E-2-Benzylidenebenzocycloalkanones. IV. Studies on transmission of substituent effects on C NMR chemical shifts of E-2-(X-benzylidene)-1-tetralones, and -benzosuberones. Comparison with the C NMR data of chalcones and E-2-(X-benzylidene)-1-indanones

Single substituent parameter (SSP) and dual substituent parameter (DSP) analyses were applied to study the transmission of substituent effects on selected ¹³C NMR chemical shifts of the cyclic chalcone analogues, E-2-(4′-X-benzylidene)-1-tetralones (2) and E-2-(4′-X-benzylidene)-1-benzosuberones (3). In order to study how the geometry of the cyclic chalcone analogues affects the transmission of substituent effects similar investigations with the respective chalcones (4) were also performed. The results obtained earlier with the five-membered analogue E-2-(4′-X-benzylidene)-1-indanones (1) were also involved in the comparisons. Geometry optimization of the unsubstituted 1a, 2a, 3a and 4a as well as the substituted 2 and 3 was performed by ab initio quantum chemical calculations. Both SSP and DSP analyses reflected that resonance effects contribute more to the chemical shift of C- (C2), while inductive effects primarily affect that of C-β (C10) of the enone moiety of all the four series. This latter effect, however, is far not as pronounced as that of the former one. It was found that DSP analysis data (ρ_F and ρ_R values) of transmission of substituent effects on the δC2 data can serve as a measure of choice to study the conformation (planarity) of the investigated enones in the four series.     

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.     

Characterization of electronic properties of the Cr(CO)3 group in chromium, tricarbonyl [3-[(η-aryl)methylene]-Z-1(3H)-isobenzofuranones] using spectral and theoretical methods

The IR, ¹³C- and ¹⁷O-NMR spectral characteristics of the Cr(CO)₃ group in a series of eight chromium, tricarbonyl[3-[(η⁶-aryl)methylene]-Z-1(3H)-isobenzofuranones] were correlated mutually as well as with theoretical data obtained by optimized MMX force-field and EHT calculations. The net charges on the carbon and oxygen atoms of the CO group and their differences were found as the most appropriate quantitative characteristics for the electronic properties of the Cr(CO)₃ group. Using the results of the previously reported linear correlations, the electron-withdrawing effect of the PhCr(CO)₃ moiety, weakened by the back-donation effect, was estimated as σ0.45 on the scale of Hammett substituent constants.     

C chemical shifts and carbonyl stretching frequencies as structural probes for ferrocenyl ketones

¹³C chemical shifts (δ(CO)) have been measured for a series of aromatic ferrocenyl ketones (FcCOC₆H₄X) and some sterically hindered analogues (FcCOR, R = mesityl, anthracyl, t-Bu, adamantyl). The shifts correlated quite well with those of the corresponding benzophenones. From the carbonyl carbon shifts (δ(CO)), estimates were made of the interplanar angle between the carbonyl sp² and the phenyl ring planes. Substituent effects of the Cp ring carbons are discussed. The solution (CCl₄) infrared spectra of the derivatives were obtained and the carbonyl stretching frequency (ν(CO)) was found to correlate roughly with δ(CO). Estimates were also made of the interplanar angle between the cyclopentadienyl ring plane and the carbonyl plane, for sterically hindered ketones using δ(CO) values.     

13C and 1H chemical shifts in 2-benzylidene[3]ferrocenophane-1,3-diones. Elucidation of the substituent dependence of carbonyl chemical shifts in different carbonyl derivatives

The ¹³C and ¹H chemical shifts of the ferrocene moiety, as well as the carbonyl carbons and styrene moiety, of substituted 2-benzylidene[3]ferrocenophane-1,3-diones have been assigned. Correlations of ¹³C substituent chemical shifts of both carbonyl carbons with the Hammett constants have been found, and the effect of the transmission of substituent effects on these chemical shifts through the styrene moiety is discussed. An explanation is given for the different sensitivities of the carbonyl carbon chemical shifts to the electronic effect of substituents in mono- and dicarbonyl derivatives.     

The H method: hydrogen atoms with a fictitious nuclear charge. A versatile theoretical tool for study of atom and group properties as substituents: electronegativity and partition of σ and π contributions

We present a preliminary work for a general method of computing the partition of σ and π electronic effects of a given atom A or substituent R on a given substrate. In this aim, the nuclear charge Z^* of a fictitious hydrogen atom H^* is fitted in order that the A–H^* (or R–H^*) bond be purely covalent, i.e. the Mulliken electron population be one electron on H^*. We obtain this way entities of the same electronegativity as A or R, thus having a comparable σ effect, without any π effect.

The values of Z^* obtained for A–H^* diatomic molecules (A=H–Br) exhibit a good linear correlation with the Allred–Rochow scale of electronegativity, as it could be expected on theoretical grounds. The method, applied to R–H^* molecules, allows a determination of the electronegativity of a variety of polyatomic R substituents, and provides H^*(R) having the same inductive effect as R. These results are discussed by comparison with some previous theoretical and experimental data.

As an example of application, the partition of σ and π contributions of R on the ¹³C chemical shifts in a series of monosubstituted benzenes RC₆H₅ has been computed.     

Heteroleptic platinum(II) complexes of macrocyclic thioethers and halides: the crystal structures of [Pt(9S3)Cl2], [Pt(9S3)Br2], and [Pt(9S3)I2]

The synthesis, spectroscopic, and crystal structures of three heteroleptic thioether/halide platinum(II) (Pt(II)) complexes of the general formula [Pt(9S3)X₂] (9S3=1,4,7-trithiacyclononane, X=Cl⁻, Br⁻, I⁻) are presented. All three 9S3/dihalo complexes form very similar structures in which the Pt(II) center is surrounded by a cis arrangement of two halides and two sulfur atoms from the 9S3 ligand. The third sulfur from the 9S3 forms a long distance interaction with the Pt center resulting in an elongated square pyramidal structure with a S₂X₂+S₁ coordination geometry. The distances between the Pt(II) center and axial sulfur shorten with larger halide ions (Cl⁻=3.260(3) Å>Br⁻=3.243(2) Å>I⁻=3.207(2) Å). These distances are consistent with the halides functioning as π donor ligands, and their Pt---S axial distances fall intermediate between Pt(II) thioether complexes involving π acceptor and σ donor ligands. The ¹⁹⁵Pt NMR chemical shift values follow a similar trend with an increased shielding of the platinum ion with larger halide ions. The 9S3 ligand is fluxional in all of these complexes, producing a single carbon resonance. Additionally, a related series of homoleptic crown thioether complexes have been studied using ¹⁹⁵Pt NMR, and there is a strong correlation between the chemical shift and complex structure. Homoleptic crown thioethers show the anticipated upfield chemical shifts with increasing number of coordinated sulfurs. Complexes containing four coordinated sulfur donors have chemical shifts that fall in the range of −4000 to −4800 ppm while a value near −5900 ppm is indicative of five coordinated sulfurs. However, for S₄ crown thioether complexes, differences in the stereochemical orientation of lone pair electrons on the sulfur donors can greatly influence the observed ¹⁹⁵Pt NMR chemical shifts, often by several hundred ppm.     

Surface chemistry of nanoporous carbon and the effect of pH on adsorption from aqueous phenol and 2,3,4-trichlorophenol solutions

Granular nanoporous activated carbon prepared from polyacrylonitrile (PAN) was investigated as a means of removing weak aromatic acids from aqueous solutions. This carbon is highly nanoporous, the BET surface area being 544 m²/g with V_tot=0.278 cm³/g, and V_micro=0.266 cm³/g. Aqueous treatment reduced the surface area to 364 m²/g.

Granular nanoporous carbon prepared from PAN contains O and N related surface functional groups. The surface concentration of both oxygen and nitrogen atoms was found by XPS to be 5.3%. Surface groups containing these hetero atoms are responsible for the acid–base character of this carbon in aqueous solutions. The pH_PZC of the carbon is 8.4. The microporous pore network produces a wide hysteresis loop, observed when the granular carbon was studied by continuous titration. This loop, which was found to diminish, but not to disappear completely when the particle size was reduced, is attributed to irreversible hydrolysis of surface esters and/or lactones. The surface concentration of the functional groups titrated by the equilibrium Boehm method is 449.2 μeq./g, of which 112.9 μeq./g have acidic and 336.3 μeq./g have basic character. Within the acidic species three subgroups, namely the regions pK_a<6.37, 6.37K_a<10.25 and 10.25K_a<15.74.

The acid–base behavior influences the adsorption performance of the granular carbon in aqueous solutions of weak aromatic acids, in this case phenol and 2,3,4-trichlorophenol. Both the adsorption capacity and the overall interaction parameter, K (both derived from a fit to the Langmuir equation) depend on the adsorbed species and on the pH. The former is a consequence of the different water solubilities of the solute molecules, while the latter stems from the pH sensitivity of both the surface functional groups and these weak acids. The K values show a sequence pH=3K values indicate different adsorption mechanisms. The effect of pH is more marked for 2,3,4-trichlorophenol.     

15N NMR chemical shifts of ring substituted benzonitriles

15N chemical shifts in an extensive series of para (15) and meta (15) as well as ortho (8) substituted benzonitriles, X-C6H4-CN, were measured in deuteriochloroform solutions, using three different methods of referencing. The standard error of the average chemical shift was less than 0.03 ppm in most cases. The results are discussed for both empirical correlations with substituent parameters and quantum chemical calculations. The 15N chemical shifts calculated at the GIAO/B3LYP/6-31 + G*//B3LYP/6-31 + G* level reproduce the experimental values well, and include nitrogen atoms in the substituent groups (range of 300 ppm with slope 0.98 and R = 0.998, n = 43). The 15N shifts in hydroxybenzonitriles are affected by interaction with the OH group. Therefore, these derivatives are excluded from the correlation analysis. The resultant 15N chemical shift correlates well with substituent constants, both in the simple Hammett or DSP relationships and the 13C substituent-induced chemical shifts of the CN carbon.     

Kinetische und mechanistische untersuchungen von Übergangsmetall-komplex-reaktionen : III. Abhängigkeit des gleichgewichts der addition von tributylphosphan an pentacarbonyl(arylmethoxycarben)wolfram vom substituenten am ring

The reaction of pentacarbonyl(arylmethoxycarbene)tungsten, (CO)₅W[C(OCH₃(p-C₆H₄R)] [R = OCH₃ (a), CH₃ (b), H (c), Br (d), CF₃ (e)], with tributylphosphane at low temperatures results in a reversible addition of the phosphane to the carbene carbon atom. The addition—dissoziation equilibrium is not only dependent on the temperature but also to a strong degree on the nature of the substituent R. ΔG, ΔH and the equilibrium constant K increase in the series from R = OCH₃ to R = CF₃. With the exception of R = OCH₃ the substituents b to e form an isentropic class. For all substituents (a to e) a linear dependency from Jaffés σ-constants was observed for ΔH. Good linear correlation for the substituents b to e was also found for log K and σ as well as for log K and the CO-force constants k_cis and k_trans.     

2,3-二氰基-2,3-二(p-X苯基)丁二酸二乙酯的分子构型和取代基电子效应对13C NMR谱的影响

测定了meso-和dl-2,3-二氰基-2,3-二(p-X苯基)丁二酸二乙酯(X=OCH₃,CH₃,H,Cl,NO₂)的¹³CNMR谱。结果表明,中心碳-碳键两端相连基团的各碳原子的化学位移值相同,与dl-异构体相比,所有相应meso-异构体的乙氧羰基¹³CNMR吸收峰均处于高场。苯环对位取代基的Hammett基团常数σ与氰基碳原子和乙氧羰基中的羰基碳及次甲基碳的化学位移间线性相关,而且meso-异构体比dl-异构体有更好的线性关系。     

Carbon-13 NMR studies of 1-aryl-3-phenyl-2-thioxo-4-imidazolidinones. Conformational isomerism and substituent effects

Characteristic ^13C chemical shift ranges and substituent shifts of heterocyclic ring carbon atoms have been identified for a number of 1-aryl-3-phenyl-2-thioxo-4-imidazolidinones. ¹³CNMR spectra may be used to detect slow internal rotation about the aryl C? N-1 bond in compounds with diastereomeric rotational isomers; many corresponding carbon atoms in the rotamers have distinctly different chemical shifts. The δ-effects originating from aryl ortho substituents are both electronic and steric in origin.     

Oxasmaragdyrin-ferrocene and oxacorrole-ferrocene conjugates: synthesis, structure, and nonlinear optical properties

Ferrocenyl macrocyclic conjugates involving 22 pi oxasmaragdyrins and 18 pi oxacorroles have been synthesized and characterized. The direct covalent linkage of the ferrocenyl moiety to the meso position of the macrocycle is achieved by simple oxidative coupling of appropriate precursors with trifluoroacetic acid as catalyst. The electronic coupling between the ferrocenyl moiety and the macrocyclic pi system is apparent from: a) the red shifts (293-718 cm(-1)) of the Soret and Q-bands in the electronic absorption spectra of ferrocenyl conjugates; b) the shift of oxidation potentials (50-130 mV) of both the ferrocene and the corrole rings to the positive potentials; and c) considerable shortening of the C-C bond which connects the ferrocene and the meso-carbon atom of the macrocycle. The single-crystal X-ray structure of oxasmaragdyrin-ferrocene conjugate 9 reveals the planarity of the 22 pi skeleton with very small deviations of the meso-carbon atoms. The meso-ferrocenyl substituent has a small dihedral angle of 38 degrees, making way for mixing of the molecular orbitals of the ferrocene and the macrocycle. However, the other two meso substituents are almost perpendicular to the mean plane, defined by the three meso carbon atoms. Classical C-H...O and nonclassical C-H...pi interactions lead to a two-dimensional supramolecular network. Ferrocene-smaragdyrin conjugate 9 bonds to a chloride ion in the protonated form and a rhodium(i) ion in the free base form. Nonlinear optical measurements reveal a larger nonlinear refractive index (-5.83 x 10(-8)cm(2)W(-1)) and figure of merit (2.28 x 10(-8)cm(3)W(-1)) for the rhodium smaragdyrin-ferrocene conjugate 19 than for the others, suggesting its possible application in optical devices.     

Einflüsse von substituenten in 6-stellung auf die 13C-chemischen verschiebungen der kohlenstoffatome des purins

The ¹³C chemical shifts of purines substituted in the 6 position are reported. Signals are assigned on the basis of general chemical shift rules and by proton “off-resonance” decoupling. Substituent effects (Z_6i) of the substituent X in the 6 position of purine on the ¹³C chemical shifts of purine ring carbon atoms are determined. A linear correlation exists between the substituent effects of X on C-6 (Z₆₆) and Pauling's electronegativity values E_x of the substituent X.     

The electronic and molecular structure of cyclopropane, isocyanomethane and isocyanocyclopropane

Ab initio SCF MO calculations have been carried out on cyclopropane, isocyanomethane and isocyanocyclopropane in order to elucidate the relative importance of σ-and π-electronic interactions between the substituent and the cyclopropane ring. Complete geometry optimizations have been carried out. The computed structures are in excellent agreement with experimental structure determinations. Bond lengths, gross charges and a detailed analysis of bond path gradients yield evidence of a conjugative interaction between the isocyano and the cyclopropyl group and a small hyperconjugative interaction in isocyanomethane. In addition, there is a considerable inductive electron flow from the hydrocarbon moiety to the nitrogen atoms as expected from electronegativity.     

Redox potential and substituent effects in ferrocene derivatives: II

The anodic behavior of 31 ferrocene derivatives (FcX) (four of which have been prepared for the first time) of the types shown below has been investigated by cyclic voltammetry (and, in some cases, also by controlled-potential electrolysis and differential pulse polarography) at a Pt electrode, in an aprotic solvent: Fc---C(Y)=Z (class A; Y = R (hydrogen, alkyl or unsaturated-carbon moiety) or Cl; Z = CRR′, derived functionalized groups or {W(CO)₅}); Fc---C(Y)=O (class B; Y --- R or OH); other types (class C, including azide, other unsaturated N moieties, acyloxy or phosphino); disubstituted ferrocenes (class D, with alkyl, aminoalkyl, phosphino, B(OH)₂ or −HGCl substituents, or the S---S---S bridge). All these substituted ferrocenes exhibit a one-electron reversible oxidation centered at iron and the effect of the substituents on the half-wave oxidation potential is discussed in terms of electronic properties. Using the accepted linear correlations between the half-wave oxidation potential and the Hammett constant σ_p of the substituent, σ_p was estimated for the first time for 29 of the substituents in the ferrocenes listed above. The anomalous behavior of complexes with a hydroxy or a carbonyl group is discussed. No correlation was observed between the oxidation potential and either the energy of the electronic absorption bands or the ¹H NMR chemical shift of the unsubstituted cyclopentadienyl ring, although there are rough correlations for class A compounds. This behaviour is compared with those of [Fc-CHYZ]. kw]Iron; Redox potentials; Ferrocenes; Electrochemistry; Substituent effects     

Infrared spectra of heterocumulenes—VII: Correlations of infrared gruop wavenumbers and integrated absorption intensities in some heterocumulenes with substituent constants

A statistical evaluation of the empirical linear relations of the ν_as(X=Y=Z) integrated absorption intensities (A) in forty various heterocumulenes with substituent constants σ and σ⁺ has been carried out. The correlations of log A with substituent constants show that the positive sign of the slopes and ⁺ has been observed, suggesting that with all heterocumulenes studied the structure of the X=Y=Z group with cumulative bonds is dominant.     

Carbon-13 and proton magnetic resonance studies of some carbonyl-bis-(amino acid esters)

A number of carbonyl-bis-(amino acid esters) have been examined by proton and carbon-13 nuclear magnetic resonance techniques. All but one of the compounds were synthesized with two chiral centers of like-configuration. In one series, the diastereotopic nonequivalence of isopropyl methyl groups attached to the asymmetric centers is apparent in both the proton and the carbon spectra, and the relative magnitude of the observed nonequivalence increases slightly with increasing ‘bulk’ of the neighboring ester groups. Carbon-13 chemical shifts are reported, and a linear correlation of Taft σ* inductive constants with ester carbonyl carbon chemical shifts and with amide proton chemical shifts (for a series in which only variation of the ester substituent occurs) is presented. In addition, the effect in terms of chemical shift differences of keeping the same ester group at the asymmetric centers while varying the other substituent group, is examined.