29. Properties and reactions of alkenes Flashcards
What are alkenes?
an acyclic unsaturated hydrocarbon that contains one or more carbon– carbon double bonds.
What is the general formula for alkenes?
an acyclic unsaturated hydrocarbon that contains one or more carbon– carbon double bonds.
What are cycloalkenes?
a cyclic unsaturated hydrocarbon that contains one or more carbon– carbon double bonds within the ring system
What is the general formula for cycloalkanes?
a cyclic unsaturated hydrocarbon that contains one or more carbon– carbon double bonds within the ring system
What is Vinyl group?
H2C=CH–
(IUPAC name: ethenyl group)
What is Allyl group?
H2C=CH–CH2–
(IUPAC name: 2-propenyl group)
What is methylene group?
CH2=
(IUPAC name: methylidene group)
Relationships of the double bonds
- Conjugated double bonds are formed, when the single and double bonds alternate.
- The electrons are delocalized and shared by more than two atoms.
What are the types of isomers possible for alkenes?
- 2 subtypes of constitutional isomers are possible
- skeletal isomers and positional isomers
- Cis–trans isomerism
Physical properties of alkenes
- Nonpolar
- Insoluble in water
- Less dense than water
- Soluble in nonpolar solvents
Why are cis-trans isomers possible for alkenes?
because there is restricted rotation about a carbon– carbon double bond
What are the 4 types of chemical reactions for alkenes?
- Synthesis
- Addition
- Oxidation
- Polymerization
How can alkenes be prepared? (3 chemical reactions)
alkenes can be prepared by either E1 or E2 elimination reactions of alkyl halides.
- Dehydrohalogentaion of haloalkenes
- Dehydration of alcohols
- Reduction of alkynes
What is an addition reaction?
A reaction in which atoms or groups of atoms are added to each carbon atom of a carbon–carbon multiple bond in a hydrocarbon or hydrocarbon derivative
What are the 2 subtypes of addition reactions?
-
Symmetrical addition reaction
- an addition reaction in which identical atoms (or groups of atoms) are added to each carbon of a carbon–carbon multiple bond
-
Unsymmetrical addition reaction
- An addition reaction in which different atoms (or groups of atoms) are added to the carbon atoms of a carbon–carbon multiple bond.
What is hydrogenation reaction?
an addition reaction in which H2 is incorporated into molecules of an organic compound.
What happen during alkene hydrogenation?
a hydrogen atom is added to each carbon atom of a double bond
→ by heating the alkene and H2 in the presence of a catalyst (usually Ni or Pt).
What is a halogenation reaction?
an addition reaction in which a halogen is incorporated into molecules of an organic compound.
What happen during alkene halogenation?
What are the 2 most common halogenation processes?
Is catalyst required?
a halogen atom is added to each carbon atom of a double bond.
- Chlorination (Cl2) and bromination (Br2) are the two halogenation processes most commonly encountered.
- No catalyst is needed.
What is a hydrohalogenation reaction?
an addition reaction in which a hydrogen halide (HCl, HBr, or HI) is incorporated into molecules of an organic compound.
no catalyst.
What happen during alkene hydrohalogenation reaction?
- 1 carbon atom of a double bond receives a halogen atom
- the other carbon atom receives a hydrogen atom.
- no catalyst.
What is a hydration reaction?
an addition reaction in which H2O is incorporated into molecules of an organic compound
What happen during alkene hydration?
- 1 carbon atom of a double bond receives a hydrogen atom
- the other carbon atom receives an —OH group.
- requires a small amount of H2SO4 (sulfuric acid) as a catalyst.
What does Markovnikov’s rule state?
When an alkene undergoes electrophilic addition, the electrophile adds to the carbon with the greatest number of hydrogen substituents. The nucleophile adds to the more highly substituted carbon.
What is polymerization reaction?
a chemical reaction in which the repetitious combining of many small molecules (monomers) produces a very large molecule (the polymer)
Examples of polymers
Polyethylene
Polypropylene
Oxidation reactions of alkenes
