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1.
Ab initio self-consistent field (SCF ) calculations are performed with the standard 6-31G* basis set for all-trans conjugated oligomers C2n+2H2n+4. The canonical occupied and virtual molecular orbitals (MO s) are separately localized by unitary transformations. Due to the localization, the perturbation operator is partitioned into two-particle and into single-particle terms; the MBPT is, therefore, a double-perturbation expansion in this case. By using the localized representation of the MBPT , the correlation energy contributions can be partitioned into local and nonlocal effects. It can be shown that the local effects are very important and well transferable, which makes possible the calculation of the correlation energy of larger molecules if the localized molecular orbitals (occupied and virtual) of smaller related molecules are known. © 1994 John Wiley & Sons, Inc.  相似文献   

2.
We studied the attraction between [C2Hn] and Tl(I) in the hypothetical [C2Hn–Tl]+ complexes (n = 2,4) using ab initio methodology. We found that the changes around the equilibrium distance C–Tl and in the interaction energies are sensitive to the electron correlation potential. We evaluated these effects using several levels of theory, including Hartree–Fock (HF), second‐order Møller–Plesset (MP2), MP4, coupled cluster singles and doubles CCSD(T), and local density approximation augmented by nonlocal corrections for exchange and correlation due to Becke and Perdew (LDA/BP). The obtained interaction energies differences at the equilibrium distance Re (C–Tl) range from 33 and 46 kJ/mol at the different levels used. These results indicate that the interaction between olefinic systems and Tl(I) are a real minimum on the potential energy surfaces (PES). We can predict that these new complexes are viable for synthesizing. At long distances, the behavior of the [C2Hn]–Tl+ interaction may be related mainly to charge‐induced dipole and dispersion terms, both involving the individual properties of the olefinic π‐system and thallium ion. However, the charge‐induced dipole term (R?4) is found as the principal contribution in the stability at long and short distances. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007  相似文献   

3.
The density functional theory (DFT) and the complete active space self‐consistent‐field (CASSCF) method have been used for full geometry optimization of carbon chains C2nH+ (n = 1–5) in their ground states and selected excited states, respectively. Calculations show that C2nH+ (n = 1–5) have stable linear structures with the ground state of X3Π for C2H+ or X3Σ? for other species. The excited‐state properties of C2nH+ have been investigated by the multiconfigurational second‐order perturbation theory (CASPT2), and predicted vertical excitation energies show good agreement with the available experimental values. On the basis of our calculations, the unsolved observed bands in previous experiments have been interpreted. CASSCF/CASPT2 calculations also have been used to explore the vertical emission energy of selected low‐lying states in C2nH+ (n = 1–5). Present results indicate that the predicted vertical excitation and emission energies of C2nH+ have similar size dependences, and they gradually decrease as the chain size increases. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009  相似文献   

4.
[CnH2n?3]+ and [CnH2n?4]+·(n = 7, 8) ions have been generated in the mass spectrometer from CnH2n?3 Br (n = 7, 8) precursors and from two steroids. The relative abundances of competing ‘metastable transitionss’ indicate (partial) isomerization to a common structure (or mixture of structures) prior to decomposition in most examples of all four types of ions. In contrast, [C8H10O]+· and [C8H12O]+· ions, generated from different sources as molecular ions and by fragmentation of steroids, do not decompose through common-intermediates.  相似文献   

5.
OH+ is an extraordinarily strong oxidant. Complexed forms (L? OH+), such as H2OOH+, H3NOH+, or iron–porphyrin‐OH+ are the anticipated oxidants in many chemical reactions. While these molecules are typically not stable in solution, their isolation can be achieved in the gas phase. We report a systematic survey of the influence on L on the reactivity of L? OH+ towards alkanes and halogenated alkanes, showing the tremendous influence of L on the reactivity of L? OH+. With the help of with quantum chemical calculations, detailed mechanistic insights on these very general reactions are gained. The gas‐phase pseudo‐first‐order reaction rates of H2OOH+, H3NOH+, and protonated 4‐picoline‐N‐oxide towards isobutane and different halogenated alkanes CnH2n+1Cl (n=1–4), HCF3, CF4, and CF2Cl2 have been determined by means of Fourier transform ion cyclotron resonance meaurements. Reaction rates for H2OOH+ are generally fast (7.2×10?10–3.0×10?9 cm3 mol?1 s?1) and only in the cases HCF3 and CF4 no reactivity is observed. In contrast to this H3NOH+ only reacts with tC4H9Cl (kobs=9.2×10?10), while 4‐CH3‐C5H4N‐OH+ is completely unreactive. While H2OOH+ oxidizes alkanes by an initial hydride abstraction upon formation of a carbocation, it reacts with halogenated alkanes at the chlorine atom. Two mechanistic scenarios, namely oxidation at the halogen atom or proton transfer are found. Accurate proton affinities for HOOH, NH2OH, a series of alkanes CnH2n+2 (n=1–4), and halogenated alkanes CnH2n+1Cl (n=1–4), HCF3, CF4, and CF2Cl2, were calculated by using the G3 method and are in excellent agreement with experimental values, where available. The G3 enthalpies of reaction are also consistent with the observed products. The tendency for oxidation of alkanes by hydride abstraction is expressed in terms of G3 hydride affinities of the corresponding cationic products CnH2n+1+ (n=1–4) and CnH2nCl+ (n=1–4). The hypersurface for the reaction of H2OOH+ with CH3Cl and C2H5Cl was calculated at the B3 LYP, MP2, and G3m* level, underlining the three mechanistic scenarios in which the reaction is either induced by oxidation at the hydrogen or the halogen atom, or by proton transfer.  相似文献   

6.
In the ion/molecule reactions of the cyclometalated platinum complexes [Pt(L? H)]+ (L=2,2′‐bipyridine (bipy), 2‐phenylpyridine (phpy), and 7,8‐benzoquinoline (bq)) with linear and branched alkanes CnH2n+2 (n=2–4), the main reaction channels correspond to the eliminations of dihydrogen and the respective alkenes in varying ratios. For all three couples [Pt(L? H)]+/C2H6, loss of C2H4 dominates clearly over H2 elimination; however, the mechanisms significantly differs for the reactions of the “rollover”‐cyclometalated bipy complex and the classically cyclometalated phpy and bq complexes. While double hydrogen‐atom transfer from C2H6 to [Pt(bipy? H)]+, followed by ring rotation, gives rise to the formation of [Pt(H)(bipy)]+, for the phpy and bq complexes [Pt(L? H)]+, the cyclometalated motif is conserved; rather, according to DFT calculations, formation of [Pt(L? H)(H2)]+ as the ionic product accounts for C2H4 liberation. In the latter process, [Pt(L? H)(H2)(C2H4)]+ (that carries H2 trans to the nitrogen atom of the heterocyclic ligand) serves, according to DFT calculation, as a precursor from which, due to the electronic peculiarities of the cyclometalated ligand, C2H4 rather than H2 is ejected. For both product‐ion types, [Pt(H)(bipy)]+ and [Pt(L? H)(H2)]+ (L=phpy, bq), H2 loss to close a catalytic dehydrogenation cycle is feasible. In the reactions of [Pt(bipy? H)]+ with the higher alkanes CnH2n+2 (n=3, 4), H2 elimination dominates over alkene formation; most probably, this observation is a consequence of the generation of allyl complexes, such as [Pt(C3H5)(bipy)]+. In the reactions of [Pt(L? H)]+ (L=phpy, bq) with propane and n‐butane, the losses of the alkenes and dihydrogen are of comparable intensities. While in the reactions of “rollover”‐cyclometalated [Pt(bipy? H)]+ with CnH2n+2 (n=2–4) less than 15 % of the generated product ions are formed by C? C bond‐cleavage processes, this value is about 60 % for the reaction with neo‐pentane. The result that C? C bond cleavage gains in importance for this substrate is a consequence of the fact that 1,2‐elimination of two hydrogen atoms is no option; this observation may suggest that in the reactions with the smaller alkanes, 1,1‐ and 1,3‐elimination pathways are only of minor importance.  相似文献   

7.
IR photodissociation spectra of mass‐selected clusters composed of protonated benzene (C6H7+) and several ligands L are analyzed in the range of the C? H stretch fundamentals. The investigated systems include C6H7+? Ar, C6H7+? (N2)n (n=1–4), C6H7+? (CH4)n (n=1–4), and C6H7+? H2O. The complexes are produced in a supersonic plasma expansion using chemical ionization. The IR spectra display absorptions near 2800 and 3100 cm?1, which are attributed to the aliphatic and aromatic C? H stretch vibrations, respectively, of the benzenium ion, that is, the σ complex of C6H7+. The C6H7+? (CH4)n clusters show additional C? H stretch bands of the CH4 ligands. Both the frequencies and the relative intensities of the C6H7+ absorptions are nearly independent of the choice and number of ligands, suggesting that the benzenium ion in the detected C6H7+? Ln clusters is only weakly perturbed by the microsolvation process. Analysis of photofragmentation branching ratios yield estimated ligand binding energies of the order of 800 and 950 cm?1 (≈9.5 and 11.5 kJ mol?1) for N2 and CH4, respectively. The interpretation of the experimental data is supported by ab initio calculations for C6H7+? Ar and C6H7+? N2 at the MP 2/6‐311 G(2df,2pd) level. Both the calculations and the spectra are consistent with weak intermolecular π bonds of Ar and N2 to the C6H7+ ring. The astrophysical implications of the deduced IR spectrum of C6H7+ are briefly discussed.  相似文献   

8.
The nature of the bonding and the aromaticity of the heavy Group 14 homologues of cyclopropenylium cations E3H3+ and E2H2E′H+ (E, E′=C–Pb) have been investigated systematically at the BP86/TZ2P DFT level by using several methods. Aromatic stabilization energies (ASE) were evaluated from the values obtained from energy decomposition analysis (EDA) of charged acyclic reference molecules. The EDA‐ASE results compare well with the extra cyclic resonance energy (ECRE) values given by the block localized wavefunction (BLW) method. Although all compounds investigated are Hückel 4n+2 π electron species, their ASEs indicate that the inclusion of Group 14 elements heavier than carbon reduces the aromaticity; the parent C3H3+ ion and Si2H2CH+ are the most aromatic, and Pb3H3+ is the least so. The higher energies for the cyclopropenium analogues reported in 1995 employed an isodesmic scheme, and are reinterpreted by using the BLW method. The decrease in the strength of both the π cyclic conjugation and the aromaticity in the order C?Si>Ge>Sn>Pb agrees reasonably well with the trends given by the refined nucleus‐independent chemical shift NICS(0)πzz index.  相似文献   

9.
It is shown that alkyl radical species present in CH4 or iso-C4H10 plasma can react with substrate molecules to give [M+CnH2n] species. These species become evident especially in negative chemical ionization as [M+CnH2n] and, less obviously, in positive chemical ionization as [M+CnH2n+1]+ ions which, for example in natural products chemistry, may be mistaken for a series of homologous compounds present in the sample.  相似文献   

10.
A neutralization-reionization study of [C3Hn]+ ions, n = 6?0, shows that neutralization efficiencies are larger for hydrocarbon radical cations than they are for even-electron carbocations with one more H atom. Reionization efficiencies to positive ions do not depend appreciably on the electronic properties of the neutral species undergoing reionization. However, reionization efficiencies to negative ions increase dramatically with the degree of unsaturation, by nearly two orders of magnitude, from C3H6 to C3. All C3Hn neutrals studied survive intact neutralization to produce a considerable fraction of stable, non-dissociating [C3Hn]+ upon cationization. All C3Hn radicals (n = 5, 3, 1) can be transferred collisionally to stable even-electron anions. For the C3Hn hydrocarbon molecules studied (n = 6, 4, 2, 0) the stability of the molecular radical anion increases substantially with the degree of unsaturation.  相似文献   

11.
The properties of alkyl sulfate and alkyl sulfonate are similar except for their Krafft points. However, alkyl sulfate and alkyl sulfonate behave quite differently when they are mixed with cationic surfactants and show some totally unexpected results. In this work sodium alkyl sulfate (CnH2n+1SO4Na,CnSO4)–alkyl quaternary ammonium bromide [CnH2n+1N(CmH2m+1)3Br, CnN, m=1–4] mixtures and sodium alkyl sulfonate (CnH2n+1SO3Na, CnSO3)–CnN mixtures were studied. It was found that, in contrast to the single surfactants, CnSO3–CnN mixtures were much more soluble than CnSO4–CnN mixtures. Besides, the two kinds of catanionic surfactant mixtures were quite different in their phase behavior and aggregate properties. The results were interpreted in terms of the interactions between surfactant molecules, which were very different in the two kinds of mixed systems owing to the distinction between alkyl sulfate and alkyl sulfonate in the molecular charge distribution.  相似文献   

12.
Summary The [h]phenylene C6h H2h+4 isomers are enumerated up toh=12. The numbers are compared with old and new data for C n H5 isomers of benzenoids, fluoranthenoids and biphenylenoids.
Anzahl möglicher Isomerer von Phenylenen
Zusammenfassung Die Anzahl der [h]Phenylen-Isomeren C6h H2h+4 wurde bish=12 ausgewertet. Die Zahlen wurden mit alten und neuen Daten für C n H s -Isomere von Benzenoiden, Fluoranthenoiden und Biphenyloiden verglichen.
  相似文献   

13.
The 12.1 eV, 75°C electron impact mass spectra of 24 urethanes, RNHCO2C2H5 [R ? H, C2H2n +1 (n = 1-8), CH2?CHCH2, Ph, PhCH2 and PhCH2CH2], and seven symmetrically disubstituted urethanes R2NCO2C2H5 (R ? Cn H2n + 1 (n = 1?4)) are reported and discussed. All 31 spectra show appreciable molecular ion peaks. For n ?Cn H2n +1 NHCO2C2H5, M+ ˙ usually is the most abundant ion in the spectrum. A peak at m/z 102 of comparable intensity also is present; this corresponds to formal cleavage of the bond connecting the α- and β-carbon atoms in the N-alkyl group, though it is unlikely that the daughter ion has the structure [CH2?NHCO2C2H5]+. In the RNHCO2C2H5 series, branching at the α-carbon atom enhances the relative abundance of the ion arising by notional α-cleavage at the expense of that of M+ ˙. Formal cleavage of the bond between β- and γ-carbon atoms occurs to some extent for [RNHCO2C2H5]+˙ ions; this reaction provides information on the degree of branching at the β-carbon, especially if metastable molecular ions are considered. The higher n-CnH2n +1NHCO2C2H5 (n = 5?8) urethanes exhibit two other significant ions in their mass spectra. First, there is a peak at [M ? C2H5]+. Secondly, a peak is present at m/z 90; the most plausible structure for this ion is [H2N(HO)COC2H5]+, arising by double hydrogen transfer from the alkyl group and expulsion of a [CnH2n ?1]˙ radical. Ions originating from secondary decomposition of the primary ionic species are generally of only very low abundance in these spectra.  相似文献   

14.
Using ab initio MO calculations at the MP2/6‐311G(2df,2pd) level of theory the most stable structures of the following seven ions were determined: H3S+ (C3v), H2S–SH+ (Cs), H2S–S–SH+ (C1), HS–S(H)–SH+ (C1), H2S–S–S–SH+ (C1), HS–S(H)–S–SH+ (C1) and S(SH)3+ (C3). In the case of the isomeric H3S3+ cations the species protonated at the terminal sulfur atom is most stable while in the case of the H3S4+ ions the protonation at the β sulfur atom is energetically preferred. However, the energy differences between isomeric cations are rather small. At the same level of theory the wavenumbers of the harmonic fundamental vibrations were calculated and compared to the available experimental data leading to a support for the existing assignments in certain cases but in some cases to revisions. The reaction enthalpies and Gibbs free energies of the proton transfer reactions H2Sn + H2Sn+1 → H3Sn+ + HSn+1 were calculated by the G2 method. For n = 1–3 the enthalpies are found in the range 639–731 kJ mol–1.  相似文献   

15.
The mass spectra of diethyl phenyl phosphates show substituent effects with electron-donating groups favouring the molecular ion M+˙, and the [M? C2H4]+˙, [M – 2C2H4]+˙ and [XPhOH]+˙ ions. The [PO3C2H6]+ (m/z 109) and [PO3H2]+ (m/z 81) ions are favoured by electron-withdrawing groups. Results suggest that the formation of the [XPhC2H3]+˙ ion involves rearrangement of C2H3 to the position ortho to the phosphate group. Ortho effects are also observed.  相似文献   

16.
The effect of solvation on the conformation of acetylene has been studied by adding one water molecule at a time. Quantum chemical calculations of the H+(C2H2)(H2O)n (n=1-5) clusters indicate that the H2O molecules prefer to form the OH…π interaction rather than the CH…O interaction. This solvation motif is different from that of neutral (C2H2)(H2O)n (n=1-4) clusters, in which the H2O molecules prefer to form the CH…O and OH…C H-bonds. For the H+(C2H2)(H2O)n cationic clusters, the first solvation shell consists of one ring structure with two OH…π H-bonds and three water molecules, which is completed at n=4. Simulated infrared spectra reveal that vibrational frequencies of OH…π H-bonded O-H stretching afford a sensitive probe for exploring the solvation of acetylene by protonated water molecules. Infrared spectra of the H+(C2H2)(H2O)n(n=1-5) clusters could be readily measured by the infrared photodissociation technique and thus provide useful information for the understanding of solvation processes.  相似文献   

17.
A method of estimating the enthalpies of formation of amino molecular ions, ΔH? ([CnH2n+1NH2]+˙) and of immonium ions ΔH([CnH2n+1N]+) is reported. It is based on the fact that CH3 is isoelectronic with NH2, CH2 with NH and CH with N. Some calculated values of the enthalpies of formation of amine molecular ions and immonium ions are reported and estimates are made of the accuracy of such calculation.  相似文献   

18.
Diagrammatic formulation of the many-body perturbation theory is investigated when both the occupied orbitals and the virtual ones are localized, i.e., they are unitary transforms of the canonical Hartree–Fock orbitals. All diagrams representing ground state correlation energy can be generated through fifth order. For cyclic polyenes C6H6 and C10H10 as model systems, the energy corrections are calculated in the Pariser–Parr–Pople approximation for a wide range of the coupling constant β?1, through fourth order including some fifth order terms. The results are compared to those obtained by other methods: perturbation theory by using canonical orbitals and full CI. The effect of neglecting contributions from orbitals localized into neighboring sites is also studied.  相似文献   

19.
Reactions that proceed within mixed ethylene–methanol cluster ions were studied using an electron impact time-of-flight mass spectrometer. The ion abundance ratio, [(C2H4)n(CH3OH)mH+]/[(C2H4)n(CH3OH)m+], shows a propensity to increase as the ethylene/methanol mixing ratio increases, indicating that the proton is preferentially bound to a methanol molecule in the heterocluster ions. The results from isotope-labelling experiments indicate that the effective formation of a protonated heterocluster is responsible for ethylene molecules in the clusters. The observed (C2H4)n(CH3OH)m+ and (C2H4)n(CH3OH)m–1CH3O+ ions are interpreted as a consequence of the ion–neutral complex and intracluster ion–molecule reaction, respectively. Experimental evidence for the stable configurations of heterocluster species is found from the distinct abundance distributions of these ions and also from the observation of fragment peaks in the mass spectra. Investigations on the relative cluster ion distribution under various conditions suggest that (C2H4)n(CH3OH)mH+ ions with n + m ≤ 3 have particularly stable structures. The result is understood on the basis of ion–molecule condensation reactions, leading to the formation of fragment ions, $ {\rm CH}_2=\!=\mathop {\rm O}\limits^ + {\rm CH}_3 $ and (CH3OH)H3O+, and the effective stabilization by a polar molecule. The reaction energies of proposed mechanisms are presented for (C2H4)n(CH3OH)mH+(n + m ≤ 3) using semi-empirical molecular orbital calculations.  相似文献   

20.
Homoadamantane derivatives can be divided into two groups according to their mass spectra. To the first group belong compounds with electron attracting substituents (COOH, CI, COOCH3, Br); compounds with electron releasing substituents (OCH3, OH, NH3, NHCOCH3) constitute the second group. The most characteristic feature of the first group compounds is the splitting off of the substituent. The hydrocarbon fragment [C11H17]+ thus formed then loses olefin molecules with the formation of corresponding ionic species C11?nH17?2n. The 3-substituted compounds of this group undergo thermal Wagner-Meerwein type rearrangements into adamantane derivatives, resulting in the [C10H15]+ (m/e 135) ion formation; this is the main difference between 1- and 3-substituted homoadamantanes. The series of [CnH2n?6X]+ ions (where X = OCH3, OH, NH2, NHCOCH3, n = 6 to 10) are characteristic of the mass spectra of the second group compounds, the ion [C6H6X]+, [M ? C5H11]+ being the most abundant. The intensity ratio of [M ? C5H11]+ to [M ? C4H9]+ ions is 10:1 for 1-substituted and 3:1 for 3-substituted compounds of this group, allowing the location of the substituent. Some individual features of the spectra are also reported.  相似文献   

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