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Importance of acids, bases and their reactions
Observing chemical reactions lab
Observing chemical reactions lab
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This experiment focuses on the SN2 nucleophile substitution reaction of converting 1-butanol (an alcohol) to 1-bromobutane (an alkyl halide). There are two types of substitution mechanisms that could be used, SN1 and SN2. SN1 mechanisms take place in two steps. The first rate-determining step is the ionization of the molecule. This mechanism is called unimolecular because its rate is only dependent on the concentration of the leaving group. The second step is the fast, exothermic nucleophile addition. In an SN2 reaction the leaving group leaves as the nucleophile attacks all in one step. Because this happens at one time, the nucleophile must attack from the opposite side from which the leaving group is leaving. For this reason, SN2 reactions …show more content…
invert the stereochemistry of the molecule. These reactions are dependent on both the carbon molecule and the nucleophile in the solution and are therefore known as a bimolecular mechanism.
There is another type of mechanism called an elimination mechanism that is competing with the substitution mechanisms to attack the molecules. There are two types of elimination reactions, E1 and E2. E1 and SN1 mechanisms compete with each other as E2 and SN2 mechanisms compete with each other. To ensure that our experiment favors the substitution reaction, an environment must be created in which the leaving group, H2O, is a weak base and the nucleophile, bromine, has strong polarity. This is obtained in this experiment by adding sulfuric acid to the reacting solution. Sulfuric acid not only donates protons but also acts as a dehydrating catalyst to push the reaction more toward the products. Without sulfuric acid …show more content…
in this reaction the H2O leaving group would be a strong base compared to its NaBr surroundings. This would favor an elimination reaction, which is not the type of mechanism this experiment is examining. This experiment is also easily reversible. Using sulfuric acid pushes the reaction to the products using Le Chatelier’s Principle, which states that when a system at equilibrium is subject to change in concentration, temperature, volume, or pressure then the system readjusts itself until a new equilibrium is reached. The downfall of using sulfuric acid is that there are side reactions that take place. There is a production of alkyl hydrogen sulfate when the alcohol used undergoes esterification. This by itself does not hinder the amount of desired product, but along with it’s own side reactions it can reduce the desired yield. To control this the temperature is controlled and the sulfuric acid is added very slowly to the solution. To determine that the reaction was a nucleophilic, SN2, aliphatic substitution the product was tested using two alkyl halide tests and running a sample through an IR (infrared spectroscopy) reading. The halide tests were used to determine if the mechanism used was SN1 or SN2. The first halide test run was the silver nitrate test. One drop of 1-bromobutane was added to 2 ml of 0.1 M AgNO3 in ethanol. This reaction takes place in accordance with an SN1 mechanism. Therefore, the reaction rate is fastest with a tertiary carbon with the reaction rate being 3°>2°>1°. The second halide test run was the sodium iodide test. 1 mL of NaI-acetone was mixed with two drops of 1-bromobutane. This reaction takes place in accordance with an SN2 mechanism. Therefore the reaction rate is fastest with a primary carbon with the reaction rate being 1°>2°>3°. Using the data from these tests it is possible to tell which mechanism was used by which reaction takes place faster. The NaI reaction took about 7 seconds to precipitate compared to about 35 seconds for the AgNO3 test to precipitate. This data supports the hypothesis that a SN2 reaction took place. The last test conducted was the IR test.
The IR machine was cleaned between uses to reduce contaminated data. The final product was run through the IR spectroscopy to measure the amount of light absorbed and compare it to a graph of pure 1-bromobutane to determine if it is the actual final product obtained. This comparison also shows any impurities in the final product. The graphs were similar but not perfect, implying that an impure product of 1-bromobutane was obtained. To identify the functional group of the molecule, the frequency range of the light absorption patterns was observed. Different functional groups are excited at different unique ranges between 4,000-1,250 cm^-1. The C-H axis could be found in this range. The structure of the molecule is determined by looking at a fingerprint region (1,250-500 cm^-1). The C-Br axis should be visible in this range but the IR machine was not sensitive enough. The fingerprint region is unique to each compound and helps determine things such as stereochemistry. It is important to add sodium sulfate to the product before running it through the IR. This will remove OH from the product so that it will not show up in the spectroscopy. There should be no peaks at OH after the test. My sample for this experiment had to be run through the IR spectroscopy twice because the first time had a significant OH peak. Adding more sodium sulfate to the solution and running the IR again eliminated
this. This experiment was done at half-scale from the book to form 1-bromobutane from a 1° alcohol. Butanol, water, and NaBr were mixed together and cooled before sulfuric acid was added dropwise to control the side reaction that occur with the addition of H2SO4. The solution had to be cooled before adding H2SO4 to control them temperature since this addition is exothermic. Instead of doing the distillation that was recommended in the book, we did a gentle reflux instead. The difference being that instead of the condensed gas going to a different beaker it returns to the original beaker. This reflux took place for 45 minutes. Afterward the solution was allowed to return to room temperature and water was added. This caused the organic layer of the solution to separate from the aqueous layer of the solution. The organic layer was extracted and dried with NaSO4 to remove excess water. Doing a half scale experiment, the theoretical yield was 2.9984 g. The actual weight of the product obtained was 2.194 g. This is a 74% yield which is high. This is most likely because all the H2O was not extracted from the solution before it was weighed.
As a final point, the unknown secondary alcohol α-methyl-2-naphthalenemethanol had the R-configuration since it reacted the fastest with S-HBTM and much slower with R-HBTM. TLC was a qualitative method and ImageJ served as a quantitative method for determining which reaction was the faster esterification. Finally, 1H NMR assisted in identifying the unknown from a finite list of possible alcohols by labeling the hydrogens to the corresponding peaks.
The goal of this two week lab was to examine the stereochemistry of the oxidation-reduction interconversion of 4-tert-butylcyclohexanol and 4-tert-butylcyclohexanone. The purpose of first week was to explore the oxidation of an alcohol to a ketone and see how the reduction of the ketone will affect the stereoselectivity. The purpose of first week is to oxidize the alcohol, 4-tert-butylcyclohexanol, to ketone just so that it can be reduced back into the alcohol to see how OH will react. The purpose of second week was to reduce 4-tert-butylcyclohexanol from first week and determine the effect of the product's diastereoselectivity by performing reduction procedures using sodium borohydride The chemicals for this lab are sodium hypochlorite, 4-tert-butylcyclohexanone
Enantiomers, a type of isomer, are non-superimposable, mirror images of each other. Diasteriomers, another type of isomer, are non-superimposable, non-mirror images of each other. Dimethyl maleate and dimethyl fumarate are diasteriomers, as they are not mirror images but instead vary in the orientation of the carbomethoxy groups around the double bond. Dimethyl maleate is the cis-isomer because both groups are on the same side and dimethyl fumarate is the trans-isomer because the two groups are on opposite sides. A bromine free radical mechanism was required for this conversion. First, energy from light is required to create two bromine free radicals from Br2. Then one of the free radicals attacks the double bond in dimethyl maleate, breaking it and creating a carbon radical on the other carbon. The bond then rotates and reforms, freeing the bromine radical and creating the trans-isomer, dimethyl fumarate. Bromine in this reaction is acting as a catalyst in this reaction and then cyclohexane is added at the end to neutralize the bromine free radicals. The activation reaction of the radical reaction is lower than the activation energy of the addition reaction, which is why it occurred more quickly. This reaction was successful because the percent yield was 67.1%, which is greater that 65%. It also demonstrated the expected principles, as the reaction did not occur without the presence of both light and bromine. The dimethyl fumarate had a measured boiling point of 100C to 103C, which is extremely close to the expected boiling point of 102C to
The primary goal of this laboratory project was to identify an unknown compound and determine its chemical and physical properties. First the appearance, odor, solubility, and conductivity of the compound were observed and measured so that they could be compared to those of known compounds. Then the cation present in the compound was identified using the flame test. The identity of the anion present in the compound was deduced through a series of chemical tests (Cooper, 2009).
The IR spectrum that was obtained of the white crystals showed several functional groups present in the molecule. The spectrum shows weak sharp peak at 2865 to 2964 cm-1, which is often associated with C-H, sp3 hybridised, stretching in the molecule, peaks in this region often represent a methyl group or CH2 groups. There are also peaks at 1369 cm-1, which is associated with CH3 stretching. There is also C=O stretching at 1767 cm-1, which is a strong peak due to the large dipole created via the large difference in electronegativity of the carbon and the oxygen atom. An anhydride C-O resonates between 1000 and 1300 cm-1 it is a at least two bands. The peak is present in the 13C NMR at 1269 and 1299 cm-1 it is of medium intensity.
Benzyl bromide, an unknown nucleophile and sodium hydroxide was synthesized to form a benzyl ether product. This product was purified and analyzed to find the unknown in the compound.
The purpose of the experiment is to study the rate of reaction through varying of concentrations of a catalyst or temperatures with a constant pH, and through the data obtained the rate law, constants, and activation energies can be experimentally determined. The rate law determines how the speed of a reaction occurs thus allowing the study of the overall mechanism formation in reactions. In the general form of the rate law it is A + B C or r=k[A]x[B]y. The rate of reaction can be affected by the concentration such as A and B in the previous equation, order of reactions, and the rate constant with each species in an overall chemical reaction. As a result, the rate law must be determined experimentally. In general, in a multi-step reac...
The article, “Asymmetric one-pot Robinson annulations” (Rajagopal et al., 2001) describes the procedure of a Robinson Annulation Reaction that converts a five-membered cyclic ketone to a two-ring, bicyclic compound. In this reaction, 1.12 g of 0.01 mol dione was added to a solution of 1.15 g of 0.01 mol S-proline in dry DMSO and mixed in a beaker, followed by 0.7 g of 0.01 mol methyl vinyl ketone. This mixture was stirred for 145 ...
The product that was recovered was tan, shiny crystals and weighed 0.916 g. The partial percent yield for this step was 45.96 %. This yield was determined by using the amount of 4-acetamidobenezenesulfonamide in this step to calculate the theoretical yield. The amount recovered was then divided by this theoretical yield to the partial percent yield. Once both partial percent yields were determined, the overall percent yield for this multistep synthesis was calculated. The overall percent yield for this experiment is 26.72 %, and was determined by taking the product of 0.4596 and 0.5814, and multiplying it by 100. One reason the overall yield is low, is the constant transferring of materials from one apparatus to another. If the reactions could be performed in one apparatus, the amount of product lost during transfers would be eliminated. Even though there was a low recovery, identification of the final product was confirmed, and tests for solubility were performed. For the solubility test, sulfanilamide was tested with 1.5 M HCl and 1.5 M NaOH. Both test resulted in sulfanilamide being soluble in each solvent. Next, the melting point for the final product was found. The melting point for this compound was determined to be 163-165 ˚C which matches the known value for sulfanilamide. The IR spectrum, RM-12-Ci, also confirms that the reaction was completed. In the IR spectrum, a carbonyl group was not present. This is important because sulfanilamide does not contain this functional group like the previous products. The only functional groups that are present in this spectrum are an amine group at 3551-3239 cm-1, a nitrogen-hydrogen bend at 1596 cm-1, a sulfone at 1305 cm-1 and 1142 cm-1, and a para substituted ring at 824 cm-1. All of the functional groups are found in the product. The 1H NMR spectrum also confirm that
Once this was completed, we moved on to the IR spectra portion of the lab. We first obtained potassium bromide and benzophenone. The benzophenone was grinded into powder and then added to the potassium bromide—and mixed. This mixture was then placed into a pellet press barrel with one of the bolts halfway up the chamber. The other bolt was then inserted and tightened by hand, later using wrenches to further tighten the bolt. Once the pellet was transparent, we were able to run it under the IR spectrum. The data was then shared with our
In todays laboratory exercise, one of the factors that affect the enzyme activity will be examined. All enzymes are proteins. The function of enzymes are to accelerate defined chemical reactions by alternating the rate of the reaction. They will not trigger a reaction to take place that would not occur naturally. Having a particular enzyme to catalyze each of the chemical reactions that take place in a living cell, total control of metabolism can be sustained by an organism.
The desired product is a white crystalline solid which indicates that it does not have an absorption band around 400-800nm, thus suggests that the compound absorbs shorter wavelengths. Whether the system is conjugated must be evaluated by TLC using the short wavelength of 254 nm.
Predictions may be made about the suitability of possible catalysts by assuming that the mechanism of catalysis consists of two stages, either of which can be first:
In order for the reflux to work well, rapid stirring must be in effect throughout. The yield of 2-bromohexane is higher when the reaction mixture is stirred. This is because when HBr is alone, it is immiscible in 1-hexene. Stirring with tetrabutyl ammonium bromide causes separation of organic and aqueous layers. When the aqueous layer is removed, we make it more reactive with alkene. Then stirring solution causes more surface area for the HBr and 1-hexene to react with each other, so more product of 2-bromohexane forms. Separating reagents between phases is important and can be contributed to total surface area. In order to increase the surface area, the reaction must be stirred to stimulate colloids and droplets of immiscible layers. If no mixture occurs, no formation of two distinct layers will occur and the organic portion product will have low content because HBr may have reaction with water and produced a weak acid H3O+. Phase transfer catalysts, like tetrabutyl ammonium bromide are amphoteric. The ammonium salt removes HBr from an aqueous phase and puts it in an organic
This is a result of a more favorable entropy contribution, due to the reduction of apolar molecular surface area during the activation process4. The substituent of the reaction does affect the rate enhance but depended on the compounds being used. The Gibbs energy transfer plot of the reaction of compounds 1.1 and 1.5 from figure 1, reveals that the rate acceleration in water relative to the alcohol was due to the destabilization of the initial state. The stabilization of the transition state relative to the initial step was proposed to be a consequence of the reduction of hydrophobic surface