Wittig Reaction Lab Essay

943 Words Apr 17th, 2013 4 Pages
Makram Youssef
Chris Wong

Calculations of percent yield:

Rf values:
(literature values: trans,trans =0.36, cis,trans=0.41)

Short-wavelength TLC plate: solvent line =3.9cm filtrate: 1.4cm/3.9cm = 0.36, 1.7/3.9cm =0.44 trans,trans-isomer: 1.5cm/3.9cm = .38

Long-wavelength TLC plate: solvent line = 3.9cm filtrate: same values appear as under short-wavelength in addition to 1.1cm/3.9cm = 0.28 trans,trans-isomer: same value as under short-wavelength


This experiment was governed by the the Wittig reaction mechanism, which is done properly yields an alkene. The percent yield for the overall experimented, after purification was approximately 4.23%, not a very high yield but enough to carry out subsequent
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Also, when looking at the filtrate values under the short-wavelength, a value of 0.44 appears to hint at the existence of the cis,trans-isomer which has a literature value of 0.41. The three values for the filtrate under the long-wavelength make sense as well, being that the value of 0.28 belongs to the oxide, the 0.36 to the trans,trans, and the 0.44 to the cis,trans.
An NMR spectrum was also taken for our product sample which was close to the ideal but was a little off. Ideally there should be five peaks for the five chemical shifts from the five hydrogen groups on the product structure. The first peak should occur in the mid six ppm and can be described as a quartet. The second peak should occur at a ppm in the high 6s and should be another quartet. The third peak should be a triplet occurring at a low 7ppm. The fourth peak should be close by to the third, being another triplet. Finally, the fifth peak should be a doublet occurring at a mid 7ppm. The ppms for the ideal and the actual differ greatly in the fact that they span from approximately 5.3-6.25 instead of the ideal 6.5-7.5. It is fact that chemical shifts caused by benzene rings occur in the 6 to 8 ppm range, thus the nmr we received as a result can be somewhat doubted.. Ideally the first and second peaks should be a result of the hydrogens furthest away from the rings and the

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