Ch. 4 - Alkanes and CycloalkanesWorksheetSee all chapters
All Chapters
Ch. 1 - A Review of General Chemistry
Ch. 2 - Molecular Representations
Ch. 3 - Acids and Bases
Ch. 4 - Alkanes and Cycloalkanes
Ch. 5 - Chirality
Ch. 6 - Thermodynamics and Kinetics
Ch. 7 - Substitution Reactions
Ch. 8 - Elimination Reactions
Ch. 9 - Alkenes and Alkynes
Ch. 10 - Addition Reactions
Ch. 11 - Radical Reactions
Ch. 12 - Alcohols, Ethers, Epoxides and Thiols
Ch. 13 - Alcohols and Carbonyl Compounds
Ch. 14 - Synthetic Techniques
Ch. 15 - Analytical Techniques: IR, NMR, Mass Spect
Ch. 16 - Conjugated Systems
Ch. 17 - Aromaticity
Ch. 18 - Reactions of Aromatics: EAS and Beyond
Ch. 19 - Aldehydes and Ketones: Nucleophilic Addition
Ch. 20 - Carboxylic Acid Derivatives: NAS
Ch. 21 - Enolate Chemistry: Reactions at the Alpha-Carbon
Ch. 22 - Condensation Chemistry
Ch. 23 - Amines
Ch. 24 - Carbohydrates
Ch. 25 - Phenols
Ch. 26 - Amino Acids, Peptides, and Proteins

Instead of being planar, cyclohexane twists into something called a chair conformation to reduce angle and torsional strain.   

Introduction to Chair Conformations

Concept #1: What is a chair conformation?

By twisting into a chair, angle strain and torsional strain are now effectively zero.

Chair Flips

Concept #2: How chairs flip from one conformation to another

In order to flip from one chair to another, the cyclohexane must first pass through a boat conformation (not stable due to flagpole interactions of hydrogens!). 

Axial and Equatorial Positions

Concept #3: How chairs flip from one conformation to another

  • Red = Axial. Follows the direction of the corner that it is on. Draw these first.
  • Blue = Equatorial. Goes in the slightly opposite direction of axials. Draw second.
Additional Problems
Ambroxol is a drug used to treat bronchopulmonary disease. Draw the structure of ambroxol in the alternative chair conformation. Which of the two conformations is more stable? 
A typical steroid skeleton is shown along with the numbering scheme used for this class of compounds. Specify in each case whether the designated substituent is axial or equatorial.  (a) Substituent at C-1 cis to the methyl groups 
Repeat Problem 3.40 for the stereoisomeric steroid skeleton having a cis ring fusion between the rst two rings. A typical steroid skeleton is shown along with the numbering scheme used for this class of compounds. Specify in each case whether the designated substituent is axial or equatorial.  (a) Substituent at C-1 cis to the methyl groups 
Draw the ring flip for each of the following compounds:
Draw the ring flip for each of the following compounds:
Provide an explanation for the surprising fact that all-trans-1,2,3,4,5,6-hexaisopropylcyclohexane is a stable molecule in which all isopropyl groups are axial. (You may find it helpful to build a handheld molecular model.)  
Below is the numbered skeleton of trans-decalin: Identify whether each of the following substituents would be in an equatorial position or an axial position: (a) A group at the C-2 position, pointing UP (b) A group at the C-3 position, pointing DOWN (c) A group at the C-4 position, pointing DOWN (d) A group at the C-7 position, pointing DOWN (e) A group at the C-8 position, pointing UP (f ) A group at the C-9 position, pointing UP
Consider the following tetra-substituted cyclohexane: (a) Draw both chair conformations of this compound.
A biosynthetic pathway was recently proposed for the polycyclic, cytotoxic compound aspernomine, isolated from the fungus Aspergillus nomius (J. Am. Chem. Soc. 2012, 134, 8078–8081): (c) Is the aromatic ring in an axial or equatorial position?
A biosynthetic pathway was recently proposed for the polycyclic, cytotoxic compound aspernomine, isolated from the fungus Aspergillus nomius (J. Am. Chem. Soc. 2012, 134, 8078–8081): (d) Consider the six-carbon acyclic substituent bound to one of the  bridgehead carbons. What is its relationship (axial or equatorial) to each of the chairs?
What is the conformation of the compound shown?
The all-trans-1,2,3,4,5,6-hexaethylcyclohexane ( 1) prefers the all-equatorial conformation while the all-trans-1,2,3,4,5,6-hexaisopropylcyclohexane (2) possesses a severely destabilized all-equatorial conformation (J. Am. Chem. Soc. 1990, 112, 893–894): (a) By examining a molecular model of cyclohexane with several all  trans-equatorial isopropyl groups and another model with several all-trans-equatorial ethyl groups, determine why adjacent equatorially oriented isopropyl groups experience severe steric interactions which are lacking in the ethyl case. Draw a chair conformation of the former case which illustrates these severe steric interactions. Also draw a Newman projection looking down one of the C—C bonds connecting the cyclohexyl ring to an equatorial isopropyl group and illustrate a conformation with severe steric strain.  
For the pair of molecules drawn below, choose the letter that corresponds to the  MORE STABLE  molecule. Does the UNSTABLE molecule chosen below have ANGLE STRAIN? Does the UNSTABLE molecule chosen below have TORSIONAL STRAIN? Does the UNSTABLE molecule chosen below have STERIC STRAIN?
Which of the following cyclohexanes could exist in a conformation with both methyls equatorial? A. cis-1,2-Dimethyl B. cis-1,4-Dimethyl C. trans-1,3-Dimethyl D. cis-1,3-Dimethyl E. None can have both methyls equatorial.
Draw the two chair conformations of molecules given below.
Is the methyl group axial or equatorial? A) Axial B) Equatorial
The axial groups in [1] are: The equatorial groups in [1] are: The axial groups in [2] are: The equatorial groups in [2] are: The axial groups in [3] are: The equatorial groups in [3] are: