239B Chem Spring, 2006 Quiz#7 Prof. Sasaki _____________________________________________________________________ 1. Fats can be either optically active or optically inactive, depending on their structure. Draw the structure of an optically active fat that yields two equivalents of stearic acid and one equivalent of oleic acid on hydrolysis. Draw the structure of an optically in active fat that yields the same products. 2. Spermaceti, a fragrant substance from sperm whales, was much used in cosmetics until it was banned in 1976 to protect the whales from extinction. Chemically, spermaceti is cetyl palmitate, the ester of cetyl alcohol (n-C16H33OH) with palmitic acid. Draw its structure. 3. Steroids have a common tetracyclic ring system. Draw the 3-dimensional structures of the following steroids.
CH3 R CH3 H 5!-Androstane a. (R = H) b. 5"-Pregnane (R = CH2 CH3 )
4. Palmitic acid (hecadecanoic acid) is the source of the hexadecyl (cetyl) group in the following compounds. Each is mild surface-acting germicide and is used as a topical antiseptic and disinfectant. They are examples of quternary ammonium detergents, commonly called "quats".
Cl
N CH2(CH2)14CH3
Cl
CH3 CH2(CH2)14CH3 CH3
CH2 N
Cetylpyridinium chloride
Benzylcetyldimethylethylammonium chloride
(a) Cetylpyridinium chloride is prepared by treating pyridine with 1-chlorohexadecane (cetyl chloride). Show how to convert palmitic acid to cetyl chloride. (b) Benzylcetyldimethylethylammonium chloride is prepared by treating benzyl chloride with N,N-dimethyl-1-hexadecanamine. Show how this tertiary amine can be prepared from palmitic acid.