JEE Main · 2025 · 29 Jan 2025 · Shift 1 · Chemical Bonding and Molecular Structure

Hex-1,3-dien-5-yne is $\mathrm{C}{\mathrm{H}}_2=\mathrm{CH}-\mathrm{CH}=\mathrm{CH}-\mathrm{C}\equiv \mathrm{CH}$. The 5 carbon-carbon linkages consist of two C=C double bonds (each 1σ+1π), one C≡C triple bond (1σ+2π) and the remaining C–C single bonds as pure σ bonds, giving 5 C–C σ bonds and 4 C–C π bonds in total. Counting hydrogens: the terminal =CH2 carbon carries 2 H, the two internal =CH– carbons carry 1 H each, and the terminal ≡CH carbon carries 1 H (the internal alkyne carbon, fully used up by its triple bond and one single bond, carries none), giving 6 C–H σ bonds.
Total σ bonds $=5+6=11$; total π bonds $=4$.