. If the following mixtures of two compounds are being separated by gas chromatography, which one of the compounds would be expected to elute from the column first (have the shortest retention time)? Consider boiling points that are only I or 2°C apart to be essentially identical. Consider compounds with the same functional groups to be identical in polarity if they differ by no more than a few carbons. Look up any necessary structures. Mixture Compound with the shortest retention time Polarity of the column packing a. ethyl acetate (bp 77°C) and ethyl butyrate (bp 120°C) polar nonpolar b, ethyl acetate (bp 77"C) and ethyl butyrate (bp 120°C) c. acetic acid (bp l 18°C) and n-butyl alcohol (bp 117c) polar d. sec-butyl alcohol (bp 100"C) nonpolar and ethyl propionate (bp 99c)

In gas chromatography, the elution order depends of boiling point and polarity of compounds. The lower boiling point will elute first and the elution depends of kind of column you are using; if column is polar, non-polar compounds will elute first and vice versa.

a. ethyl acetate (bp 77°C) and ethyl butyrate (bp 120°C) polar:

As the structures of these two molecules just change in 2 carbons it is possible to consider that are the same polarity. Thus, we will see just boiling point, as ethyl acetate has lower boiling point will elute first.

b. ethyl acetate (bp 77°C) and ethyl butyrate (bp 120°C) nonpolar

Again, we will consider the same polarity for both compunds and ethyl acetate will elute first because its boiling point

c. acetic acid (bp 118°C) and n-butyl alcohol (bp 117c) polar.

As boiling point are similar we will see polarity: Acetic acid is a carboxilic acid and n-butyl alcohol has just a OH group in tis structure, that means acetic acid is more polar. As column is polar, acetic acid will be more retained doing n-butyl alcohol elutes first.

d. sec-butyl alcohol (bp 100"C) and ethyl propionate (bp 99c) nonpolar

As boiling point are similar we will see polarity: Sec-butyl alcohol has just a OH group but ethyl propionate is an esther, that means sec-butyl alcohol is more polar. As column is nonpolar, the polar compound will elute first, that is sec-butyl alcohol.

i hope it helps!