1. Cycloalkanes

2. Cycloalkanes
Cycloalkanes: An alkane that contains a ring of carbon atoms. Ring sizes from 3 carbons to 30 or higher
If the carbon chain that forms the straight-chain hydrocarbon - - is long enough, the two ends coming together to form
a cycloalkane.
- One hydrogen atom has to be removed from each end of the hydrocarbon chain to form the CC bond that closes the
ring.
- Cycloalkanes therefore have two less hydrogen atoms than the parent alkane and a generic formula of CnH2n.

3. Examples of cycloalkanes
- The smallest alkane that can form a ring is cyclopropane, C3H6, in which the three carbon atoms lie in the same plane.
- The angle between adjacent CC bonds is only 60° as seen in the model below:

4. Nomenclature of Cycloalkanes
- The prefix cyclo- is added to the name of the alkane with the
same number of carbons
- When one substituent is present it is assumed to be at position one and is not numbered
- When two alkyl substituents are present the one with alphabetical priority is given position 1
- Numbering continues to give the other substituent the lowest number
Hydroxyl has higher priority than alkyl and is given position 1-
If a long chain is attached to a ring with fewer carbons, the cycloalkane is considered the substituent
Chapter 4

5. 1. No number is needed for a single substituent on a ring
2. Name the two substituents in alphabetical order

11. Chapter 4

12. Summary: Types of Strain
Angle strain - expansion or compression of bond angles away from most stable 109.5o
Torsional strain - eclipsing of bonds on neighboring atoms
Steric strain - repulsive interactions between nonbonded atoms in close proximity
Total strain for cyclopropane = angle strain + torsional strain

13. Conformations of Cycloalkanes
Cyclopropane
3-membered ring must have planar structure
Symmetrical with C–C–C bond angles of 60°
Requires that sp3 based bonds are bent (and weakened)
All C-H bonds are eclipsed

14. Cyclobutane
Cyclobutane has less angle strain than cyclopropane but more torsional strain because of its larger number of ring hydrogens
Cyclobutane is slightly bent out of plane - one carbon atom is about 25° above
The bend increases angle strain but decreases torsional strain