Substituent effects in electronic spectroscopy: Correlations with Platt spectroscopic moments

1980 ◽  
Vol 45 (3) ◽  
pp. 843-853 ◽  
Author(s):  
Otto Exner
Keyword(s):  
Ground State ◽  
Inductive Effect ◽  
General Trend ◽  
Electronic Spectroscopy ◽  
Substituent Effects ◽  
Spectral Shift ◽  
Mesomeric Effect ◽  
Benzene Derivatives ◽  
Classic Theory ◽  
Correct Comparison

Two correlation equations for the intensity of the 1Lb band in benzene derivatives were tested: the classic theory of Platt, Eq. (1), and the linear modification suggested by Ballester, Eq. (2). A systematic and statistically correct comparison of mono- and disubstituted derivatives revealed that Eq. (1) holds for substituents which are not conjugated or only slightly conjugated with the benzene ring, both in the ground and in the excited state (alkyls, Cl, Br, I, CH2X, CHal3). Some symmetrical properties of the substituents might be also of importance but their spectral properties (the spectroscopic moment itself, or the spectral shift) are not decisive. The conjugated substituents deviate from Eq. (1) in such a sense that the cumulative substituent effect is less than predicted; a part of the deviation may be approximately described by Eq. (2) but an exact range of validity cannot be determined. The spectroscopic moments depend mainly on the mesomeric effect of the substituent and quite little on its inductive effect; they cannot, however, be expressed only by a combination of these two effects as determined from the ground state properties. This was demonstrated on the series of compounds C6H5CH2X since the correlation with σI constants revealed only a general trend.

A refined empirical model of the sigma-inductive effect

1980 ◽  
Vol 45 (4) ◽  
pp. 1251-1268 ◽  
Author(s):  
Otto Exner ◽  
Pavel Fiedler
Keyword(s):  
Inductive Effect ◽  
Dissociation Constants ◽  
Substituent Effects ◽  
Open Chain ◽  
Topological Approach ◽  
Classic Theory ◽  
Simple Generalization ◽  
Mixed Aqueous Solvents ◽  
Improved Model ◽  
Better Than

The classic theory of the sigma-inductive effect fails in the case of more complex polycyclic molecules since it is not possible to define unambiguously the "number of paths" to be introduced into Eq. (2a). Therefore, three more sophisticated procedures were suggested and tested: 1) a model based on the charge distribution according to Smith-Eyring, or, 2) according to Del Re, and 3) a simple generalization of the classic description - Eq. (7). All the models meet some basic requirements, viz. they are compatible with the Taft equation and predict transmission of the inductive effect in either direction with the same intensity. If tested on experimental dissociation constants of carboxylic acids in mixed aqueous solvents, the third model appears to be the most satisfactory. The fit is actually better than expected for a purely topological approach, nevertheless it is impaired by solvent effects, in particular when polycyclic and open-chain acids are compared. In addition, the precision would be ultimately restricted if topologically equivalent but sterically different molecules were confronted. It follows that previous reasoning in favour of the through-space transmission of substituent effects is invalidated by our improved model. On the other hand, our results do not allow to claim the through-bonds transmission as the only process operating.

Chemometric Analysis of Substituent Effects. VII. Inductive Effect as a Basic Substituent Effect. Isoeffect Substituent Constant

1995 ◽  
Vol 60 (8) ◽  
pp. 1316-1332 ◽  
Author(s):  
Oldřich Pytela ◽  
Aleš Halama
Keyword(s):  
Inductive Effect ◽  
Chemical Shifts ◽  
Quantitative Description ◽  
Substituent Effects ◽  
Intersection Point ◽  
Chemometric Analysis ◽  
Reaction Centre ◽  
Substituent Constant ◽  
Modified Method ◽  
Substituted Benzoic Acids

The paper deals with chemometric analysis of the inductive effect. The notion of inductive effect is discussed, and unambiguous definitions are given for the notions of triad: reaction centre-basic skeleton-substituent, and the therewith connected definitions of inductive effect. For a quantitative description of inductive effect 7 types of chemical models were selected including noncyclic compounds, cyclic, and bicyclic compounds, derivatives of quinuclidine, 3-substituted benzoic acids, sulfonamides and pyridines. Altogether 139 sets of experimental data from literature have been used including altogether 1 294 points (9.3 points per set, 5 points at least) reflecting substituent effects of 34 substituents. It has been found that for a standard model the dissociation of substituted bicycloalkanecarboxylic acids only is satisfactory, all the other models reflecting also the mesomeric effects to variable extent (up to 10%). A distinctly different substitution behaviour was observed with 19F and 13C NMR chemical shifts of 4-substituted 1-fluoro- or 1-methylbicyclo[2.2.2]octanes. The earlier suggested model of substituent effects based on different way of transmission of substituent effects (3 classes) has been used for separating the inductive and mesomeric effects: it is mathematically presented as a set of straight lines with the intersection point at the so-called isoeffect substituent constant. Using the modified method of conjugated deviations a chemometric scale has been created for the inductive effect which agrees very well with the conventional scales given in literature; the only differences were observed for F and CH=O substituents (which are overestimated and underestimated, respectively, in literature). In the context given the inductive effect appears as a fundamental quantity forming a basis for quantitative description of other effects transferred by electrons.

scholarly journals Two-dimensional electronic spectroscopy as a tool for tracking molecular conformations in DNA/RNA aggregates

2018 ◽  
Vol 207 ◽  
pp. 233-250 ◽  
Author(s):  
Javier Segarra-Martí ◽  
Vishal K. Jaiswal ◽  
Ana Julieta Pepino ◽  
Angelo Giussani ◽  
Artur Nenov ◽  
...  
Keyword(s):  
Nucleic Acid ◽  
Ground State ◽  
Electronic Spectra ◽  
Crucial Role ◽  
Electronic Spectroscopy ◽  
Two Dimensional ◽  
Molecular Conformations ◽  
Computational Strategy

A computational strategy to simulate two-dimensional electronic spectra (2DES) is introduced, which allows characterising ground state conformations of flexible nucleobase aggregates that play a crucial role in nucleic acid photochemistry.

scholarly journals Macrocyclization Using RCM Reactions. Synthesis of Simple Metacyclophanes and Synthetic Efforts toward Platycarynol, a 15-Membered Aromatic Ether

2016 ◽  
Vol 11 (8) ◽  
pp. 1934578X1601100
Author(s):  
Katsuyuki Nakashima ◽  
Hatsuna Matsunaga ◽  
Masako Ito ◽  
Hiroshi Minami ◽  
Akihito Aiba ◽  
...  
Keyword(s):  
Ground State ◽  
Diphenyl Ether ◽  
Benzene Derivatives ◽  
Disubstituted Benzene ◽  
Aromatic Ether

Preparation of 13- to 19-membered carbocycles (metacyclophanes) from 1,3-disubstituted benzene derivatives has been successfully carried out using the RCM reaction, but similar starting materials having diphenyl ether did not cyclize to 15-membered compounds, whose ground state conformations were calculated and discussed. Several attempts to cyclize to form platycarynol are described.

Attenuation of the Substituent Effects Along the Aliphatic Chain

2004 ◽  
Vol 69 (5) ◽  
pp. 984-995 ◽  
Author(s):  
Stanislav Böhm ◽  
Otto Exner
Keyword(s):  
Functional Group ◽  
Inductive Effect ◽  
Substituent Effects ◽  
Transmission Factor ◽  
Isodesmic Reaction ◽  
Aliphatic Chain ◽  
Model Compounds ◽  
Derivatives Of ◽  
Methylene Group ◽  
Isolated Molecules

Two series of model compounds were devised to follow the attenuation of substituent effects with an interposed methylene group: short-chain aliphatic compounds 1 and derivatives of bicyclo[2.2.2]octane 5. In all compounds, chlorine atom acts as substituent and charged oxygen atom as the functional group; the interaction of both is measured by the reaction energy of the isodesmic reaction calculated at the B3LYP/AUG-cc-pVTZ//B3LYP/6-311+G(d,p) and/or B3LYP/6-311+G(d,p) levels. Attenuation of the substituent inductive effect with the distance is less steep than observed previously in solution. It depends also markedly on the conformation but cannot be reproduced, not even approximately, by the electrostatic formula. Only for simple regular conformations, it can be described approximately by an exponential function with the transmission factor for one methylene group equal to 0.74. The behavior of isolated molecules differs in this case distinctly from the reactivity in solution. Nevertheless, the significance of the two formulas, electrostatic and exponential, is similar in the isolated molecules and in solution. These formulas represent only two different, rather crude mathematical approximations and cannot be given any physical meaning.

Substituent Effects on the Hydrolysis of p-Substituted Benzonitriles in Sulfuric Acid Solutions at (25.0± 0.1) °C

2008 ◽  
Vol 63 (9) ◽  
pp. 603-608 ◽  
Author(s):  
Khamis A. Abbas
Keyword(s):  
Sulfuric Acid ◽  
Rate Constants ◽  
Inductive Effect ◽  
Substituent Effects ◽  
Acid Solutions ◽  
Rate Determining Step ◽  
Inductive Effects ◽  
High Concentrations ◽  
Sulfuric Acid Solutions ◽  
Hydrolysis Of

The rate constants of the hydrolysis of p-substituted benzonitriles with sulfuric acid solutions (18.2 M to 10 M) have been determined spectrophotometrically at (25.1±0.1) °C. It was found that the catalytic activity of sulfuric acid was strongly inhibited by water. The logarithms of the observed rate constants were correlated with different substituent inductive (localized) and resonance (delocalized) constants. The results of the correlation studies indicated that the rate-determining step of the hydrolysis of benzonitriles in 18.2 M sulfuric acid was the addition of a nucleophile, and the hydrolysis was clearly enhanced by the electron-withdrawing inductive effect, while the rate-determining step of the hydrolysis of p-substituted benzonitriles in 10.0 M sulfuric acid was most probably the protonation of benzonitriles, and the rate constants increased by both electron-donating resonance and inductive effects. A mixture of the two mechanisms most probably occurred in 15.3 to 17.0 M sulfuric acid. HSO4 − rather thanwater most probably acted as nucleophile in the hydrolysis of benzonitriles especially at high concentrations of sulfuric acid solutions.

scholarly journals Substituent effects on the spectral behavior and synthesis of mercury 1,5-diarylthiocarbazonates

1981 ◽  
Vol 59 (4) ◽  
pp. 679-687 ◽  
Author(s):  
Nori Y. C. Chu ◽  
Steven A. Goldstein ◽  
Philip M. Keehn
Keyword(s):  
Bathochromic Shift ◽  
Substituent Effects ◽  
Spectral Shift ◽  
Spectral Studies ◽  
Hypsochromic Shift ◽  
Electronic Effects ◽  
Activated State ◽  
Mercury Complexes ◽  
Inductive Effects ◽  
Methoxy Substituent

Symmetric and unsymmetric substituted 1,5-diarylthiocarbazones, and their mono- and bismercury complexes, were synthesized for spectral analysis. The first singlet–singlet transition of the mercury complexes was determined and the spectral shift produced by trifluoromethyl substitution was compared with that caused by different substituents in similar complexes. The large magnitude of the hypsochromic shift produced by the trifluoromethyl substituent can be explained by concerted steric and inductive effects, while the smaller bathochromic shift induced by the methoxy substituent is a result of opposing steric and electronic effects. In the trifluoromethyl substitution, a hypsochromic shift caused by steric influences was found to be 500 cm−1 in the photochromic unactivated state, and 250 cm−1 in the photochromic activated state. A similar shift caused by inductive influences was found to be 750 cm−1 in the photochromic unactivated state, and 600 cm−1 in the photochromic activated state. The smaller spectral shift observed in the photochromic activated state is consistent with the elucidated structure of the unsymmetric 1,5-diarylthiocarbazone, 6d, which was shown that the trifluoromethyl substitution was on the phenylazo portion of the molecule by chemical and spectral studies.

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