Examination: Chapters 15-18/T5 -Page 19- 20. Given the following fatty acids lua

Question

Examination: Chapters 15-18/T5 -Page 19- 20. Given the following fatty acids luaric acid palmitoleic acid arachidonic acid CH, - (CH2)10-COOH CH3-(CHJs-CH = CH-(CH2),-COOH CH)" (CH), _ (CHz-CH=CH),-(CH),-COOH Which fatty acid should have the lowest melting point?? Why? b. Which fatty acid should have the highest melting point?? Why? 21. Use figures (11) thru (16) to answer the following questions. In each case give the number of the figure that best matches the description. a. cortical steroid cortisone d. a cholesteryl ester b. a bile salt e. is a prostaglandin C. cholesterol

Explanation / Answer

20) a)

(i) Arachidonic acid has lowest melting point

(ii) Mostly, the geometry of the double bonds in fatty acids are of cis configuration. Due to this there is a bend in the molecule wherever there is a double bond therefore, these molecule do not stack very well and the melting point is lower due to lower intermolecular interactions.

b)

(i) Lauric acid has highest melting point

(ii) These saturated fatty acids are linear in geometry and are closely stacked together. This increased intermolecular interaction (vanderwaal interaction) results in higher melting point.

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