Question

a. In general is there any difference between R and S, and + and -? between d- and l-, and + and -?

b. Discuss the validity of the following statements:

1. A mixture of (+)- and (--)-carvone can be separated by column chromatography on silica gel using hexanes-acetone as elution.

2. In general, column chromatography on silica gel is run with a series of solvents of increasing polarity.

3. Carvone is more polar than limonene.

c. Which compound, limonene or carvone, do you expct would elute first from the silica gel column? Which one would have shorter retention time on the GC? Briefly justify your answer.

Answer 1

a. In general is there any difference between R and S, and + and -? between d- and l-, and + and -?

yes there is,

R and S is essentially the arrangement of a chiral carbon, therefore, the order and dipole interactions will definetively change

for + and - , we talk again about enantiomers, therefore they DO care...

for d- and l- --> similar, they talk about planes, they carry different properties

b. Discuss the validity of the following statements:

1. A mixture of (+)- and (--)-carvone can be separated by column chromatography on silica gel using hexanes-acetone as elution.

true... since the silica gel will interact with the most polar specie and the solvents with the least attached specie

2. In general, column chromatography on silica gel is run with a series of solvents of increasing polarity.

true, we typically satart with nonpolar speices and increase to polar species to redefine

3. Carvone is more polar than limonene.

carvone has a C=O group which is pretty polar, therefore, this is true

c. Which compound, limonene or carvone, do you expct would elute first from the silica gel column? Which one would have shorter retention time on the GC? Briefly justify your answer.

elute first --> limonene, since carvono will remain attached to the slica gel column