Introduction (Present tense – third person – active voice) *Maximum 1½ double-spaced pages
The first sentence of your Introduction should include a concise statement of the goal of the experiment and the methods used. Background information: As relevant, incorporate key terms and concepts in an explanation of how a technique works on the molecular level, examples of relevant techniques outside of this class, comparison and contrast of current techniques with others you have learned in this class, a balanced chemical equation, and explanation of expected outcomes (when appropriate, include mechanisms and flow charts to back them up). *Figures will not count toward the page limit, but all figures must be located at the end of the introduction section.
The goal of the experiment is to synthesize the product of 1-hexene and HBr, and to see if the product follows Markovnikov’s rule. Markovnikov’s rule says that in a reaction between an “H-X” molecule (hydrogen attached to a halide) and an alkene, the halogen would ultimately added to the carbon that has more carbons attached to it (primary versus secondary versus tertiary) . There are several factors that are important for the success of the reaction. One is the necessity to vigorously stir the solution in the conical vial while it is in the reflux condenser. The vigorous stirring is to ensure the interaction between the 1-hexene, the HBr, and the tetrabutylammonium bromide. Tetrabutylammonium bromide is used as a phase catalyst (one that helps the reactants move into the same phase phase) to help proceed the reaction faster since HBr and 1-hexene are the aqueous and organic phases respectively. The use of a reflux condenser is also crucial for the success of the reaction. The reflux condenser creates a two-part vessel (vapor and liquid parts) so that the gas evaporated from the heating of the reactants can go into another compartment, in which water is passed through. Thus, this gas condenses back into the liquid phase and go back into the reaction mixture. Essentially, heating in reflux means that the reaction mixture can be at its boiling point while nothing is lost through vapor. The use of a reflux condenser is important because it can keep all the contents in the vessel while the reaction runs to completion. If the reaction runs smoothly, it should produce 2-bromohexane (a secondary compound). In order to confirm the identity of the compound (by checking if it is a primary or secondary compound), chemical tests are performed on the product of the reaction. In one test, silver nitrate is added to 3 test tubes, already filled with the product (one from the reaction and the other two standards given). The time it takes to form the precipitate indicates if it is a primary or secondary compound. A secondary compound’s formation of precipitate is be faster than that of a primary compound. Another test involves sodium iodide. This time, sodium iodide is added to three test tubes, already with the products, and if a precipitate forms at room temperature, it is a primary compound. If the mixture precipitates at 50˚ C (after heating), then it is a secondary compound. The results of both tests will indicate the presence of primary or secondary compound.
Table 1. Reagents and Products
Table 2. Observations
Conical vial was heated to reflux for 2 hours with rapid stirring Vapor molecules move into the gas chamber and then condense back into the reaction vessel Reaction mixture was cooled to room temperature
Conical vial feels cooler
2 mL petroleum ether was added to reaction mixture
Aqueous layer and organic layer and formed and separated (one a lttle more cloudy than the other) Aqueous layer was removed
Only cloudy, organic layer was left in the vial
Added 0.5 mL Na2CO3(aq) to organic layer and stirred
Bubbles form; Aqueous and Organic...
References: Gilbert, John C., and Stephen F. Martin. Experimental Organic Chemistry: A Miniscale &
Microscale Approach. Belmont, CA: Thomson Brooks/Cole, 2006. Print.
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