Consider compounds 5-8 below in order to answer questions 20-23 give the relativ
ID: 1007542 • Letter: C
Question
Consider compounds 5-8 below in order to answer questions 20-23 give the relative polarity in decreasing order for compounds 5-8. Which compounds (5-8) would you expect to have the greatest R_f, and least R_f value of cyclohexame is used as an eluting solvent. " Brtefly explain" Which compounds (5-8) would you expect to have the greatest R_f, and least R_f value of ethanol (CH_3CH_2OH) is used as an eluting solvent. " Briefly explain" consider the initial elution of polar compound 6 with cyclohexane, and shortly afterward, you gradually add increasing amount of ethanol (a polar solvent) to the elution solvent mixture consisting now of cyclohexane and ethanol. Briefly give an account of the moment of 6 on a TLC plate or on a chromatography column before ethanol addition and after ethanol addition. "Briefly explain"Explanation / Answer
20) The decreasing order of polarity is
6 > 8 > 7 > 5
21) A compound that match the stationary phase have a low Rf value while the one that match the mobile phase have higher Rf value. Therefor if we use cyclohexane, a non-polar solvent, as an eluent than the non-polar or least polar compound will have the greatest Rf value and the most polar compound will have the least Rf value. Therefore the compound number 5 will have highest Rf value in cyclohexane whereas compound number 6 will have lowest Rf value.
22) Similarly, based on the above reason when ethanol is used as an eluting solvent, the compound which is most polar i.e compound number 6 will have greatest Rf value while compound number 5 will have least Rf value.
23) Before addition of ethanol: only in cyclohexane (non-polar solvent) the compound 6 will move slowly or not at all on the stationary phase while on increasing the amount of polar solvent the separation will be affected in positive direction. the compound will move up and have higher Rf value.