© 2011 Pearson Education, Inc. 1 Organic Chemistry 6 th Edition Paula Yurkanis Bruice Chapter 3 Alkenes: Structures, Nomenclature, and an Introduction to Reactivity Thermodynamics and Kinetics

© 2011 Pearson Education, Inc. 2 Alkenes Are an Important Part of Our Lives

© 2011 Pearson Education, Inc. 3 Systematic Nomenclature of Alkenes 1.Longest continuous chain containing the functional group:

© 2011 Pearson Education, Inc. 4 2.For a compound with two double bonds, the suffix is “diene”: 3. When there are both a functional group and a substituent, the functional group gets the lowest number:

© 2011 Pearson Education, Inc Cite the substituents in alphabetical order: 5. Name with the lowest functional group number and then the lowest substituent numbers:

© 2011 Pearson Education, Inc In a cyclic alkene, the alkene functional group is given the number 1, but the -1- is left out of the name: 6. The alkene substituent is given the lower number:

© 2011 Pearson Education, Inc. 7 Special Nomenclatures

© 2011 Pearson Education, Inc. 8 What Is an Omega Fat? This nomenclature is not IUPAC or common (both Greek letters and numbers are used). This naming is commonly used in labeling and by nutritionists.

© 2011 Pearson Education, Inc. 9 Structure of Alkene

© 2011 Pearson Education, Inc. 10 Alkene Isomers

© 2011 Pearson Education, Inc. 11 Dipole Moments of Alkene Isomers

© 2011 Pearson Education, Inc. 12 Conversion of alkene isomers requires breaking of the  bond between the two sp 2 carbons

© 2011 Pearson Education, Inc. 13 Cis-Trans Interconversion in Vision

© 2011 Pearson Education, Inc. 14 Fats: Kinky, Saturated, and Trans Cis alkenes groups produce kinks in the chain. Unsaturated fats are oils because stacking of kinked chains is not possible. Saturated fats are solids because stacking of chains is possible. Trans fats structurally resemble saturated fats. Both are considered unhealthy.

© 2011 Pearson Education, Inc. 15 E and Z Nomenclature: Z, Zusammen (together) E, Entgegen (opposite ) E,Z is from German:

© 2011 Pearson Education, Inc. 16 Naming by the E,Z System Rule 1: Consider the atomic number of the atoms bonded directly to a specific sp 2 carbon: Higher atomic number has higher priority

© 2011 Pearson Education, Inc. 17 Rule 2: If there is a tie, consider the atoms attached to the tied atoms: Rule 3: Multiple bonds are treated as attachment of multiple single bonds using “divide-duplicate.”

© 2011 Pearson Education, Inc. 18 Using divide-duplicate: Rule 4: Rank the priorities by mass number in isotopes: Divide  -bonds. Duplicate atoms attached to each  -bond.

© 2011 Pearson Education, Inc. 19 Electron-rich atoms or molecules (nucleophiles) are attracted to electron-deficient atoms or molecules (electrophiles):

© 2011 Pearson Education, Inc. 20 Your First Reaction: Addition of HBr to an Alkene 1st Step: Addition of a proton to the alkene. The proton is the electrophile. 2nd Step: Bromide traps the carbocation. Bromide is the nucleophile.

© 2011 Pearson Education, Inc. 21 Arrows in Organic Chemistry: Moving Electrons

© 2011 Pearson Education, Inc. 22 Arrows in Organic Chemistry: Showing Processes

© 2011 Pearson Education, Inc. 23 Rules on Using Curved Arrows 1. Full-headed arrows are drawn in the direction of two-electron flow. 2. The arrow must originate at the electron source.

© 2011 Pearson Education, Inc The head of the curved arrow always points to the destination of the electrons. correct incorrect 4. Half-headed arrows are used for radical processes. Bond breaking and bond formation both require two half-headed arrows.

© 2011 Pearson Education, Inc. 25 Thermodynamics and Kinetics Thermodynamics describes a reaction at equilibrium. Kinetics explains the rates of chemical reactions. Thermodynamics:The K eq value that provides the concentration at Z and Y at equilibrium. Kinetics: The k 1 and k -1 values that provide the rate at which the reaction comes to equilibrium.

© 2011 Pearson Education, Inc. 26 A Reaction Coordinate Diagram Describes the Reaction Pathway Transition states have partially formed bonds Intermediates have fully formed bonds

© 2011 Pearson Education, Inc. 27 Thermodynamics: How much product is formed?

© 2011 Pearson Education, Inc. 28 Thermodynamic Parameters Gibbs standard free-energy change (  G o ) Enthalphy (  H o ): the heat given off or absorbed during a reaction Entropy (  S o ): a measure of freedom of motion  G o =  H o - T  S o If  S o is small compared to  H o,  G o ~  H o  G o = -RTlnK eq

© 2011 Pearson Education, Inc. 29 Exergonic Reaction -Go-Go Endergonic Reaction +Go+Go

© 2011 Pearson Education, Inc. 30  H o can be calculated from bond dissociation energies

© 2011 Pearson Education, Inc. 31 Entropic Reactions An entropic reaction results in a massive change in volume without heat evolution. Air bag deployment is a common entropic reaction. TATP is an entropic explosive used by terrorists.

© 2011 Pearson Education, Inc. 32 Kinetics: How fast is the product formed? The rate-limiting step controls the overall rates of the reaction Rate of a reaction = number of collisions per unit of time fraction with sufficient energy fraction with proper orientation XX

© 2011 Pearson Education, Inc. 33 The free energy between the transition state and the reactants

© 2011 Pearson Education, Inc. 34  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)

© 2011 Pearson Education, Inc. 35 Rates and Rate Constants First-order reaction AB rate = k[A] Second-order reaction A + B C + D rate = k[A][B] A + A B rate = k[A] 2 Units of first-order rate constant k is time -1 Units of second-order rate constant k is M -1 time -1 Units of the rate is M time -1

© 2011 Pearson Education, Inc. 36 The Arrhenius Equation k = Ae -E a /RT E a =  H ‡ + RT A is the pre-exponential factor. Its value pertains to the frequency and orientation of collisions. The term provides the fraction of molecules with the activation energy (E a ) at temperature T ( o K). R is the gas constant. If E a = 0, the reaction is encounter controlled with k = A. The second order encounter-controlled k value in water is M -1 sec -1. The Arrhenius equation predicts that the rate of a reaction will double with each 10 o K increase in temperature.

© 2011 Pearson Education, Inc. 37 Transition State Versus Intermediate Transition states have partially formed bonds Intermediates have fully formed bonds intermediate

© 2011 Pearson Education, Inc. 38 Electrophilic Addition of HBr to 2-Butene The rate-limiting step controls the overall rates of the reaction