Transmission of inductive effect and polar resonance effect through the benzene and the furan ring in PMR spectra

Assuming the independence and additivity of the inductive and polar resonance effects, experimental data for chemical shifts in proton magnetic resonance (PMR) spectra of mono and disubstituted benzene and furan derivatives are used to calculate transmission coefficients for the inductive and polar resonance effects due to any substituent for a proton in the 2, 3, or 4 position in the ring. Values of ^* and ^c are tabulated. With benzene compounds transmission of the polar resonance effect decreases on passing from the p and o to the m position. The coefficient of transmission of the inductive effect to a proton in the m or p position is negligible.With furan compounds the values of the coefficient ^c for 2, 5 and 2,4 ring positions are close to the corresponding values for benzene compounds. In the furan ring a considerable part of the polar resonance is transmitted through the heteroatom. The ^* coefficients are appreciably greater with furan than with benzene compounds, because the ring carbon atoms screen the proton less from the substituent. Most of the inductive effect from the 2 to the 5 position in the furan ring is direct (transmitted through space).     

Influence of the structure of monoalkyl substituted ketenes upon the rate of their spontaneous hydrolysis in water

The kinetics of spontaneous hydrolysis of monoalkylsubstituted ketenes has been studied. The influence of inductive and steric effects of substituents upon the rate has been quantitatively estimated in terms of -analysis. Increasing length and branching of alkyl substiuents decrease the rate of ketene hydrolysis.     

Effect of Substituents on the Silicon Atom on Etherification of Organochlorosilanes with Ethanol

The kinetics of etherification of organochlorosilanes with various substituents on the silicon atom with ethanol were studied. The etherification rate is mostly controlled by the inductive constants of the substituents and increases as the electron-acceptor power of the substituents increases. The ^* value in the Taft equation for etherification of organochlorosilanes with ethanol was determined.     

Charge control of the complex formation of phenol with unsaturated compounds containing organoelement substituents from group IV

The frequency shifts (v (OH)) of phenol and the resonance components (v_r) of these shifts in the IR spectra of forty H-complexes of phenol with furan derivatives containing organic, organosilicon, organogermanium, and organotin substituents are studied. The values of v and v_R are linearly related to quantum chemical parameters of the variation of the effective charges of the furan ring atoms affected by - and -interactions with organic substituents. The effect of the conjugation between an organoelement substituent and the furan ring on the effective charges is estimated. The resonance parameters (_R) of organoelement substituents in derivatives of benzene, thiophene, and furan and the reasons for the non-versatility of _R are considered.For report 7, see Ref. 1.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 289–295, February, 1995.This work was financially supported by the Russian Foundation for Basic Research (Project No. 93-03-18372).     

Configuration interaction in a nonorthogonal determinant basis

A class of electron models which reduce to a superposition of nonorthogonal determinants is studied by methods of covariant quantum chemistry. A compact matrix representation is found which contains variational parameters only in the form of Fock-Dirac densities A, b of separate determinants ¦>,...,¦B>. Nonorthogonality of the determinants is taken into account by means of additional projectors obtained by pseudo-inversion of the products of the form AB-Orbital optimization is thus reduced to a clearly Hermitian eigenvalue problem. Inclusion in the initial model of configurations singly excited with respect to each of the determinants ¦a> ...,¦B> is discussed. This generalized Tamm-Dancoff model is studied in detail for the spin-symmetrized (half-projected) Hartree-Fock methods. Correlation effects in the excited states of model -systems of the alternant type are analyzed within the framework of the model.Translated from Teoreticheskaya i Éksperimentalnaya Khimiya, Vol. 22, No. 5, pp. 513–523, September–October, 1986.     

C-I stretching vibrations in iodobenzenes

Comparison of the calculated and experimental IR and Raman spectra of a series of iodobenzenes showed that the C-I stretching vibrations for these compounds correspond to a very highly polarized Raman band at 150–270 cm^–1 (=0.1). The position of this band depends on the mass of the para substituent and relative position of the fluorine and iodine atoms in the molecule. The UV absorption spectral data indicate an interaction of the iodine atom and para substituents through the -system. Opposite substituent effects on the change in intensity of the B-band in the UV spectra of iodobenzenes and tetrafluoroiodobenzenes were noted.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2637–2639, November, 1991.     

Regioselectivity of methoxydebromination of substituted pentabromobenzenes C6Br5X in pyridine

The kinetics and regioselectivity of methoxydebromination of some substituted pentabromobenzenes C₆Br₅X (X = NO₂, CN, NH₂, MeNH, and MeO) were studied in pyridine at 115°C. The partial rate factors (k _f) were calculated for different positions of the polybrominated ring in these compounds. The effect of substituents X on methoxydebromination at themeta- andpara-positions is satisfactorily described only by the Hammett substituent constants ( = 2.22,r = 0.96). This allows one to conclude that direct polar conjugation of the substituents contributes only slightly to the transition state of the reaction. Theorthobromine atoms have a significant steric effect.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1784–1788, September, 1995.     

Isotopic hydrogen exchange in 1- and 2-aryl-5-methyltetrazoles

The rate constants for basic deuterium exchange of the methyl group (k_D) in 2-phenyl-5-methyl-tetrazole (I) and 1-aryl-5-methyltetrazole (II) and its derivatives with a polar substituent (R) in the phenyl ring were measured. The increased CH acidity of II as compared with I [k_D(II)/k_D(I)20] is in agreement with the calculated and experimental values regarding the character of the electron-density distribution in the molecules. The effect of R on the rate of deuterium exchange of the methyl group correlates with the ° constants (=3.0, r = 0.997). The results of measurement of the kinetic isotope effect during deuterium (tritium) exchange in II (k_D/k_T1.8) are discussed in connection with the peculiarities of the stepwise reaction mechanism.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No.1, pp. 127–130, January, 1978.     

Nitrogen NMR Shieldings of Some Nitro Derivatives of 2-Amino-4-methylpyridine Systems

High precision ¹⁴N NMR shieldings (chemical shifts), bulk susceptibility corrected, are reported for dilute solutions in pure, dry acetone for a group of nitro derivatives of (N-substituted) 2-amino-4-methylpyridines, with nitro substituents in either positions 5 or 3 or both, where at least some of these should reveal serious steric hindrance between the substituents involved. The nitrogen shieldings as well as the corresponding PM3 optimized geometries show quite clearly that the 5-nitro derivatives are planar or nearly planar, without any significant hindrance to the -conjugation throughout the molecular system concerned, while the 3-nitro derivatives experience deviations from coplanarity of the pyridine ring and the nitro and amino substituents, with concomitant impairment of -conjugation between these moieties. The nitrogen shieldings of the pyridine nitrogen atoms in N-nitramino-2-alkyl-4-methyl 3 (or 5)-nitropyridines indicate that the N-nitramino group acts as a modest donor of -electrons, much weaker with respect to the donor strength of amino, alkylamino, or phenylamino substituents.     

Heterocyclic nitro compounds

The acidity of a number of nitro derivatives of 1,2,4-triazole has been determined. The acidity indices correlate well with Hammett's _I and _meta constants and somewhat less well with the _para constants. The high values of show the great sensitivity of the system to the influence of substituents. The acidities of the conjugate acids of 3-nitro-1,2,4-triazole and its C- and N-methyl derivatives have also been determined. Hammett's postulate is not observed for these compounds, and the amide scale of acidity, H_A, is more suitable for calculating their acidity indices than H_O.For part III, see [1].     

On the Interaction of Two Finite-Dimensional Quantum Systems

Interaction of quantum system S ^a described by the generalised × eigenvalue equation A| _s =E _s S ^a | _s (s=1,...,) with quantum system S ^b described by the generalised n×n eigenvalue equation B| _i = _i S ^b | _i (i=1,...,n) is considered. With the system S ^a is associated -dimensional space X ^a and with the system S ^b is associated an n-dimensional space X _n ^b that is orthogonal to X ^a . Combined system S is described by the generalised (+n)×(+n) eigenvalue equation [A+B+V]| _k = _k [S ^a +S ^b +P]| _k (k=1,...,n+) where operators V and P represent interaction between those two systems. All operators are Hermitian, while operators S ^a ,S ^b and S=S ^a +S ^b +P are, in addition, positive definite. It is shown that each eigenvalue _{k i} of the combined system is the eigenvalue of the × eigenvalue equation . Operator in this equation is expressed in terms of the eigenvalues _i of the system S ^b and in terms of matrix elements _s |V| _i and _s |P| _i where vectors | _s form a base in X ^a . Eigenstate | _k ^a of this equation is the projection of the eigenstate | _k of the combined system on the space X ^a . Projection | _k ^b of | _k on the space X _n ^b is given by | _k ^b =( _k S ^b –B)^–1(V– _k P})| _k ^a where ( _k S ^b –B)^–1 is inverse of ( _k S ^b –B) in X _n ^b . Hence, if the solution to the system S ^b is known, one can obtain all eigenvalues _{k i} } and all the corresponding eigenstates | _k of the combined system as a solution of the above × eigenvalue equation that refers to the system S ^a alone. Slightly more complicated expressions are obtained for the eigenvalues _{k i} } and the corresponding eigenstates, provided such eigenvalues and eigenstates exist.     

Effect of the structure of substituted propargyl and allyl alcohols on the rate of their liquid phase hydrogenation on a Pd-Ru alloy membrane catalyst

The rates of hydrogenation of substituted propargyl and allyl alcohols in the liquid phase on a Pd-Ru alloy membrane catalyst are described by a two-parameter Taft equation which takes into account the inductive and steric effects of the substituents. The values of the parameters at 363 K with H₂ at atmospheric pressure are: ^*=–0.20, =0.10 and ^*=–1.1, =1.3 respectively.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1740–1745, August, 1989.     

Electronic spectra of α,β-unsaturated ketones — Indole derivatives

The electronic spectra of (3-indolyl)-, (1-methyl-3-indolyl)-, and (6-nitro-3-indolyl)-substituted ,-unsaturated ketones were measured and interpreted. 3-Indolyl and N-methyl-3-indolyl substituents have a considerable bathochromic effect as compared with the phenyl group in the investigated systems as a consequence of the electron-donor effect, which surpasses that for 4-anisyl, 2,4-dimethoxyphenyl, 2-furyl, 2-thienyl, and 2-selenienyl and differs only slightly from 2-pyrrolyl. The introduction of electron-donor substituents into the p position of the benzene ring of 1-(3-indolyl)-3-phenyl-1-propenone causes a red shift of the long-wave absorption band, the difference in frequencies of which correlates with the Hammett substituent constants. Except for compounds containing a nitro group,1-(3-indolyl)-3-aryl-3-propenones and their N-methyl derivatives fluoresce well in alcohol with _max >475 nm.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 949–953, July, 1972.     

Low temperature crystal and molecular structure of nitrobenzene

The crystal and molecular structure of nitrobenzene was determined at 103 K by X-ray diffraction, yieldingR=0.034 and a highly precise geometry of the molecule (esds of bond lengths 0.001 Å and bond angles 0.1°). The bond angles in the ring agree very well with additive scheme based on angular substituent parameters. X-X electron density maps support the view that the C-N bond does not exhibit-character, and, hence, the nitro group interacts with the ring mostly by inductive effects.     

Transmission of influence of substituent in 2-arylpyrrole-5-carboxylic acids

Research on the influence of substituenis on the reaction centers of molecules, through various bridge groups, is still an urgent task in theoretical organic chemistry. This problem is usually solved using the Hammett equation f= + a, by comparing the coefficient of the particular series of compounds under investigation with the coefficient ₀ of a reference series of compounds. The ratio of coefficients / ₀=, which is called the transmission factor, characterizes structural changes of the bridge group [1, 2].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, 1182–1186, September, 1992.     

Effect of the structures of hydroperoxides on the kinetics of their acetylation by acetic anhydride

Conclusions The rates of uncatalyzed and acetic-acid-catalyzed hydroperoxide acetylation by acetic anhydride increase with an increase in the electron-donor capacity of the hydroperoxide substituent. An alteration in the structure of the acetylating agent reduces the sensitivity of the acetic-acid-catalyzed reaction to the inductive effect of the substituent: _cat ^*=–0.4 as compared with ₀=–0.7 for the uncatalyzed process.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2664–2666, December, 1982.     

Hydrodynamics and heat transfer in a plasma spouted bed reactor

The literature reveals very little intformation about plasma spouted bed hydrodynamics. Spouting of corindon particles with diameters ranging from 0.4 to 3.36 mm with argon plasma was conducted in a 90-mm-diameter column in the temperature range 300–1300°C. It was found that the maximum spoutable height (H_m) decreases with increasing particle diameter and decreasing mean bed temperature. A relation between the inlet plasma velocity and H_m is proposed. Concerning heat transport phenomena in the annulus, measurements and calculations indicate a large axial diffusivity but a poor radial mixing. Typical values of D_z and D_r are proposed on the basis of an identification procedure.Notation Ar Archimede number - Ar d ³ p (p — f) _f g ² - C_p specific heat - d_p particle diameter - d_e core diameter (or spout diameter) - D_i fluid inlet orifice diameter - D_e column diameter - D_r and D_z radial and axial diffusivity, respectively - g acceleration due to gravity - H packed static bed height - H_b bed height - H_m maximum spoutable bed height - P power     

A simple NMR method for determination of the position of the tautomeric equilibrium in diarylformazanes

Conclusions Analysis of the shielding of the¹³C nuclei in 1,3-diphenyl-5-arylformazanes permits evaluation of the position of the tautomeric equilibrium in the red formazanes. In the case of the electron-withdrawing p-NO₂ substituent, the substituted ring is attached to the NHN=hydrazone fragment. An opposite effect is found for electron-donor substituents. In the case of ortho substituents, the shift of the tautomeric equilibrium is largely determined by steric factors.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 691–694, March, 1987.     

Influence of solvent on ir spectra of aroyl(hydroxymethyl)trifluorosilanes

Conclusions Dipole-dipole interaction of the solvent with molecules of aroyl (hydroxymethyl) trifluorosilanes 4-XC₆H₄COOCH₂SiF₃ is responsible for changes in frequency of the stretching vibrations of groups included in a five-membered ring, containing an intramolecular coordination bond Si 0 (the frequencies C=O and SiF _a , are lowered, and the frequencies _asCOC are raised). The value of the orientation-induction parameter in the Buckingham equation, reflecting the dependence of C=O and SiF _a on the parameters of the medium (, n), increases with increasing electron-donor capability of the substituent X, indicating an increase in the strength of the coordination bond. The coefficient in the Hammett equation is determined by the polar properties of the medium.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2251–2254, October, 1984.     

Reversed phase liquid chromatographic separation of some mono-substituted phenols with calix[6]arene-ρ-sulfonate-modified eluents

Summary The utility of water-soluble calix[6]arene--sulfonate as a mobile phase additive has been investigated for the reversed phase liquid chromatographic separation of some monosubstituted phenol isomers. Retention factors and separation factors for regioisomers of methoxyphenol, aminophenol, and nitrophenol were measured using methanol — water and acetonitrile —water mobile phases of varying composition containing calix[6]arene--sulfonate, and the values were compared with those obtained using mobile phases containing no additive. It was observed that addition of calix[6]arene--sulfonate to both acetonitrile — water and methanol —water caused a reduction in the retention of the phenol isomers but generally increased the separation between them, thereby improving the overall separation efficiency.