The energy and geometric characteristics of the transition state in reactions of RO<Stack><Subscript>2</Subscript><Superscript>•</Superscript></Stack> with carbonyl compound C-H bonds

The energy and geometry of the transition state in reactions of the ethyl peroxyl radical with ethane, ethanol (its α and β C-H bonds), acetone, butanone-2, and acetaldehyde were calculated by the density functional theory method. In all these reactions (except EtO_2/? + ethanol α C-H bond), the C…H…O reaction center has an almost linear configuration (φ = 176° ± 2°); polar interaction only influences the r ^≠ (C…O) interatomic bond. In the reaction of EtO_2/? with the ethanol α C-H bond, it is the O-H…O H-bond formed in the transition state that determines the configuration of the reaction center with the angle φ(C…H…O) = 160°. The results were used to estimate the r ^≠ (C…H) and r ^≠ (O…H) interatomic bonds in the transition state by the method of intersecting parabolas and the contribution of polar interaction to the activation energy of reactions between peroxyl radicals and aldehydes and ketones.     

Conformational properties of permethylcyclohexane as compared to cyclohexane: A force field study

The conformational properties of the recently synthesized highly strained permethylcyclohexane molecule 2 have been studied by empirical force field calculations using three different potentials (CFF, MM2, MM2′) and second-derivative optimization methods. A comparison of the results with the conformational behavior of parent cyclohexane 1 leads to the following conclusions: The best conformation of 2 is a chair minimum whose six-membered ring is flatter than that of 1 , due to the strong H…H repulsions introduced by the methyl groups. The twist minimum of 2 is energetically less favorable than the chair by an amount similar to 1 . A potential energy barrier Δ V^# for the chair inversion of 2 of 15.32 kcal/mol results with the CFF, only about three kcal/mol higher than for 1 . The free energy of activation ΔG^# for this process obtained with the CFF is 16.96 kcal/mol (at 333 K) and agrees well with the experimental value of 16.7(2) kcal/mol.¹ MM2 and MM2′ give substantially lower and higher potential energy inversion barriers Δ V^# of 9.03 and 20.29 kcal/mol, respectively, which is attributed to inappropriate torsional energy terms in these force fields. The characteristic difference in the conformational behavior of 2 and 1 concerns the boat forms which are substantially less favorable in the per-methyl compound than in 1 . Expectedly, strong H…H repulsions between the 1,4 diaxial flagpole–bowsprit methyl groups in 2 are responsible for this difference. The particularly high strain of the boat forms of 2 leads to flexibility differences as compared to 1 which in turn affect the relative entropies of the various statiomers (stationary point conformations); e.g., the chair ring inversion activation entropies of 2 and 1 are predicted by the CFF calculations to have opposite signs (?4.82 and 3.41 cal/mol K, respectively, at 298 K). The twist and half-twist statiomers of 2 are much more rigid than those of 1 , which is a consequence of the substantially larger boat barriers along their pseudorotational interconversion paths. The boat transition state separating two enantiomeric twist minima represents a barrier calculated to be more than tenfold higher for 2 than for 1 (CFF Δ V^# values 11.14 and 0.92 kcal/mol, respectively); likewise the half-boat chair inversion barrier of 2 is calculated 5.07 kcal/mol less favorable than the respective half-twist barrier. These statiomers are practically equienergetic in the case of 1 . Except for the axial flagpole–bowsprit CH₃ substituents of the boat forms, the methyl groups of all the relevant calculated statiomers of 2 are more or less staggered. The rotational barrier of the equatorial methyl groups of the chair minimum of 2 is computationally predicted to be 5.78 kcal/mol (ΔG^#), i.e., unusually high. Interesting vibrational effects are brought about by the strong H…H repulsions in 2 ; thus the chair minimum has a largest C? H stretching frequency estimated to be 3050 cm^?1 and involves several particularly low frequencies which have a substantial influence on its entropy. CFF calculations for the lower homologue permethylcyclopentane 5 indicate that its pseudorotational properties are similar to those of cyclopentane 4 , in contradistinction to the pair 2/1 .     

Echinops bannaticus plant and Zinnia grandiflora extract as char biosource and reducing agent for the biosynthesis of Ag on magnetic char-polymer: An efficient catalyst for water treatment

In attempt to expand the use of natural compounds for waste treatment, a novel catalyst with the utility for dye reductive degradation is reported. In the catalyst synthesis procedure, the plant Echinops bannaticus was applied as a biosource and hydrothermally treated to furnish a hydrochar that served as a support. The latter was magnetized, vinyl functionalized, and then polymerized with copolymer of 2-hydroxyethyl methacrylate and methacrylate polyhedral oligomeric silsesquioxane. Subsequently, Ag nanoparticles were stabilized on the resultant composite with the aid of Zinnia grandiflora extract as a natural reducing agent. The resulting catalyst displayed high catalytic activity for the reduction of methylene orange and rhodamine B dyes in aqueous media at room temperature. The effects of the reaction variables, including the reaction time and temperature, and the catalyst loading, were examined and the kinetic and thermodynamic terms for both reactions were evaluated. E_a, ΔH^#, and ΔS^# values for the reduction of methyl orange were estimated as 50.0 kJ/mol, 51.50 kJ/mol, and −102.42 J mol⁻¹ K⁻¹, respectively. These values for rhodamine B were measured as 28.0 kJ/mol, 25.5 kJ/mol, and −187.56 J mol⁻¹ K⁻¹, respectively. The recyclability test also affirmed that the catalyst was recyclable for several runs with insignificant Ag leaching and decrement of its activity.     

Properties of strong hydrogen-bonded systems. II. Ab initioSCF-MO study of the hydrogen bond between nitric acid and ammonia

The hydrogen-bonded complex between nitric acid and ammonia molecules has been studied by the ab initio molecular orbital method using the 4-31G basis set. The calculated interaction energy for the complex (ΔE = ?91.4 kJ mole^?1) indicates that one is dealing with the strongest “nonionic” H-bonded complex considered hitherto by theoretical methods. Other properties of the hydrogen-bonded complex such as geometrical parameters, dipole moment, amount of charge transfer, and stretching force constants of the O? H and (OH)… N bonds are calculated and discussed.     

Theoretical study on the isomerization and tautomerism in barbituric acid

Isomerization and tautomerism of 16 isomers of barbituric acid (BA) were studied at the MP2 and B3LYP levels of theory. Activation energies (E _a), imaginary frequencies (υ), and Gibbs free energies (ΔG ^#) of the amine-imine and keto-enol tautomerisms and O–H internal rotations were calculated. The activation energies of amine-imine tautomerisms were in the range of 110–200 kJ/mol and for keto-enol tautomerisms were larger than 200 kJ/mol. The calculated activation energies of internal O–H rotations were smaller than 60 kJ/mol. Effect of micro-hydration on the transition state structures and activation energies of the tautomerisms were also investigated. Water molecule catalyzed the tautomerisms and decreased the activation energies of both the amine-imine and keto-enol tautomerisms about 100–120 kJ/mol.     

Gas-phase elimination kinetics of 1-substituted ethyl acetates. Effect of polar substituents at the α carbon of secondary acetates

The gas-phase elimination of several polar substituents at the α carbon of ethyl acetates has been studied in a static system over the temperature range of 310–410°C and the pressure range of 39–313 torr. These reactions are homogeneous in both clean and seasoned vessels, follow a first-order rate law, and are unimolecular. The temperature dependence of the rate coefficients is given by the following Arrhenius equations: 2-acetoxypropionitrile, log k₁ (s^?1) = (12.88 ± 0.29) – (203.3 ± 2.6) kJ/mol (2.303RT)^?1; for 3-acetoxy-2-butanone, log ±₁(s^?1) = (13.40 ± 0.20) – (202.8 ± 2.4) kJ/mol (2.303RT)^?1; for 1,1,1-trichloro-2-acetoxypropane, log ?₁ (s^?1) = (12.12 ± 0.50) – (193.7 ± 6.0) kJ/mol (2.303RT)^?; for methyl 2-acetoxypropionate, log ?₁ (s^?1) = (13.45 ± 0.05) – (209.5 ± 0.5) kJ/mol (2.303RT)^?1; for 1-chloro-2-acetoxypropane, log ?₁ (s^?1) = (12.95 ± 0.15) – (197.5 ± 1.8) kJ/mol (2.303RT)^?1; for 1-fluoro-2-acetoxypropane, log ?₁ (s^?1) = (12.83 ± 0.15)– (197.8 ± 1.8) kJ/mol (2.303RT)^?1; for 1-dimethylamino-2-acetoxypropane, log ?₁ (s^?1) = (12.66 ± 0.22) –(185.9 ± 2.5) kJ/mol (2.303RT)^?1; for 1-phenyl-2-acetoxypropane, log ?₁ (s^?1) = (12.53 ± 0.20) – (180.1 ± 2.3) kJ/mol (2.303RT)^?1; and for 1-phenyl?3?acetoxybutane, log ?₁ (s^?1) = (12.33 ± 0.25) – (179.8 ± 2.9) kJ/mol (2.303RT)^?1. The C_α? O bond polarization appears to be the rate-determining process in the transmition state of these pyrolysis reactions. Linear correlations of electron-releasing and electron-withdrawing groups along strong σ bonds have been projected and discussed. The present work may provide a general view on the effect of alkyl and polar substituents at the C_α? O bond in the gas-phase elimination of secondary acetates.     

DFT study on the isomerization in vitamin B6

Isomerization and tautomerism reactions of the active form of vitamin B6, pyridoxal phosphate, are studied at B3LYP level of theory using 6-311++G(2df,p) basis set in gas and aqueous phases. Twenty-three transition state (TS) structures for vitamin B6 isomerization are optimized, including 13 TS structures for O–H and C–C rotations, 8 TS structures for imine–enamine tautomerism, and 2 TS structures for keto–enol tautomerism. Activation energy (E _a), imaginary frequency (υ), and Gibbs free energy of activation (ΔG ^#) for the isomerization reactions are calculated. The activation energies of the imine–enamine tautomerism are in the range of 190–280 kJ/mol and of O–H and C–C rotations are mainly less than 60 kJ/mol. Also, our calculation shows that the imine forms of B6 are mainly more stable than the enamine forms. Effect of microhydration on the TS structures and activation energies is also investigated. It is found that the presence of water molecules catalyzes only the imine–enamine tautomerism.     

Inverse Halogen Bonds Interactions Involving Br Atom in the Electronic Deficiency Systems of CH3⊕ … Br-Y (Y=H,CCH, CN,NC)

Inverse halogen bonds interactions involving Br in the electronic deficiency sys-tems of CH₃^⊕…Br-Y (Y=H, CCH, CN, NC) have been investigated by B3LYP/6-311++G(d, p) and MP2/6-311++G(d, p) methods. The calculated interaction energies with basis set super-position error correction of the four IXBs com-plexes are 218.87, 219.48, 159.18, and 143.05 kJ/mol (MP2/6-311++G(d, p)), re-spectively. The relative stabilities of the four complexes increased in the order:CH₃^⊕…BrCN3^⊕…BrNC3^⊕…BrH≈CH₃^⊕…BrCCH. Natural bond orbital theory analysis and the chemical shifts calculation of the related atoms revealed that the charges flow from Br-Y to CH₃^⊕. Here, the Br of Br-Y acts as both a halogen bond donor and an electron donor. Therefore, compared with conventional halogen bonds, the IXBs complexes formed between Br-Y and CH₃^⊕. Atoms-in-molecules theory has been used to investigate the topological properties of the critical points of the four IXBs structures which have more covalent content.     

Radical addition reactions: factors determining the transition-state geometry

Interatomic distances in the reaction centers of the addition reactions of (i) H^· to the C=C, C=O, N≡C, and C≡C bonds, (ii) ^·CH₃ radical to the C=C, C=O, and C≡C bonds, and (iii) alkyl, aminyl, and alkoxyl radicals to olefin C=C bonds were determined using a new semiempirical method for calculating transition-state geometries of radical reactions. For all reactions of the type X^· + Y=Z → X— Y—Z^· the r ^# _X...Y distance in the transition state is a linear function of the enthalpy of reaction. Parameters of this dependence were determined for seventeen classes of radical addition reactions. The bond elongation, Δr ^# _X...Y, in the transition state decreases as the triplet repulsion, electronegativity difference between the atoms X and Y in the reaction center, and the force constant of the attacked multiple bond increase. __________ Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 894–902, April, 2005.     

Blue‐shifted and red‐shifted hydrogen bonds: Theoretical study of the CH3CHO· · ·HNO complexes

The blue‐shifted and red‐shifted H‐bonds have been studied in complexes CH₃CHO…HNO. At the MP2/6‐31G(d), MP2/6‐31+G(d,p) MP2/6‐311++G(d,p), B3LYP/6‐31G(d), B3LYP/6‐31+G(d,p) and B3LYP/6‐311++G(d,p) levels, the geometric structures and vibrational frequencies of complexes CH₃CHO…HNO are calculated by both standard and CP‐corrected methods, respectively. Complex A exhibits simultaneously red‐shifted C? H…O and blue‐shifted N? H…O H‐bonds. Complex B possesses simultaneously two blue‐shifted H‐bonds: C? H…O and N? H…O. From NBO analysis, it becomes evident that the red‐shifted C? H…O H‐bond can be explained on the basis of the two opposite effects: hyperconjugation and rehybridization. The blue‐shifted C? H…O H‐bond is a result of conjunct C? H bond strengthening effects of the hyperconjugation and the rehybridization due to existence of the significant electron density redistribution effect. For the blue‐shifted N? H…O H‐bonds, the hyperconjugation is inhibited due to existence of the electron density redistribution effect. The large blue shift of the N? H stretching frequency is observed because the rehybridization dominates the hyperconjugation. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006     

Rate constants and transition‐state geometry of reactions of alkyl,alkoxyl, and peroxyl radicals with thiols

Enthalpy, activation energy, and rate constant of 9 alkyl, 3 acyl, 3 alkoxyl, and 9 peroxyl radicals with alkanethiols, benzenethiol, and L ‐cysteine are calculated. The intersection parabolas model is used for activation energy calculations. Depending on the structure of attacking radical, the activation energy of reactions with alkylthiols varies from 3 to 43 kJ mol^?1 for alkyl radicals, from 7 to 9 kJ mol^?1 for alkoxyl, and from 18 to 35 kJ mol^?1 for peroxyl radicals. The influence of adjacent π‐bonds on activation energy is estimated. The polar effect is found in reactions of hydroxyalkyl and acyl radicals with alkylthiols. The steric effect is observed in reactions of alkyl radicals with tert‐alkylthiols. All these factors are characterized via increments of activation energy. Quantum chemical calculations of activation energy and geometry of transition state were performed for model reactions: C^?H₃ + CH₃SH, CH₃O^? + CH₃SH, and HO₂^? + CH₃SH with using density functional theory and Gaussian‐98. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 41: 284–293, 2009     

Synthesis,structure, and kinetic studies on [RuCl2(NCCH3)2(cod)]

[RuCl₂(NCCH₃)₂(cod)], an alternative starting material to [RuCl₂(cod)] _n for the preparation of ruthenium(II) complexes, has been prepared from the polymer compound and isolated in yields up to 87% using a new work-up procedure. The compound has been obtained as a yellow solid without water of crystallization. The complexes [RuCl₂(NCR)₂(cod)] spontaneously transform into dimers [Ru₂Cl(μ-Cl)₃(cod)₂(NCR)] (R?=?Me, Ph). ¹H NMR kinetic experiments for these transformations evidenced first-order behavior. [RuCl₂(NCPh)₂(cod)] dimerizes slower by a factor of ten than [RuCl₂(NCCH₃)₂(cod)]. The following activation parameters, ΔH ^#?=?114?±?3?kJ?mol^?1 and ΔS ^#?=?66?±?9?J?K^?1?mol^?1 for R?=?CH₃CN (ΔG ^#?=?94?±?5?kJ?mol^?1, 298.15?K) and ΔH ^#?=?122?±?2?kJ?mol^?1 and ΔS ^#?=?75?±?6?J?K^?1?mol^?1 for R?=?Ph (ΔG ^#?=?100?±?4?kJ?mol^?1, 298.15?K), have been calculated from the first-order rate constants in the temperature range 294–323?K. The kinetic parameters are in agreement with a two-step mechanism with dissociation of acetonitrile as the rate-determining step. The molecular structures of [Ru₂Cl(μ-Cl)₃(cod)₂(NCR)] (R?=?Me, Ph) have been determined by X-ray diffraction.     

Theoretical investigation on identical anionic halide‐exchange SN2 reaction processes on N‐haloammonium cation NH3X+ (X = F,Cl, Br,and I)

CCSD(T) calculations have been used for identically nucleophilic substitution reactions on N‐haloammonium cation, X^? + NH₃X⁺ (X = F, Cl, Br, and I), with comparison of classic anionic S_N2 reactions, X^? + CH₃X. The described S_N2 reactions are characterized to a double curve potential, and separated charged reactants proceed to form transition state through a stronger complexation and a charge neutralization process. For title reactions X^? + NH₃X⁺, charge distributions, geometries, energy barriers, and their correlations have been investigated. Central barriers ΔE for X^? + NH₃X⁺ are found to be lower and lie within a relatively narrow range, decreasing in the following order: Cl (21.1 kJ/mol) > F (19.7 kJ/mol) > Br (10.9 kJ/mol) > I (9.1 kJ/mol). The overall barriers ΔE relative to the reactants are negative for all halogens: ?626.0 kJ/mol (F), ?494.1 kJ/mol (Cl), ?484.9 kJ/mol (Br), and ?458.5 kJ/mol (I). Stability energies of the ion–ion complexes ΔE_comp decrease in the order F (645.6 kJ/mol) > Cl (515.2 kJ/mol) > Br (495.8 kJ/mol) > I (467.6 kJ/mol), and are found to correlate well with halogen Mulliken electronegativities (R² = 0.972) and proton affinity of halogen anions X^? (R² = 0.996). Based on polarizable continuum model, solvent effects have investigated, which indicates solvents, especially polar and protic solvents lower the complexation energy dramatically, due to dually solvated reactant ions, and even character of double well potential in reactions X^? + CH₃X has disappeared. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Kinetic parameters and geometry of the transition state of acyl radical decarbonylation

Experimental data on acyl radical decomposition reactions (RC^·O → R^· + CO, where R = alkyl or aryl) are analyzed in terms of the intersecting parabolas method. Kinetic parameters characterizing these reactions are calculated. The transition state of methyl radical addition to CO at the C atoms is calculated using the DFT method. A semiempirical algorithm is constructed for calculating the transition state geometry for the decomposition of acyl radicals and for the reverse reactions of R^· addition to CO. Kinetic parameters (activation energy and rate constant) and geometry (interatomic distances in the transition state) are calculated for 18 decomposition reactions of structurally different acyl radicals. A linear correlation between the interatomic distance r ^#(C…C) (or r ^#(C…O)) in the transition state the enthalpy of the reaction (δH _e) is established for acyl decomposition reactions (at br _e = const). A comparative analysis of the enthalpies, activation energies, and interatomic distances in the transition state is carried out for the decomposition and formation of acyl, carboxyl, and formyl radicals.     

Physical factors determining the activation energy of alkyl radical addition to unsaturated compounds

A parabolic model of the transition state is used for the analysis of experimental data (rate constants and activation energies) for reactions of addition of alkyl and phenyl radicals to multiple bonds of unsaturated compounds. The parameters describing the activation energy as a function of the enthalpy of the reactions were calculated from the experimental data. The activation energy depends also on the strength of the forming C−C bond, the presence of π-bonds in the α-position near the attacked C=C bond and the presence of polar groups in the monomer and radical. The empirical dependence of the activation energy of a thermoneutral addition reactionE _e0 on the dissociation energyD _e of the forming C−C bond was obtained:E _e0=(5.95±0.06)·10⁻⁴ D _e ² kJ mol⁻¹, indicating the important role of triplet repulsion in the formation of the transition state of radical addition. The contribution of the polar interaction to the activation energy of addition of polar radicals to polar monomers was calculated. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 445–450, March, 1999.     

Methyl-and tert-butyl-substituted hydroquinones and semiquinone radicals: Bond strength estimates, enthalpy of formation, and the rate constants of their reactions with peroxy radicals

The strength of the O-H bonds (D) in hydroquinone (HQH) and its alkyl derivatives has been estimated by the intersecting parabolas method using rate constants known for the reactions of these compounds with the styrene peroxy radical. For unsubstituted HQH, D = 352.6 kJ/mol; for substituted HQH derivatives, D = 349.9 (Me), 346.9 (2,5-Me₂), 343.0 (Me₃), 347.6 (CMe₃), and 340.2 (2,5-(CMe₃)₂) kJ/mol. The enthalpies of formation of these HQH derivatives have been calculated. The O-H bond strengths in the semiquinone radicals (HQ^.) resulting from the above HQH derivatives have been calculated using a thermochemical equation to be $D_{HQ^. } $ = 236.7, 237.4, 239.8, 244.7, 240.1, and 247.5 kJ/mol, respectively. Rate constants have been determined for the reactions of the hydroquinones with tertiary and secondary peroxy radicals and HOO^. at 323 K. The rate constants of the reactions between HOO^. and benzoquinones and the relative reactivities of the HQ^. radicals in their reactions with ROO^. have been estimated.     

Effect of hydrogen bridge geometry on the vibrational spectra of water: Three-parameter potential of H bond

The ability of water molecules to form a three-dimensional network of hydrogen bonds basically determines both the intrinsic structure and unique properties of this liquid and also a character of interactions with other molecules. However, the dependence of the H bond energy on the geometry of its hydrogen bridge, namely on the R_O…_O length and non-linearity, is unknown, i.e. the deviations of O—H group directions and the lone pair forming this bond from optimum ones (angles (φ = H—_O…_O and χ = —_O…_O correspondingly). Even in computer simulation methods, the contribution of H bonds to the total interaction potential is not separated; that does not allow one to define unequivocally these bonds in a model and to analyze quantitatively the features of their networks. The purpose of this work is to fill in this gap by expressing the energy E through geometric parameters (R, φ, χ). The obtained solution quality is proved by an agreement between the distributions of OH vibrational frequencies (which are very sensitive to the H bond strength) calculated with its help and the shape of experimental spectra in a wide temperature range. Based on this, the distributions of H bond energies P(E, T) and of their bend angles P(φ, T) and P(χ, T) are also calculated. It is shown that the main contribution to spectra is made by the shortest bonds with their lengths close to a minimum of the potential E(R). Thus, the low-frequency slope of a band corresponds to slightly bent H bonds, while the central part relates to also short but sufficiently nonlinear H bonds. LongH bonds are responsible for only well known high-frequency Walrafens’s wing near 3620 cm^-1. Moreover, these weak bonds are very strongly bent.     

Synthesis,characterization, and mechanism of trans-dichlorido-bis-(ethylenediamine)cobalt(III) with L-cystine in the presence of chloride

Substitution reactions of trans-[CoCl₂(en)₂]Cl (where en?=?ethylenediamine) with L-cystine has been studied in 1.0?×?10^?1?mol?dm^?3 aqueous perchlorate at various temperatures (303–323?K) and pH (4.45–3.30) using UV-Vis spectrophotometer on various [Cl^?] from 0.05 to 0.01?mol?L^?1. The products have been characterized by their physico-chemical and spectroscopic data. Trans-[CoCl(en)₂(H₂O)]²⁺, from the hydrolysis of trans-[CoCl₂(en)₂]⁺ in the presence of Cl^?, formed a complex with L-cystine at all temperatures in 1?:?1 molar ratio. L-cystine is bidentate to Co(III) through Co–N and Co–S bonds. Product formation and reversible reaction rate constants have been evaluated. The rate constants for SN_i mechanism have been evaluated and activation parameters E _a, ΔH ^#, and ΔS ^# are determined.     

Cocrystal Assembled by 1,2-Diiodotetrafluorobenzene and Acridine via C-I…N Halogen Bond and Tr-hole…F Bonds

The concepts on o-hole and ~-hole bonds are suggested. A cocrystal with repeated 8-F-atom unit as basic struc- tural motif is assembled based on bifurcated C-I…N…I-C halogen/σ-hole bond and antiparallel double π-hole… F bonds by 1,2-diiodotetrafluorobenzene and acridine and characterized well by XRD, powder XRD and solid 19F NMR, etc. Also the calculated interaction energies are -26.8 and -31.5 kJ/mol for bifurcated C-I…N sp……2 halogen bonds, and -14.3 kJ/mol for a pair of n-hole…F bonds. In this system C-I…N halogen bond has stronger competitive ability to C-I…π halogen bond due to stronger basicity of N than π-system in acridine. The combination of the halogen/σ-hole and π-hole bonds or together with other weak interactions could play a key role in assembling function materials, molecular recognition and design of drugs and so on.     

Correlation between the equilibrium and relaxation dielectric properties of 1,2-ethanediol

The data on the dispersion of the permittivity ?*(ω) of 1,2-ethanediol over the temperature range 161–453 K and the frequency range 0.1 Hz–150 GHz were analyzed using the Dissado-Hill cluster model. The relaxation frequency ω_p = τ _DH ^?1 and intra-(n _DH) and intercluster (m _DH) correlation parameters were calculated. The energy barrier to the libration of molecular axes in clusters was found to be B _DH = 2.96 kJ/mol. The apparent enthalpy of activation was determined; it increased from ΔH _{DH exp} ^# = 22.18 kJ/mol to ΔH _{DH exp} ^# = 129.19 kJ/mol close to the glass transition temperature. The mean dipole moments $ \bar \mu _c The data on the dispersion of the permittivity ɛ*(ω) of 1,2-ethanediol over the temperature range 161–453 K and the frequency range 0.1 Hz–150 GHz were analyzed using the Dissado-Hill cluster model. The relaxation frequency ω_p = τ_DH⁻¹ and intra-(n _DH) and intercluster (m _DH) correlation parameters were calculated. The energy barrier to the libration of molecular axes in clusters was found to be B _DH = 2.96 kJ/mol. The apparent enthalpy of activation was determined; it increased from ΔH _{DH exp}^# = 22.18 kJ/mol to ΔH _{DH exp}^# = 129.19 kJ/mol close to the glass transition temperature. The mean dipole moments of 1,2-ethanediol clusters were calculated; they decreased from 162920 to 18.08 D as the temperature increased from 161 to 453 K. According to approximate estimates, the number of 1,2-ethanediol molecules in a cluster /μ_v decreased from 72405 at 161 K to 8.04 at 453 K (μ_v is the dipole moment of the molecule in the vacuum), which substantiated the suggestion of the existence of a spatial structure close to the boiling point. Original Russian Text ? N.V. Lifanova, T.M. Usacheva, V.I. Zhuravlev, V.K. Matveev, 2008, published in Zhurnal Fizicheskoi Khimii, 2008, Vol. 82, No. 10, pp. 1973–1981.