TLC

1. In one clear paragraph, summarize all of the evidence supporting your conclusions concerning the identities of the two compounds in your unknown. Thin layer chromatography of analgesics is a method that used in this lab to identify the compounds that contained in the unknown mixture by measuring the Rf. However, after the TLC developed in a plate and the spots of five different compounds under three different eluent conditions were visualized under the UV light. The evidence that support to conclude and identify the mixture of the unknown was by measuring the distance travelled of each of the five spots starting from the baseline that had drawn before developing the TLC plate to the edge of the wet silica after elution using retention factor Rf and comparing the spot travelling distance with the unknown spots. The spots of the two compounds that had travelled approximately in equal level (same distance) to the one of the unknown helped to identify the two compounds that were mixture of the unknown which are acetanilide and phenacetin. However, the other evidence that helped to figure out the unknown mixture was the system solvent of 50% ethyl acetate /50% hexane .The solvent was ideal for determining the distance travelled approximately of the spots of the two compounds of the unknown mixture. 2. What is the general effect of increasing the proportion of ethyl acetate in the eluent on the Rf of the five analgesics studied in this lab? The general effect of increasing the proportion of ethyl acetate is increasing the Rf value (the distance travelled by spots divvied by the distance traveled by solvent). Also, because ethyl acetate is less polar, it favours the mobile phase so its move up the TLC plate which in return will increasing the Rf value. 3. a) Draw the structure of acetanilide, phenacetin and acetaminophen, and indicate(using the standard symbols) all polar bonds in both molecules. Based on these structure, and intermolecular forces involved in silica gel TLC , what order would you have predicted these three compounds would elute (explain your reasoning)? Was your prediction supported by your TLC date? The order that would have predicted these three compunds are: Acetaminophen because of the two hydrogen bond and one dipole- dipole interaction ( O-H, C-O and N-H) Phenacetin because of the one hydrogen bond and two dipole- dipole interaction (N-H and C-O) Acetanilide because of the one hydrogen bond and dipole-dipole interaction (N-H and C-O) Yes, my prediction was supported by my TLC data that determined in the lab. b) Compared to the three compounds described in part (a), what TLC properties would you predict to be observed for compounds A and B below? Give a brief reasoning for each prediction. Compound A Has three dipole- dipole interactions (Two C-O bonds and one N-C bond) its less polar than compound B Has faster traveled distance that leads in increasing the Rf value. Compound B has three hydrogen bonds and one dipole-dipole interaction (N-H , two of O-H and one C-O) very polar compound has travel distance slower than the one in compound A with decreasing in Rf value. 4. Describe how TLC could be used to confirm whether a compound was pure or not. Were all of the standard analgesic solutions provided for you in this experiment pure? In order to determine the purity or impurity of the substance using the TLC, the TLC plate should be developed first in a chamber and then visualizing the spots under the UV light. Thus, the pure compound can be determined when the dotted compound look as a single circle spot while the not pure compound will appear as two or more circle spots in one lane of the compounds. However, Three of the standard compounds analgesic solutions that were provided in this lab were pure expect two of them which are acetanilide and phenacetin (the unknown) were impure. 5. If you were to repeat this experiment using mixtures of hexane and acetone (in the same proportions) as eluent (i.e. replaced the ethyl acetate with acetone) what effect would you predict this change would have on the Rf values for the analgesics? If this experiment were repeated using hexane and acetone in the same proportions as the one were used with ethyl acetate and hexane the effect of the Rf value would be less because acetone is more polar than ethyl acetate and since the value of the Rf depends on the polarity of the compounds the traveling distance of the spotted acetone will not travel as high as the one in ethyl acetate in in TLC plate.