4. Alkanes and Cycloalkanes

Draw the two chair conformers for each of the following and indicate which conformer is more stable:

b. trans-1-ethyl-2-methylcyclohexane

Draw the two chair conformers for each of the following and indicate which conformer is more stable:

d. cis-1,2-diethylcyclohexane

Draw the more stable chair conformer of cis-1-ethyl-2-methylcyclohexane.

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

Draw the most stable chair conformation for the following trisubstituted cyclohexane.

In contrast to ethane and other alkanes studied in this chapter, there is no free rotation around any bonds in cyclopentane (shown below). Why?

For each of the following structures, draw the most stable chair conformer.

a.

b.

For each pair, indicate which conformer is more stable.

When a pyranose is in the chair conformation in which the CH2OH group and the C-1 OH group are both in axial positions, the two groups can react to form an acetal. This is called the anhydro form of the sugar (it has 'lost water'). The anhydro form of d-idose is shown here. Explain why about 80% of d-idose exists in the anhydro form in an aqueous solution at 100 °C, but only about 0.1% of d-glucose exists in the anhydro form under the same conditions.

Draw the two chair conformers for each of the following and indicate which conformer is more stable:

e. cis-1-ethyl-3-isopropylcyclohexane

For each of the following compounds, determine whether the cis isomer or the trans isomer is more stable.

a.

b.

c.

Predict which side of the equilibrium is favored for each of the chair–chair interconversions (ring flips) shown.

(c)

Predict which side of the equilibrium is favored for each of the chair–chair interconversions (ring flips) shown.

(a)

Which of the following conformers has the highest energy (is the least stable)?