Question

Why does chain length and the presence of double bonds influence the fluidity of fatty acids?

Answer 1

Fatty acids are the long aliphatic chains with carboxylic acids aliphatic chains can be unsaturated or saturated. Mostly alkyl chains of fatty acids are unbranched with even number of carbon atoms. Unsaturated fatty acids have double bonds mostly in cis- configuration. They have lower melting points as compared to saturated fatty acids of similar lengths. Hence, it increases the fluidity of the fatty acid. Long chain fatty acids with more unsaturated double bonds account for the liquid state of the fatty acids at 25 degree Celsius.

For example, olive oil has a high proportion of long (C16 and C18) and unsaturated fatty acid and hence liquid at room temperature (25 degree Celsius)

The higher proportion of long-chain (C16 and C18) and saturated fatty acids are present in butter, even higher proportion of long chain fatty acids accounts for more solid fatty acids.