In this lab, the experimenters will determine how the structure of an alkyl halide (i.e. methyl, primary, secondary, or tertiary), steric effects, nature of a leaving group, and solvent polarity affect the relative rates of SN1 and SN2 reactions. In addition, comparing the rates of reactions under varying concentrations of alkyl halides and nucleophiles will help determine the rate laws for both types of nucleophilic substitution reactions. During SN2 reactions, a good nucleophile, like iodide, will displace the leaving group on an alkyl halide in a single step that results in an inversion of configuration. Methyl, primary, and some secondary halides undergo this bimolecular substitution reaction. Minimal steric effects combined with a good leaving group and a polar, aprotic solvent …show more content…
The more stable the resulting carbocation, the quicker this step occurs. After this rate-limiting step, rapid reaction with a weak nucleophile (e.g. ethanol) attacking from either side of the carbocation completes the substitution reaction. A racemic mixture forms with a slight favoring of the inverted molecule because of ion pair formation. A good leaving group capable of delocalizing a negative charge aids in the formation of the initial carbocation. Additionally, polar, protic solvents capable of solvating and stabilizing a carbocation support the SN1 mechanism. Tertiary alkyl halides provide the ideal substrate for the formation of a stable tertiary carbocation that favors the SN1 mechanisms. When testing the factors affecting the SN2 reaction below, the experimenters will achieve the fastest reaction when using a primary alkyl halide with minimal branching and the best leaving group (i.e. 1-bromobutane). Varying the concentrations of the alkyl halide or nucleophile while keeping the other constant will change the rate of reaction for the SN2 reaction. The fastest SN1 reaction will occur for the tertiary alkyl halide with the strongest leaving group reacted in pure
During the halogenation reactions of 1-butanol, 2-butanol, and 2-methyl-2-propanol, there is a formation of water from the OH atom of the alcohol, and the H atom from the HCl solution. The OH bond of the alcohol is then substituted with the Cl atom. Therefore all of the degrees of alcohol undergo halogenation reactions, and form alkyl halides as products. This is because the functional group of alkyl halides is a carbon-halogen bond. A common halogen is chlorine, as used in this experiment.
The Diels-Alder reaction was discovered and named after the Nobel Prize winning scientists Kurt Alder and Otto Diels in 1928. Such a reaction occurs when a diene with two adjacent double bonds is mixed with a dienophile consisting of a double bond in order to create a cyclohexene. The diene must be in the s-cis conformation in order for the electron transfer to engage correctly. If the diene in question is in s-trans conformation then the access to the molecules is limited, thus, no reaction can occur. The dienophile we used was maleic anhydride. Maleic anhydride possesses high electron withdrawing characteristics which caused a very quick reaction. The reaction will
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.
Introduction: The purpose of this experiment is to understand the kinetics of the hydrolysis of t-butyl chloride.The kinetic order of reaction was studied under the effects of variations in temperature, solvent polarity, and structure. It is particularly observed in tertiarhalides i.e. in SN1mechanism, Nucleophilic Substitution which is in 1storder. It is basically a reaction that involves substitution by a solvent that pretendslikea nucleophile i.e. it donates electrons. The reaction being in firstorder means
6. Purpose: to clarify the mechanism for the cycloaddition reaction between benzonitrile oxide and an alkene, and to test the regiochemistry of the reaction between benzonitrile oxide and styrene; to purify the crude product of either trans-stilbene, cis-stilbene, or styrene reaction.
Aromatic compounds can undergo electrophilic substitution reactions. In these reactions, the aromatic ring acts as a nucleophile (an electron pair donor) and reacts with an electrophilic reagent (an electron pair acceptor) resulting in the replacement of a hydrogen on the aromatic ring with the electrophile. Due to the fact that the conjugated 6π-electron system of the aromatic ring is so stable, the carbocation intermediate loses a proton to sustain the aromatic ring rather than reacting with a nucleophile. Ring substituents strongly influence the rate and position of electrophilic attack. Electron-donating groups on the benzene ring speed up the substitution process by stabilizing the carbocation intermediate. Electron-withdrawing groups, however, slow down the aromatic substitution because formation of the carbocation intermediate is more difficult. The electron-withdrawing group withdraws electron density from a species that is already positively charged making it very electron deficient. Therefore, electron-donating groups are considered to be “activating” and electron-withdrawing groups are “deactivating”. Activating substituents direct incoming groups to either the “ortho” or “para” positions. Deactivating substituents, with the exception of the halogens, direct incoming groups to the “meta” position. The experiment described above was an example of a specific electrophilic aromatic
Anti-Markovnikov’s rule expresses the opposite. In an anti-Markovnikov reaction, the halide group attaches at the less substituted carbon, while the hydrogen attaches at the more substituted carbon. The term “less substituted carbon” refers to the carbon with the most surrounding hydrogens, and the term “more substituted carbon” refers to the carbon with the least surrounding hydrogens. The objective of the experiment was to determine which mechanism was used to create the product of either 1-hexanol or 2-hexanol after hydration of
Theory: SN2 reactions are one class of organic reactions that deal with substituting one group with another group. The group that leaves is known as the leaving group and the group that substitutes is the nucleophile. In order for SN2 to occur, there needs to be a good leaving group and good nucleophile. Good leaving groups are those that are weak bases. Nucleophiles should be strong for SN2.
A substitution is when two separate reactants exchange parts in a chemical reaction. Predicting how a particular reaction might occur is useful in many aspects, such as determining how a new compound might react under certain external conditions. In the substitution of an alkyl halide, the reaction can proceed through three options: bimolecular nucleophilic substitution (SN2), unimolecular nucleophilic substitution (SN1), or a mixture of the both SN1 and SN2. The type of reaction that occurs depends on four main factors, which include the nucleophile, the electrophile, also called the alkyl halide substrate, the leaving group, and the solvent.
The scientific aim of this experiment was to determine which reagents sped up and slowed down the time it took for the reaction to occur. In addition, an aim was to observe how temperature affects the reaction time, and to be
For trial 1, the rate of reaction was 1.61x10-5 mol L-1 s-1, k was 0.167 mol2 L2 s-1 and the ionic strength was 0.2362 mol L-1 s-1. For this reaction no electrolytes were added to speed up the reaction. The reaction run for 1 can be considered as the model reaction for this experiment, since other substances were not added in. For trial 2, the rate was 7.95x10-6 mol L-1 s-1, k was 0.331 mol2 L2 s-1, and the ionic strength was 0.1327 mol L-1 s-1. In this trial, the concentration of [S2O8-2] was reduced, while (NH4)2SO4 was added. The electrolytes from (NH4)2SO4 were able to diffuse, and replenish the reaction’s ionic strength. Thus, the k value was higher and the reaction was quick. For the third trial, the rate of reaction was 1.83x10-6 mol L-1 s-1, k was 0.305 mol2 L2 s-1, and the ionic strength was 0.1055 mol L-1 s-1. The concentration of S2O8-2 is ¼ of trial 1, thus the rate of the reaction also decreased, and the overall reaction took longer to finish. For the fourth
2nd step involves the carbocation intermediate being attacked by water that acts as a nucleophile to form protonated alcohol intermediate. This is the fast step and does not determine rate of reaction.
One way scientist gets alkyl halides is by using the manipulation of an alcohol. When alcohols are treated with HBr or HCl; they can undergo a nucleophile substation reaction to generate an alkyl halide and water2. Using the structure of the alcohols they are able to use SN1 or SN2 mechanisms. For both these mechanisms though, the –OH group must be pronated shown in Figure 1.
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
This chemical is known as butyl-ethyl ether. It is a type of ether that is a "colorless liquid" and falls within the R-O-R functional group (Chemical Book, 2012). The compound is extremely flammable, and as such, fire and other safety professionals must take great care when handling chemical fires burning with the substance. The research shows that the compound "will be easily ignited by heat, sparks or flame," but also that "vapors may form explosive mixtures with air. Vapors may travel to source of ignition and flash back" (Chemical Book, 2012). This makes the vapor from this organic compound incredibly dangerous in terms of fire risk in doors, but can also cause problems outdoors as well. Fire and safety officials must be careful in enclosed areas. Often, this flash will spread throughout lower lying areas, such as basements and sewers. Moreover, it is "incompatible with oxidizing agents," making it unsafe to try to extinguish chemical fires of this nature with water (Chemical Book, 2012).