77Se n.m.r. studies of organoselenium compounds: III—substituent effects in 4,4′-disubstituted diphenyl selenides and 4,4′-disubstituted diphenylmethanes studied by 1H, 13C and 77Se spectroscopy

⁷⁷Se N.m.r. spectra of 4,4′-disubstituted diphenyl selenides have been obtained. The chemical shifts could be correlated with substituent constants of the Hammett type or with Swain and Lupton two-parameter equations. No correlations were observed between these ⁷⁷Se shifts and the ¹³C shifts of the CH₂ group of 4,4′-disubstituted diphenylmethanes, the latter shifts showing no correlation with substituent constants. On the other hand linear correlation was observed between the ⁷⁷Se shifts of the 4,4′-disubstituted diphenyl selenides and the ¹H shifts of the CH₂ group of the diphenylmethanes, the ¹³C shifts of their 1-carbons and the ¹⁹F shifts of 4-substituted fluorobenzenes.     

13C n.m.r. chemical shifts in aliphatic alcohols and the γ-shift caused by hydroxyl and methyl groups

Empirical correlations for the prediction of the chemical shifts of the carbon atoms in aliphatic alcohols are presented. Structural and conformational effects contributing to the ¹³C chemical shifts of γ-carbons are discussed.     

Substituent effects on 13C NMR chemical shifts in the saturated framework of primary aliphatic derivatives

A general equation describing the effect of substituents on α-carbons in a saturated framework was developed from ¹³C chemical shifts obtained under uniform conditions for selected aliphatic compounds. Experimental correlations for β- and γ-carbons and a discussion of the results are presented.     

Determination of Singlet Oxygen Production and Antibacterial Effect of Nonpolar Porphyrins In Heterogeneous Systems

ABSTRACT

The possibility of using the iodide method and the method of bleaching of 4-nitroso-N, N'-dimethylaniline, developed originally for homogeneous aqueous medium for the determination of singlet oxygen production, was tested for water-insoluble nonpolar senzitizers adsorbed on the silica gel support. Sensitizers of the porphyrin and metalloporphyrin type (tetraphenylporphin (TPP), protoporphyrin IX (PPIX), tetra(4-nitrophenyl)porphin (TPP(NO₂)₄ and complexes of TPP with some divalent and trivalent metals, Cd(II)TPP, Zn(II)TPP, Co(II)TPP, Cu(II)TPP, Ni(II)TPP, Mn(II)TPPCI, and Fe(II)TPPCl) were used as model compounds. It was found that both methods used gave similar values of ¹O₂. The relative ¹O₂ production of the compounds studied decreases in the order PP=Zn(II)TPP=Cd(II)TPP > TPP(NO₂)₄> PPIX> nonactive substances.

The cytotoxic effect of ¹O₂ Produced by these substances on the silica gel support was tested using E. coli DHS-alfa bacteria. The relative ¹O₂ production values correlate with the antibacterial activity of the adsorbed substances exposed to light.     

Structure des Complexes de Meisenheimer Complexes de Courte Duree de Vie et Complexes Stables Formes par Action des Ions Méthoxydes sur les Dinitro-4,6 Anisoles X-2 Substitues

The NMR study of the reaction of methoxide ions on several substituted 2-X-4,6-dinitroanisoles (X = F, Cl, CF₃, CN) permitted the identification of various Meisenheimer complexes formed by the attack of CH₃O^? ions on the non-substituted 5- and 3-carbons. The shortlived 1,5- and 1,3-complexes undergo a fast conversion to the stable 1,1-complexes. The chemical shifts of anisoles and complexes are dependent on electronic and steric effects of the X-substituent. The influence of the negative charge held by the ring and the geometrical changes of the skeleton are shown by a comparison between the NMR parameters of anisoles and the corresponding complexes. When X = F, a study of the relative signs of the coupling constants shows that ³J(F? H) and ⁵J(F? H) are of opposite signs for the anisole and the 1,1-complex.     

Resonance Raman and Infrared Spectra of Carbene Complexes of Iron Porphyrins Dongsheng Lu

Abstract

The resonance Raman and infrared spectra of four carbene complexes, Fe(TTP)CCl₂, Fe(TPP)¹³CCl₂, Fe(TPP)CBr₂ and Fe(TMP)CCl₂ were measured in the solid state. Based on normal coordinate calculations and observed isotopic shifts by CC1₂/¹³CC1₂ substitution, the v(Fe=C), v_a(CCl₂) and v_s(CCl₂) vibrations were assigned at 1274, 878 and 437cm^?1, respectively. The bromo analogue exhibits these bands at 1270,823 and 364 cm^?1, respectively. All TPP complexes exhibit the spin-state sensitive band (v₂) at 1569 cm^?1 and the oxidation-state sensitive band (v₄) at 1370cm^?1, thus suggesting that the Fe atoms in these carbene complexes are low-spin Fe(IV).     

The nuclear magnetic resonance spectra of N-nitroso-N-alkyl amino acids

Structurally related acyclic and cyclic N-nitroso-N-alkyl amino acids were prepared and their ¹H, ¹³C and ¹⁵N NMR spectra were investigated. The changes in the ¹³C NMR spectra of the N-nitroso α-amino acids after dissolving in solvents suggest that they posses the Z-configuration in the crystalline state; in solution some of them isomerize to mixtures of the Z- and E-isomers whose composition appear to depend on steric factors. The ¹³C chemical shifts were assigned on the basis of anisotropic effects of the nitrosamino group and configurational stability. The ¹³C chemical shifts were correlated with those of the nitrosamines of the same carbon skeletons and the effects of changing a methyl group to the carboxylic acid are deshielding on the α-carbons and shielding on the β-carbons.     

Electronic effects in the cyclopentadienyl ring. The 13C NMR spectraof monosubstituted ferrocenes

The chemical shifts of C(2,5) and C(3,4) carbons in the ¹³C NMR spectra of monosubstituted ferrocenes have been assigned using deuterium labelling. An analogy is observed between the shielding of C(2,5) and C(3,4) carbons of ferrocene derivatives and ortho- and para-carbons of benzene derivatives withthe same substituents. Electron-density distribution in the cyclopentadienyl ring is discussed on the basis of ¹³C NMR data.     

1H- and 13C-NMR spectra of palladium and platinum meso-tetraphenylporphyrins

The ¹H- and ¹³C-NMR spectra of palladium and platinum mesotetraphenylporphyrins (TPP) are reported. PtTPP demonstrates spin-spin coupling between platinum and the pyrrole·β-protons and carbons. There is some evidence for spin-spin coupling between platinum and the pyrrole α-carbons. PdTPP and PtTPP also demonstrate upfield shifting of their pyrrole α-carbon ¹³C-resonances. Structural and electronic arguments are advanced to explain this behaviour.     

Direct synthesis of six-coordinate nitro complexes of cobalt meso-tetraphenylporphyrinate with trans-O-donor ligands

The formation of a series of six-coordinate complexes (B)Co(TPP)(NO₂) (B is ketone, aldehyde, ether or epoxide; TPP is meso-tetraphenylporphyrin dianion) on exposure of thin films of five-coordinate Co(TPP)(NO₂) to vapors of the O-donor ligands was established by IR and UV/Vis spectroscopy (resorting to the data on isotope-substituted ¹⁵NO₂). The complex formation is accompanied by shifts of the vibration frequencies of the trans-NO₂ ligand and gives rise to new IR bands corresponding to the O-donors in the ν(C=O) or ν(C-O) region shifted with respect to these bands of free ligands. The complexes are rather stable in the solid phase but eliminate the O-donor ligand upon dissolution in an inert solvent (or upon maintenance in a vacuum for some complexes) being converted into the initial five-coordinate nitro complex. Using the IR spectra of CCl₄ solutions of the complexes containing a large excess of O-donor molecules, the equilibrium constants and the formation enthalpies of some (B)Co(TPP)(NO₂) complexes were determined, indicating weak coordination of these ligands.     

Substitution effects in the 15N NMR chemical shifts of heterocyclic azines evaluated at the GIAO‐DFT level

A systematic study of the accuracy factors for the computation of ¹⁵N NMR chemical shifts in comparison with available experiment in the series of 72 diverse heterocyclic azines substituted with a classical series of substituents (CH₃, F, Cl, Br, NH₂, OCH₃, SCH₃, COCH₃, CONH₂, COOH, and CN) providing marked electronic σ‐ and π‐electronic effects and strongly affecting ¹⁵N NMR chemical shifts is performed. The best computational scheme for heterocyclic azines at the DFT level was found to be KT3/pcS‐3//pc‐2 (IEF‐PCM). A vast amount of unknown ¹⁵N NMR chemical shifts was predicted using the best computational protocol for substituted heterocyclic azines, especially for trizine, tetrazine, and pentazine where experimental ¹⁵N NMR chemical shifts are almost totally unknown throughout the series. It was found that substitution effects in the classical series of substituents providing typical σ‐ and π‐electronic effects followed the expected trends, as derived from the correlations of experimental and calculated ¹⁵N NMR chemical shifts with Swain–Lupton's F and R constants.     

Proton NMR studies of reduced porphyrin compounds

Detailed ¹H NMR studies of ms tetraphenylchlorins (H₂TPC), new amino- and hydroxypyrroline substituted ms tetraphenylchlorins and ms tetraphenylisobacteriochlorins (H₂TPisoB) are presented and discussed. The results obtained are consistent with the general aspects of the ring current models as applied to the parent porphyrins. According to proton chemical shifts a gradual reduction in the magnitude of the ring current is observed in the order ms tetraphenylporphyrin (H₂TPP) > H₂TPC> ms tetraphenylbacteriochlorin (H₂TPB) > H₂TPisoB. The ¹H NMR spectra show chemical non-equivalence of the pyrroline ring protons due to adjacent substituents, and effects of steric constraints on the aminoalkyl substituents due to the close vicinity to the meso phenyl rings. The non-equivalence of the methylene protons of the pyrroline ring produces geminal coupling between the two methylene protons and vicinal coupling with the adjacent pyrroline proton, more pronounced in H₂TPC? OH and in . Restricted configuration of the methylene groups in the ethyl groups of H₂TPC? C(H)(CH₃)N(CH₂CH₃)₂ produces observable geminal coupling between the methylene protons. ¹H NMR reveals the difference between two types of meso phenyls in the chlorins, and three types of meso phenyls in isobacteriochlorins, as reflected in the chemical shifts of the o-phenyl protons.     

Synthesis,Optical Properties,and Electronic Structures of Fully Core‐Modified Porphyrin Dications and Isophlorins

The synthesis, structures, optical properties, and electronic structures of the tetraphenyltetrathiaporphyrin dication (S₄TPP²⁺, 6 ) and tetrakis(pentafluorophenyl)tetrathiaisophlorin (S₄F₂₀TPP, 7 ) are reported. S₄TPP²⁺ ( 6 ) and S₄F₂₀TPP ( 7 ) were synthesized by acid‐catalyzed condensation of the corresponding hydroxylmethylthiophene, followed by oxidation. The electronic structures of S₄TPP²⁺ ( 6 ) and S₄F₂₀TPP ( 7 ) were analyzed by using UV/Vis‐absorption spectroscopy and by magnetic circular dichroism (MCD) spectroscopy and the bands were assigned by using time‐dependent density functional theory (TD‐DFT) and ZINDO/s calculations. A red‐shift of the Q bands of S₄TPP²⁺ ( 6 ) is observed relative to the spectra of tetraphenylporphyrins because a destabilization of the HOMO leads to a narrower HOMO–LUMO band‐gap. Michl′s perimeter model was used to assign the absorption bands and MCD spectra of S₄F₂₀TPP ( 7 ). Current‐density maps and nucleus‐independent chemical‐shift (NICS) calculations of S₄TPP²⁺ ( 6 ) and of a model compound predict marked modification to the diamagnetic ring current, whilst nonaromatic character is predicted for S₄F₂₀TPP ( 7 ).     

Carbon-13 nuclear magnetic resonance studies on high spin iron(III) porphyrins

Carbon-13 NMR studies on a series of high spin iron(III) porphyrins, namely tetraphenylporphyrin iron(III) halides [Fe(TPP) X, X=Cl, Br, I] in CDCl₃ solution are reported. As expected the¹³C shifts are found to be an order of magnitude larger than the corresponding proton shifts. The dipolar contribution, which is quite important for the proton NMR, becomes much less significant for the¹³C shifts. No systematic variation in the¹³C shift across the series is observed, except for the meso-carbon which shows a small but gradual decrease in going from the chloro to the iodo complex. The¹³C shift for the various carbon atoms of the porphyrin ligand shows interesting pattern which is discussed in terms of spin delocalisation mechanisms.     

Quantum‐chemical analyses of aromaticity,UV spectra,and NMR chemical shifts in plumbacyclopentadienylidenes stabilized by Lewis bases

We carried out a series of zeroth‐order regular approximation (ZORA)‐density functional theory (DFT) and ZORA‐time‐dependent (TD)‐DFT calculations for molecular geometries, NMR chemical shifts, nucleus‐independent chemical shifts (NICS), and electronic transition energies of plumbacyclopentadienylidenes stabilized by several Lewis bases, (Ph)₂(^tBuMe₂Si)₂C₄PbL₁L₂ (L₁, L₂ = tetrahydrofuran, Pyridine, N‐heterocyclic carbene), and their model molecules. We mainly discussed the Lewis‐base effect on the aromaticity of these complexes. The NICS was used to examine the aromaticity. The NICS values showed that the aromaticity of these complexes increases when the donation from the Lewis bases to Pb becomes large. This trend seems to be reasonable when the 4n‐Huckel rule is applied to the fractional π‐electron number. The calculated ¹³C‐ and ²⁰⁷Pb‐NMR chemical shifts and the calculated UV transition energies reasonably reproduced the experimental trends. We found a specific relationship between the ¹³C‐NMR chemical shifts and the transition energies. As we expected, the relativistic effect was essential to reproduce a trend not only in the ²⁰⁷Pb‐NMR chemical shifts and J[Pb‐C] but also in the ¹³C‐NMR chemical shifts of carbons adjacent to the lead atom. © 2014 Wiley Periodicals, Inc.     

Voltampérométrie et comportement rédox de métalloporphyrines inhabituelles

Tetraphenylporphyrin (TPP) compounds of rhenium-tricarbonyl have been investigated by pulse polarography, by cyclic voltammetry and by hydrodynamic voltammetry at Levich's rotated disk electrode. The metalloporphyrins HTPPRe(CO)₃ and TPP(Re(CO)₃)₂ exhibited several anodic and cathodic waves, which corresponded qualitatively to well-known one-electron transfer processes of the free base H₂TPP. Quantitatively, however, the relevant electron affinities and redox reactivities of H₂TPP where shifted appreciably by coordination with rhenium-tricarbonyl. The observed shifts in half-wave potentials and electrochemical kinetics are satisfactorily accounted for by charge distribution effects on the porphyrin moiety, induced by bonding between Re(CO)₃ and three of the four nitrogen atoms of the tetrapyrole ring.     

Ion pairing in H<Subscript>2</Subscript>O and D<Subscript>2</Subscript>O solutions of lead nitrate,as determined with <Superscript>207</Superscript>Pb NMR spectroscopy

The temperature and concentration dependences of ²⁰⁷Pb NMR chemical shifts of Pb(NO₃)₂ in D₂O are reported. The results are analyzed in terms of exchange between a solvated lead ion and the Pb(NO₃)⁺ contact-ion pair. Predictions of the chemical shift difference between the aquated ion and contact-ion pair are carried out for the gas-phase entities and for the solvated species with a DFT calculation. Previously reported data on ²⁰⁷Pb NMR chemical shifts of Pb(NO₃)₂ in H₂O are reevaluated. From the analysis, the enthalpy of dissociation of the contact-ion pair is found to be–42.3±1.0 kJ/mol.     

Carbon-13 chemical shifts of bicyclo[3.2.1]octane and bicyclo[2.2.1]heptane derivatives

¹³C chemical shifts of more than fifty bicyclo[3.2.1]octane and bicyclo[2.2.1]heptane derivatives (hydrocarbons, alcohols, ketones and esters) have been determined. The usefulness of ethyl derivatives for the assignment of close ¹³C chemical shifts in bicyclic methyl derivatives is shown both for the bicyclo[3.2.1]octane and bicyclo[2.2.1]heptane series. Comparison of substituent effects on α-, β-, γ- and δ-carbons in both series of compounds shows remarkable differences in steric interactions. In contrast to the rigid bicyclo[2.2.1]heptane system, both chair and boat conformations can be predominant in the bicyclo[3.2.1]octane series with the conformationally flexible 6-membered ring.     

13C NMR studies of reduced porphyrin compounds. Aromatic delocalization pathways

¹³C NMR spectra of ms-tetraphenylchlorins, new aminoalkyl- and hydroxy-pyrroline substituted ms-tetra-phenylchlorins, and ms-tetraphenylisobacteriochlorins are presented and discussed. Significant changes in the chemical shifts of the α-pyrrole, α-pyrroline and meso skeletal carbons are found in chlorins and isobacteriochlorins in comparison to porphyrins. In contrast, the chemical shifts of the β-pyrrole carbons are almost unaffected by the structural modifications in chlorin and isobacteriochlorin. The chemical shifts of the α-pyrrole carbons in the various chlorins and isobacteriochlorins are strongly affected by the substitutents of the pyrroline ring, or by the introduction of an additional pyrroline ring in isobacteriochlorins. The results show that most of the electron density is concentrated in the unreduced part of the molecule, i.e. in the pyrrole rings and, especially, on the α-pyrrole carbons and is transferred or removed through the aromatic pathway by substituents on the pyrroline ring. These observations are supporting evidence that the α-pyrrole, α-pyrroline and meso-carbons are in the aromatic pathway and favour the proposal of a 16 atom dianion as the preferred delocalization pathway in chlorins and isobacteriochlorins.     

13C nuclear magnetic resonance spectra of ethers and glycols

The ¹³C NMR spectra of 21 linear and branched ethers together with the corresponding alcohols have been determined in an attempt to correlate the shieldings in both series. It has been found that the shielding of a carbon in an acyclic ether can be given by the summation of additive shift parameters for substituents and correction parameters for the substitution patterns based on the shielding of the parent alcohol. On examination of solvent-induced shifts for α- and β-carbons in ethers and alcohols, significant ones have been noted in carbon tetrachloride→dimethylsulfoxide and carbon tetrachloride→trifluoroacetic acid. No appreciable concentration-dependent shifts of the shieldings have been observed in both ethers and alcohols. For the shieldings of α-carbons in acyclic glycols, it has been noticed that the observed and predicted values are in accord in 1,3-, 1,4- and 1,5-glycols but deviate in 1,2-glycols. The latter has been examined in a polycyclic system, where the deviations ( > 3·5ppm) in a cis (gauche) 1,2-glycol are larger than those (<2·5 ppm) in a trans (anti-parallel) 1,2-glycol.