Electronic structure of polychlorophenols and their carbocations

Polychlorophenols (PCP) with different numbers of chlorine atoms and their protonated forms have been calculated by the AM1 method with full optimization of geometry. The proton affinity of PCP with various types of coordination of the proton to the molecule has been estimated. The calculations show that the proton affinity averaged over isomers decreases monotonically as the number of chlorine atoms increases. Based on the calculations of the carbocations, the ⁺ constant of the OH-substituent at theipso-position is equal to 0.69. There is fair agreement between the relative energies of the isomers of the carbocations determined from the constants of the substituents and calculated by the AM1 method. These energies can be recommended for qualitative estimation of the proton affinity in definite positions of aromatic molecules with Cl- and OH-substituents.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1198–1201, July, 1994.     

Calculation of the proton affinities of polychlorobenzenes and the activation energies of 1,2-hydrogen shifts in arenonium ions

The proton affinities of benzene, chlorobenzene and polychlorobenzenes with the common formula C₆Cl _n H_6–n (n=0–6) have been calculated by the AM1 method. The proton affinity averaged over the protonated isomers increases monotonically asn growing from 0 to 5, and then decreases when passing from pentato hexachlorobenzene. The energies of proton addition to the different positions in the polychlorobenzene molecules have been estimated. It has been found that unsubstituted carbon atoms are preferred for proton attack. The positions with the highest proton affinity are the carbon atoms with the largest negative charges. The activation energies of 1,2-hydrogen shifts in arenonium ions of the polychlorobenzenes have been calculated.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1213–1217, July, 1993.     

Charge control of phenol complexation with unsaturated compounds containing organosilicon substituents. Thiophene derivatives

The frequency shifts of the O-H stretching modes and the resonance components _R of these shifts in the IR spectra of H-complexes of phenol with thiophene derivatives having organic and organosilicon substituents have been analyzed. Relationship of and _R parameters to values calculated by nonempirical methods that characterize the electronic effect of organic substituents on the effective charges of the thiophene ring atoms has been established. It has been shown that in the complexation of phenol (hard acid) with thiophene derivatives charge control prevails over frontier orbital control. The changes in the effective charges of the thiophene ring atoms due to the effect of organosilicon substituents have been calculated.For the previous publication of this series see Ref. 1.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2163–2168, December, 1994.This work was supported by the Russian Foundation for Basic Research, Project No. 93-03-18725.     

Structure and isomerization of arenonium ions of dichlorobenzenes in the gas phase. A theoretical study

Ab initio MP2 calculations of all isomeric arenoium ions (AI) ofortho-, meta-, andpara-dichlorobenzenes in the gas phase were carried out with full optimization of geometry with the 6–31 G^* basis set. The calculated proton affinities depend substantially on the position of geminal center in the corresponding dichlorobenzenonium ion and decrease in the series 1,2-dichloro-4H-benzenonium>1,2-dichloro-3H-benzenonium>1,2-dichloro-2H-benzenonium; 1,3-dichloro-4H-benzenonium>1,2-dichloro-3H-benzenonium >1,3-dichloro-5H-benzenonium>1,3-dichloro-3H-benzenonium; 1,4-dichloro-2H-benzenonium >1,4-dichloro-4H-benzenonium. The structures of transition states and activation energies (E _a) of almost all 1,2-shifts of H and Cl atoms in Al were determined. The activation energies of migrations of H atoms are about 6 kcal mol⁻¹ less than those of migrations of Cl atoms in similar structures. The isomerization routes and relations between the rate constants for isomerization of dichlorobenzenes through Al were established. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1726–1731, September, 1998.     

Protonation of ferrocene,ruthenocene, and osmocene: a density functional study

Protonated forms of the ferrocene, ruthenocene, and osmocene molecules in the gas phase were calculated using the density functional approach with the Becke—Lee—Young—Parr functional. The proton affinity energies of ferrocene, ruthenocene, and osmocene were estimated at 214.2, 220.3, and 229.7 kcal mol^–1, respectively. The addition of a proton to carbon atoms of the cyclopentadienyl ring in the ferrocene molecule and to the metal atom in the ruthenocene and osmocene molecules is more energetically favorable. No minimum corresponding to ring protonation was located on the potential energy surface of protonated osmocene. The C—H _endo bond in the ring-protonated [C₁₀H₁₁M]⁺ (M = Fe, Ru) cations is involved in agostic interaction with the metal atom. Transition states of interconversions between the ring-protonated and metal-protonated forms were identified. A specific group of protonated forms of the ferrocene and ruthenocene molecules includes four types of structures, viz., ring-protonated (1a,b) and metal-protonated (2a,b) structures, transition states of the 1 2 interconversion (3a,b), as well as ring-protonated structures with the cyclopentadiene ring folded along the C(2)—C(5) line so that the M—H _endo interaction is virtually negligible. The latter structures are required for [1,5]-sigmatropic shift of the exo-hydrogen atom in the Cp ring to occur. The results obtained were used for the interpretation of the available schemes of electrophilic substitution reactions in metallocenes and of the sigmatropic shift mechanisms.     

peri-Naphthylenediamines. 33. Further studies of the reactions of 1,8-bis(dimethylamino)naphthalene with trifluoroacetic anhydride

The reaction of 1,8-bis(dimethylamino)naphthalene (1) (proton sponge) with a large excess of trifluoroacetic anhydride in the absence of a solvent afforded a complex mixture of products among which were trans- (2) and cis-diols (3) of the naphtho[1,8-c,d]pyran series, the double proton sponge (4), its di- (5) and tetrafluoroacetyl (6) derivatives, and compound 7. These results differ substantially from those obtained previously in the reactions performed in various solvents. Some conversions of compounds 4 and 7 were investigated. The ¹⁹F NMR spectra of the compounds synthesized are discussed.     

Crystal and Molecular Structure of Cu(II) Bis-(2-methoxy-2,6-dimethyl-3-imino-5-heptanonate)

A new compound from the series of alkoxyketoiminates, Cu(II) bis-(2-methoxy-2,6-dimethyl-3-imino-5-heptanonate), has been synthesized and studied by X-ray crystallography. Crystal data for CuO₄N₂C₂₀H₃₆: a=10.154(1), b=9.921(1), c=11.684(2) , =96.17(1)°, space group P2₁/c, Z=2, dcalc =1.226 g/cm³, R=0.037. The structure is molecular and built from isolated trans-complexes. The copper atom has a plane square environment of two oxygen atoms (Cu–O 1.93 ) and two nitrogen atoms (Cu–N 1.90 ). The O–Cu–N chelate angle is 91.7°. The complex has an intramolecular hydrogen bond, N–H...O 2.16 , involving the alkoxy oxygen atom. The molecular packing in the crystal is close to that of copper(II) dipivaloylmethanate. The calculated van der Waals intermolecular interaction energies and thermogravimetric characteristics of the complexes are compared.     

Ab initio MP2 calculations of the products of acetylene addition to HgCl2

Gas-phase reaction of acetylene with HgCl₂ resulting in -chlorovinylmercury derivatives and their interaction with Cl^– and I^– anions and KI molecule was studied by the ab initio MP2 method with the Dunning—Hay double zeta basis set and LanL pseudopotential for Hg, K, and I atoms. The reaction was shown to proceed via a -complex of acetylene and HgCl₂ (the calculated enthalpy of formation is –6.5 kcal mol^–1). According to calculations, the activation energy of formation of cis--chlorovinylmercury chloride from acetylene and HgCl₂ is 31 kcal mol^–1. Chloride and iodide anions and KI molecule are readily added to both cis- and trans-isomer of -chlorovinylmercury chloride to give stable species.     

Novel boracycles from 2-amino-2-methylpropan-1-ol and borane methyl sulfide: Synthesis and X-ray crystal structures

On reacting the simple 1,2-amino alcohol: 2-amino-2-methylpropan-1-ol, with borane methyl sulfide (BMS), the expected five member oxazaborolidine ring is not obtained. Instead, two polycyclic structures with trigonal boron atoms 6 and 7 were obtained, and their structure were determined by X-ray crystallography. Compound 6 was obtained in 39% yield and compound 7 was obtained in 7% yield.     

Stereochemical studies, 73. Saturated heterocycles, 60

N-Substituted-2-carboxamido-1-cycloalkanols were cyclized with 1,1-carbonyldiimidazole to synthesizecis- andtrans-N-alkyl-,N-aralkyl- andN-aryl-2,4-dioxo tri- and tetramethyleneperhydro-1,3-oxazines. The structures of the compounds and theircis ortrans ring anellation were confirmed by IR,¹H- and¹³C-NMR spectroscopy, and thecis andtrans pairs of isomers were compared to establish the predominant conformation of the flexiblecis isomers. It was found that—similarly to the 1,3-oxazin-2- and -4-ones studied earlier—the O-endo conformers are preferred, in which the 1-oxygen atom isaxial to the alicyclic ring; this is independent of the number of ring atoms in the alicycle, and of the presence of an oxazinedione ring, even though this is more flexible that the ring of oxazinones.

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Synthese und Konformation voncis undtrans 2-substituierten kondensierten 1,3-Oxazin-2,4-dionen

Zusammenfassung cis- undtrans-N-Alkyl-,N-Aralkyl- undN-Aryl-2,4-dioxo-, tri- und tetramethylen-perhydro-1,3-oxazine wurden aus 2-Carboxamido-1-cycloalkanolen und 1,1-Carbonyldiimidazol dargestellt. Mit Hilfe der IR,¹H- und¹³C-NMR Spektroskopie wurden die Struktur, diecis- odertrans-Annellierung der Ringe und die bevorzugte Konformation der flexiblencis-Isomeren im Vergleich zumcis-trans Isomerenpaar nachgewiesen. Ähnlich zu den früher untersuchten 1,3-Oxazine-2- und -4-onen ist hier ebenfalls das O-endo Konformere bevorzugt; in diesem ist der Sauerstoffaxial angeordnet, und zwar unabhängig von der Zahl der alicyklischen Ringatome und dem flexibleren Oxazindionring.

     

Theoretical studies on tautomerism of imidazole-2-selenone

The tautomerism of all possible forms of imidazole selenone (ISe1–ISe6), induced by proton transfer was studied theoretically in different environments including gas phase, continuum solvent, and microhydrated environment with one explicit water molecule. The calculations were performed at the MP2 and CAM-B3LYP levels of theory, separately. It was found that the imidazole selenone, in the form of ISe3, is the most stable isomer in both gas phase and solvent. The activation energy for conversion of ISe3 to imidazole selenol (ISe6), as the second stable form, is 41.72 and 43.0 kcal/mol in the gas phase and water, respectively. The infrared spectral frequencies as well as the vibrational frequency shifts were reported and assigned to their corresponding vibrational modes. In addition, the variation of dipole moments and charges on the atoms with change of solvent was studied. The energies of HOMO, LUMO, and HOMO–LUMO gap were calculated in both gas phase and solvent. Specific solvent effects with addition of water molecule near the electrophilic centers of tautomers and the transition states of proton transfer, assisted by water molecule, were investigated. It was found that the water molecule can form different hydrogen bonds with the molecule. Aggregation of the isomers with water molecule does not change the order of stability of isomers, but proton transfer reaction assisted by a water molecule needs less energy than when the proton shifts through the intramolecular process.     

Theoretical studies on the conformation of saccharides

Conformations of 2-methoxytetrahydropyran as a model for the six-membered ring in aldopyranosides have been calculated by the PCILO method using the algorithm of the conjugated gradient to optimize the geometry. The calculated geometry of the fourteen basic forms of 2-methoxytetrahydropyran was found to be in agreement with the available data obtained by X-ray diffraction of pyranosides. The results indicate differences in the geometry of 2-methoxytetrahydropyran resulting from the change of the axial vs. equatorial position of the methoxyl group. These changes are particularly meaningful in the values of bond angles and they are in agreement with the anomeric and exoanomeric effects. The experimentally found differences in the energies of an axial (⁴ C ₁) and equatorial (¹ C ₄) conformer, G = 2.9–3.7 kJ/mol, and the dipole moment, = 1.20 ± 0.05 D (1D = 3.33 10^–30mAs) agree well with the calculated values E = 3.18 kJ/mol and <> = 1.18 D which, in turn, suggest that the axial conformer is preferred over the equatorial one by a ratio a:e = 78:22.     

13C NMR of 2,3,14-Trisubstituted Δ4,7-6-Ketosteroids and Related Compounds

¹³ Spectra have been studied and signals of C atoms assigned for steroids 3-5 and 7-10, which are close structural analogs of the natural ecdysteroids 4-dehydroecdysterone 1, diaulusterol A 2, and 5,20-dihydroxyecdysone 6     

Decay Mechanisms of Protonated 4-Quinolone Antibiotics After Electrospray Ionization and Ion Activation

This study presents a detailed experimental investigation of charge isomers of protonated 4-quinolone antibiotics molecules formed during electrospray ionization (ESI) with proposed dissociation mechanisms after collisional activation. Piperazinyl quinolones have been previously shown to exhibit erratic behavior during tandem MS analyses of biological samples, which originated from varying ratios of two isomeric variants formed during ESI. Here, a combination of ESI-collision-induced dissociation (CID), differential ion mobility spectrometry (DMS), high resolution MS, and density functional theory (DFT) was used to investigate the underlying mechanisms of isomer formation and their individual dissociation behaviors. The study focused on ciprofloxacin; major findings were confirmed using structurally related 4-quinolones. DFT calculations showed a reversal of basicity for piperazinyl quinolones between liquid and gas phase. We provide an experimental comparison and theoretical treatment of factors influencing the formation ratio of the charge isomers during ESI, including solvent pH, protic/aprotic nature of solvent, and structural effects such as pK _a and proton affinity. The actual dissociation mechanisms of the isomers of the protonated molecules were studied by separating the individual isomers via DMS-MS, which allowed type-specific CID spectra to be recorded. Both primary CID reactions of the two charge isomers originated from the same carboxyl group by charge-remote (CO₂ loss) and charge-mediated (H₂O loss) fragmentation of the piperazinyl quinolones, depending on whether the proton resides on the more basic keto or the piperazinyl group, followed by a number of secondary dissociation reactions. The proposed mechanisms were supported by calculated energies of precursors, transition states, and products for competing pathways. Graphical Abstract

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The inclusion complex of piromidic acid with dimethyl-β-cyclodextrin in aqueous solution and in the solid state

Inclusion complex formation of piromidic acid (PA) with dimethyl--cyclodextrin (DM--CD) in aqueous solution and in the solid state was confirmed by the solubility method, differential scanning calorimetry (DSC) and proton nuclear magnetic resonance (¹H-NMR) spectroscopy. The apparent stability constant,K _c , of the complex was estimated to be 244 M^–1. The stoichiometry of the complex was given as the ratio 1:2 of PA to DM--CD. The dissolution rate of the PA/DM--CD complex was much greater than that of intact PA.Presented at the Fourth International Symposium on Inclusion Phenomena and the Third International Symposium on Cyclodextrins, Lancaster, U.K., 20–25 July 1986.     

Local-density-functional approximation for exchange-correlation potential

Local exchange-correlation potential has been derived starting from the free electron gas model.Ab initio way of calculating the parameter of the X method is presented. Self-consistent and statistical exchange-correlation parameters have been determined. The self-consistent parameters have been used to calculate the electron binding energies of Neon, Argon and Krypton. We suggest using statistical exchange-correlation parameter in molecular calculations. The statistical exchange-correlation parameter has been applied to study the electron binding energies of the molecules H₂O and HF. It is shown that the electron binding energies calculated with the self-consistent and the statistical parameters show agreement with the experimental values.Dedicated to Professor J. Koutecký on the occasion of his 65th birthday     

peri-Naphthylenediamines. 38. Naphthalene and acenaphthene “proton sponges” with +M substituents in ortho positions with respect to peri-dimethylamino groups

Previously unknown 4,5,6,7-tetrakis(dimethylamino)acenaphthene, which is the first acenaphthene derivative containing four vicinal dialkylamino groups, was synthesized based on 5,6-bis(dimethylamino)-4,7-dinitroacenaphthene. The total synthesis of 1,2,7,8-tetrakis(dimethylamino)naphthalene was carried out starting from 3,6-dinitronaphthalic anhydride. Other proton sponges of this type, viz., 1,7,8-tris(dimethylamino)-2-methoxy- and 1,8-bis(dimethylamino)-2,7-dipiperidinonaphthalenes, were prepared by the nucleophilic substitution in 2,7-dimethoxy-1,8-dinitronaphthalene. In solutions, 1,2,7,8-tetrakis(dimethylamino)naphthalene and its analogs can form di- and trications in the presence of acids. The basicity constants pK _a ¹ of the compounds measured in DMSO depend in a complex way on their structures but correlate with the basicity index B, which is determined by changes in the chemical shifts _H after the addition of the first proton. Due to low C-nucleophilicity of ortho-disubstituted proton sponges in combination with high basicity, these compounds hold considerable promise as reagents in organic synthesis.     

1-(Nitrosoamino)benzimidazoles Containing Electron-acceptor Substituents at the Amine Nitrogen. Theoretical and Experimental Investigation of Conformational Mobility

The previously unknown 1-(N-nitrosoallylamino)- and 1-(N-nitrosopropargylamino)benzimidazoles have been synthesized and they exist in solution as a mixture of the E- and Z-conformers due to hindered rotation around the N-N(O) bond. The activation energies for the EZ transition in these compounds and for the model N-benzyl analog have been determined by a dynamic ¹H NMR method. With a view to studying the effect of a substituent at the amino nitrogen on the EZ isomerization we have carried out 3-21G and 6-31G** type ab initio calculations of the stable conformers of a series of N-nitrosohydrazines.     

1H NMR spectra of ethane‐1,2‐diol and other vicinal diols in benzene: GIAO/DFT shift calculations

The proton NMR spectra of several 1,2‐diols in benzene have been analysed so as to associate each magnetically nonequivalent proton with its chemical shift. The shifts and coupling constants of the OH and methylene protons of ethane‐1,2‐diol have been determined in a wide range of solvents. The conformer distribution and the proton NMR shifts of these 1,2‐diols in benzene have been computed on the basis of density functional theory. The solvent is included using the integral–equation–formalism polarizable continuum model implemented in Gaussian 09. Relative Gibbs energies for all stable conformers are calculated at the Perdew, Burke and Enzerhof (PBE)0/6‐311 + G(d,p) level, and shifts are calculated using the gauge‐including atomic orbital method with the PBE0/6‐311 + G(d,p) geometry but using the cc‐pVTZ basis set. Previous calculations on ethane‐1,2‐diol and propane‐1,2‐diol have been corrected and extended. New calculations on tert‐butylethane‐1,2‐diol, phenylethane‐1,2‐diol, butane‐2,3‐diols (dl and meso) and cyclohexane‐1,2‐diols (cis and trans) are presented. Overall, the computed NMR shifts are in good agreement with experimental values for the OH protons but remain systematically high for CH protons. Some results based on the Gaussian 03 solvation model are included for comparison. Copyright © 2012 John Wiley & Sons, Ltd.     

A molecular orbital study of the bonding in complexes of lithium with polynuclear aromatic hydrocarbons

In a preliminary investigation of the bonding between the sub-lattices of lithium and of graphite in intercalation compounds, molecular orbital calculations are performed on systems of Li atoms complexed to one or both sides of polynuclear aromatic hydrocarbons. Energy wells calculated reveal possible sites offered to the Li atoms above the aromatic plane to form complexes in both central and edge regions of the molecule. The influence of additional complexed Li atoms on the migratory tendency of a given Li atom is also investigated, and observations made on the effect of the complexed Li atoms on the C-C bonds of the hydrocarbon.