Organic Chemistry

26.2 Waxes

Waxesare esters formed from long-chain carboxylic acids and long-chain alcohols.

For example, beeswax, the structural material of beehives, has a 16-carbon carboxylic

acid component and a 30-carbon alcohol component. The word waxcomes from the

Old English weax,meaning “material of the honeycomb.”Carnauba wax is a par-

ticularly hard wax because of its relatively high molecular weight, arising from a

32-carbon carboxylic acid component and a 34-carbon alcohol component. Carnauba

wax is widely used as a car wax and in floor polishes.

Waxes are common in living organisms. The feathers of birds are coated with wax to

make them water repellent. Some vertebrates secrete wax in order to keep their fur lubri-

cated and water repellent. Insects secrete a waterproof, waxy layer on the outside of their

exoskeletons. Wax is also found on the surfaces of certain leaves and fruits, where it

serves as a protectant against parasites and minimizes the evaporation of water.

26.3 Fats and Oils

Triacylglycerols, also called triglycerides, are compounds in which the three OH

groups of glycerol are esterified with fatty acids. If the three fatty acid components of a

triacylglycerol are the same, the compound is called a simple triacylglycerol. Mixed

triacylglycerols, on the other hand, contain two or three different fatty acid compo-

nents and are more common than simple triacylglycerols. Not all triacylglycerol mole-

cules from a single source are necessarily identical; substances such as lard and olive

oil, for example, are mixtures of several different triacylglycerols (Table 26.2).

Raindrops on a feather

004 CHAPTER 26 Lipids

Table 26.2 Approximate Percentage of Fatty Acids in Some Common Fats and Oils

Saturated fatty acids Unsaturated fatty acids

mp lauric myristic palmitic stearic oleic linoleic linolenic

(°C)

Animal fats

Butter 32 2 11 29 9 27 4 —

Lard 30 — 1281248 6—

Human fat 15 1 3 25 8 46 10 —

Whale blubber 24 — 8 12 3 35 10 —

Plant oils

Corn 20 — 1 10 3 50 34 —

Cottonseed 1 — 1 23 1 23 48 —

Linseed 24 —— 6 3 19 24 47

Olive 6 —— 7 2 84 5 —

Peanut 3 —— 8 3 56 26 —

Safflower 15 —— 3 3 19 70 3

Sesame 6 ——10 44540—

Soybean - 16 ——10 22951 7

C 12 C 14 C 16 C 18 C 18 C 18 C 18

a major component of

beeswax

structural material

of beehives

CH 3 (CH 2 ) 24 CO(CH 2 ) 29 CH 3

O

a major component of

carnauba wax

coating on the leaves

of a Brazilian palm

CH 3 (CH 2 ) 30 CO(CH 2 ) 33 CH 3

O

a major component of

spermaceti wax

from the heads of

sperm whales

CH 3 (CH 2 ) 14 CO(CH 2 ) 15 CH 3

Layers of honeycomb in a beehive O