You\'re the TA in an organic lab and the students are running a column to separa
ID: 540519 • Letter: Y
Question
You're the TA in an organic lab and the students are running a column to separate the following compounds Me trans-cinnamic acid methyl cinnamate HW 1. Student A calls you over and explains that after running his column and showing you the TLC of fractions 1-5 which only have one spot by UV. He combined these fractions, removed the s 38°C and not 133°C. How would you advise him? olvent and took a melting point. He is worried something is wrong because he got HW 2. Student B calls you over and explains that after running her column on a mixture of two compounds and collecting 25 fractions, the first compound has come off the column completely (eluted). She's got to run to class and needs to collect the second compound. What would you advise her to do to expedite the collection of the second spot? Explain your reasoning.Explanation / Answer
HW 1:
The melting point of tran-cinnamic acid is 132 – 135 oC and that of methyl cinnamate is 34 – 38 oC. The compound separated by student A has melting point of 38 oC. Thus, the isolate compound is methyl cinnamate.
However, student is expecting melting point of 133 oC, which is that of trans-cinnamic acid. The molecule of trans cinnamic acid is polar compared with methyl cinnamate which is nonpolar. Thus, methyl cinnamate will elute out first from the column. Therefore, in order to get trans-cinnamic acid student must elute the second compound from column by increasing polarity of the solvent used for column.
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HW 2:
Student B has collected first spot from the column in first 25 fractions. Now column contains only second compound. The remaining second compound can be eluted out from the column by using high polarity solvent system.
Therefore, student B can expedite the collection of second spot by increasing the polarity of the solvent system rapidly instead of using slow gradient system.
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