CHAPTER 20 – FATS
LIPIDS: Substances found in living organisms
that are not soluble in water.
Not water soluble because the largest part of the molecule
is hydrophobic = dislikes water
(small part of the molecule is hydrophilic = likes water).
4 Groups of Lipids: 1) fats, 2) complex lipids, 3) steroids,
4) prostaglandins & leukotrienes
FATS used as an energy source (immediate or stored).
Fats provide more than twice as much energy (9 kcal/g) as
carbohydrates (4 kcal/g). Body stores some carbohydrates
for quick energy (glycogen).
Fats are esters (made up of an acid and alcohol part)
Alcohol Part: always glycerol
CH2-OH
CH-OH
CH2-OH
Glycerol
IUPAC name: _________________
Acid part:




Straight chain carboxylic acids (no branching)
10-20 carbons per acid
even number of carbons
no additional functional groups, except sometimes
double bonds
O
i.e. CH3(CH2)8C-OH
Capric acid
IUPAC name ________________
(see Table 20.1)
Glycerol has 3 OH groups, so up to 3 acid molecules can
react forming esters
O
CH2 -O-C-(CH2)8-CH3
O
CH-O-C-(CH2)7-CH=CH-(CH2)7-CH3
CH2 -O-C-(CH2)12-CH3
O
Acids can be the same or different and have single or
double bonds.
Triglycerides: 3 acids attached to glycerol
Diglycerides: 2 acids attached to glycerol
Monoglycerides: 1 acid attached to glycerol
Fats are Hydrophobic
(Hydrophobic Character)
O
Hydrophilic part
CH2 -O-C - (CH2)8-CH3
O
CH-O -C - (CH2)7-CH=CH-(CH2)7-CH3
CH2 -O-C - (CH2)12-CH3
O
Hydrophobic part
Water can’t get to hydrophilic part because buried in the
molecule.
Saturated & Unsaturated fatty acids
Saturated fatty acids contain single bonds in hydrocarbon
chain (solid at room temperature: fat)
Hydrocarbon chains line up so closely packed together
(harder to break apart, requires more heat to melt, so a
higher melting point than unsaturated fatty acids)
Unsaturated fatty acids contain at least one C=C double
bond in hydrocarbon chain (liquid at room temp.: oils)
Hydrocarbon chains are not closely packed together
More space between chains, easier to break apart
(lower melting point)
Which one has a higher melting point?
O
CH3(CH2)16C-OH
O
CH3(CH2)7-CH=CH-(CH2)7C-OH
Stearic acid
Oleic acid
PROPERTIES OF FATS
 Fats and oils are odorless, colorless and tasteless
 Fats from mammals are generally solids (i.e. beef fat,
lard) (contain more saturated fatty acids)
 Fats from plants and fish are generally liquids (i.e. fish
oil, peanut oil) (contain more unsaturated fatty acids)
Polyunsaturated oils have more than one double bond per
fatty acid chain.
Is this a saturated, unsaturated or polyunsaturated fat?
O
CH2 -O-C-(CH2)7CH=CHCH2CH=CH(CH2)4CH3
O
CH-O-C-(CH2)7CH=CHCH2CH=CH(CH2)4CH3
CH2 -O-C-(CH2)7CH=CHCH2CH=CH(CH2)4CH3
O
Hydrogenation
 Addition of hydrogen (H2) to the double bond
 Used to convert unsaturated liquid oils to solid fats (i.e.
margarine and Crisco); margarine is softer than Crisco
because more unsaturated (more double bonds)
O
CH2 -O-C-(CH2)7-CH=CH-(CH2)7-CH3
O
CH-O-C-(CH2)7-CH=CH-(CH2)7-CH3 +
CH2 -O-C-(CH2)7-CH=CH-(CH2)7-CH3
O
3H2
Pt
Saponification – the making of soap
 “sapon” – French word for soap
 one of oldest chemical reactions: before 500 B.C.
discovered animal fats heated with wood ashes (basic
substances in ashes) gave a curdy substance (soap)
 Currently soap made by boiling animal or vegetable fat
with sodium hydroxide (lye).
 Sodium hydroxide (NaOH) breaks fat into alcohol &
acid parts (sodium salt of fatty acid)
 Soap is the sodium salt of a fatty acid
O
CH2 -O-C-(CH2)16-CH3
O
CH-O-C-(CH2)16-CH3 + 3 NaOH
CH2-OH
H2O
CH2 -O-C-(CH2)16-CH3
O
tristearin
(beef fat)
CH-OH
CH2-OH
glycerol
+
O
3 Na O-C-(CH2)16CH3
+-
sodium stearate (soap)
What products are produced in this reaction?
O
CH2 -O-C-(CH2)8-CH3
O
CH-O-C-(CH2)8-CH3 + 3 NaOH
H2O
CH2 -O-C-(CH2)12-CH3
O
How soap cleans:
The COO- end of molecule is ionic, so water soluble
(hydrophilic), the other end is not water soluble
(hydrophobic). The hydrophobic end interacts with nonwater soluble dirt, once dirt particle surrounded by many
soap molecules, a micelle forms with dirt in the middle.
Micelle – cluster of soap molecules with dirt in the middle
See Figure Box 20C
Solid soap – sodium salt of fatty acid
Liquid soap – potassium salt of fatty acid
Calcium & magnesium ions are found in hard water.
Ca2+ & Mg2+ salts of fatty acids are not water soluble (ppt
formed “soap scum”)