Alkenes GapFill

Like alkanes, alkenes contain only carbon and hydrogen atoms, making them  carbohydrateshydrocarbonscarboxyliccarbonic. However, alkenes contain at least one carbon−carbon double bond and, hence, do not contain as many hydrogen atoms as the corresponding alkane; they are said to be  cyclicchiralunsaturatedsaturated. The general formula for a non-cyclic alkene with n carbon atoms and one double bond is   CnHn+2CnH2n-2CnH2nCnH2n+2.

Carbons involved in a double bond are found in a trigonal planar environment, with bond angles around  104.5º120º109.5º107º. Carbon−carbon double bonds consist of one σ(sigma)−bond, formed by end-to-end overlap of p−orbitals, and one   ψ(psi)θ(theta)φ(phi)π(pi) bond, formed by side-on overlap of p−orbitals. This second component prevents rotation about the double bond, as it would disrupt the side-on overlap of orbitals. This leads to  chainopticalgeometricspin isomerism around double bonds. Different isomers of the same alkene are labelled as either   A or XE or ZE or XA or Z.

Carbon−carbon double bonds are electron-rich, and a common class of reactions for alkenes is  nucleophilic additionelectrophilic additionnucleophilic substitutionelectrophilic substitution. In fact, a reaction of this type is used to test for unsaturation in organic molecules: a sample is reacted with   astatinebrominetennessinechlorine water, which changes from   blackbluepinkorange to colourless in the presence of a double bond. These reactions involve the formation of an intermediate with a positively charged carbon atom called a   carbanioncarbocationnucleocarboncarbonyl.

Alkenes can also form   substitutioncondensationeliminationaddition polymers. The polymers can be made more flexible by the addition of small molecules called   derigidifierselasticiserspliablisersplasticisers, which slip between the polymer chains and disrupt intermolecular forces.