because the resulting radical is resonance stabilized by both double bonds. This radical
reacts with forming a peroxy radical with conjugated double bonds. The peroxy
radical removes a hydrogen from a methylene group of another molecule of fatty acid,
forming an alkyl hydroperoxide. The two propagating steps are repeated over and over.
The reaction of fatty acids with causes them to become rancid. The unpleasant
taste and smell associated with rancidity are the results of further oxidation of the alkyl
hydroperoxide to shorter chain carboxylic acids such as butyric acid that have strong
odors. The same process contributes to the odor associated with sour milk.
PROBLEM 5Draw the resonance contributors for the radical formed when a hydrogen atom is removed
from C-10 of arachidonic acid.O 2O 2 ,Section 26.3 Fats and Oils 007resonance contributor with
isolated double bondsresonance contributor with
conjugated double bondsinitiationpropagationpropagationa peroxy radicalRCH CH CH
HCH CH + X RCH CH CH CH CH + HXRCH CH CHOOCH CHRCH CH CH 2 CH CHRCH CH CH CH CHOOan alkyl hydroperoxideRCH CH CH CH CH + RCH CH CH CH CHOOHWHALES AND ECHOLOCATION
Whales have enormous heads, accounting for 33%
of their total weight. They have large deposits of
fat in their heads and lower jaws. This fat is very different from
both the whale’s normal body fat and its dietary fat. Because
major anatomical modifications were necessary to accommo-
date this fat, it must have some important function for the
animal. It is now believed that the fat is used for echolocation—
emitting sounds in pulses and gaining information by analyzing
the returning echoes. The fat in the whale’s head focuses the
emitted sound waves in a directional beam, and the echoes are
received by the fat organ in the lower jaw. This organ transmits
the sound to the brain for processing and interpretation, provid-
ing the whale with information about the depth of the water,
changes in the seafloor, and the position of the coastline. The
fat deposits in the whale’s head and jaw therefore give the ani-
mal a unique acoustic sensory system and allow it to compete
successfully for survival with the shark, which also has a well-
developed sense of sound direction. Humpback whale in Alaska