consider the two pigments phcophytin a and phcophy tin b. Based upon your knowle

Question

consider the two pigments phcophytin a and phcophy tin b. Based upon your knowledge of their respective structures, which one of the two pigments would exhibit a higher R_f value if a mixture of the two were to be spotted on an alumina TLC plate which is then developed in a 30% acetone/70 % hexane solvent system? (Note that the alumina stationary phase is slightly more polar than the silica gel stationary phase). Explain the answer that you have provided in the adjacent blank. Citral a compound present in lemons and limes exists as a mixture of two isomeric compounds Geranial and Neral whose structures are shown on the right. Answer the follow ing questions pertaining to these two isomeric compounds. Geranial and Neral are a pair of (Insert the letter corresponding to the correct choice in the following blank). Enantiomcrs diastercomers If a mixture of these two isomeric compounds was spotted on a TLC plate would you see one or two spots on the developed TLC plate Explain the answer that you have provided in the adjacent blank.

Explanation / Answer

I will answer question 7 for now.

a) They are diasteroisomers, basically because if you look at the C=C the only change between both molecules is the fact that the methyl group is pointing in different directions, in other words, you have those substituyents in cis and trans in the other molecule. (In this case, isomer Z and E). Enantiomers are just the image of another molecule.

b) You have both diasteroisomers, but esentially they have the same bonds, substituyents, and stuff pointing in difrent directions. However in a TLC plates you will see two spots, because both isomers have different melting points, and differents physical chemistry properties, so, even when they are very similar, the spot on TLC will be different too.

Hope this helps

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