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1.
Twenty-two isomers/conformers of C 3H 6S +√ radical cations have been identified and their heats of formation (Δ Hf) at 0 and 298 K have been calculated using the Gaussian-3 (G3) method. Seven of these isomers are known and their Δ Hf data are available in the literature for comparison. The least energy isomer is found to be the thioacetone radical cation (4 +) with C2v symmetry. In contrast, the least energy C 3H 6O +√ isomer is the 1-propen-2-ol radical cation. The G3 Δ Hf298 of 4 + is calculated to be 859.4 kJ mol −1, ca. 38 kJ mol −1 higher than the literature value, ≤821 kJ mol −1. For allyl mercaptan radical cation (7 +), the G3 Δ Hf298 is calculated to be 927.8 kJ mol −1, also not in good agreement with the experimental estimate, 956 kJ mol −1. Upon examining the experimental data and carrying out further calculations, it is shown that the G3 Δ Hf298 values for 4 + and 7 + should be more reliable than the compiled values. For the five remaining cations with available experimental thermal data, the agreement between the experimental and G3 results ranges from fair to excellent. Cation CH3CHSCH2+√ (10+) has the least energy among the eleven distonic radical cations identified. Their ΔHf298 values range from 918 to 1151 kJ mol−1. Nevertheless, only one of them, CH2=SCH2CH2+√ (12+), has been observed. Its G3 ΔHf298 value is 980.9 kJ mol−1, in fair agreement with the experimental result, 990 kJ mol−1. A couple of reactions involving C3H6S+√ isomers CH2=SCH2CH2+√ (12+) and trimethylene sulfide radical cation (13+) have also been studied with the G3 method and the results are consistent with experimental findings. 相似文献
2.
The reactivity of borane carbonyl (BH 3CO) and its isoelectronic counterpart the acetylium cation (CH 3CO +) are compared resulting in the formulation of (carbonyl)trihydroborate anions, BH 3C(O)X −, which are isoelectronic and isostructural with organic carbonyls. By analogy with the ease of reduction of organic carbonyl compounds by hydroborate, the relative stability towards self-reduction-oxidation (hydride transfer from boron to carbonyl carbon) in BH 3C(O)X − is proposed. The postulated order, with increasing stability is BH 3C(O)Cl − < BH 3C(O)H − < BH 3C(O)R − < BH 3C(O)OR − < BH 3C(O)NR −2 < BH 3C(O)O 2−. Experimental results of this study together with known chemistry are shown to be consistent with the proposed order. Further, it is suggested that a similar predictive scheme may be applicable to the chemistry of the amine-carboxyboranes (boron analogues of -amino acids) and their derivatives. 相似文献
3.
Raman and infrared spectra of propylgermane, CH 3CH 2CH 2GeH 3, and its Ge-deuterated analog, CH 3CH 2CH 2GeD 3, were investigated in their gaseous, liquid and solid states. The normal coordinate treatment was carried out by density functional theory (DFT) calculation, using B3LYP/6-31G * and 6-311++G ** basis sets, and the corresponding fundamental vibrations were assigned. The trans ( T) and gauche ( G) forms around the central C–C bond coexisted in the gaseous and liquid states and only the T form existed in the solid state. From the temperature dependent measurements of the Raman spectra in the liquid state, the enthalpy difference was found to be Δ H( T− G)=−0.36±0.02 kcalmol −1 with the T form being more stable. The energy differences between the isomers obtained by DFT calculations were Δ E( T− G)=−0.46 kcalmol −1 and Δ E( T− G)=−0.87 kcalmol −1 by the 6-31G * basis set and 6-311++G ** basis set, respectively. 相似文献
4.
The preparations and spectroscopic characteristics are reported of a series of (trimethylgermyl)methyl- and (trimethylstannyl)methylplatinum(II) complexes with diene and P-donor ancillary ligands, cis-Pt(CH 2GeMe 3) 2L 2 (L = PPh 3 or PPh 2Me; L 2 = dppe or cod) and cis-Pt(CH 2SnMe 3) 2L 2 (L = PPh 3; L 2 =cod). Thermolysis of toluene solutions of cis-Pt(CH 2GeMe 3) 2(PPh 3) 2 leads to cis-Pt(Me)(CH 2GeMe 2CH 2GeMe 3)(PPh 3) 2 via β-alkyl migration, after (non-rate-limiting) phosphine dissociation. Estimated activation parameters (Δ H298 K‡ = 126 ± 3 kJ mol −1, Δ S‡ = + 17 ± 7 J mol −1 K −1 and hence Δ 298 K‡ = 121 ± 5 kJ mol −1) suggest that this system is more migration labile than its silicon analogue, primarily as a result of a lower activation enthalpy. While cis-Pt(CH 2GeMe 3) 2(PPh 2Me) 2 reacts similarly but less readily, Pt(CH 2GeMe 3) 2(dppe) 2 is inert at operable temperatures. Thermolysis of Pt(CH 2GeMe 3) 2(cod) generates 1,1,3,3,-tetramethyldi-1,3-germacyclobutane as the major organogermanium product, while from cis-Pt(CH 2SnMe 3) 2(PPh 3) 2, 1,1,3,3-tetramethyldi-1,3-stannacyclobutane predominates. Mechanistic implications are discussed. 相似文献
5.
A mixture of NF 3 and Ar is passed through an rf discharge in a flow-system to produce, among other species, F and NF 2. When H 2, D 2, or CH 4 are added downstream, reactions with F atoms produce vibrationally excited HF or DF together with H, D, or CH 3. The latter free radicals can react with NF 2, probably by an elimination reaction to produce electronically excited NF: NF 2( 2B 1) + H(D, CH 3) → HF *(DF * + NF(a 1Δ). A vibrational-to-electronic energy transfer process between the products of this reaction then produces the next higher state of NF: HF(ν 2) + NF(a 1Δ) → HF(ν−2) + NF(b 1Σ +). A similar transfer process has also been found between the electronically excited a 1Δ states of O 2 and NF: O 2(a 1Δ) + NF(a 1Δ) → O 2(X 3Σ −) + NF(b 1Σ +). The H or D atoms but not the CH 3 radicals are then found to react with either NF(a 1Δ) or NF(X 3Σ −) to produce electronically excited N( 2D) atoms, which in turn react with the NF(a 1Δ) molecules to produce N 2(B 3Π g). The observed nitrogen first positive radiation has been demonstrated to be produced entirely by this reaction mechanism rather than by the N( 4S) recombination that accounts for the Rayleigh afterglow. In addition, the occurrence of the reaction N( 2D) + N 2O → NO(B 2Π r) + N 2 (X 1Σ +g) has been verified. Finally we have observed emission at 3344 Å, which we attribute to the NF(A 3Π), which has not been previously reported. 相似文献
6.
The calculations reported here assign a charge qN = −0.52 electron units to the terminal nitrogen atoms in the azide ion and a value of 141.9 kJ mole −1 to the enthalpy of formation of the gaseous azide ion, Δ Hf0(N 3−(g)). The total lattice potential energies are found to be: Epot(NaN 3) = 725.1 kJ mole −1; Epot(KN 3) = 650.7 kJ mole −1 and Epot(RbN 3) = 632.1 kJ mole −1. 相似文献
7.
Thermal decomposition of mixed ligand thymine (2,4-dihydroxy-5-methylpyrimidine) complexes of divalent Ni(II) with aspartate, glutamate and ADA ( N-2-acetamido)iminodiacetate dianions was monitored by TG, DTG and DTA analysis in static atmosphere of air. The decomposition course and steps of complexes [Ni(C 5H 6N 2O 2)(C 4H 5NO 4) 2−(H 2O) 2]·H 2O, [Ni(C 5H 6N 2O 2)(C 5H 7NO 4) 2−(H 2O) 2]·H 2O and [Ni(C 5H 6N 2O 2)(C 6H 8N 2O 5) 2−(H 2O) 2]·1.5H 2O were analyzed. The final decomposition products are found to be the corresponding metal oxides. The kinetic parameters namely, activation energy ( E*), enthalpy (Δ H*), entropy (Δ S*) and free energy change of decomposition (Δ G*) are calculated from the TG curves using Coats–Redfern and Horowitz–Metzger equations. The stability order found for these complexes follows the trend aspartate > ADA > glutamate. 相似文献
8.
The excess molar volumes VmE { x(CH 3OH or CH 3CH 2OH or CH 3(CH 2) 2OH or CH 3CH(OH)CH 3 + (1 - x){CH 3(CH 2) 2} 2O or CH 3C(CH 3) 2OCH 3 or CH 3CH 2C(CH 3) 2OCH 3} have been calculated from measured values of density over the whole composition range at the temperature 298.15 K in order to investigate OH … O specific interactions. The results are explained in terms of the strong self-association of the alkanols, the specific interaction between the alkanol, and the ether molecules and packing effects upon mixing. The experimental Vmh results presented here, together with the previously reported data for the molar excess enthalpy HmE, has been used to test the Extended Real Associated Solution (ERAS) model. 相似文献
9.
The complex equilibria between HCrO 4− and Cl − ions has been studied spectrophotometrically at a constant ionic strength of 3.0 mol dm −3 and the data have been analyzed both graphically and numerically by means of the program LETAGROP-SPEFO (L. G. Sillen and B. Warnquist, Arkiv. kemi. 1968, 31, 377). The experimental results can be explained on the basis of the following reaction: HCrO 4−+H ++Cl − = CrO 3Cl −+H 2O (log β 11 = 1.37±0.08). Molar absorptivities of HCrO 4− and CrO 3Cl − were also reported. 相似文献
10.
The relative thermodynamic stabilities of ten allyl ethers (ROCH 2CH=CH 2) and the corresponding isomeric ( Z)-propenyl ethers (where R is an alkyl group, or a methoxysubstituted alkyl group) have been determined by chemical equilibration in DMSO solution with t-BuOK as catalyst. From the variation of the equilibrium constant with temperature, the values of the thermodynamic parameters ΔGΘ, ΔHΘ and ΔSΘ of isomerization at 298.15 K were evaluated. The propenyl ethers are highly favored at equilibrium, the values of both ΔGΘ and ΔHΘ for the allyl → propenyl reaction being ca. −18 to −25 kJ mol −1. The favor of the propenyl ethers is increased by bulky alkyl substituents, and decreased by methoxy-substituted alkyl groups. In most cases the entropy contribution is negligible; however, for R = (MeO) 2CH and R = (MeO) 3C the values of ΔSΘ are ca. −5 J K −1 mol −1. 相似文献
11.
Ab initio calculations were performed for special points of the minimal energy pathways (MEP) of the nucleophilic addition reactions of the isolated H − anion, LiH molecule and Li +/H − ion pair to acetylene (A) and methylacetylene (MA) molecules, proceeding in accordance ( M) and against ( aM) the Markovnikov's rule. All structural parameters were optimized using the restricted Hartree–Fock (RHF) method. For the addition of H −, the 6-31++G * basis set was used and for the reactions of LiH and Li +/H − the 6-31G * basis set with the subsequent recalculation of single point energies, taking into account of electron correlation energy by means of the second-order Möller–Plesset perturbation theory at the MP2/6-31++G ** level. The results of calculations demonstrate, that the energy characteristics of both M- and aM-additions with H − do not differ sufficiently (0.1–1.2 kcal/mol for the activation energies (Δ Ea) and the reaction heats (Δ Q)). The substitution of the H atom by the CH 3 group in A molecule results in practically the same values of Δ Q and Δ Ea. On the contrary, for the LiH molecule and Li +/H − ionic pair, the M-addition is favorable (charge control). It is found that the presence of electrophile decreases the activation energy by 3–5 kcal/mol as compared with the addition of the isolated hydride ion H −. 相似文献
12.
As a part of the European EUROCORE and GRIP (Greenland Ice Core Project) operations aimed at recovering deep ice cores at Summit (Central Greenland), we have for the first time successfully performed ion chromatography measurements in the field and investigated in detail the soluble impurities, including Na +, NH +4, K +, Mg 2+, Ca 2+, F −, CH 3COO −, CH 2 OHCOO −, HCOO −, CH 3SO 3−, Cl −, NO −2, SO 42− and C 2O 42−, trapped in ice deposited over some 200 000 years in Greenland. 相似文献
13.
The reaction of HOCl + HCl → Cl 2 + H 2O in the presence of chlorine anion Cl − has been studied using ab initio methods. The overall exothermicity is 15.5 kcal mol −1 and this reaction has been shown to have a high activation barrier of 46.5 kcal mol −1. Cl − is found to catalyze the reaction via the formation of HOCl·Cl −, ClH·HOCl·Cl − and Cl −·H 2) intermediate ion-molecule complexes or by interacting with a concerted four-center transition state of the reaction of HOCl + HCl. 相似文献
14.
Synthesized hydrated lamellar acidic crystalline magadiite (H 2Si 14O 29·2H 2O) nanocompound was used as host for intercalation of polar n-alkylmonoamine molecules of the general formula H 3C(CH 2) nNH 2 ( n = 1–6) in aqueous solution. The original interlayer distance ( d) of 1500 pm, determined by X-ray powder diffraction patterns, increases after intercalation. The values correlated with the number of aliphatic amine carbon ( nc) atoms: d = [(1312 ± 11) + (21 ± 2)] nc. The amount of intercalated amines ( Ns), decreased as nc increased: Ns = [(5.82 ± 0.04) − (0.45 ± 0.01)] nc. The acidic layered nanocompound was calorimetrically titrated with the amines and the thermodynamic data gave exothermic values for all guest molecules, as shown by the correlation: Δ intH = −[(24.45 ± 0.49) − (1.91 ± 0.10)] nc and d = [(1576 ± 16) − (10.8 ± 1.0)]Δ intH. The negative values of the Gibbs energies and the positive entropies also presented the correlations: Δ intG = −[(22.8 ± 0.2) − (0.2 ± 0.1)] nc and Δ intS = [(6 ± 1) + (5 ± 1)] nc, respectively. 相似文献
15.
The molecular structure and conformational properties of O=C(N=S(O)F 2) 2 (carbonylbisimidosulfuryl fluoride) were determined by gas electron diffraction (GED) and quantumchemical calculations (HF/3-21G* and B3LYP/6-31G*). The analysis of the GED intensities resulted in a mixture of 76(12)% syn– syn and 24(12)% syn– anti conformer (Δ H0= H0( syn– anti)− H0( syn– syn)=1.11(32) kcal mol −1) which is in agreement with the interpretation of the IR spectra (68(5)% syn– syn and 32(5)% syn– anti, Δ H0=0.87(11) kcal mol −1). syn and anti describe the orientation of the S=N bonds relative to the C=O bond. In both conformers the S=O bonds of the two N=S(O)F 2 groups are trans to the C–N bonds. According to the theoretical calculations, structures with cis orientation of an S=O bond with respect to a C–N bond do not correspond to minima on the energy hyperface. The HF/3-21G* approximation predicts preference of the syn– anti structure (Δ E=−0.11 kcal mol −1) and the B3LYP/6-31G* method results in an energy difference (Δ E=1.85 kcal mol −1) which is slightly larger than the experimental values. The following geometric parameters for the O=C(N=S) 2 skeleton were derived ( ra values with 3 σ uncertainties): C=O 1.193 (9) Å, C–N 1.365 (9) Å, S=N 1.466 (5) Å, O=C–N 125.1 (6)° and C–N=S 125.3 (10)°. The geometric parameters are reproduced satisfactorily by the HF/3-21G* approximation, except for the C–N=S angle which is too large by ca. 6°. The B3LYP method predicts all bonds to be too long by 0.02–0.05 Å and the C–N=S angle to be too small by ca. 4°. 相似文献
16.
The reaction of Ru II(PPh 3) 3X 2 (X = Cl, Br) with o-(OH)C 6H 4C(H)=N-CH 2C 6H 5 (HL) under aerobic conditions affords Ru II(L) 2(PPh 3) 2, 1, in which both the ligands (L) are bound to the metal center at the phenolic oxygen (deprotonated) and azomethine nitrogen and Ru III(L 1)(L 2)(PPh 3), 2, in which one L is in bidentate N,O form like in complex 1 and the other ligand is in tridentate C,N,O mode where cyclometallation takes place from the ortho carbon atom (deprotonated) of the benzyl amine fragment. The complex 1 is unstable in solution, and undergoes spontaneous oxidative internal transformation to complex 2. In solid state upon heating, 1 initially converts to 2 quantitatively and further heating causes the rearrangement of complex 2 to the stable RuL 3 complex. The presence of symmetry in the diamagnetic, electrically neutral complex 1 is confirmed by 1H and 31P NMR spectroscopy. It exhibits an Ru II → L, MLCT transition at 460 nm and a ligand based transition at 340 nm. The complex 1 undergoes quasi-reversible ruthenium(II)—ruthenium(III) oxidation at 1.27V vs. SCE. The one-electron paramagnetic cyclometallated ruthenium(III) complex 2 displays an L → Ru III, LMCT transition at 658 nm. The ligand based transition is observed to take place at 343 nm. The complex 2 shows reversible ruthenium(III)—ruthenium(IV) oxidation at 0.875V and irreversible ruthenium(III)—ruthenium(II) reduction at −0.68V vs. SCE. It exhibits a rhombic EPR spectrum, that has been analysed to furnish values of axial (6560 cm −1) and rhombic (5630 cm −1) distortion parameters as well as the energies of the two expected ligand field transitions (3877 cm −1 and 9540 cm −1) within the t 2 shell. One of the transitions has been experimentally observed in the predicted region (9090 cm −1). The first order rate constants at different temperatures and the activation parameter Δ H#/Δ S# values of the conversion process of 1 → 2 have been determined spectrophotometrically in chloroform solution. 相似文献
17.
The influence of several anions on Fe-based Fischer-Tropsch catalyst,used in the synthesis of light olefins from synthesis gas,was studied.The results indicated that the addition of anions resulted in the reduction of catalytic activity.When the anion content in the catalyst was 500 ppm,the influence of different anions on the catalysis activity was as follows:S~(2-)>Cl~->SO_4~(2-)>NO_3~-.The addition of S~(2-)improved the selectivity of total hydrocarbons in the products,and Cl~- reduced this selectivity but increased the olefin content in the total hydrocarbons at the same time.When the contents of S~2 and Cl~- in the catalyst were less than 50 ppm,their influence could be ignored.The XRD results indicated that the addition of anions reduced the contents ofα-Fe and Fe_3C,which were the active components in the catalyst. 相似文献
18.
The gas phase fragmentation reactions of protonated cysteine and cysteine-containing peptides have been studied using a combination of collisional activation in a tandem mass spectrometer and ab initio calculations [at the MP2(FC)/6-31G*//HF/6-31G* level of theory]. There are two major competing dissociation pathways for protonated cysteine involving: (i) loss of ammonia, and (ii) loss of the elements of [CH 2O 2]. MS/MS, MS/MS of selected ions formed by collisional activation in the electrospray ionization source as well as ab initio calculations have been carried out to determine the mechanisms of these reactions. The ab initio results reveal that the most stable [M + H − NH 3] + isomer is an episulfonium ion (A), whereas the most stable [M + H − CH 2O 2] + isomer is an immonium ion (B). The effect of the position of the cysteine residue on the fragmentation reactions of the [M + H] + ions of all the possible simple dipeptide and tripeptide methyl esters containing one cysteine (where all other residues are glycine) has also been investigated. When cysteine is at the N-terminal position, NH 3 loss is observed, although the relative abundance of the resultant [M + H − NH 3] + ion decreases with increasing peptide size. In contrast, when cysteine is at any other position, water loss is observed. The proposed mechanism for loss of H 2O is in competition with those channels leading to the formation of structurally relevant sequence ions. 相似文献
19.
The enthalpy of formation (Δ Hf0), enthalpy of evaporation (Δ Hv0) and enthalpy of atomization (Δ Ha) of permethylcyclosilazanes (Me 2SiNH) n ( n = 3, 4) and 1,1,3,3-tetramethyldisilazane (Me 2SiH) 2NH have been determined. The enthalpies of formation of these compounds were compared with those calculated by the Benson-Buss-Franklin and Tatevskii additive schemes. In higher permethylcyclosilazanes the energy of the endocyclic Si---N bond is 306 ± 2 kJ mol −1 (73 kcal mol −1), that is 12 ± 2 kJ mol −1 (3 kcal mol −1) lower than the energy of the acyclic Si---N bond. The strain energy of the cyclotrisilazane ring is estimated to be 10.5 kJ mol −1 (2.5 kcal mol −1), whereas the energy of the ring Si---N bond is 295 kJ mol −1 (70.5 kcal mol −1). The thermochemical data for permethylcyclosilazanes were compared with the corresponding values for permethylcyclosiloxanes calculated from the results of previously reported studies. 相似文献
20.
Calorimetric measurements of enthalpies of change of state (sublimation or vaporization) of methylnaphthalenes gave the following results: 1-methylnaphthalene: (ΔH√vap)m=(57.32±0.42) kJ mol−1 2-methylnaphthalene: (ΔH√sub)m=(65.69±0.84) kJ mol−1 Combination of these values with those obtained by Speros and Rossini1 for enthalpies of combustion of these compounds makes it possible to determine their energy of isomerization more accurately. This energy is (2.97±2.41) kJ mol−1 and should be attributed to steric hindrance in the 1-methylnaphthalene molecule. The comparison of energies of conjugation, theoretical as well as experimental, which we have determine for both molecules studied, confirms the present result. 相似文献
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