As discussed in lecture, the determining factors of a substitution reaction is likely to occur in either S_N 1 or S_N 2 by: substrates, leaving group, strength of the nucleophile, and the type of solvent.
When conducting the S_N 1 portion of the experiment, the solvent used was 1% silver nitrate in ethanol solution (〖AgNO〗_3). This solvent is polar protic. This is the best type of solvent needed for an S_N 1 reaction because the hydrogen atom is positively charged while the nucleophile is negatively charged achieving a hydrogen bond. Two factors that contributed to the rate of reaction for S_N 1 are stability of the carbocation and the leaving group departure. The more stable the carbocation, the faster the reaction generates and the better the leaving group, it creates a carbocation faster, which in turn leads to a
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The following six of the nine alkyl halides produced precipitates at room temperature: 2-bromobutane, t-butyl chloride, crotyl chloride, bromocyclohexane, bromocyclopentane, and benzyl chloride. All of these alkyl halides reacted in room temperature because they were either secondary or tertiary carbons except for crotyl chloride. These types of structures (tertiary) are favored in the case of S_N 1 while secondary can undergo either S_N 1 or S_N 2. The only primary carbon that reacted quickly was crotyl chloride because it is an allylic substrate, which can undergo S_N 1. On the other hand the three remaining alkyl halides did not react at room temperature: 1-chlorobutane, 2-chlorobutane, and bromobenzene. These three alkyl halides were then heated at 80℃. 1-chlorobutane’s alpha carbon is primary, so heat is needed in order to create more collision resulting in a reaction. 2-chlorobutane and 2-bromobutane have similar structures, but the latter reacted in room temperature because Br is a better leaving group than Cl. Lastly, bromobenzene did not react even after adding heat
The objective of this laboratory experiment is to study both SN1 and SN2 reactions. The first part of the lab focuses on synthesizing 1-bromobutane from 1-butanol by using an SN2 mechanism. The obtained product will then be analyzed using infrared spectroscopy and refractive index. The second part of the lab concentrates on how different factors influence the rate of SN1 reactions. The factors that will be examined are the leaving group, Br versus Cl-; the structure of the alkyl group, 3◦ versus 2◦; and the polarity of the solvent, 40 percent 2-propanol versus 60 percent 2-propanol.
In this experiment, we alkylate sodium saccharin to N-ethylsaccharin with iodoethane in an aprotic solvent N,N dimethylformamide. Nucleophiles in this experiment will react better in an aprotic solvent. Aprotic solvents have dipoles due to its polar bonds but they do not have H atoms that can be donated into a H-bond. The anions which are the O- and N- of sodium saccharin are not solvated therefore are “naked” and the reaction is not inhibited and preceded in an accelerated rate. The reaction was an SN2 reaction. Since the Oxygen and Nitrogen are more electronegative than the carbon on which they’re attached electrons are pulled towards O- and N- attracting the ethane from Iodoethane. Iodine being more electronegative
In this lab experiment we determined the kinetic rate constant for a solvoysis reaction and observed how a change in polarity of the solvents affects the reaction rate. For the specific reaction that we did in the lab we actually measured the formation of HCl since the rate of
Many reactions that exist in nature involve a double displacement between ions and reactants with solvents. A bimolecular nucleophilic substitution, or SN2 reaction, involves a nucleophilic attack on a substrate and the departure of a leaving group. A nucleophile is a compound or ion that donates electrons to promote bond formation (Caldwell, 1984). In order for a leaving group in a compound to leave, it must possess the characteristics of a weak base and be able to occupy electrons. Several factors affect the rate and favorability of such reaction, such as (Bateman, 1940). In addition, the substrate that is attacked by the nucleophile is commonly an unhindered primary substrate to allow the reaction to occur quicker. An SN2 reaction follows the second-order rate law.
The solution that was performed in this experiment was to use sulfuric acid in order to form a protonated alcohol, so when the halogen or nucleophile back attacks the compound, water is displaced. Once the alcohol is protonated, the solution reacts in either an SN1 or SN2 mechanism.
SN1 reactions are considered unimolecular nucleophilic substitution mechanisms and are a first-order process. Meaning that the reaction forms a carbocation intermediate and that the concentration of the nucleophile does not play a role in the rate-determining step, which is the slowest step in the reaction. All of the SN1 reaction mechanisms in this procedure can react two different ways. The expected mechanism for these reactions would be that the carbocation would react with the weak nucleophile nitrate, attaching the nitrogen to the positively charged carbon. However, while nitrate is the intended nucleophile in all of the reactions, it is a poor nucleophile. The ethanol used in this reaction is a polar protic ionizing solvent,
In this reaction, a rate-determining step should occur through the ionization between carbon and –OH bond to form an intermediate.11 This step should be followed by rapid reaction of a nucleophile to wrap up the substitution.11 For this experiment, hydrochloric acid was used to drive off the reaction, which contains a chlorine ion, a common nucleophile. (1)Chlorine ion is more effective as a nucleophile than water; because an ion holds a negative charge and resulting in a faster rate of reaction, whereas water holds a neutral charge, resulting in a slower rate of reaction with a carbocation intermediate.13 The starting
6. Summarize in a few sentences the halogenation and controlled oxidation reactions of 1°, 2°, and 3° alcohols.
Objective: The objective of this lab is to observe the synthesis of 1-bromobutane in an SN2 reaction, to see how a primary alky halide reacts with an alcohol.
Both Sn1 and Sn2 reactions are nucleophilic substitution reactions, though they are slightly different. Sn2 reactions have bimolecular displacement and are also concerted, meaning the bond making and the bond breaking processes happen in one step.1 Sn1 reactions require two steps and have unimolecular displacement. This difference can be seen when comparing Figure 1 and Figure 2 below. The strength of the nucleophile does not effect Sn1 reactions, while the strongest nucleophile is required for Sn2 substitution reactions.2 Other important considerations include the effect of
While the mechanisms for SN2 is a biomolecular reaction. These two species are involved in the rate-determine step3. Once the nucleophile attacks, though it is allowed to form a nucleophile, that then forms a transition state and then results in the final product, as shown in Figure 3.
In the first reaction using NaI in acetone, we could compare the rate of reaction of two substrates, 1-bromobutane and 2-bromo-2-methylpropane. 1-bromobutane has a partial positive carbon atom attached to a partial negative bromide. This partial positively charged carbon is classified as primary alkyl halide. As the nucleophile I- in NaI approached the partial positively charged carbon, it induced the bromide to leave the substrate . An unstable primary carbocation is formed, which has a higher energy and is highly favorable to undergo a reaction. The negative iodine charge was attracted to the primary carbocation in the substrate. This nucleophilic reaction is a type of SN2 reaction, given the participation of the substrate and the nucleophile in ionizing the halogenoalkane. The rate of reaction of 1-bromobutane was 9.091E-5 M/s whereas the rate of reaction of 2-bromo-2-methylpropane was around 3.367E-05 M/s. 2-bromo-2-methylpropane is a tertiary alkyl halide and shows steric hindrance. In this case, for a nucleophile, it was impossible to get at the partial positively charged carbon, given the obstruction of the methyl groups and the bromide. The halogenoalkane will ionize slowly and that is why the rate of the reaction took a longer time, around 297 seconds. As soon as the bromide is repelled from the substrate, the nucleophile rapidly
Fig. 3. Effect of reaction time on (a) Monomer conversion, (b) Hydroxyl value, and (c) Iodine value of products (reaction conditions: temp. = 110 C, A/K ratio = 0.2).
introducing the parabolic profile for laminar flow in a pipe results in α = 2, for turbulent flow, we have α ≈ 1.0 and for uniform flow, α = 1.
in Set 2, the Red highlighted cells with value difference greater than Set1 belong to the same