IR spectral and structural changes caused by the conversion of 3-hydroxybenzaldehyde into the oxyanion

The spectral and structural changes, caused by the conversion of the 3-hydroxybenzaldehyde molecule into the corresponding oxyanion have been studied by IR spectra, and MP2 and DFT force field calculations. The conversion causes a 13 cm(-1) decrease in the frequency of the carbonyl stretching band nu(Cz=O), a 1.3-fold increase in its integrated intensity, strong intensity increases (2.1-5.3-fold) of the aromatic skeletal nu8 and nu19 as well as formyl nu(CH) bands. According to the calculations the oxyanionic charge is delocalized over aldehyde group (0.37 e-), phenylene ring (0.12 e-) and oxyanionic center (0.52 e-). The conversion into the oxyanion leads to geometry changes in the whole species, but it remains planar.     

Ab initio HF, density functional and experimental studies on the IR spectra and structure of 1,2-benzisothiazol-3-(2H)-thione-1,1-dioxide (thiosacchanin) and its nitranion

The spectral and structural changes taking place in the course of the conversion of 1,2-benzisothiazol-3-(2H)-thione-1,1-dioxide (thiosaccharin) into a nitranion have been studied on the basis of both IR spectra and ab initio HF 6-31G(d) and BLYP 6-31G(d,p) force field calculations. The conversion causes nu(as)SO2 and nu(s)SO2 frequency decreases of 47 and 13 cm(-1), respectively, and other spectral changes. The nuC=S coordinate is strongly delocalized. The ab initio geometries of the isolated molecule and nitranion agree well with the single-crystal X-ray ones, determined for thiosaccharin and its sodium (potassium) monohydrate salts, respectively. The nitranionic charge is delocalized almost uniformly within the thiocarbonyl (0.29 e-), sulfonyl (0.24 e-), and phenylene (0.24 e-) groups, and the nitranionic center (0.23 e-).     

The conversion of phenylpropanedinitrile (phenylmalononitrile) into the carbanion, followed by IR spectra, ab initio and DFT force field calculations

The spectral and structural changes, caused by the conversion of phenylpropanedinitrile (phenylmalononitrile) into the carbanion, have been followed by IR spectra, ab initio HF, MP2 and DFT BLYP force field calculations. In agreement between theory and experiment, the conversion is accompanied with strong frequency decreases (with 114 cm(-1), mean value) of the cyano stretching bands nu(C triple bond N), dramatic increases in the corresponding integrated intensities (136-fold, total value), strong enhancement of the nu(C triple bond N) vibrational coupling and other essential spectral changes. According to the calculations, the strongest structural changes take place at the carbanionic center: (i) shortenings of the Cz-Ph and Cz-CN bonds with 0.064-0.092 A, and increases in the corresponding bond orders with 0.14-0.21 U; (ii) simultaneous enlargements of the bond angles at the same carbon atom with 7.6 degrees -9.7 degrees, as from tetrahedral its configuration becomes trigonal. The carbanionic charge is distributed between the two cyano groups (0.44-0.52 e(-)), phenyl ring (0.31-0.34 e(-)) and carbanionic center (0.14-0.25 e(-)). The formation of moderately strong (CH(3))(2)S=O...H-C(CN)(2)C(6)H(5) hydrogen bonds has been found experimentally.     

Spectrochemical, ab initio and density functional studies on the conversion of 2-hydroxybenzonitrile (o-cyanophenol) into the oxyanion

The spectral and structural changes caused by the conversion of 2-hydroxybenzonitrile (o-cyanophenol) into the corresponding oxyanion have been followed by IR spectra, ab initio and density functional force field calculations. In agreement between theory and experiment, the conversion is accompanied by a 29 cm(-1) frequency decrease of the cyano stretching band, 2.7-fold increase in its integrated intensity, 5.8-fold (total value) intensification of the aromatic skeletal bands of Wilson's 8 and 19 types, and other essential spectral changes. According to the calculations, the strongest structural changes are the shortening of the Ph-O bond with 0.10 A, lengthenings of the adjacent CC bonds in the phenylene ring with 0.06 A and bond angle variations near the oxyanionic center. All these changes are connected with the formation of a quasi-ortho-quinonoidal structure of the o-phenylene ring in the oxyanion. According to the electronic density analysis, 0.41 e(-) (Mulliken) or 0.56 e(-) (natural bond orbital, NBO) of the anionic charge remain localized at the oxyanionic center. Conformations and hydrogen bonds have also been discussed on the basis of experimental and theoretical data.     

Theoretical study of the vibrational spectra of the hydrogen-bonded systems between pyridine-3-carboxamide (nicotinamide) and DMSO

The vibrational characteristics (vibrational frequencies and infrared intensities) for the hydrogen-bonded systems of nicotinamide (NA(Z) and NA(E)) with dimethyl sulfoxide (DMSO) have been predicted using ab initio SCF/6-31G(d,p) and DFT (BLYP/6-311++G(d,p)) calculations. The changes in the vibrational characteristics from free monomers to a complex have been calculated. The ab initio and BLYP calculations show that the complexation between nicotinamide (NA(Z) and NA(E)) and DMSO leads to large red shifts of the stretching vibrations for the hydrogen-bonded N-H bonds of nicotinamide and very strong increase in their IR intensity. The results from the BLYP/6-311++G(d,p) calculations show that the predicted red shifts of the nu(s)(NH) and nu(as)(NH) vibrations for the complex NA(E)-DMSO (1:2) (Deltanu(as)(NH)=-186 cm(-1) and Deltanu(s)(NH)=-198 cm(-1)) are in better agreement with the experimentally measured. The magnitudes of the wavenumber shifts are indicative of strong NH...O hydrogen-bonded interactions in both complexes. The calculations predict an increase of the IR intensity of nu(s)(NH) and nu(as)(NH) vibrations in the complexes up to 14 times. Having in mind that in more cases the predicted changes in the vibrational characteristics for the complexes studied are very near, it could be concluded that both conformers of nicotinamide, Z-conformer and E-conformer, are present in the solution forming the hydrogen-bonded complexes with DMSO.     

DFT and experimental study on the IR spectra and structure of 2-hydroxy-3-methoxybenzaldehyde (o-vanillin) and its oxyanion

The structure of o-vanillin molecule and its oxyanion have been studied by density functional theory (DFT), employing the B3LYP functional and 6-311++G** basis set. All conformational isomers of o-vanillin and of its anion have been located and their relative energies have been determined. The IR spectral changes, caused by the conversion of the molecule into the corresponding oxyanion have been studied. In a general agreement between theory and experiment, the conversion causes a frequency decrease of the carbonyl stretching band ν(CO) and essential intensity increases of the aromatic skeletal bands as well as methyl stretching band ν(CH₃). According to the NBO electric charge analysis, the oxyanionic center bears 60% of the whole anionic net charge.     

Comprehensive Analysis of Fragment Orbital Interactions to Build Highly π‐Conjugated Thienylene‐Substituted Phenylene Oligomers

π‐Conjugated thienylene? phenylene oligomers with fluorinated and dialkoxylated phenylene fragments have been designed and prepared to understand the interactions in fragment orbitals, the influence of the substituents (F, OMe) on the HOMO–LUMO gap, and the role of intramolecular non‐covalent cumulative interactions in the construction of π‐conjugated nanostructures. Their strong conjugation was also evidenced in the gas phase by UV photoelectron spectroscopy and theoretical calculations. These results can be explained by the crucial role of the relative energetic positions of the π orbitals of the dimethoxyphenylene, which was used to model the dialkoxyphenylene entity, in determining the π/π^* orbital levels of the fluorinated phenylene entity. Dialkoxyphenylenes raise the HOMO orbitals, whereas fluorinated phenylenes lower the LUMO orbitals in the oligomers. In addition, the presence of S???F and H???F interactions in the fluorinated phenylene? thienylene compounds add to the S???O interactions in the mixed targets and contribute to the full conjugation in the oligomer, inducing weak inter‐ring angles between the involved aromatic cycles. These results, which showed extended conjugation of the π system, were corroborated by a narrow HOMO–LUMO gap (according to DFT calculations) and by a relatively strong maximum wavelength (as obtained by TD‐DFT calculations and experimental UV/Vis measurements). The crystallographic data of two mixed thienylene? (fluorinated and dialkoxylated phenylene) five‐ring oligomers agree with the above results and show the formation of quasi‐planar conformations with non‐covalent S???O, H???F, and S???F interactions. These studies in the solid and gas phases show the relevance of associating dialkoxyphenylene and fluorinated phenylene fragments with thiophene to lead to oligomers with improved electronic delocalization for electronic or optoelectronic devices.     

Fluorescence and ultraviolet absorption spectra and structure of coumaran and its ring-puckering potential energy function in the S1(pi,pi*) excited state

The fluorescence excitation (jet cooled), single vibrational level fluorescence, and the ultraviolet absorption spectra of coumaran associated with its S1(pi,pi*) electronic excited state have been recorded and analyzed. The assignment of more than 70 transitions has allowed a detailed energy map of both the S0 and S1 states of the ring-puckering (nu45) vibration to be determined in the excited states of nine other vibrations, including the ring-flapping (nu43) and ring-twisting (nu44) vibrations. Despite some interaction with nu43 and nu44, a one-dimensional potential energy function for the ring puckering very nicely predicts the experimentally determined energy level spacings. In the S1(pi,pi*) state coumaran is quasiplanar with a barrier to planarity of 34 cm(-1) and with energy minima at puckering angles of +/-14 degrees. The corresponding ground state (S0) values are 154 cm(-1) and +/-25 degrees . As is the case with the related molecules indan, phthalan, and 1,3-benzodioxole, the angle strain in the five-membered ring increases upon the pi-->pi* transition within the benzene ring and this increases the rigidity of the attached ring. Theoretical calculations predict the expected increases of the carbon-carbon bond lengths of the benzene ring in S1, and they predict a barrier of 21 cm(-1) for this state. The bond length increases at the bridgehead carbon-carbon bond upon electron excitation to the S1(pi,pi*) state give rise to angle changes which result in greater angle strain and a nearly planar molecule.     

High-resolution infrared study of vinyl fluoride in the 750-1050 cm(-1) region: rovibrational analysis and resonances involving the nu8, nu10, and nu11 fundamentals

The FTIR spectra of CH2[double bond]CHF have been investigated in the nu(8), nu(10), and nu(11) region between 750 and 1050 cm(-1) at a resolution of about 0.002 cm(-1). The nu(8) vibration of symmetry species A' gives rise to an a/b-type hybrid band, while the nu(10) and nu(11) modes of A' ' symmetry produce c-type absorptions. Due to the proximity of their band origins, the three vibrations perturb each other by Coriolis and high-order anharmonic resonances. In particular, the interactions between the nu(8) and nu(10) modes are very strong and widespread with band origins separated by only 1.37 cm(-1). Besides the expected c-type characteristics, the nu(10) band shows a very intense pseudo a-type component caused by the strong first-order Coriolis resonances with the nu(8) state. Furthermore, the 2nu(9) "dark state" was found to be involved in the interacting band systems. The spectral analysis resulted in the identification of 3144, 3235, and 3577 transitions of the nu(8), nu(10), and nu(11) vibrations, respectively. Almost all the assigned data were simultaneously fitted using the Watson's A-reduction Hamiltonian in the Ir representation and the perturbation operators. The model employed includes nine types of resonances within the tetrad nu(8)/nu(10)/nu(11)/2nu(9) and a set of spectroscopic constants for the nu(8), nu(10), and nu(11) fundamentals as well as parameters for the "dark state" 2nu(9), and fourteen coupling terms have been determined.     

Strong binding affinity of a zinc-porphyrin-based receptor for halides through the cooperative effects of quadruple C-H hydrogen bonds and axial ligation

A new type of host compound (1), tetraphenyl zinc-porphyrin (ZnTPP) that contains four triazole groups at the ortho-position of each phenyl group, has been synthesized and characterized by using (1)H, (13)C NMR, and MALDI-TOF-MS analyses. The host-guest complex formation between 1 and halides was investigated by using (1)H NMR spectroscopy in [D(6)]DMSO. The triazole, benzyl, and phenylene proton signals were shifted upfield by the addition of halides in the form of tetrabutylammonium salts, which implies that the triazole protons in 1 are allocated very closely to the porphyrin ring and are directed toward the binding pocket over the porphyrin ring during the formation of hydrogen bonds. The UV/Vis absorption spectra showed that both the Soret and Q band absorptions of 1 underwent a strong redshift due to the addition of halides. Compound 1 exhibited surprisingly strong binding affinities for the halides, where the association constants for Cl(-), Br(-), and I(-) binding were estimated to be larger than 10(8), 1.79×10(7), and 1.84×10(5) M(-1), respectively. The UV/Vis absorption changes and the result of competitive titration using 4-tert-butylpyridine indicated that the cooperative effects of axial coordination and C-H···X hydrogen bond interactions resulted in the strong binding affinity of 1 to halides.     

Theoretical and Experimental Study of Medium Effects on the Structure and Spectroscopy of the [Fe(CN)(5)NO](2)(-) Ion

The influence of the solvent on the structure and IR spectrum of the [Fe(CN)(5)NO](2)(-) ion is investigated by using gradient corrected density functional theory. IR spectra are also measured on different solvents and the results obtained are compared with the predicted ones. We have treated the solvent effects with a continuum model, based on the Onsager's reaction field approach; in order to mimic strong specific interactions, calculations were also performed on the complex protonated at the cyanide trans to the nitrosyl group. The reaction field calculations predict only qualitatively the most important observed trends, e.g., the shifts in the nitrosyl stretching wavenumber, but fail in accounting quantitatively for the differences between the spectra in water and acetonitrile. The possible role of specific interactions is consistently accounted for by interpreting the experimental shifts of the NO stretching wavenumber nu(NO), as well as the visible absorption energies, when changing the Lewis acidity of the solvent, as measured by the Gutmann's acceptor number. Ligand population analysis was performed to relate the solvent effects with the sigma donor and pi acceptor behavior of cyanide and nitrosyl ligands. The significance of nu(NO) shifts as a result of changes in the medium is discussed in view of the physiological relevance of transition-metal nitrosyl chemistry.     

Density functional theory (DFT) calculations of the infrared absorption spectra of acetaminophen complexes formed with ethanol and acetone species

We have investigated the infrared (IR) vibrational spectra of acetaminophen (N(4-hydroxyphenyl) acetamide or paracetamol) complexes formed with ethanol and acetone in relation to the nature of the specific intermolecular interactions involved in the stabilization of the complexes. The structures and binding energies of the complexes have been determined using Hartree-Fock (HF) and DFT-B3PW91 procedures and different Pople's basis sets as well. The main results are presented and discussed by considering the hydroxyl (OH), amino (NH), and carbonyl (CO) chemical groups of acetaminophen interacting with the acetone or ethanol molecules either separately or in conjunction in the complex formation. The frequency shifts and IR intensity variations associated with the internal modes of acetaminophen (namely nu(OH), nu(NH), and nu(CO)) as well as the most pertinent vibrational probes of ethanol (nu(OH)) and acetone (symmetric nu(CO) and nu(CCC) stretching modes) interacting with acetaminophen have been analyzed. The predicted spectral changes have been critically discussed in comparison with IR absorption measurements of acetaminophen dissolved as a solute in ethanol or acetone CO2 expanded solutions. It is argued that the exchange-correlation contribution taken into account in DFT calculations is likely significant in determining the main IR spectral features of acetaminophen complexes formed with acetone or involving hydrogen-bonded as with ethanol.     

Nickel dithiolenes revisited: structures and electron distribution from density functional theory for the three-member electron-transfer series [Ni(S2C2Me2)2]0,1-,2-

The complexes [Ni(S2C2Me2)2](z) (z = 0, 1-, 2-) have been isolated for the purpose of investigating their electronic structures in a reversible three-member electron-transfer series. Members are interrelated by reversible redox reactions with E(1/2)(0/1-) = -0.15 V and E(1/2)(1-/2-) = -1.05 V versus SCE in acetonitrile. The three complexes have nearly planar structures of idealized D(2)(h) symmetry. As the series is traversed in the reducing direction, Ni-S and C-S bond lengths increase; the chelate ring C-C bond length decreases from the neutral complex to the monoanion and does not change significantly in the dianion. Structural trends are compared with previous results for [Ni(S2C2R2)2)](1-,2-). Following the geometrical changes, values of nu(Ni)(-)(S) and nu(C)(-)(S) decrease, while the value of nu(C)(-)(C) increases with increased reduction. Geometry optimizations at the density functional theory (DFT) level were performed for all members of the series. Geometrical parameters obtained from the calculations are in good agreement with the experimental findings. The 5b(2g) orbital was identified as the LUMO in [Ni(S2C2Me2)2], the SOMO in [Ni(S2C2Me2)2](1-), and the HOMO in [Ni(S2C2Me2)2]2-. Unlike in the situation in the [M(CO)2-(S2C2Me2)2]z series (M = Mo, W; z = 0, 1-, 2-), the apparent contribution from the metal d orbital in the electroactive orbital is not constant. In the present series, the d(xz) contribution increases from 13 to 20 to 39% upon passing from the neutral to the monoanionic to the dianionic complex. Accurate calculation of EPR g-values of [Ni(S2C2Me2)2]1- by DFT serves as a test for the reliability of the electronic structure calculations.     

Direct determination of the complete set of iron normal modes in a porphyrin-imidazole model for carbonmonoxy-heme proteins: [Fe(TPP)(CO)(1-MeIm)

Detailed Fe vibrational spectra have been obtained for the heme model complex [Fe(TPP)(CO)(1-MeIm)] using a new, highly selective and quantitative technique, Nuclear Resonance Vibrational Spectroscopy (NRVS). This spectroscopy measures the complete vibrational density of states for iron atoms, from which normal modes can be calculated via refinement of the force constants. These data and mode assignments can reveal previously undetected vibrations and are useful for validating predictions based on optical spectroscopies and density functional theory, for example. Vibrational modes of the iron porphyrin-imidazole compound [Fe(TPP)(CO)(1-MeIm)] have been determined by refining normal mode calculations to NRVS data obtained at an X-ray synchrotron source. Iron dynamics of this compound, which serves as a useful model for the active site in the six-coordinate heme protein, carbonmonoxy-myoglobin, are discussed in relation to recently determined dynamics of a five-coordinate deoxy-myoglobin model, [Fe(TPP)(2-MeHIm)]. For the first time in a six-coordinate heme system, the iron-imidazole stretch mode has been observed, at 226 cm(-)(1). The heme in-plane modes with large contributions from the nu(42), nu(49), nu(50), and nu(53) modes of the core porphyrin are identified. In general, the iron modes can be attributed to coupling with the porphyrin core, the CO ligand, the imidazole ring, and/or the phenyl rings. Other significant findings are the observation that the porphyrin ring peripheral substituents are strongly coupled to the iron doming mode and that the Fe-C-O tilting and bending modes are related by a negative interaction force constant.     

The effect of phenyl ring on the physical properties of liquid crystals containing 4-pyridyl terminal group

ABSTRACT

Liquid crystals with 4-pyridyl end group containing one triple bond and phenylenes have been synthesised. Their structures were confirmed by traditional spectroscopic methods. The properties were measured by differential scanning calorimetry (DSC), polarising optical microscopy (POM), Abbe refractometer and an electrical constants instrument. The results show that all of the compounds exhibit nematic phase. The addition of a phenylene to the molecular skeleton brings about an obvious increase of the mesophase intervals (from 8.8 to 95.5) and birefringence (up to 0.33), as well as minus or plus effect of dielectric anisotropies depending on the position of the phenylene. Density Functional Theory (DFT) calculations of molecular conformation, polarisability and dipole moment were used to further study the molecular structure–property relationship.     

基于噻吩和亚苯基合成的新物质的结构和电子性质

Theoretical study on the geometries and electronic properties of new conjugated compounds based on thiophene and phenylene was carried out. The theoretical ground-state geometries and electronic structures of the studied molecules were obtained using the density functional theory (DFT) method at B3LYP level with 6-31G(d) basis set. The electronic properties were determined by ZINDO/s, CIS/3-21G(d), and TD//B3LYP/3-21G(d) calculations performed on the B3LYP/6-31(d) optimized geometries. The effects of the ring structure and the substituents on the geometries and electronic properties of these materials were discussed. The results of this study indicate how the electronic properties can be tuned by the backbone ring or side group and suggest these compounds as good candidates for opro-electronic applications.     

Structural and Electronic Properties of New Materials Based on Thiophene and Phenylene

Theoretical study on the geometries and electronic properties of new conjugated compounds based on thiophene and phenylene was carried out. The theoretical ground-state geometries and electronic structures of the studied molecules were obtained using the density functional theory (DFT) method at B3LYP level with 6-31G(d) basis set. The electronic properties were determined by ZINDO/s, CIS/3-21G(d), and TD//B3LYP/3-21G(d) calculations performed on the B3LYP/6-31(d) optimized geometries. The effects of the ring structure and the substituents on the geometries and electronic properties of these materials were discussed. The results of this study indicate how the electronic properties can be tuned by the backbone ring or side group and suggest these compounds as good candidates for opto-electronic applications.     

Phosphorescence excitation spectrum of the T(1)(n,pi*)<--S(0) transition of 4H-pyran-4-one

The phosphorescence excitation (PE) spectrum of 4H-pyran-4-one (4PN) vapor at 40-50 degrees C was recorded near 366 nm. The most intense vibronic feature in this region of the spectrum is the T(1)(n,pi*)<--S(0) origin band. The value of nu(0) for the 0(0)(0) transition was determined to be 27 291.5 cm(-1) by comparing the observed spectrum to a simulation in the T(1)<--S(0) origin-band region. Attached to the origin band in the PE spectrum are several Deltav=0 sequence bands involving low-frequency ring modes. From the positions of these bands, together with the known ground-state combination differences, fundamental frequencies for nu(18') (ring bending), nu(13') (ring twisting), and nu(10') (in-plane ring deformation) in the T(1)(n,pi*) excited state were determined to be 126, 269, and 288 cm(-1), respectively. These values represent drops of 15%, 32%, and 43%, compared to the respective fundamental frequencies in the S(0) state. The changes in these ring frequencies indicate that the effects of T(1)(n,pi*)<--S(0) excitation extend beyond the nominal carbonyl chromophore and involve the conjugated ring atoms as well. The delocalization may be more extensive for T(1)(n,pi*) than for S(1)(n,pi*) excitation.