Alkenes Flashcards
What is the general formula for alkenes?
CnH2n
How are alkenes classified in terms of saturation?
Unsaturated hydrocarbons
What are the common methods for the preparation of alkenes?
Elimination of haloalkanes (dehydrohalogenation)
Elimination of alcohols (dehydration)
What is the Saytzeff rule in relation to alkenes?
The alkene with the greater number of alkyl groups on the C of C=C is the major product.
Name the types of reactions alkenes undergo.
- Addition
- Oxidation
- Hydrogenation
- Halogenation
- Hydrohalogenation
- Hydration
For unsymmetrical alkene, we use Markovnikov’s rule to determine the major or minor product, What does Markovnikov’s rule state?
The more electropositive atom of the reagent will attach to the unsaturated carbon atom with the greater number of H atoms.
In the addition of HX to unsymmetrical alkenes, where does the H atom attach?
To the carbon atom that has the larger number of H atoms.
What is the order of carbocation stability from least to most stable?
- Methyl
- 1° (primary)
- 2° (secondary)
- 3° (tertiary)
What observation indicates the occurrence of mild oxidation of alkenes?
Purple color is decolorized or brown precipitate is formed.
What are the products of strong oxidation (oxidative cleavage) of alkenes using concentrated KMnO4?
- CO2
- H2O
- Ketone
- Carboxylic acid
What happens during oxidative cleavage of alkenes?
The C=C bond breaks to produce two fragments.
Fill in the blank: The reaction of alkenes with KMnO4 in heat and H+ results in _______.
Oxidative cleavage
What is the observation when strong oxidation occurs with alkenes?
Purple color is discharged.
What is the product of the reaction between 2-methyl-2-butene and H2(g) in the presence of Pt & heat?
Alkane
True or False: The more stable carbocation will produce the minor product.
False
What is the chemical test used to determine the structure of an alkene?
Oxidative cleavage using concentrated KMnO4
What is the expected product when alkenes react with bromine water at room temperature?
Dibromide
In the reaction of alkenes with H-OH under acidic conditions, what is the product formed?
Alcohol
What are the conditions for dehydration to occur?
- Conc. H2SO4 (excess)
- 170-180
What is the reagent and condition for hydrogenation of alkene?
Reagent: H2
Condition: Heat and Ni (catalyst)
Halogenation has two condition for it to happen, what are the conditions?
- in inert solvent
- in water
For halogenation in inert solvent, what are the reagent and condition of it?
Reagent: Halogen (at room temp.)
Condition: CH2Cl2 and room temp
For halogenation in water, what are the reagent and condition of it?
Reagent: Halogen (that dissolved in water, (aq) )
Condition: room temp.
What is the reagent and condition for hydrohalogenation of alkene?
Reagent: HX (X-halogen)
Condition: room temp.
What is the reagent and condition for hydration of alkene?
Reagent: H2O (g) / steam
Condition:
- H3PO4 (catalyst)
- high T
- high P
What are the condition for mild oxidation to happen?
Catalyst: KMnO4 / H+ at room temp.
What are the condition for strong oxidation to happen?
Catalyst: KMnO4 / H+ with heat.
Under strong oxidation, What are the products when alkene (primary carbon) undergoes oxidation?
CO2 + H2O + Mn2+
Under strong oxidation, What are the products when alkene (secondary carbon) undergoes oxidation?
Carboxylic acid + Mn2+
Under strong oxidation, What are the products when alkene (tertiary carbon) undergoes oxidation?
Ketone + Mn2+
