Relative Reaction Rates Research Articles

A Photoswitchable Olefin Metathesis Catalyst

A dithienylethene-functionalized N-heterocyclic carbene-Ru(II) complex was synthesized and found to undergo a reversible photoisomerization which influenced its intrinsic catalytic activity. UV-induced ring-closure enhanced the rate of ring-closing metathesis reactions (kclosed/kopened = 1.4–1.7) and attenuated the rate of ring-opening metathesis polymerizations (kclosed/kopened = 0.56–0.66). Visible light irradiation promoted cycloreversion and restored the initial activity. The ability to switch between the isomeric states of the catalyst was also utilized to modulate the rate of ongoing olefin metathesis reactions via photoirradiation. A computational investigation revealed how steric and electronic effects separately influence the transition states adopted by each form of the catalyst and afforded activation energies that were in agreement with the relative reaction rate constants determined by experiment.

Di-tertiary-butyl Peroxide Decomposition and Combustion with Air: Reaction Mechanism, Ignition, Flame Structures, and Laminar Flame Velocities

This study investigates the ignition/combustion of di-tertiary-butyl peroxide (DTBP) over a wide range of fuel/air ratios using numerical flame calculations to gain insight into species profiles and ignition/combustion characteristics of DTBP/air mixtures. The results are flame zone and reaction zone structures as well as the corresponding laminar flame speeds and propagation speeds of reaction zones. Several detailed reaction mechanisms are evaluated in the flame simulations, and sensitivity of the computed results to important reaction steps was evaluated. The ignition of DTBP in the absence of oxygen belongs in the category of thermal runaway because there is no chain branching associated with the early stages of the reaction; i.e., decomposition steps lead to acetone and ethane. In the presence of oxygen, the development of a flame is more complex and exhibits a two-stage ignition, where the first stage, at lower temperatures, involves the thermal decomposition of DTBP to acetone, which further oxidizes to the final combustion products. This second high-temperature ignition process involves chain-branching reactions for the combustion of acetone and ethane and the usual chain-branching reactions of the H2/O2 system. The calculations reproduce this two-stage ignition behavior for fuel-rich flames, and the calculated flame structures reflect the interaction of decomposition of DTBP to acetone and ethane and the subsequent combustion. DTBP has a relatively weak RO–OR bond and readily undergoes dissociation at higher temperatures to two RO• radicals, and it is widely used as a radical source, reaction initiator. Five reaction mechanisms (M1–M5) were employed in this study for analysis of the reaction system, which differ mainly in the reaction rates for the initial DTBE decomposition reaction. When using relative high reaction rates for the initial decomposition reactions (M1 and M2), the flame velocities of DTBP/air mixtures exhibit two maxima over the entire range of the mixture fraction. The first maximum is located at stoichiometric conditions, while the second prevails under fuel-rich conditions. Decelerating the primary decomposition reactions (M3–M5) in favor of the combustion reactions of the DTBP decomposition products shows the second maximum disappearing as result of the relative low propagation speed of the reaction zone. The first maximum is only slightly altered by varying the reaction rates, because the decomposition step of DTBP and the combustion of the primary decomposition products merge at stoichiometric conditions and temperatures are high enough to result in high decomposition rates.

Preparation and characterization of the ethylene‐vinyl acetate copolymer partially hydrolyzed assisted by microwave radiation

ABSTRACTEthylene‐vinyl acetate copolymer (EVA) was modified by hydrolysis using dielectric heating. The modified EVA was characterized by Fourier transform infrared spectroscopy, differential scanning calorimetry, thermogravimetric analysis (TG), 1H Nuclear magnetic resonance (NMR), gel permeation chromatography, and small‐angle X‐ray scattering. The results showed that the EVA was hydrolyzed with degree between 36.1 and 42.6% according to 1H NMR and TG results. The relative reaction rate for the sample prepared in the oil bath was ∼9%/h, while in the dielectric was ∼150%/h for 15 min. This significant improvement was due to the specific effect of microwave‐assisted reactions through dipole rotation and ionic polarization contributions. The hydrolysis reaction promoted a reduction of the pendent group size of EVA backbone. This change directly contributed to increasing melt temperature, crystallization temperature, melt and crystallization enthalpies. Also, decreased the long period, increased the volume crystallinity, and caused reductions amorphous/crystalline interface and two‐phase model deviations. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44558.

Effect of the ligand nature in cobalt complexes on the selectivity of the reaction of carbon dioxide and propylene oxide

The reaction of carbon dioxide with propylene oxide in the presence of the (salen)CoCl or (TPP)CoCl (salen = bis(3,5-di-tert-butyl-salicylidene)-1,2-diaminocyclohexane, TPP = 5,10,15,20-tetraphenylporphyrin) catalyst and the PPNCl (bis(triphenylphosphine)iminium chloride) cocatalyst has been carried out at 20–60°С and a СО2 pressure of 0.6 MPa to investigate the effect of the ligand nature on the reaction rate and selectivity. The change in the reaction rate and selectivity in relation to the temperature and cocatalyst/catalyst ratio has been studied. The activation energy of the copolymerization of СО2 with propylene oxide catalyzed by the (salen)CoCl complex have been obtained.

Role of water clusters in the reaction of the simplest Criegee intermediate CH2OO with water vapour

A comprehensive theoretical study on the role of water clusters ((H2O) n , n = 3–5) in the reaction of CH2OO with water vapour is done at the CCSD(T)//M06-2X/6-311 + G(2df,2p) level of theory. Our simulation results show that the contribution of entropic effect is significantly increased with the increase in the number of water molecules involved. The main products of CH2OO reaction with water vapour are α-hydroxymethyl hydroperoxide and its isomers. Contrary to the reaction of CH2OO with unimolecular water (10.91 kcal mol−1), the barriers of reactions with bi- and trimolecular water are further reduced to 5.25 and 4.75 kcal mol−1, respectively. Among these three reactions, the predominant pathway is the reaction of CH2OO with bimolecular water owing to its lower barrier and the high concentration of (H2O)2 ([(H2O)2] ≈ 2.47 × 1014 molecules cm−3). The presence of water clusters exhibits a dramatic catalytic effect in the CH2OO reaction with bimolecular water as it lowers the energy barrier by 4.0 kcal mol−1. The relative reaction rates, which are determined at temperatures from 273 to 323 K and 85 % relative humidity, reveal that the most favourable pathway for the atmospheric removal of CH2OO is indeed via its reaction with bimolecular water.

Spatial Mapping of Methanol Oxidation Activity on a Monolithic Variable-Composition PtNi Alloy Using Synchrotron Infrared Microspectroscopy

The use of synchrotron-sourced infrared radiation to map the electrochemical activity of a binary metal (Pt and Ni) alloy is demonstrated. The alloy is created in such a way that its metal concentration varies along one of its dimensions thus creating a continuum of electrocatalyst compositions on a single electrode. Localized methanol oxidation activity is determined spectroscopically by measuring the rate of CO2 production at variable positions along the alloy concentration gradient using an infrared microscope. Numerical simulations of the kinetically controlled reaction demonstrate that qualitative assessment of relative reaction rates is possible as long as the reaction is followed on time scales smaller than those that lead to diffusional broadening. Characterization of the alloy before and after electrochemical experiments reveals significant levels of base metal leaching. Highly dealloyed regions of the sample show the highest rates of methanol activity and have a final Ni atomic composition of approximately 5%. Surface roughening from the dealloying process is shown to be at least partially responsible for enhanced activity.

Effects of Void Environment and Acid Strength on Alkene Oligomerization Selectivity

The effects of channel connectivity, void environment, and acid strength on the relative rates of oligomerization, β-scission, and isomerization reactions during light alkene conversion (ethene, propene, isobutene; 2–400 kPa alkene; 473–533 K) were examined on microporous (TON, MFI, MOR, BEA, FAU) and mesoporous (amorphous silica–alumina (SiAl), MCM-41, Keggin POM) Bronsted acids with a broad range of confining voids and acid strength. Skeletal and regioisomers equilibrate under all conditions of pressure and conversion and on all catalysts, irrespective of their acid strength, void size, or framework connectivity, consistent with rapid hydride and methyl shifts of alkoxides intermediates and with their fast adsorption–desorption steps. Such equilibration is evident from detailed chemical speciation of the products and also from intramolecular isotopic scrambling in all oligomers formed from 2-13C-propene on TON, MFI, SiAl, and POM clusters. Previous claims of kinetic control of skeletal isomers in oligom...

The Influence of Copper Coatings on the Corrosion of Carbon Steel Substrates

Within the multi-barrier system proposed for the permanent disposal of spent nuclear fuel, the primary engineered barrier is the sealed metallic container. The proposed Canadian container design involves a carbon steel vessel coated with 3 mm of Cu. Since they will be buried ~500 m below ground, the carbon steel provides the necessary structural support, while the Cu coating provides corrosion resistance.1 The coatings will be formed by either electrodeposition or a cold spray technique. Despite a considerable amount of research into the corrosion behaviour of the outer Cu coating,2 the impact of a defect in the coating on the corrosion of steel remains largely unstudied. Should a defect simultaneously expose both Cu and steel to groundwater, galvanically accelerated corrosion of the steel could increase the accumulation of corrosion damage, by either corrosion propagation through the steel or de-adhesion of the Cu coating from the steel. The goal of this research is to determine the influence of the coating process on these modes of damage accumulation when a through-coating defect is present. To simulate this scenario, Cu-coated carbon steel specimens with a small hole (0.5 mm in diameter) drilled through the coating to the Cu-steel interface are being used. Since strongly saline ground waters are possible, the specimens are exposed to 3 M NaCl solutions with various concentrations of dissolved O2. Using X-ray microtomography, a non-destructive 3D imaging technique, the progression of corrosion damage at the base of the simulated defect is being monitored both in-situ and ex-situ. The corrosion process is also being followed electrochemically by monitoring the corrosion potential and periodically recording the polarization resistance using the linear polarization technique. The potential reflects the relative rates of the chemical reactions occurring on the sample surface and the polarization resistance values reflect the changes in the overall corrosion rate. Results to date show that galvanically accelerated steel corrosion occurs, as expected, in oxygenated solutions, with the corrosion rate and distribution of damage being dependent on the dissolved O2 concentration. The corrosion behaviour also differs depending on the nature of the coating. Coatings produced by a cold spray process exhibited damage propagation along the Cu/steel interface, while electrodeposited coatings did not. Despite this difference in geometry, the overall extent of corrosion is very similar based on damage volume measurements obtained from the X-ray microtomography imaging. The long term goal of this project is to develop a computational model to determine the extent of corrosion damage which could occur on a waste container emplaced in a repository ~500 m below ground in which the redox conditions are evolving from oxic to anoxic. With this goal in mind, a finite element model (based on a COMSOL framework) is being developed to describe the galvanic corrosion process. (1) Scully, J. R.; Edwards, M. Review of the NWMO Copper Corrosion Allowance; NWMO TR-2013-04; NWMO: Toronto, ON, 2013. (2) King, F. Critical Review of the Literature on the Corrosion of Copper by Water; TR-10-69; SKB: Stockholm, Sweden, 2010.

Reaction and Mass Transport Simulation of Polymer Electrolyte Fuel Cell for the Analysis of the Key Factors Affecting the Output Performance in the Catalyst Layer

Polymer electrolyte fuel cell (PEFC) has been developed as a power source for fuel cell vehicle (FCV). To have FCV used more commonly, it is required to reduce PEFC system cost[1]. Increasing output density is effective measures for cost reduction because it is necessary to reduce total cost of PEFC in addition to quantity of platinum catalyst. In recent years, high performance cathode catalyst layers (CLs) are proposed, which made contrivances to its catalyst structure[2-3]. However, the method for developing catalyst is trial and error and there is no clear design guideline for further improvement. The purpose of this study is to propose the optimum design of cathode catalyst (Pt/CB) by simulating the electrochemical reaction and PEFC transport phenomena. In this study, based on the our previous research[4], diffusion phenomenon in the catalyst is newly reflected on the 1D model to compare catalyst structures. Fig.1 shows the image of transport phenomena in the catalyst pore. As shown in the structure (A), if Pt is covered with ionomer, oxygen reduction reaction (ORR) rate per unit Pt surface area is reduced by sulfonic group in ionomer. Thus it is assumed that if Pt exists in the pore as shown in the structure (B), ORR rate increases compared with structure (A) because there is no sulfonic group in the pore. However, oxygen concentration on the surface of Pt decreases compared with structure (A) because oxygen diffusion resistance increases. In this research, reflecting this trade-off between ORR rate and diffusion resistance, we constructed the model to compare catalyst structures. Based on the porous electrode theory[4], ORR and mass transport at the fuel cell evaluation test were simulated. In this research, generated water was considered as vapor, carbon corrosion reaction and suppress elution of platinum were neglected. The temperature profile in the cell was presumed to be uniform (80 ℃). Fig.2 shows some catalyst structures for simulation. Spherical diameter of carbon black (CB) and Pt catalyst carrying rate of CB are same in all structures. Assuming that pores of the porous CB is filled with the generated water. In addition, diffusion coefficient of GDL and MPL are determined by the experimental correlation equation for porous structures of PEFC. Each structure was simulated under various exchange current density. And oxygen distribution and relative reaction ratio were investigated in the catalyst. Fig. 3 shows the current-voltage characteristic curves obtained from the simulation (Exchange current density in the pore is five times as large as covered with ionomer.) Str.2-6 has larger output density at low current density region. In this case, this result shows porous carbon black has larger output density than Str.1 for PEFC because practical voltage region is 0.6 V - 0.8 V. Fig.4 shows the radial relative reaction rate in the pore.Reaction rate decreasing for the center direction, we were able to reflect oxygen diffusion resistance and compare catalyst structures. Furthermore, we attempt to separate factors of performance degradation of fuel cell and evaluate each factors quantitatively to confirm the appropriateness of the model.

Synthetic and Organocatalytic Studies of Quinidine Analogues with Ring-Size Modifications in the Quinuclidine Moiety.

Six highly enantiopure analogues of [2.2.2] were synthesized with five- or seven-membered rings in the (original) quinuclidine skeleton. Five of these compounds were prepared through epoxide opening by a secondary cyclic amine, providing the nor- and homoquinuclidine moieties through five- and six-membered ring formation. This method failed in the case of seven-membered ring formation, so for that particular ring size a different synthetic route starting from 3-quinuclidone was applied. The six novel analogues were examined as organocatalysts in four asymmetric conjugate addition reactions and the results compared with those of known cinchona alkaloid catalysts. This study shows that modification of the quinuclidine ring can have a substantial influence on catalyst activity and enantioselectivity. To acquire more insight into the characteristics of the new catalysts, the pKaH values were determined by means of fluorescence spectroscopy. Furthermore, relative reaction rates of conjugate thiol additions reactions catalyzed by these quinidine analogues were measured through polarimetry.

Cationic emulsion polymerization of dimethylcyclosiloxane utilizing anionic surfactant: A mechanism study

Cationic Emulsion polymerization (EP) of dimethylcyclosiloxanes in emulsion with an acidic anionic surfactant as catalyst (surfcat) was studied using heterogeneous two phase liquid–liquid kinetics. Octamethylcyclotetrasiloxane EP has a reaction half-life much greater than the time for diffusion into the aqueous phase, indicating that the EP does not begin at the droplet surface. The EP process exhibits all the characteristics of a two phase liquid–liquid heterogeneous reaction beginning in the aqueous phase. The mechanism of cationic EP was found to be the same as in anionic EP-coagulative homogeneous nucleation.Evidence indicates that octamethylcyclotetrasiloxane redistribution to form other cyclosiloxanes begins by micellar hydrolysis in surfcat micelles. Depolymerization occurs by interfacial hydrolysis at the surface of the polymer particles, producing dimethylsilanediol which diffuses into the aqueous phase to subsequently form cyclosiloxanes by condensation and cyclization. It is proposed that percent conversion of cyclosiloxane to polymer may be affected by the relative reaction rates of polymerization, redistribution and depolymerization.

Control of silicate weathering by interface-coupled dissolution-precipitation processes at the mineral-solution interface

Abstract The mechanism of surface coating formation (the so-called surface altered layers [SALs] or leached layers) during weathering of silicate minerals is controversial and hinges on understanding the saturation state of the fluid at the dissolving mineral surface. Here we present in-situ data on the evolution of the interfacial fluid composition during dissolution of wollastonite (CaSiO3), obtained using interferometry and micro pH and ion-selective electrodes. Steep concentration gradients develop at the mineral interface as soon as it makes contact with the solution. This interfacial fluid becomes supersaturated with respect to amorphous silica that forms a surface coating, limiting fluid access to the mineral surface and hence affecting the dissolution rate. The thickness of the supersaturated zone and the precipitated layer depends on the relative rates of mass transport and surface reaction in the system; this effect could contribute to the discrepancy between dissolution rates measured in the field and in the laboratory. As well, our results have implications for predictions of silicate weathering rates and hence climate evolution, as different assumptions on dissolution mechanisms affect calculations on CO2 drawdown during weathering and consequent effects on estimates of global mean temperatures.

Massively Screening the Temporal Spectra of Single Nanoparticles to Uncover the Mechanism of Nanosynthesis.

Nanosynthesis is the basis of nanotechnology and its applications. It is necessary to understand the growth mechanism of nanoparticles and the functions of growth factors. An effective way to study the synthesis is at the single nanoparticle level. This study reports a single nanoparticle spectrometer, which is based on a commercial dark-field microscopy and a group of narrowband filters. This spectrometer has many advantages, such as high light transparency (35%-75%), low cost (<$1500), massive screening (≈200 nanoplates at a time), and a high time resolution (<5 s). By using this spectrometer, the galvanic replacement reaction (GRR) is studied on single Ag nanoplates in situ and in real time. The research reveals that GRR on single Ag nanoplates has three different types according to the change of peak wavelength during reaction. Such diverse reaction types can be attributed to the different relative reaction rates of GRR on the faces and edges of Ag nanoplate with different facets. Further research shows that the relative reaction rates of different facets vary a lot under different concentrations of tri-sodium citrate. This research successfully demonstrates that the new single nanoparticle spectrometer can study the growth of single nanoparticles and the effect of growth factors.

Upscaling study of the cyclic solvent injection process for post‐chops reservoirs through numerical simulation

AbstractThe cyclic solvent injection (CSI) process has been suggested as the most promising solvent‐based recovery method for post‐CHOPS reservoirs. Six CSI experiments were performed in three sandpacks with different scales and wormhole locations. Numerical simulations were conducted to history‐match the six CSI experiments. The effects of uncertain parameters such as relative permeability, capillary pressure, reaction rate (foamy oil model), and dispersion coefficient on the history‐matching were studied. The sensitivity analysis indicated that relative permeability and capillary pressure significantly affected the production performance of the CSI process in the numerical simulation. In particular, capillary pressure played the greatest role in upscaling in both axial and radial directions. Furthermore, capillary pressure effects were aggravated when the wormhole was located in the top of the experimental model. Thus, all CSI experimental production data were matched successfully by tuning the capillary pressure based on the same matched relative permeability curves.A heavy oil post‐CHOPS reservoir in western Canada was evaluated for the CSI process at field scale. Wormholes were considered by applying the multi‐lateral well model. Post‐CHOPS conditions were established by history‐matching the field's production of oil and water. The parameters obtained from the history match upscaling studies were adopted in simulating the subsequent CSI process and were set with certain constraints to consider its uncertainty at field scale. The recovery factor after ten years of the CSI process was in the range of 13.5–16.0 %.

Evaluation of 5‐cis‐Substituted Prolinamines as Ligands in Enantioselective, Copper‐Catalyzed Henry Reactions

AbstractThe development of a new catalytic system for enantioselective Henry reactions, which permits superb 99 % ee with a broad variety of aldehydes, is presented. In‐depth structure–selectivity investigations with 33 5‐cis‐substituted prolinamines, prepared from methyl Boc‐l‐pyroglutamate, revealed that an aromatic or sterically demanding aliphatic substituent in 5‐cis position is crucial for high levels of stereocontrol, while bulkier substituents at the nitrogen atoms diminish both, enantioselectivities and reaction rates. The scope of the prime catalyst was expanded to gram‐scale and diastereomeric Henry reactions (up to 84:16 dr, 99 % ee). In the course of mechanistic studies, it was proven that the resulting β‐nitro alcohols are configurationally stable under the reaction conditions. In addition, competition experiments were used to determine the relative reaction rates of some of the prolinamine‐modified catalysts.

Scanning Single-Molecule Fluorescence Correlation Spectroscopy Enables Kinetics Study of DNA Hairpin Folding with a Time Window from Microseconds to Seconds.

Single-molecule fluorescence measurements have been widely used to explore kinetics and dynamics of biological systems. Among them, single-molecule imaging (SMI) is good at tracking processes slower than tens of milliseconds, whereas fluorescence correlation spectroscopy (FCS) is good at probing processes faster than submilliseconds. However, there is still shortage of simple yet effective single-molecule fluorescence method to cover the time-scale between submilliseconds and tens of milliseconds. To effectively bridge this millisecond gap, we developed a single-molecule fluorescence correlation spectroscopy (smFCS) method that works on surface-immobilized single molecules through surface scanning. We validated it by monitoring the classical DNA hairpin folding process. With a wide time window from microseconds to seconds, the experimental data are well fitted to the two-state folding model. All relevant molecular parameters, including the relative fluorescence brightness, equilibrium constant, and reaction rate constants, were uniquely determined.

Positioning a Carbon-Fluorine Bond over the π Cloud of an Aromatic Ring: A Different Type of Arene Activation.

It is known that the fluoro group has only a small effect on the rates of electrophilic aromatic substitutions. Imagine instead a carbon-fluorine (C-F) bond positioned tightly over the π cloud of an aryl ring-such an orthogonal, noncovalent arrangement could instead stabilize a positively charged arene intermediate or transition state, giving rise to novel electrophilic aromatic substitution chemistry. Herein, we report the synthesis and study of molecule 1, containing a rigid C-F⋅⋅⋅Ar interaction that plays a prominent role in both its reaction chemistry and spectroscopy. For example, we established that the C-F⋅⋅⋅Ar interaction can bring about a >1500 fold increase in the relative rate of an aromatic nitration reaction, affording functionalization on the activated ring exclusively. Overall, these results establish fluoro as a through-space directing/activating group that complements the traditional role of fluorine as a slightly deactivating aryl substituent in nitrations.

Experimental and Computational Assessment of Reactivity and Mechanism in C(sp(3))-N Bond-Forming Reductive Elimination from Palladium(IV).

This report describes a combined experimental and computational investigation of the mechanism of C(sp(3))-N bond-forming reductive elimination from sulfonamide-ligated Pd(IV) complexes. After an initial experimental assessment of reactivity, we used ZStruct, a computational combinatorial reaction finding method, to analyze a large number of multistep mechanisms for this process. This study reveals two facile isomerization pathways connecting the experimentally observed Pd(IV) isomers, along with two competing SN2 pathways for C(sp(3))-N coupling. One of these pathways involves an unanticipated oxygen-nitrogen exchange of the sulfonamide ligand prior to an inner-sphere SN2-type reductive elimination. The calculated ΔG(⧧) values for isomerization and reductive elimination with a series of sulfonamide derivatives are in good agreement with experimental data. Furthermore, the simulations predict relative reaction rates with different sulfonamides, which is successful only after considering competition between the proposed operating mechanisms. Overall, this work shows that the combination of experimental studies and new computational tools can provide fundamental mechanistic insights into complex organometallic reaction pathways.

Reaction Mechanisms of the Initial Oligomerization of Aluminophosphate

The mechanisms of aluminophosphate oligomerization were investigated using density functional theory with the SMD solvation model. Two aluminum species, Al(OH)4(-) and Al(H2O)6(3+), and four phosphorus species, H3PO4, H2PO4(-), HPO4(2-), and PO4(3-), were considered as the monomers for polycondensation reactions. It was found that the most favorable pathway to dimerization was a Lewis acid-base reaction: the aprotic oxygen of phosphoric acid (P═O) performs a nucleophilic attack on the central aluminum atom of Al(OH)4(-). Using this mechanism as a pattern, plausible dimerization mechanisms were investigated by varying the proticity and hydration of the phosphorus and aluminum monomers, respectively. The relative reaction rates of each mechanism were estimated under different pH conditions. The chain growth of aluminophosphates to trimers, tetramers, and pentamers and the cyclization of a linear tetramer were also investigated. For oligomerization reactions beyond dimer formation, it is found that cluster growth favors the addition of the phosphoric monomers rather than aluminum monomers.

The Importance of Relative Reaction Rates in the Optimization of Detailed Kinetic Models

ABSTRACTNumerous mathematical tools intended to adjust rate constants employed in complex detailed kinetic models to make them consistent with multiple sets of experimental data have been reported in the literature. Application of such model optimization methods typically begins with the assignment of uncertainties in the absolute rate constants in a starting model, followed by variation of the rate constants within these uncertainty bounds to tune rate parameters to match model outputs to experimental observations. The present work examines the impact of including information on relative reaction rates in the optimization strategy, which is not typically done in current implementations. It is shown that where such rate constant data are available, the available parameter space changes dramatically due to the correlations inherent in such measurements. Relative rate constants are typically measured with greater relative accuracy than corresponding absolute rate constant measurements. This greater accuracy further reduces the available parameter space, which significantly affects the uncertainty in the model outcomes as a result of kinetic parameter uncertainties. We demonstrate this effect by considering a simple example case emulating an ignition event and show that use of relative rate measurements leads to a significantly smaller uncertainty in the output ignition delay time in comparison with results based on absolute measurements. This is true even though the same range of absolute rate constants is sampled in each case. Implications of the results with respect to the maintenance of physically realistic kinetics in optimized models are discussed, and suggestions are made for the path forward in the refinement of detailed kinetic models.