B1.1.10

• The R group hydrocarbon tail is variable.
• There are two kinds of fatty acids: saturated and unsaturated. The difference is in their hydrocarbon tails.
• Hydrocarbon tail: a chain of carbon atoms bonded together with hydrogen atoms bonded on each side of the carbon.
• Saturated fatty acids: all the carbon atoms are joined by single bonds
• Monounsaturated fatty acids: have one double bond between carbon atoms which causes the chain to kink
• Polyunsaturated acids: have many double bonds between carbon atoms which causes the chain to kink at many places
• Cis-fatty acids have the hydrogen atoms on the same side of the two double-bonded carbon atoms.
• If the hydrogen atoms are on opposite sides of the carbons they are called trans-fatty acids.
• Cis-fatty acids are less good at packing together because there is a bend in the hydrocarbon chain at the double bond. This makes them have a low melting point -> they are liquid at room temperature: oils.
• Trans-fatty acids do not have a bend in the hydrocarbon chain at the double bond. They have straight chains and a higher melting point -> they are solid at room temperature: they are produced artificially and are banned in some countries.