Alkenes

Alkenes are unsaturated hydrocarbons containing at least one carbon-carbon double bond (C=C). They have the general formula CₙH₂ₙ (for non-cyclic alkenes with one double bond) and are far more reactive than alkanes. The C=C double bond is the defining feature and the site where almost all alkene reactions take place.

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Structure and Bonding

The C=C double bond consists of two components:

1. A sigma (σ) bond — formed by the head-on overlap of sp² hybridised orbitals
2. A pi (π) bond — formed by the sideways overlap of unhybridised p orbitals above and below the plane of the molecule

Each carbon in the C=C is sp² hybridised, giving a trigonal planar geometry with bond angles of approximately 120°. The three sp² orbitals lie in a plane and the remaining p orbital is perpendicular to this plane.