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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
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Unit3: 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)
3.1 Molecular Formula and the Degree of Unsaturation Alkene CH3(CH2)nCH3 CnH2n Cyclic alkane CnH2n Cyclic alkene CnH2n-2 Alkane CH3(CH2)nCH3 CnH2n+2 Degree of unsaturation = 2 1 p bond or 1 ring, degree of unsaturation = 1
3.4 cis-trans Isomerism Rotational barrier 63kcal/mol H3C—CH3 rotational barrier = 2.9 kcal/mol
3.6 Reactivity Considerations Functional group
Organic 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
3.7 Thermodynamics and Kinetics Reaction coordinate digram
Thermodynamics Describes the properties of a system at equilibrium The more stable the compound, the greater its concentration at equilibrium
Gibbs standard free energy change This symbol indicates that the reaction takes place under standard conditions --all species at 1 M, 25 OC, and 1 atm. ↓ R is the gas constant (1.986 cal/mol OK) T is the absolute temperature (OK)
Free Energy, Enthalpy and Entropy DHO < 0, exothermic reaction; DHO > 0, endothermic reaction In condensed phase, DSO≈ 0. Therefore DGO ≈ DHO
Solvation: the interaction between a solvent and a molecule (or ion) in solution Solvation can have a large effect on the DHO of a reaction, and it can also affect the DSO of a reaction.
Kinetics Deals with the rates of chemical reactions and the factors that affect those rates Free energy of activation
Rate Law First-order reaction Second-order reaction Second-order reaction
Rate Constant and Equilibrium Constant At equlibrium, forward rate = reverse rate. k1 [A] = k-1 [B] therefore
Reaction Coordinate Diagram for the Addition of HBr to 2-Butene Bonds being broken pDH = 61 kcal/mol H-BrDH = 87 kcal/mol DHtotal = 148 kcal/mol Bonds being formed C-H DH = 101 kcal/mol Bonds being formed C-Br DH = 69 kcal/mol Total DH change = +47 kcal/mol Over all DH change = -22 kcal/mol
Reaction Coordinate Diagram for the Addition of HBr to 2-Butene -22 kcal/mol
sp3 sp2 Inductive effect
Constitutional isomers Major product Minor product Major product Minor product Regioselective reaction Non-regioselective reaction
3.13 Addition of Water and Alcohols hydration
3.14 Rearrangement of Carbocations According Markovnikov’ rule This compound should be major product