Transmission Of Electronic Substituent Effects Research Articles

The transmission of electronic substituent effects along the polyene chain: evaluation of through-bond and through-space contributions

Transmission between various parts of molecules determines their reactivity and is important from the perspective of molecular recognition. In a recent paper, the correlation between substituent electronic properties and those of the rest of molecules has been studied using long substituted polyphenylene hydrocarbons. The distance attained between interacting sites (between a substituent and an extreme carbon atom) was 119 A. The present study was planned to investigate whether similar interactions can be found when the transmitting medium is not a polyphenylene unit, but a polyene one. Some questions had to be answered: How rapidly do interactions between a substituent at one end of a molecule and phenyl ring at the other end decline with the increasing distance between two sites? How would this interaction change upon the removal of some polyene units from inside the molecule and what contribution would the units have to the through-space interactions? What measure characterizes the electronic properties of a substituent attached to the end of a polyenic chain? It was found that the through-space interaction contributions increased as molecules lengthened, but even for the longest molecules, the through-bond mechanism was responsible for about one half of the overall transmission whereas the through-bond transmission dominated for shorter molecules.

Structural variation, π-charge transfer, and transmission of electronic substituent effects through the carbon-carbon triple bond in β-substituted phenylacetylenes: a quantum chemical study, and a comparison with (E)-β-substituted styrenes

The transmission of electronic substituent effects through a carbon-carbon triple bond has been investigated from the small changes induced by a variable substituent X on the geometry of the phenyl group in β-substituted phenylacetylenes, Ph−C≡C−X. The geometries of many such molecules were determined by quantum chemical calculations at the B3LYP/6-311++G** level of theory. The structural variation of the phenyl probe is best represented by a linear combination of the internal ring angles, termed SFPHA. Multiple regression analysis of SFPHA using appropriate explanatory variables reveals a composite polar effect. The main components are, in order of decreasing importance: (i) the field effect of the substituent, enhanced by field-induced π-polarization of the −C≡C− spacer, (ii) the resonance-induced field effect, and (iii) the electronegativity effect. These results are compared with those obtained for (E)-β-substituted styrenes, Ph−CH=CH−X, using the same statistical technique, applied to a structural parameter termed SFSTY. The comparison shows that in β-substituted phenylacetylenes, the field effect of the substituent plays a more important role, and the resonance effect a less important, than in (E)-β-substituted styrenes. This is a consequence of the greater polarizability of the C≡C bond as compared with the C=C bond. The role played by the electronegativity of the substituent is the same for the two sets of molecules. A peculiar feature of the −C≡C− spacer is that its π-system consists of two separate parts, corresponding to the two π-bonds that concur to the formation of the triple bond. Only the part orthogonal to the plane of the phenyl probe may interact with the probe π-system, making it possible to transfer π-electron density from substituent to probe, or vice versa. The part coplanar with the phenyl probe may exchange π-electron density with the substituent, but not with the probe. Thus, π-interactions between substituent, spacer, and probe depend critically on the electronic structure and conformation of the substituent. We have classified the substituents in three categories according to the different types of π-interactions that occur in β-substituted phenylacetylenes. First category substituents exchange π-electron density with the orthogonal part of the π-system of the spacer, and hence with the π-system of the probe. While the orthogonal part of the π-system of the spacer acts as a π-electron channel, the coplanar part cannot exchange electrons with the π-system of the phenyl probe. With second category substituents, the conformation of the molecule inhibits the exchange of π-electron density between substituent and probe. The substituent can only exchange π-electrons with the part of the π-system of the spacer that is coplanar with the phenyl probe. Third category substituents exchange π-electron density with both parts of the π-system of the spacer. While the π-charge transferred into the orthogonal part can be further delocalized into the π-system of the phenyl probe, the π-charge transferred into the coplanar part cannot and remains blocked in the spacer. From there, however, it gives rise to an inductive effect that polarizes the π-electron system of the phenyl probe. The π-charge distribution in 45 β-substituted phenylacetylenes and the corresponding (E)-β-substituted styrenes has been determined by Natural Atomic Orbital analysis at the B3LYP/6-311++G** level of theory. The results of the analysis support our classification of the substituents in three categories and reveal the existence of a number of important correlations involving charges as well as structural parameters.

How Far Does Substituents' Impact Reach? The Transmission of Electronic Substituent Effects along the Polyphenylene Chain and the Evaluation of Through-Bond and Through-Space Contributions.

Interactions between various parts of molecules determine their reactivities and are important from the point of view of molecular recognition. Concerning substituted aromatics, the correlation between the substituents' electrical properties with those of the rest of a molecule has been widely studied. However, the distances between the interacting sites generally did not exceed a dozen Å. This study deals with the long polyphenylene substituted hydrocarbons and aims to answer two questions. The first question involves how rapidly interactions between a substituent in the phenyl ring and a site on the other end of the molecule decline with increasing distance between the two sites. The second is regarding how this interaction would be changed after chopping out the benzene rings, spacing units, from inside the molecules, leaving only the first, substituted benzene ring, and the last. The interactions were gauged by the electrostatic potential at the carbon atom the most distant from the substituent, and at two points in space. It was found that the interaction between two sites on a long molecule, about 120 Å apart, is almost as precisely controlled by the substituent properties as in the substituted benzene molecules. The contributions of the through-bond and through-space interactions were that the latter increased as the molecules lengthened.

Quantitative structure-activity relationship analysis of substituted arylazo pyridone dyes in photocatalytic system: Experimental and theoretical study

A series of arylazo pyridone dyes was synthesized by changing the type of the substituent group in the diazo moiety, ranging from strong electron-donating to strong electron-withdrawing groups. The structural and electronic properties of the investigated dyes was calculated at the M062X/6-31+G(d,p) level of theory. The observed good linear correlations between atomic charges and Hammett σp constants provided a basis to discuss the transmission of electronic substituent effects through a dye framework. The reactivity of synthesized dyes was tested through their decolorization efficiency in TiO2 photocatalytic system (Degussa P-25). Quantitative structure-activity relationship analysis revealed a strong correlation between reactivity of investigated dyes and Hammett substituent constants. The reaction was facilitated by electron-withdrawing groups, and retarded by electron-donating ones. Quantum mechanical calculations was used in order to describe the mechanism of the photocatalytic oxidation reactions of investigated dyes and interpret their reactivities within the framework of the Density Functional Theory (DFT). According to DFT based reactivity descriptors, i.e. Fukui functions and local softness, the active site moves from azo nitrogen atom linked to benzene ring to pyridone carbon atom linked to azo bond, going from dyes with electron-donating groups to dyes with electron-withdrawing groups.

Transmission of electronic substituent effects along polyenic chains: a quantum chemical study based on structural variation and π-charge distribution

The transmission of electronic substituent effects along chains of conjugated double bonds has been investigated by analyzing the small structural changes induced by a variable substituent X in the phenyl group of Ph–(CH=CH) n –X molecules (n = 2, 3, and 4). The structures of many such molecules with charged or dipolar substituents have been determined from quantum chemical calculations at the B3LYP/6-311++G** level of theory. The structural variation of the phenyl probe is best represented by a linear combination of the internal ring angles, termed S F PE (n = 2, 3, and 4). Multiple regression analysis of the S F PE parameters using appropriate explanatory variables reveals a composite electronic effect, the main component of which is the field effect of the variable substituent, enhanced by field-induced π-polarization of the polyenic chain. Also important is the role of resonance-induced field effects. An electronegativity term contributes significantly to the structural variation of the phenyl probe in (E)-β-substituted styrenes, Ph–CH=CH–X, but is marginally significant in Ph–(CH=CH)2–X molecules and not significant at all in Ph–(CH=CH)3–X and Ph–(CH=CH)4–X molecules. The structural substituent parameters S F PE2 , S F PE3 , S F PE4 , as well as S F STY from (E)-β-substituted styrenes, are all correlated to each other. However, even though the correlation coefficients are high, it appears unequivocally that the data points corresponding to dipolar substituents and those corresponding to charged groups are aligned along slightly different straight lines. An analysis of π-charge distribution in Ph–(CH=CH) n –X molecules (n = 1–4) has also been carried out. It appears that as the number of double bonds increases, the π-charge transmitted from the variable substituent to the hydrocarbon frame becomes larger, while the π-charge transmitted to the phenyl probe becomes smaller. In each of the three series of Ph–(CH=CH) n –X molecules (n = 2, 3, and 4), the π-charge of the phenyl probe is linked by an excellent nonlinear relationship to the corresponding structural substituent parameter S F PE (n = 2, 3, and 4). The effect of the variable substituent on the geometry of the polyenic chain has been studied by analyzing the alternation of C–C bond lengths along the chain in Ph–(CH=CH)4–X molecules. The alternation is most pronounced and regular when the variable substituent X is an uncharged group, irrespective of whether it is a π-acceptor or a π-donor. For the five strongest resonant substituents in our data set (namely, the charged groups CH2 +, CH2 −(c), NH−, O−, and N2 +), there is a region in the chain where the alternation between adjacent C–C bonds decreases and inverts, a structural feature known as geometric soliton.

Transmission of electronic substituent effects across the 1,12-dicarba-closo-dodecaborane cage: a computational study based on structural variation, atomic charges, and ¹³C NMR chemical shifts.

The ability of the 1,12-dicarba-closo-dodecaborane cage to transmit long-range substituent effects has been investigated by analyzing the structural variation of a phenyl probe bonded to C1, as caused by a remote substituent X at C12. The geometries of 41 Ph-CB10H10C-X molecules, including 11 charged species, have been determined by MO calculations at the B3LYP/6-311++G** level of theory. The structural variation of the phenyl probe is best represented by a linear combination of the internal ring angles, termed SF(CARB). Multiple regression analysis of SF(CARB), using appropriate explanatory variables, reveals the presence of resonance effects, superimposed onto the field effect of the remote substituent. The ability of the para-carborane cage to transmit resonance effects is, on average, about one-half of that of the para-phenylene frame in coplanar para-substituted biphenyls. Analysis of the π-charge variation of the phenyl probe confirms that the para-carborane frame is less capable than the coplanar para-phenylene frame of transmitting π-electrons from the remote substituent to the phenyl probe, or vice versa. The para-carborane cage is a better π-acceptor than π-donor; this makes π-donor substituents less effective than π-acceptors in exchanging π-electrons with the phenyl probe across the cage. When the remote substituent is an uncharged group, the para-carborane cage acts as a very weak π-acceptor toward the phenyl probe. The structural variation of the para-carborane cage has also been investigated. It consists primarily of a change of the C1···C12 nonbonded separation, coupled with a change of the five B-C-B angles at C12. This concerted geometrical change is controlled by the electronegativity of the substituent and the resonance interactions occurring between substituent and cage. These, however, appear to be important only when π-donor substituents are involved. The (13)C NMR chemical shifts of the para-carbon of the phenyl probe correlate nicely with SF(CARB), pointing to the reliability of these quantities as measures of long-range substituent effects. On the contrary, the (11)B and (13)C chemical shifts of the cage atoms do not convey information on electronic substituent effects.

Linear Free‐Energy Relationships Applied to the 13C NMR Chemical Shifts in 4‐Substituted N‐[1‐(Pyridine‐3‐ and ‐4‐yl)ethylidene]anilines

Two series of 4‐substituted N‐[1‐(pyridine‐3‐ and ‐4‐yl)ethylidene]anilines have been synthesized using different methods of conventional and microwave‐assisted synthesis, and linear free‐energy relationships have been applied to the 13C NMR chemical shifts of the carbon atoms of interest. The substituent‐induced chemical shifts have been analyzed using single substituent parameter and dual substituent parameter methods. The presented correlations describe satisfactorily the field and resonance substituent effects having similar contributions for C1 and the azomethine carbon, with exception of the carbon atom in para position to the substituent X. In both series, negative ρ values have been found for C1′ atom (reverse substituent effect). Quantum chemical calculations of the optimized geometries at MP2/6‐31G++(d,p) level, together with 13C NMR chemical shifts, give a better insight into the influence of the molecular conformation on the transmission of electronic substituent effects. The comparison of correlation results for different series of imines with phenyl, 4‐nitrophenyl, 2‐pyridyl, 3‐pyridyl, 4‐pyridyl group attached at the azomethine carbon with the results for 4‐substituted N‐[1‐(pyridine‐3‐ and ‐4‐yl)ethylidene]anilines for the same substituent set (X) indicates that a combination of the influences of electronic effects of the substituent X and the π1‐unit can be described as a sensitive balance of different resonance structures.

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 A 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.

Experimental and theoretical study of substituent effect on 13C NMR chemical shifts of 5-arylidene-2,4-thiazolidinediones

The electronic structure of 5-arylidene-2,4-thiazolidinediones has been studied by using experimental and theoretical methodology. The theoretical calculations of the investigated 5-arylidene-2,4-thiazolidinediones have been performed by the use of quantum chemical methods. The calculated 13C NMR chemical shifts and NBO atomic charges provide an insight into the influence of such a structure on the transmission of electronic substituent effects. Linear free energy relationships (LFERs) have been further applied to their 13C NMR chemical shifts. The correlation analyses for the substituent-induced chemical shifts (SCS) have been performed with σ using SSP (single substituent parameter), field (σF) and resonance (σR) parameters using DSP (dual substituent parameter), as well as the Yukawa–Tsuno model. The presented correlations account satisfactorily for the polar and resonance substituent effects operative at Cβ, and C7 carbons, while reverse substituent effect was found for Cα. The comparison of correlation results for the investigated molecules with those obtained for seven structurally related styrene series has indicated that specific cross-interaction of phenyl substituent and groups attached at Cβ carbon causes increased sensitivity of SCS Cβ to the resonance effect with increasing of electron-accepting capabilities of the group present at Cβ.

Structural variation, π-charge transfer, and transmission of electronic substituent effects in (E)-β-substituted styrenes: a quantum chemical study

The nature and transmission mechanism of substituent effects in (E)-β-substituted styrenes, C6H5–CH=CH–X, have been investigated from the structural changes induced by a variable substituent on the phenyl group. The molecular structures of 46 (E)-β-substituted styrenes were determined from MO calculations at the B3LYP/6-311++G** level of theory. The structural variation of the phenyl probe is best represented by two orthogonal linear combinations of the internal ring angles, S F STY and S R STY . Regression analysis of S F STY using appropriate explanatory variables reveals a composite field effect, the main component of which originates from the long-range effect of the substituent enhanced by field-induced π-polarization of the vinylene spacer and resonance-induced field effects. The electronegativity of the substituent also plays a role in determining the value of S F STY . Comparison with coplanar 4-substituted biphenyls reveals that the components of the field effect in the two molecular systems are of the same nature (apart from the electronegativity contribution, which is not present in biphenyl derivatives). However, the structural variation of the phenyl probe is more pronounced in (E)-β-substituted styrenes due to the shorter distance between substituent and probe. Analysis of π-charge distribution shows that the aptitude of the substituents to exchange π-electrons with the styrene and coplanar biphenyl frames is nearly the same. Nevertheless, the π-charge variation on the phenyl probe of (E)-β-substituted styrenes is 57 % greater than the corresponding quantity in coplanar 4-substituted biphenyls. Thus, the vinylene spacer is more effective than the phenylene spacer in transmitting π-charges. The S R STY parameter is related to the amount of π-charge transferred from the –CH=CH–X moiety into the π-system of the benzene ring, or vice versa, due to the resonance effect of the variable substituent and, to a lesser extent, to field-induced π-polarization.

Substituent effect on IR, 1H and 13C NMR spectral data in n-(substituted phenyl)-2-cyanoacetamides: A correlation study

Linear free energy relationships (LFER) were applied to the IR, 1H and 13C NMR spectral data of N-(substituted phenyl)-2-cyanoacetamides. A variety of substituents were employed for phenyl substitution and fairly good correlations were obtained using the simple Hammett and the Hammett-Taft dual substituent parameter equations. The correlation results of the substituent induced 13C NMR chemical shifts (SCS) of the C1, C=O and N-H atom indicated different sensitivity with respect to electronic substituent effects. A better correlation of the SCSC=O with a combination of electrophilic and nucleophilic substituent constants indicated a significant contribution of extended resonance interaction (?-delocalization) within the ?1-unit. The conformations of the investigated compounds were studied using the DFT B3LYP/6-311G method and, together with the results of 13C NMR and IR spectroscopic studies, a better insight into the influence of such a structure on the transmission of electronic substituent effects was obtained.

Transmission of Electronic Substituent Effects through a Benzene Framework: A Computational Study of 4-Substituted Biphenyls Based on Structural Variation

The transmission of substituent effects through a benzene framework has been studied by a novel approach, based on the structural variation of the Ph group in p-Ph-C(6)H(4)-X molecules. The molecular structures of many 4-substituted biphenyls were determined from MO calculations at the HF/6-31G* and B3LYP/6-311++G** levels of theory. The twist angle between the phenyl probe (ring B) and the benzene framework carrying the substituent (ring A) was set at 90° to prevent π-electron transfer from one ring to the other and at 0° to maximize it. The structural variation of the probe is best represented by a linear combination of the internal ring angles, termed S(F)(BIPH(o)) and S(F)(BIPH(c)) for the orthogonal and coplanar conformations of the molecules, respectively. Regression analysis of these parameters using appropriate explanatory variables reveals a composite field effect, a substantial proportion of which is originated by resonance-induced π-charges on the carbon atoms of ring A. Field-induced polarization of the π-system of ring A also contributes to the structural variation of the probe. Thus, the S(F)(BIPH(o)) parameter is very well reproduced by a linear combination of the π-charges on the ortho, meta, and para carbons of ring A, an uncommon example of a quantitative relationship between molecular geometry and electron density distribution. Comparison of S(F)(BIPH(o)) with the gas-phase acidities of para-substituted benzoic acids shows that, while the deprotonating carboxylic probe is more sensitive to π-electron withdrawal than donation, the phenyl probe is equally sensitive to both. While the ability of the orthogonal biphenyl system to exchange π-electrons with the para substituent is the same as that of the benzene ring in Ph-X molecules, an increase by about 18% occurs when the conformation is changed from orthogonal to coplanar. The structural variation of the probe becomes more complicated, however. This is due to π-electron transfer from one ring to the other, which is shown to introduce quadratic terms in the regressions.

Correlation analysis of IR, 1H and 13C NMR spectral data of N-alkyl and N-cycloalkyl cyanoacetamides

Linear free energy relationships (LFER) were applied to the IR, 1H and 13C NMR spectral data in Nalkyl and N-cycloalkyl cyanoacetamides. N-alkyl and N-cycloalkyl cyanocetamides were synthesized from corresponding amine and ethyl cyanoacetate. A number of substituents were employed for alkyl substitution, and fairly good correlations were obtained, using simple Hammett equation. In N-alkyl and N-cycloalkyl cyanoacetamides substituent cause SCS of N-H hydrogen primarily by steric interaction, polar subtituent effect influences SCS shift of C=O carbon, while steric effect of N-alkyl substituent causes IR stretching frequencies of N-H, C=O and CN group. The conformations of investigated compounds have been studied by the use of semiempirical PM6 method, and together with LFER analysis, give a better insight into the influence of such a structure on the transmission of electronic substituent effects. Negative ? values for several correlations (reverse substituent effect) were found.

Linear free energy relationships applied to the reactivity and the 13C NMR chemical shifts in 4-[[(substituted phenyl)imino]methyl]benzoic acids

Abstract Linear free energy relationships (LFER) were applied to the kinetic data and 13 C NMR chemical shifts in 4-[[(substituted phenyl)imino]methyl]benzoic acids. The correlation analysis for the kinetic data and substituent-induced chemical shifts (SCS) with σ using single substituent parameter (SSP), as well as inductive ( σ I ) and various resonance ( σ R ) parameters using dual-substituent parameter (DSP), were carried out. The presented calculations account satisfactorily for the polar and resonance substituent effects having similar contributions at all carbons studied. Negative ρ values were found for several correlations (reverse substituent effect). Exceptionally good Hammett correlation of 13 C NMR chemical shifts of azomethine carbon with electrophilic substituent constants σ + indicates a significant resonance interaction in the aniline part of molecules. The conformations of investigated compounds have been studied by the use of DFT method, and together with 13 C NMR chemical shifts and kinetic data, give a better insight into the influence of such a structure on the transmission of electronic substituent effects. New σ constants for substituted phenyliminomethyl group have been calculated.

Electronic Substituent Effects in Bicyclo[1.1.1]pentane and [n]Staffane Derivatives: A Quantum Chemical Study Based on Structural Variation

The transmission of electronic substituent effects through one or more bicyclo[1.1.1]pentane units has been investigated by ascertaining how a variable substituent at a bridgehead position perturbs the geometry of a phenyl group at the opposite end of the molecule. We have analyzed the molecular structures of many bicyclo[1.1.1]pentane and [n]staffane derivatives of general formula Ph-[C(CH(2))(3)C](n)-X (n = 1-5), as obtained from molecular orbital calculations at the HF/6-31G* and B3LYP/6-311++G** levels of theory. When n = 1, the structural variation of the benzene ring is controlled primarily by the long-range polar effect of X, with significant contributions from electronegativity and pi-transfer effects. The capability of the bicyclo[1.1.1]pentane framework to transmit these short-range effects originates from the rather high electron density inside the cage and the hyperconjugative interactions occurring between substituent and framework. A set of at least two bicyclo[1.1.1]pentane units appears to be necessary to remove most of the electronegativity and pi-transfer effects. In higher [n]staffanes (n >or= 3), the very small variation of the benzene ring geometry is controlled entirely by the long-range polar effect of X. With charged groups and for n >or= 2, the potential energy of the ring deformation decreases linearly with n(-3). In Ph-C(CH(2))(3)C-X molecules, the relatively large deformation of the bicyclo[1.1.1]pentane cage is determined primarily by the electronegativity of X, similar to the electronegativity distortion of the benzene ring in Ph-X molecules. Transfer of pi electrons from substituent to cage or vice versa also plays a role in determining the cage deformation.

Correlation analysis of the13C chemical shifts of substituted benzaldehyde 2-aminobenzoylhydrazones. Study of the propagation of substituent effects along a heteroatomic chain

The 13C chemical shifts of eight series of para- or meta-substituted benzaldehyde 2-aminobenzoylhydrazones possessing both amide and imine functionalities were measured. The 13C chemical shifts were used to study the transmission of electronic substituent effects along the heteroaromatic side-chain of the substituted aromatic ring. In addition to the CN bond, the benzoylhydrazones possess in their side-chain polarizable CO and phenyl π-units. The benzylidenic ring-substituent chemical shifts were analysed by the dual substituent parameter approach to separate the inductive and resonance effects. The negative ρI and ρR values observed (i.e. reverse substituent effects) indicate a significant π-polarization of the CN bond. The highly negative ρR values, especially those in the case of meta substitution, suggest a contribution from a marked secondary field-transmitted resonance effect. The results are compared with those obtained for other hydrazones or imines. Variation of the electron-withdrawing ability of the N2 substituent is seen to have a systematic effect on the ρI values. Reverse substituent effects are also observed at the C-1″ site of the 2-aminobenzoyl ring while C-4″ shifts show normal behaviour, consistent with the general concept of the π-polarization that each π-unit of the side-chain is polarized largely as a localized system. Accordingly, the π-polarization effect is seen efficiently to propagate also along a heteroaromatic chain. On the other hand, the CO sites exhibit normal, although fairly slight, dependence on the benzylidenic substituent indicating an insignificant role of π-polarization at that site. The effects of the solvent, CDCl3 vs. DMSO-d6, on the ρI and ρR values are also considered. © 1997 John Wiley & Sons, Ltd.

Correlation analysis of the 13C chemical shifts of substituted benzaldehyde 2-aminobenzoylhydrazones. Study of the propagation of substituent effects along a heteroatomic chain

The 13C chemical shifts of eight series of para- or meta-substituted benzaldehyde 2-aminobenzoylhydrazones possessing both amide and imine functionalities were measured. The 13C chemical shifts were used to study the transmission of electronic substituent effects along the heteroaromatic side-chain of the substituted aromatic ring. In addition to the CN bond, the benzoylhydrazones possess in their side-chain polarizable CO and phenyl π-units. The benzylidenic ring-substituent chemical shifts were analysed by the dual substituent parameter approach to separate the inductive and resonance effects. The negative ρI and ρR values observed (i.e. reverse substituent effects) indicate a significant π-polarization of the CN bond. The highly negative ρR values, especially those in the case of meta substitution, suggest a contribution from a marked secondary field-transmitted resonance effect. The results are compared with those obtained for other hydrazones or imines. Variation of the electron-withdrawing ability of the N2 substituent is seen to have a systematic effect on the ρI values. Reverse substituent effects are also observed at the C-1″ site of the 2-aminobenzoyl ring while C-4″ shifts show normal behaviour, consistent with the general concept of the π-polarization that each π-unit of the side-chain is polarized largely as a localized system. Accordingly, the π-polarization effect is seen efficiently to propagate also along a heteroaromatic chain. On the other hand, the CO sites exhibit normal, although fairly slight, dependence on the benzylidenic substituent indicating an insignificant role of π-polarization at that site. The effects of the solvent, CDCl3 vs. DMSO-d6, on the ρI and ρR values are also considered. © 1997 John Wiley & Sons, Ltd.

Transmission of electronic substituent effects in 4-substituted bicyclo[2.2.2]octyl systems

Transmission of electronic substituent effects in 4-substituted bicyclo[2.2.2]octyl systems

Substituent parameter analysis of the carbon-13 nuclear magnetic resonance chemical shifts 4-substituted p-terphenyls

The effects, ..delta..delta values, of substituents at the 4-position of 1:1',4':1''-terphenyl on the /sup 13/C NMR chemical shifts were measured. For the set of substituents R = NO/sub 2/, COOCH/sub 3/ CN, H, CH/sub 3/, I, Br, Cl, NH/sub 2/, and N(CH/sub 3/)/sub 2/, correlations between ..delta..delta values and various inductive and resonance sigma parameters were sought by using three models: a single-parameter relationship, ..delta..delta = psigma; a dual substituent parameter (DSP) relationship, ..delta..delta = p/sub I/sigma/sub I/ + p/sub R/sigma/sub R/; a nonlinear dual substituent parameter (DSP-NLR) relationship, ..delta..delta = p/sub I/sigma/sub I/ + p/sub R/sigma/sub R//(1 - epsilonsigma/sub R/). No acceptable correlations were obtained for the /sup 13/C shifts of C-3,5 and C-4. A single parameter, sigma/sub R//sup 0/, was adequate at only two positions, C-2',6' and C-2'', 6''. At positions C-1, C-2,6, C-3',5', C-1'', C-3'',5'', and C-4'' the DSP model and sigma/sub R//sup 0/ were best. At para-type positions in the central ring (C-1' and C-4') the DSP-NLR model was best. The magnitude of the ratio lambda = p/sub R//p/sub I/ of mesomeric to inductive transmission of electronic substituent effects ranged from 0.535 to 4.58, indicating the importance of inductive electronic effects at nearly all positions inmore » p-terphenyl, even at C-4'', the carbon farthest from the substituent, where lambda = 1.70.« less

Triruthenium clusters containing dinethylamino-substituted allyl and allenyl ligands: The transmission of electronic substituent effects through clusters

The NMe 2 substituent in CH 3C≡CCH 2NMe 2 facilitates oxidative addition to RU 3(CO) 12 to give the isomeric allenyl cluster HRU 3(CO) 9(MeCCCHNMe 2) and allylic cluster HRu3 (CO)g (MeCCHCNMe 2). The barrier to rotation about the internal ligand CNMe 2 bond is sensitive to the nature of L in HRu 3(CO) 8L(MeCCHCNMe 2), even though L is remote from this bond, and also to protonation of the cluster. Lower barriers are associated with increased electronavailability on the cluster.