Introduction: Given five samples of a known ketone derivative, the purpose of this experiment is to identify which unknown ketone derivative corresponds to the five known samples.Highly conjugated carbonyl groups give deep red 2,4-DNP derivatives while non-conjugated carbonyl groups give yellow 2,4-DNP compounds. Thin-layer chromatography TLC is a popular method in laboratories for separating the components of compounds. Preliminary test used two known compounds also the unknowns. The rule is if you want to have a compound run further up a plate higher Rf , go to a more polar solvent. The paper was then placed in the covered solvent containing beaker in a fume hood and after 20 minutes removed. 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. The slides as well as the Rf values of 2-heptanone and my unknown were very similar. Fractions 3 and 4 have pure ketone.
Circle the spots and calculate the Rf values for your lab report. There could have been several causes for this observation. Subtract the Rf of the slower-moving spot from that of the faster-moving spot and make use that the resulting number is at least 0.
I looked at height and size of the spots on the slides to determine this. Thomson Learning: Ohio, Two lab periods are scheduled for this experiment.
Switch to the more polar solvent system hexanes:ethyl acetate and collect 6 fractions fractions Spot the fractions on a single TLC plate. Make sure that the slower-moving spot moves significantly slower in the same system. Again fill the pipet with solvent and force the solvent through the column.
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. NMR utilizes radio frequency waves to determine the number of carbons present and what they are connected to.Fractions have nothing. One drop of the known ketones and around 0. Two different methods have been suggested to identify the ketones. Please see this spectroscopy page for a detailed procedure. In that experiment, the compounds you were separating were colored and the separation was relatively easy to follow. You are looking for the system that gives an Rf of 0. P , Boiling Point B. 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. In order to have a strong background about the solubility test, we first classify organic compounds of known. We will do this by making 2, 4 a DNPH derivative and checking the melting points.