Electrophilic Aromatic Substitution
Objective
The objective of this experiment was to illustrate electrophilic aromatic substitution by synthesizing p-nitroanilide (as well as ortho) from acetanilide by nitration. The para form was separated from the ortho form based on solubility properties using recrystallization techniques.
Synthetic equations:
Physical Properties & Hazards of Reagents/Products: (all taken from Sigma-Aldrich website)
Acetanilide
MM = 135.16 g/mol
Melting point = 113-115°C
Hazards: acute toxicity
Sulfuric acid
MM = 98.08 g/mol
Boiling point = 290°C
Density = 1.840 g/mL
Hazards: corrosive to metals and skin, serious eye damage
Nitric acid
MM = 63.01 g/mol
Boiling point = 120.5°C
Density =
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Discussion 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
We know that that the end point of the titration is reached when, after drop after careful drop of NaOH, the solution in the flask retains its pale pink color while swirling for about 30
Chemistry relates to everything we touch, see, smell, hear, and taste because atoms make up everything in the universe. Chemistry influences so much in our everyday lives that it is hard to think of an activity that does not involve a chemical process in some way. The science also plays a major role in the human body. Our bodies are made up of chemicals, in fact almost 96% of our body mass is made up of four different elements: hydrogen, oxygen, carbon, and nitrogen. Besides the physical way I am affected by elements, chemistry also majorly affects me in my line of work as a certified nursing assistant. As a certified nursing assistant I work in a nursing home and
For this experiment, an organometallic reagent was used for the synthesis and isolation of benzoic acid. The Grignard reaction is the addition reaction of an organometallic reagent, which in this case was an organomagnesium reagent. An organometallic reagent is a carbon bonded to a metal. This reagent was combined with an electrophile, a carbonyl compound such as a ketone or aldehyde. Carbons are electrophilic when bound to a nonmetal thus the atoms are more electronegative than the carbon and metals are less electronegative than carbon.
11) Dry out the methylene chloride solution that contain the benzoin and the dibromobenzene by the use of anhydrous sodium sulfate.
pH was recorded every time 1.00 mL of NaOH was added to beaker. When the amount of NaOH added to the beaker was about 5.00 mL away from the expected end point, NaOH was added very slowly. Approximately 0.20 mL of NaOH was added until the pH made a jump. The pH was recorded until it reached ~12. This was repeated two more times. The pKa of each trial are determined using the graphs made on excel.
1. 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.
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.
A unimolecular nucleophilic substitution or SN1 is a two-step reaction that occurs with a first order reaction. The rate-limiting step, which is the first step, forms a carbocation. This would be the slowest step in the mechanism. The addition of the nucleophile speeds up the reaction and stabilizes the carbocation. This reaction is more favorable with tertiary and sometimes secondary alkyl halides under strong basic or acidic conditions with secondary or tertiary alcohols. In this experiment, the t-butyl halide underwent an SN1 reaction. Nucleophiles do not necessarily effect the reaction because the nucleophile is considered zero order, (which makes it a first order reaction.) The ion that should have the strongest effect in an SN1 reaction is the bromide ion. The bromide ion should be stronger because it has a lower electronegativity than chloride as well as a smaller radius.
The purpose of Experiment 6 - Part 1, was to use electrophile addition to synthesize 1,2‐dibromo‐1,2‐diphenylethane from (E)-1,2-diphenylethene. The final product was correctly identified by the use of TLC and melting point determination. The final product was meso-1,2‐dibromo‐1,2‐diphenylethane. Figure 1. Reaction for Experiment 6, Part 1. Created by Chem Doodle.
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.
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 this preparative lab, an aldol (trans-p-anisalacetophenone) was produced from the reaction between p-anisaldehyde and acetophenone with the presence sodium hydroxide. The reaction also showed the importance of an enolate and the role it played in the mechanism. Sodium hydroxide acts as a catalyst in this experiment and is chosen because of its basic conditions and pH. The acetophenone carries an alpha hydrogen that has a pKa between 18 and 20. This alpha hydrogen is acidic because of its location near the carbonyl on acetophenone. When the sodium hydroxide is added, it deprotonates the hydrogen and creates an enolate ion. This deprotonation creates a nucleophilic carbon that can attack an electrophilic carbon (like a parent
A Cobalt-Amine-Halide compound is synthesized from cobalt (II) chloride hexahydrate. An orange-tinted solid is produced and is considered to be unknown since the specific ligand amounts are unknown. By determining the percent composition of various elements and compounds in the unknown, its true identity can be predicted. Chloride, ammonia, and cobalt are three examples of percent compositions determined to help narrow the selection of possible unknowns. Titrations using Na2S2O3 and HCl to determine percent cobalt and ammonia, respectively, are used. Silver nitrate is used to precipitate the chloride ions in the unknown, which can be measured to determine the percent composition of chloride
The description is for dichloromethane-aqueous solution mixture, but you will use the same technique for your tert-butyl methyl ether-aqueous solution mixture. Note, however, that the ether is less dense than water, while dichloromethane is denser than water.
In this experiment, a nucleophilic substitution was performed, where a chloride nucleophile substituted a tertiary hydroxyl group on 2-methyl-2-butanol. In a nucleophilic substitution reaction, an electron rich nucleophile attacks a positively or partially positively charged electrophile, and replaces a leaving group. In this reaction, chloride ions are the nucleophile, the tertiary carbon in 2-methyl-2-butanol is the electrophile, and water is the leaving group. In the mechanism for this reaction, the oxygen from the hydroxyl group of the 2-methyl-2-butanol attacks the hydrogen of the HCl, causing heterolytic cleavage of the HCl, resulting in a chloride ion, and in the oxygen bonding to an extra hydrogen, and becoming positively charged.