Tuesday, May 5, 2020

Diels Alder Reaction free essay sample

Lizz Radican Lab 4 2/24/14 The Diels-Alder Reaction: Results and Problems 1. ) Table 1: Mass, Percent Yield and Melting Points for Diels-Alder Reaction Products. Product Mass (g) Percent Yield Melting Points ( °C) Anhydride 8. 87 88. 2% 164. 4-165. 8 Dicarboxylic Acid 3. 20 71. 9% 176. 6-180. 1 Unknown 1. 66 111% 168. 7-176. 0 2. ) See attached calculations. 3. ) Table 2: Anhydride Product IR Data: Functional Group or Bond Peak Location(s) (cm-1) Peak Intensity Symmetric C=O Stretch 1840 Weak Asymmetric C=O Stretch 1765 Strong C-O Stretch 901 Very strong Table 3: Dicarboxylic Acid Product IR Data: Functional Group or Bond Peak Location(s) (cm-1) Peak Intensity C=O Stretch 1702 Strong O-H Stretch 3200-2500 Broad, medium Sp2 C-H Stretch(s) 3021, 3082 Medium Table 4: Lactone (Unknown) Product IR Data Functional Group or Bond Peak Location(s) (cm-1) Peak Intensity O-H Stretch 3100-2500 Broad, medium C=O-O Stretch(s) 1175, 1158 Very strong C=O Stretch(s) 1769, 1691 Strong 4. The reaction of the unknown with bromine gave a negative result meaning the solution did not turn clear, but rather, maintained an orangish brown color. We will write a custom essay sample on Diels Alder Reaction or any similar topic specifically for you Do Not WasteYour Time HIRE WRITER Only 13.90 / page This is interpreted to mean that bromine in not adding to either side of an alkene bond, so there is no C=C bond in the unknown compound. The reaction of the dicarboxylic acid with bromine gave a positive result meaning that the solution turned clear as a result of bromine adding to both sided of the C=C bond. The dicarboxylic acid has a C=C bond. Problems: 1. The carbonyl that is NOT incorporated into the ring structure has the greater IR stretching frequency. This is because the carbonyl incorporated into the ring structure shares some of its double bond character with the other double bond in the ring, giving it more single bond character. Thus, conjugated double bonds lower the stretching frequency of a carbonyl group by sharing the dipole character of the carbonyl group with the double bond. 2. Some C=C groups sometimes do not show up on an IR spectrum. This is because the C=C groups of aromatic compounds show weak overtones between 1650-2000 cm-1. This area of aromatic overtones could be partially covered up by a strong C=O peak(s) over the same frequency range. An aromatic C=C stretch could also be hidden by a nitrile stretch or an alkene C=C. 3. Maleic anhydride is an excellent dienophile because it is a cyclic alkene where the double bond is conjugated to two carbonyl groups. These groups, as well as the oxygen to which they are bonded, serves as a large electron withdrawing group which pulls electron density away from the double-bonded carbons. Because of this dipole effect, these carbons have a much more positive character, which will readily react with an available electron-rich diene. (See drawings on attached pages. ) 4. Yes, the reaction will be successful because the molecule possesses a conjugated diene that can rearrange through resonance where the double bonds localize to the same ring and react with a dienophile to form a bicyclo ring. 5. Drawings on attached pages. Diels alder reaction free essay sample The experimental product yield is 0. 28g (some solid left on the filter paper and some for the melting point measurement. ) The % yield of hydrolysis is 70. 7% Discussion: The cycloaddition of a conjugated diene and a dienophile, which is drove by forming new ? -bonds from ? -electrons of the diene and dienophile, which are energetically more stable than the ? -bonds. During the Diels-Alder reaction, the temperature should be kept between 60-70. Because the boiling point of the butadiene is low and do not let it vaporize. After cycloaddition, pour the reaction mixture into 50 ml water under room temperature, the product would precipitate because of the low temperature. The acid added for the hydrolysis part is very important because acids have been used to accelerate the rate of the intra-molecular Diels-Alder reaction. The PEG 200 used in this experiment as the solvent for maleic anhydride is  make the experiments more green, which is less harmful and more environmental friendly. We will write a custom essay sample on Diels alder reaction or any similar topic specifically for you Do Not WasteYour Time HIRE WRITER Only 13.90 / page The melting point measurement is helping us to determine what we get basically. Compare with the IR spectra I got, the peak at 1792. 62 cm-1 in the first spectra express the C=O bonds of the initial cycloaddition product, and the peak at 1697. 14 cm-1 in the second IR spectra shows the C=O bonds of carboxylic acid ( RCOOH) of the final product.

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