S. N. 1 Lab Report

6. Summarize in a few sentences the halogenation and controlled oxidation reactions of 1°, 2°, and 3° alcohols.

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

This experiment is based on the concept of performing SN2 reactions and analyzing how different factors affect said reactions. The factors in question for this experiment are steric hindrance, nucleophilicity, and nature of the leaving group. An SN2 reaction is a type of substitution reaction. A substitution reaction entails an alkyl having its leaving group (typically a halogen) replaced by a different atom. A nucleophilic substitution involves a nucleophile attacking a leaving group on a carbon atom. The nucleophile utilizes its lone pair of electrons to form a new bond with the carbon atom. There are two different types of substitution reactions. There are SN1 reactions (first order) and SN2 reactions (second order) (Weldegerima 2016). SN1 reactions are unimolecular and involve two separate steps. One of the two steps takes longer than the other and is called the rate limiting step. SN1 reactions tend to favor tertiary alkyl halides. SN2 reactions involve a strong nucleophile interacting with an electrophile carbon and making the leaving group detach from the

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.

In the method of continuous variations the total number of moles of reactants is kept constant for the series of measurements. Each measurement is made with a different mole ratio of reactants. A mole ratio is ratio between the amounts in moles of any two compounds involved in a chemical reaction. Mole ratios are used as conversion factors between products and reactants in many chemistry problems.

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

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.

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).

The purpose of this lab was to discover the effects that an alkyl group and solvent have on the rate of SN1 and SN2 reactions. Two separate mechanisms can be used to perform the nucleophilic substitution of alkyl halides: SN1 and SN2. A SN1 reaction, or unimolecular displacement, is a 1st order, nucleophilic substitution that involves two steps. The rate law for this reaction, Rate = k[Rx], doesn’t include the nucleophile in it.1 These two step reactions have a carbocation intermediate. SN1 reactions work best when the central carbon has as many bulky groups surrounding it as possible. These substituents increase the possibility of the carbocation intermediate forming by increasing the steric strain of the molecule. This idea is which causes a carbocation intermediate to develop in reactions of secondary or tertiary alkyl halides, and a primary alkyl halide to not be able to go through a SN1 reaction. The carbocation intermediate that forms is a sp2 carbon that allows the nucleophile to attack from both sides of the molecule. If neither attack is favored, they both occur equally, making it a racemic mixture. The solvent of choice for the SN1 reactions are both polar and protic, because a solvent that will not react with the carbocation intermediate is needed, since this will give an unwanted product. In polar protic solvents you get a hydrogen atom that is very highly polarized since it is attached to an electronegative atom, because of this it can interact

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

in Set 2, the Red highlighted cells with value difference greater than Set1 belong to the same

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.