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1.
The molecular structure of caffeine (3,7-dihydro-1,3,7-trimethyl-1H-purine-2,6-dione) was determined by means of gas electron diffraction. The nozzle temperature was 185 °C. The results of MP2 and B3LYP calculations with the 6-31G7 basis set were used as supporting information. These calculations predicted that caffeine has only one conformer and some of the methyl groups perform low frequency internal rotation. The electron diffraction data were analyzed on this basis. The determined structural parameters (rg and ∠α) of caffeine are as follows: <r(NC)ring> = 1.382(3) Å; r(CC) = 1.382(←) Å; r(CC) = 1.446(18) Å; r(CN) = 1.297(11) Å; <r(NCmethyl)> = 1.459(13) Å; <r(CO)> = 1.206(5) Å; <r(CH)> = 1.085(11) Å; ∠N1C2N3 = 116.5(11)°; ∠N3C4C5 = 121. 5(13)°; ∠C4C5C6 = 122.9(10)°; ∠C4C5N7 = 104.7(14)°; ∠N9–C4=C5 = 111.6(10)°; <∠NCHmethyl> = 108.5(28)°. Angle brackets denote average values; parenthesized values are the estimated limits of error (3σ) referring to the last significant digit; left arrow in parentheses means that this parameter is bound to the preceding one.  相似文献   

2.
KOH activation of petroleum coke (PC) was conducted with 30 vol%H2 + 70 vol% N2 as carrier gas. TG-DTG, FTIR, elemental analysis, N2 adsorption, GC and XRD techniques were used to investigate the effects of hydrogen on the activation. During the initial stage of the activation, i.e. the carbonization of the PC, additional CH and CH2 species were formed due to the chemisorption of hydrogen on the nascent sites of the PC created by the removal of the surface heteroatom groups. The formation of the CH and CH2 species increased the quantity of ‘active sites’ which is favorable to the further activation reaction, and developed the porous structure of the activated carbons. The micropore volume and BET surface areas of the activated carbon prepared under 30 vol% H2 + 70 vol% N2 and with a relatively low KOH/PC weight ratio of 2:1 have been increased from 0.78 cm3/g and 1936 m2/g to 0.97 cm3/g and 2477 m2/g, respectively, compared to that prepared in pure N2 atmosphere with the same KOH/PC ratio.  相似文献   

3.
Although 1,1-bis(trifluoromethyl)butadiene-1,3 (1) reacts with dimethylamine with selective formation of 1,4-adduct [trans-(CF3)2CHCHCHCH2N(CH3)2], halogenation of 1 proceeds with predominant formation (>92%) of 1,2-adducts (CF3)2CCHCHXCH2X (X = Cl or Br). Electrophilic conjugated addition of “ClF” or “BrF” to 1 proceeds exclusively with the formation of 1,2-adducts (CF3)2CCHCHFCH2X (major) and (CF3)2CCHCHXCH2F (X = Cl or Br). Difluorocarbene adds selectively to CHCH2 moiety of 1 forming thermally stable vinylcyclopropane. In Diels-Alder reaction with linear or cyclic dienes (butadienes, cyclopentadiene, cyclohexadiene-1,3) and quadricyclane compound 1 behaves as dienophile providing for the reaction electron-deficient CHCH2 bond. The relative rate of cycloaddition of 1 and other fluoroolefins to quadricyclane, measured by high temperature NMR, indicates that (CF3)2CCH acts as very strong electron-withdrawing substituent. Synthetic utility of products based on 1 was also demonstrated.  相似文献   

4.
《Vibrational Spectroscopy》2009,49(2):259-262
In order to evidence the structural changes induced by CuO and V2O5 in the phosphate glass network and their modifier or former role, x(CuO·V2O5)(100  x)[P2O5·CaO] glass system was prepared and investigated using Raman spectroscopy (0  x  40 mol%).Raman spectra of the studied glasses present the specific bands of the phosphate glasses at low concentration of transition metal (TM) ions, but at higher concentration (x > 7 mol%) a strong depolymerization of the phosphate network appears; non-bridging oxygen atoms are involved in VOP and CuOP bonds and new short units are formed. For a high concentration of V2O5 (x > 10 mol%) the Raman bands of V2O5 prevail in the spectra; this fact suggests that vanadium oxide imposes its structural units in the network acting thus as a network glass former.2D correlation analysis was also applied for the concentration-dependent Raman spectra in order to verify the assignments of the vibration modes and to find correlations in the changes induced by TM ions content. 2D correlation maps indicate a good correlation between the bands at ∼705 cm−1 assigned to POP stretching vibration and at ∼1175 cm−1 assigned to PO2 groups which suggest the depolymerization of the phosphate network. The correlation between the 1270 cm−1 and 930 cm−1 bands also suggests that V2O5 oxide is responsible for PO bonds breaking and POV formation.  相似文献   

5.
《Comptes Rendus Chimie》2015,18(12):1277-1283
A theoretical study of the [3+2] cycloaddition (32CA) reaction between benzonitrile sulfide BNS1 and trichloroacetonitrile TCAN2 at the MPWB1 K/6-311G(d) level was undertaken. Among two feasible C1N5 and C1C4 regioisomeric channels, the former is completely preferred, in the presence of toluene, over the latter, both kinetically, ΔΔGactivation = 17.5 kcal/mol, and thermodynamically, ΔΔGreaction = –12.8 kcal/mol, in excellent agreement with experimental outcomes. The strong global electrophilic and nucleophilic characters found for TCAN2 and BNS1, respectively, allow the studied 32CA reaction to take place via a polar process. Interestingly, the analysis of the TSs geometries clarifies that in the case under study, regioselectivity is controlled by destabilizing steric repulsion interactions rather than electronic ones. The ELF topological patterns indicate that while the formation of S3C4 single bond takes place exactly according to Domingo's model, that of the C1N5 single bond is a direct consequence of the nucleophilic attack of the C5 carbon atom on the N5 nitrogen atom supporting a two-stage one-step molecular mechanism.  相似文献   

6.
An overview is given on synthesis and structures of new bidentate phosphaalkene ligands [(RMe2Si)2CP]2E (E = O, NR, N?) and (RMe2Si)2CPN(R′)PR′′2. Exceptional properties of these ligands, extending beyond predictable properties of phosphaalkenes are: (i) the NSi bond cleavage of [(iPrMe2Si)2CP]2NSiMe3 with AuI and RhI chloro complexes under mild conditions leading to binuclear complexes of the 6π-delocalised imidobisphosphaalkene anion [(iPrMe2Si)2CP]2N?, and (ii) the chlorotropic formation of molecular 1:2 PdII and PtII metallochloroylid complexes with novel ylid-type ligands [(RMe2Si)2CP(Cl)N(R)PR2]?, and the transformation of a P-platina-P-chloroylid complex into a C-platina phosphaalkene by intramolecular chlorosilane elimination. Properties of the heavier congeners [(RMe2Si)2CP]2E (E = S, Se, Te, PR, P?, As?) and (RMe2Si)2CPEPR′′2 (E = S, Se, Te) are also described.  相似文献   

7.
Bis(betainium) p-toluenesulfonate monohydrate (abbreviated as BBTSH) was studied at various temperatures by X-ray diffraction, differential scanning calorimetry and vibrational spectroscopy methods. DSC curves of BBTSH show a peak at about 349 K which corresponds to water escape from the crystal, and reveal the “cold crystallization” phenomenon. BBTSH crystallizes in the P21/c space group of monoclinic system. After heating above 349 K the compound dehydrates, the crystal system changes to triclinic, the monocrystalline samples become non-merohedral twins. The BBTSH crystal comprises p-toluenesulfonic anions, monoprotonated betaine dimers and water molecules. Three kinds of hydrogen bonds are present in the crystal: strong, asymmetric and almost linear OH⋯O hydrogen bond (R(O⋯O) = 2.463(2) Å), weak OwH⋯O hydrogen bonds (R(Ow⋯O) = 2.820(2)  2.822(2) Å) and weak CH⋯O hydrogen bonds (R(C⋯O) = 3.295(2)  3.416(2) Å). The νaOHO vibration of the strongest hydrogen bond in the crystal gives rise to an intense broad absorption with numbers of transmission windows in the low wavenumber region of the infrared spectra. Coupling between νCO stretching vibrations of two COO groups of the betaine dimer was detected. The process corresponding to the loss of water is accompanied by the breakage of strong OH⋯O hydrogen bonds in betaine dimers and rearrangement inside half of the betaine dimers. This rearrangement results in formation of the new betaine dimers with OH∙∙∙O hydrogen bond of similar strength as corresponding bond in the hydrated form (BBTSH).  相似文献   

8.
《Vibrational Spectroscopy》2006,40(1):142-147
A novel compound, (4,4′-Hbpy)2(K2Mo8O26) 1 (bpy = bipydine), was synthesized by hydrothermal method and characterized by X-ray single analysis, thermalgravimetric analysis, one-dimensional (1D) infrared spectroscopy and two-dimensional (2D) correlation infrared spectroscopy under thermal perturbation. In the compound 1, the [Mo8O26] units link to potassium ions to form layer structure, and the protonated 4,4′-bpy are linked to chains by hydrogen bonds. The 2D IR correlation spectroscopy study indicates that the intensity changes of MoO, NH and CC stretching vibration are sensitive to the temperature variation, and the intensity changes of asymmetry stretching vibration of the terminal MoO occur prior to that of terminal MoO linked by K atom. At the same time, the peaks of asymmetry stretching vibrations of the terminal MoO and the stretching vibrations of NH split into two peaks respectively in 2D IR correlation spectroscopy.  相似文献   

9.
Continuous gradient temperature Raman spectroscopy (GTRS) applies the temperature gradients utilized in differential scanning calorimetry (DSC) to Raman spectroscopy, providing a straightforward technique to identify molecular rearrangements that occur near phase transitions. Herein we apply GTRS and DSC to the solid dipeptides Ala-Pro, Pro-Ala, and the mixture Ala-Pro/Pro-Ala 2:1. A simple change in residue order resulted in dramatic changes in thermal stability and properties. Characteristic Pro vibrations were observed at ∼75 °C higher temperature in Pro-Ala than Ala-Pro. The appearance/disappearance of characteristic vibrational modes with increasing temperature showed that a double peak in the Ala-Pro major phase transition (174–184 °C) was due to a gauche to anti 165° rotation of H3CC*NH3 about C*. CH2 rocking and wagging frequencies present in Pro-Ala were not observed in Ala-Pro. For Ala-Pro, the Ala +NH3, and Pro COO sites were flexible whereas the Pro ring moiety was not; since the OCN (C)2 amide bond is planar the CNC moiety keeps the Pro ring rigid. For Pro-Ala, CH2 sites in the Pro ring were flexible and the OCNH amide bond is perpendicular to the Pro ring. Since the mass of the Pro ring is significantly larger than the mass of the flexible Ala +NH3 moiety, Pro-Ala absorbs more thermal energy, corresponding to a higher phase transition temperature (240–260 °C). Ala-Pro, Pro-Ala, and Ala-Pro/Pro-Ala 2:1 exhibited α-helix, β-sheet, α-helix secondary structure conformations, respectively.  相似文献   

10.
《Polyhedron》2007,26(5):981-988
New π-conjugated butadiynyl ligand FcC(CH3)2Fc′–CC–CC–Ph (L1) has been synthesized and its reaction with Co2(CO)8 has been studied. New clusters [FcC(CH3)2Fc′–CC–CC–Ph][Co2(CO)6]n [(1): n = 1; (2): n = 2] and [Fc–CC–CC–Ph][Co2(CO)6]n [(3): n =  1; (4): n = 2] were obtained by the reaction of ligands FcC(CH3)2Fc′–CC–CC–Ph (L1) and Fc–CC–CC–Ph (L2) with Co2(CO)8 respectively and the composition and structure of the clusters and ligands have been characterized by elemental analysis, FTIR, 1H and 13C NMR and MS. The crystal structures of compounds L1, L2, 2 and 4 have been determined by X-ray single crystal analysis.  相似文献   

11.
Three 1D bimetallic M(II)/Ni(II) (M = Cu, Zn and Cd) complexes, [Cu(OHepy)2Ni(CN)4]n (1), [Zn(OHepy)2Ni(CN)4]n (2) and [Cd(OHepy)2Ni(CN)4]n (3) (2-(2-hydroxyethyl)pyridine abbreviated to OHepy), have been synthesized and characterized by FT-IR and Raman spectroscopy, elemental, thermal analyses and single crystal X-ray diffraction techniques. FT-IR and Raman spectra of OHepy have been experimentally and theoretically investigated in the region of 4000–250 cm−1. The corresponding vibrational assignments of OHepy are examined by means of B3LYP hybrid density functional theory (DFT) method together with 6-311++G(d, p) basis set. Moreover, reliable vibrational assignments have been made on the basis of potential energy distribution (PED). The structures of the complexes consist of one-dimensional polymeric chain M(OHepy)2NCNi(CN)2CNM(OHepy)2−, in which the M(II) and Ni(II) atoms are linked by CN groups. The nickel atom is fourfold coordinated with four cyanide-carbon atoms in a square planar arrangement and the metal(II) atoms are sixfold coordinated with two cyanide nitrogen, two OHepy nitrogen and two OHepy oxygen atoms, in a distorted octahedral arrangement. In all the complexes adjacent chains are connected by π⋯π, CH⋯Ni and OH⋯N hydrogen bonding interactions to form two and three dimensional networks.  相似文献   

12.
The reaction of RuTp(COD)Cl (1) with PR3 (PR3 = PPh2iPr, PiPr3, PPh3) and propargylic alcohols HCCCPh2OH, HCCCFc2OH (Fc = ferrocenyl), and HCCC(Ph)MeOH has been studied.In the case of PR3 = PPh2iPr, PiPr3 and HCCCPh2OH, the 3-hydroxyvinylidene complexes RuTp(PPh2iPr)(CCHC(Ph)2OH)Cl (2a) and RuTp(PiPr3)(CCHC(Ph2)OH)Cl (2b) were isolated.With PR3 = PPh2iPr and HCCCFc2OH as well as with PR3 = PPh3 and HCCCPh2OH dehydration takes place affording the allenylidene complexes RuTp(PPh2iPr)(CCCFc2)Cl (3b) and RuTp(PPh3)(CCCPh2)Cl (3c).Similarly, with PPh2iPr and HCCC(Ph)MeOH rapid elimination of water results in the formation of the vinylvinylidene complex RuTp(PPh2iPr)(CCHC(Ph)CH2)Cl (4).In contrast to the reactions of the RuTp(PR3)Cl fragment with propargylic alcohols, with HCC(CH2)nOH (n = 2, 3, 4, 5) six-, and seven-membered cyclic oxycarbene complexes RuTp(PR3)(C4H6O)Cl (5), RuTp(PR3)(C5H8O)Cl (6), and RuTp(PR3)(C6H10O)Cl (7) are obtained. On the other hand, with 1-ethynylcyclohexanol the vinylvinylidene complex RuTp(PPh2iPr)(CCHC6H9)Cl (8) is formed. The reaction of the allenylidene complexes 3ac with acid has been investigated. Addition of CF3COOH to a solution of 3ac resulted in the reversible formation of the novel RuTp vinylcarbyne complexes [RuTp(PPh2iPr)(C–CHCPh2)Cl]+ (9a), [RuTp(PPh2iPr)(C–CHCFc2)Cl]+ (9b), and [RuTp(PPh3)(C–CHCPh2)Cl]+ (9c). The structures of 3a, 3b, and 5b have been determined by X-ray crystallography.  相似文献   

13.
The curing dynamics and network formation of cyanate ester resin/graphene oxide (GO) nanocomposites were studied by means of Differential Scanning Calorimetry (DSC), Fourier Transform Infrared (FT-IR) and Raman spectroscopies. The incorporation of GO into the resin showed a strong catalytic effect on the cure of the resin, especially in the initial stages. Addition of 4 wt.% GO resulted in the decrease of curing temperature significantly about 97 °C. Activation energy of the nanocomposites also maintained at a low level till the end of the cure. The most effective catalytic behavior was observed with 1 wt.% GO. Both FT-IR and Raman spectra revealed that OH group in GO reacted with cyanate group OCN in the resin to form O(CNH)O bond in the early stages of the cure. These results could provide a low temperature curing route for cyanate ester resins with improved curing efficiency.  相似文献   

14.
Methyl aziridine-2-carboxylate (MA2C) has been isolated in low temperature argon and xenon matrices and its structure and photochemistry were studied by FTIR spectroscopy. The reactant as well as the main photoproducts were characterized by comparison of their experimental IR spectra with spectra calculated at the DFT(B3LYP)/6-311++G(d,p) level. The theoretical calculations predicted the existence of two low energy MA2C conformers, differing by the orientation of the OCCN dihedral angle. Both conformers were identified in the studied matrices. Both narrowband tunable and broadband UV irradiations of matrix-isolated MA2C yielded isomerization photoproducts resulting from cleavage of the CC and weakest CN bonds of the aziridine ring. Irradiation with UV laser-light at λ = 235 nm resulted in the formation of the E isomer of methyl 2-(methylimino)-acetate (MMIA) and the Z isomer of methyl 3-iminopropanoate (M3IP). Subsequent irradiation at 290 nm led to observation of new bands resulting from E  Z isomerization of MMIA, while bands due to M3IP remained unchanged. The photoproduced Z isomer of MMIA could be subsequently consumed upon higher-wavelength irradiation (λ = 330 nm). The initially produced MMIA conformer was found to obey the nonequilibrium of excited rotamers (NEER) principle. No photoproducts resulting from the cleavage of the strongest CN bond of the MA2C aziridine ring were observed, nor that of methyl 3-aminoacrylate (M3AA), which could in principle be obtained also by cleavage of the weakest CN bond of the MA2C aziridine ring, but would imply a different H-atom migration simultaneous with the ring opening process. These results indicate that both the differential electronic characteristics of the CN bonds of substituted aziridine rings and the type of required H-atom migration are major factors in determining the specific photochemistries of substituted aziridines. Photofragmentation reactions of MA2C were also observed, through identification of various related products, e.g., acetonitrile, methanol, methane, CO and CO2.  相似文献   

15.
The RuC bond of the bis(iminophosphorano)methandiide-based ruthenium(II) carbene complexes [Ru(η6-p-cymene)(κ2-C,N-C[P{NP(O)(OR)2}Ph2]2)] (R = Et (1), Ph (2)) undergoes a C–C coupling process with isocyanides to afford ketenimine derivatives [Ru(η6-p-cymene)(κ3-C,C,N-C(CNR′)[P{NP(O)(OR)2}Ph2]2)] (R = Et, R′ = Bz (3a), 2,6-C6H3Me2 (3b), Cy (3c); R = Ph, R′ = Bz (4a), 2,6-C6H3Me2 (4b), Cy (4c)). Compounds 34ac represent the first examples of ketenimine–ruthenium complexes reported to date. Protonation of 34a with HBF4 · Et2O takes place selectively at the ketenimine nitrogen atom yielding the cationic derivatives [Ru(η6-p-cymene)(κ3-C,C,N-C(CNHBz)[P{NP(O)(OR)2}Ph2]2)][BF4] (R = Et (5a), Ph (6a)).  相似文献   

16.
《Vibrational Spectroscopy》2007,43(1):104-110
The Raman spectra of serine [α-amino-β-hydroxypropionic acid; HOCH2CH(NH3)+COO] and 3,3-dideutero-serine [HOCD2CH(NH3)+COO] in aqueous solution were studied in the range 4000–300 cm−1. The data obtained for the deuterated compound are novel and provide compelling evidence that previously reported assignments for the undeuterated amino acid should be revised.  相似文献   

17.
The structure of the complex of dimethylphenyl betaine (DMPB) with dichloroacetic acid (DCA) (1) has been investigated by X-ray diffraction, FTIR and Raman spectroscopy, and B3LYP/6-311 + + G(d,p) calculations. The crystal is monoclinic, space group P21. The acid is connected with betaine through the OH⋯O hydrogen bond of 2.480(2) Å. In the optimized structure the short, asymmetric O⋯O distance is 2.491 Å. FTIR spectrum shows a broad absorption in the 1500–400 cm−1 region characteristic of very short OH⋯O hydrogen bond caused by Fermi resonance between νOH and overtones of δOH and γOH. In the Raman spectrum this broad absorption is not observed. The potential energy distributions (PED) were used for the assignments of IR and Raman frequencies in the experimental and calculated spectra. The FTIR and Raman spectra of the crystal complex are consistent with the X-ray results.  相似文献   

18.
《Fluid Phase Equilibria》2005,235(1):83-91
Densities and speeds of sound for the binary mixtures acetone, 2-butanone and 2-pentanone + diethyl carbonate, over the whole composition range, at T = 298.15 K and atmospheric pressure have been measured. Excess molar volumes and deviations in isentropic compressibility for the binary systems were fitted to the Redlich–Kister polynomial. Isobaric vapor–liquid equilibria for the binary systems acetone + diethyl carbonate, 2-butanone + diethyl carbonate and 2-pentanone + diethyl carbonate at P = 101.3 kPa have been determined. The activity coefficients were calculated to be thermodynamically consistent and they were correlated with the Wilson, NRTL, UNIQUAC and Redlich–Kister equations. Interaction parameters related to the carbonate (OCOO) and ketone (CO) groups, in ASOG and UNIFAC methods, have been determined using our experimental VLE data.  相似文献   

19.
Two original dinuclear (LnYb, 3 and LnEr, 4) and one trinuclear CuIILnIIICuII (LnGd, 5) complexes derived from a polydentate non symmetrical Schiff base ligand H2L have been prepared. The ligand possesses two functions (phenol and oxime) able to coordinate the Ln ions, but structural studies (X-ray diffraction and powder X-ray diffraction) show that the CuII and LnIII ions are only bridged by the oximato (NO) pair. The missing phenoxo bridge is replaced by a surprising pseudo-bridge involving one oxygen atom of the nitrato anion linked to the Cu and Ln ions according to a η2: η1: μ mode. Although this latter contact has no role from the magnetic point of view, it introduces a large deformation of the unique bridging network. The CuYb complex 3 and the trinuclear CuGdCu complex 5 present antiferromagnetic interactions, with a JCuGd interaction equal to ?1.25 cm?1 in 5. The genuine single bridge can be considered as responsible for the antiferromagnetic character of the interaction.  相似文献   

20.
The 1:1 complex of N-methylmorpholinium-acetate, MMB, with hydrobromic acid (1) has been investigated by single-crystal X-ray analysis, infrared spectroscopy and theoretical calculations. The proton-transfer complex has been observed in the crystalline state, with the COOH⋯Br hydrogen bond with the O⋯Br distance of 3.107(2) Å. In the structure optimized at the B3LYP/6-311++G(d,p) levels of theory the proton is closer to the bromide anion, with the BrH⋯OOC distance of 3.069 Å. The potential energy distributions (PED) have been used for the assignments of IR bands. The experimental and theoretical infrared spectra have been discussed.  相似文献   

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