Alkenes and AlkynesTomato, tomato – Alkane, alkene, alkyne

Unsaturated Hydrocarbons

A hydrocarbon containing carbon–carbondouble or triple bonds is called an unsaturated hydrocarbon because each molecule contains fewer than the maximum number of hydrogen atoms.

Acetylene (ethyne)

Ethene

A hydrocarbon that contains at least one carbon–carbon double bond is called analkene.

Alkenes with one double bond have the general formula CnH2n.

The simplest alkene is ethene, C2H4

An unsaturated hydrocarbon that contains at least one triple bond between 2 carbon atoms is called an alkyne.

Alkynes with one triple bond have the formulaCnH2n–2.

The simplest alkyne is ethyne.

Naming and Drawing Alkenes and Alkynes

Cis–Trans Isomerism

Groups on different sides of a double bond are in a fixed position relative to each other.

Stereoisomers have the same kind and number of atoms bonded in the same order but have different arrangements in space.

Stereoisomers cannot be changed from one to another by simple rotation. Bonds would have to be broken and re-formed.

Stereoisomers are distinct compounds with different properties, such as different melting points

A cis isomer has matching alkyl groups located on the same side of the double bond.

A trans isomer has the groups located on opposite sides of the double bond.

Reactions of Alkenes and Alkynes

functional group: a group of atoms withina molecule that determines the propertiesof the molecule

One common type of reaction that alkenes and alkynes undergo is an addition reaction. In an addition reaction two molecules react to form one.

Hydrogenation reactions, in which hydrogen atoms are added on either side of a multiple bond, can occur with alkenes, alkynes, or cyclic alkenes

Addition reactions may also occur with halogens, hydrogen halides such as hydrogen chloride, and water.

In a hydration reaction, water reacts with an unsaturated hydrocarbon.This reaction produces a type of organic compound that contains a hydroxyl group (-OH).

This compound is called an alcohol.

In hydration reactions and hydrohalogenationreactions 2 non-identical atoms are added to the multiple bond. Therefore, more than one product is possible

Markovnikov’s Rule

Markovnikov’s rule is the rule for predictingthe products of addition reactions: whena hydrogen halide or water is added to analkene, the hydrogen atom generally bondsto the carbon atom within the double bondthat already has more hydrogen atomsbonded to it.