Study Set Content:
Hydrocarbon containing a carbon-carbon double bond. Sometimes called olefin.
Alkene
Physical Properties:
Of alkene
- Insoluble in water and soluble in polar solvents
- Densities is less than water
- The boiling and melting points of an alkene is usually lower than that of an alkane with the same number of carbon atoms.
- Alkenes with 2 to 4 carbon atoms are gases at room temperature.
- Unsubstituted alkenes with 5 to 17 carbon atoms are liquids
- Alkenes with >17C atoms are solid
Chemical Properties:
Alkene
Alkenes are valued mainly for addition reactions, in which one of the bonds in the double bond is broken. Each of the carbon atoms in the bond can then attach another atom or group while remaining joined to each other by a single bond.
Pharmaceutical Use
alkene
- Use in pharmaceutical preparations is very restricted as a result of their toxicity to the body.
- They are more commonly used in industry as raw materials for the manufacturing of alcohols and aldehydes.
The ene suffix (ending) indicates an
Alkene or cycloalkene
IUPAC Rules for Alkene and Cycloalkene Nomenclature
- The ene suffix (ending) indicates an alkene or cycloalkene.
- The longest chain chosen for the root name must include both carbon atoms of the double bond.
- The root chain must be numbered from the end nearest a double bond carbon atom. If the double bond is in the center of the chain, the nearest substituent rule is used to determine the end where numbering starts.
- The smaller of the two numbers designating the carbon atoms of the double bond is used as the double bond locator. If more than one double bond is present the compound is named as a diene, triene, or equivalent prefix indicating the number of double bonds, and each double bond is assigned a locator number.
- In cycloalkenes the double bond carbons are assigned ring locations #1 and #2. Which of the two is #1 may be determined by the nearest substituent rule.
- Substituent groups containing double bonds are:
H2C=CH2
Ethene
ethene common name
Ethylene
CH3CH=CH2
Propene
Common name
Propylene
2-methylpropene
2-methylpropene common name
Isobutylene
2-Methyl-1,3-
butadiene
2-Methyl-1,3-
butadiene
common name
Isoprene
- a reaction with hydrogen (H2) in the presence of a catalyst such as nickel (Ni) or platinum (Pt).
Hydrogenation
The addition of halogens
Halogenation
requires a catalyst–usually a strong acid, such as sulfuric acid
Hydration
General reaction mechanism of electrophilic addition
- Attack on electrophile, such as HBr, by π bond of alkene
- Produces carbocation and bromide ion
- Carbocation is an electrophile, reacting with a nucleophilic bromide ion
In electrophilic addition reactions, unsymmetrical substituted alkenes give a
Single product
Reaction in which only one of two possible orientations of an addition occur
Regiospecific
