4. Alkanes and Cycloalkanes

Which compound is more stable: cis-1-ethyl-2-methylcyclohexane or trans-1-ethyl-2-methylcyclohexane?

Draw the MOST STABLE conformation of cis-1-tert-butyl-4-methylcyclohexane.

Draw the LEAST STABLE conformation of trans-1-tert-butyl-3-neopentylcyclohexane.

Draw the most stable conformation of

c. cis-1-tert-butyl-4-isopropylcyclohexane.

Draw the most stable conformation of

b. 3-isopropyl-1,1-dimethylcyclohexane.

Draw the most stable conformation of

a. ethylcyclohexane.

Draw the two chair conformations of each compound, and label the substituents as axial and equatorial. In each case, determine which conformation is more stable.

c. cis-1-ethyl-3-methylcyclohexane

d. trans-1-ethyl-3-methylcyclohexane

Draw the two chair conformations of each of the following substituted cyclohexanes. In each case, label the more stable conformation.

a. cis-1-ethyl-2-methylcyclohexane

b. trans-1,2-diethylcyclohexane

The most stable form of the common sugar glucose contains a six-membered ring in the chair conformation with all the substituents equatorial. Draw this most stable conformation of glucose.

Table 3-6 shows that the axial–equatorial energy difference for methyl, ethyl, and isopropyl groups increases gradually: 7.6, 7.9, and 8.8 kJ/mol (1.8, 1.9, and 2.1 kcal/mol). The tert-butyl group jumps to an energy difference of 23 kJ/mol (5.4 kcal/mol), over twice the value for the isopropyl group. Draw pictures of the axial conformations of isopropylcyclohexane and tert-butylcyclohexane, and explain why the tert-butyl substituent experiences such a large increase in axial energy over the isopropyl group.

Draw the most stable conformation of

c. trans-1-tert-butyl-3-(1,1-dimethylpropyl)cyclohexane.

Draw the most stable conformation of

b. trans-1-tert-butyl-2-methylcyclohexane.

Draw the most stable conformation of

a. cis-1-tert-butyl-3-ethylcyclohexane.

a. Draw both chair conformations of cis-1,4-dimethylcyclohexane, and determine which conformer is more stable.

b. Repeat for the trans isomer.

c. Predict which isomer (cis or trans) is more stable.