How many distinct geometrical isomers exist for the conjugated diene 2,4-hexadiene ()? — Hydrocarbons Chemistry Question

💡 Solution & Explanation

2,4-hexadiene has $n=2$ double bonds capable of exhibiting cis-trans isomerism. Because the molecule is structurally symmetrical from both ends (methyl groups on both sides), the formula for the number of geometrical isomers is $2^{n-1} + 2^{(n/2)-1}$ (for even $n$). $2^{2-1} + 2^{(2/2)-1} = 2^1 + 2^0 = 2 + 1 = 3$. The isomers are cis,cis; trans,trans; and cis,trans (which is identical to trans,cis).