Effect of substituents on ionization potentials of phosphorus compounds. Conjugation in radical cations

The first vertical ionization potentials (I) of phosphorus compounds P(X_i)₃, OP(X_i)₃, SP(X_i)₃, (4-XC₆H₄)₃P, and PCX are related to the inductive, resonance, and polarizability parameters of inorganic, organic, and organometallic substituents X by dependences of the type I = I _H + a_I + b_R ⁺ + c, where I _H is the I value for X = H. The I values are also affected by hyperconjugation. The ratio of the contributions of the resonance (b_R ⁺) and polarizability (c) effects to the I value is determined by the degree of delocalization of the unpaired electron and the positive charge in the radical cations formed upon ionization of neutral molecules. The _R ⁺ resonance parameters of organosilicon, organogermanium, and organotin substituents bound to the P ^·+ radical cation center were calculated for the first time.     

Ionization potentials of halides. Substituent effects in Cl-, Br-, and I-centered radical cations

The first vertical ionization potentials (I) of halides HalX (Hal = Cl, Br, I; X is an inorganic or organic substituent) are linearly related to the inductive (_I), resonance (_R ⁺), and polarizability () constants of the substituents X (I = a + b_I + c_R ⁺ + d). As the atomic number of the Hal element in the Hal^·+X radical cations increases, the inductive interaction is strengthened while the polarizability interaction is weakened. Conjugation remains virtually independent of the Hal atom. The resonance _R ⁺-constants of the MX₃ (M = Si, Ge, Sn, Pb) substituents bound to the Hal^·+ radical cation centers were first calculated.     

Electronic absorption spectra of charge-transfer complexes and effects of substituents in radical cations

The effects of X substituents on the energies of charge-transfer bandshv _CT in electronic absorption spectra of charge-transfer complexes of π-, n-, or σ-donors (DX) with π- or σ-acceptors (A) as well as on the ionization potentialsI _D of individual DX molecules are described by the equationhv _CT(l _D)=a +bσ₁ +cσ _R ⁺ +dσ_α. When DX and A are fixed, the inductive (bσ₁), resonance (cσ _R ⁺ ), and polarization (dσ_α) contributions tohv _CT andI _D are virtually identical. The electronic structure of the D^.+X donor component of the compact [A^.−, D^.+X] radical-ionic pair in a solution is similar to that of the radical cation generated upon photoionization of the individual DX molecule in the gaseous phase. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1002–1006, June, 2000.     

Conjugation in radical cations of benzene, ethylene, and acetylene derivatives. Nonuniversality of the resonance parameters of group 14 organoelement substituents

The first vertical ionization potentialsl ₁ of molecules R_πX (X=Ph, H₂C=CH, and HC≡C) depend on the joint influence of the inductive, resonance, and polarizability effects of substituents X, which are characterized by parameters σ₁, σ_R+, and σ_α, respectively. The mechanism of conjugation in radical cations formed upon ionization of R_πX is changed as compared to neutral R_πX molecules, while the substituent X becomes polarized. The conjugation and polarizability effects are strenthened in the sequence Ph < H₂C=CH <HC≡C as R_π changes from Ph to H₂C=CH and HC≡C. The σ_R+ parameters of Si-, Ge-, and Sn-containing substituents X are dependent on the type of R_π but are connected by linear dependences in the series of benzene, ethylene, and acetylene derivatives. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1481–1486, August, 1998.     

Substituent effects in radical cations of linear oligosilanes

The dependence was analyzed of the first ionization potentialI(Si−Si) corresponding to detachment of an electron from the σ(Si−Si) highest occupied molecular orbital on the parameters of organic (X=Me, Et, Bu ^t , Ph, CH=CH₂), inorganic (X=F, Cl, Br), and organosilicon (X=SiR₃; R is organic radical) substituents in di-, tri-, and tetrasilanes X₃SiSiX₃. It was found by correlation analysis that out of the three possible effects of substituents X (the inductive, polarizability, and resonance effects), only the first two of them affect theI(Si−Si) values. This means that no conjugation between the substituent X and the radical cation center occurs in X₃Xi±SiX₃. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 253–257, February, 2000.     

DFT(B3LYP) calculations of silatranes and their radical cations. First ionization potentials

DFT(B3LYP) and 2 quantum chemical calculations have been performed for 1-substituted silatranes XSi(OCH₂CH₂)N (X = H, CH₃, CH₂Cl, F), their radical cations, and first ionization potentials (IP₁) of these silatranes. The calculated values of IP₁ agree well with the experiment and make it possible to assign the first band to IP₁ in the photoelectron spectra. Analysis of spin density distribution and electronic charges in the radical cations suggests that ionization occurs mainly due to the lone electron pair of nitrogen, participating in intramolecular coordination. The N → Si interaction is broken, and the N...Si distance increases to 335–340 pm.     

Ionization potentials of non-metal monosulfides. Conjugation in radical cations containing Group IV elements

The first vertical ionization potentialsI(n_s) of 69 monosulfides XSY (X, Y=H, Hal, organic, or heteroorganic substituent) are related to the inductive σ_I resonance (σ _R ⁺ ) and polarizability (σ_α) constants of the substituents by dependences of theI(n_S)=a+bΣσ_I+bΣσ_R+bΣσ_α type. TheI(n_s) values are also affected by hyperconjugation which increases on going from XSH to XSY (Y≠H) compounds. The first calculations of the σ _R ⁺ parameters characterizing the conjugation of Si-, Ge-, Sn-, and Pb-containing substituents with the S^.+ radical cation center are reported. The reasons for weakening of resonance donor properties of heteroorganic substituents of the +M-type in the systems studied as compared to those of the same substituents in the corresponding aromatic radical cations are considered. Translated fromIzvestiya Akademii Nauk. Seriya Khmicheskaya, No. 1, pp. 25–31, January, 2000.     

Ionization potentials of non-metal monosulfides. Conjugation in radical cations containing Group IV elements

The first vertical ionization potentialsI(n_s) of 69 monosulfides XSY (X, Y=H, Hal, organic, or heteroorganic substituent) are related to the inductive σ_I resonance (σ _R ⁺ ) and polarizability (σ_α) constants of the substituents by dependences of theI(n_S)=a+bΣσ_I+bΣσ_R+bΣσ_α type. TheI(n_s) values are also affected by hyperconjugation which increases on going from XSH to XSY (Y≠H) compounds. The first calculations of the σ _R ⁺ parameters characterizing the conjugation of Si-, Ge-, Sn-, and Pb-containing substituents with the S^.+ radical cation center are reported. The reasons for weakening of resonance donor properties of heteroorganic substituents of the +M-type in the systems studied as compared to those of the same substituents in the corresponding aromatic radical cations are considered. Translated fromIzvestiya Akademii Nauk. Seriya Khmicheskaya, No. 1, pp. 25–31, January, 2000.     

Effect of substituents on the first ionization potentials of aromatic and heteroaromatic compounds. The {ie2532-1} resonance parameters of Si-, Ge-, Sn-, and Pb-containing fragmentsresonance parameters of Si-, Ge-, Sn-, and Pb-containing fragments

The first vertical ionization potentials (IP) of monosubstituted benzenes, hexafluorobenzenes, naphthalenes, anthracenes, furans, thiophenes, and selenophenes and the secondIP of monosubstituted tellurophenes are related to the inductive, resonance, and polarization parameters of substituents by dependences of the type {ie2532-2}. The contribution of polarizability effect, {ie2532-3}, to theIP value is determined by the degree of delocalization of the positive charge in radical cations formed upon photoionization of the compounds studied. The {ie2532-4} resonance parameters of nineteen Si-, Ge-, Sn-, and Pb-containing substitutents in naphthalene, furan, and thiophene series were calculated. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2434–2438, December, 1998.     

First ionization potentials and conjugation in molecules of ethylene derivatives containing organoelemental substituents of Group IV elements

Unlike theE _HOMO energies, the first vertical ionization potentials (I ₁) of monosubstituted ethylenes dependen not only on both the inductive and resonance effects but also on the polarizability of the substituents, which can be characterized by the σ_α parameters. The σ _R ⁺ , σ _p ⁺ , and σ_α parameters for 12 silicon-, germanium-, and tin-containing groups were determined using the equations relating theI ₁ values and the σ_I, σ _R ⁺ , σ _p ⁺ and σ_α parameters of the substituents in the molecules of organic compounds. The conjugation of organoelemental substituents with the double bond is stronger than that with benzene ring; the σ _R ⁺ parameters in the ethylene and benzene series are related by a linear dependence. Translated fromIzvestiya Akademii Nauk Seriya Khimicheskaya, No. 9, pp. 1626–1631, September, 1997.     

Correlation analysis of quantum chemical data and the polarizability effect in H-complexes

The study is concerned with analysis of the energies of formation (E), frequency shifts (Δν) in IR spectra, ionization potentials (IP) of H-complexes, hydrogen bond lengths (r), and spin densities (sd) in H-complexes involving radical cations, obtained from quantum chemical calculations for 20 series of H-complexes. It was for the first time established that the E, IP, r, and sd values and the changes in enthalpy (δH) depend not only on the inductive and resonance effects but also on the polarizability effect of the substituents bound to the donor and acceptor centers in the H-complexes. Interrelations between the polarizability effect and the molecular structure of H-complexes are considered. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 602–608, April, 2006.     

Peculiarities of the effect of the electronic nature of substituents on the basic properties of aliphatic amines

Changes in the hybrid state of atomic orbitals of nitrogen and p-character of LEP, which occur under the effect of saturated hydrocarbon radicals and polar substituents in aliphatic amines, differ substantially. Therefore, the effect of the both substituents on the basicity constants of amines cannot be described by the single formal type of interaction. The anomalous changes in the basicity in the series of primary, secondary, and tertiary alkylamines, which are discussed in the literature, and the correlations pK _BH+ = f(*) and G _B = f(*) are, in fact, imaginary, because the alkyl radicals at the N atom do not manifest the electron-donor properties.     

Transition metal NMR chemical shifts and polarizability effect in organometallic complexes

The literature data on substituent influence on the ⁵¹V, ⁵⁵Mn, ⁵⁷Fe, ⁵⁹Co, ⁶¹Ni, ⁹⁵Mo, ¹⁰³Rh, ¹⁸³W, ¹⁸⁷Os and ¹⁹⁵Pt NMR chemical shifts (δ) and on J (M, P; M = Mn, Fe, Mo, Rh, W, Os) coupling constants have been analyzed for 30 series of the organometallic complexes. It has been established for the first time that the δ and J values depend on the inductive, resonance and polarizability effects of substituents. The polarizability effect is caused by the partial charge on the central M atom. The contribution of this effect ranges from 3 to 86%. Copyright © 2009 John Wiley & Sons, Ltd.     

EPR studies of amine radical cations, part 1: thermal and photoinduced rearrangements of n-alkylamine radical cations to their distonic forms in low-temperature freon matrices

The thermal and photochemical transformations of primary amine radical cations (n-propyl 1.+, n-butyl 5.+) generated radiolytically in freon matrices have been investigated by using low-temperature EPR spectroscopy. Assignment of the spectra was facilitated by parallel studies on the corresponding N,N-dideuterioamines. The identifications were supported by quantum chemical calculations on the geometry, electronic structure, hyperfine splitting constants and energy levels of the observed transient radical species. The rapid generation of the primary species by a short exposure (1-2 min) to electron-beam irradiation at 77 K allowed the thermal rearrangement of 1.+ to be monitored kinetically as a first-order reaction at 125-140 K by the growth in the well-resolved EPR signal of the distonic radical cation .C(2CH2CH2NH3+. By comparison, the formation of the corresponding .CH2CH2CH2CH2NH3+ species from 5.+ is considerably more facile and already occurs within the short irradiation time. These results directly verify the intramolecular hydrogen-atom migration from carbon to nitrogen in these ionised amines, a reaction previously proposed to account for the fragmentation patterns observed in the mass spectrometry of these amines. The greater ease of the thermal rearrangement of 5.+ is in accordance with calculations on the barrier heights for these intramolecular 1,5- and 1,4-hydrogen shifts, the lower barrier for the former being associated with minimisation of the ring strain in a six-membered transition state. For 1.+, the 1,4-hydrogen shift is also brought about directly at 77 K by exposure to approximately 350 nm light, although there is also evidence for the 1,3-hydrogen shift requiring a higher energy. A more surprising result is the photochemical formation of the H2C=N. radical as a minor product under hard-matrix conditions in which diffusion is minimal. It is suggested that this occurs as a consequence of the beta-fragmentation of 1.+ to the ethyl radical and the CH2=NH2+ ion, followed by consecutive cage reactions of deprotonation and hydrogen transfer from the iminonium group. Additionally, secondary ion-molecule reactions were studied in CFCl2CF2Cl under matrix conditions that allow diffusion. The propane-1-iminyl radical CH3CH2CH=N. was detected at high concentrations of the n-propylamine substrate. Its formation is attributed to a modified reaction sequence in which 1.+ first undergoes a proton transfer within a cluster of amine molecules to yield the aminyl radical CH3CH2CH2N.H. A subsequent disproportionation of these radicals can then yield the propane-1-imine precursor CH3CH2CH=NH, which is known to easily undergo hydrogen abstraction from the nitrogen atom. The corresponding butane-1-iminyl radical was also observed.     

胺、醇和醚类化合物电离能的估算

脂肪族胺、醇、醚、硫醇和硫醚的第一电离能Ip与N、O、S原子的电负性X~Z^O、分子中N、O、S原子的部分电荷q~z以及烷基的极化效应指数PEI的关系可以表示为:Ip(eV)=4.4851+3.0727X~Z~O+7.1702q~z-1.3949∑PEI上式较好地表达了脂肪族胺、醇、醚、硫醇和硫醚的第一电离能变化的共同规律。     

Infrared spectroscopy of hydrogen bond and substituent effects in electron donor molecules

The frequency shift, , of the O—H stretching mode in the IR spectra of the H-complexes of phenol with electron donor molecules BX_i (B is the n- or -donor center and X_i are substituents; a total of eight series), the change in the Gibbs free energy, G, due to H-complexation, and the parameter (a measure of the ability of BX_i molecules to donate an electron pair; two series) are determined by both the electrostatic interaction and charge transfer in the formation of H-complex. The , G, and values depend not only on the inductive and resonance effects, but also the polarizability of substituents characterized by the parameters.     

丁烯和丁烷自由基阳离子的分子结构和超精细结构的 理论研究

用密度函数理论B3LYP方法和6-31G(d,p),6-311G(d,p)及6-311+G(d,p)基组，分别对1-C4H^+~8,2-C4H^+~8和C4H^+~10进行了构型优化和频率分析计算，预言1-C4H^+~8具有非平面构型，与以往报道的从头算和密度函数理论计算结果不同。在各自由基阳离子的B3LYP构型上，进行了B3LYP、MP2及MRSDCI方法的超精细偶合常数计算，得到了比以往更好的结果，特别是MP2/B3LYP计算值是至今与实验值符合得最好的理论计算结果。     

Vibronic spectra of the allyl radical at 6-8 eV with resonance-enhanced multiphoton ionization technique

The allyl radical was produced in molecular beam by pyrolysis of allyl iodide. The vi-bronic spectra from ground state to six new electronic states of the allyl radical at 6-8 eV, π→3dxz, π→3dxy, and π→ns (n=4, 6, 7, 8) were observed firstly with the aid of time-of-flight mass spectros-copy and resonance-enhanced multiphoton ionization technique. Vibrational progression of v7 (C3 bend) with gross spacing of about 430 cm-1 was observed in ns Rydberg states. The adiabatic ionization potential of the allyl radical was obtained to be (65641 ± 20) cm-1 ((8.138± 0.002) eV) by fitting the term values of ns (n=4,6,7,8) Rydberg states with Rydberg formula.     

胺、醇、醚类化合物电离能的自相关拓扑研究

原子的染色序数 fi 定义为 :fi=gi·xi,式中 gi 为原子i在分子中的序数 ,xi 为其染色系数 .基于fi 建立改进的原子序数自相关拓扑指数mF ,其中的1F对烷烃及其衍生物具有良好的结构选择性 .使用第一电离能 (Ip)与0 F ,1F的数量关系模型对 32种脂肪族胺、醇、醚进行估算、预测 ,结果令人满意     

Possible molecular hydrogen formation mediated by the radical cations of anthracene and pyrene

Hydrogen molecules cannot be formed readily by the association of gaseous hydrogen atoms. Possible H(2) formation mediated by the radical cations of typical polycyclic aromatic hydrocarbons (PAHs), anthracene and pyrene, was studied at the B3LYP/6-31G** level of theory. We presumed that H(2) is formed by way of two elementary reactions: the addition of an H atom to a PAH molecular cation, and the H abstraction from the resulting monohydro-PAH cation (i.e., arenium ion) by a second H atom to yield H(2). The first reaction takes place without any activation energy. The second reaction is also predicted to proceed along almost barrierless pathways, although it is far from being a typical ion-molecule reaction. There is a possibility that these reactions might constitute one of the mechanisms for H(2) formation in extremely cold interstellar space. Deuterium enrichment in PAH cations is possibly accompanied by such H(2) formation because deuteration lowers the energies of polyatomic PAH cations appreciably.