Allenes and Optical Activity: A Surprising Twist!

The video tutorial explains optical activity in compounds like allenes, spiro compounds, and biphenyls. It introduces optical isomerism in allenes, first described by Van T Hoff, and details the structure of allenes, which have two adjacent carbon-carbon double bonds but no chiral carbon atom. Despite having a plane of symmetry, allenes are optically active due to their orbital structure. The central carbon is SP hybridized, while terminal carbons are SP2 hybridized, allowing for pi bond formation. The lack of symmetry makes allenes dissymmetric, existing as pairs of anachomers.

Which of the following compounds is categorized under optical activity along with allenes?

• Alkanes

• Aromatic compounds

• Spiro compounds

• Alkynes

What is the hybridization of the central carbon atom in an allene?

• None of the above

• SP

• SP2

• SP3

Why are allenes expected to be optically inactive?

• Due to their linear structure

• Because they have a plane of symmetry

• Due to the presence of a chiral carbon

• Because they lack double bonds

How is the first π bond in an allene formed?

• By lateral overlap of P orbitals along the XY direction

• By lateral overlap of P orbitals along the YZ plane

• By end-to-end overlap of S orbitals

• By lateral overlap of P orbitals along the XZ plane

What causes the optical activity in allenes despite the expected inactivity?

• Presence of only single bonds

• Dissymmetry due to lack of a plane of symmetry

• Presence of a chiral center

• Symmetrical distribution of atoms