1. Chapter 3 - Alkenes

2. Change the suffix from ane to ene
Naming Alkenes
Change the suffix from ane to ene

3. Naming Alkenes The longest chain must include the double bond
Chain is numbered to give the double bond carbons the lowest numbers
Numbers indicating location of double bond are placed before chain length

4. Double bond gets precedence over substituents
Naming Alkenes
Double bond gets precedence over substituents

5. For more than one double bond
Naming Alkenes
For more than one double bond
use diene, triene etc

6. Double bond in a cyclic always get
Naming Alkenes
Double bond in a cyclic always get
numbers 1 and 2

7. Naming Subtleties

8. Terms Vinylic carbons – sp2 carbons
Allylic carbons – ones next to the vinylic carbons

9. Energy for single bond 2.9 kcal/mol for double 62 kcal/mol
Alkenes
Double bond locks the molecule and there is no rotation about the double bond
Energy for single bond 2.9 kcal/mol for double 62 kcal/mol

10. Lowest Energy
The Second Bond Must Break (Promote Electrons to the Antibonding Orbital). Then it Can Rotate

11. Different Molecules
The connections are the same, but that’s about all!!!

12. Cis/Trans – Just Not Good Enough

13. Configuration - E,Z

14. E/Z Rules Assign priority based on the higher atomic number
Increasing priority

15. E/Z Rules
If priority cannot be assigned on the basis of the atoms bonded to the CARBON, look to the next set of atoms. Priority is assigned at the first point of difference.

16. E/Z Rules
When a double or tripple bond shows up, count it as though there are two or three of the same atom

17. E/Z nomenclature

18. Thermodynamics and Kinetics How Far and How Fast
Description of a reaction at equilibrium (Keq)
Kinetics
Description of rates of a chemical reaction
rate = k [A] [B]2 / [C]0

19. For The Following Energy Discussion, Consider this Reaction

20. Energy considerations
Mechanisms describe bond breaking-bond making

21. Energy considerations
Exergonic vs. Endergonic Reactions
( Note: The more stable the species, the lower its energy. )
Ok, OK, OK, - What is exergonic and endergonic? Isn’t that supposed
To be exothermic and endothermic???? Next slide!!!!!!!!

22. Energy Terms DGo = DHo - TDSo
Endergonic and Exergonic describe the free energy used or expelled from a reaction.
Endothermic and exothermic describe the heat ΔH used or expelled from a reaction
DGo = DHo - TDSo
G and H are often close to the same unless
you have a large temperature value
For almost all normal processes the +/- value
of G and H will be the same

23. Energy considerations
DGo , Gibbs free energy change…
Predicts whether a reaction will happen “spontaneously”
Exergonic reactions = - DGo  (spontaneous)
Endergonic reactions = + DGo 

24. DHo = energy bonds broken - energy bonds formed

25. Calculate ΔH DHo = energy bonds broken - energy bonds formed
Notice the table doesn’t list the breaking of the pie bond without the breaking of the sigma bond. This value is 62 kcal/mol.
DHo = energy bonds broken - energy bonds formed

26. Where are Calculations Valid
Just in the Gas Phase
The solvent makes a difference!
Solvents can have a large effect on DH
Water can solvate cations +++ or anions - - -

27. Rate of Reaction The number of collisions/time
Rate depends on:
The number of collisions/time
Fraction of collisions with sufficient energy
Fraction of collisions with proper orientation

28. Kinetics
Energy of Activation, Ea (or DG**)
Fast vs. Slow reactions:

29. Organic Chemistry Lingo
Kinetic Product : formed most rapidly
Thermodynamic Product: most stable product
Many times the Kinetic Product is the Thermodynamic Product!

30. Thermodynamic vs. Kinetic Control
If the kinetic product and thermodynamic product differ, the major product will depend on reaction conditions.
If carried out at mild (low-temp) conditions, the reaction will be irreversible and the kinetic product will be favored.

31. Thermodynamic vs. Kinetic Control
If carried out at sufficiently vigorous (hi-temp) conditions, the reaction will be reversible and the thermodynamic product will be favored.

32. Thermodynamic vs. Kinetic Control
Kinetic product and thermodynamic product:
Formed fastest
Most stable

33. Reaction Coordinate Diagrams
Intermediate = product of one step, becomes reactant of next step
Transition state = intermediate that cannot be isolated (partially formed bonds, highest energy structures!)
Rate determining step = step with highest energy
Transition state

34. Reaction Coordinate Diagrams
1) How many intermediates are there?
2) Is the first formed intermediate more apt to revert to reactants or go on to form products?
3) Which step in the reaction is the rate determining?
4) Is the reaction endergonic or exergonic? What is the sign of Go?
5) Which step has the greatest free energy of activation?
6) Where are the transition states?

35. Reaction Order
First Order Reaction – reaction is proportional to the concentration of one reactant
Second Order Reaction – reaction that is proportional to the concentration of two reactants