Greetings,
This post focuses on melting point effects from varying degree of unsaturation for straight-chain fatty acid compounds. This is essentially the difference between olive oil and lard. A principle ingredient of olive oil is oleic acid and lard contains much less; 45% vs. 70%. Lard also contains about twice the amount of palmitic acid (a higher mp than oleic acid) compared to oleic acid.
It may be noted that melting point is known to be a function of molecular weight, but degree of unsaturation also shows some effect because the molecules take up more space. Bulkier hydrocarbon molecules exhibit weaker intermolecular forces because of steric hindrance: This occurs because there are greater distances between the molecules (such as oleic acid) and because there are fewer molecules attracting each other.
As saturation increases, melting point rises, as well. This is because molecules with greater degrees of saturation will more readily pack together due to decreased steric hindrance. Overall intermolecular forces are higher which requires more thermal energy (higher temperature) to overcome intermolecular forces and allow molecules to move about more freely (the melting process).
As the table shows, compared to olive oil, lard contains more of the higher melting Palmitic Acid and less of the lower melting Oleic Acid. There is a net increase in concentration of saturated molecules which causes an increase in mp for lard, as explained above.
Thank you for reading.
Sincerely, Richard Pastore
This post focuses on melting point effects from varying degree of unsaturation for straight-chain fatty acid compounds. This is essentially the difference between olive oil and lard. A principle ingredient of olive oil is oleic acid and lard contains much less; 45% vs. 70%. Lard also contains about twice the amount of palmitic acid (a higher mp than oleic acid) compared to oleic acid.
It may be noted that melting point is known to be a function of molecular weight, but degree of unsaturation also shows some effect because the molecules take up more space. Bulkier hydrocarbon molecules exhibit weaker intermolecular forces because of steric hindrance: This occurs because there are greater distances between the molecules (such as oleic acid) and because there are fewer molecules attracting each other.
As saturation increases, melting point rises, as well. This is because molecules with greater degrees of saturation will more readily pack together due to decreased steric hindrance. Overall intermolecular forces are higher which requires more thermal energy (higher temperature) to overcome intermolecular forces and allow molecules to move about more freely (the melting process).
Substance
|
% Palmitic Acid (higher mp)
|
% Oleic Acid (Lower mp)
|
Olive Oil
|
13
|
70
|
Lard
|
25
|
45
|
As the table shows, compared to olive oil, lard contains more of the higher melting Palmitic Acid and less of the lower melting Oleic Acid. There is a net increase in concentration of saturated molecules which causes an increase in mp for lard, as explained above.
Thank you for reading.
Sincerely, Richard Pastore
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