Alkenes
1. Alkenes
Alkenes are hydrocarbons containing a double bond at its C-atom chains. (- C = C -). Alkene compound containing H atoms fewer than the number of H atoms in alkanes. Thus, alkene compounds called unsaturated compound or olefin compounds. (The term comes from the Latin word olefin = olein oil, ficare = shaping). The term olefin derived from the fact, that the first member of the alkene series is C2H4 (ethene) reacts with chlorine to produce ethylene chloride are tangible such as oil.
Examples of alkenes:
CH2 = CH2              CH3 - CH = CH2           CH3 - CH2 - CH = CH2
Ethene                             propene                                 1-butene


Nomenclature Alkenes
Naming alkenes according to the IUPAC system the same as in alkanes. The names of alkenes considered a derivative of alkanes. Therefore, the name derived from the name of alkanes alkenes the same number of atoms C it by replacing the suffix ana with ena. Some rules for naming alkenes are as follows:
1. Main chain selected the longest carbon chain containing a double bond.
2. Carbon atoms in the main chain be numbered so that the double bonded carbon atoms have a small number.
3. Main chain were given the suffix ena
4. To show the location of double bonds the main chain name preceded by the serial number of double bonded carbon atoms.
5. Carbon compounds which have more than one double bond, for example compounds containing two diene double bond is called, and which contains 3 double bond is called triena.

Terms of geometric isomers of alkenes is
a. Each carbon atom that binds double binds two different groups, such as H and Cl or CH3 and Cl
b. At least a pair of groups attached to the C atom double bonded


Example:
Geometric isomers
  CH3                 CH2 - CH3   CH3 H
\         /                         \         /
.C = C.                         C = C
/         \                         /         \
H        H                   H         CH2 - CH3

Cis-2-pentena Trans-2-pentena

The properties and usefulness of alkenes

The reactions of alkenes
Alkene is much more reactive than alkanes. This is due to the double bond
- C = C -. Alkene reactions mainly occur at the double bond.

1). Additive (binding of simple molecules by double bond = saturation)
The most important reactions of alkenes and all other compounds which are unsaturated addition reactions. In addition double bond saturated.

Example:
a. Addition of hydrogen to produce ethane ethene

CH2 = CH2 + H2 ----.Pt/Ni--- CH3 - CH3

(Pt or Ni serves as a catalyst, a substance that can accelerate the course of a reaction, but the substance was at the end of the reaction can be recovered).
b. Halogen addition to alkenes yield dihalo alkanes

CnH2n + X2 ---Pt/Ni--- CH2X - ​​CH2X


CH2 = CH2 + Cl2 ---Pt/Ni--- CH2 - CH2
   Ethene l            l
C                                                        Cl
                                      1,2-ethane dichlorine
c. HX addition to alkenes produce alkanes monohalo

CH3 - CH2 = CH2 + HCl ---Pt/Ni--- CH3 - CH - CH3
Propene                                                 l
                                                             Cl
                                                  2-chloro propene

2). Combustion reaction
Such as alkanes, alkenes also flammable. Burning of alkenes and other compounds that are not saturated, resulting in a lot of soot. Soot is carbon atoms that do not burn. Some unburnt carbon atoms because of alkenes containing a high carbon content so that it requires a lot of oxygen. However, because not enough oxygen from the air, then partially unburned carbon atoms. Complete combustion of alkenes produces CO2 and water vapor.

C2H4 + O2 ----- 2 CO2 + 2 H2O