Organic Chemistry Key Concepts: Alkenes & Alkynes
-The alkenes are hydrocarbons of the general formula C H ; 2 ne2n Hs because of the presence of a
double-bond. The alkynes have the general formula C H n 2n – 2nd contain a triple bond.
-Each reduction of 2 hydrogens in the general alkane formula represents one unit of unsaturation.
Examples of one unit of unsaturation include a π bond or a ring. Examples of 2 units of unsaturation
include a π bond in a ring or 2 π bonds (in a triple bond).
-Isolated arrangements include 2 or more σ bonds between the π bonds. Conjugated arrangements
include multiple bonds which alternate with single bonds. Cumulated arrangements include two double
bonds on a single carbon. For C = C, change the suffix to ene. For C = C, change the suffix to yne.
-The longest carbon chain must contain as many π bonds as possible.
-Potential for exam: CH =C2- : vinyl CH 2CH-Cl: vinyl chloride CH =2HCH -: 2llyl
CH 2CHCH Br:2allyl bromide
-In an alkene’s shape, there is a double bond (between 2 atoms such as C, N or O) which requires two
adjacent sp hybridized atoms. Note that π bonds have a region of high electron density both above and
below the molecular plane.