Alkenes

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Structure
*From a homologous seriese of general formula CnH2n non-cyclic alkenes only
* Contain a Carbon - Carbon double bond (C=C) somewhere in their structure
*Unsaturated hydrocarbons - can still have atoms added to their formula

Naming
*Select longest chain of C atoms containing the double bonds end in -ENE
* Number the chain starting from the end nearer the double bond; use a number to indicate the first carbon in the double bond
*Prefix with substituents. Side chain positions are baised on the number allocated to the first carbon in the double bond.
*If Cis-Trans isomerism exists, prefix with cis or trans

e.g. CH 3-CH=CH-CH2(CH3)-CH3    

Isomerism
Two types of isomerism are found in alkenes.
Structural -
*Position - due to different positions of the double bond (but-1-ene & but-2-ene)
*Branching - (but-1-ene & 2-methylpropene)

E/Z
*Due to restricted rotation of the C=C
*Single bonds cannot torate so the groups are frozen in position.
*Double bonds cannot rotate freely, thus freezing groups on either side of C=C
*Not all alkenes exhibit this type of isomerism.
*If there are two H's and two non-hydrogen groups attatched to each carbon it is called cis-trans isomerism.

Z - Higher priority of groups on the same side of the C=C bond
E - Higher priority of groups on opposite sides of the C=C bond.

Priority of atoms/groups
I>Br>Cl>F>C>H
C5H7>C2H5>CH3>H

Structural isomers - but-1-ene, but-2-ene & 2-methylpropene
E/Z or cis-trans isomers Cis(Z) and trans(E) but-2-ene

Physical Properties
Boiling Points -
*Increases as molecular mass/size increases - increased van der waals forces
*for isomers the greater the degree of branching, the lower the boiling point
*the lower members of the seriese are gasses at room temp - cyclohexene is a liquid

Solubility
*Non polar so they are insoluble in water but soluble in organic solvents.

Chemical Properties
Theory
*Spacial arrangment arround the C=C is planar the bond angles are 120 degrees
*The 2p orbitals overlap to form a new pi orbital; it exists above and below the plane of

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