Effect of Structure on melting points

Question 1

Increase in chain length (more C)

Answer 1

Increase in melting point of the lipids

-More likely to be solid at room temperature

Question 2

Increase unsaturation (more double bonds)

Answer 2

Decrease in melting points

-More likely to be liquid at room temperature

Question 3

Effect of Structure on Melting Points - Kinks

Answer 3

1)Cis-configuration will create a bend or kink in the fatty acid chain that is not found in saturated fatty acid

2)These kinks prevent unsaturated fatty acids from packing closely together

3)As a result, they form less london dispersion forces between fatty acids

4)This leads to fatty acids with lower melting points

Question 4

Effect of Structure on Melting Points -
Trans isomer vs Cis isomer

Answer 4

1)The cis form of the fatty acid usually bends with greater angle (e.g. 90°)

2)The trans form of the fatty acid bends with smaller angle (as compared to the cis form)

Question 5

Effect of Structure on Melting points -
Trans isomer vs Cis isomer (packing)

Answer 5

1)The cis form creates more space in the layer and prevents tight packing.

2)The trans form of the fatty acid bends with smaller angle (as compared to the cis form)

Question 6

Kink on fatty acid carbon chain affects
packing density

Answer 6

-Packed tightly-

1)Saturated FA

2)Unsaturated FA - trans form

3)Unsaturated FA - cis form

-Not packed tightly-