Practical - Eucalyptus Oil Lab Report - Identification Of A Conjugated Diene PDF

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Eucalyptus Oil Lab Report...

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Identification of a Conjugated Diene From Eucalyptus Oil Purpose: The purpose of this experiment is to understand and perform a Diels-Alder reaction between an unknown diene from Eucalyptus Oil and the known dienophile Maleic Anhydride. We will then try to identify the unknown diene through properties such as melting point and IR spectra of the adduct. Results: 1. In performing the reaction, we used 4.11g of the unknown diene. Given that the molecular weight of the unknown diene was 136.2 g/mol, this means we had used 0.0302 moles of reactant. Thus, we should expect 0.0302 moles of the adduct, as there is a 1:1:1 stoichiometry between the diene, dienophile, and adduct in a Diels-Alder Reaction. Later on in the analysis, we identify the adduct to be the compound shown in Image 1. Image 1: Final Adduct This adduct has a molecular formula of C14H18O3, which translates to a molecular weight of 234.29 g/mol. Given that we expected 0.0302 mol of adduct, this translates to a theoretical final mass of 7.08 g. Our crude mass was 4.15 g, which equals a 58.6% yield. Our recrystallized mass had a 83% yield from the crude product used (we chose to use 1.00 g of crude product, which recrystallized into 0.83 g of recrystallized product). To calculate the percent yield of the recrystallized product, we can use the product of the percent yield of the crude product and the percent recovery from the crude product to the recrystallized product. 0.83 * 0.586 = 49% recrystallized yield. 2. The melting point of our product was experimentally obtained as being 124.0 ℃ - 124.9 ℃. This was the main result that allowed us to figure out the final adduct was the one shown above. This will be explained later. 3. According to the IR spectrum of the adduct, sp2 and sp3 C-H bonds were present at 2969.42 cm-1, 2945.51 cm-1  , 2888.56 cm-1  , and at 2868.65 cm-1  . An acid anhydride stretching band -1 appeared at 1836.27 cm ; a C=O bond appeared at 1744.88 cm-1  ; sp3 C-O stretching bands -1 -1 appeared at 1087.80 cm and 1233.24 cm ; alkene (RCH=CH2 ) bands appeared 908.12 cm-1  and 956.57 cm-1.

Discussion: 1. The unknown diene was ɑ-phellandrene. We were able to determine the identity of the diene by first figuring out the final adduct as being the one shown in Image 1 above. The reason we were able to determine the adduct in Image 1 as the final product was due to the following table of potential adduct products that was provided in the UChicago Organic Chemistry Lab Manual (uchicago.grtep.com): Table 1: Diels-Alder Adduct Melting Points

Given that our final adduct had a melting point between 124.0 ℃ - 124.9 ℃, the only possible Diels-Alder adduct is the one with a melting point of 126 ℃ - 127 ℃. By knowing its structure and the structure of maleic anhydride, we can use retrosynthetic analysis and our knowledge of Diels-Alder reactions to predict that the diene is ɑ-phellandrene. The reaction of ɑ-phellandrene and maleic anhydride is as follows:

3. The UChicago Organic Chemistry Lab Manual provided 7 polyenes that are found in Eucalyptus Oil: Image 2: Potential Dienes for D-A Rxn Limonene is not a possible candidate for a D-A reaction because the double bonds are not conjugated. β-phellandrene is not viable for D-A reaction because it is conformationally locked in the trans  diene configuration, which would create a lot of ring strain if it were to undergo D-A. β-ocimene is not viable for D-A because its diene is also in the trans c onformation. Lastly, allo-ocimene is not viable for the same reason, as its conjugated double bonds are all trans to their neighbors. This leaves three possible dienes for the D-A reaction: ɑ-phellandrene, ɑ-terpinene, and β-myrcene. 4. The D-A reaction of ɑ-phellandrene and maleic anhydride may yield-- through the two endo and two exo  transition states-- any of the following adducts as shown below:

As we know from our understanding of Diels-Alder reactions, the exo  transition state is scarcely favored, unless there is some MAJOR steric bulk in the dienophile that disfavors the endo transition state. Since maleic anhydride doesn't exhibit major steric bulk, we can only consider the endo  products. Between the top and the bottom endo p  roducts, the top one is more likely to

be favored, as there will be less hindrance between the isopropyl group and the carbonyl group of the maleic anhydride. Thus, the top endo  product is favored and this is the adduct we obtained above....