Substituent and coupling effects in the IR spectra of arylidenecyclanones

By studying the IR spectra of arylidenecyclanones possessing exocyclic CC double bonds, a correlation has been found between the wave number and intensity values of the ν CO and ν CC vibrations and the substituent constants. Transmissive factors of the CC double bond have been calculated and these indicated that the most pronounced conjugation occurs in the case of the indanones and the smallest for 1-thiochromanones. It has also been established that the substituent effect transmitted by the CC double bond is mainly of a resonant character. Coupling of the ν CO and ν CC vibrations has been studied by the method of Taylor and Smith. It has been concluded that in the case of arylidene-indanones possessing strong coupling, of the two intense bands between 1600 and 1800 cm⁻¹ the one found at higher wave number is a result of an out-of-phase (ν_as) coupling of the ν CO and ν CC vibrations while the other originates from an in-phase (ν_s) coupling. Coupling was less in the case of the other compounds investigated. Our studies prove that for the evaluation of the substituent effects the coupling phenomena should be taken into consideration.     

Characterization of NH overtone and combination bands in the near-infrared absorption spectra of simple cyclic imides

Bands due to overtone and combination vibrational modes attributable to the imide grouping have been elucidated in the near-IR absorption spectra of small-ring cyclic imides, in which the grouping is in a cis, cis conformation. The spectra closely parallel the spectra of cis lactams except that two combination modes involving the carbonyl stretching fundamental, [ν(NH) + ν(CO)] and [2ν(C=O) + imide III], occur at higher wavenumbers in the imide spectra, reflecting the higher frequency at which this fundamental absorbs. This same factor results in a reversal in the wavenumber positions of the [2ν(CO) + imide III] and [ν(NH) + imide III] combination bands in the imide spectra relative to those in the lactam spectra. In addition, in-phase and out-of-phase vibrational coupling between the two carbonyl groups in the imides may compound the band due to the [ν(NH) + ν(CO)] combination mode. These three spectral characteristics serve to distinguish the imides from the lactams in the near-IR.     

Formation,microwave spectrum and preliminary structure of selenoketene

Hitherto unknown selenoketene, CH₂CSe, has been produced by pyrolysis of 1,2,3-selenodiazole and identified by observation of microwave absorption from CH₂C&.dbnd;⁸⁰Se and CH₂C⁷⁸Se. The CC and CSe bond lengths of selenoketene agree with bond lengths in ketene, CH₂CO, and in carbonyl sulphide, OCS.     

Spectral effects in cyclobutane derivatives : The bathochromic-hypochromic shifts in compounds related to verbenone

The bathochromic-hypochromic spectral shifts, observed in bicyclic enones that contain a 4- or a 3-membered ring, are discussed in molecular-mechanical and molecular-orbital terms. It is proposed that the effect, not only by the cyclopropane but also by the cyclobutane ring, is due to extension of the CCCO chromophore, and not to its mere distortion from “normal” geometry. The high-energy absorption of umbellulone (3), 220 nm in ethanol, is characterized as a second π-π^*. 2-Methylbicyclo[3.2.1]oct-2-en-4-one (7) has been synthesized, and its preparation and spectrum are described.     

Determination of the stereochemistry of condensation products between α,β-diamines and α,γ-dioxo compounds by circular dichroism, 1H NMR and x-ray diffraction

The absolute configuration of molecules containing two chromophores of the type -NH-CC-CO bridged by -?-?- have been studied in solution by UV absorption and circular dichroism. The spectra have been simulated by means of component curves shaped as skew gaussians. The data have been interpreted by means of exciton theory for coupled chromophores to give information about the relative orientation of the chromophores. The result is compared with the result of an X-ray structure determination of N,N'-bis(4-oxo-2-penten-2-yl)-R-1,2-diaminopropane.     

Vibrational spectra of β-lactams—II. 1-Methyl-2-azetidinone and its deuterated compounds

The i.r. and Raman spectra of 1-methyl-2-azetidinone and its 3,3-d₂ and methyl-d₃ compounds have been recorded, and the observed bands have been assigned on the basis of the isotope effects and the normal coordinate analysis. Comparison of the CO and CN force constants between 2-azetidinone and 1-methyl-2-azetidinone indicates that, depending on amide resonance, these constants are related to each other. The solvent effects on the CO frequencies of four to seven-membered lactams have also been examined.     

Neutral and zwitterionic glycine.H(2)O complexes: A theoretical and matrix-isolation Fourier transform infrared study

The H-bond interaction between glycine and H2O has been studied by a combined theoretical (DFT(B3LYP)/6-31++G(**)) and experimental (matrix-isolation FT-IR) methodology. The 1:1 and 1:2 complexes of the most stable conformation (I) of glycine appear to be neutral complexes which have been vibrationally characterized in detail. The higher stoichiometry complexes (glycine).(H2O)n with n larger than 3 are demonstrated to be zwitterionic H-bonded complexes. A set of characteristic IR absorption bands for this zwitterionic structure has been observed in low-temperature Ar matrices. This would be the first experimental IR evidence for proton transfer occurring between the NH2 and COOH groups of amino acids by a H-bonded water molecular channel in isolated conditions.     

Analyse conformationnelle de derives carbonylés du furanne et du thiophène par utilisation de la position et de l'intensite des bandes infrarouges

The carbonyl bands of 2-formyl and 3-formyl-furans [¹⁸O] are determined and explained. The magnitude of the inductive and mesomeric effects in 2-acyl and 3-acyl-thiophenes and furans is discussed on the basis of a comparison of the frequencies and the intensities of the v(CO) and v(CC) bands. The conformational preference of some aroyl-furans and aroyl-formyl-furans and the rotation around the C(Ar)-C(O) bonds are related to these parameters.     

Intermolecular vibrations of the water trimer, a matrix isolation study

Infrared spectra from 25 to 4000 cm(-1) have been recorded of water (H2O, D2O and H218O) matrix isolated in neon, argon, and krypton matrices. Intermolecular absorption bands of different isotopologues of the water trimer and tetramer have been assigned from concentration dependencies and diffusion behavior, using the well-known mid-infrared trimer and tetramer absorption bands as measures of the trimer and tetramer concentrations. The results are compared to ab initio calculations.     

Vibrational (i.r. and Raman) spectra and conformational studies of 1-formyl-3-thiosemicarbazide

The i.r. and Raman spectra (30–4000 cm⁻¹) of 1-formyl-3-thiosemicarbazide (FTSC) and deuterated ftsc-d₄, have been studied. Most of the vibration modes reveal pairs of bands and show strong temperature dependence. A band group {ν(NNH₂)} at ∼ 1100 cm⁻¹ exhibits well resolved doublet (1095 and 1112 cm⁻¹) structure below 100 k. The intensity in the 11 12 cm⁻¹ band decreases regularly (band disappears at 150 K) with the rise in temperature. Two new bands at 955 and 1070 cm⁻¹ appear while measured above 400 K. The system eventually exists in several conformers in simultaneous equilibria. Moreover, a few bands {e.g. ν(CO), ν(CS) and ν(CH)} that show strong intensifies in i.r. exhibit weak (or zero) intensifies in the Raman and vice-versa. The features (characteristic of u and g vibration species) could be explained by a C_2h pseudo symmetry space group proposed for the system. Both the FTSC and FTSC-d₄ represent strong molecular associations. This favours the maximum abundance in the dimer stabilized conformers.     

Infrared spectroscopic study of the CO2 adsorption effect on the surface acidity of zinc oxide

Taking account the bands ν_a(O¹²CO) and ν_a(O¹³CO) (in natural abundance) due to linear species, the study by FT-infrared spectroscopy of the CO₂ adsorption on ZnO has shown particular sites which can be described as Zn²⁺ ions with two vacancies, with a reactive oxygen ion in an adjacent position. Using the usual probe molecules (CO, acetonitrile, ammonia, pyridine), we have compared the Lewis acidity of ZnO and ZnO which has been pretreated with CO₂. This preadsorption causes an increase of the Lewis acidity. Moreover we have found that it prevents the dissociative adsorption of acetonitrile, ammonia, pyridine, propene and butenes. The model site described above well accounts for these results. It is concluded that the increase of the acidity due to CO₂ preadsorption is related to the formation of bidentate carbonates.     

Dehydration of 3- and 4-aryl- substituted 3-hydroxy acids in acetic anhydride in presence of zinc chloride

The reaction of several di- and triaryl-substituted 3-aryl-3-hydroxy acids and a 4-aryl-3-hydroxy acid in acetic anhydride in the presence of anhydrous zinc chloride has been investigated. It has been shown that the reaction discovered with 3-(2′-thienyl)-substituted 3-hydroxy acids, namely, their conversion under the above stated conditions into α, β-unsaturated methyl ketones,^1,2 occurs also with 3-aryl 3-hydroxy acids but to a smaller degree due to the concurrent cyclization reaction which leads to indene-1-ones. It has been established that the unsaturated methyl-ketones obtained, containing three aromatic substituents at the CC bond, exist in s-cis-(CC, CO)-conformation. It has been found that with the 4-aryl-substituted 3-hydroxy acid almost no unsaturated ketone is obtained, whereas instead the main product is a 2,3-disubstituted 1-naphthol which is acetylated under the conditions of the reaction. Its structure has been proved by its UV, IR and NMR spectra and confirmed by the mass spectrum of the compound.     

CuCl3]- and [CuCl4]2- hydrates in concentrated aqueous solution: a density functional theory and ab initio study

In this work, structures and thermodynamic properties of [CuCl(3)](-) and [CuCl(4)](2-) hydrates in aqueous solution were investigated using density functional theory and ab initio methods. Contact ion pair (CIP) and solvent-shared ion pair (SSIP) structures were both taken into account. Our calculations suggest that [CuCl(3)(H(2)O)(n)](-) clusters might favor a four-coordinated CIP structure with a water molecule coordinating with the copper atom in the equatorial position for n = 3 and 4 in aqueous solution, whereas the four-coordinated SSIP structure with one chloride atom dissociated becomes more stable as n increases to 5. For the [CuCl(4)](2-) cluster, the four-coordinated tetrahedron structure is more stable than the square-planar one, whereas for [CuCl(4)(H(2)O)(n)](2-) (n ≥ 1) clusters, it seems that four-coordinated SSIP structures are slightly more favorable than CIP structures. Our calculations suggest that Cu(2+) perhaps prefers a coordination number of 4 in CuCl(2) aqueous solution with high Cl(-) concentrations. In addition, natural bond orbital (NBO) calculations suggest that there is obvious charge transfer (CT) between copper and chloride atoms in [CuCl(x)](2-x) (x = 1-4) clusters. However, compared with that in the [CuCl(2)](0) cluster, the CT between the copper and chloride atoms in [CuCl(3)](-) and [CuCl(4)](2-) clusters becomes negligible as the number of attached redundant Cl(-) ions increases. This implies that the coordination ability of Cl(-) is greatly weakened for [CuCl(3)](-) and [CuCl(4)](2-) clusters. Electronic absorption spectra of these different hydrates were obtained using long-range-corrected time-dependent density functional theory. The calculated electronic transition bands of the four-coordinated CIP conformer of [CuCl(3)(H(2)O)(n)](-) for n = 3 and 4 are coincident with the absorption of [CuCl(3)](-)(aq) species (～284 and 384 nm) resolved from UV spectra obtained in CuCl(2) (ca. 10(-4) mol·kg(-1)) + LiCl (>10 mol·kg(-1)) solutions, whereas the calculated bands of [CuCl(3)(H(2)O)(n)](-) in their most stable configurations are not when n = 0 - 2 or n > 4, which means that the species [CuCl(3)](-)(aq) exists in those CuCl(2) aqueous solutions in which the water activity is neither too low nor too high. The calculated bands of [CuCl(4)(H(2)O)(n)](2-) clusters correspond to the absorption spectra (～270 and 370 nm) derived from UV measurements only when n = 0, which suggests that [CuCl(4)](2-)(aq) species probably exist in environments in which the water activity is quite low.     

Zur reaktion von metall-koordiniertem kohlenmonoxid mit yliden: XXI. Ambidentes verhalten von eisenacyl-phosphor-yliden gegenüber methylfluorsulfonsäureester: Umwandlung in eisenacyl-phosphoniumsalze oder β-phosphoniovinyl- eisenkomplexe

]The reaction of the acyliron phosphorus ylide Cp(CO)₂FeC(O)CHPMe₃ with MeOSO₂F yields the acyliron phosphonium salt [Cp(CO)₂FeC(O)C(Me)- HPMe₃]SO₃F, while Cp(CO)₂FeC(O)C(Me)PEt₃ undergoes exclusively O-alkylation to the complex salt [Cp(CO)₂FeC(OMe)C(Me)PEt₃]SO₃F, (A). The acyliron ylides Cp(CO)₂FeC(O)C(R)PR₃ (R  R′  Me; or R  H, R′  Et) are converted to a mixture of the O- and C-methylated products. According to spectroscopic data and X-ray diffraction analysis of A the O- alkylation products have to be described as phosphoniovinyliron complexes.     

Determination of the conformation in thioester compounds containing the NSO group through pre-resonance Raman study: Spectroscopic properties of S(N-sulphinylimine)-fluorocarbonylsulphane,FC(O)SNSO

Starting from fluorocarbonylsulphenyl chloride, FC(O)SCl, and N-trimethylsilysulphinylimine, (CH₃)₃SiNSO, the compound S(N-sulphinylimine)-fluorocarbonylsulphane, FC(O)SNSO, has been prepared. The IR, pre-resonant Raman, ¹³C NMR, mass, and UV spectra have been obtained and interpreted.The two bands appearing in the CO stretching fundamental mode region of the vibrational spectra were specially investigated to probe the existence of conformational isomerism in the molecule. From the analysis of the bands and their contours in the vapour-IR spectra, and the depolarization ratios together with the pre-resonant behaviour in the Raman spectrum of the liquid (whose extension is also evaluated), two planar forms can be determined for the molecule.The study of the CO envelope in the IR spectrum of the vapour phase reveals syn conformation (with respect to the CO and SN bonds) as the most stable structure for the molecule, and the anti conformation as the second structure.     

Hydrated alizarin complexes: hydrogen bonding and proton transfer

We investigated the hydrogen bonding structures and proton transfer for the hydration complexes of alizarin (Az) produced in a supersonic jet using fluorescence excitation (FE), dispersed laser induced fluorescence (LIF), visible-visible hole burning (HB), and fluorescence detected infrared (FDIR) spectroscopy. The FDIR spectrum of bare Az with two O-H groups exhibits two vibrational bands at 3092 and 3579 cm(-1), which, respectively, correspond to the stretching vibration of O1-H1 that forms a strong intramolecular hydrogen bond with the C9=O9 carbonyl group and the stretching vibration of O2-H2 that is weakly hydrogen-bonded to O1-H1. For the 1:1 hydration complex Az(H(2)O)(1), we identified three conformers. In the most stable conformer, the water molecule forms hydrogen bonds with the O1-H1 and O2-H2 groups of Az as a proton donor and proton acceptor, respectively. In the other conformers, the water binds to the C10=O10 group in two nearly isoenergetic configurations. In contrast to the sharp vibronic peaks in the FE spectra of Az and Az(H(2)O)(1), only broad, structureless absorption was observed for Az(H(2)O)(n) (n≥ 2), indicating a facile decay process, possibly due to proton transfer in the electronic excited state. The FDIR spectrum with the wavelength of the probe laser fixed at the broad band exhibited a broad vibrational band near the O2-H2 stretching vibration frequency of the most stable conformer of Az(H(2)O)(1). With the help of theoretical calculations, we suggest that the broad vibrational band may represent the occurrence of proton transfer by tunnelling in the electronic ground state of Az(H(2)O)(n) (n≥ 2) upon excitation of the O2-H2 vibration.     

Infrared spectra of the water-nitrogen complexes (H2O)2-(N2)n(n = 1-4) in argon matrices

The infrared spectra of the water-nitrogen complexes trapped in argon matrices have been studied with Fourier transform infrared absorption spectroscopy. The absorption lines of the H20-N2 1:1, 1:2, 1:n, and 2:1 complexes have been confirmed on the basis of the concentration effects. In addition, we have observed a few lines and propose the assignments for the 2:2, 2:3, and 2:4 complexes in the nu1 symmetric stretching and nu2 bending regions of the proton-acceptor molecule, and in the bonded OH stretching region of the proton-donor molecule. The redshifts in the bonded OH stretching mode and blueshifts in the OH bending mode suggest that the hydrogen bonds in the (H2O)2-(N2)n complexes with n = 1-4 are strengthened by the cooperative effects compared to the pure H2O dimer. Two absorption bands due to the 3:n complexes are also observed near the bonded OH stretching region of the H2O trimer.     

Synthesis and proposed conformations of l-prolyl-l-leucyl-β-alanine alkylamides

The synthesis of H-Pro-Leu-β-Ala-NH₂, H-Pro-Leu-β-Ala-NHCH₃ and H-Pro-Leu-β-Ala-N(CH₃)₂ is described. On the basis of IR and ¹H NMR spectral data, a 7-membered ring including the NH of β-alanine with the CO of proline should be assigned for the H-Pro-Leu-β-Ala-N(CH₃)₂. Consequently, the plausible conformations for H-Pro-Leu-β-Ala-NH₂ and H-Pro-Leu-β-Ala-NHCH₃ derive from the formation of an 11-membered ring, between the trans amide proton and the CO of Pro, or from the formation of an 8-membered ring, between this carboxamide proton and the CO of Leu, plus the aforementioned 7-membered ring.     

Some biological transformations involving unsaturated linkages: the importance of charge separation and charge neutralization in enzyme catalysis

Current status of knowledge on the biological reduction of CC and CO is briefly reviewed. It is Argued that the crucial event in the reduction of CC is the addition of a proton to the more electron-rich terminal of the double bond to produce an electron-deficient species which is then neutralized through hydride transfer from NADPH. The activation for the reduction of a CO group may also be achieved by a related process in which the carbonyl oxygen is polarized by H-bonding to an acidic group on the enzyme, prior to hydride transfer from NAD(P)H.Thus with both these systems an early event in catalysis is the protonation of the substrate for which, normally, strong adds win be required. Since the groups available at the active-met of enzymes are weak acids, a mechanism through which powerful proton donating species could be transiently generated from them is proposed. The salient features of this mechanism may be enuinciatcd as follows: Let us consider the enzyme-substrate complex (A) in which an imidazolium group is about to play a role as a proton donating species. It is argued that rearrngement of initial complex(A)to the catalytic-complex(B), in which the negatively chared counter ion is removed away from the imidazolium cation, would transiently convert the latter group into a powerful proton danating species. the rearrangement (A)→(B) could occur through a protein conformational change or via a charge-relay system or a combination of both processes.     

Prying apart a water molecule with anionic H-bonding: a comparative spectroscopic study of the X-.H2O (X = OH, O, F, Cl, and Br) binary complexes in the 600-3800 cm(-1) region

A detailed picture of the structural distortions suffered by a water molecule in direct contact with small inorganic anions (e.g., X = halide) is emerging from a series of recent vibrational spectroscopy studies of the gas-phase X-.H2O binary complexes. The extended spectral coverage (600-3800 cm(-1)) presently available with tabletop laser systems, when combined with versatile argon "messenger" techniques for acquiring action spectra of cold complexes, now provides a comprehensive survey of how the interaction evolves from an ion-solvent configuration into a three-center, two-electron covalent bond as the proton affinity of the anion increases. We focus on the behavior of H2O in the X-.H2O (X = Br, Cl, F, O, and OH) complexes, which all adopt asymmetric structures where one hydrogen atom is H-bonded to the ion while the other is free. The positions and intensities of the bands clearly reveal the mechanical consequences of both (zero-point) vibrationally averaged and infrared photoinduced excess charge delocalization mediated by intracluster proton transfer (X-.H2O --> HX.OH-). The fundamentals of the shared proton stretch become quite intense, for example, and exhibit extreme red-shifts as the intracluster proton-transfer process becomes available, first in the vibrationally excited states (F-.H2O) and then finally at the zero-point level (OH-.H2O). In the latter case, the loss of the water molecule's independent character is confirmed through the disappearance of the approximately 1600 cm(-1) HOH intramolecular bending transition and the dramatic (>3000 cm(-1)) red-shift of the shared proton stretch. An unexpected manifestation of vibrationally mediated charge transfer is also observed in the low frequency region, where the 2 <-- 0 overtones of the out-of-plane frustrated rotation of the water are remarkably intense in the Cl-.H2O and Br-.H2O spectra. This effect is traced to changes in the charge distribution along the X-.O axis as the shared proton is displaced perpendicular to it, reducing the charge transfer character of the H-bonding interaction and giving rise to a large quadratic contribution to the dipole moment component that is parallel to the bond axis. Thus, all of these systems are found to exhibit distinct spectral characteristics that can be directly traced to the crucial role of vibrationally mediated charge redistribution within the complex.