Chapter 3 Alkenes : Structure, Nomenclature, Reactivity
ethylene multifidene Sex attractant muscaline
Nomenclature of Alkenes Longest chain containing double bond
alphabetical order lowest possible numbers.
A number is not needed to denote the position of the double bond in a cyclic alkene lowest substituent number
E and Z nomenclature for alkenes Zusammen (together) Entgegen (opposite) Z isomer has the highest priority group on the same side E isomer has the highest priority group on opposite sides Priorities : 1. atomic number 2. atomic number of substituent 3. atomic mass (in case of isotopes)
Isotopes Z isomer E isomer C=C, C≡C are considered to be ……..
Electrophiles & Nucleophiles(친핵체, 친전자체) Br2 , BF3, Ag+ HBr CH2=CH2, C6H6 p- electrons n.e.p.
Electrophiles & Nucleophiles Curved arrows are used to indicate the movement of electrons Electrophilic addition reaction (친전자성첨가반응) why?
Curved Arrows Full curved arrow : direction of the flow of electron pairs Half curved arrow : direction of the flow of single electron 1. The arrow starts at the electron source, not an atom. : covalent bond (s or p bond, pair of electrons in each bond), or nonbonding electron pair in C, N, O, or halogen atom → disappearance of the bond or n.e.p. 2. The head of a curved arrow points at a bond or at an atom. → formation of a new covalent bond (s or p bond) or formation of a nonbonding electron pair 3. Be careful about the formal charges of the atoms.
Reaction Coordinate (반응도표) Gibbs Free energy G = H -TS
Thermodynamics : How much product is formed? Gibbs Free energy change DG˚ = DH˚ –TDS˚ = -RT ln Keq
Le Châtelier’s principle : When a system in equilibrium is disturbed, the system will adjust to offset the disturbance. DG˚ = DH˚ – TDS˚ = -RT ln Keq Gibbs Free energy change =(free energy of products) - (free energy of reactants) DH˚ = H˚(products) - H˚(reactants), enthalpy : energy 에너지는 … = (energy of the bonds being broken) - (energy of the bonds being formed) DS˚ = S˚(products) - S˚(reactants), entropy : degree of freedom = (freedom of motion of products) - (freedom of motion of reactants) DH = DE + PDV , DH ≈ DE in solution
Kinetics : How fast is the product formed? Elementary reaction (단일단계 반응) , Ttransition state (전이상태), ‡ : double dagger
DG‡ = DH‡ – TDS‡ DG‡ = (free energy of the transition state) – free energy of the reactants) DH‡ =(enthalpy of the transition state) - (enthalpy of the reactants) DS‡ =(entropy of the transition state) - (entropy of the reactants) DG‡ > 0, repulsion between electrons Normally DS‡ < 0, decreased freedom of motion. The smaller the DG‡ , the faster is the reaction. Anything that destabilizes the reactants or stabilizes the transition state will make the reaction go faster.
First order reaction (1차반응) Second order reaction (2차반응)
The Arrhenius equation k = Ae-Ea/RT R = 1.982 cal/mol•K = 1.982 x 10-3 kcal/mol•K = 8.314 J/mol•K = 8.314 x 10-3 kJ/mol•K ln k = ln A - Ea/RT Ea : activation energy
Thermodynamics in terms of Kinetics For a reversible reaction, DGb‡or Ea for reverse reaction DGf‡ or Ea for forward reaction DG
Transition states for hydrohalogenation : first step in the addition of HBr to 2-butene
Reaction coordinate diagrams : two steps in the addition of HBr to 2-butene first step second step
Reaction coordinate diagrams : two steps in the addition of HBr to 2-butene