Ch. 4 - Alkanes and CycloalkanesSee 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

Solution: 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.  

Problem

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.