Organic Chemistry 4 th Edition Paula Yurkanis Bruice Chapter 3 Alkenes: Structures, Nomenclature, and an Introduction to Reactivity Thermodynamics and Kinetics Irene Lee Case Western Reserve University Cleveland, OH ©2004, Prentice Hall

Hydrocarbons containing double bonds Alkenes

Noncyclic alkene: C n H 2n Cyclic alkene: C n H 2n–2 Molecular Formula of Alkene

Systematic Nomenclature of Alkenes Longest continuous chain containing the functional group

Cite the substituents in alphabetical order Name with the lowest functional group number and then the lowest substituent numbers

No numbering of the functional group is needed in a cyclic alkene

Special Nomenclatures

Structure of Alkene

Isomers of Alkene

Dipole Moments of Alkene Isomers

Conversion of alkene isomers requires breaking of the  bond between the two sp 2 carbons

Cis-Trans Interconversion in Vision

E and Z isomers

Naming by the E,Z System Rule 1: Consider the atomic number of the atoms bonded directly to a specific sp 2 carbon.

Rule 2: If there is a tie, consider the atoms attached to the tie.

Rule 3: Multiple bonds are treated as attachment of multiple single bonds.

Rule 4: Rank the priorities by mass number in isotopes.

An alkene is an electron-rich molecule Nucleophile: an electron-rich atom or molecule that shares electrons with electrophiles Examples of Nucleophiles A nucleophile

Nucleophiles are attracted to electron-deficient atoms or molecules (electrophiles) Examples of Electrophiles

Electrophilic Addition of HBr to Alkene

Curved Arrows in Reaction Mechanisms Movement of a pair of electrons Movement of one electron

Utilization of Curved Arrows

Rules for Use of Curved Arrows

A Reaction Coordinate Diagram Transition states have partially formed bonds Intermediates have fully formed bonds

Thermodynamics describes the properties of a system at equilibrium

Thermodynamic Parameters Gibbs standard free energy change (  G ° ) Enthalpy (  H ° ): the heat given off or absorbed during a reaction Entropy (  S ° ): a measure of freedom of motion  G ° =  H ° – T  S ° If  S ° is small compared to  H °,  G ° ~  H °

Exergonic Reaction –G°–G° Endergonic Reaction +G°+G°

 H ° can be calculated from bond dissociation energies

Solvation: the interaction between a solvent and a molecule (or ion) in solution Solvation can affect  H ° and/or  S °, which ultimately affects  G °

Kinetics deals with the rate of chemical reactions and the factors that affect those rates The rate-limiting step controls the overall rate of the reaction Rate of a reaction = number of collisions per unit time fraction with sufficient energy fraction with proper orientation xx

The free energy between the transition state and the reactants

 G ‡ : (free energy of transition state) – (free energy of reactants)  G ‡ =  H ‡ – T  S ‡  H ‡ : (enthalpy of transition state) – (enthalpy of reactants)  S ‡ : (entropy of transition state) – (entropy of reactants)

Rates and Rate Constants First-order reaction AB rate = k[A] Second-order reaction A + B C + D rate = k[A][B]

The Arrhenius Equation k = Ae –E a /RT E a =  H ‡ + RT Rate Constants and the Equilibrium Constant k1k1 k –1 K eq = k 1 /k –1 = [B]/[A]

Transition State versus Intermediate Transition states have partially formed bonds Intermediates have fully formed bonds intermediate

Electrophilic Addition of HBr to 2-Butene The rate-limiting step controls the overall rate of the reaction