Question 29.SE.4: Which of the following compounds is not classified as a lipi...
Which of the following compounds is not classified as a lipid?
(a) 
(b) 
(c) 
(d) 
Analyze We are asked to differentiate between compounds based on their functionality and to class them accordingly.
Plan By definition, lipids are naturally occurring substances that can be extracted from cells and tissue by non-polar organic solvents such as hexane. So we will use this definition as a means of classification.
Solve Structure (a) is a wax, similar to beeswax. It is soluble in hexane and so is classed as a lipid. Structure (b) is a member of the steroid hormones. Its large carbon framework suggests this compound will be soluble in non-polar solvents. Hence this compound can be generally classed as a lipid. Structure (c) is a prostaglandin. Despite the presence of three OH and a carboxylic acid group, the two large alkyl chains would suggest this molecule is hexane soluble. This compound is also a lipid. Structure (d) is a nucleotide. Its collection of nitrogen- and oxygen-containing heterocycles and polar phosphate group would mean this compound is more aqueous than hexane soluble. Therefore, this class of compound is not a lipid.