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Density functional theory (DFT) and Atoms-in-Molecules (AIM) analyses as well as Fourier transform Infrared, Raman, and UV spectra have been used to investigate the structure and vibrational spectra of bis(3,5-heptanedionato)copper(II) (Cu(HPD)2). To explore the effect of ethyl substitution with the methyl and t-But groups in the β-position, two different complexes have been chosen, namely, copper (II) acetylacetonate Cu(acac)2 and copper (II) 2,2,6,6-tetramethylheptane-3,5-dionate (Cu(TMHD)2), respectively. The experimental IR and Raman wavenumbers have been fully assigned, using the calculated ones. The calculated and experimental results are in good agreement. The metal–O bond strength was investigated by geometry calculations and spectroscopic results to realize the substitution effect. The metal–ligand bond strength in Cu(HPD)2 is between the corresponding ones in Cu(THMD)2 and Cu(acac)2.

The isomerism, optimized molecular structure, UV spectrum, metal-ligand bond strength, and vibrational assignment of tris(triflouroacetylacetonato)iron(III), Fe(TFAA)3, were investigated by the aid of theoretical calculations (using DFT and Atoms-in-Molecules (AIM) at the B3LYP/6-311++G(d,p) level) and experimental methods (vibrational and UV spectroscopy). To explore the effect of the CF3 substituent in the β-position on the properties of complex, the above theoretical and experimental results of the titled complex compared with the corresponding data for tris(acetylacetonato) iron(III), Fe(AA)3. Both theoretical and experimental results confirmed that there is no significant difference in the strength of the Fe−O bond in these complexes. The effect of the CF3 group on the experimental vibrational bands of the chelated ring agrees with the calculated results. Comparing the observed and calculated vibrational spectra suggests that vibrational spectroscopy cannot be used to determine the type of isomer in the sample. However, due to the small difference of energy between the fac and mer isomers in the Fe(TFAA)3, the presence of both isomers in the sample is possible. The computed quantum chemical descriptors of Fe(TFAA)3 and Fe(AA)3 were also compared.

Tris(α-cyanoacetylacetonate)iron(III), Fe(CNacac)3, was synthesized and its molecular geometry, Raman, IR, and UV spectra were recorded and analyzed with the mentioned calculated spectra by using the B3LYP/6-311++G(d,p) level and comparing with tris(acetylacetonate)iron(III), Fe(acac)3, as parent molecule. A full assignment along to major contributes for of UV and vibrational experimental bands with their potential energy distribution (PED) of Fe(CNacac)3, has been done. The calculated and experimental results, including molecular geometry, Atoms in Molecules (AIM), Natural bond orbital (NBO) analysis, vibration and UV-Vis spectra were shown the cyano substitution in α position, increases the resonance of chelating ring and increases the Fe−O bond strength of the mentioned molecule in comparison to that Fe(acac)3.

The vibrational spectra of pyridine and its C 2v deuterated isotopomers were reconsidered by means of density functional theory (DFT) methods. The B3LYP level, with 6–311++G** and cc-pVTZ basis sets, is used for geometrical optimization and calculations of harmonic vibrational wavenumbers. Furthermore, the anharmonic vibrational wavenumbers were also calculated at the B3LYP/6-311++G** level. The calculated internal coordinates were used to perform complete normal coordinate analysis (NCA) and potential energy distribution (PED) calculations for pyridine and its 2 H-isotpomers.

Introduction and importance Ischemic colitis, also rare, is the most common ischemic pathology of the digestive system. It usually affects the ageing population and those suffering from end-stage renal disease (ESRD), hypertension, and heart failure. Its incidence varies from 4.5 to 44 cases per 100,000 annually. Case presentation We have reported a case of gangrenous colitis in a 62-year-old man suffering from acute promyelocytic leukaemia (APL) and myelofibrosis. He had hypertension and ESRD due to obstructive uropathy from seven years ago in his past medical history. His recurrent constitutional symptoms and persistent leukocytosis of more than 20,000 in μL was always treated as catheter-related infection or sepsis until acute abdomen emerged. The surgical team encountered a vast gangrenous right hemicolon. The leukocytosis did not resolve. Thus, the haematological investigations proved APL with myelofibrosis. The affected colon was free of leukemic infiltration. Clinical discussion Hypoperfusion due to ESRD and hemodialysis accompanied with malignancy induced hypercoagulative state provided a context in which small vessels of the bowel were obstructed. Conclusion Malignancies are associated with thrombophilia, and colonic involvement is not always related to lymphatic infiltration in leukaemia patients., Highlights • Ischemic colitis, also rare, is the most common ischemic pathology of the digestive system. • Not every leukocytosis should be viewed as sepsis. • Although rare, acute promyelocytic leukaemia can be accompanied by myelofibrosis. • Ischemic colitis may be a result of a hypercoagulable state caused by leukaemias, not necessarily leukaemic invasion. • The cecum is within a watershed of the colon in which incomplete anastomoses of the marginal arteries make its blood supply poor and vulnerable to ischemia.

We studied the electronic transportation properties of 1-(Phenyldiazenyl)naphthalen-2-ol and its derivatives, as optical molecular switches, by using the nonequilibrium Green’s function (NEGF) formalism combined with the first-principles density functional theory (DFT). To describe this switching, we applied the geometrical and topological parameters, Time-dependent density functional theory (TD-DFT), and the second-order interaction energies, E(2), results. The mentioned switching for titled molecules occurred between their tautomers, hydrazo and azo forms, upon photoexcitation. According to our results the current rate of titled molecules is more than that the other reported molecules, about 40,000 nA. Therefore, titled molecules show appropriate potential for using in molecular switch tools. The transmittance spectra and I–V curves show the current of the azo tautomer is more than that in the hydrazo tautomer. This result agree with increasing of the intramolecular hydrogen bond strength, electron densities of aromatic and chelated rings, and the hyperconjugations in the azo forms. In addition, the −OCH3 and -NO2 groups, does not remarkably affected the current rate with Y (111) (Y =Au, Ag, and Pt) electrodes. The best performance obtained in Ag electrode, in while in the other reported molecular switchers Au electrode was appropriated.

Cis and trans isomerism, conformers, molecular structure, relative energies, spectroscopic analysis, metal-ligand strength, and complete vibrational assignment of bis(4,4-dimethyl-1-phenylpentane-1,3-dionato) copper (II), Cu(dmpd)2, were investigated by applying calculated parameters such as density functional theory (DFT), Atoms in Molecules (AIM) study at the B3LYP/6-311G(d) level of theory and experimental techniques contains of vibrational spectra and UV spectroscopy. A comprehensive assignment of the experimental bands of Cu(dmpd)2 has been done. The DFT and spectroscopy techniques applied to consider the assessment of methyl and phenyl and t-But substituents in the β-position on the geometrical and vibrational analysis of complexes. So, the structure, Cu-O strength of the complex, UV spectrum, and vibrational bands of Cu(dmpd)2 compared to bis(benzoylacetonato) copper (II), Cu(bzac)2 and bis(2,2,6,6-tetramethylheptane-3,5-dionato)copper(II), Cu(tmhd)2, by the mentioned theoretical and experimental techniques. All of the simulated and spectroscopic methods supported that the Cu-O bond strength of Cu(dmpd)2is closeto Cu(bzac)2 and more than that Cu(tmhd)2 complex. Comparing the experimental and theoretical vibrational wavenumbers indicates that the transform is the major configuration in the specimen, which agrees with reported the single crystallography results.

Ab initio calculations, Natural Bond Orbital (NBO) and Atoms-in-Molecules (AIM) analyses, and Fourier transform Raman (3200–350 cm−1) and infrared (4000–200 cm−1) spectral measurements have been made for bis(α-cyanoacetylacetonato)Cu(II), Cu(CNacac)2. The molecular structure and vibrational spectra of Cu(CNacac)2 is compared with those of bis(acetylacetonato)Cu(II), Cu(acac)2. The molecular electronic energies and the equilibrium geometries for all theoretically possible conformations are calculated. A normal coordinate analysis of the vibrational modes has been computed for the most stable conformation of Cu(CNacac)2, D2h symmetry. A complete assignment of the observed band frequencies has been proposed. The metal–O bond strength was investigated by geometry calculations, NBO, AIM, and spectroscopic results to realize the effect of cyano substitution at α-position. All theoretical and vibrational spectroscopic studies confirm stronger metal–ligand bond in Cu(CNacac)2 than that in Cu(acac)2.

The copper (II) Schiff base complex of [CuL2] (1), HL = 2-{(E)-[2-chloroethyl) imino]methyl}phenol, has been synthesized and characterized by elemental (CHN) analysis, UV–Vis and FT-IR spectroscopy. The molecular structure of 1 was determined by single crystal X-ray diffraction technique. The conformational analysis and molecular structures of CuL2 were investigated by means of density functional theory (DFT) calculations at B3LYP/6-311G* level. An excellent agreement was observed between theoretical and experimental results. The Schiff base ligand of HL acts as a chelating ligand and coordinates via one nitrogen atom and one oxygen atom to the metal center. The copper (II) center is coordinated by two nitrogen atoms and two oxygen atoms from two Schiff base ligands in an approximately square planar trans-[MN2O2] coordination geometry. Thermogravimetric analysis of CuL2 showed that it was decomposed in five stages. In addition, the CuL2 complex thermally decomposed in air at 660 °C and the XRD pattern of the obtained solid showed the formation of CuO nanoparticles with an average size of 34 nm.

The experimental and theoretical studies on asymmetrical Schiff base, salicylideneimino-ethylimino-pentan-2-one (SEIPO) were studied. The tautomerism of SEIPO was also studied by calculations using density functional theory (DFT). Two of the four tautomers were shown to coexist. Tautomerism and the effect of solvent on the tautomeric equilibria in the gas phase and in different solvents were studied. According to calculated results, L3, L4 tautomers are more stable than the L1, L2 tautomers. The 1 H NMR spectra give the additional evidence for the coexistence of the tautomers keto-amine and enol-imine for SEIPO. UV–vis spectra of SEIPO were recorded in various organic solvents to check the dependence of tautomerism on solvent types. The theoretical calculations and spectroscopic results indicate that the intramolecular hydrogen bonding (IHB) strength of SEIPO is stronger than that in 4-amino-3-penten-2-one)APO(. In addition, natural atomic charges, global reactivity parameters, and HOMO–LUMO gaps have also been discussed.

Fourier transform Raman and infrared spectral measurements have been made for the heptane-3,5-dione (HPD) and simultaneously compared with those of acetylacetone (AA) to give a clear understanding of substitution effect of ethyl groups (in β-positions) on the structure, electron delocalization, and intramolecular hydrogen bonding (IHB). Molecular structure, conformational stabilities, and intramolecular hydrogen bonding of different oxo-enol forms of HPD, have been investigated by MP2, BLYP, B2PLYP, TPSSh, and B3LYP methods, using various basis sets, and experimental results. The energy differences between four stable E1-E4 chelated forms are relatively negligible. The theoretical and experimental results obtained for stable oxo-enol forms of HPD have been compared with each other and also with those of AA. According to the theoretical calculations, HPD has a hydrogen bond strength of about 15.9 kcal/mol, calculated at the B3LYP/6-311++G** level, which is the same as AA, 15.9 kcal/mol. This similarity in the IHB strength is also consistent with the experimental results of the band frequency shifts for the OH/OD and O···O stretching and OH/OD out-of-plane bending frequencies and chemical shift of the O–H group. The molecular stability and the hydrogen bond strength also were investigated by applying the topological analysis, geometry calculations, and spectroscopic results. Potential energy distribution (PED) and normal coordinate analysis have also been performed. A complete assignment of the observed band frequencies has been suggested the presence of four HPD forms at comparable amounts in the sample.

The molecular structure and vibrational spectra of α-chloro and α-bromo derivatives of tris(acetylacetonato)chromium(III), Cr(ClAA)3 and Cr(BrAA)3, were investigated using the density functional theory (DFT) calculations. The geometrical parameters and harmonic vibrational wavenumbers of the titled compounds were obtained at the B3LYP level, using 6-311 + G(d) and 6-31G** basis sets. The calculated vibrational wavenumbers were compared with the corresponding experimental results and those of tris(acetylacetonato)chromium(III), Cr(AA)3. The effects of chlorine and bromine substitutions at the α-position on the vibrational spectra and geometry of Cr(AA)3 were studied. The α-halo substitution effects were also investigated using the natural bond orbital, NBO, analysis.

In this research, using nonequilibrium green's function (NEGF) integrated with density functional theory (DFT), we investigated the electronic transport properties of a bicyclic aziridine (2-nIiitro-4-(6-(4-nitrophenyl)-4-phenyl-1,3-diaza-bicyclo[3.1.0]hex-3-en-2-yl)phenol) molecular wire. The title molecule can be converted between two open and closed forms. The electronic transmission factors, spatial spreading of molecular projected self-consistent Hamiltonian (MPSH) orbitals, on-off ratio, I–V characteristics, the alteration of the electrode materials, Y, (Y = Au, Ag, and Pt), and HOMO–LUMO gaps relevant to these forms are thoroughly discussed. It can be concluded that due to the deformation of the title molecule (open → closed), there is a noticeable change in conductivity.

The synthesis and molecular structure of 3-nitroso-2,4-pentanedione, entitled to oxime-acetylacetone (oxime-AA), was studied utilizing Density Functional Theory (DFT) calculations and the results were compared with those of 3-nitro-pentane-2,4-dione (NO2AA) and 2-nitromalonaldehyde (NO2MA). The vibrational frequencies of the most stable cis-enol form were calculated using the B3LYP functional and 6-311++G(d,p) basis set. The calculated frequencies and chemical shifts of oxime-AA were compared with the experimental results. The calculated geometrical parameters for oxime-AA show a medium hydrogen bond compared with their α-substituted (NO2AA) and (NO2MA) which manifested the strong hydrogen bond. The calculated O⋯O distance of 2.460–2.561 A is about 0.002-0.104 A longer than in NO2AA and NO2MA. According to the theoretical calculations, oxime-AA has a structure with a hydrogen bond strength of about 21.0 kcal/mol (calculated with 6-311++G(d,p) basis set), which is 4.0–6.0 kcal/mol weaker than the hydrogen bond strength of NO2AA and NO2MA. This decrease in the hydrogen bond strength is also consistent with the experimental results. Natural Bond Orbital (NBO) and AIM analyses were applied for considering the hydrogen bond strength in oxime-AA that indicates the effect of NOH group decreases the hydrogen bond strength.

4-Alkylamino-3-penten-2-ones (R-APO), R = H, CH3, C2H5, CH(CH3)2, and C(CH3)3, were synthesized by amination of acetylacetone and the products were characterized by 1HNMR spectroscopy. The intramolecular hydrogen bonding (IHB) of R-APO molecules is studied, using 1HNMR and density functional theory calculations, also the effects of substitutions are investigated. According to the calculation results, the number of stable theoretical conformations of ethyl, isopropyl, methyl, and t-butyl substitutions is 2, 1, 1 and 1, respectively. All calculations are performed at the B3LYP/6–311++G(d,p) level. To understand the substitution effects on the nature of IHB and the electronic structure of the chelated ring system, the topological parameters, 1H NMR chemical shifts, geometrical parameters, natural bond orders, vibrational frequencies, and the natural charges over atoms involved in the chelated ring of 4-amino-3-penten-2-one (APO) and its derivatives were calculated. The Wiberg bond orders and the natural charges over atoms involved in the chelated ring have been computed by using the natural bond orbital (NBO) analysis. Based on the experimental 1HNMR and theoretical results, the strength of the intramolecular hydrogen bond in APOs is in the following order: t-Bu > ISO∼ Et ∼ Met > H. Several correlations between geometrical and topological parameters, vibrational wavenumbers, bond orders, and natural charges with the IHB strength and 1H NMR chemical shift are obtained.

The molecular structure and vibrational spectra of tris(acetylacetonato)chromium(III), Cr (AA) 3 , its mono-deuterated, Cr (DAA) 3 , and per-deuterated analogous, Cr(D 7 AA) 3 , were investigated using density functional theory (DFT) calculations. The geometry of the titled compound was fully optimized at the B3LYP level using 6-311 + G* and 6-31G** basis sets. The harmonic vibrational frequencies were obtained at the B3LYP/6-311 + G** level. Raman scattering activities were calculated at the B3LYP/6-31G** level. The calculated frequencies are compared with the experimental IR and Raman spectra. All of the measured IR and Raman bands were interpreted in terms of the calculated vibrational modes and isotopic frequency shifts. The scaled theoretical frequencies and the structural parameters are in excellent agreement with the experimental data. Analysis of the vibrational spectra indicates a strong coupling between the chelated ring modes. Several bands at 933, 680, 611, 594, 495, 250, 224, and 179 cm −1 are found to be engaged in Cr–O vibrational movements. The IR bands at 611 and 594 cm −1 are attributed to the asymmetric Cr–O stretching and the very strong Raman band at 460 cm −1 is assigned to the totally symmetric Cr–O stretching mode ( a1 species).

Molecular structures of the stable conformers of cis-enol and keto forms of 3-bromo-pentane-2,4-dione (α-bromo-acetylacetone, BrAA) have been investigated by means of Density Functional Theory (DFT) calculations and the results were compared with those of acetylacetone, AA, α-choloro-acetylacetone, ClAA, and α-fluoro-acetylacetone, FAA. The harmonic and anharmonic vibrational frequencies of the most stable cis-enol and keto forms were calculated at the B3LYP/6-311++G∗∗ level of theory. The calculated frequencies and the Raman and IR intensities were compared with the experimental results. According to the theoretical calculations the hydrogen bond strength for BrAA, ClAA, AA, and FAA are 90.5, 87.4, 75.8, and 65.9 kJ/mol, respectively. These results are in agreement with the vibrational and 1H NMR spectroscopy results. Natural bond orbital (NBO) and Atoms-in-Molecule (AIM) analyses were also used to investigate the nature of intramolecular hydrogen bond in the molecules.

A new copper (II) Schiff base complex, CuL1, was prepared from the reaction of asymmetrical Schiff base ligand of L1 and Cu(OAC)2 (L1 = salicylidene imino-ethylimino-pentan-2-one). The Schiff base ligand, L1, and its copper (II) complex, CuL1, have been characterized by elemental analysis (CHN) and FT-IR and UV–vis spectroscopy. In addition, 1H NMR was employed for characterization of the ligand. Thermogrametric analysis of the CuL1 reveals its thermal stability and its decomposition pattern shows that it is finally decomposed to the copper oxide (CuO). The crystal structure of CuL1 was determined by the single crystal X-ray analysis. The CuL1 complex crystallizes in the monoclinic system, with space group P21/n and distorted square planar coordination around the metal ion. The Schiff base ligand of L1 acts as a chelating ligand and coordinates via two nitrogen and two oxygen atoms to the copper (II) ion with C1 symmetry. The structure of the CuL1 complex was also studied theoretically at different levels of DFT and basis sets. According to calculated results the C O bond length of the salicylate fragment is slightly higher than that in the acetylacetonate fragment of ligand, which could be interpreted by resonance increasing between phenyl and chelated rings in ligand in relative to the acetylacetonate fragment.

Fourier transform Raman (3200–150 cm −1 ) and infrared (4000–100 cm −1 ) spectral measurements have been made for the solid copper (II) benzoylacetonate, Cu(bzac) 2 and, for comparison, copper (II) acetylacetonate, Cu(acac) 2 . The molecular electronic energies, equilibrium geometries, IR and Raman spectra, and the internal coordinates for the vibrational modes have been computed for the cis and trans structures of Cu(bzac) 2 at the B3LYP/6-311G * level of theory. Potential energy distribution (PED) and normal mode analysis have also been performed. A complete assignment of the observed band frequencies has been proposed. Comparing of observed and calculated vibrational spectra suggests that the predominant isomer in the sample is the trans isomer. To realize the effect of CH 3 substitution by phenyl group on the structure, metal–O bond strength, and vibrational spectra, the geometrical parameters and vibrational wavenumbers of Cu(acac) 2 were also calculated at the same level of theory. The calculated vibrational frequencies were compared with the experimental results. All of the measured IR and Raman bands were interpreted in terms of the calculated vibrational modes. The metal–O bond strength was investigated by geometry calculations and spectroscopic results. All theoretical and vibrational spectroscopic studies confirm stronger metal–ligand bond in Cu(bzac) 2 than that in Cu(acac) 2 .

1,2-Bis (monochloroacetyl) cyclopentadiene (MCACP) was synthesized and its molecular structure, intramolecular hydrogen bonding, and vibrational frequencies were investigated by means of density functional theory (DFT) calculations, NMR, and IR spectroscopies. It was found that the most stable conformers are those stabilized by intramolecular hydrogen bridges. Calculations at the B3LYP level, using 6-31G(d,p), 6-311G(d,p), and 6-311++G(d,p) basis sets, have been carried out for understanding the strength of hydrogen bond. In addition, the energies of the stable chelated conformers and their corresponding open structures were obtained at the MP2/6-31G(d,p) level of theory. The harmonic vibrational wavenumbers of MCACP and its deuterated analogue were obtained at the B3LYP/6-311++G(d,p) level. 1 H and 13 CNMR spectra were recorded and 1 H and 13 C nuclear magnetic resonance chemical shifts of the molecule were calculated using the gauge independent atomic orbital (GIAO) method. The calculated geometrical parameters and relative energies show formation of a very strong intramolecular hydrogen bond that is consistent with the frequency shifts for OH/OD stretching, OH/OD out-of-plane bending, and O⋯O stretching modes and proton chemical shift. The rotation of terminal CH 2 Cl groups indicates existence of two stable conformers that their hydrogen bond energy was estimated to be, on average, about 75.6 kJ/mol. The nucleus-independent chemical shift (NICS) data in the keto and enol forms indicated that in addition to differences in stability due to hydrogen bonding, differing stability also arises from the aromaticity increase of cyclopentadene (CP) ring in the chelated forms.

Molecular structure, intramolecular hydrogen bond (IHB), 1 H and 13 C chemical shifts, and vibrational assignment of newly prepared 1,2-bis (dichloroacetyl) cyclopentadiene (DCACP) , have been investigated by means of density functional theory (DFT) calculations. In addition, the geometry of the most stable conformer was also optimized at the MP2/6-31G** level. By calculations at the B3LYP level, using 6-311++G** basis set, the IR band frequencies of the most stable conformer and its deuterated analogue and the 13 C and 1 H chemical shifts were clearly assigned. In addition, the anharmonic vibrational wavenumbers in solution were also calculated at the B3LYP/6-31G** level. All theoretical calculations and experimental spectroscopy data are consistent with a very strong intramolecular hydrogen bond in this ζ-diketone. According to the theoretical calculations, the enolated proton in DCACP slightly deviates from half way between the two oxygen atoms, C s symmetry, which suggests existence of a low barrier double minimum potential for this system.

A series of β-substituted enaminones were prepared through the one-pot reaction of β-dicarbonyl compounds with various amines in the presence of silica ferric hydrogensulfate under solvent free conditions at room temperature. The reactions proceed smoothly in excellent yield, high chemoselectivity and with an easy work-up. Catalytic amount of Fe(HSO4)3·SiO2 catalyzed one-pot reaction of linear and cyclic β-diketones and β-keto esters with aromatic and aliphatic amines. The B3LYP/6-31G** full optimizations were carried out for enol-enamine tautomers of enaminones.

An efficient and easy method for one-pot three-component synthesis of 1,3-disubstituted-3H-benzo[f]chromenes by the condensation of naphtol, aromatic aldehyde derivatives and phenylacetylene in the presence of ferric hydrogensulfate [Fe(HSO4)3], has been described. The catalyst displayed high activity which afforded the corresponding 1,3-disubstituted-3H-benzo[f]chromenes in satisfying yields. Alkyl-substituted phenols were examined and the corresponding benzopyran derivatives were synthesized in moderate yields. Heterogeneous nature of the using catalyst made it reusable for further chemical reactions.

Molecular structure, intramolecular hydrogen bonding (IHB) and vibrational frequencies of 2,2,6,6-tetramethyl-3,5-heptanedione (TMHD, also known as dipivaloylmethane), have been investigated by means of the density functional theory (DFT) calculations and IR and Raman spectroscopies. In addition, the geometry of the cis- and trans-enol conformers were also optimized at the MP2/6-31G∗∗ level of theory. The results are compared with those of acetylacetone (AA), benzoylacetone (BA), and dibenzoylmethane (DBM). The energy differences between two stable E1 and E2 chelated enol forms, calculated at different levels of theory, are negligible. Comparing the calculated and experimental band frequencies and intensities suggests coexisting of two stable cis-enol conformers in comparable proportions in the sample. Also the IR and Raman spectra of TMHD and its deuterated analogue were clearly assigned. According to the theoretical calculations, TMHD has a hydrogen bond strength of about 17.8–18.0 kcal/mol, calculated at the B3LYP/6-311++G∗∗ level of theory, which is about 3.0 kcal/mol stronger than that of AA. This enhancement in the IHB strength is also consistent with the experimental results of the band frequency shifts for the modes of OH/OD and O ⋯ O stretching and OH/OD out-of-plane bending frequencies. The theoretical calculations and spectroscopic results indicate that the IHB strength of TMHD is between those of AA and DBM.

The conformational stabilities of different tautomers of 2-thenoyltrifluoroacetone (4,4,4-trifluoro-1-(2-thienyl)butane-1,3-dione, TTFA) in several solutions have been investigated at the B3LYP level using 6-311++G** basis set. The self-consistent Onsager reaction field model was used to study the solvent effects. It was determined that the energy differences of the most stable conformers (stabilized by the hydrogen bridge), which are negligible in the gas phase, increase in the solvent media. The harmonic vibrational frequencies were calculated at the B3LYP level using 6-31G** and 6-311G** basis sets. A complete vibrational assignment has been clearly provided for the experimental IR and Raman spectra of TTFA and its deuterated analogue, which shows coexisting of four conformations in the sample. This vibrational spectroscopy analyses confirms more content of the “A” forms in the solution than the “B” forms, although the reverse is true in the solid state, in agreement with the theoretical DFT calculations and the experimental X-ray results.

Molecular structure and vibrational frequencies of 4,4,4-trifluoro-1-phenyl-1,3-butanedione, known as trifluorobenzoylacetone (TFBA), have been investigated by means of density functional theory (DFT) calculations. The results were compared with those of benzoylacetone (BA), acetylacetone (AA), and trifluoroacetylacetone (TFAA). Comparing the calculated and experimental band frequencies and intensities suggests coexisting of both stable cis-enol conformers in comparable proportions in the sample. The energy difference between the two stable chelated enol forms is negligible, 0.96 kcal/mol, calculated at B3LYP/6-311++G** level of theory. The molecular stability and the hydrogen bond strength were investigated by applying the natural bond orbital (NBO) theory and geometry calculations. The theoretical calculations and spectroscopic results indicate that the hydrogen bond strength of TFBA is between those of TFAA and AA, considerably weaker than that of BA.