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
To predict the relative Rf values for the three components in the sample, we need to consider the properties of the compounds and the solvent system that is being used.
Rf value stands for "retardation factor" and it is a measure of how far a compound travels on a TLC (thin-layer chromatography) plate relative to the solvent front. It is calculated by dividing the distance traveled by the compound by the distance traveled by the solvent front.
In this case, the sample is spotted on a TLC plate and developed in a methylene chloride cyclohexane mixture.
To predict the relative Rf values, we need to consider the polarity of the compounds and the polarity of the solvent mixture.
Biphenyl is nonpolar, benzoic acid is a weak acid (polar), and benzyl alcohol is a polar compound.
Methylene chloride is a relatively nonpolar solvent, while cyclohexane is also nonpolar. When these two solvents are mixed together, they create a moderately nonpolar solvent system.
Based on these properties, we can make some predictions:
1. Biphenyl: Since it is nonpolar, it is expected to have a relatively higher Rf value in a nonpolar solvent system. Therefore, it is likely to have the highest Rf value among the three components.
2. Benzyl alcohol: Being a polar compound, it would have a lower Rf value compared to biphenyl, as the nonpolar solvent system is less compatible with polar compounds.
3. Benzoic acid: Since it is a weak acid, it may exhibit mixed polar and nonpolar characteristics. It will most likely have an intermediate Rf value.
Keep in mind that these predictions are based on the general properties of the compounds and the solvent system. The actual Rf values can vary depending on the concentration of the solvents and other factors. It is always a good idea to perform an actual experiment to determine the precise Rf values for a sample.
To predict the relative Rf values for the three components (biphenyl, benzoic acid, and benzyl alcohol) in the sample spotted on a TLC plate and developed in a methylene chloride cyclohexane mixture, we can consider several factors.
Relative Rf values depend on the polarity of the compounds and the polarity of the solvent system used for the TLC development. In this case, methylene chloride and cyclohexane are both nonpolar solvents.
Based on their structures, we can make predictions about the relative Rf values:
1. Biphenyl: Biphenyl is a nonpolar compound. As the solvent system is nonpolar, biphenyl will have a relatively high affinity for the mobile phase (solvent) and a lower affinity for the stationary phase (TLC plate). Therefore, biphenyl is likely to have a higher Rf value.
2. Benzoic acid: Benzoic acid is a polar compound due to the presence of the carboxylic acid group. However, the carboxylic acid group can form hydrogen bonds with both methylene chloride and cyclohexane. This could lead to an intermediate affinity for both the mobile and stationary phases. Therefore, benzoic acid is likely to have a moderate Rf value.
3. Benzyl alcohol: Benzyl alcohol is also a polar compound due to the presence of the hydroxyl group. Similar to benzoic acid, the hydroxyl group can form hydrogen bonds with both solvents. Thus, benzyl alcohol is expected to have an intermediate Rf value as well.
However, due to the complexity of the system and the fact that the solvent mixture is not specified in detail, it is challenging to provide precise numerical values for the relative Rf values. The specific ratio of methylene chloride to cyclohexane, along with other experimental conditions, would affect the separation and relative movement of the compounds on the TLC plate.
If you have access to more information about the solvent system and specific conditions, you can refer to table 12.3 on page 676 of your Organic Chemistry book for better guidance.