Rank the following fatty acids according to increasing melting point. I: CH₃(CH₂) ₁₆CO₂H
II: CH₃(CH₂) ₇CH=CH(CH₂) ₇CO₂H (cis)
III: CH₃(CH₂) ₇CH=CH(CH₂) ₇CO₂H (trans)
IV: HO₂C(CH₂) ₇CH=CHCH₂CH=CH(CH₂) ₇CH₃(cis,cis)

Question

Quizplus · Accepted Answer

The melting point of fatty acids increases with the degree of saturation and decreases with the introduction of cis double bonds due to the kinks they introduce, which prevent tight packing. I is fully saturated, thus has the highest melting point. III has a trans double bond, which allows tighter packing than cis, making its melting point higher than II and IV, which both have cis double bonds. IV has more cis double bonds than II, making it the least tightly packed and thus having the lowest melting point.

Rank the Following Fatty Acids According to Increasing Melting Point