Transmission of electronic effects of substituents in vinyl esters

To elucidate the transmission mechanism of electronic effects of substituents in vinyl esters on the optical parameters of the absorption bands in the IR spectra, a comparison was made of the frequencies of corresponding absorption bands in vinyl ethers, vinyl esters, alkyl esters of carboxylic acids, ketones, and acid anhydrides. Calculation of the - and -electron structure of the molecules by the Hückel and Del Re approximations was made. The results were compared with the spectral characteristics. The conclusion was reached that the ester oxygen atom in vinyl esters reduces interaction of the carbonyl and vinyl groups, although it is not removed completely. In vinyl esters of aromatic acids the effect of benzene ring substituents is displayed by a change of the -electron structure of the CH₂=CH-O-CO- fragment. In vinyl esters of aliphatic acids the electronic influence of radicals of the acid portion is transmitted by the ester oxygen, mainly inductively, which, in its turn, shows a change in the ability of this atom to conjugate with the vinyl group.The authors express their thanks to Yu. A. Kruglyak for allowing use of the programs for the computation and for helpful advice.     

Transmission of the electronic effects of substituents by the thiophene ring

The shifts in the frequencies of the stretching vibrations of the hydroxyl group of phenol and pentachlorophenol that arise during the formation of hydrogen bonds with a number of substituted acetophenones and 2-acetylthiophenes, 2-acetylfuran, and 2-acetylselenophene and the frequencies of the stretching vibrations of the carbonyl group of the latter were subjected to a correlation analysis (with the Hammett, Brown, Taft, Yukawa-Tsuno, and Swain-Lupton equations), and it was shown that the thiophene ring in the investigated molecules in both the static state and during the formation of H complexes transmits the conjugation effects better than the benzene ring.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 918–923, July 1974.     

The dissociation constants of diprotonated chalcogenobispyridines: Transmission of electronic effects across chalcogen bridges

The dissociation constants of the diprotonated chalcogenobispyridines have been determined using potentiometric titrations to establish a method for the measurement of the ability of a bridging ligand to relay electronic effects. The relationship between pK_a and structure of the chalcogenobispyridines results from a balance between inductive, mesomeric, and steric effects. Delocalization of cationic charge onto the bridgehead increases the apparent electronegativity of the bridging atom, thereby relaying a strong base‐weakening effect to the site of first deprotonation. Such delocalization was found to be a function of both the substitution site (4‐X > 2‐X ? 3‐X) and orbital overlap requirements (S > O ≈ Se > Te). J. Heterocyclic Chem., (2011).     

Side-chain effects in molecular electronic devices

We discuss the effect of an abundant structural element of molecules on the transmission probabilities of molecular electronic devices. We show that an attachment of side chains to a molecular conductor may lead to zero transmission probabilities. The gaps in the transmission-probability appear approximately at the eigenvalues of the isolated side chains, provided that the corresponding eigenstates are not localized away from the molecular conductor. Simple Hückel-type calculations serve to illustrate the described effect. Furthermore, we show that complex transmission-probability curves, obtained with Kohn-Sham density-functional theory, also exhibit the described side-chain effect.     

Conformational and electronic effects in dehydroaminoacid derivatives

The electronic structure of the cyclic dipeptide of dehydrophenylalanine has been investigated by vapour-phase He(I) and He(II) UV photoelectron spectroscopy. Assignments are proposed by comparison with related molecules and supported by INDO/S calculations. Analogies and differences with respect to the photoelectron results of the cyclic dipeptide of dehydroalanine and corresponding acyclic compounds are discussed.     

Relativistic effects in low-lying electronic states of iron

Excited electronic states of Fe I have been calculated using the MRCI Douglas?CKroll?CHess method. Average spin-free excitation energies of the eight lowest even electronic terms ( $\hbox{a}^5\hbox{D}, \hbox{a}^5\hbox{F}, \hbox{a}^3\hbox{F}, \hbox{a}^5\hbox{P}, \hbox{a}^3\hbox{P2}, \hbox{a}^3\hbox{H}, \hbox{b}^3\hbox{F2}, \hbox{and a}^3\hbox{G}$ ) are reported. The RASSI method was employed for calculation of individual J levels of the four lowest terms. All reported values are in good agreement with experiment. Our study pointed out significant relativistic effects even in relatively light element like iron.     

Quantum-chemical study of intramolecular electronic effects in phosphaalkenes

The semiempirical CNDO/2 method has been used in a quantum-chemical study of the electronic and spatial structures of a series of phosphaalkenes as influenced by the nature of the substituents on the two-coordinated phosphorus atom and the carbon atom forming the P=C bond, as well as simple models for these. The data are compared with results from nonempirical calculations found in the literature for the latter. The authors discuss the effects of the substituents on the -electron structures of the phosphaalkenes and the character of the outer orbitals. It is found that the d AO of phosphorus plays only a slight part in forming the bonds in these compounds. The electron-density distributions are close to those found for ethylene derivatives. The conclusions agree with spectral and structural studies on the phosphaalkenes.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 22, No. 5, pp. 545–553, September–October 1986.     

Transmission of electronic substituent effects through cage polycyclic alkanes: a computational study of diamantane derivatives based on structural variation

The transmission of long-range polar effects (field effects) across the diamantane cage has been investigated by analyzing the small structural changes induced by a variable substituent X in the phenyl group of 9-substituted 4-phenyldiamantane derivatives. The structures of many such molecules with charged or dipolar substituents have been determined from quantum chemical calculations at the HF/6-31G* and B3LYP/6-311++G** levels of theory. Comparison with the results of a similar study carried out on 4-substituted 1-phenylbicyclo[2.2.2]octane derivatives, where the distance between probe and substituent is substantially smaller, shows that the ability of the diamantane framework to transmit field effects is 45 % of that of the bicyclo[2.2.2]octane framework when X is a dipolar, uncharged substituent. This figure increases to 59 % in the case of charged groups. The structural results support the idea that the field effect of a dipolar substituent attenuates more rapidly with distance than that of a charged group. This makes it impossible to construct a single, universal scale of field parameters including both dipolar and charged groups. A single scale can only be set up for a fixed separation between substituent and probe. The presence of the variable substituent X has a pronounced effect on the geometry of the diamantane cage. The nonbonded distance between the bridgehead carbons C4 and C9 spans an interval about 0.20 Å wide and correlates quite well with the mean value of the three cage angles at C9. These geometric changes are closely similar to those of the corresponding parameters in 4-substituted 1-phenylbicyclo[2.2.2]octane derivatives. The concerted structural variation of the polycyclic cage is controlled primarily by the group electronegativity of X and does not correlate with the much smaller structural variation of the phenyl probe.     

X-ray electronic spectra of certain tetraaza macrocyclic complexes of cobalt (III)

The electronic structure-Of several tetraaza macrocyclic complexes of cobalt (III), containing different axial acido ligands was studied using X-ray electron spectroscopy. The bond energies of electrons of nitrogen, cobalt, chlorine, bromide, and sulfur atoms were measured. It was shown that the bond energy of isoelectrons of the macrocyclic ligand nitrogen atoms is not a constant value, but depends on the nature of the additionally coordinated axial ligand, which reflects the cis-effect of the ligands in the macrocyclic complexes.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 21, No. 4, pp. 497–500, July–August, 1985.     

Transmission of trans effects in dinuclear complexes.

The substitution of a terminal hydride ligand in the complexes [Ir(2)(mu-H)(mu-Pz)(2)H(3)(L)P(i)Pr(3))(2)] (L = NCCH(3) (1) or pyrazole (3)) by chloride provokes a significant change in the lability of the L ligand, despite the fact that the substituted hydride and the L ligand lie in opposite extremes of the diiridium(III) complexes. Detailed structural studies of complex 3 and its chloro-trihydride analogue [Ir(2)(mu-H)(mu-Pz)(2)H(2)Cl(HPz)(P(i)Pr(3))(2)] (4) have shown that this behavior is a consequence of the transmission of ligand trans effects from one extreme of the molecule to the other, with the participation of the bridging hydride. Extended Hückel calculations on model diiridium complexes have suggested that such trans effect transmissions are due to the formation of molecular orbitals of sigma symmetry extended along the backbones of the complexes. This is also an expected feature for metal-metal bonded complexes. The feasibility of the transmission of ligand trans effects and trans influences through metal-metal bonds and its relevance to the understanding of both the reactivity and structures of metal-metal bonded dinuclear compounds have been substantiated through structural studies and selected reactions of the diiridium(II) complexes [Ir(2)(mu-1,8-(NH)(2)naphth)I(CH(3))(CO)(2)(P(i)Pr(3))(2)] (isomers 6 and 7) and their cationic derivatives [Ir(2)(mu-1,8-(NH)(2)naphth)(CH(3))(CO)(2)(P(i)Pr(3))(2)](CF(3)SO(3)) (isomers 8 and 9).     

Exchange effects on electronic states in jellium clusters

Hartree-Fock calculations are done for finite number of valence electrons (8, 20, 40, and 58) in a positively charged uniform background (jellium) with the density of bulk sodium. Differences and similarities with the results of Kohn-Sham local-density calculations are discussed. State-dependence and suppression of the wave functions are the two important effects coming from the nonlocality of the Hartree-Fock potential. These two effects, however, cancel in the density profile of electrons. The Kohn-Sham calculations consequently produce similar density profiles as in the Hartree-Fock calculations. The dipole polarizability is also calculated for 8-mers. The calculated value is still smaller than the measured one and is not an improvement of the insufficient Kohn-Sham result.deceased     

Molecular structure effects in intramolecular electronic energy transfer

A study of intramolecular energy transfer (intra-ET) in a series of bichromophoric molecules composed of cyclic α-diketones and para substituted benzene ring is reported. Preliminary results show that the transfer efficiency is strongly structure dependent suggesting that Dexter-type exchange interaction is responsible for intra-ET between close chromophores in a bichromophoric molecule.     

Solvate-shell effects on solute-molecule electronic structure

Research Institute for Physical and Organic Chemistry, Rostov University. Translated from Zhurnal Strukturnoi Khimii, Vol. 29, No. 2, pp. 84–88, March–April, 1988     

The electronic effects of substituents containing phosphorus

Dissociation constants are reported for p-phosphorophenols, p-RC₆H₄OH, in aqueous alcohol (1:1 by volume), and the nucleophilic constants ^– of the R are found to be as follows: (C₆H₅)₂P 0.26, (C₆H₅)P(O) 0.68, (C₆H₅)₂P(S) 0. 63, and (C₆H₅)₂(CH₃)P⁺ 1.28.See [1–3] for previous communications in this series.