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Unit 3 : Reactions of Alkenes. Thermodynamics and Kinetics. Hydrocarbons that contain only C-C bond are called alkane s. Hydrocarbons that contain C=C bond are called alkene s or olefins (oil forming). 尤加利樹油. 3.1 Molecular Formula and the Degree of Unsaturation. Alkene - PowerPoint PPT Presentation
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Unit 3: Reactions of Alkenes.Thermodynamics and Kinetics
Hydrocarbons that contain only C-C bond are called alkanes
Hydrocarbons that contain C=C bond are called alkenes or olefins (oil forming)
尤加利樹油
CH2 (CH2)n
AlkaneAlkane
CH3(CH2)nCH3
CnH2n+2
AlkeneAlkene
CHCH33(CH(CH22))nnCHCH33
CCnnHH2n2n
Cyclic alkaneCyclic alkane
CCnnHH2n2n
Cyclic alkeneCyclic alkene
CCnnHH2n-22n-2
H2C (CH2)n
HH
3.1 Molecular Formula and the Degree of Unsaturation3.1 Molecular Formula and the Degree of Unsaturation
Degree of unsaturation = 2Degree of unsaturation = 2
1 1 bond or 1 ring, degree of unsaturation = bond or 1 ring, degree of unsaturation = 11
3.3 The Structure of Alkenes3.3 The Structure of Alkenes
3.4 cis-trans3.4 cis-trans Isomerism Isomerism
Rotational barrier 63kcal/molRotational barrier 63kcal/mol
HH33C—CHC—CH33 rotational barrier = 2.9 kcal/mol rotational barrier = 2.9 kcal/mol
Cis-Trans Interconversion in VisionCis-Trans Interconversion in Vision
cis-transcis-trans Isomerism Isomerism
3.6 Reactivity Considerations3.6 Reactivity Considerations
Functional group
Organic ReactionsOrganic Reactions
• Electron-rich atoms or molecules are attracted to electron-deficient atoms or molecules
• Nucleophile: an electron-rich atom or molecule
• Electrophile: an electron-deficient atom or molecule
• A nucleophile and an electrophile react with each other
Electrophiles and NucleophilesElectrophiles and Nucleophiles
`
Mechanism of the ReactionMechanism of the Reaction
3.7 Thermodynamics and Kinetics3.7 Thermodynamics and Kinetics
Reaction coordinate digramReaction coordinate digram
ThermodynamicsThermodynamics
The more stable the compound, The more stable the compound, the greater its concentration at equilibriumthe greater its concentration at equilibrium
Describes the properties of a system at equilibriumDescribes the properties of a system at equilibrium
Gibbs standard free energy changeGibbs standard free energy change
This symbol indicates that the reaction takes place under standard conditionsThis symbol indicates that the reaction takes place under standard conditions--all species at 1 M, 25 --all species at 1 M, 25 OOC, and 1 atm.C, and 1 atm.↓↓
R is the gas constant (1.986 cal/mol OK)T is the absolute temperature (OK)
Free Energy, Enthalpy and EntropyFree Energy, Enthalpy and Entropy
HHOO < 0, exothermic reaction; < 0, exothermic reaction; HHOO > 0, endothermic reaction > 0, endothermic reaction
In condensed phase, In condensed phase, SSOO ≈ 0. ≈ 0. Therefore Therefore GGOO ≈ ≈ HHOO
Calculate Calculate HHOO for a Certain Reaction for a Certain Reaction
p.130
Solvation: Solvation: the interaction between a solvent and the interaction between a solvent and a molecule (or ion) in solutiona molecule (or ion) in solution
Solvation can have a large effect on the Solvation can have a large effect on the HHOO of a reaction, of a reaction, and it can also affect the and it can also affect the SSOO of a reaction. of a reaction.
KineticsKinetics
Free energy of activationFree energy of activation
Deals with the rates of chemical reactions and the factors that affect those rates
Rate LawRate Law
First-order reactionFirst-order reaction
Second-order reactionSecond-order reaction
Second-order reactionSecond-order reaction
The Arrhenius equation:The Arrhenius equation:
Rate Constant and Equilibrium ConstantRate Constant and Equilibrium Constant
A Bk1
k-1
At equlibrium, forward rate = reverse rate.At equlibrium, forward rate = reverse rate.
kk1 1 [A] = [A] = kk-1-1 [B] [B]
Keq =k1
k-1=
[B]
[A]
therefore
Reaction Coordinate Diagram for the AdditioReaction Coordinate Diagram for the Addition of HBr to 2-Butenen of HBr to 2-Butene
Bonds being broken H = 61 kcal/molH-Br H = 87 kcal/molHtotal = 148 kcal/mol
Bonds being formed C-H H = 101 kcal/mol
Total Total H changeH change = +47 kcal/mol
Bonds being formed C-Br H = 69 kcal/mol
Over all Over all H changeH change = -22-22 kcal/mol
Reaction Coordinate Diagram for the AdditioReaction Coordinate Diagram for the Addition of HBr to 2-Butenen of HBr to 2-Butene
-22 kcal/mol-22 kcal/mol
3.8 General Mechanism for Electrophilic Addition3.8 General Mechanism for Electrophilic Addition
3.9 Addition of Hydrogen Halides3.9 Addition of Hydrogen Halides
H2C CH2 + HCl CH3CH2Cl
Relative Stabilities of CarbocationsRelative Stabilities of Carbocations
sp2sp3
Inductive effectInductive effect
Relative Stabilities of CarbocationsRelative Stabilities of Carbocations
3.11 The Structure of the Transition State3.11 The Structure of the Transition State
The Hammond postulateThe Hammond postulate
3.12 Regioselectivity of Electrophilic Additio3.12 Regioselectivity of Electrophilic Addition Reactionsn Reactions
Major productMajor product
Major productMajor product
Minor productMinor product
Minor productMinor product
Constitutional isomers
Regioselective reaction
H3CHC CHCH2CH3 + HBr H3CCH CH2CH2CH3 H3CH2C CHCH2CH3
Br
+Br
Non-regioselective reaction
H3CH2CCH CH2 H3CH2CHC CH2
HH
vs
3.13 Addition of Water and Alcohols3.13 Addition of Water and Alcohols
hydrationhydration
Addition of Alcohol to AlkeneAddition of Alcohol to Alkene
3.14 Rearrangement of Carbocations3.14 Rearrangement of Carbocations
According Markovnikov’ ruleThis compound should be major product
Mechanism for the Formation of Rearranged ProductMechanism for the Formation of Rearranged Product
a secondary carbocationa tertiary carbocation
attack on unrearrangedcarbocation
attack on rearrangedcarbocation
minor product major product
Mechanism for the Formation of Rearranged ProductMechanism for the Formation of Rearranged Product
major productminor product
attack on unrearrangedcarbocation
attack on rearrangedcarbocation
a secondary carbocation a tertiary carbocation
Carbocation rearrangements also can occur by ring expansionCarbocation rearrangements also can occur by ring expansion
1,2-alkyl shift
3.15 Addition of Halogens3.15 Addition of Halogens
p.154 last sentence
unstable
F2 reacts explosively with alkenes!!!
Formation of HalohydrinsFormation of Halohydrins
3.18 Addition of Radicals.3.18 Addition of Radicals. The Relative Stabilities of Radicals The Relative Stabilities of Radicals
Radical addition reactionRadical addition reaction
Addition of HBr through Radical MechanismAddition of HBr through Radical Mechanism
Addition of HBr through Radical MechanismAddition of HBr through Radical Mechanism
3.19 Addition of Hydrogen.3.19 Addition of Hydrogen. The Relative Stabilities of Alkenes The Relative Stabilities of Alkenes
Heat of HydrogenationHeat of Hydrogenation
Relative Stabilities of AlkenesRelative Stabilities of Alkenes