Question

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

Answer 1

1.

Correct option is

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

Since this reaction is the addition of Grignard reagent to the benzaldehyde, which results in the formation of alcohol which is more polar than the benzaldehyde. Hence to get the better separation of both the starting material (benzaldehyde) and alcohol more polar solvent (ethyl acetate) has to be used to increase the Rf value.

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

The correct option is Proton connected to oxygen.

Protons that are connected to heteroatoms like oxygen and nitrogen are broad in nature.

What solvent do the authors run their NMR in

The correct option is d- DMSO (since the product is more polar, and it is soluble in d-DMSO)

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

Residue THF impurity, as THF was used as a solvent in the reaction.

The additional peak at 1.76ppm is due to CH2 group of THF, and 3.60ppm due to OCH2 group of THF

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

Barbier Reaction is the first developed organometallic reaction, which was the trigger point reaction to develop the Grignard reaction. Barbier was the research supervisor of Grignard during his doctoral studies.