Density functional theory calculations reveal that the DMAP-mediated allylation of cyclic Baylis-Hillman alcohols proceeds through a concerted substitution pathway in which proton transfer is directly coupled to bond reorganization, as an alternative to stepwise pathways involving discrete ionization. Although formation of an allylic cation has been invoked to rationalize this transformation, the energetic feasibility of ionization under neutral conditions has not been explicitly examined. Intrinsic reaction-coordinate (IRC) analysis provides direct insight into how proton transfer and bond reorganization evolve along the substitution coordinate. The computed reaction landscape shows that heterolytic C-O bond cleavage from the DMAP adduct is associated with a prohibitively high barrier (ΔG‡ ≈ 45 kcal·mol-1) and does not yield a discrete cationic intermediate, but instead collapses into a strongly associated ion pair, indicating that charge separation is incomplete and disfavors pathways requiring prior ionization under the reaction conditions. In contrast, rapid proton transfer between DMAP and the active methylene compound establishes a low-barrier acid-base pre-equilibrium (ΔG‡ ≈ 13 kcal·mol-1), generating a reactive carbanion-DMAPH+ ion pair. Subsequent C-C bond formation proceeds through a single proton-coupled transition state in which nucleophilic attack, proton transfer, and C-O bond cleavage occur in a concerted manner. This pathway avoids high-energy charge separation and provides a kinetically viable route consistent with prolonged heating under refluxing toluene, where slow but feasible turnover can be achieved over extended reaction times. Competing O-allylation pathways involve multiple high-energy intermediates and are therefore mechanistically less competitive. These results demonstrate that substitution can proceed through a concerted reaction coordinate in which proton transfer and bond cleavage are directly coupled, offering an alternative to pathways that rely on prior ionization and providing a general physical-chemistry perspective on metal-free allylic substitution.

Inhibition performance of the aqueous Curcuma.L extract as a corrosion inhibitor for an iron surface in a 0.1 M HCl solution was investigated using the ac impedance technique. The inhibition efficiency for iron was determined in the presence of the Curcuma.L extract in a 0.1 M HCl solution and reached 81.1% at the optimum concentration. The corrosion inhibitive effect was achieved through the adsorption of Curcuma.L molecules onto the iron surface, which followed the Langmuir adsorption isotherm model. The inhibitive strength of the main compounds in the Curcuma.L extract, namely Curcumin (Inh A), demethoxycurcumin (Inh B), and bis-demethoxycurcumin (Inh C), might have a direct relationship with the electron-donating ability of the molecules, as revealed by quantum chemical parameters. Theoretical investigations were conducted using DFT methods with the B3LYP/6-311G++(d,p) basis set. Mulliken charge and ESP calculations were performed to illustrate the mechanism of inhibition of this extract on the iron surface. The interaction energies derived from Monte Carlo simulations followed the order Inh A > Inh B > Inh C. The aqueous extract of Curcuma.L has been shown to effectively inhibit iron corrosion in acidic environments.

Oxidative addition of aliphatic amine on monocyclic 2-R-1,3,2-dioxaphospholane (R = methyl or phenyl) leading to phosphoranes bearing a P-H axial bond was investigated using a combined theoretical and experimental approach. The reaction followed first order kinetics for both reactants. The activation parameters were consistent with a concerted mechanism exhibiting stereo, enantio, and regio specificities. Systematic density functional theory studies including reactivity descriptors, structural parameters, determination of all possible phosphorane isomers, their transition states and their formation mechanisms were carried out to delineate the reaction pathway. Depending on the nature of the atom in the final apical position (H, N of the amine, or C of the methyl), three types of phosphoranes were identified. Energy profiles, using the intrinsic reaction coordinate technique for the formation of each isomer, were established. It was shown that the phosphorus biphilicity acts in three consecutive sequences, namely nitrogen nucleophilic attack leading to a supermolecule structure, nucleophilic behavior of phosphorus in the transition state zone of influence, and electrophilic approach of the nitrogen atom to complete the reaction. Phosphorane with an equatorial P-H bond was found to be a kinetic product that transforms rapidly to the thermodynamically stable isomer with axial P-H via two consecutive Berry pseudo-rotations. A new tool, referred to reactive internal reaction coordinates, was introduced to represent the reaction path more clearly.

In this work, the optical properties of tetra(imidazole) of palladium phthalocyanine (PdPc(Im)4) in solution form and thin films on glass and fluorine-doped tin oxide (FTO) substrates were investigated via the thermal evaporation technique. The optical band gap was evaluated by ultraviolet–visible spectroscopy (UV-Vis). The energy band gap values were determined based on the Tauc graph. In addition, time-dependent density functional theory (TD-DFT) was used to simulate the UV-Vis absorption spectrum of the (PdPc(Im)4) molecule in the Dimethyl Sulfoxide (DMSO) solution phase. A good correlation was found between the DFT results and the experimental optical results. The band gap values between the experimental and DFT-simulated values are presented. The energy band gap of (PdPc(Im)4) obtained from the DFT calculations showed that it can be efficiently regulated. Frontier molecular orbitals and molecular electrostatic potentials were also proposed in this work. The surface study of the layers deposited on FTO was considered by atomic force microscopy (AFM) and scanning electron microscopy (SEM), and the results demonstrated good homogeneity covering the entire surface. The SEM image showed a homogeneous distribution of the grains with some spherical or rod-shaped structures and no agglomeration structures. This work rendered a strategy for regulating the energy band gap and compared the experimental observations obtained with theoretical studies, which provides a fundamental insight into the optical band for optoelectronic and thin-film solar cells.

In this work, a comparative theoretical conformational analysis of the commercially most successful herbicide compound, glyphosate (N-phosphonomethylglycine), has been made at various quantum chemical levels of theory, in the gas phase and aqueous solution, using the integral equation-formalism polarizable continuum model (IEFPCM) and the solvation model density (SMD) approaches. The stable conformers of non-ionized (NE) and ionized or zwitterionic (ZW) neutral forms of glyphosate and the inter-conversions between them are described. Calculations revealed that several NE conformers of glyphosate exist in the gas phase but the zwitterionic form (ZW) is unstable in vacuo at all levels of theory. In aqueous solution, the stabilization of the zwitterion form of glyphosate was unable to be predicted satisfactorily within the equilibrated framework of the IEFPCM polarizable continuum model and using the standard UFF-radii cavity. However, the calculation with the density-based solvation model (SMD) was consistent with the experimental findings and led to the identification of the phosphonate zwitterionic (ZWP) structure as the global minimum energy in aqueous solution. The ZWP ⇋ NE tautomeric equilibrium between the non-ionized and zwitterionic forms of glyphosate was studied in aqueous solution at the SMD-B3LYP-D3/6-311++(2d,2p) level. Zwitterion formation in solution could occur by means of a concerted intramolecular proton transfer from the nitrogen to the oxygen of the phosphonate group. An analysis of the intermolecular mechanism shows that the addition of one water molecule favours the process either thermodynamically or kinetically. The possibility that the tautomerization process of glyphosate via a nonconcerted mechanism with zwitterion carboxylate (ZWC) as the intermediate can be excluded and the ZWP → ZWC proton transfer conversion can be a nearly barrierless process in PES and FES surfaces. comparison with similarly related biologically active systems was made.

Beryllium complexes of the types [BeCl2L2] (L = (Me2N)3P(O) (1), (Me2N)2P(O)F (2), Me2NP(O)F2 (3) and P(O)F3 (4)) have been theoretically studied by means of DFT geometry optimization and NMR chemical shift calculations (B3LYP/6-31G(d)). A good correlation was found between calculated and experimental data for complex 2. On going from complex 1 to 4, the Be-L bond underwent considerable lengthening, while that of Be-Cl was shortened (Be-O: 1.646 in 1 vs. 1.740 A° in 4; Be-Cl: 2.043 in 1 vs. 1.953 A° in 4). In the same way, the Be-O-P bond angle was found to decrease from 135° for 1 to 124° for 4. The trends are in good agreement with the calculated metal-ligand binding energies of complexes 1-4. Interestingly, the structural changes are accompanied by increased 9Be chemical shifts towards higher frequencies as the Me2N groups in the ligand are substituted by fluorine atoms. The results were compared to corresponding complexes with tin (IV) chloride, [SnCl4L2]. The theoretical data showed that the use of the 6-31G* basis set could efficiently predict the 9Be NMR chemical shifts in the complexes [BeCl2L2].

A convenient synthesis of a series of new β-fluoroalkoxyvinyl aldehydes and their corresponding alcohols from β-chloro-α,β-unsaturated aldehydes was developed. The etherification reaction and the carbonyl reduction were successfully achieved, affording the desired products in good yields. The mechanism of the nucleophilic vinylic substitution reaction of the 3-chloro-3-phenylacrylaldehyde has been studied using DFT methods. IRC analysis shows the presence of a hidden intermediate, in agreement with a one kinetic step two-stage process. The isomerization of hidden intermediate Z-3-chloro-3-phenylacrylaldehyde (IntZ) into hidden intermediate E-3-chloro-3-phenylacrylaldehyde (IntE) was explained in terms of the small energy gap difference between the two intermediates IntZ and IntE and the thermodynamic stability of stereoisomer E compared to Z.

In this study, we investigated the potential of palladium tetrakis (imidazole) phthalocyanine (PdPc(Imz)4) for use as an organic semiconductor for improving the photovoltaic performance. In order to get more information about the prevailing model of the conduction mechanism (correlated barrier hopping (CBH)) for PdPc(Imz)4, electrical impedance measurements were performed at different temperatures and the obtained data were simulated by the Kohlraush Williams Watt (KWW) approach. Theoretical studies (density functional theory (DFT)) were performed and molecular electrostatic potential (MEP) maps were also extracted to understand the relationship between the molecular structures and the molecular electronic structure of PdPc(Imz)4 and its semiconductor properties. Furthermore, studies on the AC electrical process as a function of temperature highlighted a hopping charge transport according to an equivalent electrical circuit composed of a parallel constant-phase element (CPE), capacitance in the grain boundary layer (C g), and resistance of the grain boundary (R g). To improve interpretation of the results, an in-depth analysis of the behavior of the electric transport was conducted. As a result, the correlated barrier hopping (CBH) conduction mechanism was shown to be the most suitable predominant conduction mechanism.

DFT/M062X/6-311+G(2d,2p) theoretical calculations have been applied to the reaction mechanism of the SNAr describing the action of the piperidine C5H10NH on the 2-bromo-3,5-dinitrothiophene. In a first predictive approach, the role of the ligand X in position 5 (X = NO2, CN and H) of the 2-bromo-3-nitrothiophene motif has been studied. Our results show that the dinitro compound represents the best element playing the role of electrophile. In a second part focused on this latter compound, we elucidate the aromatic substitution of bromide by piperidine mechanism. To do this, we first use the traditional tools such as the energy, force and internal coordinate profiles based on the intrinsic reaction coordinate. Then, we strengthen our study by tracing the atomic charge and Wiberg bond indice profiles. All the results demonstrate that we were in the presence of a concerted but asynchronous reaction. This excluded the zwitterion to act as a reaction intermediate. However, by using our new technique, called Reactive Internal Reaction Coordinate (RIRC), which gives access to the reaction path according to the selected active internal coordinates, we were able to locate without ambiguity a singular point associated with the Hidden Reaction Intermediate (HRI), compatible with the zwitterion structure. The latter compound corresponded to a long-lived transient species.

In this study, a series of new metal phthalocyanines with imidazole function MPc(Imz) (M: Cd, Hg, Zn and Pd) were synthesized to improve the photocatalyst performances. All physical properties such as total energy, HOMO, LUMO energies of MPc(Imz), as well as their vibrational frequencies have been determined by DFT method using B3LYP theory level at 6-311G (d, p) and sdd basis set. The gap of energy level between work function (WF) of ITO and LUMO of PdPc(Imdz) was 1.53 eV and represents the highest barrier beneficial to electron injection compared to WF of ZnPc(Imz), HgPc(Imz), and CdPc(Imz). Furthermore, the PdPc(Imdz) thin films on indium tin oxide (ITO) glass were prepared by spin coating and vacuum evaporation technique, and were characterized by X-ray diffraction (XRD), surface electron morphology (SEM), atomic force microscopy (AFM), and UV–Vis spectroscopy. The photocatalytic activity of the ITO/glass supported thin films and degradation rates of chlorinated phenols in synthetic seawater, under visible light irradiation were optimized to achieve conversions of 80–90%. Experiments on synthetic seawater samples showed that the chloride-specific increase in photodegradation could be attributed to photochemically generated chloride radicals rather than other photoproduced reactive intermediates [e.g., excited-state triplet PdPc(Imz) (3PdPc(Imz)*), reactive oxygen species]. The major 2,3,4,5-Tetrachlorophenol degradation intermediates identified by gas chromatography-mass spectrometry (GC/MS) were 2,3,5-Trichlorophenol, 3,5-dichlorophenol, dichlorodihydroxy-benzene and 3,4,5-trichlorocatechol.

A unified CO2-amine reaction mechanism applicable to absorption in aqueous or nonaqueous solutions and to adsorption on immobilized amines in the presence of both dry and humid conditions is proposed. Key findings supported by theoretical calculations and experimental evidence are as follows: (1) The formation of the 1,3-zwitterion, RH2N+-COO-, is highly unlikely because not only the associated four-membered mechanism has a high energy barrier, but also it is not consistent with the orbital symmetry requirements for chemical reactions. (2) The nucleophilic attack of CO2 by amines requires the catalytic assistance of a Bro̷nsted base through a six-membered mechanism to achieve proton transfer/exchange. An important consequence of this concerted mechanism is that the N and H atoms added to the C=O double bond do not originate from a single amine group. Using ethylenediamine for illustration, detailed description of the reaction pathway is reported using the reactive internal reaction coordinate as a new tool to visualize the reaction path. (3) In the presence of protic amines, the formation of ammonium bicarbonate/carbonate does not take place through the widely accepted hydration of carbamate/carbamic acid. Instead, water behaves as a nucleophile that attacks CO2 with catalytic assistance by amine groups, and carbamate/carbamic acid decomposes back to amine and CO2. (4) Generalization of the catalytic assistance concept to any Bro̷nsted base established through theoretical calculations was supported by infrared measurements. A unified six-membered mechanism was proposed to describe all possible interactions of CO2 with amines and water, each playing the role of a nucleophile and/or Bro̷nsted base, depending on the actual conditions.

A novel hybrid material, [C10H22N2](3)center dot PbCl5 center dot 3Cl center dot 3H(2)O, has been synthesized and its structure was determined by single-crystal X-ray diffraction. In the atomic arrangement, the different entities are held together through N-H center dot center dot center dot Cl, O-H center dot center dot center dot Cl and O-H center dot center dot center dot O hydrogen bonds to form a three-dimensional network. Intermolecular interactions were investigated by Hirshfeld surfaces. The powder XRD data confirms the phase purity of the crystalline sample. The resulting IR spectrum calculated by the DFT/B3LYP/LanL2DZ method, is similar to the experimental spectrum allowing a good correlation between the experimental and theoretical wavenumbers. The optical properties in the UV-visible region have been explored by the UV-visible absorption. The photoluminescence (PL) spectroscopy, which was investigated at room temperature, exhibited one emission at 426 nm. Thermal analysis discloses a phase transition at 435 K and the decomposition of the sample starts from 554 K. (c) 2019 Published by Elsevier B.V.

The SNAr mechanism invoked in this work concerned the substitution reaction of the methoxy group by a secondary amine on the 2-methoxy-5-nitrothiophene and 2-methoxy-3,5-dinitrothiophene molecules. We performed theoretical DFT and TD-DFT calculations. It was examined by theoretical DFT calculations. The hypothesis of a zwitterion formation during the kinetically determining step has been confirmed. However, our calculations have shown that the structure of this reaction intermediate is much more diffuse than commonly accepted. Its geometry can be described as one situation in which the nitrogen of the nucleophilic entity is not totally bound to the carbon, whereas the oxygen of the leaving group prepares to be separated from the substrate. The transition state corresponding to the formation of the zwitterion has a barrier of 17.78 kcal mol−1 in methanol. Three pathways have been studied to describe the second step, leading to the formation of methanol or methoxyammonium. The most probable pathway uses, in a first sequence, a second amine molecule to convert the zwitterion, a dipolar compound, into a hydrogen-bonding association of a carbanion located on the carbon C5 carrying the nitro group and an ammonium with a weak activation barrier of 2.25 kcal mol−1. The electron density supplement provided by the nucleophile is stored at the oxygen atoms of the 5-nitro group in position α of the sulfur atom. The presence of a second nitro group in position β modifies the structure of this carbanion by locating the negative charge on the carbon C3 carrying the second nitro. To visualize the reaction mechanism, we propose an innovative technique called reactive internal reaction coordinate that traces the reaction pathway in a 3D figure as a variation of the energy according to the most active internal coordinates in the transition-state zone of influence.

Abstract An investigation of the solid-state X-ray structure of the new organic–inorganic compound [C5H14N2]2PbCl6·3H2O shows a layered organization of the (PbCl6)4– anions, with (R2NH2)+ groups and water molecules developed in the [001] plane at x = (2n + 1)/4. The crystal structure is stabilized by N − H···Cl, N − H···O, O − H···Cl, O − H···O, and C − H···Cl hydrogen bonds. The powder X-ray diffraction and X-ray photoelectron spectroscopic (XPS) analyses confirm the phase purity of the crystal sample. The intermolecular contacts are quantified using the Hirshfeld surfaces computational method. The major inter-contacts contributing to the Hirshfeld surfaces are H…Cl, H…H, and O…H. The vibrational modes were identified and assigned by IR and Raman spectroscopies. The optical properties were investigated by UV–visible and photoluminescence spectroscopic studies. The compound was characterized by thermal analysis to determine its thermal behavior with respect to the temperature. Finally, X-ray photoelectron spectroscopy analysis is reported for analyzing the surface chemistry of [C5H14N2]2PbCl6·3H2O. Graphical Abstract

The new organic-inorganic compound, (C9H14N)(2)[SnCl6], has been synthesized and characterized by single-crystal X-ray diffraction at room temperature. Structural analysis indicates that this compound crystallizes in the monoclinic system with C2/m space group. The N-H center dot center dot center dot Cl hydrogen bonds between (C9H14N)(+) cations and [SnCl6](2-) dianions contribute to the cohesion and the stability of the atomic arrangement. Hirshfeld surface analysis was used to investigate intermolecular interactions, as well 2D finger plots were conducted to reveal the contribution of these interactions in the crystal structure quantitatively. Furthermore, the room temperature Infrared (IR) spectrum of the title compound was analyzed on the basis of data found in the literature. The optical properties of the crystal were studied using optical absorption UV-visible and photoluminescence (PL) spectroscopy, which were investigated at room temperature exhibited one band at 237 nm and a photoluminescence emission at 407 nm. Experimental room-temperature X-ray studies were supported by theoretical methods using the DFT/B3LYP methods with the LanL2DZ basis set. The X-ray powder is in agreement with the X-ray structure. To determine molecular electrical transport properties we studied the energy difference between Occupied, HOMO, and Lowest Unoccupied, LUMO orbitals. Moreover, this compound was characterized by thermal analysis between 300 and 750 K and shows that the compound remains stable up to the temperature 383 K. Finally, X-ray photoelectron spectroscopy (XPS) analysis is reported to determine the degree of oxidation of tin in this compound and analyze the surface chemistry of (C9H14N)(2)[SnCl6]. (C) 2019 Published by Elsevier B.V.

Kinetics of the reactions of 3,5-dinitrothiophene 1 and 3-cyano-5-nitrothiophene 2 with a series of parasubstituted phenoxide anions 3a-c have been investigated in aqueous solution at 20 degrees C. Two unsubstituted electrophilic centers (C(2) and C(4)) of the two thiophenes have been identified. The Fukui functions correctly predict the C(2) and C(4) atoms as the most electrophilic centers of these electron-deficient thiophenes 1 and 2. Analysis of the experimental data in terms of BrOnsted relationships reveals that the reaction mechanism likely involves a single-electron transfer (SET) process. The excellent correlations upon plotting the rate constants versus the oxidation potentials E-o values is an additional evidence that reactions between thiophenes and phenoxide anions are proceeding through an initial electron transfer. It is of particular interest to note that the systems studied in this paper provide a rare example of a SET mechanism in sigma-complexation reactions. According to the free energy relationship log k = s(N + E) (Angew. Chem., Int. Ed. Engl., 1994, 33, 938-957), the electrophilicity parameters E of the C-4 and C-2 positions of the thiophenes have been determined and compared with the reactivities of other ambident electrophiles. On the other hand, the second-order rate constants for the reactions of these thiophenes with the hydroxide ion has been measured in water and 50% water-50% acetonitrile and found to agree with those calculated theoretically using Mayr's equation from the E values determined in this work and from the previously published N and s parameters of OH-.

In this study, a new organic-inorganic hybrid metal compound (C5H14N2)(2)[SnCl6](2)center dot 5H(2)O was crystallized at room temperature in the orthorhombic system (space group P2(1) 2(1) 2(1)) where the structure is determined by single crystal X-ray diffraction analysis. The examination of the structure shows the cohesion and stability of the atomic arrangement result from the establishment of N-H center dot center dot center dot Cl, O(W)-H(W)center dot center dot center dot Cl, N-H center dot center dot center dot O(W) and O(W)-H(W)center dot center dot center dot O(W) hydrogen bonds between 1-methylpiperazine-1,4-diium (C5H14N2)(2+) cations, isolated (SnCl6)(2+) anions and water molecules to form organic and inorganic layers parallel to the (a, c) plane and alternate along the b-axis. Hirshfeld surface analysis was used to investigate intermolecular interactions, as well 2D fingerprint plots were conducted to reveal the contribution of these interactions in the crystal structure quantitatively. The solid phase FTIR and FT-Raman spectra of this compound have been recorded in the regions 400-4000 and 100-500 cm(-1), respectively. The vibrational frequencies were also predicted from the calculated intensities by DFT method and were compared with the experimental frequencies, which yield good agreement between observed and calculated frequencies. Besides, the optical proprieties were investigated by UV-visible and photoluminescence spectroscopy studies in the region 200-700 nm and the electronic properties HOMO and LUMO energies were measured by TD-DFT approach. Moreover, this compound was characterized by thermal analysis between 300 and 500 K which revealing two phase transitions. Finally, X-ray photoelectron spectroscopy (XPS) analysis is reported to determine the degree of oxidation of tin in this compound and analyzing the surface chemistry of (C5H14N2)(2) [SnCl6](2)center dot 5H(2)O.

PurposeThis study aims to investigate the inhibition performance of an aqueous extract ofMatricaria recutitachamomile on the corrosion of S235JR steel in 0.5 M NaCl by using electrochemical impedance spectroscopy (EIS) and polarization measurements.Design/methodology/approachThe inhibition performance was investigated using EIS and polarization measurements. Surface analysis demonstrates the presence of a protective layer on the steel surface in the presence of the extract. Quantum chemical parameters calculated for the molecules contained in the aqueous extract are interpreted to predict the corrosion inhibition efficiency of the considered extract.FindingsThe inhibition efficiency of chamomile aqueous extract for S235JR steel increases with increasing amounts of plant concentration and with an increase in the immersion time. The optimal inhibition efficiency of chamomile extract, 98.90 per cent, was achieved for S235JR steel when immersed in 15 per cent v/v of extract concentration for 2 h. The surface analysis in the absence and presence of the chamomile extract confirmed the formation of a protective layer on steel surface. The quantum chemical calculations allowed to explain the great inhibition efficiency values by interpreting the calculated quantum parameters.Originality/valueThis is the first study carrying out an experimental and theoretical investigation onM. recutitachamomile as a green corrosion inhibitor, with interesting potential industrial applications.

The formation of substituted 1,2-diamines via the regiospecific nucleophilic ring opening of 2-methylaziridine with methylamine was performed by nucleophilic attack at aziridine carbon atoms. A detailed theoretical study was investigated by density functional theory (DFT) at the B3LYP level and second order Moller Plesset perturbation theory (MP2) by using the 6-311G(d,p) basis set. The third Grimme correction term (D3) was used to take into account weak interactions. Solvent effects were computed in methanol and dimethylsulfoxide using the polarizable continuum model (PCM). Emphasis was placed on the ring opening mechanisms of neutral aziridines and aziridinium ions obtained through N-complexation with the BF 3 Lewis acid. Moreover, the effect of substituent groups on the regioselectivity of the ring opening was investigated. The nucleophilic attack was carried out via two pathways (frontside attack M1 and backside attack M2) where activation barriers proved the preference for ring opening through the backside attack at the C3 aziridine carbon atom. The obtained results showed that the frontside attack with methylamine takes place along a concerted mechanism that leads to formation of products through one transition state. However, the backside attack is carried via a stepwise process in which the methylamine attack takes place in an S N 2 fashion where the leaving group is the ring nitrogen. It first conduces a ring opening considered as the rate-determining step followed by formation of a zwitterionic intermediate. This latter undergoes a rotation to allow the proton transfer step and finally leads to formation of the thermodynamic products.

New poly‐phenylenevinylenes PPVs containing 1,3,4‐thiadiazole as candidates for organic semiconductors have been theoretically studied at density functional theory (DFT) and time‐dependent DFT levels. This study has been conducted in order to investigate the geometrical and electronic properties as well as the conductivity of a series of PPV–thiophene–1,3,4–thiadiazole–thiophene (H–PhTAT–H) containing –CHO, –CH 2 –P(=O)(OCH 3 ) 2 , and phenyl–CHO (PhCHO) terminal groups. The impact of terminal groups on the optical bandgaps, electron affinity, LUMO energy, and intramolecular reorganization energy was studied for different oligomers and for a limit polymer. The incorporation of terminal groups did not affect the chain length evolution and the vertical transition energy E vert value for a polymer limit compared with the unsubstituted oligomer (H–PhTAT–H). All studied properties showed that CHO–PhTAT–PhCHO and H–PhTAT–H oligomers can be considered as n‐type semiconductors.