Rate and product studies with 2‐adamantyl fluoroformate under solvolytic conditions

The specific rates of solvolysis of 2‐adamantyl fluoroformate have been measured at 25.0 °C in 20 pure and binary solvents. These are well correlated using the extended Grunwald–Winstein equation, with incorporation of the N_T solvent nucleophilicity scale and the Y_Cl solvent ionizing power scale. The sensitivities (l = 2.15 ± 0.17 and m = 0.95 ± 0.07) toward the changes in solvent nucleophilicity and solvent ionizing power, and the k_F/k_Cl values are very similar to those previously observed for solvolyses of n‐octyl fluoroformate, consistent with the addition step of an addition‐elimination pathway being rate‐determining. For aqueous ethanol, measurement of the product ratio allowed selectivity values (S) to be determined. The results are compared with those reported earlier for 2‐adamantyl chloroformate and mechanistic conclusions are drawn. Copyright © 2007 John Wiley & Sons, Ltd.     

The SN3–SN2 spectrum. Rate constants and product selectivities for solvolyses of benzenesulfonyl chlorides in aqueous alcohols

Rate constants for a wide range of binary aqueous mixtures and product selectivities (S) in ethanol–water (EW) and methanol–water (MW) mixtures, are reported at 25 °C for solvolyses of benzenesulfonyl chloride and the 4‐chloro‐derivative. S is defined as follows using molar concentrations: S = ([ester product]/[acid product]) × ([water solvent]/[alcohol solvent]). Additional selectivity data are reported for solvolyses of 4‐Z‐substituted sulfonyl chlorides (Z = OMe, Me, H, Cl and NO₂) in 2,2,2‐trifluoroethanol–water. To explain these results and previously published data on kinetic solvent isotope effects (KSIEs) and on other solvolyses of 4‐nitro and 4‐methoxybenzenesulfonyl chloride, a mechanistic spectrum involving a change from third order to second order is proposed. The molecularity of these reactions is discussed, along with new term ‘S_N3–S_N2 spectrum’ and its connection with the better established term ‘S_N2–S_N1 spectrum’. Copyright © 2009 John Wiley & Sons, Ltd.     

A DFT study of transition structures and reactivity in solvolyses of tert‐butyl chloride,cumyl chlorides,and benzyl chlorides

DFT computations were performed on the S_N1 and S_N2 solvolyses of substituted cumyl chlorides and benzyl chlorides in ethanol and water, by increasing stepwise the C? Cl distance and by optimization. The total energy increases with the increase in the Cl? C distance in S_N1 reactions, while free energy of activation pass through maximum. To validate the results, the calculated free energies of activation were compared with data obtained by kinetic measurements. The structural parameters of the transition states were correlated with the Hammett substituent constants and compared with the data of hydrolyses of tert‐butyl chloride and methyl chloride, which proceed with known mechanisms. Conclusions on the mechanisms of the reactions were driven from the effect of substituents on free energies of activation. Cumyl chlorides substituted with electron‐donating (e‐d) groups solvolyze with S_N1 mechanism, while the reactions of substrates that bear electron‐withdrawing groups proceed with weak nucleophilic assistance of the solvent. Benzyl chlorides hydrolyze through an S_N2 pathway except those derivatives that have strongly e‐d groups, where the reaction has S_N1 character, but a weak nucleophilic assistance of the water should also be taken into consideration. Copyright © 2007 John Wiley & Sons, Ltd.     

Breathing viability into cyclonona‐3,5,7‐trienylidenes via α‐dimethyl and ά‐moieties at DFT

Cyclonona‐3,5,7‐trienylidene ( 1 ) changes from being a transition state (TS) to minimum states when substituted by α‐methyl groups and ?‐X, where X = CMe₂, NMe, PMe, O, S, cyclopropyl, and SiMe₂ ( 2 , 3 , 4 , 5 , 6 , 7 , 8 , respectively) at density functional theory. Specifically, the parent carbene 1 exhibits a negative vibrational force constant and proves to be an unreachable electrophilic TS while shows C_s symmetry with an NBO atomic charge of +0.70 on its carbenic center. It has a triplet ground state with a rather small singlet‐triplet energy gap (ΔE_s–t = ?4.1 kcal/mol). In contrast, all of its seven scrutinized derivatives enjoy reachable global minima, with C₁ symmetry, desired nucleophilicity, and singlet closed shell (S_cs) ground states (for all but 8 which remains triplet). Stability is indicated by relative ΔE_s–t values: 2 > 3 > 4 > 5 > 6 > 7 > 1 > 8 . The highest ΔE_s–t as well as NBO carbenic atomic negative charge (?0.74) are displayed by 2 . Our carbenes ( 2 , 3 , 4 , 5 , 6 , 7 ) appear more nucleophilic than the synthesized N‐heterocyclic carbenes (imidazol‐2‐ylidenes). Copyright © 2013 John Wiley & Sons, Ltd.     

Synthesis,properties, and solvatochromism of 1,3‐dimethyl‐5‐{(thien‐2‐yl)‐[4‐(1‐piperidyl) phenyl]methylidene}‐(1H,3H)‐pyrimidine‐2,4,6‐trione

A new merocyanine dye, 1,3‐Dimethyl‐5‐{(thien‐2‐yl)‐[4‐(1‐piperidyl)phenyl]methylidene}‐ (1H, 3H)‐pyrimidine‐2,4,6‐trione 3 , has been synthesized by condensation of 2‐[4‐(piperidyl)benzoyl]thiophene 1 with N,N′‐dimethyl barbituric acid 2 . The solvatochromic response of 3 dissolved in 26 solvents of different polarity has been measured. The solvent‐dependent long‐wavelength UV/Vis spectroscopic absorption maxima, v_max, are analyzed using the empirical Kamlet–Taft solvent parameters π* (dipolarity/polarizability), α (hydrogen‐bond donating capacity), and β (hydrogen‐bond accepting ability) in terms of the well‐established linear solvation energy relationship (LSER): (1) The solvent independent coefficients s , a , and b and (v_max)₀ have been determined. The McRae equation and the empirical solvent polarity index, E_T(30) have been also used to study the solvatochromism of 3 . Copyright © 2007 John Wiley & Sons, Ltd.     

Catalysis by hydrogen chloride in the gas‐phase elimination kinetics of 2‐phenyl‐2‐propanol and 3‐methyl‐1‐buten‐3‐ol

A homogeneous, molecular, gas‐phase elimination kinetics of 2‐phenyl‐2‐propanol and 3‐methyl‐1‐ buten‐3‐ol catalyzed by hydrogen chloride in the temperature range 325–386 °C and pressure range 34–149 torr are described. The rate coefficients are given by the following Arrhenius equations: for 2‐phenyl‐2‐propanol log k₁ (s^?1) = (11.01 ± 0.31) ? (109.5 ± 2.8) kJ mol^?1 (2.303 RT)^?1 and for 3‐methyl‐1‐buten‐3‐ol log k₁ (s^?1) = (11.50 ± 0.18) ? (116.5 ± 1.4) kJ mol^?1 (2.303 RT)^?1. Electron delocalization of the CH₂?CH and C₆H₅ appears to be an important effect in the rate enhancement of acid catalyzed tertiary alcohols in the gas phase. A concerted six‐member cyclic transition state type of mechanism appears to be, as described before, a rational interpretation for the dehydration process of these substrates. Copyright © 2007 John Wiley & Sons, Ltd.     

Conformational analysis of N‐phenyl‐ and N‐trifyl‐4,4‐dimethyl‐4‐silathiane 1‐sulfimides

N‐Substituted 4,4‐dimethyl‐4‐silathiane 1‐sulfimides [R = Ph ( 1 ), CF₃ ( 2 )] were studied experimentally by variable temperature dynamic NMR spectroscopy. Low temperature ¹³C NMR spectra of the two compounds revealed the frozen ring inversion process and approximately equal content of the axial and equatorial conformers. Calculations of the 4‐silathiane derivatives 1 , 2 and the model compound [R = Me ( 3 )] as well as their carbon analogs, the similarly N‐substituted thiane 1‐sulfimides [R = Ph ( 4 ), CF₃ ( 5 ), Me ( 6 )] at the DFT/B3LYP/6–311G(d,p) level in the gas phase and in chloroform solution using the PCM model at the same level of theory showed a strong dependence of the relative stability of the conformer on the solvent. The electronegative trifluoromethyl group increases the relative stability of the axial conformer. Copyright © 2010 John Wiley & Sons, Ltd.     

The nature of the electronic factor governing diastereofacial selectivity in remotely substituted (X) 2‐adamantyl cations: 5‐X versus 4‐X substitution

A limited series of 4^eq‐substituted (X) 2‐methyleneadamantanes ( 6 , Y?CH₂, X?F, Cl, Br, I, and SnMe₃) has been synthesized and diastereoselectivities for their hydrochlorination (HCl/CH₂Cl₂) have been determined. Diastereoselectivities for the fluorination (DAST/CH₂Cl₂) of secondary alcohol mixtures, obtained from the hydride reduction of the precursor ketones ( 6 ,Y?O) to the alkenes, have also been measured. A comparison of this selectivity data for nucleophilic trapping of 4^eq‐substituted (X) 2‐adamantyl cations ( 4 , R?H and Me) with the corresponding information for 5‐substituted (X) 2‐adamantyl cations ( 1 , R?H and Me) has revealed important distinctions between the two series. In particular, whereas extended hyperconjugative effects appear to be the predominant electronic effect governing facial selectivity in the 5,2‐series, electrostatic influences prevail in the 4,2‐disposition. Copyright © 2007 John Wiley & Sons, Ltd.     

Solvent network at the transition state in the solvolysis of hindered sulfonyl compounds

Alcoholysis rates of unhindered benzenesulfonyl chlorides (X‐ArSO₂Cl, X = H‐; 4‐Br‐; 4‐Me‐) are similar in methanol; the same behavior is also observed in ethanol, whereas the reactivity order in iso‐propanol is 4 Me‐ < H‐ < 4‐Br‐. On the other hand, alcoholysis of sterically hindered arenesulfonyl chlorides (X‐ArSO₂Cl) (X = 2,4,6‐Me₃‐3‐NO₂‐; 2,6‐Me₂‐4‐tBu‐; 2,4,6‐Me₃‐; 2,3,5,6‐Me₄‐; 2,4,6‐iPr₃‐; 2,4‐Me₂‐; 2,4,6‐(OMe)₃‐) in all studied alcohols show a significant increase in reactivity, the so‐called positive steric effect. Most of the substrates showed a reaction order b ~ 2 with respect to the nucleophile in methanol and ethanol, and b ~ 3 in iso‐propanol. The correlation between reactivity and the Kirkwood function (1/ξ) gives negative sensitivity (U) for all systems. All substrates showed high sensitivity to media nucleophilicity that depends on Σσ_X. Obtained results suggest the alcoholysis of benzenesulfonyl chlorides proceeds through S_N2 mechanism where the transition state (TS) involves the participation of 2–3 alcohol molecules; such a TS can be cyclic, in the case of unbranched alcohols, or linear, for alcohols with bulkier hydrocarbon groups like iso‐propanol. To include the number of alcohol molecules playing such a role in the TS, the following terminology is proposed: cS_N2s_n for S_N2 reactions involving n solvent molecules in a cyclic (c) TS, where “s” stands for the solvent and “n” is either the closest integer or half‐integer to the reaction order relative to the solvent or, in computational studies, the proposed number of solvent molecules taking part in the TS, whereas S_N2s_n is proposed when the TS is not cyclic. Copyright © 2016 John Wiley & Sons, Ltd.     

Reactivity of sodium arenesulfinates in the substitution reaction to γ‐functionalized allyl bromides

The kinetics of nucleophilic bimolecular substitution reactions of γ‐functionalized allyl bromides with non‐substituted and p‐substituted sodium arenesulfinates has been studied. Both the structure of allyl bromides and nucleophilicity of arenesulfinate ions exerted a significant effect on the values of the kinetic parameters such as the second‐order rate constants k, activation energy E_A, and changes in the entropy ΔS^≠, enthalpy ΔH^≠, and free energy ΔG^≠ of the formation of the activated complex from reactants. Based on the evaluation of kinetic parameters, the reactants could be arranged, according to their decreasing reactivity in the S_N2‐reactions as follows: p‐toluenesulfinate ion > benzenesulfinate ion > p‐chlorobenzenesulfinate ion and 4‐bromo‐2‐butenenitrile > 1,3‐ dibromopropene, respectively. Comparison was also made between the kinetic data obtained and some delocalization reactivity indexes for both the substrates and nucleophiles. The enthalpy–entropy compensation effect was observed for the reactions of sodium arenesulfinates with γ‐functionalized allyl bromides. Copyright © 2009 John Wiley & Sons, Ltd.     

Hydrolysis and retro‐aldol cleavage of ethyl threo‐2‐(1‐adamantyl)‐3‐hydroxybutyrate: competing reactions

The hydrolysis of ethyl threo‐2‐(1‐adamantyl)‐3‐hydroxybutyrate ( 1 ) and the parent ester ethyl 3‐hydroxybutyrate ( 4 ) has been studied experimentally and computationally. In the hydrolysis of threo‐ester 1 with 2 M NaOH, predominantly retro‐aldol product was observed, whereas the hydrolyzed product was present in a minor amount. When the reaction is carried out under the same conditions with the parent ester ethyl 3‐hydroxybutyrate ( 4 ), hydrolyzed product is exclusively observed. The competitive pathways, namely hydrolysis and the retro‐aldol reaction for 1 and 4 were investigated using DFT calculations in the both gas and solvent phase. The calculated results in the solvent phase at B3LYP/6–31 + G* level revealed that the formation of retro‐aldol products is kinetically preferred over the hydrolysis of threo‐ester 1 in the presence of a base. However, the parent ester 4 showed that the retro‐aldol process is less favored than the hydrolysis process under similar conditions. The steric effect imposed by the bulky adamantyl group to enhance the activation barriers for the hydrolysis of the ethyl threo‐2‐(1‐adamantyl)‐3‐hydroxybutyrate ( 1 ) was further supported by the calculations performed with tert‐butyl group at the α‐carbon atom of ethyl 3‐hydroxybutyrate ( 7 ). Copyright © 2010 John Wiley & Sons, Ltd.     

Diastereofacial selectivity in some 4‐substituted (X) 2‐adamantyl derivatives: electronic versus steric effects

π‐Facial selectivity data for the reduction and methylation of some 4^ax‐substituted (X) 2‐adamantanones ( 3 , Y = O) as well as the nucleophilic trapping of secondary and tertiary 4^ax‐substituted (X)‐2‐adamantyl cations ( 4 ; R = H and CH₃, respectively) and the 4‐methylene‐2‐adamantyl radical ( 8 ) are presented. The pronounced anti‐face selectivities observed for ( 3 , Y = O and 4 , R = CH₃) emphasize the importance of the steric factor as expected for systems with a strong steric bias. However, the dominant syn‐face capture of 4 (R = H) was completely unexpected and highlights a subtle interplay between steric and electronic effects. Finally, the very high anti‐face stereoselectivity for the trapping of ( 8 ) with the trimethylstannyl anion (Me₃Sn^?) is rationalized in terms of an electrostatic effect overwhelming the steric factor. Copyright © 2007 John Wiley & Sons, Ltd.     

Reaction of bicyclo[2.2.1]hept‐5‐ene‐endo‐2‐ylmethylamine and nitrophenyl glycidyl ethers

Reactions of 2‐nitro‐, 4‐nitro‐ and 2,4‐dinitrophenylglycidyl ethers with bicyclo[2.2.1]hept‐5‐ene‐endo‐2‐ylmethylamine in isopropanol have been studied. The mixtures of products were chromatographed on silica gel and eluted with ether or ether/2‐propanol (1:1), the structures of individual products have been confirmed by IR spectra, NMR ¹H, ¹³C spectra, using experiments that involve homonuclear and heteronuclear scalar coupling interactions (COSY, TOCSY, HMQC, HMBC), and mass spectrometry. Amino alcohols as the major products of regioselective aminolysis of epoxides (according to the Krasusky rule) have been obtained. The minor products were the compounds with two hydroxyalkyl fragments at the nitrogen atom. In case of dinitrophenylglycidyl ether, it was the minor product of aryl nucleophilic substitution (S_NAr). The abnormal course of aminolysis has been confirmed by the results of quantum‐chemical calculations of activation barries and Free Gibbs energies of the competitive reactions of epoxides (at the B3LYP/6‐311 + G(d,p) level of theory). Copyright © 2010 John Wiley & Sons, Ltd.     

Rate and product studies in the solvolyses of methanesulfonic anhydride and a comparison with methanesulfonyl chloride solvolyses

The specific rates of solvolysis of methanesulfonic anhydride have been measured conductometrically at ?10 °C in 41 solvents. Use of the extended Grunwald–Winstein equation, with the N_T scale of solvent nucleophilicity and the Y_OTs scale of solvent ionizing power, leads to sensitivity to changes in solvent nucleophilicity (? value) of 0.95 and a sensitivity to changes in solvent ionizing power (m value) of 0.61, with a multiple correlation coefficient (R) of 0.973. Product selectivity values (S) in binary hydroxylic solvents favor alcohol attack in EtOH–H₂O (a value of 1.2 in 90% EtOH rising to 4.0 in 40% EtOH) and in MeOH–H₂O (a value of 3.7 in 90% MeOH rising to 6.0 in 50% MeOH). In 2,2,2,‐trifluoroethanol–H₂O, the S values are much lower at about 0.1. Entropy of activation values are appreciably negative. Literature values for the specific rates of solvolysis of methanesulfonyl chloride have been extended to fluoroalcohol‐containing solvents (titrimetric method) and, at 45.0 °C, for an overall 43 solvents values are obtained (using N_T and Y_C1 scales) of 1.20 for ? and of 0.52 for m (R = 0.969). It is proposed that both substrates solvolyze by an S_N2 pathway. Copyright © 2007 John Wiley & Sons, Ltd.     

Enols of 2‐nitro‐ and related 2‐substituted malonamides

The structures of 2‐substituted malonamides, YCH(CONR¹R²)CONR³R⁴ (Y = Br, SO₂Me, CONH₂, COMe, and NO₂) were investigated. When Y = Br, R¹R² = R³R⁴ = HEt; Y = SO₂Me, R¹–R⁴ = H and for Y = CONH₂ or CONHPh, R¹–R⁴ = Me, the structure in solution is that of the amide tautomer. X‐ray crystallography shows solid‐state amide structures for Y = SO₂Me or CONH₂, R¹–R⁴ = H. Nitromalonamide displays an enol structure in the solid state with a strong hydrogen bond (O^…O distance = 2.3730 Å at 100 K) and d(OH) ≠ d(O^…H). An apparently symmetric enol was observed in solution, even in appreciable percentages in highly polar solvents such as DMSO‐d₆, but K_enol values decrease on increasing the solvent polarity. The N,N′‐dimethyl derivative is less enolic. Acetylmalonamides display a mixture of enol on the acetyl group and amide in non‐polar solvents, and only the amide in DMSO‐d₆. DFT calculations gave the following order of pK_enol values for Y: H > CONH₂ > COMe ≥ COMe (on acetyl) ≥ MeSO₂ > CN > NO₂ in the gas phase, CHCl₃, and DMSO. The enol on the C?O group is preferred to the aci‐nitro compound, and the N? O? H^…O?C is less favored than the C?O? H^…O?C hydrogen bond. Copyright © 2009 John Wiley & Sons, Ltd.     

Time‐resolved resonance Raman and density functional theory study of the photochemistry of 4‐benzoylpyridine in acetonitrile and 2‐propanol

A nanosecond time‐resolved resonance Raman (ns‐TR³) spectroscopic investigation of the intermolecular hydrogen‐abstraction reaction of the triplet state of 4‐benzoylpyridine (4‐BPy) in 2‐propanol solvent is reported. The TR³ results reveal a rapid hydrogen abstraction (<10 ns) by the 4‐BPy triplet state (nπ*) with the 2‐propanol solvent, leading to formation of a 4‐BPy ketyl radical and an associated dimethyl ketyl radical partner from the solvent. The recombination of these two radical species occurs with a time constant about 200 ns to produce a para‐N‐LAT (light absorbing transient). The structure, major spectral features, and identification of the ketyl radical and the para‐N‐LAT coupling complex have been determined and confirmed by comparison of the TR³ results with results from density functional theory (DFT) calculations. A reaction pathway for the photolysis of 4‐BPy in 2‐propanol deduced from the TR³ results is also presented. The electron‐withdrawing effect of the heterocyclic nitrogen for 4‐BPy on the triplet state makes it have a significantly higher chemical reactivity for the hydrogen abstraction with 2‐propanol compared to the previously reported corresponding benzophenone triplet reaction under similar reaction conditions. In addition, the 4‐BPy ketyl radical reacts with the dimethyl ketyl radical to attach at the para‐N atom position of the pyridine ring to form a cross‐coupling product such as 2‐[4‐(hydroxy‐phenyl‐methylene)‐4h‐pyridin‐1‐yl]‐propan‐2‐ol instead of attacking at the para‐C atom position as was observed for the corresponding benzophenone reaction reported in an earlier study. Copyright © 2008 John Wiley & Sons, Ltd.     

Concerted SN2 mechanism for the hydrolysis of acid chlorides: comparisons of reactivities calculated by the density functional theory with experimental data

DFT computations have been performed in acetone and water solvents in order to investigate the mechanism of hydrolysis of acid chlorides. Acetyl chloride and chloroacetyl chloride hydrolyze via concerted, one‐step S_N2 mechanism, with the attack of water at the sp² hybridized carbon atom of the C?O group, and the transition state (TS) has distorted tetrahedral geometry. Solvent molecules act as general base and general acid catalysts. The TS of chloroacetyl chloride is tighter and less polar than the TS of acetyl chloride. The structure of the S_N2 TS for the hydrolysis of benzoyl chlorides changes with the substituents and the solvent. Tight and loose TSs are formed for substrates bearing electron withdrawing (e‐w) and electron donating (e‐d) groups, respectively. In acetone, only the e‐w effect of the substituents increase the reactivity of the substrates, and the change of the structure of the TSs with the substituents is small. In water, polar and very loose TSs are formed in the reactions of benzoyl chlorides bearing e‐d substituents, and the rate enhancing effect of both e‐d and e‐w groups can be computed at higher level of theory. Calculated reactivities and the changes of the structure of the TSs with substituents and solvent are in accordance with the results of kinetic studies. In S_N2 nucleophilic substitutions late/early TSs are formed if the attacking reagent is poorer/better nucleophile than the leaving group, and loose/tight TSs are formed for substrates bearing e‐d/e‐w substituents and in protic/aprotic solvents. Copyright © 2010 John Wiley & Sons, Ltd.     

A combined experimental and density functional study of 1‐(arylsulfonyl)‐2‐R‐4‐chloro‐2‐butenes reactivity towards the allylic chlorine

Nucleophilic substitution and dehydrochlorination reactions of a number of the ring‐substituted 1‐(arylsulfonyl)‐2‐R‐4‐chloro‐2‐butenes are studied both experimentally and theoretically. The developed synthetic procedures are characterized by a general rapidity, cheapness, and simplicity providing moderate to high yields of 1‐arylsulfonyl 1,3‐butadienes (48–95%), 1‐(arylsulfonyl)‐2‐R‐4‐(N,N‐dialkylamino)‐2‐butenes (31–53%), 1‐(arylsulfonyl)‐2‐R‐2‐buten‐4‐ols (37–61%), and bis[4‐(arylsulfonyl)‐3‐R‐but‐2‐enyl]sulfides (40–70%). The density functional theory B3LYP/6‐311++G(2d,2p) calculations of the intermediate allylic cations in acetone revealed their high stability occurring from a resonance stabilization and hyperconjugation by the SO₂Ar group. The reactivity parameters estimated at the bond critical points of the diene/allylic moiety display a high correlation (R² > 0.97) with the Hammett (σ_p) constants. 1‐Arylsulfonyl 1,3‐butadienes are characterized by a partly broken π conjugated system, which follows from analysis of the two‐centered delocalization (δ) and localization (λ) index values. The highest occupied molecular orbital energies of 1‐arylsulfonyl 1,3‐butadienes are lower than those of 1,3‐butadiene explaining their low reactivity towards the Diels–Alder condensation. Copyright © 2015 John Wiley & Sons, Ltd.     

Decay Dynamics of 3‐methyl‐3‐pentene‐2‐one from the light absorbing S2(ππ*) state ‐ Resonance Raman Spectroscopy and CASSCF Study

The photophysics of 3‐methyl‐3‐pentene‐2‐one (3M3P2O) after excitation to the S₂(ππ*) electronic state were studied using the resonance Raman spectroscopy and complete active space self‐consistent field (CASSCF) method calculations. The A‐band resonance Raman spectra were obtained in cyclohexane, acetonitrile, and methanol with excitation wavelengths in resonance with the first intense absorption band to probe the structural dynamics of 3M3P2O. The B3LYP‐TD/6‐31++G(d, p) computation was carried out to determine the relative A‐band resonance Raman intensities of the fundamental modes, and the result was used to reproduce the corresponding fundamental band intensities of the 223.1 nm resonance Raman spectrum and thus to examine whether the vibronic‐coupling existed in Franck‐Condon region or not. CASSCF calculations were carried out to determine the minimal singlet excitation energies of S_{1, FC}, S_1,min (nπ*), S_{2, FC}, S_2,min (ππ*), the transition energies of the conical intersection points S_n/S_π, S_n/S₀, and the optimized excited state geometries as well as the geometry structures of the conical intersection points. The A‐band short‐time structural dynamics and the corresponding decay dynamics of 3M3P2O were obtained by the analysis of the resonance Raman intensity pattern and CASSCF computations. It was revealed that the initial structural dynamics of 3M3P2O was towards the simultaneous C₃=C₄ and C₂=O₇ bond elongation, with the C₃=C₄ bond length lengthening greater at the very beginning, whereas the C₂=O₇ bond length changing greater at the later evolution time before reaching the CI(S₂/S₁) conical intersection point. The decay dynamics from S₂(ππ*) to S₁(nπ*) via S₂(ππ*)/S₁(nπ*) in singlet realm and from S₁(nπ*) to T₁(nπ*) via ISC[S₁(nπ*)/T₂(ππ*)/T₁(nπ*)] in triplet realm are proposed. Copyright © 2014 John Wiley & Sons, Ltd.     

Palladium‐catalyzed cyclization of 2‐alkynyl‐N‐ethanoyl anilines to indoles: synthesis,structural, spectroscopic,and mechanistic study

This study reports a facial regio‐selective synthesis of 2‐alkyl‐N‐ethanoyl indoles from substituted‐N‐ethanoyl anilines employing palladium (II) chloride, which acts as a cyclization catalyst. The mechanistic trait of palladium‐based cyclization is also explored by employing density functional theory. In a two‐step mechanism, the palladium, which attaches to the ethylene carbons, promotes the proton transfer and cyclization. The gas‐phase barrier height of the first transition state is 37 kcal/mol, indicating the rate‐determining step of this reaction. Incorporating acetonitrile through the solvation model on density solvation model reduces the barrier height to 31 kcal/mol. In the presence of solvent, the electron‐releasing (–CH₃) group has a greater influence on the reduction of the barrier height compared with the electron‐withdrawing group (–Cl). These results further confirm that solvent plays an important role on palladium‐catalyzed proton transfer and cyclization. For unveiling structural, spectroscopic, and photophysical properties, experimental and computational studies are also performed. Thermodynamic analysis discloses that these reactions are exothermic. The highest occupied molecular orbital?lowest unoccupied molecular orbital gap (4.9–5.0 eV) confirms that these compounds are more chemically reactive than indole. The calculated UV–Vis spectra by time‐dependent density functional theory exhibit strong peaks at 290, 246, and 232 nm, in good agreement with the experimental results. Moreover, experimental and computed ¹H and ¹³C NMR chemical shifts of the indole derivatives are well correlated. Copyright © 2015 John Wiley & Sons, Ltd.