SN1 & SN2 Substitution Reaction Analyses Diana ZermenoPartner: Yoselin AcostaTA: Muneeb MohiuddinLab: Thursday, 12:00pm Room # PSE 307 Abstract:The goal of this experiment was to perform a series of reactions with the sameseven halides; once with 15% sodium iodide and another with 1% silver nitrate.
The purpose was for the halide in the substrate structures to become a goodleaving group and have an overall result of a precipitation under twotemperatures, which depended on whether it was an SN1 or SN2 reaction. Thegroup results had the majority of the SN2 results in a 50°C reaction condition;while the SN1 reactions occurred in a room temperature conditions. Compared tothe lab results, there was roughly the same amount of reactions between roomtemperature and the designated temperature for both SN2 and SN1, which was dueto the ambiguity of the experiment. SubstitutionAnalysis of SN1 & SN2 Reactions Introduction.
Thepurpose of the experiment was to observe the different conditions that SN1 andSN2 reactions occur in. SN1 and SN2 are substitution reactions that requirebreaking a bond and creating a new one. The reactant is a Lewis Base/nucleophile that does the substituting. The aim is to see how and why thevarious halides react the way they do and how the structures affect it. Bromineand chlorine substituents are chosen because of how easily they can be removed.The easiness in removal is due their size and the need to have a full octet.Hence, it is expected that the chlorine is better leaving group because it islarger.
Since, chlorine is a better leaving group, it will also have a higherreactivity.SN2reactions, as shown in Figure 1, are more likely to occur with primarysubstrates, compared to tertiary. This is because it wants the maximum amountof surrounding space to continue the substitution reaction. On the other hand,SN1 reactions favor tertiary substrates because the reaction is performed insteps, with intermediates.
Le Chatelier’s principle is when the precipitation of theby-product moves the reaction from the left to the right. This is important tothis experiment because it signals whether the substitution reaction occurredand under which conditions. Furthermore, the results that will be gathered inthis experiment, will not be completely reliable. The uncertainty is because thereis no distinguishing factor between substitution and elimination reactions, atthis level.
Experimental.1 Determine theMechanism of Substitution. To begin, 14 clean, dry test tubeswere gathered. Each bromide and chloride structure had 2 labelled test tubes.Four drops of each halide were added to the corresponding test tubes.
Beforecontinuing the experiment, a water bath was set up and warmed to 50°C.Testfor SN2 Reaction. One set of the labelled test tubes wasused for this part of the experiment. Two mL of 15% sodium iodide in acetonesolutions was added to each of the tubes. The solutions were left for 5 minutesto react. The solutions that produced precipitate was recorded, and the otherswere places in the water bath for another 5 minutes.
After, the solutions withprecipitate were recorded. The results were given to the TA and the water bathwas heated to 80°C. Testfor SN1 Reaction. Two mL of 1% silver nitrate in ethanolsolution was added to the remaining 7 test tubes. After they were left for 5minutes to react, the precipitated solutions were recorded.
The unreactedsolutions were placed in the heated water bath for 5 minutes. The solutionswith precipitate were recorded and given to the TA. Results.Asshown below, most of the SN2 reactions occurred under 50°C conditions.
Table1.Results for SN2 reaction Name Group Results Lab Results Room Temp 50°C Room Temp 50°C 1-bromobutane x – 12 – 1-chlorobutane – x 8 4 2-bromobutane – x 2 4 2-chlorobutane – x 1 3 t-butylbutane – x – 1 t-butylchloride – x – – bromobenzene – – – – As seen in Table 2, the majority of the SN1 reactionswere completed in room temperature conditions. Table2.Results for SN1 reaction Name Group Results Lab Results Room Temp 50°C Room Temp 50°C 1-bromobutane x – – 1 1-chlorobutane – – – 1 2-bromobutane x – 2 4 2-chlorobutane – x 1 3 t-butylbutane x – 12 – t-butylchloride x – 7 4 bromobenzene – – – – Discussion.Asmentioned before, Le Chatelier’s principle is used to determine if the halidestructures reacted in SN1/SN2 and in which temperature conditions.
Theprecipitate formed by the by-product is that determinant. For SN1 reactions, aweak nucleophile was used, and a strong nucleophile was used for SN2 reactions.As demonstrated in Figure 2, SN2 is a fast reaction because there are not anyintermediates involved. Therefore, since SN2 is a fast reaction, bromine is astrong nucleophile. While SN1 is slower, therefore chlorine is a weaknucleophile. SN2 reactions occurred mostly in 50°C conditions because it has ahigher activation energy it needs to reach.
Compared to SN1, room temperatureconditions were ideal because of the lower activation energy. As seen in the results, SN2 reactionsoccurred more in 50°C and SN1 reactions were in room temperature. The betterleaving group, chlorine, had a higher chemical reactivity at room temperature.In Table 2, it is shown that SN1 reactions mostly occurred with tertiarysubstrates; while in Table 1, SN2 reactions were with primary substrates. Thisaligns with the hypothesis because of the size trends for each reaction. SN2 reactions prefer easily accessible centeratoms and SN1 do not.
Since SN2 is a fast reaction, the activation energyrequired is higher than SN1, which is why it occurs in higher temperatures. Comparing Group and Lab results, there were a few discrepancies.This was due to the confusion as to what was considered precipitation.
Additionally, there could have been competing reactions and possibly confusingan elimination reaction with substitution. Conclusion.The objective of thisexperiment was to see why SN2 and SN1 reactions occurred in the conditions setand certain halide structures. It was observed and concluded that SN1 reactionsoccur in low temperatures with tertiary substrates, since it has a lowactivation energy.
Also, SN2 reactions occur in high temperatures with primarysubstrates, because it has a high activation energy.WorkCited.1. ArizonaState University (2017a, November 5). Substitution Synthesis Lab Package.Retrievedfrom https://myasucourses.asu.edu/