Analysis Of Sn1 Reaction

Improved Essays
The expression "SN1" is the abbreviation of "unimolecular nucleophilic substitution reaction", one of the most common reactions in organic chemistry. As a fundamental reaction type, the mechanism of SN1 reaction has long been clear to the researchers, and the rate of the reaction concluded from the mechanism is quite simple. According to the mechanism, the rate of an "ideal" SN1 reaction is only proportional to the concentration of the substrate, which can be expressed as the following formula: rate=k[RX] ([RX] is the concentration of the substrate). However, experiments have shown some exceptions including some of which follow the formula at the early period of the reaction but change the rates later (O. T. Benfey, E. D. Hughes, and C. K. …show more content…
However, there are three types of deviations between the results and the theoretical ones which can not be neglected. One of them is the ‚Äúreversibility of the initial heterolysis‚ÄĚ (O. T. Benfey, E. D. Hughes, and C. K. Ingold, J. Chem. Soc. 2489) which makes the reaction a pure first-order one at the beginning but slower than it should be in the later period. One sort of examples are the hydrolysis reactions of diarylmethyl halides. For illustration, the hydrolysis of diphenylmethyl chloride is discussed here. The reason for the dropping rate at the later period is that the leaving group having disassociated may compete with the reactant to combine with the diphenylmethyl cation. At the beginning, although chloride ion is a better nucleophilic reagent than water, its concentration is so small that it can be neglected, while the concentration of water is so large that it does not appear in the rate formula as the solvent. During the process of the reaction, the concentration of chloride ion increases gradually and the effect of the competition between chloride ion and water becomes important enough to be taken into consideration in the later period, so the rate drops later. The case shows that the formula should be modified to meet more general cases, applying the steady-state approximation, the rate formula can be modified to be a more universal one taking no consideration of the …show more content…
However, if the leaving ion can decrease the rate, adding additional leaving ion can also decrease the rate of the reaction in the same way (Michael B Smith and Jerry March, 434). This is a common effect in the inorganic reactions called common-ion effect. Since there are many organic reactions occurring in organic solvents, the effect is not discussed in organic reactions often. However, some SN1 reactions like the hydrolysis discussed is proceeded in the solvents suitable and there are ions produced during the processes in which the common-ion effect should be taken into consideration. While other SN1s are not affected by the common-ion effect because no ion is involved in these reactions. The common-ion effect discussed is a qualitative effect, which makes the reaction rates with such effect difficult to express with formulas, but it is a kinetic effect to be considered which slows down the rate of a reaction in certain

Related Documents

  • Improved Essays

    The effect of the increased or decreased [OH-] on the rate law is very minimal. As the concentration of OH- is increasing, the rate of reaction is increasing at a very low rate. This is a plausible conclusion because a reaction involving a tertiary alkyl halide will follow SN1 mechanism.…

    • 1172 Words
    • 5 Pages
    Improved Essays
  • Decent Essays

    In most cases, a chemical reaction is able to occur in more than one way; enzyme kinetics studies the effect of how biological catalysts can influence biochemical reactions.…

    • 177 Words
    • 1 Pages
    Decent Essays
  • Improved Essays

    When the catechol is the substrate in excess and the enzyme increased, the rate of reaction increases exponentially due to the increasing amount of enzymes able to catabolize more…

    • 753 Words
    • 4 Pages
    Improved Essays
  • Improved Essays

    In Experiment 12B we used an umpolung reagent in an umpolung synthesis to synthesize benzoin from benzaldehyde. Umpolung synthesis is a synthetic approach that allows us to switch the identity of a reacting species. For example, the normal chemical reactivity of a nucleophile can be switched to one of an electrophilic compound. Two common agents are cyanide and thiamine (Vitamin B). The mechanisms for both agents are the same. In this experiment, thiamine was used to turn benzaldehyde, an electrophile, into a nucleophile. This nucleophilic benzaldehyde then reacts with another molecule of benzaldehyde to make benzoin. This means that benzaldehyde is the source of the electrophile and nucleophile in this reaction. The two molecules of benzaldehyde…

    • 484 Words
    • 2 Pages
    Improved Essays
  • Decent Essays

    Some of the factors that that may affect the rate that the chemical reaction is the quantity of each chemical, the temperature of the chemicals and the pressure inside the container that the chemicals are in.…

    • 121 Words
    • 1 Pages
    Decent Essays
  • Improved Essays

    Elimination reactions can occur instead of substitution reactions. There are two kinds of elimination reactions: E1 and E2. E1 reactions are 2 step; the leaving group will leave, forming a carbocation and a leaving group anion. Then, a hydrogen on a neighboring carbon will leave; the electrons from the C-H will remain on the C, forming a double bond between the two Carbons that had the LG or H leave. The positive Hydrogen that left will bond with the nucleophile. E2 reactions are one step; the leaving group will leave at the same time that the anti-periplanar hydrogen on a neighboring carbon leaves, resulting in a double C=C bond. A leaving group anion and an H-Nu will both form. Nucleophiles that are very polarizable and are slightly basic such as Cl- and H2O will typically undergo substitution reactions. Weakly polarizable nucleophiles that are very basic will typically undergo elimination reactions. The solvent in which the reaction occurs is also important; polar protic solvents can cause Sn1/E1 reactions to occur, due to how the solvent will interact with the…

    • 995 Words
    • 4 Pages
    Improved Essays
  • Decent Essays

    Synthesis Lab Report

    • 585 Words
    • 3 Pages

    TLC can be used to determine which reaction runs faster; if the ether spot from the S-HBTM reaction mixture is darker than the ether spot from the R-HBTM reaction mixture, then the conformation of the unknown secondary alcohol is R. And if the ether spot from the R-HBTM reaction mixture is darker than the ether spot from the S-HBTM reaction mixture, then the conformation of the unknown secondary alcohol is S. Using this information, along with an 1H NMR to determine structure, it was determine that unknown #1was…

    • 585 Words
    • 3 Pages
    Decent Essays
  • Improved Essays

    Reaction Lab

    • 1809 Words
    • 8 Pages

    From 10oC to 20oC, the average rate of reaction of the class results is higher than the raw results rate of reaction by a maximum of 0.75mL/sec. However, from 30oC to 50oC, the raw results presented a slightly higher lot of rate of reaction than the average rate of reaction from the class results. The highest rate of reaction difference was for 50oC, with a difference of 0.3mL/sec between the raw and average results. This information supports the hypothesis, yet the result for 10oC and 20oC do not support the hypothesis, as due to the information known about enzymes, the lower the temperature, the slower the rate of reaction should be, therefore the average rate of reaction does not support the…

    • 1809 Words
    • 8 Pages
    Improved Essays
  • Improved Essays

    Uncatalyzed Reaction Lab

    • 882 Words
    • 4 Pages

    The concentration of the reactants was varied such that the order of the reaction could be determined, and the temperature was also changed to determine the activation energy of the reaction. The rate law was found to be rate = k[KI]1[H2O2]1, and the activation energy was calculated to be 53.9 kJ/mol. This activation energy was 21.1 kJ/mol less than that of the uncatalyzed reaction, showing that the catalyst was effective at decreasing the activation energy, and increasing the rate of the reaction. One possible cause of error is the inconsistency of reactions, the reactants must collide in the correct orientation to react, so there is always a possibility for some small variation. When calculating the activation energy, warmer water was used to increase the temperature of the reactants; however, because the surroundings were still room temperature, the temperature may not have been consistent throughout the reaction, leading to an error in the observed rate, and consequently an error in the activation energy. A final potential error could come from the decision not to account for the vapor pressure of the water, or for the change in vapor pressure when the temperature of the water was increased in trial 4, this could have indicated a higher rate of production of O2 than was actually…

    • 882 Words
    • 4 Pages
    Improved Essays
  • Improved Essays

    Nucleophilic aliphatic substitution involves chemical reactions where a neutral molecule or an anion called a nucleophile substitutes a leaving group by attacking an electrophilic, Lewis acidic carbon atom. Leaving groups are molecular compounds that are departed and replaced by the nucleophile. This interconversion is commonly known as the attack of the nucleophile. Two different mechanisms…

    • 796 Words
    • 4 Pages
    Improved Essays
  • Improved Essays

    By calculating the rate of reaction and studying the effects of varied conditions on the reaction, a great deal can be learnt about the enzyme, including how the enzyme could be inhibited, the catalytic mechanism of the enzyme etc. One of the most well-known ways to look at enzyme kinetics is the Michaelis-Menton equation, which relates reaction rate (V) to concentration of substrate ([S]). Its equation can be used to work out the maximum rate of reaction of the system (Vmax) and the substrate concentration at which the reaction rate is half of Vmax (Km, also known as the Michaelis constant). Michaelis-Menton shows that the rate of reaction is dependent of the rate of formation of the enzyme-substrate complex and rate of formation of the product. This means that in the enzyme assay, the rate of reaction is dependent on the formation of NAD+ from NADH (Scopes, R.,…

    • 1627 Words
    • 7 Pages
    Improved Essays
  • Improved Essays

    One important aspect of organic chemistry is the synthesis of new compounds. It is also important for chemists to understand how to perform certain techniques, such as extraction and distillation, to produce the new products, which are usually drugs and cures for illnesses. In this experiment, n-butyl bromide was produced. n-Butyl bromide is an alkyl halide, which are usually synthesized by an alcohol and an acid. In the case of n-butyl bromide, n-butyl alcohol was used along with sodium bromide and sulfuric acid. The sodium bromide reacts with the sulfuric acid to produce hydrobromic acid, which will then react with n-butyl bromide to produce n-butyl alcohol via an SN2 reaction. Sulfuric acid also serves as an excess reagent to shift equilibrium…

    • 234 Words
    • 1 Pages
    Improved Essays
  • Improved Essays

    The purpose of conducting this experiment was to explore how different factors affect the reaction rate of enzymes reacting with their corresponding substrates in order to learn more about how enzymes function in different environments. The independent variables investigated in this experiment were the concentration of different substrates, the temperature of the environment, and the effect of a catalyst on the reaction rate. The dependent variable for all of the investigations was the time it took for the reaction to occur.…

    • 1027 Words
    • 5 Pages
    Improved Essays
  • Great Essays

    As I increase the concentration of hydrochloric acid and add it to the sodium thiosulphate the rate of reaction will decrease.…

    • 2652 Words
    • 11 Pages
    Great Essays
  • Improved Essays

    Paracetamol Lab Report

    • 651 Words
    • 3 Pages

    These two steps were already carried out and 4 amino-phenol was the amine used in the first part of this experiment. 4 amino phenol and acetic anhydride undergo a nucleophilic addition-elimination reaction. A reaction mechanism is a step-by-step process when reactant molecules change in their geometry in order to produce new products. This occurs due to omission or addition of reagents, where bonds are broken down to form new ones4. 4 amino-phenol contains two functional groups, an OH and a NH2 group attached to a benzene ring while acetic anhydride is a derivative of a carboxylic acid group. It is formed by the removal of water from two ethanoic acid molecules. Because acetic anhydride is the second most reactive carboxylic acid derivative, they can be readily converted into other less reactive carboxylic acid…

    • 651 Words
    • 3 Pages
    Improved Essays