consider a sample that is a mixture of biphenyl, benzoic acid, and benzyl alchohol. The sample is spotted on a TLC plate and developed in a methylene chloride cyclohexane mixture.
Predict the relative Rf values for the three components in the sample.
For assistance use the table 12.3 on page 676.
~ Well on pg 676 in my organic chem book it's talking about organic layer seperation and on table 12.3 on page 683 note that it talks about common signs that a solution is dry.
Basically the wrong pages...
I have no clue how to predict relative Rf values for these compounds especially since it's using a mix of 2 solvents which I haven't tried in the lab. I've used either or but not both and not with these compounds either.
I would think it would depend on the polarity of the substances but that would also require me to look at the mix of the solvent which both have different polarities so technically I would think that it would only be feasible to go and find the positions such as this would go first and second and so on but are they asking for numbers?? Also I'm confused as to the solvent combination..I really don't know what would be the effect it would have since they don't say how much they used..but if they don't say I'm guessing it would be equal...
I really need help on this...
Thank You
So I guess Nobody can help me out..?
=(
To predict the relative Rf values for the three components (biphenyl, benzoic acid, and benzyl alcohol) in the sample, we can consider their relative polarities.
The relative Rf (retention factor) value is a measure of how far a compound travels on a TLC plate relative to the solvent front. It can be influenced by various factors such as the polarity of the compound and the polarity of the solvent.
In general, compounds with higher polarity tend to have lower Rf values, as they interact more strongly with the stationary phase on the TLC plate. Conversely, less polar compounds tend to have higher Rf values, as they interact less with the stationary phase and move more readily with the mobile phase (solvent).
Since we know that biphenyl, benzoic acid, and benzyl alcohol are all organic compounds, we can consider their polarities based on their functional groups and molecular structures:
1. Biphenyl: Biphenyl is a nonpolar compound consisting of two phenyl rings connected by a single bond. It does not have significant functional groups that can participate in hydrogen bonding or other polar interactions. Therefore, biphenyl is generally expected to be less polar compared to the other two compounds.
2. Benzoic acid: Benzoic acid contains a carboxylic acid functional group (-COOH). Carboxylic acids are polar compounds that can form hydrogen bonds. Due to the presence of this polar functional group, benzoic acid is expected to be more polar compared to biphenyl and benzyl alcohol.
3. Benzyl alcohol: Benzyl alcohol contains a hydroxyl group (-OH), which is also polar and capable of hydrogen bonding. While not as polar as the carboxylic acid functional group, the presence of the hydroxyl group makes benzyl alcohol more polar than biphenyl.
Now, considering the solvent mixture of methylene chloride and cyclohexane, we know that methylene chloride is a polar solvent, while cyclohexane is a nonpolar solvent.
When biphenyl, benzoic acid, and benzyl alcohol are spotted on a TLC plate and developed in this solvent mixture, the following general trends can be expected:
- Biphenyl, being the least polar compound, is expected to have the highest Rf value as it will move more easily with the nonpolar cyclohexane.
- Benzyl alcohol, being more polar than biphenyl due to the hydroxyl group present, is expected to have an intermediate Rf value.
- Benzoic acid, being the most polar compound among the three due to the carboxylic acid functional group, is expected to have the lowest Rf value as it will interact more strongly with the polar methylene chloride.
However, without specific information about the exact composition of the solvent mixture and the concentrations used, it is difficult to provide precise numerical values for the Rf values of each compound. The relative Rf values are utilized to compare the migration distance of the compounds of interest to the solvent front, allowing for qualitative analysis of the TLC results.
Remember to always refer to your textbook or reference materials for additional guidance and specific values if provided.
To predict the relative Rf (retention factor) values for the three components in the sample, you need to consider the polarity of the components and the polarity of the solvent system. Here's how you can approach it:
1. Understand the concept of Rf value: Rf value is the ratio of the distance traveled by a compound (spot) to the distance traveled by the solvent front. It is a measure of how far a compound moves on the TLC plate relative to the solvent.
2. Consider the polarity of the components: Biphenyl, benzoic acid, and benzyl alcohol all have different polarities. Benzyl alcohol is more polar than biphenyl, and benzoic acid is even more polar due to the carboxylic acid group.
3. Consider the polarity of the solvent system: Methylene chloride is a non-polar solvent, while cyclohexane is a relatively non-polar solvent as well. A mixture of these solvents would create an intermediate non-polar to slightly polar environment.
4. Use Table 12.3 (on the correct page in your organic chemistry book) or reference materials to determine the general Rf values for the compounds in different solvent systems. Compare the polarities of your components to those in the reference data.
5. Make predictions based on polarity: In general, non-polar compounds tend to have higher Rf values in non-polar solvents, while polar compounds have lower Rf values. Biphenyl, being relatively non-polar, would likely have the highest Rf value. Benzyl alcohol, being more polar, would have a lower Rf value. Benzoic acid, being the most polar, would likely have the lowest Rf value.
6. Keep in mind that the solvent system can affect the Rf values, so the predictions can only be approximate. The actual Rf values can vary depending on the specific concentration of each solvent in the mixture and the nature of the TLC plate.
7. It may also be helpful to perform a test spot with known references (compounds of known polarities) to validate your predictions.
Remember, these predictions are based on general principles, and in practice, it is always a good idea to have reference data and to perform TLC experiments to confirm the Rf values for specific components and solvent systems.
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