Structural Characteristics
The general formula for monoalkenes is CₙH₂ₙ (n ≥ 2). The double bond consists of one σ (sigma) bond and one easily broken π (pi) bond; the carbons involved in the double bond are sp²-hybridized, and the associated atoms lie in the same plane.
They exhibit structural isomerism (carbon chain and double-bond position isomers) and, due to the restricted rotation of the double bond, *cis-trans* (geometric) isomerism.
Physicochemical Characteristics
Physical properties: C₂–C₄ alkenes are gases at room temperature; they are insoluble in water but readily soluble in organic solvents, have densities lower than water, and exhibit melting and boiling points that increase with the number of carbon atoms.
Chemical properties: Due to the easily broken π bond, they are more reactive than alkanes. They undergo three key types of reactions-addition (following Markovnikov's rule), oxidation, and polymerization-and can decolorize bromine water and acidic potassium permanganate solution.
