional coordination polymer with an intramolecularly to two OH groups grafted hexane diol loop, while the second hexane diol is connecting intermolecularly. In the cyclohexane diol adduct 4 all OH groups of the central Al4(OH)4 ring bind to different diols, leaving one alcohol group per diol uncoordinated. These “free” OH groups form an (O-H ··· )4 assembly creating a three-dimensional overall structure. When reacting with (Ph2SiO)8[Al(O)OH]4 lysine loses water, turns into the cyclic 3-amino-2-azepanone, and transforms through chelation of one of the aluminum atoms the starting material into a new polycycle. The isolated compound has the composition (Ph2SiO)12[Al(O)OH]4[Al2O3]2 · 4 C6H12N2O · 6(CH2)4O ( 5 ). 相似文献
6.
Leon G A van de Water Martijn A Zwijnenburg Willem G Sloof Jan C van der Waal Jacobus C Jansen Thomas Maschmeyer 《Chemphyschem》2004,5(9):1328-1335
The effect of the isomorphous substitution of some of the Si atoms in ZSM‐5 by Ge atoms on the Brønsted acid strength has been investigated by i) DFT calculations on cluster models of the formula ((HO)3SiO)3‐Al‐O(H)‐T‐(OSi(OH)3)3, with T=Si or Ge, and ((HO)3SiO)3‐Al‐O(H)‐Si‐(OGe(OH)3)(OSi(OH)3)2, ii) a 31P NMR study of zeolite samples contacted with trimethyl phosphine oxide probe molecules and iii) a X‐ray photoelectron spectroscopy (XPS) study of ZSM‐5 and Ge‐ZSM‐5 samples. The calculations reveal that the effect of Ge incorporation on the framework acidity strongly depends on the degree of substitution and on the exact T‐atom positions that are occupied by Ge. High Ge concentrations allow for enhanced stabilisation of the deprotonated Ge‐ZSM‐5 through structural relaxation, resulting in a slightly higher acidity as compared to ZSM‐5. This structural relaxation is not achievable in Ge‐ZSM‐5 with a low Ge content, which therefore has a slightly lower acidity than ZSM‐5. The NMR study indicates no difference between the Brønsted acidity of ZSM‐5(47) and Ge(0.09)ZSM‐5(36). Instead, evidence for the presence of a substantial amount of Ge? OH groups in the Ge‐containing samples was obtained from the NMR results, which is consistent with earlier FTIR studies. The XPS results do not point to an effect of Ge on the framework acidity of ZSM‐5(47), instead, the results can be best interpreted by assuming the presence of additional Ge? OH and Si? OH groups near the surface of the Ge(0.08)ZSM‐5(47) sample. 相似文献
7.
Humberto Soscun Javier Hernndez Olga Castellano 《International journal of quantum chemistry》2000,76(1):1-9
The topologic properties of the electronic charge distribution of conformers of H3SiO(H)AlH3 molecule hydroxyl groups of zeolites are reported. The studied properties—total density, Laplacian density, and bond ellipticity—were evaluated at the position of the critical points of the O Si, O Al, and O H bonds, by using Hartree–Fock and second‐order Møller–Plesset levels of theory, and the STO/6‐31+G(d,p) standard basis set. For the H3SiO(H)AlH3 molecule, four conformers are identified. It is demonstrated that for these conformers, the total density and Laplacian density remain almost constant by effect of the rotations of the T H bonds, T=(Si, Al), around the corresponding O T bonds, respectively. However, these rotations induce sensible variations in the ellipticity at the position of the critical point of the O Al bonds, which are reflected in the OH bond distance, OH vibrational mode, and the stabilization energy of conformers. These results lead to a linear relationship between the magnitude of the bond ellipticity at the critical point of the O Al bonds and the frequency values of the OH bonds, with a correlation coefficient of r2=0.98. In addition, a good linear relationship between the ellipticity of the O Al bond and the pattern of the stabilization energy of conformers was also found. © 1999 John Wiley & Sons, Inc. Int J Quant Chem 76: 1–9, 2000 相似文献
8.
4‐Fluorinated levoglucosans were synthesised to test if OH???F H‐bonds are feasible even when the O???F distance is increased. The fluorinated 1,6‐anhydro‐β‐D ‐glucopyranoses were synthesised from 1,6 : 3,4‐dianhydro‐β‐D ‐galactopyranose ( 8 ). Treatment of 8 with KHF2 and KF gave 43% of 4‐deoxy‐4‐fluorolevoglucosan ( 9 ), which was transformed into the 3‐O‐protected derivatives 13 by silylation and 15 by silylation, acetylation, and desilylation. 4‐Deoxy‐4‐methyllevoglucosan ( 19 ) and 4‐deoxylevoglucosan ( 21 ) were prepared as reference compounds that can only form a bivalent H‐bond from HO? C(2) to O? C(5). They were synthesised from the iPr3Si‐protected derivative of 8 . Intramolecular bifurcated H‐bonds from HO? C(2) to F? C(4) and O? C(5) of the 4‐fluorinated levoglucosans in CDCl3 solution are evidenced by the 1H‐NMR scalar couplings h1J(F,OH) and 3J(H,OH). The OH???F H‐bond over an O???F distance of ca. 3.0 Å is thus formed in apolar solvents, at least when favoured by the simultaneous formation of an OH???O H‐bond. 相似文献
9.
Dietmar Seyferth Cynthia Nivert Rudie Mara Ozolins Nestle 《Journal of organometallic chemistry》1979,178(1):227-247
The reaction of bromomethylidynetricobalt nonacarbonyl or, more effectively, of methylidynetricobalt nonacarbonyl with diverse silicon hydrides (R3SiH, Ph3SiH, Me2(EtO)SiH, RnCl3-nSiH (n = 02), etc. results in formation of silylmethylidynetricobalt nonacarbonyl complexes. Silicon-functional interconversions such as SiCl → SiOH, SiCl → SiOMe, SiOH → SiF, and SiOH → SiOSiMe3, have provided still other substituted silylmethylidynetricobalt nonacarbonyl complexes, generally in high yield. The compounds Me(HO)2SiCCO3(CO)9 and (HO)3SiCCo3(CO)9 have been incorporated into methylsilicone polymers by H2SO4-induced reactions with cyclo-(Me2SiO)3. 相似文献
10.
Jens Beckmann Dainis Dakternieks Andrew Duthie Megan L. Larchin Edward R. T. Tiekink 《应用有机金属化学》2003,17(1):52-62
The tert‐butoxychlorosilanes (t‐BuO)3SiCl ( 1 ), (t‐BuO)2SiCl2 ( 2 ), and [(t‐BuO)2SiCl]2O ( 3 ) were prepared by the reaction of SiCl4 or (Cl3Si)2O with t‐BuOK. Subsequent hydrolysis afforded the tert‐butoxysilanols (t‐BuO)3SiOH ( 4 ), (t‐BuO)2Si(OH)2 ( 5 ), HO[(t‐BuO)2SiO]2H ( 6 ) in high yields. The controlled condensation of 2 and 5 provided HO[(t‐BuO)2SiO]3H ( 7 ) in reasonable yields. The tendency of 4 – 7 to undergo self‐condensation is small, thus enabling their characterization in solution and in the solid state by 29Si NMR spectroscopy, IR spectroscopy and electrospray mass spectrometry, and in the case of 4 and 6 also by X‐ray diffraction. The key feature of the crystal structures is the incorporation of tert‐butoxy groups into the hydrogen bonding. The results obtained are discussed in relation to the sol–gel process. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
11.
Qiang‐Gen Li Chao Deng Yi Ren Ning‐Bew Wong San‐Yan Chu Xin Wang 《International journal of quantum chemistry》2008,108(1):142-150
Computational investigations by an ab initio molecular orbital method (HF and MP2) with the 6‐311+G(d,p) and 6‐311++G(2df, 2pd) basis sets on the tautomerism of three monochalcogenosilanoic acids CH3Si(?O)XH (X = S, Se, and Te) in the gas phase and a polar and aprotic solution tetrahydrofuran (THF) was undertaken. Calculated results show that the silanol forms CH3Si(?X)OH are much more stable than the silanone forms CH3Si(?O)XH in the gas‐phase, which is different from the monochalcogenocarboxylic acids, where the keto forms CH3C(?O)XH are dominant. This situation may be attributed to the fact that the Si? O and O? H single bonds in the silanol forms are stronger than the Si? X and X? H single bonds in the silanone forms, respectively, even though the Si?X (X = S, Se, and Te) double bonds are much weaker than the Si?O double bond. These results indicate that the stability of the monochalcogenosilanoic acid tautomers is not determined by the double bond energies, contrary to the earlier explanation based on the incorrect assumption that the Si?S double bond is stronger than the S?O double bond for the tautomeric equilibrium of RSi(?O)SH (R?H, F, Cl, CH3, OH, NH2) to shift towards the thione forms [RSi(?S)OH]. The binding with CH3OCH3 enhances the preference of the silanol form in the tautomeric equilibrium, and meanwhile significantly lowers the tautomeric barriers by more than 34 kJ/mol in THF solution. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 相似文献
12.
Hans-Volkhard Gründler Heinz-Dieter Schumann Eberhard Steger 《Journal of Molecular Structure》1974,21(1):149-157
Normal coordinate analyses and force constant calculations were carried out using frequencies of infrared and Raman-spectra of the molecules and ions RAsO32?, RAs(O)(OR)2, RAs(O)(OH)2, RAs(OH)O2?, RzAsO2?, R2As(O)OH, and [R'2As(OH)2]+ (R = CH3, R' = C2H5). Comparing bond orders of the AsO bond with those in corresponding phosphorus, selenium and sulphur compounds, we found influences of the electron deficiency effect and of bond polarity. 相似文献
13.
A. Jenichen 《International journal of quantum chemistry》1994,52(1):117-125
The local mechanisms of dissociative chemisorption and reactive etching are investigated by molecular models modeling ?SiOH groups and ?SiOSi? bridges at SiO2 surfaces. The elementary reaction paths for the reactions of HF and HCl with Si? O bonds of the models, Si(OH)4 and (HO)3SiOSi(OH)3, are calculated by the Hartree–Fock method. The local transition-state structures are nearly plane quadrangles with neighboring pentacoordinated silicon and tricoordinated oxygen atoms. For the reaction and activation energies, the electron correlation is considered by the Møller–Plesset perturbation theory. The results agree with experimental findings. © 1994 John Wiley & Sons, Inc. 相似文献
14.
Zhengyu Zhou Yuhui Qu Aiping Fu Benni Du Faxin He Hongwei Gao 《International journal of quantum chemistry》2002,89(6):550-558
The hydrogen bonding complexes formed between the H2O and OH radical have been completely investigated for the first time in this study using density functional theory (DFT). A larger basis set 6‐311++G(2d,2p) has been employed in conjunction with a hybrid density functional method, namely, UB3LYP/6‐311++G(2d,2p). The two degenerate components of the OH radical 2Π ground electronic state give rise to independent states upon interaction with the water molecule, with hydrogen bonding occurring between the oxygen atom of H2O and the hydrogen atom of the OH radical. Another hydrogen bond occurs between one of the H atoms of H2O and the O atom of the OH radical. The extensive calculation reveals that there is still more hydrogen bonding form found first in this investigation, in which two or three hydrogen bonds occur at the same time. The optimized geometry parameter and interaction energy for various isomers at the present level of theory was estimated. The infrared (IR) spectrum frequencies, IR intensities, and vibrational frequency shifts are reported. The estimates of the H2O · OH complex's vibrational modes and predicted IR spectra for these structures are also made. It should be noted that a total of 10 stationary points have been confirmed to be genuine minima and transition states on the potential energy hypersurface of the H2O · HO system. Among them, four genuine minima were located. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002 相似文献
15.
The empirical correlation between the stretching frequency of the carbonyl group and the shift of the vXH absorption band, proposed in the literature [3], is interpreted with a simple model, where the CO group is considered as a two π-electron system in terms of the parametric Hückel approximation. The model clearly distinguishes between the associations with OH, NH and CH groups, and offers an explanation of the different behaviour based on the properties of the donor and acceptor groups.The assumptions required for the previous simple treatment have then been tested through the analysis of a CNDO/2 treatment applied to the association of methanol with formaldehyde, acetaldehyde and acetone. After optimization of the association geometry with respect to the CO, and O-H ? O bond-lengths and to the angle between the O-H and CO groups, it is found that the calculated ?vOH correlates with the calculated association enthalpy, transferred charge, dipole moment increment, and π-bond order, and also with the observed vCO frequency of acetaldehyde and acetone.The empirical correlation can therefore be explained in terms of both Huckel and CNDO approximations. 相似文献
16.
Cubic Siloxanes with Both Si−H and Si−OtBu Groups for Site‐Selective Siloxane Bond Formation
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Shohei Saito Nao Yamasue Prof. Dr. Hiroaki Wada Prof. Dr. Atsushi Shimojima Prof. Dr. Kazuyuki Kuroda 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(39):13857-13864
Cage‐type siloxanes have attracted increasing attention as building blocks for silica‐based nanomaterials as their corners can be modified with various functional groups. Cubic octasiloxanes incorporating both Si?H and Si?OtBu groups [(tBuO)nH8?nSi8O12; n=1, 2 or 7] have been synthesized by the reaction of octa(hydridosilsesquioxane) (H8Si8O12) and tert‐butyl alcohol in the presence of a Et2NOH catalyst. The Si?H and Si?OtBu groups are useful for site‐selective formation of Si?O?Si linkages without cage structure deterioration. The Si?H group can be selectively hydrolyzed to form a Si?OH group in the presence of Et2NOH, enabling the formation of the monosilanol compound (tBuO)7(HO)Si8O12. The Si?OH group can be used for either intermolecular condensation to form a dimeric cage compound or silylation to introduce new reaction sites. Additionally, the alkoxy groups of (tBuO)7HSi8O12 can be treated with organochlorosilanes in the presence of a BiCl3 catalyst to form Si?O?Si linkages, while the Si?H group remains intact. These results indicate that such bifunctional cage siloxanes allow for stepwise Si?O?Si bond formation to design new siloxane‐based nanomaterials. 相似文献
17.
The prominent (SiO(2))(8)O(2)H(3) (-) mass peak resulting from the laser ablation of hydroxylated silica, attributed to magic cluster formation, is investigated employing global optimization with a dedicated interatomic potential and density functional calculations. The low-energy spectra of cluster isomers are calculated for the closed shell clusters: (SiO(2))(8)OH(-) and (SiO(2))(8)O(2)H(3) (-) giving the likely global minima in each case. Based upon our calculated cluster structures and energetics, and further on the known experimental details, it is proposed that the abundant formation of (SiO(2))(8)O(2)H(3) (-) clusters is largely dependent on the high stability of the (SiO(2))(8)OH(-) ground state cluster. Both the (SiO(2))(8)O(2)H(3) (-) and (SiO(2))(8)OH(-) ground state clusters are found to exhibit cagelike structures with the latter containing a particularly unusual tetrahedrally four-coordinated oxygen center not observed before in either bulk silica or silica clusters. The bare ground state (SiO(2))(8)O(2-) cluster ion core is also found to have four tetrahedrally symmetric Si==O terminations making it a possible candidate, when combined with suitable cations, for extended cluster-based structures/materials. 相似文献
18.
《Journal of organometallic chemistry》1989,359(2):C36-C40
Radical reactions of Me3SiPH2 with Me2Si(CHCH2)2 or Si(CHCH2)4 yield the 4-silaphosphorinanes Me2Si(CH2CH2)2PSiMe3, (CH2CH)2Si(CH2CH2)2PSiMe3, or [Me3SiP(CH2CH2)2]2Si; methanolysis of these produces quantitatively the secondary phosphorinanes Me2Si(CH2CH2)2PH, (CH2CH)2Si(CH2CH2)2PH, or [HP(CH2CH2)2]2Si. Me2Si(CH2CH2)2PSiMe3 with O2/H2O yields the phosphinic acid Me2Si(CH2CH2)2P(O)OH. All compounds are characterized by spectral data; an X-ray crystal analysis confirms the structure of Me2Si(CH2CH2)2P(O)OH. 相似文献
19.
The oligoalumosiloxanes {[Ph2SiO]8[Al(O)OH]4·2,5Et2O·HOtBu} ( 6 ) and {[Ph2SiO]8[Al(O)OH]4·2Et2O·2HOiPr} ( 7 ) have been obtained from the reaction of diphenylsilanediol with aluminium‐tri‐tert‐butoxide and aluminium‐tri‐iso‐propoxide in ethyl ether with reasonable yields. In a 1:1 molar mixture of toluene and the respective alcohol (iso‐propanol or tert‐butanol), the ethyl ether molecules in {[Ph2SiO]8[Al(O)OH]4·4Et2O}, in 6 or 7 can be completely displaced forming the compounds [Ph2SiO]8[Al(O)OH]4·4HOiPr ( 8 ) and [Ph2SiO]8[Al(O)OH]4·nHOtBu ( 9 ). Whereas 6 , 7 and 8 are crystalline, 9 is obtained as a viscous liquid. An X‐ray structure determination on {[Ph2SiO]8[Al(O)OH]4·3Et2O·HOtBu} reveals different bonding modes of the diethyl ether molecules to the oligoalumosiloxane compared to the tert‐butanol, which forms two hydrogen bonds (one to the OH‐group of the inner Al4(OH)4 cycle and one through the alcohol OH‐group to a Si–O–Al moiety. The alcohol adducts have been characterized in solution through 1H‐, 13C‐ and 29Si‐NMR and show dynamic equilibria between the oligoalumosiloxane [Ph2SiO]8[Al(O)OH]4 and the alcohol molecules. 相似文献
20.
The geometries of molecules H_3AXAH_3(X=O,S,Se and A=C,Si)have been optimizedusing STO-3G ab initio calculations and gradient method and the results are in good agreement withreported experimental values.From the STO-3G optimized geometries,we have also calculated theelectronic structures of these molecules using 4-31G and 6-31G basis sets to obtain the MO energies.atomic net charges and dipole moments.The ionization potentials calculated by 6-31G basis set are ingood agreement with experimental values. 相似文献