Strong Nucleophilic Substitution Report

Theory: One of the methods of preparing alkyl halides is via the nucleophilic substitution reactions of alcohols. Alcohols are inexpensive materials and easy to maintain. However, they are a poor leaving group the OH group is a problem in nucleophilic substitution, this problem is fixed by converting the alcohol into H2O.

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

This was concluded by combining information on melting points and TLC; melting range narrowed when filtered product was mixed with the standard product. Also, the Rf value of the pure product is closely related to the Rf value of the standard. TLC of filtrate showed no movement of the substance in the mixture under 9:1 ratio declaring the substance to be extremely polar. Of the three potential unknown reactants, 4-methoxyphenol would be the most polar and therefore would travel least up the TLC plate. (Q14:Yield) 81.2% product yield was collected. “Matter cannot be created nor destroyed”, therefore some product could have filtered through. TLC of filtrate confirmed remnants of product present. Filtering the filtrate could have increased the yield. (Q15:Recovery) The percent recovery of the product makes sense because it is the mass of the crystallized product divided by the crude product: 94.9%. The percentage reflects the mass of pure product (without the presence of impurities). (Q16:MP) Melting point coincides with the unknown nucleophile being 4-methoxyphenol because when the standard product was combined with our pure product, the melting range narrowed. When compared to the melting ranges obtained when mixed with the other two possible products the melting ranges significantly decreased and widened. This is often an indication of impurities being present, but because this was a

The SN1 mechanism leads to substitution products, and the E1 mechanism leads to formation of alkenes, therefore in this case, it is shown that this mechanism leads to a substitution of products since the Cl- ion is replacing the OH group by the addition of a strong acid (HCl). When the nucleophile

The solvolysis of t-butyl bromide is an SN1 reaction, or a first order nucleophilic substitution reaction. An SN1 reaction involves a nucleophilic attack on an electrophilic substrate. The reaction is SN1 because there is steric obstruction on the electrophile, bromine is a good leaving group due to its large size and low electronegativity, a stable tertiary carbocation is formed, and a weak nucleophile is formed. Since a strong acid, HBr, is formed as a byproduct of this reaction, SN1 dominates over E1. The first step in an SN1 reaction is the formation of a highly reactive carbocation, in which a leaving group is ejected. The ionization to form a carbocation is the rate limiting step of an SN1 reaction, as it is highly endothermic and has a large activation energy. The subsequent nucleophilic attack by solvent and deprotonation is fast and does not contribute to the rate law for the reaction. The Hammond Postulate predicts that the transition state for any process is most similar to the higher energy species, and is more affected by changes to the free energy of the higher energy species. Thus, the reaction rate for the solvolysis of t-butyl bromide is unimolecular and entirely dependent on the initial concentration of t-butyl bromide.

Reaction 1 involved a primary alcohol (OH), weak leaving group in the starting material and a reaction with a strong nucleophile (sodium bromide) and a polar protic solvent (sulfuric acid). The reaction was carried out through reflux and the product had a relatively high yield (75%) (Scheme 1).

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.

The purpose of this experiment is to examine the reactivities of various alkyl halides under both SN2 and SN1 reaction conditions. The alkyl halides will be examined based on the substrate types and solvent the reaction takes place in.

This experiment utilized the dehydration process of 2-methylcyclohexanol to give a mixture of 1-methylcyclohexene, 3-methylcyclohexene, and methylenecyclohexane. According to Zaitsef’s rule, 1-methylcyclohexene is the major product because it is the most highly substituted product, making it the most stable. 25 mL of 2-methylcyclohexanol was placed into a 100mL round-bottom flask along with 10mL of 9 M sulfuric acid and swirled to mix the contents. [1] H2SO4 is used for the E2 reaction of dehydrating a primary alcohol. The –OH group in 2-methylcyclohexanol donated two electrons to a proton from H2SO4, which forms an alkyloxonium ion. [5] The HSO4- nucleophile attacks an adjacent hydrogen and the alkyloxonium ion leaves, forming a double bond. [5]

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,

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.

As an enzyme-catalyzed reaction may be the main reason for a reaction to occur faster, many factors can

As we knew from the background that these reactions are depend on several factors such as, the substrate which is the most priority, the solvent, and the nucleophile. For the substrate, the SN1 is favor tertiary alkyl halide, while the SN2 is favor the primary alkyl halide. For the solvent, it is an important factor. For example, in this experiment, we used AgNO3 in ethanol and NaI in acetone solvent. We used AgNO3 in ethanol in SN1 because the ethanol is protic polar and will able to stabilize the intermediate state of the SN1.

This lab consisted of the conversion of alcohols into alkyl halides through common substitution methods. These methods include SN1 and SN2 mechanism, both of which can occur for this type of reaction. For both reactions, the first step of protonation will be to add hydrogen to the –OH group and then the rest of the reaction will proceed according to the type of mechanism. SN1 reactions form a cation intermediate once the H2O group leaves, then allowing a halide (such as Br) to attack the positively charged reagent1. On the other hand, SN2 reactions are one-step mechanism in which no intermediate is formed and the halide attaches as the leaving