Alkenes: Definition, Formula, and Properties

Questions and Answers

Match the functional groups with their respective types of hydrocarbons:

Carbon-carbon double bonds = Alkenes Carbon-carbon triple bonds = Alkynes Carbon-carbon single bonds = Alkanes

Match the general formulas with their respective types of hydrocarbons:

CnH2n = Alkenes CnH2n-2 = Alkynes CnH2n+2 = Alkanes

Match the chemical properties with their respective types of hydrocarbons:

Electrophilic addition reactions = Alkenes Acid-base reactions = Alkynes Substitution reactions = Alkanes

Match the reaction types with their respective products:

Dehydrohalogenation = Alkenes Dehydration = Alkenes Dehalogenation = Alkynes Signup and view all the answers

Match the nomenclature rules with their respective types of hydrocarbons:

Suffix: -ene = Alkenes Suffix: -yne = Alkynes Prefix: cyclo- = Cycloalkanes Signup and view all the answers

Match the physical properties with their respective types of hydrocarbons:

Lower boiling points and densities than alkanes = Alkenes Higher boiling points and densities than alkenes = Alkynes Higher boiling points and densities than alkanes = Alcohols Signup and view all the answers

Match the isomerism types with their respective types of hydrocarbons:

Cis-trans isomerism = Alkenes Structural isomerism = Alkanes Optical isomerism = Chiral molecules Signup and view all the answers

Match the reaction types with their respective reactants:

Alkylation = Alkynes Dehydrohalogenation = Alkyl halides Dehydration = Alcohols Signup and view all the answers

Study Notes

Alkenes

Definition: Alkenes are unsaturated hydrocarbons containing one or more carbon-carbon double bonds.
General Formula: CnH2n
Nomenclature:
- Prefix: alk- (e.g., eth-, prop-, but-)
- Suffix: -ene (e.g., -ene, -diene, -triene)
- Numbering starts from the end closest to the double bond
Physical Properties:
- Lower boiling points and densities than alkanes
- Insoluble in water, soluble in organic solvents
Chemical Properties:
- Electrophilic Addition Reactions: react with electrophiles to form carbocations
- Markovnikov's Rule: in asymmetric alkenes, the electrophile adds to the more substituted carbon
- Stereochemistry: alkenes exhibit cis-trans isomerism due to restricted rotation around the double bond
Synthesis:
- Dehydrohalogenation: elimination reaction of alkyl halides
- Dehydration: elimination reaction of alcohols

Alkynes

Definition: Alkynes are unsaturated hydrocarbons containing one or more carbon-carbon triple bonds.
General Formula: CnH2n-2
Nomenclature:
- Prefix: alk- (e.g., eth-, prop-, but-)
- Suffix: -yne (e.g., -yne, -diyne, -triyne)
- Numbering starts from the end closest to the triple bond
Physical Properties:
- Higher boiling points and densities than alkenes
- Insoluble in water, soluble in organic solvents
Chemical Properties:
- Acid-Base Reactions: alkynes are acidic due to the high electronegativity of the triple bond
- Reduction Reactions: alkynes can be reduced to alkenes or alkanes using hydrogen and catalysts
- Cycloaddition Reactions: alkynes participate in Diels-Alder reactions with dienes
Synthesis:
- Dehalogenation: reaction of alkyl dihalides with strong bases
- Alkylation: reaction of alkynes with alkyl halides and strong bases

Alkenes

Unsaturated hydrocarbons with one or more carbon-carbon double bonds
General formula: CnH2n
Nomenclature rules:
- Use alk- prefix (e.g., eth-, prop-, but-)
- Use -ene suffix (e.g., -ene, -diene, -triene)
- Numbering starts from the end closest to the double bond
Physical properties:
- Lower boiling points and densities compared to alkanes
- Insoluble in water, but soluble in organic solvents
Chemical properties:
- Undergo electrophilic addition reactions to form carbocations
- Follow Markovnikov's Rule in asymmetric alkenes
- Exhibit cis-trans isomerism due to restricted rotation around the double bond
Synthesis methods:
- Dehydrohalogenation: elimination reaction of alkyl halides
- Dehydration: elimination reaction of alcohols

Alkynes

Unsaturated hydrocarbons with one or more carbon-carbon triple bonds
General formula: CnH2n-2
Nomenclature rules:
- Use alk- prefix (e.g., eth-, prop-, but-)
- Use -yne suffix (e.g., -yne, -diyne, -triyne)
- Numbering starts from the end closest to the triple bond
Physical properties:
- Higher boiling points and densities compared to alkenes
- Insoluble in water, but soluble in organic solvents
Chemical properties:
- Acidic due to the high electronegativity of the triple bond
- Undergo reduction reactions to form alkenes or alkanes using hydrogen and catalysts
- Participate in Diels-Alder reactions with dienes
Synthesis methods:
- Dehalogenation: reaction of alkyl dihalides with strong bases
- Alkylation: reaction of alkynes with alkyl halides and strong bases