Structures and energetics of C3H6S isomers: a Gaussian-3 ab initio study

Twenty-two isomers/conformers of C₃H₆S^+√ radical cations have been identified and their heats of formation (ΔH_f) at 0 and 298 K have been calculated using the Gaussian-3 (G3) method. Seven of these isomers are known and their ΔH_f data are available in the literature for comparison. The least energy isomer is found to be the thioacetone radical cation (4⁺) with C_2v symmetry. In contrast, the least energy C₃H₆O^+√ isomer is the 1-propen-2-ol radical cation. The G3 ΔH_f298 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 ΔH_f298 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 ΔH_f298 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 ΔH_f298 values range from 918 to 1151 kJ mol⁻¹. Nevertheless, only one of them, CH₂=SCH₂CH₂^+√ (12⁺), has been observed. Its G3 ΔH_f298 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.     

Predictive schemes for the reactivity of borane carbonyl and the stability of carbonyltrihydroborate anions, BH3C(O)X

The reactivity of borane carbonyl (BH₃CO) and its isoelectronic counterpart the acetylium cation (CH₃CO⁺) are compared resulting in the formulation of (carbonyl)trihydroborate anions, BH₃C(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 BH₃C(O)X⁻ is proposed. The postulated order, with increasing stability is BH₃C(O)Cl⁻ < BH₃C(O)H⁻ < BH₃C(O)R⁻ < BH₃C(O)OR⁻ < BH₃C(O)NR⁻₂ < BH₃C(O)O²⁻. 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.     

Vibrational spectra and density functional study of propylgermane

Raman and infrared spectra of propylgermane, CH₃CH₂CH₂GeH₃, and its Ge-deuterated analog, CH₃CH₂CH₂GeD₃, 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 ΔH(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 ΔE(T−G)=−0.46 kcalmol⁻¹ and ΔE(T−G)=−0.87 kcalmol⁻¹ by the 6-31G^* basis set and 6-311++G^** basis set, respectively.     

Syntheses, spectroscopic characteristics and thermolytic rearrangements of bis-[(trimethylgermyl)methyl]platinum(II) and bis-[(trimethylstannyl)methyl]platinum(II) complexes

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(CH₂GeMe₃)₂L₂ (L = PPh₃ or PPh₂Me; L₂ = dppe or cod) and cis-Pt(CH₂SnMe₃)₂L₂ (L = PPh₃; L₂ =cod). Thermolysis of toluene solutions of cis-Pt(CH₂GeMe₃)₂(PPh₃)₂ leads to cis-Pt(Me)(CH₂GeMe₂CH₂GeMe₃)(PPh₃)₂ via β-alkyl migration, after (non-rate-limiting) phosphine dissociation. Estimated activation parameters (ΔH_{298 K}^‡ = 126 ± 3 kJ mol⁻¹, ΔS^‡ = + 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(CH₂GeMe₃)₂(PPh₂Me)₂ reacts similarly but less readily, Pt(CH₂GeMe₃)₂(dppe)₂ is inert at operable temperatures. Thermolysis of Pt(CH₂GeMe₃)₂(cod) generates 1,1,3,3,-tetramethyldi-1,3-germacyclobutane as the major organogermanium product, while from cis-Pt(CH₂SnMe₃)₂(PPh₃)₂, 1,1,3,3-tetramethyldi-1,3-stannacyclobutane predominates. Mechanistic implications are discussed.     

The chemical production of electronically excited states in the H/NF2 system

A mixture of NF₃ and Ar is passed through an rf discharge in a flow-system to produce, among other species, F and NF₂. When H₂, D₂, or CH₄ are added downstream, reactions with F atoms produce vibrationally excited HF or DF together with H, D, or CH₃. The latter free radicals can react with NF₂, probably by an elimination reaction to produce electronically excited NF: NF₂(²B₁) + H(D, CH₃) → HF^*(DF^* + NF(a¹Δ). 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(a¹Δ) → HF(ν−2) + NF(b¹Σ⁺). A similar transfer process has also been found between the electronically excited a¹Δ states of O₂ and NF: O₂(a¹Δ) + NF(a¹Δ) → O₂(X³Σ⁻) + NF(b¹Σ⁺). The H or D atoms but not the CH₃ radicals are then found to react with either NF(a¹Δ) or NF(X³Σ⁻) to produce electronically excited N(₂D) atoms, which in turn react with the NF(a¹Δ) molecules to produce N₂(B³Π_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) + N₂O → NO(B²Π_r) + N₂ (X¹Σ⁺_g) has been verified. Finally we have observed emission at 3344 Å, which we attribute to the NF(A³Π), which has not been previously reported.     

The gaseous azide ion, N3: Enthalpy of formation, ΔHf(N3(g)) and charge distribution lattice energies of sodium, potassium and rubidium azides

The calculations reported here assign a charge q_N = −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, ΔH_f⁰(N₃⁻(g)). The total lattice potential energies are found to be: E_pot(NaN₃) = 725.1 kJ mole⁻¹; E_pot(KN₃) = 650.7 kJ mole⁻¹ and E_pot(RbN₃) = 632.1 kJ mole⁻¹.     

Thermal decomposition study on mixed ligand thymine complexes of divalent nickel(II) with dianions of some dicarboxylic acids

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(C₅H₆N₂O₂)(C₄H₅NO₄)²⁻(H₂O)₂]·H₂O, [Ni(C₅H₆N₂O₂)(C₅H₇NO₄)²⁻(H₂O)₂]·H₂O and [Ni(C₅H₆N₂O₂)(C₆H₈N₂O₅)²⁻(H₂O)₂]·1.5H₂O were analyzed. The final decomposition products are found to be the corresponding metal oxides. The kinetic parameters namely, activation energy (E*), enthalpy (ΔH*), entropy (ΔS*) and free energy change of decomposition (ΔG*) 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.     

The excess molar volumes of (an alkanol + a branched chain ether) at the temperature 298.15 K and the application of the ERAS model

The excess molar volumes V_m^E {x(CH₃OH or CH₃CH₂OH or CH₃(CH₂)₂OH or CH₃CH(OH)CH₃ + (1 - x){CH₃(CH₂)₂}₂O or CH₃C(CH₃)₂OCH₃ or CH₃CH₂C(CH₃)₂OCH₃} 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 V_m^h results presented here, together with the previously reported data for the molar excess enthalpy H_m^E, has been used to test the Extended Real Associated Solution (ERAS) model.     

Spectrophotometric study of complexation equilibria between HCrO4 and Cl ions

The complex equilibria between HCrO₄⁻ 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: HCrO₄⁻+H⁺+Cl⁻ = CrO₃Cl⁻+H₂O (log β₁₁ = 1.37±0.08). Molar absorptivities of HCrO₄⁻ and CrO₃Cl⁻ were also reported.     

Relative thermodynamic stabilities of isomeric alkyl allyl and alkyl (Z)-propenyl ethers

The relative thermodynamic stabilities of ten allyl ethers (ROCH₂CH=CH₂) 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.     

Ab initio calculations of minimum-energy pathways of the nucleophilic addition of the H anion, LiH molecule and Li/H ion pair to acetylene and methylacetylene

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 (ΔE_a) and the reaction heats (ΔQ)). The substitution of the H atom by the CH₃ group in A molecule results in practically the same values of ΔQ and ΔE_a. 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⁻.     

Field investigation of major and minor ions along Summit (Central Greenland) ice cores by ion chromatography

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⁺, Mg²⁺, Ca²⁺, F⁻, CH₃COO⁻, CH₂ OHCOO⁻, HCOO⁻, CH₃SO₃⁻, Cl⁻, NO⁻₂, SO₄²⁻ and C₂O₄²⁻, trapped in ice deposited over some 200 000 years in Greenland.     

Can chlorine anion catalyze the reaction of HOCl with HCl?

The reaction of HOCl + HCl → Cl₂ + H₂O 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⁻·H₂) intermediate ion-molecule complexes or by interacting with a concerted four-center transition state of the reaction of HOCl + HCl.     

Crystalline polysilicate magadiite with intercalated n-alkylmonoamine and some correlations involving thermochemical data

Synthesized hydrated lamellar acidic crystalline magadiite (H₂Si₁₄O₂₉·2H₂O) nanocompound was used as host for intercalation of polar n-alkylmonoamine molecules of the general formula H₃C(CH₂)_nNH₂ (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 (n_c) atoms: d = [(1312 ± 11) + (21 ± 2)]n_c. The amount of intercalated amines (N_s), decreased as n_c increased: N_s = [(5.82 ± 0.04) − (0.45 ± 0.01)]n_c. 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)]n_c 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)]n_c and Δ_intS = [(6 ± 1) + (5 ± 1)]n_c, respectively.     

Structure and conformational properties of carbonylbisimidosulfuryl fluoride, O=C(N=S(O)F2)2

The molecular structure and conformational properties of O=C(N=S(O)F₂)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 (ΔH⁰=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, ΔH⁰=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)F₂ 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 (ΔE=−0.11 kcal mol⁻¹) and the B3LYP/6-31G* method results in an energy difference (ΔE=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 (r_a values with 3σ 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°.     

Paramagnetic ruthenium(III) cyclometallated complex. Synthesis, spectroscopic studies and electron-transfer properties

The reaction of Ru^II(PPh₃)₃X₂ (X = Cl, Br) with o-(OH)C₆H₄C(H)=N-CH₂C₆H₅ (HL) under aerobic conditions affords Ru^II(L)₂(PPh₃)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(L¹)(L²)(PPh₃), 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 RuL₃ 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 t₂ 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 ΔH^#/ΔS^# values of the conversion process of 1 → 2 have been determined spectrophotometrically in chloroform solution.     

Effect of Several Anions on Fe-Based Catalyst for Fischer-Tropsch Synthesis

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.     

Role of the sulfhydryl group on the gas phase fragmentation reactions of protonated cysteine and cysteine containing peptides

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 [CH₂O₂]. 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 − NH₃]⁺ isomer is an episulfonium ion (A), whereas the most stable [M + H − CH₂O₂]⁺ 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, NH₃ loss is observed, although the relative abundance of the resultant [M + H − NH₃]⁺ 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 H₂O is in competition with those channels leading to the formation of structurally relevant sequence ions.     

Thermochemistry of organosilicon compounds VII. Permethylcyclosilazanes and 1,1,3,3-tetramethyldisilazane

The enthalpy of formation (ΔH_f⁰), enthalpy of evaporation (ΔH_v⁰) and enthalpy of atomization (ΔH_a) of permethylcyclosilazanes (Me₂SiNH)_n (n = 3, 4) and 1,1,3,3-tetramethyldisilazane (Me₂SiH)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.     

Étude thermochimique des méthylnaphtalènes

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.