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Transforming polyolefin waste into liquid alkanes through tandem cracking‐alkylation reactions catalyzed by Lewis‐acid chlorides offers an efficient route for single‐step plastic upcycling. Lewis acids in dichloromethane establish a polar environment that stabilizes carbenium ion intermediates and catalyzes hydride transfer, enabling breaking of polyethylene C−C bonds and forming C−C bonds in alkylation. Here, we show that efficient and selective deconstruction of low‐density polyethylene (LDPE) to liquid alkanes is achieved with anhydrous aluminum chloride (AlCl3) and gallium chloride (GaCl3). Already at 60 °C, complete LDPE conversion was achieved, while maintaining the selectivity for gasoline‐range liquid alkanes over 70 %. AlCl3 showed an exceptional conversion rate of 5000 gLDPEmolcat-1h-1 ${{{\rm g}}_{{\rm L}{\rm D}{\rm P}{\rm E}}{{\rm \ }{\rm m}{\rm o}{\rm l}}_{{\rm c}{\rm a}{\rm t}}^{-1}{{\rm \ }{\rm h}}^{-1}}$ , surpassing other Lewis acid catalysts by two orders of magnitude. Through kinetic and mechanistic studies, we show that the rates of LDPE conversion do not correlate directly with the intrinsic strength of the Lewis acids or steric constraints that may limit the polymer to access the Lewis acid sites. Instead, the rates for the tandem processes of cracking and alkylation are primarily governed by the rates of initiation of carbenium ions and the subsequent intermolecular hydride transfer. Both jointly control the relative rates of cracking and alkylation, thereby determining the overall conversion and selectivity. [ABSTRACT FROM AUTHOR]

Transforming polyolefin waste into liquid alkanes through tandem cracking‐alkylation reactions catalyzed by Lewis‐acid chlorides offers an efficient route for single‐step plastic upcycling. Lewis acids in dichloromethane establish a polar environment that stabilizes carbenium ion intermediates and catalyzes hydride transfer, enabling breaking of polyethylene C−C bonds and forming C−C bonds in alkylation. Here, we show that efficient and selective deconstruction of low‐density polyethylene (LDPE) to liquid alkanes is achieved with anhydrous aluminum chloride (AlCl3) and gallium chloride (GaCl3). Already at 60 °C, complete LDPE conversion was achieved, while maintaining the selectivity for gasoline‐range liquid alkanes over 70 %. AlCl3 showed an exceptional conversion rate of 5000 gLDPEmolcat-1h-1 ${{{\rm g}}_{{\rm L}{\rm D}{\rm P}{\rm E}}{{\rm \ }{\rm m}{\rm o}{\rm l}}_{{\rm c}{\rm a}{\rm t}}^{-1}{{\rm \ }{\rm h}}^{-1}}$ , surpassing other Lewis acid catalysts by two orders of magnitude. Through kinetic and mechanistic studies, we show that the rates of LDPE conversion do not correlate directly with the intrinsic strength of the Lewis acids or steric constraints that may limit the polymer to access the Lewis acid sites. Instead, the rates for the tandem processes of cracking and alkylation are primarily governed by the rates of initiation of carbenium ions and the subsequent intermolecular hydride transfer. Both jointly control the relative rates of cracking and alkylation, thereby determining the overall conversion and selectivity. [ABSTRACT FROM AUTHOR]

The novel organic salt 7-((5-bromo-1H-indol-3-yl)(4-methoxyphenyl)methyl)1,3,5-triaza-7-phosphaadamantan-7-ium tetrafluoroborate was synthesized from a Lewis acid (LA) and Lewis-base (LB) reaction between 1,3,5-triaza-7-phosphaadmantane (LB) and 5-bromo-3-(4-methoxybenzylidene)-3-H-indol-1-ium tetrafluoroborate (LA). The obtained Lewis acid base adduct, being the title compound, was analyzed and validated by 1H, 13C, 31P, and 19F 1D-NMR-spectroscopy, ESI mass spectrometry, CHN-elemental analysis, and a single crystal X-ray diffraction investigation. [ABSTRACT FROM AUTHOR]

Deamination of 1-aminoalkylphosphonic acids in the reaction with HNO2 (generated "in situ" from NaNO2) yields a mixture of substitution products (1-hydroxyalkylphosphonic acids), elimination products (vinylphosphonic acid derivatives), rearrangement and substitution products (2-hydroxylkylphosphonic acids) as well as H3PO4. The variety of formed reaction products suggests that 1-phosphonoalkylium ions may be intermediates in such deamination reactions. [ABSTRACT FROM AUTHOR]

Electrochemical activation of trialkylstannylmethyl group as an electroauxiliary for carbenium ion generation enables the intramolecular Friedel–Crafts alkylation. Electrochemical activation of stannylmethyl group forms carbenium ion which can be trapped by intramolecular (het)aromatic nucleophiles for the formation of new 6-membered cycles. [ABSTRACT FROM AUTHOR]

The electrochemical activation of stannylmethyl ethers was exploited for Friedel–Crafts alkylation of arenes at near‐neutral conditions. Single cell anodic oxidation of stannylmethyl ethers leads to oxonium ions which fragment to carbenium ions in the presence of electron rich arenes. Low oxidation potential of stannylmethyl ethers and buffered conditions enable the Friedel–Crafts reaction with a wide range of arenes including the substrates with acid‐sensitive groups. [ABSTRACT FROM AUTHOR]

The ambident nature of the electrophile generated in a reaction system controls the outcome of a reaction. Electrophilic nitrenium ion which is convertible to carbenium ion via resonance was in situ generated by the reactions of iodine(III)‐reagent PhI(OAc)2 and arylsulfonamides. The nucleophile added in the reaction controls the reaction for the regiospecific ortho C−H arylation or C2‐H arylation. The electron rich arenes react with carbenium ion (electrophiles) to undergo C−H arylation. Electron donating effect (+I or +R effect) of the substituents on sulfonamide stabilizes the carbenium ion to favor oxidative coupling reaction with nucleophiles. Overall, the feasibility of C2‐H arylation of the sulfonamides has been demonstrated by steric and electronic factor that facilitates C−H arylation of sulfonamides. [ABSTRACT FROM AUTHOR]

• Transfer learning allows for data-efficient molecular property prediction. • SHAP analysis proves the physical principles incorporated in machine learning. • Group additive predictions are excellent for transfer learning pretraining. • Transfer learning holds great potential to improve various group additive models. The accuracy of thermochemical prediction methods is strongly dependent on the size of the set of training data. Group additivity is an interpretable modeling strategy that can be developed from a limited dataset, but fails to consider delocalized molecular effects such as inductive stabilization, delocalized resonance stabilization, and steric effects. In contrast, machine learning allows the incorporation of these effects but requires an extensive amount of high-quality data. Therefore, a new transfer learning approach is proposed, uniting group additivity with machine learning. First, a machine learning model is pretrained on a large set of group additive predictions, after which it is refined on a limited high-quality dataset with transfer learning. The proposed approach was tested to predict the standard enthalpy of formation, standard molar entropy, and heat capacity of a wide range of hydrocarbons, hydrocarbon radicals, and carbenium ions. By using transfer learning, chemically accurate predictions for hydrocarbons, radicals, and carbenium ions could be obtained, drastically reducing the group additive error using less than 450 molecular datapoints per model. A SHapley Additive exPlanations analysis reveals that a data-efficient but interpretable transfer learning methodology is obtained, achieving chemically accurate predictions for a wide range of hydrocarbons. [ABSTRACT FROM AUTHOR]

Relative initial reaction rates for both double bond isomerization and direct esterification with heptanoic acid were determined for the series of linear 1-alkenes from 1-octene to 1-octadecene. In competitive reactions between two 1-alkenes on Amberlyst®15 catalyst at 90 °C, rates for both double bond isomerization and esterification decreased with increasing carbon chain length. Data suggested each 1-alkene had two different adsorption coefficients on the catalyst, one for an isomerization site and one for a site for the addition reaction. Results were consistent with previous data suggesting that Amberlyst®15 catalyst has two different types of active sites. [Display omitted] • For linear 1-alkenes, rates of double bond isomerization and direct esterification correlate with adsorption coefficients. • Short linear 1-alkenes adsorb more strongly than long ones on Amberlyst®15 catalytic sites. • Double bond isomerization occurs on a different site than direct esterification. • Stereochemistry of acidic sites on Amberlyst®15 catalyst results in two different types of acidic sites. • Alkene adsorption is weak on isomerization sites and strong on addition sites. [ABSTRACT FROM AUTHOR]

Bis(trichloroacetimidoyloxymethyl)cyclopropanes provide intramolecular amination products of intermediate cyclobutyl or cyclopropylmethyl carbenium ion when exposed to Lewis acid catalyst or thermal ionization. The ratio of the two amination products of cyclobutyl carbenium ion depends primarily on the substituent at the alkoxymethyl group of the substrate and can be altered by the solvent used and the ionization conditions. An oxazoline derivative forms as the major amination product in the case of unsubstituted bis(trichloroacetimidoyloxymethyl) cyclopropane or if the substrate contains isopropyl or alkoxymethyl substituents. The amination of cyclobutyl carbenium ion formed in situ proceeds with high diastereoselectivity leading to exclusive formation of trans-cyclobutane derivatives. The latter can be transformed to N-Boc-protected cyclobutane-based amino alcohols in high yields. [ABSTRACT FROM AUTHOR]

Highly electronically deactivated benzylic alcohols, including those with a CF3 group adjacent to the OH-bearing carbon, undergo dehydrative Friedel-Crafts reactions upon exposure to catalytic Brønsted acid in 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) solvent. Titration and kinetic experiments support the involvement of higher order solvent/acid clusters in catalysis. [ABSTRACT FROM AUTHOR]

Ion/molecule reactions of saturated hydrocarbons ( n-hexane, cyclohexane, n-heptane, n-octane and isooctane) in 28-Torr N2 plasma generated by a hollow cathode discharge ion source were investigated using an Orbitrap mass spectrometer. It was found that the ions with [M+14]+ were observed as the major ions (M: sample molecule). The exact mass analysis revealed that the ions are nitrogenated molecules, [M+N]+ formed by the reactions of N3+ with M. The reaction, N3+ + M → [M+N]+ + N2, were examined by the density functional theory calculations. It was found that N3+ abstracts the H atom from hydrocarbon molecules leading to the formation of protonated imines in the forms of R′R″CNH2+ (i.e. C-H bond nitrogenation). This result is in accord with the fact that elimination of NH3 is the major channel for MS/MS of [M+N]+. That is, nitrogen is incorporated in the C-H bonds of saturated hydrocarbons. No nitrogenation was observed for benzene and acetone, which was ascribed to the formation of stable charge-transfer complexes benzene⋅⋅⋅⋅N3+ and acetone⋅⋅⋅⋅N3+ revealed by density functional theory calculations. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

ABSTRACT Recently, the direct substitution of allylic, benzylic, and tertiary alcohols has been achieved via SN1-type reactions with catalytic amounts of Brønsted or Lewis acids. When a new stereogenic center is formed most of these transformations produce the desired product as a racemate, as these reactions proceed through carbenium ions. The arsenal of activation modes available in organocatalysis can be used to set up suitable reaction conditions in which chiral nucleophiles (enamine ) or chiral electrophiles (iminium , chiral counterion ) can easily be generated. Recently, we have used stabilized carbenium ions, directly available or obtained from the corresponding alcohols, in new organocatalytic SN1-type reactions. The commercially available carbenium ion benzodithiolylium tetrafluoroborate 1 can be used for the straightforward organocatalytic . In this account we will illustrate the application of this methodology in the total synthesis of natural products and the preparation of valuable starting materials. Chirality 26:607-613, 2014. © 2014 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Abstract: Two new dodecaferrocenyl dendrimers have been prepared using a sixfold Sonogashira coupling reaction and sixfold Huisgen cycloaddition, respectively. In addition, a dendron containing four ferrocenyl groups has been synthesised by conventional synthetic methods. Electrochemical studies have shown that all the ferrocene units are electrochemically equivalent. Moreover, when treated with acid these compounds form multicharged methylium near-infrared-absorbing dendritic dyes with a high extinction coefficient. [Copyright &y& Elsevier]

A new mechanism for the origin of multiple skeletal isomers observed in the cationic dimerization of 1-decene is proposed, and products that should form based on this mechanism are predicted. A protonated cyclopropyl intermediate appeared to form directly from combination of 2-decyl carbocation with 1-decene; formation of this intermediate did not appear to occur via ring closure of a branched secondary carbocation. The authors propose that rapid, repeated isomerizations of the protonated cyclopropyl intermediates lead to multiple skeletal isomers in decene dimers. The proposed mechanism can account for structures previously identified in mixtures of decene dimers and butene dimers. [ABSTRACT FROM AUTHOR]

Abstract: Dimethyl ether (DME) homologation forms isobutane and triptane (2,2,3-trimethylbutane) with supra-equilibrium selectivities within C4 and C7 hydrocarbons on both mesoporous solid acids (SiO2–Al2O3, H3PW12O40/SiO2) and the acid forms of various zeolites (BEA, FAU, MFI) via methylation and hydride transfer steps that favor isobutane and triptane formation because of the relative stabilities of ion-pairs at transition states for chains along the preferred growth path. The stabilities of ion-pair transition states increase as acid sites become stronger and energies for charge separation decrease and as van der Waals interactions within pores become stronger, which respectively lead to higher rates on H3PW12O40/SiO2 and aluminosilicate zeolites than on amorphous SiO2–Al2O3. Solid acids with different strengths and abilities to solvate ion-pairs by confinement differ in selectivity because strength and solvation influence transition states for the hydride transfer, methylation, and isomerization steps to different extents. Stronger acid sites on H3PW12O40/SiO2 favor isomerization and hydride transfer over methylation; they lead to higher selectivities to n-butane and non-triptane C7 isomers than the weaker acid sites on BEA, FAU, and mesoporous SiO2–Al2O3. This preference for hydride transfer and isomerization on stronger acids reflects transition states with more diffuse cationic charge, which interact less effectively with conjugate anions than more localized cations at methylation transition states. The latter recover a larger fraction of the energy required to form the ion-pair, and their stabilities are less sensitive to acid strength than for diffuse cations. Large-pore zeolites (BEA, FAU) form triptane with higher selectivity than SiO2–Al2O3 because confinement within large pores preferentially solvates the larger transition states for hydride transfer and methylation, which preserve the four-carbon backbone in triptane, over smaller transition states for alkoxide isomerization steps, which disrupt this backbone and cause growth beyond C7 chains and subsequent facile β-scission to form isobutane. MFI forms isobutane and triptane with much lower selectivity than mesoporous acids or large-pore zeolites, because smaller pores restrict the formation of bimolecular methylation and hydride transfer transition states required for chain growth and termination steps to a greater extent than those for monomolecular alkoxide isomerization. These data and their mechanistic interpretations show that the selective formation of isobutane and triptane from C1 precursors like DME is favored on all acids as a result of the relative stability of methylation, hydride transfer, and isomerization transition states, but to a lesser extent when small confining voids and stronger acid sites preferentially stabilize monomolecular isomerization transition states. The observed effects of acid strength and confinement on rates and selectivities reflect the more effective stabilization of all ion-pairs on stronger acids and within solvating environments, but a preference for transition states with more diffuse charge on stronger acids and for ion-pairs with the appropriate solvation within voids of molecular dimensions. [Copyright &y& Elsevier]

Abstract: The indole alkaloid α-cyclopiazonic acid 1 has been synthesised by a route, which features at its core an acid-catalysed cationic cascade cyclisation terminated by a sulfonamide group. [Copyright &y& Elsevier]

Density functional theory and atoms in molecules theory were used to study bond breakage and bond formation in the trans-2-butene protonation reaction in an acidic zeolitic cluster. The progress of this reaction along the intrinsic reaction coordinate, in terms of several topological properties of relevant bond critical points and atomic properties of the key atoms involved in these concerted mechanisms, were analyzed in depth. At B3LYP/6-31++G(d,p)//B3LYP/6-31G(d,p) level, the results explained the electron density redistributions associated with the progressive bond breakage and bond formation of the reaction under study, as well as the profiles of the electronic flow between the different atomic basins involved in these electron reorganization processes. In addition, we found a useful set of topological indicators that are useful to show what is happening in each bond/atom involved in the reaction site as the reaction progresses. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Abstract: We report here kinetic and isotopic evidence for the elementary steps involved in dimethyl ether (DME) homologation and for their role in the preferential synthesis of 2,2,3-trimethylbutane (triptane) and isobutane. Rates of methylation of alkenes and of hydrogen transfer, isomerization and β-scission reactions of the corresponding alkoxides formed along the homologation path to triptane were measured using mixtures of 13C-labeled dimethyl ether (13C-DME) and unlabeled alkenes on H-BEA. DME-derived C1 species react with these alkenes to form linear butyls from propene, isopentyls from n-butenes, 2,3-dimethylbutyls from isopentenes, and triptyls from 2,3-dimethylbutenes; these kinetic preferences reflect the selective formation of the more highly substituted carbenium ions and the retention of a four-carbon backbone along the path to triptane. Hydrogen transfer reactions terminate chains as alkanes; chain termination probabilities are low for species along the preferred methylation path, but reach a maximum at triptyl species, because tertiary carbenium ions involved in hydrogen transfer are much more stable than those with primary character required for triptene methylation. Alkenes and alkanes act as hydrogen donors and form unsaturated species as precursors to hexamethylbenzene, which forms to provide the hydrogen required for the DME-to-alkanes stoichiometry. Weak allylic C–H bonds in isoalkenes are particularly effective hydrogen donors, as shown by the higher termination probabilities and 12C content in hexamethylbenzene as 12C-2-methyl-2-butene and 12C-2,3-dimethyl-2-butene pressures increased in mixtures with 13C-DME. The resulting dienes and trienes can then undergo Diels–Alder cyclizations to form arenes as stable by-products. Isomerization and β-scission reactions of the alkoxides preferentially formed in methylation of alkenes are much slower than hydrogen transfer or methylation rates, thus preventing molecular disruptions along the path to triptane. Methylation at less preferred positions leads to species with lower termination probabilities, which tend to grow to C8+ molecules; these larger alkoxides undergo facile β-scission to form tert-butoxides that desorb preferentially as isobutane via hydrogen transfer; such pathways resolve methylation “missteps” by recycling the carbon atoms in such chains to the early stages of the homologation chain and account for the prevalence of isobutane among DME homologation products. These findings were motivated by an inquiry into the products formed via C1 homologation, but they provide rigorous insights about how the structure and stability of carbenium ions specifically influence the rates of methylation, hydrogen transfer, β-scission, and isomerization reactions catalyzed by solid acids. [Copyright &y& Elsevier]

The adsorption and transformation of cyclopentadiene on HY and HZSM-5 zeolites were investigated by infrared (IR) spectroscopy and temperature-programmed desorption (TPD). The stoichiometric formation of monomeric cyclopentenyl carbenium ions (C5H+ 7) was observed on the acidic sites in the supercages of zeolite HY and in the channels of zeolite HZSM-5 at room temperature, without formation of oligomerized cyclopentadiene. The IR spectra indicate that addition of quantitative cyclopentadiene led to the stoichiometric consumption of acidic OH groups. These cyclopentenyl carbocations formed in the supercages affected the vibration of the remaining OH groups at both high and low frequencies, resulting in a shift of the OHHF from 3642 to 3530 cm−1 as well as a shift of the OHLF from 3552 to 3500 cm−1. The TPD-MS results reveal that the cyclopentadiene transformation on these H-form zeolites occurred at a temperature range of 473–800 K and followed a hydride ion-transfer pathway. The monomeric cyclopentenyl carbocation was the key intermediate initiating the cracking chain proceeding by the cationic mechanism. [Copyright &y& Elsevier]

The alkyl-bridged iron(II) complexes [{Cp(CO)2Fe}2{μ-(CnH2n)}] (n=6–10, Cp=η5-C5H5) undergo both single and double hydride abstraction when reacted with one equivalent of Ph3CPF6 to give both the monocationic complexes, [{Cp(CO)2Fe}2{μ-(CnH2n−1)}]PF6, and the dicationic complexes, [{Cp(CO)2Fe}2{μ-(CnH2n−2)}](PF6)2. The ratios of monocationic to dicationic complexes decrease with the increase in the value of n. The complexes where n=4 and 5 undergo only single hydride abstraction under similar conditions. When reacted with two equivalents of Ph3CPF6, the complexes where n=6–10 undergo double hydride abstraction to give dicationic complexes only. In contrast, the complex where n=5 gives equal amounts of the monocationic and the dicationic complexes, while the complex where n=4 only gives the monocationic complex. 1H and 13C NMR data show that in the monocationic complexes one metal is σ-bonded to the carbenium ion moiety while the other is bonded in a η2-fashion forming a chiral metallacylopropane type structure. In the dicationic complexes both metals are bonded in the η2-fashion. The monocationic complexes where n=4–6, react with methanol to give η1-alkenyl complexes[Cp(CO)2Fe(CH2)nCH＝CH2] (n=2–4) as the major products and σ-bonded ether products [{Cp(CO)2Fe}2{μ-(CH2)nCH(OCH3)CH2}] as the minor products. The complex where n=8 reacted with iso-propanol to give the η1-alkenyl complex [Cp(CO)2Fe(CH2)6CH＝CH2]. The dicationic complexes where n=5, 8 and 9 were reacted with NaI to give the respective α,ω-dienes and [Cp(CO)2FeI]. [Copyright &y& Elsevier]

The β-scission mechanisms of catalytically chemisorbed carbenium ions are further investigated using density functional theory computations and explicit-contact modelling, but with slightly larger catalyst fragment models than in our previous work. Some variations are seen, including the existence of formal one-step and three-step (rather than two-step) mechanisms. The activation barriers are most affected by the basicity of the catalyst model than by any other characteristics: the stronger the base, the greater the barrier. A general mechanism for β scission is presented, as are the specific mechanisms for all the step variations observed from computations to date. [ABSTRACT FROM AUTHOR]

Abstract: The formation and transformation of adsorbed alkoxide intermediates to active carbenium-ion species over solid acid catalysts are essential steps that determine the rate and selectivity of many hydrocarbon conversion processes. Herein, density functional theory is used to examine these processes for a t-butyl species adsorbed to phosphotungstic acid, a Keggin structured polyoxometalate. The tertiary carbenium ion is found to be a meta-stable intermediate state. The conversion of a physisorbed, π-bound isobutene state to the t-butyl alkoxide state occurs in a two-step process through formation of this tertiary carbenium-ion intermediate. Both the intermediate and transition states contain a positive charge and are properly termed carbenium ions, and the interaction with the catalyst surface is mainly Coulombic. The dehydrogenation of isobutane and the dehydration of 2-methyl-2-propanol are also examined. Tertiary carbenium ions are found to be transition states for both of these processes as well. [Copyright &y& Elsevier]

A series of new intensely coloured multicharged methylium compounds containing the 4-[2-ferrocenylethenyl]phenyl group and with significant electronic absorption in the near infrared have been prepared via acidification of the tertiary carbinols obtained by reaction of 4-[FcCH=CH]C6H4Li with diethyl isophthalate, diethyl terephthalate, diethyl phthalate or the triethyl ester of 1,3,5-benzene carboxylic acid. Even more stable dyes were prepared from two new triarylmethanol derivatives containing 2,6-dimethoxy-4-[2-(ferrocenyl)ethenyl]phenyl or 2,6-dimethoxy-4-[2-[4-(dimethylamino)phenyl]ethenyl]phenyl groups which were prepared by reaction of 4-[FcCH=CH]-2,6-MeO2C6H2Li or 4-[4-Me2NC6H4CH=CH]-2,6-MeO2C6H2Li (Fc=ferrocenyl) with diethyl carbonate. These carbinols on treatment with acid deposit dark-purple crystals which have been isolated and characterised spectroscopically. They absorb in the near infrared and, whereas their solutions begin to decolourise only after several days, they display long-term stability to air and moisture in the solid state. [Copyright &y& Elsevier]

The β-scission mechanism of physisorbed and chemisorbed pentenium ions, as catalyzed by AlH2(OH)2– and by AlHCl3– anions, was investigated using density functional theory computations and explicit-contact modelling. A thorough search of intermediates was performed for each catalyst. On the aluminum chloride, β scission of an aliphatic, secondary carbenium ion featured chemisorbed and physisorbed ion intermediates, while on the aluminum hydroxide, β scission featured chemisorbed ions but physisorbed neutral species. The importance of this work is its demonstration of a qualitatively different mechanism, with qualitatively different intermediates, due only to the different basicity of the two catalysts. [ABSTRACT FROM AUTHOR]

A theoretical analysis of the interaction between cyclohexene and a HZSM-5 zeolite model system is presented. Two different models were used to represent this catalyst: a ring structure model consisting of 10ㅡTO4ㅡ tetrahedral sites (where T=Si, Al) and a smaller model containing 3ㅡTO4ㅡtetrahedral sites. Two different reaction pathways were studied: the hydrogen exchange between the HZSM-5 cluster model and the cyclohexene molecule, and the proton addition to double bond of the cyclohexene. The alkoxy species can be stabilized/destabilized depending of the arrangement restriction between the olefin and the local geometry of the active site. When cyclohexene molecule interacts with the 3T model the reaction involves an alkoxy species formation. Due to the allowed relaxation in the ring framework around the active site, the local arrangement restriction of the alkoxy species and therefore the covalent alkoxy bond is too weak giving rise to a more ionic intermediate species (carbenium ion-like), which is characterized as a minimum in the PES. By using the non-interacting system, as a reference, and based on the calculated changes in the total energy of the different complexes, one is able to determine that both carbenium ion-like and alkoxy species are destabilized with respect to physisorbed complexes. [Copyright &y& Elsevier]

A series of triarylmethanol derivatives containing combinations of phenyl, 1-naphthyl, 4-dimethylamino-4′-stilbenyl, ferrocenyl or 4-[2-ferrocenylethenyl]phenyl groups have been prepared by reaction of 4-[4-Me2NC6H4C=C]C6H4Li or 4-[FcC=C]C6H4Li (Fc = ferrocenyl) with ferrocenecarboxaldehyde, ferrocenyl phenyl ketone, methyl ferrocenecarboxylate, 1-naphthyl phenyl ketone, ethyl benzoate or diethyl carbonate. The carbinols readily form the corresponding intensely coloured carbenium ions in acid solution which have significant electronic absorption in the near infrared. Initial studies indicate that they also possess substantial first hyperpolarisabilities. [Copyright &y& Elsevier]

Steric effect in the complexes of tri-coordinate silylenium and carbenium ions with model nucleophiles is discussed based on calculated energies of complex formation and on natural steric analysis (a part of the NBO theory). While the energies of complexation of CH3+ are greater than those of SiH3+, for trimethyl-substituted cations the order is reversed. This observation is interpreted in terms of smaller steric hindrance of trimethylsilyl cation compared to t-butyl cation. Natural steric analysis points to the potentials and difficulties in separate treatment of steric and electron delocalization effects on stabilization of these species. [Copyright &y& Elsevier]