Macroscale and Microscale Organic Experiments
7th Edition
ISBN: 9781305577190
Author: Kenneth L. Williamson, Katherine M. Masters
Publisher: Brooks Cole
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Chapter 8, Problem 10Q
A TLC plate showed two spots with
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A standard sample of compound A was placed on a silica TLC plate. After elution in 30/70 ethyl
acetate/hexane, the sample showed a single spot at 3.4 cm (relative to the initial point) after the
solvent had risen to 7.1 cm (relative to the initial point). A sample which was thought to contain
this compound was analyzed by TLC and showed two spots after elution in the same solvent
system. The solvent height for this plate was 6.5 cm (relative to the initial point) and the spots
were located at 3.6 cm and 5.2 cm (relative to the initial point). Can either of these spots possibly
be compound A? Explain.
Include a discussion of the R, for each spot.
You are monitoring the reaction A --> B via periodic GC analysis. Initially, you only see one peak in your chromatogra
m; however, over time you find that a new peak is growing while the original peak is shrinking. What is happening?
A student used thin layer chromatography to confirm whether he could successfully separate two compounds. Here is the TLC plate he obtained after 30 min. Stationary phase was silica gel and mobile phase was 95 % ethyl acetate and 5 % Hexane mixture.
Chapter 8 Solutions
Macroscale and Microscale Organic Experiments
Ch. 8 - Prob. 1QCh. 8 - Prob. 2QCh. 8 - What problem will ensue if the level of the...Ch. 8 - Prob. 4QCh. 8 - Prob. 5QCh. 8 - Arrange the following in order of increasing Rf...Ch. 8 - What will be the result of applying too much...Ch. 8 - Prob. 8QCh. 8 - Prob. 9QCh. 8 - A TLC plate showed two spots with Rf values of...
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- The identity and ratio of solvents are necessary in chromatography for achieving a good separation. What would happen if your solvent had an overly polar TLC developer? What would happen if it was overly non-polar?arrow_forwardIn order to obtain better separation of the mixture, the above analysis was repeated using an HPLC technique. The retention times of compounds A and B were found to be 15.25 and 16.80 min, respectively, on a 40-cm packed column. An unretained species passed through the column in 1.25 min. The peak base width for A and B are 1.15 and 1.27 min, respectively. Calculate: i) The column resolution. ii) The average number of plates in the column. iii) The plate height. iv) The length of column required to achieve a resolution of 1.5.arrow_forwardHow does increasing the polarity of the developing solvent affect the Rf of a compound on a silica gel TLC plate?arrow_forward
- b. Our ability to separate compounds like the four above are dependent on the properties of the column. Using the data from a 250 mm column shown below, please calculate the retention factor for compound A, the number of theoretical plates for compound C and the plate height for compound C. compoun t, (min) w (min) tm 5.04 0.10 A 7.10 0.16 В 7.15 0.17 7.23 0.16 c. Do you want a large or small number of theoretical plates? In no more than two sentences, explain why.arrow_forwardHPLC VFA analysis - why do I get so different peaks for very similar samples?arrow_forwardA student places an unknown sample on a thin-layer chromatography plate and develops it in dichloromethane as a solvent. Only one spot whose Rf is 0.98 is observed. Does this result indicate that the unknown material is a pure compound? If not a pure compound, suggest an alternate procedure to verify the purity of the sample.arrow_forward
- You spotted a mixture of three compounds, labeled A-C, on a silica plate. The resulting thin layer chromatography (TLC) plate with a mobile solvent mixture of 95 % hexanes and 5 % ethyl acetate is shown below. Which of the spots traveled the furthest up the TLC plate corresponding to spot 3?arrow_forwardIn TLC, why does a 3:1:1 ratio of the developing solvent of n-butanol/acetic acid/water move up the TLC plate so slowly?arrow_forwardNeed help with a and b. A mixture of 1-hexanol, hexane, and 1-chlorohexane is injected on a gas chromatography column. a) Predict the sequence of retention times indicating which compound will have the shortest, middle, and longest retention time. b) The sample vial of (a) was not carefully sealed and left partially open for a couple hours. A GC is taken again with only two peaks realized. The first peak to appear has an area of 24 mm2 and the second peak 40 mm2. What mole% of each compound (specify the compound name) is most likely present?arrow_forward
- A student spots an unknown sample on a TLC plate. A single spot with an Rf of 0.55 showed up on the plate after developing the sample in hexanes-ethyl acetate 50:50. Does this prove that the unknown is a pure compound?arrow_forwardOn a paper chromatogram, a spot produced by blue ink traveled 2.7 cm, and the solvent "front" traveled 5.7 cm during the experiment. Calculate rate of retention of flow, Rf, for the blue ink.arrow_forwardDoes the presence of a benzene ring or carboxylic acid functional group in a substance affect the retention factor (Rf) when doing TLC on silica gel ?arrow_forward
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