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Organic chem lab work
Organic Chem Lab Ii (CHEM 345)
Saint Louis University
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Kalinda Dhawan SN2 reaction Theory- Q1 at the rates of the reactions you saw in the TA Demo. Why did you see those rates? Explain using the theory of the reactions. What could have happened if the tertiary alkyl bromide reacted faster than expected? We saw the rates such as primary, secondary and tertiary because of the theory of the reactions which stateselectron affinity of key atoms, bond strengths and steric hindrance. It influences how fast a reaction will occur and which reactions will occur first tertiary alkyl bromide reacted faster than expected then instead of SN2 it would have been SN1 reaction. Q2 looking at Section 7 in your textbook, you see the chart of leaving groups. With those in mind, explain the reaction of the TA demo. Why did the TA demo work? Does that seem contradictory to Section 7? The TA reaction went through SN2 for 3 of the reactions since it was a good leaving group, and then went through a synthesis reaction for the final product which was through a SN1. SN2 is caused by asthe nucleophile approaches the carbon atom to which the leaving group is attached, the bond between the carbon atom and the leaving group breaks reason for SN1 was because it left a carbocation from the NaBr. The TA demo worked since all the reactions were good leaving groups, even though reaction B was said to show no reaction happened, it actually did happen just very slowly. Yes it does seem contradictory to section 7 the reason for this is iodine is a better leaving group than bromine which means iodine should be the leaving group. The reason that it works is because the reaction proceeds in a polar aprotic solvent which means anions better than nucleophiles. Q3 what physical property played a role in the three extractions. For each extraction specify why table 1 places the organic layer in a specific layer. The physical properties such as boiling point, melting point, solubility in a given solvent all play a role in extraction. In table 1, wash with water the organic layer was on top. The reason for this is because the organic layer must be more dense than water. With NaOH it is less dense, and which would allow for it to be more soluble in the aqueous layer. The third extraction then the organic layer was on the bottom, this is because the concentrated salt solution wants to become more dilute and because salt has a stronger attraction to water than to organic solvents, causing the organic layer to be on the bottom. Q4 the difference in glassware chosen to measure out sulfuric acid versus the alcohol. Why was each selected? The reason for using different glassware to measure out sulfuric acid and alcohol was for accuracy. Another reason would be in one we had to measure out more solutions, it was also used with precision. By using different glassware we were able to be more
precise as to how much solution we wanted and our measurements would correspond with it. Q5 product will be produced if you treat the t-butanol with the same reaction conditions you followed in the alkyl bromide synthesis? Is this product
different from the product obtained in the SN2 lab? Explain what type of intermediate forms
during this product formation? Remember the mechanism of SN1 reaction. The product that would be formed would be tert-butyl bromide. It is different from the obtained one in the lab, in the lab it was 1-bromobutane. The intermediate product that forms during the reaction of t-butanol is a carbocation intermediate of bromine when it becomes a tertiary carbocation intermediate. It is still a SN1 reaction that takes place. Q6 Chemistry is the study of how, as scientists, we can make chemistry safer on humans and the environment by using fewer chemicals, creating less waste, and picking safer chemicals for use. One way to reduce waste and the amount of chemicals used is to use a solvent-less system for synthesis. In many synthesis reactions, we need to add a solvent, such as DCM or DMSO, in order for the components to be soluble together and therefore react. Based on what you know about this reaction, would you consider this a solventless reaction? Explain your answer. It would be solventless because the 1-butanol and NaBr are the reactants and H2SO is a catalyst so it does the protonation which is usually the responsibility of the solvent. Since there is such a small amount and is soluble in the 1-butanol, it's not really a solvent like the DSCM or DMSO, and no extra solvent was needed, only heat.
Results and implications Table 1,
Test tube number/Letter Rank of Reaction Compound structure
A 1, will react fastest 1
B 3, second fast 2
C 2, slowest 3
Table 1.
Amount Moles Percent yield
RI IR bands
Sulfuric Acid
25 0 s
NA NA NA
Q3 your product 100% pure? How do you know? Did we run any tests that proved one way or another? With this in mind, do you think that your value for percent yield for alkyl bromide is accurate? Why or why not? No it was not 100% pure. This was known because based on the calculations from the product and the limiting reagent we were able to calculate the percent yield which showed that the product was not pure. It was only 40% pure. We ran tests that proved one way or another such as using the IR and RI techniques which then were close to the product but not exact. I do not think this is accurate because there could have been human error done, or some of the product that was being transferred could have not fully transferred, or even machine misreading which could have all affected the results. Errors- Q1 analyzing your results, did you identify any errors that might have skewed your data? If so, discuss how these errors affected your results (at least two). One error that could have skewed the results was reading the ir spectra wrong. The reason for this was that it was difficult to see the line in the machine which then indicated the IR spectra that we needed. This could have been due to not putting too much solution onto it, or from over using the machines. Another error that may have occurred was spilling the solution onto the countertops or accidentally knocking over vials which caused a spill. The reason for this is not paying attention to what one is doing, and then causing a spill which would also cause one to lose their product and not have the full set of data and information needed.
Organic chem lab work
Course: Organic Chem Lab Ii (CHEM 345)
University: Saint Louis University
