Alkenes contain the unsaturated C=C functional group which characteristically undergo addition reactions. This is driven by the conversion of the weaker π bond into 2 new, stronger σ bonds. The reactions of alkenes can seem a little bewildering as a wide variety of reagents undergo this type of reaction providing access to products with various regioselectivities and stereoselectivities depending on the reagent and / or reaction conditions, but ultimately on the mechanism by which the reaction occurs. There are potentially 3 factors associated with each of the addition reactions of alkenes: • overall transformation (i.e. C=C to what functional group) • regioselectivity (provided the two atoms that add are different) • stereoselectivity (most easily revealed with cyclic alkenes