Hydrophobic rate acceleration. Breslow and his co-workers first explored the effect of water on the rate of Diels-Alder reactions in a quantitative manner3. This was done by comparing the rates of reaction in Figure 2 in isooctane, methanol and water. It was found that all three reactions proceeded significantly faster in water than in nonpolar organic solvent. Solvent polarity effect was not the reason for the enhancement of the reaction. It was found that the reaction between 1.1 (cyclopentadiene) and 1.2 (acrylonitrile) was only slightly faster than isooctane. The reaction between 1.8 (9-hydroxymethylanthracene) and 1.9 (N-ethylmaleimide) was found to be slower in methanol than the isooctane due to the disrupted hydrogen-bonded association of the diene and dienophile. This was a good evidence that there are other factors affecting the reaction in water. The evidence of a hydrophobic effect involved from a series of experiments that measured rates of reactions in the presence of additives known to increase or decrease hydrophobic effect1. Agents such as lithium chloride (LiCl), prohydrophobic, causes the free water molecules to collapse around its ions, acting as an internal pressure which increases the reaction rate with negative activation volume1,3. Enforced hydrophobic interactions. …show more content…
This is a result of a more favorable entropy contribution, due to the reduction of apolar molecular surface area during the activation process4. The substituent of the reaction does affect the rate enhance but depended on the compounds being used. The Gibbs energy transfer plot of the reaction of compounds 1.1 and 1.5 from figure 1, reveals that the rate acceleration in water relative to the alcohol was due to the destabilization of the initial state. The stabilization of the transition state relative to the initial step was proposed to be a consequence of the reduction of hydrophobic surface
The experiment of Diels-Alder reactions, in particular the furan and maleic anhydride as used in my experiment, observed the exo product as oppose to the exo product. This shows the tendency for the stereochemistry of the Diels-Alder to yield an exo product in preference to the endo product. To determine the stereochemistry, a melt temperature of the product was taken and compared to literature values. The melt temperature for the product was roughly around 113oC, corresponding to the exo Diels-Alder product of furan and maleic anhydride. When compared to the class data of melting ranges, the melting temperature from the reaction was relatively consistent to the majority. Based off this, the assumption can be made that the Diels-Alder prefers
...teraction of the HOMO of the diene and the LUMO of the dienophile. This reaction was done at relatively low temperatures as the dry ether has a boiling point of 34.6 °C. At low temperature the endo preference predominates unless there is extreme steric hindrance, which in this case there is not. The endo product forms almost exclusively because of the activation barrier for endo being much lower than for exo. This means that the endo form is formed faster. When reactions proceed via the endo for the reaction is under kinetic control. Under kinetic control the adduct is more sterically congested, thus thermodynamically less stable. The endo form has a lower activation energy, however, the EXO form has a more stable product. As this is a symmetrical Diels-Alder reaction there is not two possible isomers of the product.
Abstract: This week we experimentally determined the rate constant k for the reaction 2HCl (aq) +Na2S2O3 (aq) → S (s) + SO2 (aq) + H2O (l) + 2NaCl (aq). In order to do this the average reaction time was recorded in seconds during two trials. The data from the experiment shows this reaction is in the first order overall: rate=.47s-1 [HCl]0 [Na2S2O3]1. These findings seem to be consistent with the expected results
The purpose of the experiment is to study the rate of reaction through varying of concentrations of a catalyst or temperatures with a constant pH, and through the data obtained the rate law, constants, and activation energies can be experimentally determined. The rate law determines how the speed of a reaction occurs thus allowing the study of the overall mechanism formation in reactions. In the general form of the rate law it is A + B C or r=k[A]x[B]y. The rate of reaction can be affected by the concentration such as A and B in the previous equation, order of reactions, and the rate constant with each species in an overall chemical reaction. As a result, the rate law must be determined experimentally. In general, in a multi-step reac...
Examining different properties of compound action potentials (CAPs) by studying the effects of stimulus voltage and stimulus interval in the sciatic nerve of Rana pipiens
The experiment is aimed at giving a better understatement of osmosis process and the different conditions in which osmosis occurs.
The speed of a reaction can be affected by a few factors. One of these
The reaction rate was a strong function of oxygen partial pressure with a significant increase in reaction rate with increase oxygen partial pressure. The reaction order of 0.37 for reaction with respect to dissolved oxygen concentration was obtained.
Aim The aim of this experiment is to investigate the effects of different concentrations of sugar solutions on the rate of osmosis in plant cells.
The aim of this experiment was to investigate the affect of the use of a catalyst and temperature on the rate of reaction while keeping all the other factors that affect the reaction rate constant.
Diffusion and osmosis in living cells are greatly effected by factors such as solution concentration, temperature, and surface area of the cell. This was studied using agar cubes of different sizes, dialysis tubing, and potato cores to demonstrate how the different factors affect cells. The process of cellular respiration can be altered due to temperature differences. Enzymes also greatly affect the molecular processes that occur. Enzymes are denatured at variety of pH and causes inactivity of the enzyme in the reactions.
There are five factors which affect the rate of a reaction, according to the collision theory of reacting particles: temperature, concentration (of solution), pressure (in gases), surface area (of solid reactants), and catalysts. I have chosen to investigate the effect of concentration on the rate of reaction. This is because it is the most practical way to investigate. Dealing with temperatures is a difficult task, especially when we have to keep constant high temperatures. Secondly, the rate equation and the constant k changes when the temperature of the reaction changes.
The dispersal of seeds or fruits plants by means of water currents. Hydrochory is used primarily by several species of aquatic plants or plants that inhabit near bodies of water. However, there are species which also uses this method of transmission as a secondary means of dispersal.
Investigating the Effects of Temperature on the Rate of Reaction between Magnesium and Hydrochloric Acid Introduction Chemical kinetics is the study and examination of chemical reactions regarding re-arrangement of atoms, reaction rates, effect of various variables, and more. Chemical reaction rates, are the rates of change in amounts or concentrations of either products or reactants. Concentration of solutions, surface area, catalysts, temperature and the nature of reactants are all factors that can influence the rate of reaction. Increasing the concentration of a solution allows the rate of reaction to increase because highly concentrated solutions have more molecules and as a result the molecules collide faster. Surface area also affects reaction rate because when the surface area of a reactant is increased, more particles are exposed to the other reactant.
One vital process in the human body observed in chemistry is the idea of chemical kinetics. Chemical kinetics is the study of the rate of reactions, or how fast reactions occur.1 Three factors that affect chemical kinetics are concentration, temperature, and catalysis. As the concentration of a substance increases, the rate of the reaction also increases.1 This relationship is valid because when more of a substance is added in a reaction, it increases the likelihood that the