Molecules that share the same atomic composition but differ in how those atoms are arranged — including isomers having conjugated double bonds — a difference that can transform properties entirely. Glucose and fructose are isomers, yet taste and behave differently; the same holds for fatty-acid isomers with conjugated double bonds. Recognizing isomeric differences is essential in flavour chemistry, nutrition, and food analysis. Structural, geometric, and optical isomerism each create distinct molecules from identical atoms, so analytical methods must distinguish them.