1. Monosubstituted Cyclohexanes
Substituents can occupy an axial or equatorial position
Equatorial is preferred by larger groups. Why?
7.3 Monosubstituted Cyclohexanes. Conformational Analysis

2. 1,3-Diaxial Interactions
1,3-Diaxial Interactions: van der Waals repulsions between an axial substituents on a cycloalkane ring

6. Problems
What is the energy cost of a 1,3-diaxial strain in methylcyclohexane?
What about bromocyclohexane?
Which of the two molecules above will have a higher percentage of its molecules in the equatorial conformation?

7. More on Ring Flip
Note that the “up” substituent remains up and the “down” substituent remains down after chair interconversion

8. Disubstituted Cyclohexanes 1-chloro-2-methylcyclohexane
Trans: the two groups have an up-down relationship
Cis: the two groups have a down-down (or up-up) relationship

9. Conformational Analysis
For disubstituted derivatives, the larger group will preferentially occupy the equatorial position
7.4 Disubstituted Cyclohexanes

10. Problem
Which subsituent will most likely occupy the equatorial position for a greater amount of time in cis-1-chloro-2-methylcyclohexane?
Prove this with calculation.

11. Polycyclic Molecules
Polycyclic molecules: compounds with two or more rings fused together
Spirocyclic: two rings that have only a single common atom
Bicyclic: two rings that share two or more common atoms

12. 7.6 Bicyclic and Polycyclic Compounds

13. Classification and Nomenclature
Fused and bridged bicyclic compounds
7.6 Bicyclic and Polycyclic Compounds

14. Naming Bicyclic Systems
Indicate the number of rings using the prefix “bicyclo-”
Indicate the bridge lengths
Number of atoms connecting one bridgehead atom to another (excluding the bridgehead atoms)
Separate by full periods and place in square brackets.
Cited in decreasing order of size (e.g. [3.2.1])
the name of the hydrocarbon indicating the total number of skeletal atoms

15. Problems Name the following polycyclic molecules:
If you were just given the IUPAC names for a couple of bicyclic molecules, how would you tell the difference between a fused and a bridged variety?
Norbornane
Decalin

16. Cis and Trans Ring Fusion: Decalin
7.6 Bicyclic and Polycyclic Compounds

17. Each ring in cis-decalin can undergo ring flip
Ring fusion causes trans-decalin to be conformationally locked

18. Ring Fusion with Small Rings
Bicyclic compounds with small rings are restricted to cis ring fusion
Trans fusion would incur too much ring strain
7.6 Bicyclic and Polycyclic Compounds

19. Steroids Organic compounds with 20 carbon, tetracyclic core
Variations in substituents dictate biological activity
7.6 Bicyclic and Polycyclic Compounds

20. Many consist of all trans-fused rings
Steroids
Many consist of all trans-fused rings
No conformational change
Many have methyl groups at C-10 and C-13
7.6 Bicyclic and Polycyclic Compounds

22. Stereochemistry of Cycloalkene Reactions Addition Reactions
Syn-addition:
Anti-addition:
7.9 Stereochemistry of Chemical Reactions

23. Stereochemistry of Bromine Addition
Addition of bromine to an alkene is a highly stereoselective reaction
Exclusively anti-addition
Gives all trans products
7.9 Stereochemistry of Chemical Reactions

25. Stereochemistry of Halohydrin Formation
Exclusively anti-addition
Gives all trans products

26. Stereochemistry of Hydroboration-Oxidation
Hydroboration is a stereospecific syn-addition
7.9 Stereochemistry of Chemical Reactions

28. Stereochemistry of Hydroboration-Oxidation
The oxidation of organoboranes is a stereospecific substitution reaction
7.9 Stereochemistry of Chemical Reactions

29. Stereochemistry of Hydroboration-Oxidation
The two steps of hydroboration-oxidation result in net syn-addition of H-OH to the alkene
Note that the trans designation of the name has nothing to do with the way H-OH added
7.9 Stereochemistry of Chemical Reactions

30. Stereochemistry of Hydrogenation
Catalytic hydrogenation is a stereospecific syn-addition
7.9 Stereochemistry of Chemical Reactions

31. Problem
Draw the products for the following reactions