Rank the melting points of the following fatty acids from highest to lowest:
(1) cis-oleic(18:1)
(2) trans-oleic (18:1)
(3) linoleic (18:2)
(4) steraic (18:0)
(5) palmitic (16:0)

A)1 2 3 5 4
B)4 5 2 1 3
C)4 5 3 2 1
D)5 4 2 1 3
E)none of the above

Question

Rank the melting points of the following fatty acids from highest to lowest:
(1) cis-oleic(18:1)
(2) trans-oleic (18:1)
(3) linoleic (18:2) 
(4) steraic (18:0)
(5) palmitic (16:0)

A)1 > 2 > 3 > 5 > 4
B)4 > 5 > 2 > 1 > 3
C)4 > 5 > 3 > 2 > 1
D)5 > 4 > 2 > 1 > 3
E)none of the above

Quizplus · Accepted Answer

Fatty acids with longer carbon chains and those that are saturated (no double bonds) have higher melting points. Stearic acid (18:0) is fully saturated and has the highest melting point. Palmitic acid (16:0), also saturated but with a shorter chain, comes next. Trans-oleic acid (18:1) has one double bond but its trans configuration allows tighter packing than cis-oleic acid (18:1), giving it a higher melting point than cis-oleic. Linoleic acid (18:2) has two cis double bonds, making it the least tightly packed and thus it has the lowest melting point.

Rank the Melting Points of the Following Fatty Acids from Highest