Synthesis, Experimental and Theoretical Study of Azidochromones.

A series of 2-(haloalkyl)-3-azidomethyl and 6-azido chromones has been synthetized, characterized and studied by theoretical (DFT calculations) and spectroscopic methods (UV-Vis, NMR). The crystal structure of 3-azidomethyl-2-difluoromethyl chromone, determined by X-ray diffraction methods, shows a planar framework due to extended π-bond delocalization. Its molecular packing is stabilized by F···H, N···H and O···H hydrogen bonds, π···π stacking and C-O···π intermolecular interactions. Moreover, AIM, NCI and Hirshfeld analysis evidenced that azido moiety has a significant role in the stabilization of crystal packing through weak intermolecular interactions, where analysis of electronic density suggested closed-shell (CS) interatomic interactions.

Survey of clenbuterol in bovine muscle and liver in Ecuador.

Clenbuterol is a steroid-type drug used in respiratory treatments in both humans and animals. However, it has a secondary effect related to the hypertrophy process in muscle and fat reduction. The illegal or bad use of clenbuterol has been reported in several countries, but there is scarce information in South America, where the production and consumption of meat are considerable. In this sense, the present study aimed at evaluating the occurrence of clenbuterol in bovine muscle and liver samples from a high cattle production area of Ecuador in 2015 and 2018. For this purpose, 57-58 samples were evaluated in 2015 and 20 samples in 2018 using the Enzyme-Linked Inmuno Sorbent Assay and ultrahigh-performance liquid chromatography-tandem mass spectrometry. The results showed complained results for clenbuterol in meat samples from both years and 23% (2015) and 85% (2018) of the samples of meat complied the maximum residue level defined by CODEX.

Enol-imino-Keto-enamine Tautomerism in a Diazepine Derivative: How Decisive Are the Intermolecular Interactions in the Equilibrium?

The strange tautomeric equilibrium behavior exhibited by a new o-hydroxyphenyl diazepine derivative when the compound is analyzed both in solution and solid state opens the structural study of the enol-imino-keto-enamine forms and the influence of the intermolecular interactions in their equilibrium. The expected enol-imino form, in which the enol is part of a phenyl system and a strong O-H···N intramolecular hydrogen bond is established, results the most stable tautomer in gas phase (theoretical calculations) and was detected by NMR spectroscopy when the compound was dissolved in aprotic solvents. Nevertheless, the keto-enamine form ,in which the keto group integrates a cyclohexadienone moiety and the aromaticity of the phenol is lost, was the only tautomer in the crystal lattice according to single-crystal X-ray diffraction, vibrational spectroscopy, and diffuse reflectance results. The last form was also found as the main tautomer in UV-vis and NMR spectroscopy when a protic solvent was employed.

Exploratory Monitoring of the Quality and Authenticity of Commercial Honey in Ecuador.

Honey is one of the oldest sweetening foods and has economic importance, making this product attractive to adulteration with cheap sugars. This can cause a critical problem in the honey industry and a possible health risk. The present work has the aim of evaluating the authenticity of honey commercialized in two different provinces of Ecuador (Pichincha and Loja) by performing physicochemical and spectroscopic analyses. For this study 25 samples were collected from different places and markets and characterized by water, sucrose, reducing sugars and electric conductivity measurement. Also, their Raman and Infrared (IR) spectra were recorded and analysed using a Principal Component Analysis (PCA) in order to verify the quality of the honeys. In addition, a screening of several pesticides was performed in order to verify possible chemical threats to human health and honey bees. It was found that 8 samples have a deviation from the Standard established parameters. Two of them have a high difference in the content of sucrose and reducing sugars, which are located deviated from all the other samples in the PCA of the applied vibrational spectroscopy (IR/Raman), shaping two clear clusters. The results show that Raman and IR spectroscopy is appropriate techniques for the quality control of honey and correlates well with the physicochemical analyses.

Dimers of perhaloacetyl cyanides: CClF2C(O)OC(CN)2CClF2 and CF3C(O)OC(CN) 2CF3. preparation, properties, and spectroscopy.

The vapor of the new compound 1,1-dicyano-2-chloro-2,2-difluoroethyl chlorodifluoroacetate, CClF2C(O)OC(CN)2CClF2 and of the known 1,1-dicyano-2,2,2-trifluoroethyl trifluoroacetate, CF3C(O)OC(CN)2CF3, were investigated using vibrational spectroscopy tools. The existence of rotational isomerism was confirmed for CClF2C(O)OC(CN)2CClF2 when the matrix isolated compound was examined in combination with the computational results applying quantum chemical models. From the four conformers gauche-syn-gauche, gauche-syn-anti, syn-syn-anti, syn-syn-gauche (the used nomenclature is with respect to the ϕ(ClC-C(O)), ϕ((O)C-OC), and ϕ(OC-CCl) torsion angles, respectively) predicted for CClF2C(O)OC(CN)2CClF2 the first two forms can be evidenced using Ar-matrix IR spectroscopy, with the first one being the most abundant at room temperature. On the other side, the results obtained for CF3C(O)OC(CN)2CF3 reveals the existence of only one syn-syn-anti form. CClF2C(O)OC(CN)2CClF2 melts at -40 °C and its vapor pressure was fitted by the equation ln p = -4732.6 (1/T) + 10.75 (p [Atm], T [K]) in the range -20 to 20 °C. Its extrapolated boiling point is 167 °C. The first ionization potentials occur for CClF2C(O)OC(CN)2CClF2 and CF3C(O)OC(CN)2CF3 at 12.13 and 12.43 eV, respectively, and were attributed to the ejection of electrons formally located at the carbonylic oxygen lone-pair electrons (nO). The proposed interpretation of the photoelectron spectrum is consistent with related molecules reported previously, and also with the prediction of Outer Valence Green's Functions (OVGF).

Matrix photochemical study and conformational analysis of CH3C(O)NCS and CF3C(O)NCS.

The vapor of acetyl isocyanide, CH3C(O)NCS, and trifluoroacetyl isocyanide, CF3C(O)NCS, were isolated in solid Ar at 15 K. The existence of rotational isomerism was confirmed when the matrixes were irradiated with broad-band UV-vis light (200 ≤ λ ≤ 800 nm) and also by temperature-dependent Ar-matrix IR spectroscopy. The initial spectra showed the vapor of CH3C(O)NCS and CF3C(O)NCS consist of two conformers syn-syn and syn-anti (with the C═O bond syn with respect to the C-H or C-F bond and syn or anti with respect to the N═C double bond). When CH3C(O)NCS is irradiated, simultaneously with the randomization process, H2CCO and HSCN are produced. In the case of the photolysis of CF3C(O)NCS, the main products are CF3NCS and CO. The assignment of the IR bands to the different photoproducts was made on the basis of the usual criteria, taking account reported antecedents in the literature.

Chlorodifluoroacetyl isothiocyanate, ClF2CC(O)NCS: preparation and structural and spectroscopic studies.

Chlorodifluoroacetyl isothiocyanate, ClF2CC(O)NCS, was synthesized by the reaction of ClF2CC(O)Cl with an excess of AgNCS. The colorless product melts at -85 °C, and its vapor pressure follows the equation ln p = -4471.1 (1/T) + 11.35 (p [atm], T [K]) in the range -38 to 22 °C. The compound has been characterized by IR (gas phase, Ar matrix, and matrix photochemistry), by liquid Raman, by (19)F and (13)C NMR, gas UV-vis, and photoelectron spectroscopy (PES), by photoionization mass spectrometry (PIMS), and by gas electron diffraction (GED). The conformational properties of ClF2CC(O)NCS have been analyzed by joint application of vibrational spectroscopy, GED and quantum chemical calculations. The existence of two conformers has been detected in the gas and liquid phases, in which the C-Cl bond adopts a gauche orientation with respect to the C═O group; the C═O group is in syn- or anti-position with respect to the N═C double bond of the NCS group. The computed ΔG° difference between these two gauche-syn and gauche-anti forms is ΔG° = 0.63 kcal mol(-1) in the B3LYP/6-31G(d) approximation. The most significant gas-phase structural parameters for gauche-syn ClF2CC(O)NCS are re(NC═S) 1.559(2) Å, re(N═CS) 1.213(2) Å, re(N-C) 1.399(7) Å, re(C═O) 1.199(2) Å, and ∠e(CNC) 134.7(13)°. Photolysis of ClF2CC(O)NCS using an ArF excimer laser (193 nm) mainly yields ClF2CNCS, CO, and ClC(O)CF2NCS. The valence electronic properties of the title compound were studied using PES and PIMS. The experimental first vertical ionization energy of 10.43 eV corresponds to the ejection primarily of the sulfur lone-pair electrons of the in-plane nonbonding orbital on the NCS group.

Spectroscopic characterization and constitutional and rotational isomerism of ClC(O)SCN and ClC(O)NCS.

Chlorocarbonylthio- and isothiocyanate (ClC(O)SCN and ClC(O)NCS) have been isolated and characterized by IR (Ar matrix, gas), Raman (liquid), (13)C NMR and UV-visible spectroscopies. Vibrational and quantum chemical studies suggest the presence of the syn and anti conformers (SCN group with respect to the C═O bond) in the gas phase for both constitutional isomers. syn-ClC(O)SCN is preferred by ΔH° (anti/syn) = 1.3(0.3) kcal mol(-1). The solid-state structure of ClC(O)SCN has been determined by single crystal X-ray diffraction analysis at low temperature. The crystalline solid consists exclusively of molecules in the syn conformation. On the other hand, the anti form is more stable for the ClC(O)NCS isomer. The structure of ClC(O)NCS and its conformational composition were determined by gas electron diffraction. An unusual low syn → anti interconversion energy barrier of 0.98 (0.15) kcal mol(-1) was detected for ClC(O)NCS at cryogenic temperatures. The photochemistry of both constitutional isomers isolated in solid argon at 15 K was studied. Rearrangement of ClC(O)SCN to ClC(O)NCS was observed in the neat liquid and under UV-vis irradiation of ClC(O)SCN isolated in solid argon. Properties have been discussed in terms of the valence electronic structure, including the analysis of the He(I) photoelectron spectrum of ClC(O)SCN.

Chlorodifluoroacetyl isocyanate, ClF2CC(O)NCO: preparation and structural and spectroscopic studies.

Chlorodifluoroacetyl isocyanate, ClF2CC(O)NCO, was prepared by the reaction of ClF2CC(O)Cl with excess of AgNCO. The colorless compound melts at −83 °C and the vapor pressure follows the equation ln p = −3868.3 (1/T) + 10.89 (p [Atm], T [K]) in the range −38 to +22 °C, extrapolated bp ca. 82 °C. It has been characterized by IR (gas phase, Ar matrix), liquid Raman, 19F and 13C NMR, gas UV­vis spectrum, photoelectron spectroscopy (PES), photoionization mass spectrometry (PIMS), and gas electron diffraction (GED). The matrix photochemistry has been studied and the conformational properties of ClF2CC(O)NCO have been analyzed by joint application of vibrational spectroscopy, GED, and quantum chemical calculations. Two conformers were detected in gaseous and liquid phases, in which the C­Cl bond adopts a gauche orientation with respect to the C═O group, whereas this group can be in syn or anti orientation with respect to the N═C bond of the NCO group. An enthalpy difference ΔH(exp)° = 1.3 ± 0.2 kcal mol(­1) between the most stable syn­gauche and the less stable anti-gauche form was derived using the van't Hoff equation, which is in reasonable agreement with the computed difference of ΔH° = 0.8 kcal mol(­1) (B3LYP/6-311+G(3df) approximation). The most significant gas phase structural parameters for gauche­syn ClF2CC(O)NCO are r(e)(NC═O) = 1.157(1) Å, r(e)(N═CO) = 1.218(1) Å, r(e)(N­C) = 1.378(9) Å, r(e)(C═O) = 1.195(1) Å, angle(e)(CNC) = 128.6(19)°. Photolysis of ClF2CC(O)NCO using an ArF excimer laser (193 nm) mainly yield ClF2CNCO along with some ClF2CC(O)N nitrene. The valence electronic properties of the title compound were studied using the PES and PIMS. The experimental first vertical ionization energy of 11.54 eV corresponds to the ejection of a carbonylic oxygen lone pair electron.

Chlorodifluoroacetyl azide, ClF2CC(O)N3: preparation, properties, and decomposition.

Chlorodifluoroacetyl azide, ClF(2)CC(O)N(3), was prepared and characterized by IR (gas, Ar matrix), Raman (liquid), UV-vis (gas), and (19)F, (13)C NMR spectroscopy. The vibrational spectra were analyzed in terms of a single conformer, gauche-syn, where the Cl-C and the N(α)═N(ß) bonds are gauche and syn to the C═O bond, respectively. The photo and thermal decomposition reactions of the azide were studied with the aid of matrix isolation. In both cases, a new isocyanate species ClF(2)CNCO was produced and characterized by matrix IR spectroscopy. The conformational properties and the Curtius rearrangement pathways of this new carbonyl azide were theoretically explored, which suggest the preference of a concerted over stepwise decomposition for the global minimum gauche-syn conformer.

Chlorodifluoroacetyl cyanide, ClF2CC(O)CN: synthesis, structure, and spectroscopic characterization.

The novel molecule difluorochloroacetyl cyanide, ClF(2)CC(O)CN, has been characterized by IR (gas phase, Ar matrix), Raman (liquid), (19)F and (13)C NMR, and photoelectron (PES) spectroscopies; photoionization mass spectrometry (PIMS); and gas electron diffraction (GED). The conformational properties of ClF(2)CC(O)CN have been studied by joint application of vibrational spectroscopy, GED, and quantum chemical calculations. The existence of two conformers is detected in the gas and liquid phases, in which the C-Cl bond adopts gauche and syn orientations with respect to the C═O group. The computed enthalpy difference is in harmony with the experimental results of the gauche being more stable than the syn conformer by ΔH° = 1.3 kcal mol(-1) (MP2/cc-pVTZ). The valence electronic properties and the possible ionization and dissociation processes of the title compound are studied using the PES and PIMS. The experimental first vertical ionization energy of 12.0 eV corresponds to the ejection of an electron of the oxygen lone pairs. Taking into account the properties and broad applications of acyl cyanides, ClF(2)CC(O)CN is a promising new precursor in preparative chemistry.

2-Chloroethylisocyanate. Thermal decomposition and spectroscopic properties.

2-Chloroethylisocyanate has been studied in a thorough way. NMR, Raman, FTIR, and Ar-matrix vibrational spectra of the molecule are presented and discussed with the complement of ab initio and DFT methods. The spectroscopic results reveal the existence of anti and gauche conformers that are equally populated in the gas phase. Thermal decomposition between 393 and 648 K shows two different pathways depending on the temperature, which can be interpreted in terms of simple second- and first-order mechanisms, respectively. Quantum mechanical calculations reproduce the experimental results.

Vibrational spectra, crystal structures, constitutional and rotational isomerism of FC(O)SCN and FC(O)NCS.

Fluorocarbonyl thio- and isothiocyanate, FC(O)SCN and FC(O)NCS, were fully characterized by IR (gas, Ar and N(2) matrixes), Raman (liquid and solid), UV (gas), and (13)C NMR (liquid) spectroscopy, as well as single-crystal X-ray diffraction. Their vibrational and conformational properties were analyzed using matrix isolation techniques guided by quantum chemical calculation at the ab initio [MP2 and CCSD(T)], density functional theory B3LYP, and CBS-QB3 levels of theory. A complete assignment of the fundamental modes of FC(O)SCN was performed. In both the gas and liquid states, FC(O)SCN and FC(O)NCS were found to exist as two conformers (C(s) symmetry), in which the carbonyl double bond (C═O) adopts a synperiplanar (syn) and an antiperiplanar (anti) orientation with respect to either the SCN or NCS group. For FC(O)SCN, the conformational enthalpy difference, ΔH° = H°(anti) - H°(syn), was determined by matrix IR experiments to be 0.9 ± 0.2 kcal mol(-1). The conformational equilibria were evaluated by fast-cooling gaseous samples highly diluted in argon at different temperatures as cryogenic matrixes. The conformational properties of both molecules were analyzed in terms of the hyperconjugative electronic effect applying the natural bond orbital method. The kinetics of the thermal conversion of the high-energy anti into the syn FC(O)NCS conformer was studied in Ar and N(2) matrixes at cryogenic temperatures. The reversed syn → anti photoisomerization was observed using UV-vis light. Rearrangement of FC(O)SCN into FC(O)NCS was observed in the neat liquid and in solution. Under 193 nm (ArF excimer laser) irradiation, FC(O)NCS isolated in cryogenic Ar matrixes forms FC(O)SCN. At low temperature, single crystals of the two constitutional isomers were obtained using a miniature zone melting procedure. According to X-ray diffraction, they exclusively crystallize in their syn forms (C(s) symmetry) in the orthorhombic crystal system.

Synthesis, spectroscopic characterization, and conformational properties of trichloromethanesulfenyl acetate, CCl3SOC(O)CH3.

Trichloromethanesulfenyl acetate, CCl 3SOC(O)CH 3, belongs to the family of sulfenic esters. This molecule has been characterized by vibrational spectroscopy. The conformational and geometrical properties of this species have been determined by IR and Raman spectroscopy, X-ray diffraction, and quantum chemical calculations. Geometry optimizations of the most stable forms were performed with ab initio (HF, MP2) and density functional theory (B3LYP) methods. According to our data, this compound results in a gauche-syn conformer with C 1 symmetry (gauche orientation around the S-O bond and syn orientation of the CO double bond with respect to the S-O single bond) for the most stable geometry, and trans-syn conformer with C s symmetry (trans orientation around the S-O bond and syn orientation of the CO double bond with respect to the S-O single bond) for the second stable conformer (1.1 and 0.53 kcal/mol higher in energy than the most stable C 1 form according to the matrix FTIR spectroscopy and MP2/6-31G* level of the theory, respectively). The crystalline solid (monoclinic, P2 1/ n, a = 8.0152(17) A, b = 5.7922(13) A, c = 17.429(4) A, alpha = gamma = 90 degrees , beta = 100.341(3) degrees ) consists exclusively of the main form. The geometrical parameters (X-ray diffraction) are d C-Cl = 1.767(19) A, d C-S = 1.797(2) A, d S-O = 1.663(14) A, d CO = 1.189(2) A, d O-C = 1.389(3) A, d C-C = 1.483(3) A, angles Cl-C-Cl = 110.3(11) degrees , Cl-C-S = 111.8(12) degrees , C-S-O = 97.4(8) degrees , S-O-C = 116.7(11) degrees , O-CO = 122.8(19) degrees , OC-C = 127.1(2) degrees , and the main torsion angles are delta(CSOC) = 105.9(15) degrees and delta(SOC(O)) = 7.6(3) degrees . The geometrical data calculated with B3LYP/6-31G++(3df,3pd), B3LYP/6-311G++(3df,3pd), B3LYP/aug-cc-pVTZ, and MP2/6-31G* are in good agreement with diffraction data.

Preparation and properties of trifluorothioacetic acid-S-(trifluoromethyl)ester, CF3C(O)SCF3.

Trifluorothioacetic acid-S-(trifluoromethyl)ester, CF3C(O)SCF3, was prepared by reacting CF3C(O)Cl and AgSCF3 at 50 degrees C. The compound was characterized by (13)C-, (19)F-NMR, UV, and vibrational spectroscopy as well as by gas electron diffraction (GED) and quantum chemical calculations (HF, MP2, and B3LYP methods 6-31G(d) and 6-311+G(2df) basis sets). GED and vibrational spectroscopy result in the presence of a single conformer with C1 symmetry and synperiplanar orientation of the S-CF3 bond relative to the CO bond. This result is in agreement with quantum chemical calculations which predict the anti conformer to be higher in energy by about 4 kcal/mol. An assignment of the IR (gas) and Raman (liquid) spectra is proposed, and the GED analysis results in the following skeletal geometric parameters (r(a) and angle(a) values with 3sigma uncertainties; these parameters are thermal averages and are not inconsistent with calculated equilibrium values): C=O = 1.202(6) A, C-C = 1.525(10) A, S-C(sp(2)) = 1.774(3) A, S-C(sp(3)) = 1.824 (3) A. O=C-C = 118.7(21) degrees, O=C-S = 127.1(15) degrees, C-S-C = 99.8 (13) degrees.

S-(fluoroformyl)O-(trifluoroacetyl) thioperoxide, FC(O)S-OC(O)CF3: gas-phase structure and conformational properties.

The geometric structure and conformational properties of S-(fluoroformyl)O-(trifluoroacetyl) thioperoxide, FC(O)S-OC(O)CF3, were investigated by gas electron diffraction, matrix isolation infrared spectroscopy, and quantum chemical calculations (B3LYP with the 6-31G and aug-cc-pVTZ basis sets and MP2 with the 6-31G basis set). The experimental methods result in a mixture of two conformers with gauche conformation around the S-O bond. In the main conformer (82(7)% according to GED at 298 K), the C=O bond of the FC(O) group is oriented syn with respect to the S-O bond and phi(C-S-O-C) = 75(3) degrees . In the minor conformer (18(7)%), this C=O is oriented anti. Both conformers possess syn orientation of the C=O bond of the CF3C(O) group. The conformational properties and geometric parameters are reproduced reasonably well by the quantum chemical calculations, except for the S-O bond length, which is predicted too long by 0.04 A (B3LYP/aug-cc-pVTZ).

Trifluoromethanesulfenyl acetate, CF3S-OC(O)CH3, and trifluoromethanesulfenyl trifluoroacetate, CF3S-OC(O)CF3: unexpected conformational properties.

Structural and conformational properties of two sulfenyl derivatives, trifluoromethanesulfenyl acetate, CF3S-OC(O)CH3 (1), and trifluoromethanesulfenyl trifluoroacetate, CF3S-OC(O)CF3 (2), were determined by gas electron diffraction, vibrational spectroscopy, in particular with IR (matrix) spectroscopy, which includes photochemical studies, and by quantum chemical calculations. Both compounds exist in the gas phase as a mixture of two conformers, with the prevailing component possessing a gauche structure around the S-O bond. The minor form, 15(5)% in 1 and 11(5)% in 2 according to IR(matrix) spectra, possesses an unexpected trans structure around the S-O bond. The C=O bond of the acetyl group is oriented syn with respect to the S-O bond in both conformers. UV-visible broad band irradiation of 1 and 2 isolated in inert gas matrixes causes various changes to occur. Conformational randomization clearly takes place in 2 with simultaneous formation of CF3SCF3. For 1 the only reaction channel detected leads to the formation of CH3SCF3 with the consequent extrusion of CO2. Quantum chemical calculations (B3LYP/6-31G and MP2 with 6-31G and 6-311G(2df,pd) basis sets) confirm the existence of a stable trans conformer. The calculations reproduce the conformational properties for both compounds qualitatively correct with the exception of the B3LYP method for compound 2 which predicts the trans form to be prevailing, in contrast to the experiment.