Monomolecular Reaction Research Articles

Asymmetric Rh Diene Catalysis under Confinement: Isoxazole Ring‐Contraction in Mesoporous Solids

AbstractCovalent immobilization of chiral dienes in mesoporous solids for asymmetric heterogeneous catalysis is highly attractive. In order to study confinement effects in bimolecular vs monomolecular reactions, a series of pseudo‐C2‐symmetrical tetrahydropentalenes was synthesized and immobilized via click reaction on different mesoporous solids (silica, carbon, covalent organic frameworks) and compared with homogeneous conditions. Two types of Rh‐catalyzed reactions were studied: (a) bimolecular nucleophilic 1,2‐additions of phenylboroxine to N‐tosylimine and (b) monomolecular isomerization of isoxazole to 2H‐azirne. Polar support materials performed better than non‐polar ones. Under confinement, bimolecular reactions showed decreased yields, whereas yields in monomolecular reactions were only little affected. Regarding enantioselectivity the opposite trend was observed, i. e. effective enantiocontrol for bimolecular reactions but only little control for monomolecular reactions was found.

From lithium and sodium superoxides to singlet-oxygen - insights into the mechanism of dissociation using SHARC-MD.

The parasitic formation of singlet oxygen in aprotic alkaline/air batteries presents a challenge for the technical development of these systems. Avoidance strategies and investigation of reaction paths such as disproportionation of LiO2 and NaO2 have been presented. Furthermore, the dissociation of these superoxide systems have been discussed be as an alternative reaction channel. Here, we present a fundamental study of the electronic nature and dissociation behaviour of the alkali superoxides. The molecular systems were calculated at the CASSCF/CASPT2-level of theory. We determined the minimum energy crossing points along the dissociation required to form 3O2 and 1O2. Building on these results, a surface-hopping AIMD-simulation was performed employing the SHARC program package to follow the electronic transitions along the minimum energy crossing pooints during the dissociation. The feasibility of populating the electronic state corresponding to the formation of singlet oxygen during dissociation was demonstrated. For LiO2, 6.85% of the trajectories were found to terminate under formation of 1O2, whereas for NaO2 only 1.68% of the trajectories ended up in 1O2 formation. This represents an inverse trend to that reported in the literature. This observation suggests that the dissociation is a viable, monomolecular reaction path to 1O2 that complements the disproportionation pathway.

Theoretical study of the reaction of organic peroxyl radicals with alkenes and their accretion products involved in the atmospheric nucleation

Organic peroxy radicals, including alkyl peroxy radicals (RO2) and acyl peroxy radicals (RC(O)O2), are crucial intermediates in the atmospheric photochemical reactions of volatile organic compounds and directly or indirectly affect the distribution of other species (e.g., HO2 radicals, NOx, OH radicals, and alkenes). However, the atmospheric reactions of organic peroxyl radicals with alkenes (RO2 + alkene reactions) are not fully understood. The present study used theoretical calculations to investigate the reaction mechanisms of various organic peroxy radicals with different alkenes, with the aim of clarifying the influence of molecular structure on RO2 + alkene and RC(O)O2 + alkene reactions. Furthermore, we investigated the nucleation mechanisms of the subsequent oxidation products. The results show that the reaction rate constants for RC(O)O2 + alkene reactions are 1–6 orders of magnitude higher than those for RO2 + alkene reactions. The addition products formed by organic peroxy radicals with alkenes not only undergo monomolecular reactions to generate epoxides, but also participate in O2 addition to yield the accretion products ROOR’. H2SO4 molecules synergistically interact with low-volatility ROOR’ to grow clusters up to the 1–2 nm scale, and the ROOR’ molecules can form pure organic clusters larger than 1 nm, even in the absence of H2SO4 molecules. Our study provides a new perspective on the formation of accretion products in the atmosphere and their involvement in new particle formation.

Contribution of a C-Terminal Extension to the Substrate Affinity and Oligomeric Stability of Aldehyde Dehydrogenase from Thermus thermophilus HB27.

Aldehyde dehydrogenase enzymes (ALDHs) are widely studied for their roles in disease propagation and cell metabolism. Their use in biocatalysis applications, for the conversion of aldehydes to carboxylic acids, has also been recognized. Understanding the structural features and functions of both prokaryotic and eukaryotic ALDHs is key to uncovering novel applications of the enzyme and probing its role in disease propagation. The thermostable enzyme ALDHTt originating fromThermus thermophilus, strain HB27, possesses a unique extension of its C-terminus, which has been evolutionarily excluded from mesophilic counterparts and other thermophilic enzymes in the same genus. In this work, the thermophilic adaptation is studied by the expression and optimized purification of mutant ALDHTt-508, with a 22-amino acid truncation of the C-terminus. The mutant shows increased activity throughout production compared to native ALDHTt, indicating an opening of the active site upon C-terminus truncation and giving rationale into the evolutionary exclusion of the C-terminal extension from similar thermophilic and mesophilic ALDH proteins. Additionally, the C-terminus is shown to play a role in controlling substrate specificity of native ALDH, particularly in excluding catalysis of certain large and certain aromatic ortho-substituted aldehydes, as well as modulating the protein's pH tolerance by increasing surface charge. Dynamic light scattering and size-exclusion HPLC methods are used to show the role of the C-terminus in ALDHTt oligomeric stability at the cost of catalytic efficiency. Studying the aggregation rate of ALDHTt with and without a C-terminal extension leads to the conclusion that ALDHTt follows a monomolecular reaction aggregation mechanism.

Hydrothermally Ce modified HZSM-5 zeolite enhancing its strong acidity and Brønsted/Lewis acid ratio: Stably boosting ethylene/propylene ratio for cracking n-heptane

Modulating zeolite acidity by conventional metal impregnation is a challenge in preparing hydrocarbon cracking catalyst, which often eliminates its intrinsic strong acidity, resulting in reduced the hydrocarbon conversion capacity and low light olefins (C2=-C4=) yield. Here, the Ce/HZ5-HM and CeO2/HZ5-HM catalysts were readily prepared by hydrothermally modifying HZSM-5 zeolite (HZ5) with cerium salts (Ce3+) and cerium oxide (CeO2), respectively. Comparatively, Ce/HZ5-IW catalyst was obtained by modifying HZ5 with Ce3+ using the incipient wetness impregnation. It is revealed that, compared to HZ5, Ce/HZ5-HM and CeO2/HZ5-HM catalysts have an increased ratio of strong/weak (S/W) acid and Brønsted/Lewis (B/L) acid, while Ce/HZ5-IW sample has reduced strong acidity. Further, the Ce/HZ5-HM exhibits higher acid strength, acid density, and B/L value than that of CeO2/HZ5-HM sample. When applied to cracking n-heptane reaction, compared with HZ5 and Ce/HZ5-IW, heptane conversion and ethylene yield on Ce/HZ5-HM and CeO2/HZ5-HM catalysts increase by 6–11 % and 7–9 %, yielding the ratio of ethylene/propylene (E/P) more than 1. Moreover, Ce/HZ5-HM and CeO2/HZ5-HM catalysts perform a lifetime of 117 h and 150 h, with four-to-five times longer than that of HZ5 zeolite (∼29 h) and Ce/HZ5-IW catalyst (∼39 h). The characterization results demonstrate that, adopting hydrothermal method ensures more Ce3+ interacting with the silanol groups in Ce/HZ5-HM, generating the new Brønsted acid sites and makes CeOx species incorporating into the hydroxyl nest of zeolite, which can heal the defective sites and improve stabilization of acidity and framework structure of zeolite. Therefore, the above two catalysts can highlight the monomolecular cracking reaction, low coke deposit rate, long catalytic stability.

Regulating framework aluminum location towards boosted light olefins generation in ex-situ catalytic pyrolysis of low-density polyethylene

Amidst the global focus on recycling and treatment of waste plastics for resource sustainability, it remains an enormous challenge to convert waste plastics into light olefin. Herein, the impact of framework Al (AlF) location in ZSM-5 catalyst, controlled by regulating Al sources, on the ex-situ catalytic pyrolysis of low-density polyethylene (LDPE) has been investigated. Based on multi-techniques, such as 27Al MAS NMR, ICP-AES, Co-UV–vis-DRS, XRD, SEM, N2 adsorption-desorption, NH3-TPD, Py-IR and FTIR. It is found that the AlF located at the channel intersections show more Al pairs, and this location offers ample space for secondary reactions, which include Diels-Alder reaction, cyclization reaction and dehydrogenation reaction, resulting in the low yield of light olefins (10.6 wt%) and the generation of light alkanes and aromatics from light olefins. In contrast, AlF located in the straight and sinusoidal channels exists mainly in the form of single Al. The substantial steric hindrance for this location facilitates the cracking reaction, mainly referring to the cracking reactions of LDPE that produce light olefins and generate enhanced yield of light olefins (52.8 wt%). These results provide new perspectives towarding boosted light olefins generation in ex-situ catalytic pyrolysis of LDPE.

Insight into catalytic cracking pathways of n‐pentane over bifunctional catalysts to produce light olefins

AbstractRevealing the reaction mechanism to guide the industrial production of targeted products still remains a grand challenge for catalytic cracking of light alkanes to olefins over metal‐acid bifunctional catalyst. Herein, we systematically investigated the reaction mechanism of n‐pentane cracking on the Ag/ZSM‐5 bifunctional catalyst featuring both dehydrogenation and cracking capabilities. Specifically, overall cracking network of n‐pentane was comprehensively constructed to show the roles of metal dehydrogenation sites and acid sites respectively, in which metal Ag could substitute the H of the Brønsted acid site to form the Al–O–Ag linkage with enhanced adsorption and activation of n‐pentane, while Brønsted acid site with weak acid strength relay to promote cracking reaction. Thanks to this synergy of the two active sites, the apparent activation energy of n‐pentane cracking to light olefins was decreased from 82.77 KJ/mol to 68.26 KJ/mol and the proportion of specific path (C5H12 → H2 + C5H10) in n‐pentane monomolecular cracking reaction increased from 14.62% to 69.24%. In addition, 0.57Ag/ZSM‐5 catalyst exhibited the conversion of n‐pentane up to 67.55 wt%, which improved the performance of the parent ZSM‐5 by 13.42 wt%. These analysis results of reaction mechanism may provide some insights for the rational design of catalysts and the full utilization of petrochemical resources.

Assessing Markovian and Delay Models for Single-Nucleus RNA Sequencing.

The serial nature of reactions involved in the RNA life-cycle motivates the incorporation of delays in models of transcriptional dynamics. The models couple a transcriptional process to a fairly general set of delayed monomolecular reactions with no feedback. We provide numerical strategies for calculating the RNA copy number distributions induced by these models, and solve several systems with splicing, degradation, and catalysis. An analysis of single-cell and single-nucleus RNA sequencing data using these models reveals that the kinetics of nuclear export do not appear to require invocation of a non-Markovian waiting time.

Poisson distributions in stochastic dynamics of gene expression: What events do they count?

The Poisson distribution is the probability distribution of the number of independent events in a given period. Although the Poisson distribution appears ubiquitously in various stochastic dynamics of gene expression, both as time-dependent distributions and stationary distributions, underlying independent events that give rise to such distributions have not been clear, especially in the presence of the degradation of gene products, which is not a Poisson process. I show that the variable following the Poisson distribution is the number of independent events where biomolecules are created, destined to survive until the end of a given time duration. This new viewpoint enables me to rederive the Poisson distribution as a time-dependent probability distribution for molecule numbers in various monomolecular reaction models of stochastic gene dynamics. Additionally, it allows me to derive an analytic form of the time-dependent probability distribution for multispecies monomolecular reaction models with species whose lifetimes follow nonexponential distributions, which is the convolution of the Poisson distribution with the multinomial distribution. This distribution is then utilized for deriving a novel series expansion form of a time-dependent distribution for a model with a stochastic production rate.

Insight into performance over IM-5, ZSM-5 and ZSM-11 zeolites for n-heptane cracking to light olefins in the absence & presence of steam

The three dimension (3D) 10-membered ring channels zeolite has a unique advantage in increasing light olefins for catalytic cracking reaction. Herein, zeolites IM-5, ZSM-5 and ZSM-11 were synthesized hydrothermally to achieve comparable texture properties and SiO2/Al2O3 ratios. The acid content and acid strength of the three zeolites were as follows: IM-5 > ZSM-5 > ZSM-11. Meanwhile, 1H DQ MAS NMR confirmed that there was a synergistic effect between Brønsted and Lewis acids in IM-5 zeolite. However, IM-5 zeolite with lots of strong BAS had an unexpected low TOF in n-heptane cracking. Furthermore, the light olefins selectivity was as follows: IM-5 > ZSM-11 > ZSM-5 at 550–650 ℃ in the absence of steam. IM-5 zeolite had the particular advantage in ethylene, and its selectivity was up to 44.9 %. After steam was introduced, the monomolecular cracking reaction, the aromatization of propylene and the deep cracking of C3 and C4 hydrocarbons were inhibited over the three zeolites. Steam could prolong the activity of IM-5 zeolite, but accelerate the deactivation of ZSM-5 and ZSM-11 zeolites. The primary cause for the rapid deactivation of ZSM-5 and ZSM-11 zeolites was dealuminization in steam, whereas for the IM-5 zeolite, it was the rapid formation of coke on its surface, thereby blocking its micropore channels.

Regionally spatial framework Al distribution in MFI channels and its impact on the n-butane cracking reaction pathways

The regulation of the engineering regionally spatial framework aluminum (AlF) distribution in MFI channels has been considered as an effective way for the production of light olefins by targeted fluid catalytic cracking (TCO) technology. In this work, ZSM-5 zeolites with controlled AlF distributions are facilely synthesized by tuning the combinations of pentaerythritol (PET), tetrapropylammonium (TPA) and Na cations. The AlF atoms in the prepared HZ5-[PET + Na] and HZ5-[TPA] samples are enriched in the straight channels and intersection channels, respectively, which are favorable to the n-butane monomolecular reaction pathway, promoting the propylene production. Whereas the AlF atoms in the HZ5-[TPA + Na] sample are simultaneously distributed in both the straight and intersection channels, the n-butane molecules preferentially take place monomolecular reaction in the straight channels to generate carbonium ions (e.g., C2H5+, C3H7+ and C4H9+). Subsequently, all of them enter into the intersection channels to induce the occurrence of bimolecular reaction. Such a process is conducive to the formation of ethylene. These insights can help to clarify the catalytic behavior of regional framework acid sites in ZSM-5 channels and then provide an effective approach to design efficient TCO catalysts.

Catalytic cracking of heavy atmospheric gas oil to light olefins over ZSM-5 zeolite: Effect of crystal size in the absence/presence of steam

The catalytic cracking of heavy atmospheric gas oil (AGO) has been investigated to study the effect of ZSM-5 zeolite crystal size on the selectivity to light olefin in the absence and presence of steam. Dodecane (used as model compound) and heavy AGO feed streams were utilized to study the influence of changing pore shape selectivity when comparing cracking performance by nano and micro ZSM-5 zeolites. The zeolites were characterized using BET, XRD NMR, NH3-TPD and Py-FTIR. In the presence of steam, the short pores length nano ZSM-5 crystals showed enhanced catalytic cracking activity and selectivity to light olefins. The nano ZSM-5 catalyst promoted higher selectivity to light olefins through β-scission while reducing the extent of hydrogenation reactions towards the formation of liquefied petroleum gas components (LPG). In contrast, the long pores length of micro ZSM-5 tended to favor the production of more naphtha, kerosene and LPG through hydrogen transfer routes, resulting in lower selectivity to light olefins. The resulting propylene/ethylene (P/E) ratios were altered by the type of feed used, cracking reaction temperature, influence of steam and catalyst crystal size. Specifically, higher P/E ratio was achieved over nano ZSM-5 zeolite, especially with the cracking of heavy AGO feed in the presence of steam, due to an increase of monomolecular reactions through β-scission cracking mechanism.

Improved Catalytic Performances of the NaOH-Treated ZSM-22 Zeolite in the 1-Butene Skeletal Isomerization Reaction: Effect of External Acid Sites.

In this paper, a series of alkaline-treated ZSM-22 zeolite samples were prepared by treating the parent ZSM-22 zeolite using NaOH aqueous solution with different concentrations. By investigating the effects of alkaline treatment on the parent ZSM-22 zeolite, we discovered that the alkaline treatment contributed to the reduction of Brønsted acid sites due to the coverage of extra-framework Al on its external surface. In addition, it was found that the alkaline-treated samples were favorable to the improvement of the isobutene yield and selectivity, while these features appeared to be low for the subsequent acid-washed counterparts in the skeletal isomerization reaction of 1-butene. These results indicate that the catalytic performance of ZSM-22 zeolite is related to reduced amounts of Brønsted acid sites in it. To further reveal the reasons for the promoted catalytic performances of the alkaline-treated ZSM-22 series zeolites, we studied the properties of coke deposited on the two series of samples using Raman spectroscopy and thermogravimetric analysis and mass spectrometry (TG/MS-TPO). It was shown that the carbon deposited on the alkaline-treated series samples was mainly distributed at the outer surface, while the coke was distributed to a relatively lesser extent at the exterior surface for the acid-washed series samples. Moreover, by partially passivating outer acid sites of the parent zeolite, the selected alkaline-treated zeolite, and acid-washed zeolite, their isobutene selectivities were all improved with the decrease in outer acid sites. These phenomena confirmed that the improved catalytic performances of the alkaline-treated samples are related to their decreased external Brønsted acid site density, which further demonstrated that the high isobutene yield and selectivity in the skeletal isomerization reaction of 1-butene is realized via the monomolecular reaction pathway of 1-butene.

High-Temperature Cracking of Pentene to Ethylene and Propylene over H-ZSM-5 Zeolites: Effect of Reaction Conditions and Mechanistic Insights

The effects of reaction conditions on the yield of ethylene and propylene from pentene cracking were investigated in a fixed-bed reactor at 500–750 °C and for a weight hourly space velocity (WHSV) of 15–83 h−1. The total yield of ethylene and propylene reached a maximum (67.8 wt%) at 700 °C and 57 h−1. In order to explore the reaction mechanism at high temperatures, a thermal/catalytic cracking proportion model was established. It was found that the proportion of pentene feed chemically adsorbed with the acid sites and cracked through catalytic cracking was above 88.4%, even at 750 °C. Ethylene and propylene in the products were mainly derived from catalytic cracking rather than thermal cracking at 650–750 °C. In addition, the suitable reaction network for pentene catalytic cracking was deduced and estimated. The results showed that the monomolecular cracking proportion increased from 1% at 500 °C to 95% at 750 °C. The high selectivity of ethylene and propylene at high temperatures was mainly due to the intensification of the monomolecular cracking reaction. After 20 times of regeneration, the acidity and pore structure of the zeolite had hardly changed, and the conversion of pentene remained above 80% at 650 °C.

Alkene adsorption and cracking on acidic zeolites – A gradual process of understanding

Cracking of light alkenes on solid acids and, in particular on zeolites, is ubiquitous in refineries. Different zeolite framework topologies in the catalysts used provide spatial constraints for reactants and products, leading to discrete reaction routes and varying selectivities. The conversion of alkenes in cracking proceeds either via monomolecular or bimolecular reaction pathways. In both routes, the reacting alkene adsorbs first on Brønsted acid sites forming the initial state (e.g., π-complex, carbenium ion or alkoxide), followed by β-cleavage in the carbenium transition state, generating a smaller alkene and a carbenium ion (monomolecular route) or forming a dimer by alkene addition that cracks subsequently (bimolecular route). The current state of understanding alkene sorption and cracking is critically discussed and four questions are formulated that may be the central questions from our perspective in further developing new generations of catalysts and processes for alkene conversion.

Micro-mesoporous catalysts based on ZSM-5 zeolite synthesized from natural clay nanotubes: Preparation and application in the isomerization of C-8 aromatic fraction

Micro-mesoporous zeolite with ZSM-5 morphology was successfully synthesized by soft template and template-free methods using natural halloysite aluminosilicate nanotubes as a hard template and a source of aluminum and silicon. Formation of ZSM-5 crystal structure was confirmed by XRD. Textural properties and structural characteristics of functional materials, supports, and Pt-containing catalysts were examined by N2 physisorption, NH3-TPD, Py-FTIR, TEM, SEM, XRF techniques. Specific BET surface area of ZSM-5 zeolite prepared using TPABr as an organic template (ZSM-5(t):HNT) is 583 m2/g, whereas for the template-free counterpart (ZSM-5(tf):HNT) it reaches 225 m2/g. According to the Py-FTIR data, concentrations of Brønsted acid sites for ZSM-5(t):HNT and ZSM-5(tf):HNT are 295 and 93 μmol/g, whereas concentrations of Lewis acid sites are 79 and 41 μmol/g, respectively. Activity and selectivity of Pt catalysts based on the micro-mesoporous ZSM-5 zeolite-derived supports were evaluated in isomerization of C-8 aromatic fraction depending on the process conditions (temperature, feed space velocity). Because of the hierarchical micro-mesoporous structure, both catalysts provide xylenes transformation through the two isomerization routes (intra- and intermolecular). However, for the catalyst based on support synthesized through the template-free methods, the monomolecular reaction route is more preferable, and therefore the number of side reactions (disproportionation, transalkylation, and dealkylation) decreases.

Acid Catalysis over Low-Silica Faujasite Zeolites

Low-silica faujasite (FAU) zeolites (with Si/Al ratio of ca. 1.2-1.8) sustain framework integrity and porosity upon moderate ion exchange (0.01 M NH4NO3 solution for 1 h at ambient temperature), which introduces two kinds of protons, distinctive in reactivity and coordination to the zeolite framework, within supercages (HSUP). Moderate ion exchange limited within supercages transpires while maintaining full occupancy of Na+ cations within associated sodalite cages; this in turn helps stabilize the framework of low-silica H-FAU zeolites. Protons located on site II (H3630) and site III (H3650) within supercages on low-silica FAU zeolites can be classified and enumerated by virtue of infrared spectroscopy, providing an opportunity to compare reactivities of these distinct protons for monomolecular protolytic reactions of propane. Protons on site II exhibit prominently higher reactivity for monomolecular propane dehydrogenation and cracking than protons on site III. Low-silica proton-form FAU zeolites (zeolite X) upon moderate ion exchange possess protons on site III that are unavailable on high-silica FAU zeolites (zeolite Y) and limit ion exchange within supercages, providing unprecedented high-temperature structural and chemical stability (>773 K) and enabling their application as solid-acid catalysts.

The mechanism of thermal ionization of methenamine on the surface intermetallic compound NaAux

Thermal ionization of methenamine (C6H12N4) on the surface of the NaAux intermetallic compound has been studied. It has been established that the processes of decomposition, desorption and ionization of adsorbed compounds, thermally stimulated on the surface, proceed due to the accumulation of energy at the degrees of freedom of the adsorption complex, including the adsorbed compound and a solid, by the mechanism of monomolecular decomposition reactions. In this case, the decomposition of the adsorption complex is accompanied by the desorption of ions that are not in thermal equilibrium with the solid. The uniformity of the temperature dependences of the ion current and their distribution over two groups allowed us to conclude that ions are desorbed from the surface, which correspond to the decays of individual adsorbed molecules, as well as the decays of dimers formed on the surface. The decay of methenamine molecules during thermal ionization occurs in the same way as their decay in vacuum during electron ionization, which indicates the preservation of the bulk structure of methenamine molecules during adsorption and a significant lifetime of the excited state of compounds on NaAux. Keywords: thermal ionization, methenamine, intermetallic compound, NaAux.

Механизм термической ионизации уротропина на поверхности интерметаллида NaAu-=SUB=-x-=/SUB=-

Thermal ionization of methenamine (C6H12N4) on the surface of the NaAux intermetallic compound has been studied. It has been established that the processes of decomposition, desorption and ionization of adsorbed compounds, thermally stimulated on the surface, proceed due to the accumulation of energy at the degrees of freedom of the adsorption complex, including the adsorbed compound and a solid, by the mechanism of monomolecular decomposition reactions. In this case, the decomposition of the adsorption complex is accompanied by the desorption of ions that are not in thermal equilibrium with the solid. The uniformity of the temperature dependences of the ion current and their distribution over two groups allowed us to conclude that ions are desorbed from the surface, which correspond to the decays of individual adsorbed molecules, as well as the decays of dimers formed on the surface. The decay of methenamine molecules during thermal ionization occurs in the same way as their decay in vacuum during electron ionization, which indicates the preservation of the bulk structure of methenamine molecules during adsorption and a significant lifetime of the excited state of compounds on NaAux.

(Invited) Chemistry in a Nanoscale Gap

In the realm of the Single-Molecule Electronics, a suite of advanced electrical characterization approaches have emerged allowing measuring charge transport in an electric contact made out of an individual molecule[1]. The field has (and is still) drawn(ing) an scenario where individual molecules can be chemically modified to deliver a particular electrical function in a nanoscale circuit, e.g. variable resistors[2], diodes[3], switches[4], etc. Along this excursion, we have observed that single molecules trapped in a nanoscale tunneling junction experience conformational structural changes and changes in molecule/electrode contact geometries, which are usually accompanied by large conductance variations and can be easily detected electrically[1]. Such changes are induced by the imposed forces fields experienced by the molecules within the nanoscale gap, namely, a mechanical force and/or an electric field. In the past decade, we have learnt that under certain force field conditions, the individual molecules wired in a nanoscale junction undergo chemical transformations. Here, we will present a couple of illustrative examples of the use of single-molecule junction to study and control reactivity at the nanoscale using electric fields, a concept that is inherent in the natural enzymatic molecular machinery[5]. Tunable, well-oriented electric fields can be easily delivered along the main junction axis of a nanoscale electrical device[6]. We exploited the latter to study; (1) a simple monomolecular cis-trans isomerization reaction[7], and (2) a bi-molecular Diels-Alder reaction[8]. Along with the experimental design and fundamental chemistry aspects, we will discuss the advantages these examples can bring to possible technological applications.[1]. L. Sun et al. Chem. Soc. Rev., 2014,43, 7378-7411.[2]. A. C. Aragones et al. Chem. Eur.J.2015, 21,7716 –7720.[3]. I. Diez-Perez et al. Nature Chemistry 1, 635–641 (2009).[4]. N. Darwish et al. Nano Lett. 2014, 14, 12, 7064–7070.[5]. Stephen D. Fried et al. Annu Rev Biochem. 2017; 86: 387–415.[6]. N. Darwish et al. “Principles of Molecular Devices Operated by Electric Fields” in Effects of Electric Fields on Structure and Reactivity: New Horizons in Chemistry, Royal Society of Chemistry, Ed. Sason Shaik.[7]. C. S. Quintans et al. Appl. Sci. 2021, 11(8), 3317.[8]. A. C. Aragones et al. Nature 531, 88–91 (2016).