Chemical Reactivity Indices Research Articles

The Reactivities of Polyaromatic Hydrocarbons in Catalytic Hydrogenation over Supported Noble Metals

Abstract The reactivities of several polyaromatic hydrocarbons (pyrene: P, fluoranthene: FL, anthracene: An, fluorene: F, acridine: Ac, and carbazole: C) in the catalytic hydrogenation were studied and compared over supported noble metals (Pt, Pd, Rh, and Ru on a carbon or alumina support). The specific reactivity and selectivity were found to be strongly dependent upon the combination of the catalyst species and the substrate. The catalysts exhibited the activity order of Rh > Pd >> Pt > Ru for tricyclic aromatics of An, F, Ac, and C, although the catalysts provided very variable selectivities of the partially hydrogenated products which were produced via both consecutive and competitive routes, apparently according to the type of ring-skeleton and the presence of a nitrogen atom. The reactivity of the starting substrates and intermediates are compared to the quantum chemical reactivity indices, calculated based on MNDO (modified neglect of diatomic overlap). The values of the LUMO electron density, the π-bond order, and the stability of the product appear to govern the reactivity and selectivity of the hydrogenation, depending upon the combination of the catalyst species and the substrate. No hydrogenation of a substrate proceeds when its reactivity indices are less than the threshold value, which is subject to the activity of the catalyst and the reaction conditions defining product selectivity via both competitive and consecutive schemes.

Feasibility of a quantitative description of halide anion abstraction from aromatic radical-anions using quantum chemical reactivity indices

A quantum chemical reactivity has been proposed which permits the prediction of the rate constant of the halide anion from aromatic halide radical-anions in a rather broad range.

Density functional rationale of chemical reaction coordinate

A dynamical partitioning of the reaction field is proposed in order to study the electron density flow along the reaction coordinate. The density functional is constructed in a universal form, and a one-to-one correspondence is established between the density matrix and the electron density. The density functional is free from the constraints of N or v representability and is treated as a thermodynamic function that obeys the principle of maximum entropy. The functional derivative of the density functional with respect to the electron density is introduced as a response operator. The reaction paths are combinations of the dynamical processes of the electron density; the corresponding response operators and new type of thermodynamic functions and potentials are defined and shown to be useful. The characteristic features of the chemical reaction coordinate is discussed in terms of the new thermodynamic quantities. The importance of the softest vibrational mode as the chemical reactivity index is rationalized in terms of the density functional theory.

Acid deuterium exchange in benzazoles

The kinetics of acid deuterium exchange in benzazoles carrying electron-donor substituents in the 5-, 6-, or 7-positions have been studied. Mass spectrometric studies have shown that exchange in 5-methoxy-1, 2-dimethylbenzimidazole takes place exclusively at one position in the benzene ring, in 5-chloro-, 7-chloro-,5-methoxy-2-methylbenzothiazole and 6-methoxy-2-methylbenzoxazole simultaneously in two positions, and in 6-methoxy-2-methylbenzothiazole the hydrogen at all three possible positions is exchangeable. Using quantum chemical reactivity indices (CNDO/2) in dynamic and state approximations, the orientational features of the reaction have been ascertained. The lack of agreement between the reactivities of the most reactive sites to exchange in heteroaromatic bicycles of similar structure and electrophilic localization energies is explained by differences in the energy profile of the reaction.

The isomeric composition of poly(acid)amides according to 13C-NMR spectral data

The complete decoding of the 13C-NMR spectra of poly-(acid)amides (PAA) produced by polycondensing some tetracarboxylic acid dianhydrides, i.e. those of pyromellitic, 3,4,3′,4′-diphenyloxy, 3, 4,3′, 4′-benzophenone, and 3,4,3′,4′-diphenyl, with p-phenylenediamine or benzidine, gave the proportions of the m- and p-isomeric chain units present in the PAA. The composition was found to be independent of the diamine present, but dependent on the dianhydride component. A correlation exists between the experimentally determined isomer proportions and the calculated quantum chemical reactivity indices.

Linear free energy relationships in heterogeneous catalysis: XI. Deep oxidation of lower olefins on nickel oxide catalyst

Linear free energy relationship studies were made on the rates of deep oxidation of some lower olefins over a nickel oxide catalyst. Since the trend of reactivities of olefins seems to be determined by the type of allylic hydrogens and their number for each olefin, quite similar treatments as previously reported on the dehydrogenation of cyclohexanes may be applied to this case. That is, the overall rate of deep oxidation of olefin R at temperature T, υ(R, T), can be represented as the weighted sum of the characteristic rates for allylic hydrogen atoms as v( R,T)= ∑ m w( R,m)·v(m,T) where w(R, m) means the statistical factor, i.e., the number of mth allylic hydrogen (primary, secondary, or tertiary) for olefin R and υ( m, T), the rate of the mth hydrogen at temperature T. The logarithm of υ( m, T) is demonstrated to have a linear relationship with delocalizability, D r R( H), a quantum chemical reactivity index for hydrogen abstraction, as log υ(m,T) = log υ(0,T) + γ(T) · ΔD r R ( H m) 2.3RT where υ(0, T) is the rate of hypothetical hydrogen with delocalizability of 1.00 and γ( T) is a proportional constant. Furthermore, γ( T) is proved to be practically independent of temperature. This means that the preexponential factor of the mth hydrogen, υ( m,∞), is independent of the type of allylic hydrogen but its activation energy, E A( m) , decreases proportionately with D r R(H m ). Finally, the overall rates can be expressed as follows: v( R,T)= ∑ m w( R,m)·v(0,∞)· exp{−[E A(0)−λ D·ΔD r R( H m)]/ RT} where υ(0,∞) and E A(0) are the preexponential factor and the activation energy, respectively, for hypothetical hydrogen defined above and γ( T) is rewritten as γ D. Finally, the rate of deep oxidation of any olefin at any temperature can be predicted according to the above equation using the delocalizability inherent to allylic hydrogen and three parameters characteristic of the type of catalyst, i.e., υ(0,∞), E A(0) and γ D. This treatment is compatible with the tentative mechanism that the deep oxidation of olefins over nickel oxide involves an abstraction of allylic hydrogen as a rate determining step.

On the alleged correlations between simple LCAO‐MO reactivity indices and proton chemical shifts in planar, condensed, benzenoid hydrocarbons

AbstractPrevious investigations into the proposed correlations between proton chemical shifts in conjugated hydrocarbons and the various LCAO‐MO ‘reactivity indices’ (at the corresponding carbon atoms to which the peripheral protons are bonded), are here reassessed in the light of more‐recently acquired experimental data, for the case of the planar, alternant, condensed, benzenoid hydrocarbons. A correlation coefficient of 0·73, statistically ‘significant’ at less than the ½% level, is obtained. Nevertheless, there are several unsatisfactory features of such proposed correlations (which are discussed), and, in the final analysis, no causative relation is expected between proton chemical shifts and reactivity indices in these molecules. Furthermore, the relative chemical shifts of the sterically unhindered protons in planar, alternant, benzenoid hydrocarbons can be accounted for by the ‘ring current’ effect alone, without the need to postulate a dependence of the proton chemical shifts on reactivity indices, which is in any case considered to be unlikely on physical grounds.

NMR spectra and the reactivity of organic compounds. I. Correlations between proton chemical shifts of alternant hydrocarbons and HMO chemical reactivity indices

NMR spectra and the reactivity of organic compounds. I. Correlations between proton chemical shifts of alternant hydrocarbons and HMO chemical reactivity indices

Electronic structure of non-alternant hydrocarbons, their analogues and derivatives. XII. Chemical reactivity indices of fluoranthene and the benzofluoranthenes

Electronic structure of non-alternant hydrocarbons, their analogues and derivatives. XII. Chemical reactivity indices of fluoranthene and the benzofluoranthenes

Physical properties and chemical reactivity of alternant hydrocarbons and related compounds. VIII. Quantum chemical reactivity indices of pyridine-like heterocycles

Physical properties and chemical reactivity of alternant hydrocarbons and related compounds. VIII. Quantum chemical reactivity indices of pyridine-like heterocycles

Relationship between chemical reactivity indices and carcinogenic activity of larger benzenoid hydrocarbons

Relationship between chemical reactivity indices and carcinogenic activity of larger benzenoid hydrocarbons

Correlation of infra-red intensity data with chemical reactivity indices

Correlation of infra-red intensity data with chemical reactivity indices