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A Molecular Electron Density Theory (MEDT) study of the regio- and stereoselectivity of the [3 + 2] cycloaddition (32CA) reaction of 1 H -phosphorinium-3-olate and 1-methylphosphorinium-3-olate with methyl methacrylate was carried out using the B3LYP/6-31G(d) method. In order to test the method dependence for the most favorable reaction path leading to the 1 H -substituted 6- exo cycloadduct (CA) various functionals using higher basis sets were taken into consideration in the gas phase. An analysis of the energetic parameters indicates that the reaction path leading to 6- exo CA are kinetically as well as thermodynamically favored in the gas phase, THF and ethanol. The calculated energetic parameters of the 32CA reaction of these phosphorus derivatives were compared with those of methyl acrylate and their nitrogen analogues. Investigation of the global electron density transfer at the TSs indicates that these 32CA reactions have non-polar character, while electron localisation function topological analysis of the C-C bond formation along the most favorable reaction path indicates that these 32CA reactions take place through a non-concerted two-stage one-step mechanism, via highly asynchronous TSs., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

We have theoretically studied the non-identity S N 2 reactions of M n OH (n-1) +CH 3 Cl (M + =Li + , Na + , K + , and MgCl + ; n=0, 1) in the gas phase and in THF solution at the OLYP/6-31++G(d,p) level using polarizable continuum model (PCM) implicit solvation. We want to explore and understand the effect of the metal counterion M + and solvation on the reaction profile and the stereoselectivity of these processes. To this end, we have explored the potential energy surfaces of the backside (S N 2-b) and frontside (S N 2-f) pathways. To explain the computed trends, we have carried out analyses with an extended activation strain model (ASM) of chemical reactivity that includes the treatment of solvation effects., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A novel Pd-ZnO-expanded graphite (EG) photoelectrode was constructed from a Pd-ZnO-EG nanocomposite synthesised by a hydrothermal method and characterised using various techniques such as X-ray diffractometry (XRD), Raman spectroscopy, UV-Vis diffuse reflectance spectroscopy, nitrogen adsorption-desorption analysis, transmission electron microscopy (TEM), scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS). Cyclic voltammetry and photocurrent response measurements were also carried out on the electrode. The Pd-ZnO-EG electrode was employed in the photoelectrocatalytic removal of 4-nitrophenol as a target water pollutant at a neutral pH and with a current density of 7 mA cm -2 . Optical studies revealed that the Pd-ZnO-EG absorbed strongly in the visible light region. The Pd-ZnO-EG electrode showed improved photoelectrocatalytic activity in relation to ZnO-EG and EG electrodes for the removal of the 4-nitrophenol. The photocurrent responses showed that the Pd-ZnO-EG nanocomposite electrode could be employed as a good photoelectrode for photoelectrocatalytic processes and environmental remediation such as treatment of industrial waste waters. Density functional theory method was used to model the oxidative degradation of 4-nitrophenol by the hydroxyl radical which generates hydroquinone, benzoquinone, 4-nitrocatechol, 4-nitroresorcinol and the opening of the 4-nitrophenol ring. Furthermore, the hydroxyl radical is regenerated and can further oxidise the ring structure and initiate a new degradation process., Competing Interests: There are no conflicts of interest to declare., (This journal is © The Royal Society of Chemistry.)

Density functional theory and time-dependent density functional theory computations were used to understand the electronic and photophysical parameters of NIR β-thiophene-fused BF 2 -azadipyrromethene dyes. The computed data are in good agreement with those obtained experimentally and they provide insights into the origin of red shifted optical spectra compared to the parent aza-BODIPY, low Stokes shift, non-linear optical responses and quantitative description of the singlet-triplet energy gap. The resultant decrease in the HOMO - LUMO energy gap is responsible for the red shift. The possible use as non-linear optical materials is supported by large enhancement in the non-linear optical properties. On the basis of vertical triplet energies, their possible potential therapeutic use as a photosensitizer in photodynamic therapy is proposed. The singlet-triplet energetic gaps suggest that the β-thiophene-fused BF 2 -azadipyrromethene dyes can act as a sensitizer to produce an efficient generation of singlet oxygen. Their optimal use as an efficient singlet fission materials has been proposed on the basis of excitation energies in the ground, lowest singlet and triplet excited states.

Metal-cyclen complexes have a number of important applications. However, the coordination chemistry between metal ions and cyclen-based macrocycles is much less well studied compared to their metal ion-crown ether analogues. This work, which makes a contribution to address this imbalance by studying complex ions of the type [M(Me 4 cyclen)(L)] + , was initiated by results of an experimental study which prepared some Group 1 metal cyclen complexes, namely [Li(Me 4 cyclen)(H 2 O)][BAr F ] and [Na(Me 4 cyclen)(THF)][BAr F ] and obtained their X-ray crystal structures [J. M. Dyke, W. Levason, M. E. Light, D. Pugh, G. Reid, H. Bhakhoa, P. Ramasami, and L. Rhyman, Dalton Trans., 2015, 44, 13853]. The lowest [M(Me 4 cyclen)(L)] + minimum energy structures (M = Li, Na, K, and L = H 2 O, THF, DEE, MeOH, DCM) are studied using density functional theory (DFT) calculations. The geometry of each [M(Me 4 cyclen)(L)] + structure and, in particular, the conformation of L are found to be mainly governed by steric hindrance which decreases as the size of the ionic radius increases from Li + → Na + → K + . Good agreement of computed geometrical parameters of [Li(Me 4 cyclen)(H 2 O)] + and [Na(Me 4 cyclen)(THF)] + with the corresponding geometrical parameters derived from the crystal structures [Li(Me 4 cyclen)(H 2 O)] + [BAr F ] - and [Na(Me 4 cyclen)(THF)] + [BAr F ] - is obtained. Bonding analysis indicates that the stability of the [M(Me 4 cyclen)(L)] + structures originates mainly from ionic interaction between the Me 4 cyclen/L ligands and the M + centres. The experimental observation that [M(Me 4 cyclen)(L)] + [BAr F ] - complexes could be prepared in crystalline form for M + = Li + and Na + , but that experiments aimed at synthesising the corresponding K + , Rb + , and Cs + complexes failed resulting in formation of [Me 4 cyclenH][BAr F ] is investigated using DFT and explicitly correlated calculations, and explained by considering production of [Me 4 cyclenH] + by a hydrolysis reaction, involving traces of water, which competes with [M(Me 4 cyclen)(L)] + formation. [Me 4 cyclenH] + formation dominates for M + = K + , Rb + , and Cs + whereas formation of [M(Me 4 cyclen)(L)] + is energetically favoured for M + = Li + and Na + . The results indicate that the number and type of ligands, play a key role in stabilising the [M(Me 4 cyclen)] + complexes and it is hoped that this work will encourage experimentalists to prepare and characterise other [M(Me 4 cyclen)(L)] + complexes.

This study reports the synthesis and comparative investigation of the substituent effects of a new series of highly luminescent homoleptic tris-cyclometalated iridium(III) complexes of the type [Ir(N ˄ C)₃]. These are based on two ligand type derivatives comprising of 4-fluorophenylvinylquinolines and 4-methoxyphenylvinylquinolines with electron-donating and/or electron-withdrawing groups as aryl substituents at 2-position. The structures of the ligands and their complexes were characterized by means of FT-IR, UV-Vis and NMR spectrometry complemented with photoluminescence and cyclic voltammetry. The photophysical properties of 2-aryl-4-(4-fluorophenylvinyl)quinoline and its corresponding complex were also studied using the density functional theory method. The photoluminescent properties of the ligands and the corresponding complexes showed high fluorescent intensities and quantum yields in solvents of different polarities. The photoluminescence spectra of the complexes in solid film, showed common transmission curves at longer wavelengths maximum (λ em = 697 nm) possibly originating from the interference of scattered light of higher-order transmission of monochromators., Competing Interests: The authors declare no conflict of interest.

The processing of the input and output files of quantum chemical calculations often necessitates a spreadsheet as a key component of the workflow. Spreadsheet packages with a built-in programming language editor can automate the steps involved and thus provide a direct link between processing files and the spreadsheet. This helps to reduce user-interventions as well as the need to switch between different programs to carry out each step. The ExcelAutomat tool is the implementation of this method in Microsoft Excel (MS Excel) using the default Visual Basic for Application (VBA) programming language. The code in ExcelAutomat was adapted to work with the platform-independent open-source LibreOffice Calc, which also supports VBA. ExcelAutomat provides an interface through the spreadsheet to automate repetitive tasks such as merging input files, splitting, parsing and compiling data from output files, and generation of unique filenames. Selected extracted parameters can be retrieved as variables which can be included in custom codes for a tailored approach. ExcelAutomat works with Gaussian files and is adapted for use with other computational packages including the non-commercial GAMESS. ExcelAutomat is available as a downloadable MS Excel workbook or as a LibreOffice workbook.

2,4-Ditellurouracil exhibits keto-enol tautomerism via different pathways resulting in seven tautomers. These pathways were studied in the gas phase using density functional theory method. The functionals used were BLYP, B3LYP and BHLYP and the basis sets were 6-311++G(d,p) for all atoms except that LanL2DZ ECP was used for tellurium atom only. The results indicate that the diketo form is more stable as observed for uracil and its sulfur and selenium analogues. The effect of introducing fluorine at position 5 was also investigated and the energy difference between the diketo and dienol forms is reduced. 2,4-Ditellurouracil and its 5-fluoro analogue are expected to exist exclusively as the diketo form due to the high interconversion energy barrier. We extended the investigation to predict ADME parameters of the most stable diketo and dienol tautomers in view of understanding their biological properties. This research enlightens keto-enol tautomerism of 2,4-ditellurouracil and its 5-fluoro derivative with additional insights to biological functions., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

The electronic structures and spectroscopic properties of triphenylamine-based monostyryl and bis(styryl) dyes were studied using quantum chemical methods. The ground-state geometries of these dyes were optimized using the density functional theory (DFT) method. The lowest singlet excited state was optimized using time-dependent density functional theory (TD-DFT). The absorption was also calculated using the ground-state geometries. All the calculations were carried out in the gas phase and in solvent. The results indicate that the absorption maxima calculated using the TD-DFT are in good agreement with those obtained experimentally. These dyes possess a large second-order non-linear property and this is mainly due to the strong donor-π-acceptor conjugation which is attributed to the excited state intramolecular charge transfer (ICT). There is a relationship between the hardness and first hyperpolarizability and second hyperpolarizability of mono- and bis(styryl) dyes. The efficiency of the intersystem crossing process can be improved by reducing the energy gap between the singlet and triplet excited states.

The structures of the mono- and the dihalogenated N -unsubstituted 2-aminobenzamides were characterized by means of the spectroscopic (¹H-NMR, UV-Vis, FT-IR, and FT-Raman) and X-ray crystallographic techniques complemented with a density functional theory (DFT) method. The hindered rotation of the C(O)-NH₂ single bond resulted in non-equivalence of the amide protons and therefore two distinct resonances of different chemical shift values in the ¹H-NMR spectra of these compounds were observed. 2-Amino-5-bromobenzamide ( ABB ) as a model confirmed the presence of strong intramolecular hydrogen bonds between oxygen and the amine hydrogen. However, intramolecular hydrogen bonding between the carbonyl oxygen and the amine protons was not observed in the solution phase due to a rapid exchange of these two protons with the solvent and fast rotation of the Ar-NH₂ single bond. XRD also revealed the ability of the amide unit of these compounds to function as a hydrogen bond donor and acceptor simultaneously to form strong intermolecular hydrogen bonding between oxygen of one molecule and the NH moiety of the amine or amide group of the other molecule and between the amine nitrogen and the amide hydrogen of different molecules. DFT calculations using the B3LYP/6-311++G(d,p) basis set revealed that the conformer ( A ) with oxygen and 2-amine on the same side predominates possibly due to the formation of a six-membered intramolecular ring, which is assisted by hydrogen bonding as observed in the single crystal XRD structure.

The 2,2'-dinaphtholazobenzene molecular framework (P) was designed, synthesized and characterized. Its absorption and fluorescence properties revealed that P is a dual sensor for copper ions (Cu 2+ ) and fluoride ions (F - ) in DMSO. The colorimetric activities were clearly visible by naked eye upon the addition of the two ions. Fluorescence quenching and enhancement were observed when Cu 2+ and F - ions were added respectively. Density Functional Theory (DFT) calculations were carried out to provide an insight into the interaction of guest ions (Cu 2+ and F - ) with P, and to explain how the molecular orbitals were affected. Graphical Abstract ᅟ.

Hanson et al. [Org. Lett., 2011] reported the absorption and emission spectrum of 5,6-dichloro-1,3-bis(2-pyridylimino)-4,7-dihydroxyisoindole but the excited-state intramolecular proton transfer (ESIPT) process was not investigated. The photo-physical behaviour of 5,6-dichloro-1,3-bis(2-pyridylimino)-4,7-dihydroxyisoindole was studied using the density functional theory (DFT) and time-dependent density functional theory (TD-DFT). The functional used was B3LYP and 6-31G(d) was the basis set for all the atoms. All the ten tautomers were studied for the absorption and emission properties. It is found that the tautomer where hydroxyl groups are syn to nitrogen of isoindoline ring is most stable and thus, responsible for the ESIPT process. The computed absorption and emission values of tautomers using TD-DFT are in good agreement with those obtained experimentally.

The photo-physical behaviour of bis-2,5-(2-benzoxazolyl) hydroquinone and 2,5-bis (benzo[d]oxazol-2-yl)-4-methoxyphenol was studied using the Density Functional Theory (DFT) and Time-Dependent Density Functional Theory (TD-DFT). All the possible rotamers were optimized to obtain global minimum optimized structure. The theoretical absorption and emission values of rotamers estimated by using TD-DFT [TD-B3LYP/6-31G(d)] are in good agreement with experimental absorption and emission wavelengths. Based on the absorption values, the contribution of respective rotamer is determined theoretically.

The ion-pair SN 2 reactions of model systems MnF(n-1) +CH3Cl(M(+) =Li(+), Na(+), K(+), and MgCl(+); n=0, 1) have been quantum chemically explored by using DFT at the OLYP/6-31++G(d,p) level. The purpose of this study is threefold: 1) to elucidate how the counterion M(+) modifies ion-pair SN 2 reactivity relative to the parent reaction F(-) +CH3Cl; 2) to determine how this influences stereochemical competition between the backside and frontside attacks; and 3) to examine the effect of solvation on these ion-pair SN2 pathways. Trends in reactivity are analyzed and explained by using the activation strain model (ASM) of chemical reactivity. The ASM has been extended to treat reactivity in solution. These findings contribute to a more rational design of tailor-made substitution reactions., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Can cyclen (1,4,7,10-tetraazacyclododecane) bind alkali metal azides? This question is addressed by studying the geometric and electronic structures of the alkali metal azide-cyclen [M(cyclen)N3] complexes using density functional theory (DFT). The effects of adding a second cyclen ring to form the sandwich alkali metal azide-cyclen [M(cyclen)2N3] complexes are also investigated. N3(-) is found to bind to a M(+) (cyclen) template to give both end-on and side-on structures. In the end-on structures, the terminal nitrogen atom of the azide group (N1) bonds to the metal as well as to a hydrogen atom of the cyclen ring through a hydrogen bond in an end-on configuration to the cyclen ring. In the side-on structures, the N3 unit is bonded (in a side-on configuration to the cyclen ring) to the metal through the terminal nitrogen atom of the azide group (N1), and through the other terminal nitrogen atom (N3) of the azide group by a hydrogen bond to a hydrogen atom of the cyclen ring. For all the alkali metals, the N3-side-on structure is lowest in energy. Addition of a second cyclen unit to [M(cyclen)N3] to form the sandwich compounds [M(cyclen)2N3] causes the bond strength between the metal and the N3 unit to decrease. It is hoped that this computational study will be a precursor to the synthesis and experimental study of these new macrocyclic compounds; structural parameters and infrared spectra were computed, which will assist future experimental work., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A comprehensive approach based on the density functional theory method was used to elicit the molecular and photophysical properties of four difluoroboron analogs of curcumin. The ground state geometry optimization, vertical absorption and the first excited state optimization were carried out using the B3LYP/6-31G(d) method. The geometry of the molecules remains planar both in the ground and excited states. There is a good correlation between the observed absorption (maximum deviation of 8%) and emission wavelength (maximum deviation of 22%) with the computed values. Different polarizability parameters were computed and compared with urea. The values obtained for the difluoroboron dyes are larger than those of urea, suggesting considerable charge transfer characteristics of the first excited state. This is further supported by the significant difference in the dipole moment. The outcome of this work should be useful towards the industrial applications of these curcumin-based dyes., (Copyright © 2015 Elsevier B.V. All rights reserved.)

The Group 1 complexes, [M(Me6[18]aneN6)][BAr(F)] (M = Li-Cs; Me6[18]aneN6 = 1,4,7,10,13,16-hexamethyl-1,4,7,10,13,16-hexaazacyclooctadecane; BAr(F) = tetrakis{3,5-bis(trifluoromethyl)-phenyl}borate), are obtained in high yield by reaction of the macrocycle with M[BAr(F)] in anhydrous CH2Cl2 solution, and characterised spectroscopically ((1)H, (13)C{(1)H}, (7)Li, (23)Na, and (133)Cs NMR), by microanalysis and, for M = Li, K, and Rb, by single crystal X-ray analysis. The structures show N6-coordination to the metal ion; the small ionic radius for Li(+) leads to a puckered conformation. In contrast, the K(+) ion fits well into the N6 plane, with the [BAr(F)](-) anions above and below, leading to two K(+) species in the asymmetric unit (a hexagonal planar [K(Me6[18]aneN6)](+) cation and a '[K(Me6[18]aneN6)(κ(1)-BAr(F))2](-) anion', with long axial KF interactions). The Rb(+) ion sits above the N6 plane, with two long axial RbF interactions in one cation and two long, mutually cis RbF interactions in the other. The unusual sandwich cations, [M(Me3tacn)2](+) (M = Na, K; distorted octahedral, N6 donor set) and half-sandwich cations [Li(Me3tacn)(thf)](+) (distorted tetrahedron, N3O donor set), [Li(Me4cyclen)(OH2)](+), and [Na(Me4cyclen)(thf)](+) (both distorted square pyramids with N4O donor sets) were also prepared (Me3tacn = 1,4,7-trimethyl-1,4,7-triazacyclononane, Me4cyclen = 1,4,7,10-tetramethyl-1,4,7,10-tetraazacyclododecane). Density functional theory (DFT) calculations, using the BP86 and B3LYP functionals, show that the accessibility of the [M(Me3tacn)2](+) sandwich cations depends strongly on the M(+) ionic radius, such that it is sufficiently large to avoid steric clashing between the Me groups of the two rings, and small enough to avoid very acute N-M-N chelate angles. The calculations also show that coordination to the Group 1 cation involves significant donation of electron density from the p-orbitals on the N atoms of the macrocycle, rather than purely electrostatic interactions.

The reactivity of the 2-aryl-4-chloro-6-iodoquinazolines towards palladium catalyzed sequential (Sonogashira/Suzuki-Miyaura) and one-pot two-step cross-coupling (bis-Sonogashira, and successive Sonogashira/Stille) reactions to afford novel unsymmetrical polycarbo-substituted quinazolines has been evaluated. In contrast to the chloro-bromo substituted quinazolines in which selectivity has been previously found to generally favor substitution at the more activated C(4)-Cl bond over the weaker Csp(2)-Br bond, substitution in the case of the chloro-iodo derivatives favors cross-coupling through the intrinsically more reactive Csp(2)-I bond. The electronic absorption and emission properties of the prepared 2,3-diaryl-6-(phenylethynyl)quinazolines were studied in solvents of different polarity (dichloromethane, toluene, DMF, methanol) and CH2Cl2-TFA mixture using UV-Vis and emission spectroscopic techniques complemented with density functional theory method to establish the effect of substituents on intramolecular charge transfer properties.

Molecular structure and properties of 2-fluoro-4-bromobenzaldehyde (FBB, C7H4BrFO) was experimentally investigated by X-ray diffraction technique and vibrational spectroscopy. Experimental results on the molecular structure of FBB were supported with computational studies using the density functional theory, with the Becke-3-Lee-Yang-Parr functional and the 6-311+G(3df,p) basis set. Molecular dimer formed by the intermolecular hydrogen bonding was investigated. Potential energy distribution analysis of normal modes was performed to identify characteristic frequencies. FBB crystallizes in orthorhombic space group P2(1)2(1)2(1) with the O-trans conformation. In order to investigate halogen effect, the chloro- (CBB) and bromo- (BBB) analogs of FBB have also been studied theoretically. It is observed that all compounds prefer the stable O-trans conformation. Although the free energy difference between the O-cis and O-trans conformers is less than 2.5 kcal/mol, the free energy rotational barrier is at least 7.4 kcal/mol. There is a good agreement between the experimentally determined structural parameters, and vibrational frequencies of FBB and those predicted theoretically., (Copyright © 2015 Elsevier B.V. All rights reserved.)

Red emitting dyes are of interest in various technological applications. Coumarins, though being an important class of fluorescent molecules, those with red emission, have been rarely studied theoretically. The structural and electronic aspects of three novel red emitting coumarins were studied using DFT and TD-DFT methods. The functionals employed were the hybrid functionals B3LYP, CAM-B3LYP, PBE0 and the highly parameterized empirical functional M06. The geometry at ground state reveals the electron donor N,N-diethylamino group is coplanar with the chromophoric system and the nitrile group induces a red shift to the absorption and emission. The electronic energies and dipole moments were solvent dependent. The basis sets and functionals were benchmarked for their performance with these molecules. B3LYP has been proved to be more efficient in computations whereas the basis sets do not have noticeable effect on the electronic properties. However, adding a polarization function to the basis set has improved the calculation of vertical excitation. The B3LYP functional gives maximum absolute deviation of 0.20 eV in calculating the vertical excitations and 0.18 eV for emission.

The structure of 3-iodobenzaldehyde (3IB) was characterized by FT-IR, Raman and single-crystal X-ray diffraction techniques. The conformational isomers, optimized geometric parameters, normal mode frequencies and corresponding vibrational assignments of 3IB were examined using density functional theory (DFT) method, with the Becke-3-Lee-Yang-Parr (B3LYP) functional and the 6-311+G(3df,p) basis set for all atoms except for iodine. The LANL2DZ effective core basis set was used for iodine. Potential energy distribution (PED) analysis of normal modes was performed to identify characteristic frequencies. 3IB crystallizes in monoclinic space group P21/c with the O-trans form. There is a good agreement between the theoretically predicted structural parameters, and vibrational frequencies and those obtained experimentally. In order to understand halogen effect, 3-halogenobenzaldehyde [XC6H4CHO; X=F, Cl and Br] was also studied theoretically. The free energy difference between the isomers is small but the rotational barrier is about 8kcal/mol. An atypical behavior of fluorine affecting conformational preference is observed., (Copyright © 2015 Elsevier B.V. All rights reserved.)

The photophysical and electrochemical properties of eleven polycyclic benzimidazole fused organic pigments (four based on phthalic anhydride, four based on naphthalic anhydride and three based naphthalene tetra carboxylic acid dianhydride) were investigated using density functional theory and time dependent density functional theory methods (B3LYP/6-31G(d) and M06/6-31G(d)). The predicted geometries are comparable using both functionals. The electrochemical properties are in good agreement with the experimental results. However, the experimental absorption-emission properties are closer to the values computed using the M06/6-31G(d) method. Both the methods perform equally well in explaining the intramolecular charge transfer characteristics. This work can help to understand the modern age functional materials at molecular level and to design new molecules.

Unprecedented homoleptic octathioether macrocyclic coordination to Na(+) in [Na([24]aneS8)](+) has been achieved by using Na[B{3,5-(CF3)2-C6H3}4] as a source of "naked" Na(+) ions and confirmed crystallographically, with d(Na-S) = 2.9561(15)-3.0524(15) Å. Density functional theory calculations show that there is electron transfer from the S 3p and C 2p valence orbitals of the ligand to the 3s and 3p orbitals of the Na(+) ion upon complexation.

The effects of halogen and solvent on the conformation and NH stretching of 1,1-dihalogeno-heptan-1-amines [CH3(CH2)5CX2NH2; X=F, Cl or Br] were investigated using the density functional theory method. The functional used was B3LYP employing the 6-31++G(d,p) basis set for all atoms. Computations were carried out for ten possible conformational isomers of the compounds, in the gas phase and both in a non-polar solvent (benzene) and in a polar solvent (methanol). This research work indicates that both the halogen and the medium affect conformational preference, geometrical parameters and NH vibrational frequency. The findings of this work can be useful to those systems involving changes in the conformations analogous to the compounds studied., (Copyright © 2014 Elsevier B.V. All rights reserved.)

A novel (2E)-1-(5-chlorothiophen-2-yl)-3-{4-[(E)-2-phenylethenyl]phenyl}prop-2-en-1-one [C21H15ClOS] compound has been synthesized and its structure has been characterized by FT-IR, Raman and single-crystal X-ray diffraction techniques. The conformational isomers, optimized geometric parameters, normal mode frequencies and corresponding vibrational assignments of the compound have been examined by means of HF, MP2, BP86, BLYP, BMK, B3LYP, B3PW91, B3P86 and M06-2X functionals. Reliable vibrational assignments and molecular orbitals have been investigated by the potential energy distribution and natural bonding orbital analyses, respectively. The compound crystallizes in the triclinic space group P-1 with the cis-trans-trans form. There is a good agreement between the experimentally determined structural parameters and vibrational frequencies of the compound and those predicted theoretically using the density functional theory with the BLYP and BP86 functionals., (Copyright © 2015 Elsevier B.V. All rights reserved.)

A novel (2E)-1-(5-chlorothiophen-2-yl)-3-(naphthalen-2-yl)prop-2-en-1-one [C17H11ClOS] compound has been synthesized and its structure has been characterized by FT-IR, Raman and single-crystal X-ray diffraction techniques. The isomers, optimized geometrical parameters, normal mode frequencies and corresponding vibrational assignments of the compound have been examined by means of the density functional theory method, employing, the Becke-3-Lee-Yang-Parr functional and the 6-311+G(3df,p) basis set. Reliable vibrational assignments and molecular orbitals have been investigated by the potential energy distribution and natural bonding orbital analyses, respectively. The compound crystallizes in the monoclinic space group P2₁/c with the unit cell parameters a=5.7827(8)Å, b=14.590(2)Å, c=16.138(2)Å and β=89.987 (°). The CC bond of the central enone group adopts an E configuration. There is a good agreement between the theoretically predicted structural parameters and vibrational frequencies and those obtained experimentally., (Copyright © 2014 Elsevier B.V. All rights reserved.)

The reaction between 1,5,6-trimethylpyrazinium-3-olate and methyl methacrylate (MMA) yielding a lactone-lactam has been studied using the DFT method at the B3LYP/6-31G(d) level. It is concluded that formation of the lactone-lactam is a domino process involving three consecutive reactions: (i) a 1,3-dipolar cycloaddition (13DC) reaction between the pyrazinium-3-olate and MMA yielding a [3 + 2] cycloadduct (CA); (ii) a skeletal rearrangement, which converts the [3 + 2] CA into a formal [4 + 2] CA, possessing a diazabicyclo[2.2.2]octane structure; and finally, (iii) an S(N)2 reaction, promoted by halide anion, with concomitant nucleophilic attack of the created carboxylate anion on an iminium carbon with formation of the lactone ring present in the lactone-lactam. Analysis of the four competitive channels associated with the 13DC reaction indicates that this cycloaddition takes place with complete endo stereoselectivity and 6 regioselectivity, yielding [3 + 2] CA. The subsequent skeletal rearrangement also takes place in an elementary step via a non-concerted mechanism. Electron localization function bonding analysis makes it possible to establish that the bicyclo[2.2.2]octane skeleton present in the lactone-lactam complex structure is not attained via a Diels-Alder reaction between pyrazinium-3-olate and MMA.

The atmospherically relevant reactions between dimethyl selenide (DMSe) and the molecular halogens (X(2) = Cl(2), Br(2), and I(2)) have been studied with ab initio calculations at the MP2/aug-cc-pVDZ level of theory. Geometry optimization calculations showed that the reactions proceed from the reagents to the products (CH(3)SeCH(2)X + HX) via three minima, a van der Waals adduct (DMSe:X(2)), a covalently bound intermediate (DMSeX(2)), and a product-like complex (CH(3)SeCH(2)X:HX). The computed potential energy surfaces are used to predict what molecular species are likely to be observed in spectroscopic experiments such as gas-phase photoelectron spectroscopy and infrared matrix isolation spectroscopy. It is concluded that, for the reactions of DMSe with Cl(2) and Br(2), the covalent intermediate should be seen in spectroscopic experiments, whereas, in the DMSe + I(2) reaction, the van der Waals adduct DMSe:I(2) should be observed. Comparison is made with previous related calculations and experiments on dimethyl sulfide (DMS) with molecular halogens. The relevance of the results to atmospheric chemistry is discussed. The DMSeX(2) and DMSe:X(2) intermediates are likely to be reservoirs of molecular halogens in the atmosphere which will lead on photolysis to ozone depletion.

The reactions of dimethylsulfide (DMS) with molecular iodine (I(2)) and iodine monochloride (ICl) have been studied by infrared matrix isolation spectroscopy by co-condensation of the reagents in an inert gas matrix. Molecular adducts of DMS + I(2) and DMS + ICl have also been prepared using standard synthetic methods. The vapour above each of these adducts trapped in an inert gas matrix gave the same infrared spectrum as that recorded for the corresponding co-condensation reaction. In each case, the infrared spectrum has been interpreted in terms of a van der Waals adduct, DMS : I(2) and DMS : ICl, with the aid of infrared spectra computed for their minimum energy structures at the MP2 level. Computed relative energies of minima and transition states on the potential energy surfaces of these reactions were used to understand why they do not proceed further than the reactant complexes DMS : I(2) and DMS : ICl. The main findings of this research are compared with results obtained earlier for the DMS + Cl(2) and DMS + Br(2) reactions, and the atmospheric implications of the conclusions are also considered.