Question

Hi can someone help me with my pre lab theory questions (1,2,3) on rate of elution or Rf? Here is some background below. Please help explain as many as possible (1-3)! I dont really get the relation ships in this lab, thank you!

1. What factors affect the rate of elution in organic compounds? 2. Explain what is the relationship between polarities of compounds (polar/non- polar compound) and rate of elution (Rf). 3. Explain what is the relationship between solvent polarity (polar/non-polar solvent) and rate of elution (Rf)

Answer 1

Solution: 1 Factors affect the rate of elution in organic co Nature of adsobent. The adsorbent is that usually silica gel or alumina. Both are polar and bind polar compound more strongly than non-polar compound. If adsobent is basic or neutral than it compound elute fast as compared to acidic silica gel olvent: Polar and non- polar solvent organic compound elute faster solve at In polar than non-polar solunt ③ (Rf). Relationship between polarities of compound and rate of elution. The rate of elution of polar compound is less as compared to non-polar compound. Non-polar compound give higher Rf value as compare to polar compound. eg Acid and olefin. The rate of elution of olefin is faster as compare to acid. ③ Relationship between solvent polarity and Rf value he rate of elution The higher the percentage of polar solvent, the faster compon compound will elute. The eluting power of solvents increases. with polarity. Therefore, low polarity compounds can be a with low polarity solvents, while higher polarily compounds. require solvents of higher polarity.

The given structures are Cool truns-stil bene o g fluorenone Benzoic acid The polarity of the above compound is Benzoic acid > 9. fluosenone > truns-stilbene. So on TLC trans-stil bene elute first as compare to g-fluorenone and g. fluo renone elute fast as compare to benzoic acid. So the Rf value of order of trans- stil bene > 9. fluorenante > Benzoic acid