Question

A gas chromatogram of the organic components of a sample of beer using a column that separated compounds on the basis of their relatives boiling points provides a GLC trace with several peaks. Two of the smaller peaks, with retention times of 9.56 and 16.23 minutes, are believed to be ethyl acetate and ethyl butyrate, respectively.

c) The major component of the sample elutes first. What organic compound present in beer do you suspect is responsible for this peak? Is your speculation consistent with the reported boiling point of the component you are proposing? Explain.

Please explain, I don't understand the question. Thanks.

Answer 1

Ethyl acetate and ethyl butyrate have very similar structures, and as a consequence very similar polarities. Therefore in a normal-phase GC, the major determining factor for which compound will elute first would be the vapor pressure (or boiling points). Because ethyl acetate has fewer atoms than ethyl butyrate, it would make fewer intermolecular attractions, and therefore have a higher equilibrium vapor pressure, or lower boiling point. The opposite is true for ethyl butyrate. Therefore ethyl acetate would elude faster from the GC.

Repoted boiling point of the two component are

Ethyl acetate : 77^oC

Ethyl butyrate : 121^oC

So according to our proposing the reported boiling points of the components are speculation.