Question

Organic Chemistry: Intro to Gas Chromatography

6 known compounds are: propyl acetate, butyl acetate, methanol, ethanol, 2-butanone, 4-methyl-2-pentanone

1. Discuss the retention times of the six known compounds with regards to their molecular weights. Describe any pattern that emerges.

2. Discuss the retention times of the six known compounds with regard to their boiling points. Describe any pattern that emerges.

3. Identify the compounds that are present in your unknown mixture. Support your identification.

For the unkown, I got three different retention times: 1.645min, 4.190min and 7.815min.

Retention time measure by GC (minutes)

propyl acetate: 3.765

butyl acetate: 6.365

methanol:1.535

ethanol:1.840

2-butanone:none

4-methyl-2-pentanone:4.360

Answer 1

Gas chromatography

1. Typically as the molecular weights increases the boiling point increases and thus the retention time also increases on the gas chromatographic column. So methanol with lowest molecular weight will elute first from the column and butyl acetate with highest molecular weight will elute at the end.

2. The retention time of compounds are directly related to thier boiling points. Thus a low boiling point compound as methanol would elute first and the highest boiling point compound butyl acetate will elute at the end from gas chromatograph.

3. In the unknown,

1.645 min corressponds to methanol

4.190 min corresponds to 4-methyl-2-pentanone

7.815 min corressponds to butyl acetate

The retention times closely match with the retention times reported for the standard compounds above.