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12 Nov 2019

If the following three chemicals (benzyl alcohol, benzaldehyde and benzoic acid) were
chromatographed using silica gel TLC plates, which should have the highest Rf value? Hint:
What intramolecular forces are involved between each of these chemicals and the SiO2 of the
silica gel

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Lelia Lubowitz
Lelia LubowitzLv2
16 Oct 2019

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Related questions

An unknown mixture was analyzed using TLC on a silica gel plate and developed in 1:6 ethyl acetate:hexane, and gave 2 spots with Rf values of 0.6 and 0.5 respectively. 1)Would this be considered a good separation between the two? Briefly explain. 2)Which spot represents the more polar compound(s)? 3)Can you say for sure how many compounds are contained in the mixture? If so, how many are there? Briefly explain. 4)If not, what further conditions might be performed to determine the number of components in the mixture or to obtain a better separation? Explain. 5)Suppose you carry out a TLC separation of acetaminophen and aspirin on silica gel using a nonpolar eluting solvent, hexane. Which should have the larger Rf value? Briefly explain. 6)What are the methods for "visualizing" spots on TLC plates that we will use in this lab?

Answer the questions below 7-10

1. When monitoring the reaction by TLC you see that the most benzaldehyde starting material has an Rf of 0.25. What should you do?

a. Use a greater amount of Ethyl Acetate in relation to the amount of Hexane until the Rf is 0.5

b. Use a greater amount of Hexane in relation to the amount of Ethyl Acetate until the Rf is 0.5

c. Rf value of 0.25 is fine as the product of this reactions the product will be more non-polar than the starting material and will travel further up the TLC plate
d. Let the TLC run longer

The NMR data giving for the product is as follows:

d 7.05 (s, 5 H), 5.95–5.30 (m, 1 H), 5.19–4.80 (m, 2 H), 4.60 (t, J = 6 Hz, 1 H), 2.44 (t, J = 6 Hz, 2 H), 2.06 (br s, 1 H).

What proton is represented at "2.06 (br s, 1 H)"?

a. Proton connected to oxygen
b. Internal proton of the alkene
c. The proton that is on the carbon alpha to the alcohol
d. This is the impurity of water in DMSO

What solvent do the authors run their NMR in?

a. CDCl3
b. d-DMSO
c. d-Acetone
d. -Benzene

The NMR data giving for the product is as follows:

d 7.05 (s, 5 H), 5.95–5.30 (m, 1 H), 5.19–4.80 (m, 2 H), 4.60 (t, J = 6 Hz, 1 H), 2.44 (t, J = 6 Hz, 2 H), 2.06 (br s, 1 H).

If you ran the NMR in d-DMSO and see an additional peak at 1.76ppm and 3.60ppm, what do these peaks represent.

a. Residue THF impurity, as THF was used as a solvent in the reaction
b. Allyl Bromide Statring Material
c. Benzaldehyde Statring Material

d. water impurity as water was used as a solvent in the reaction
e. These resonances representatives the protons of ammonium chloride which was used in the reaction

This paper states this addition of an allyl halide to a aldehyde is a "Grignard-Like" reaction. Although, traditionally reactions using allyl halides and zinc to perform carbon-carbon bond formation are known as the Barbier Reaction

a. True
b. False

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