What do the terms 'cis' and 'trans' refer to in fatty acid nomenclature?

The terms 'cis' and 'trans' in fatty acid nomenclature specifically refer to the configuration of double bonds in the fatty acid chain. In a 'cis' configuration, the hydrogen atoms adjacent to the double bond are positioned on the same side, leading to a bend or kink in the fatty acid chain. This kink affects how the molecules pack together, generally resulting in a lower melting point and liquid state at room temperature.

In contrast, the 'trans' configuration has the hydrogen atoms on opposite sides of the double bond, allowing the fatty acid chain to remain straight. This linear shape promotes tighter packing and higher melting points, often resulting in a more solid form at room temperature.

This property is crucial for understanding the physical characteristics of fats and oils, including their nutritional and health implications. Identifying the configuration of double bonds in fatty acids helps to determine their behavior in biological systems, impacting everything from membrane fluidity to energy storage.