Электронное строение молекул моноалкиламинов R-NH2 и соответствующих радикалов R-N●H изучено в рамках квантовой теории атомов в молекулах. Представлены значения зарядов и объемов атомных групп. Проведено сравнение влияния на углеводородную цепь функциональных групп, содержащих атомы O-, N-, S-. The electronic structure of the molecules of monoalkylamines R-NH2 and the corresponding radicals R-N●H has been studied in the framework of the quantum theory of atoms in molecules. The values of charges and volumes of atomic groups are presented. The effect of functional groups containing O-, N-, S- atoms on the hydrocarbon chain is compared.

КВАНТОВО-МЕХАНИЧЕСКИЙ РАСЧЕТ СТРУКТУРНЫХИ ЭНЕРГЕТИЧЕСИХ ХАРАКТЕРИСТИК ФТОРЗАМЕЩЕННЫХ БУТАНОВ А.В.Котомкин, Ю.Д.Орлов, Е

The paper presents the results of a study of the effect of free valence (when a hydrogen atom is separated) on the electronic structure of n-alcohol radicals by the example of radicals of n-heptanol derivatives ((CH2)-H-center dot-(CH2)(6)OH, CH3-(CH)-H-center dot-(CH2)(5)OH, C2H5-(CH)-H-center dot-(CH2)(4)OH, C3H7-(CH)-H-center dot-(CH2)(3)OH, C4H9-(CH)-H-center dot-(CH2)(2)OH, C5H11-C.H-CH2OH, C6H13-(CH)-H-center dot-OH, C7H15-O-center dot). Geometry optimization and the electron density distribution in these compounds was obtained by the density functional method B3LYP/6-311++G(3df,3pd) 6d 10f. The electronic structure of the selected molecules and radicals was investigated within the framework of the "quantum theory of atoms in a molecule" (QTAIM): the electronic parameters of atoms and atomic groups were calculated, the spin density distribution was studied, the concepts of "radical center" and "free valence" were quantitatively characterized. The inductive effect and the tolerability of atomic groups are considered, and a qualitative scale of group electronegatives is compiled. The disturbing effect of various atomic groups, including those containing free valence, on the hydrocarbon chain is compared by comparing the integral parameters of the groups included in the compounds under study with the parameters of the "standard" groups.

Analytical expressions for matrix elements of the dipole moment operator for internal rotation are obtained. Quantitative measures for spectroscopic parameters of transitions associated with specific potential wells on the potential energy surface (conformers) are proposed. The relations obtained are illustrated by numerical examples and diagrams.

The TD-DFT/B97-D/6-311G** method is used to calculate the electronic absorption spectra of А⋯Х⋯А supramolecules with intermolecular hydrogen bonds (HBs), where А is 4-n-propoxycinnamic acid, Х is a nonmesogen molecule with bifunctional HB acceptors. Nonmesogens Х (B, C, D, E) consist of two pyridyl fragments connected by bridging groups of different natures: 4,4′-bipyridine (В), 1,2-bis(4-pyridyl)ethane (С), 1,2-bis(4-pyridyl)ethylene (D), 4,4′-azopyridine (Е). It is shown that the introduction of bridging groups (–CН2–CН2–, –CН=СН–, –N=N–) significantly affects the energy of frontier orbitals and electronic absorption spectra (EAS) of nonmesogens Х in the near-UV region. The EAS of two structural units A⋯В⋯A, A⋯A, which may be formed due to the self-assembly in two-component mesogen А–nonmesogen В systems, are compared. Due to hydrogen bonds (O–H⋯N and O–H⋯O), having different types and strengths in these complexes, the high-intensity band shifts to shorter wavelengths in complex А⋯В⋯А and to longer wavelengths in complex А⋯А with respect to the λ = 333 nm band of monomer А. It is shown that EAS of hydrogen-bonded complexes А⋯Х⋯А are not superpositions of EAS of individual components. The spectra show electronic transitions related to charge transfer between the components of the complexes. Using nonmesogens Х of different nature in supramolecules А⋯Х⋯А will allow one to change purposefully their electro-optical properties and to achieve intense absorption in particular regions of UV spectra.

Для супрамолекул с межмолекулярными водородными связями (ВС) типа А⋯Х⋯А, где А — 4-н-пропилоксикоричная кислота, Х — молекула немезогена с бифункциональными акцепторами ВС, методом TD-DFT/B97-D/6-311G** рассчитаны электронные спектры поглощения. Немезогены Х (B, C, D, E) состоят из двух пиридильных фрагментов с разной природой мостиковой группы между ними: В — 4,4'-бипиридин, С — 1,2-бис(4-пири­дил)этан, D — 1,2-бис(4-пиридил)этилен, Е — 4,4'-азопиридин. Показано, что введение мостиковых групп (—CН2—CН2—, —CН=СН—, —N=N—) существенно изменяет энергии граничных орбиталей и электронные спектры поглощения (ЭСП) немезогенов Х в области ближнего УФ. Выполнено сравнение ЭСП двух структурных единиц A⋯В⋯A, A⋯A, которые могут быть образованы в результате самосборки в двухкомпонентных системах мезоген А—немезоген В. Отмечено, что наличие разных по типу (O—H⋯N и O—H⋯O) и силе водородных связей в этих комплексах приводит к смещению высокоинтенсивной полосы в область меньших длин волн в комплексе А⋯В⋯А и в область больших длин волн — в комплексе А⋯А по отношению к полосе λ = 333 нм мономера А. Показано, что ЭСП водородосвязанных комплексов А⋯Х⋯А не являются суперпозицией ЭСП отдельных компонентов. В них наблюдаются электронные переходы, связанные с переносом заряда между составляющими комплексов. Использование немезогенов Х разной природы в супрамолекулах А⋯Х⋯А позволит направленно изменять их электрооптические свойства и обеспечивать интенсивное поглощение в заданных областях УФ спектра.

The distribution of electron densities of the symmetrical branched alkanes of the types (CH3(CH2)n)3CH and (CH3(CH2)n)4C is studied using the quantum theory of atoms in molecules. The integral electronic characteristics of standard CH and C groups are defined. The distance of the induction of the influence of CH and C groups in a C–C branched chain in alkanes is established, and the steric effect of the hydrocarbon substituents is considered.

The electronic structure of the homologous series of CH3(CH2)nCHCHCH2 (n = 0÷5) allyl all radicals is studied. The obtained spin density distribution is used to determine the fragment serving as the radical center. The delocalization of spin density over the basin of the radical center is shown to be responsible for two free valencies associated with two classical canonical structures (the conjugated fragment). The conjugation phenomenon is studied and electronic parameters are determined for the “standard” conjugated fragment CHCHCH2.

H-bonded complexes A center dot center dot center dot B(C) center dot center dot center dot A, where A is 4-n-propyloxycinnamic acid, B is 4,4'-bipyridyl and C is 1,2-bis(4-pyridyl) ethane have been prepared. DSC curves of the studied complexes showed that in the temperature range between Cr -> I there are additional maxima that can be attributed to the Cr -> LC -> I transitions. Thus, the elongation of the core of the supermolecule A center dot center dot center dot B(C) center dot center dot center dot A due to the introduction of molecules B or C between molecules A with short substituents can lead to the appearance of LC properties of the system. The formation of H-complexes was confirmed by IR spectra in which wide bands were observed at 2450 and 1870 cm(-1) for the complex A center dot center dot center dot B center dot center dot center dot A and at 2400 and 1923 cm(-1) for the complex A center dot center dot center dot C center dot center dot center dot A. The quantum-chemical method DFT/B97D/6-311++G** was used to study changes of complexes' properties depending on the nature of the bridge group between two pyridine moieties. In addition to the complexes A center dot center dot center dot B center dot center dot center dot A and A center dot center dot center dot C center dot center dot center dot A, the complexes A center dot center dot center dot D center dot center dot center dot A and A center dot center dot center dot E center dot center dot center dot A, where D is 1,2-bis(4-bipyridyl) ethylene, and E is 4,4'-azopyridine, were considered. For all complexes, a geometric structure, parameters of geometric anisotropy, elements of the polarizability tensor and the energy of the hydrogen bond are determined. Due to the anisotropy of electronic and geometric parameters and the high strength of the intermolecular H-bonds the considered complexes are systems capable of exhibiting LC properties. Analysis of the boundary orbitals energies and their differences shows that the complexes should differ significantly in photoelectronic characteristics and oxidizing properties. Thus, the introduction of different bridging groups -CH2-CH2-, -CH=CH-, -N=N-into 4,4'-bipyridyl allows to regulate oxidizing properties of H-complexes and also influence their spectral characteristics.

By means of B3LYP/6-311++G(3df,3pd) the electron density distribution in the propargyl radical CH2CCH is obtained. Within the Quantum Theory of Atoms in Molecules the phenomenon of conjugation and the spin density distribution of the unpaired electron in CH2CCH are studied at the qualitative level. Characteristics of the electronic structure of CH2CCH and its parent molecules CH3–C≡CH and CH2=C=CH2 are compared. With the use of the rigid rotator-anharmonic oscillator model the thermodynamic properties of the propargyl radical and enthalpies of bond cleavage in propyne and allene are calculated in the temperature range 298-1500 K. The relationship between the electronic and thermodynamic properties of CH2CCH is considered and its conjugation energy is calculated.

Using B3LYP/6-311++G(3 df ,3 pd ), the electron density distribution (ρ( r )) of trans - and gauche -conformers of normal monohydric alcohols CH 3 (CH 2 ) n OH ( n = 0÷9) is obtained and within the quantum theory of atoms in molecules (QTAIM), the inductive and steric effects are quantitatively studied. Based on the analysis of ρ( r ), an additive scheme for calculating the extensive properties is proposed.

The database on the enthalpies of formation (Δ f H ○ ) of aliphatic acetyl radicals of the RC·(O) type is analyzed and extended. Δ f H ○ values are estimated for the first time for three compounds on the basis of experimental data. The data were analyzed using the additive group approach with the determination and correction of parameters. Good correspondence between the Δ f H ○ (RC·(O)) values calculated according to parameters with experimental data is observed.

Within additive-group approach the quantitative correlation «structure — property» for the radicals of the type RC(O)O ● was found. The enthalpies of formation of 18 radicals and the groups’ contributions (increments) to the enthalpy were defined. Matching and verification of data were carried out.