Chemistry 250-02 Organic Chemistry I Fall, 2014 Day 14 10/3/14 Chemistry 250-02 Organic Chemistry I Fall, 2014 Day 14 10/3/14 Chapter 6 Start to Read Chapter 7 Alkene Structure Chem Activity 6C An Overview of Organic Reactions What Kind of Reactions Are There? Why do Reactions Happen? How do Reactions Happen? What Factors Control Reactions?

Some Types of Organic Reactions Addition Elimination Substitution hydrolysis - reaction with H2O condensation - formation of H2O Rearrangement

Garoutte ChemAct 33 p. 133-134

Garoutte ChemAct 33 p. 133-134 Oxidation Reduction Substitution Hydrolysis Elimination (reverse is Addition) Acid-Base Oxidation - 3 types add oxygen lose hydrogen loss of electrons Substitution Condensation Addition (reverse is Elimination)

How do we classify these reactions How do we classify these reactions? Addition, Elimination, Substitution, Rearrangement

How do we classify these reactions How do we classify these reactions? Addition, Elimination, Substitution, Rearrangement Substitution Nucleophilic Polar-Ionic H+ Elimination Addition Δ Substitution Radical hν

Reaction Types

What Kinds of Organic Reactions Are There What Kinds of Organic Reactions Are There ? How Can We Describe These Reactions ? Problem 6.1

What Kinds of Reactions Are These?

What Kinds of Reactions Are These? Substitution Substitution Elimination

Polar Reactions Recall polarity These reactions involve a nucleophile (e- - rich) and an electrophile (e- - poor) What kind of reaction is this ?

Nucleophiles attack Electrophiles

Reaction Types

What kind of reaction is the transformation shown below? an elimination reaction a rearrangement reaction a substitution reaction an addition reaction none of these

In the reaction shown below which is the electrophile? propene the H of HCl the Cl of HCl propane none of these all of these

In the reaction shown below which is the nucleophile? propene the H of HCl the Cl of HCl propane none of these all of these

Free Energy Diagrams What Does the TS (‡) Look Like ?

Which statement best describes the energetics of the reaction shown below? C2H4 + H2 → C2H6 exothermic with positive activation energy exothermic with negative activation energy endothermic with positive activation energy endothermic with negative activation energy cannot be determined without knowing BDE’s

On the reaction energy profile shown below which has the highest energy? II III IV V

On the reaction energy profile shown below which is the highest energy intermediate? II III IV V

On the reaction energy profile shown below which represents the slowest step? I to II II to III III to IV IV to V All steps proceed at the same rate

On the reaction energy profile shown below which represents the energy of the reaction? The energy difference between: I and II I and III II and III III and IV III and V I and V

Organic Rxns and Biological Rxns

Reaction Types

Addition to Pi Bonds (C=C)

Alkene (C=C) Nomenclature Name longest chain containing the double bond Number the chain so that 1. Double bond gets lowest #, then 2. Substituents get lowest #s Name as “(stereochem) - # - substituents - # -prefixene” Do ChemAct 6C Alkene Stereoisomers Read Models 9 -11 and answer CTQ 31-36

Assign stereochemistry of bonds a, b, & c E, Z, & E Z, Z, & E E, Z, & Z E, E, & E Neither, Z, & E Neither, E, & Z

CA 6C Alkene Stereoisomers Read Model 11 and answer CTQ 35-36.

Assign stereochemistry to bonds a, b Z, Z E, E E, Z Z, E Neither, E Neither, Z

CA 6C Alkene Stereoisomers Read Model 12 and answer CTQ 37.

What is the stereochemistry about bonds a, b? E, Z Z, E E, E Z, Z Neither, Z Neither, neither

CA 6C Alkene Stereoisomers Read Model 13 and answer CTQ 38. After naming, check with CTQ 37: only conformers have the same name! If the name differs only by E/Z, the molecules are configurational stereoisomers.

The more substituted the alkene the lower the energy (the more stable)

Alkene Stability (McMurry 7.6 ) Trans (E) more stable than cis (Z) Substitution increases stability (decreases PE)

Alkene Stability (PE) from ΔHHydrogenation C=C + H2 -> H-C-C-H

The George Hammond Postulate (McMurry 7.10) How does the stability of an intermediate (ΔG°) relate to the rate of the reaction (ΔG‡)? Postulate: the TS for an endergonic reaction step structurally resembles the product of that step. Thus: for an exergonic reaction, the TS resembles the reactant.

Which of the following represents a correctly drawn reaction mechanism?

Electrophilic Addition to Alkenes

Electrophilic Addition to Alkenes

Problems 5.6 and 5.7

Where are the electrophilic sites? Where are the nucleophilic sites?

Follow the arrows to the products

Two Reactions of Radicals R-H → R-H →

Radical Substitution The Mechanism

Radical Addition in Prostaglandin Synthesis

Polar Bonds and Polar Reactivity

Some Nucleophiles and Electrophiles

Nucleophiles and Electrophiles React !

C-H bond breaking in alkanes

How Can Bonds Be Broken and Made ?

Polar Reactions

Nucleophiles and Electrophiles

Problem 5.4 and 5.8