Reactions of alkenes

C-C (σ) bond enthalpy: 347kJ/mol⁻¹

C=C (π): 612kJ/mol⁻¹

π bond needs 265kJ/mol (612-347) to undergo f...

SO π has lower b... ... than σ - weaker - C=C breaks f... → addition reactions

fission, bond enthalpy, first

Electrophiles: ... ions/... molecules which ... ...

positive, polar, accept electrons

Electrophiles: ... ... ...

electron pair acceptors

Mechanism name: ... ...

electrophilic addition

1. Alkenes + Hydrogen-halides → ....?

Reagent: .... (H = slightly positive - electrophile)

Condition: ... ...

Equation: C₂H₄ (g) + HX (g) → C₂H₅X (l)

haloalkane, H-X, room temp

Alkene → haloalkane steps: ethane + HBr

1. Curly arrow from C=C (π) to Hδ⁺

2. Curly arrow from H-Br bond to Brδ⁻ - h... fission in electrophile HBr (Br gets both)

FORMS: - c... (+) alkane + n... (∙∙Br⁻)

3. Curly arrow from ∙∙Br⁻ to c....

FORMS: haloalkane

heterolytic, carbocation, nucleophile, carbocation

Curly arrows show: movement of an ... ... from a lone pair/bond to an .../bond

MUST START: at a l... ... or a b...

MUST END: on an a... or a b...

Curly arrows represent: bonds breaking (h...) or forming

electron pair, atom, lone pair, bond, atom, bond, heterolytic

If unsymmetrical alkenes: .. products can form - m.../m... depending on c... s...

e.g 1-bromo propane + 2-bromopropane

2, major, minor, carbocation stability

Markovnikov's Rule: H⁺ attaches to carbon w the most .....

The major product is formed via the more s... hydrocarbon

hydrogens, stable

3°>2°>1°

Name in order of most stable → least:

tertiary, secondary, primary

Primary: .. R group

Secondary: .. R groups

Tertiary: .. R groups

More alkyl (R) groups = more s... carbocation - reactions occur via low energy i....

1, 2, 3, stable, intermediates

2. Alkenes + Halogens (halogenation) → ....?

Reagent: .../bromine

Condition: ... ...

Equation: C₂H₄ (g) + Br₂ (g) → CH₂BrCH₂Br (C₂H₄Br₂) (l)

dihaloalkane, halogen, room temp

Halogenation:

C=C = ... rich - repels electrons in X-X

I... ... in X-X (δ⁺ X-X δ⁻) (e.g δ⁺ Br-Br δ⁻)

δ⁺ side = attracted to ... rich C=C

electron, induces dipole, electron

3. Alkene + hydrogen (hydrogenation) → ...?

Reagent: ...

Condition: n... c... (finely divided)

Equation: ethene → ethane

C₂H₄ (g) + H₂ (g) → C₂H₆ (g)

alkane, hydrogen, nickel catalyst

4. Alkene + H₂O (hydration) → ..?

Reagent: ... (330°C)

Conditions: high ... + p... a... c... (H₃PO₄)

alcohol, steam, pressure, phosphoric acid catalyst

Bond enthalpies: (kJ/mol⁻¹)

O-H = 463

H-Br = 366

OH = ...

higher