Purpose: from a list of knowns. This
Purpose: The purpose of this experiment was to identify one ketone with Thin Layer Chromatography and one using NMR spectrometry. We will do this by making 2, 4 a DNPH derivative and checking the melting points. Theory: By Using specific methods of compounds detection, we can match an unknown compound with a known compound because similar compounds will display similar characteristics. In this experiment, identifications of the unknown ketone was accomplished using thin layer chromatography, melting point, and NMR spectrometry.Thin layer chromatography is very quick but sensitive way of determining the components of a mixture or a specific compound from a list of knowns.
This method is the one which was utilized in the following experiment. When comparing a sample of known compounds with an unknown’s Rf values and appearance on the thin layer chromatograph these characteristics can be used to easily determine which known the unknown is. The Rf values are important in determining the more polar molecules from each other, while the color and appearance can be used to separate compounds with similar polarities.The color added by the reaction with 2,4-dinitrophneylhydrazine eliminates the need to compare colors of the different knowns with the unknown. The other method used to help determine which ketone the unknown was, was nuclear magnetic resonance spectrometry or NMR.
NMR utilizes radio frequency waves to determine the number of carbons present and what they are connected to. With this information and the type of hydrogen present from the NMR, an accurate estimate of the unknown ketone can be made. Ketone| Mol Wt| BP(deg C)| D (g/mL)| Derivative MP| 2-propanone| 58. | 56| . 791| 126| 2-butanone| 72. 1| 80| . 805| 117| 2-hexanone| 100.
2| 128| . 811| 106| 2-heptanone| 114. 2| 151| . 811| 89| 2-octanone| 128. 2| 173| . 819| 58| Reaction/Calculations: There were no reactions in this lab. Known ketones: 2-propanone2-butanone2-hexanone 2-heptanone2-octanone Mass of unknown: .
17g Melting Point of Unknown: 87 deg C TLC Slides: Rf Values: Unknown K = 3cm/6cm = . 5 2-Propanone: 2. 6cm/5. 5cm = .
47 2-Hexanone: 2. 9cm/5. 4cm = . 53 2-Heptanone: 3. 2cm/6. 2cm = .
51 2-Butanone: 2. 3cm/6. 4cm = . 35 Methods/SafetyThe experiment was followed verbatim pages 122-123 in Lehman with the following exceptions.
As time was an issue, students worked in groups to prepare known ketones with 2,4-dinitrophenylhydrazine instead of each student preparing every known individually. Also, NMR printouts of already tested ketones were provided instead of doing the spectrometry during lab. When performing this experiment, we were to remember the following safety precautions. Ketones are flammable and may be harmful if inhaled or absorbed through skin.
Avoid contact, breathing in vapors, and putting near flames. ,4-dinitrophenylhydrazine is harmful if absorbed and will dye hands yellow. Ethyl Acetate, Toluene, and Petroleum are also flammable and may be harmful. Finally, Neuterochloroform is toxic and may be carcinogenic. We should avoid contact and inhalation with it. Data/Observations/Results It was observed that when 2,4-dinitrophenylhydrazine was added, a yellow substance was formed. The results for the thin layer chromatography were pretty decisive.
The slides as well as the Rf values of 2-heptanone and my unknown were very similar.I looked at height and size of the spots on the slides to determine this. Rf value of the unknown (K) was . 5. This value was closest to my Heptane Rf value of .
51. Also, the melting point of my unknown (87 deg C) was very close to the melting point of 2-heptanone derivative (89 deg C) found in the table in the Theory section of this report. Therefore, I found that 2-heptanone was my unknown (K).
The results for the NMR were found rather easily. By observing the peaks of my Carbon NMR for the unknown (A), I found that I only had two peaks.This indicates that I have one carbon on each side of the line of symmetry. Next, I observed my Proton NMR which had only one peak. The multiplicity is six.
Therefore, I have six hydrogens. Using this information, I was able to conclude that my unknown is 2-propanone. Discussion/Conclusion This experiment was done to identify one ketone with Thin Layer Chromatography and one using nuclear magnetic resonance spectrometry. When using Thin Layer Chromatography, I was able to determine my unknown by observing my slides and seeing that the spots of my unknown are most like hose of 2-heptanone in height and size. Furthermore, I calculated my Rf values and determined that my Rf value of Unknown K (.
5) was most near my Rf value of 2-heptanone (. 51). Finally, comparing the derivative melting points of these two substances confirms that 2-heptanone is my unknown. The derivative melting point of 2-heptanone is 89 while my unknown was 87. When using nuclear magnetic resonance spectrometry, I had unknown A.
With this unknown, I had two peaks on my CNMR which told me I had one carbon on both sides of the line symmetry.Also, on my HNMR I had one peak with a multiplicity of six, therefore, I had six hydrogens. Using this information I was able to conclude that my unknown as was 2-propanone. Furthermore, in this experiment we learned that NMR takes advantage of the magnetic properties of the 1H and 13C nuclei. We are not concerned with 12C because it does not have a magnetic spin and will therefore not be detected in the NMR spectrum.
I learned how to read a NMR as well. I also noticed that we used a mixed solvent recrystallization due to 2,4-DNPH dissolving too readily in ethanol, while dissolving too sparingly in water.So, in order to make the derivative a good recrystallization solvent, we must create a mixed solvent. Exercises 2) Describe and explain any relationship between chain length and Rf value that you observe from your TLC separation.
Based on my TLC separation, it is hard to see much of a relationship between chain length and Rf values. However, since overall, the Rf increased as the chain length increased I would assume that this should be a characteristic every time. For instance, my 2- Propanone Rf is slightly larger than my 2-Butanone and my 2-Hexanone is very slightly larger than my 2- Heptanone.
So, because of the more drastic difference between these two groups as well as 2-Octanone, I can conclude that Rf values should probably increase with chain length, but my TLC slides are slightly off. This could be due to accidental contamination or slight inconsistencies since each one of us did not make every ketone. 6) Draw structures for all ketones that have the molecular formula C5H10O, and sketch the 1H NMR spectrum you would expect to obtain from each one. Your sketches should show the relative area, multiplicity, and approximate chemical shift of each signal.