4. Alkanes and Cycloalkanes

Calculate the difference in Gibbs free energy between the alternative chair conformations of trans-4-iodo-1-cyclohexanol. 

Calculate the difference in Gibbs free energy between the alternative chair conformations of cis-2-ethyl-1-phenylcyclohexane. 

Calculate the energy difference between the two chair conformers of trans-1,4-dimethylcyclohexane.

What is the energy difference between the two chair conformers of cis-1,4-dimethylcyclohexane?

One of the chair conformers of cis-1,3-dimethylcyclohexane is 5.4 kcal/mol less stable than the other. How much steric strain does a 1,3-diaxial interaction between two methyl groups introduce into the conformer?

Calculate the energy difference between each pair of conformations shown by drawing and comparing Newman projections down the indicated bonds in each.

(b)

Calculate the energy difference between the two chair conformers of trans-1,2-dimethylcyclohexane.

Draw the conformers for the following trisubstituted cyclohexane. Calculate the strain energy of each conformer. (The gauche interaction between a methyl and an ethyl group is 0.96 kcal/mol; the 1,3-diaxial interaction between a methyl and an H is 0.87 kcal/mol and between an ethyl and an H is 1.00 kcal/mol.)

Given that the free energy of the twist-boat conformer of cyclohexane is 5.3 kcal/mol greater than that of the chair conformer, calculate the percentage of twist-boat conformers present in a sample of cyclohexane at 25 °C. Does your answer agree with the statement made in Section 3.13 about the relative number of molecules in these two conformations?

a. Draw the two chair conformations of cis-1,3-dimethylcyclohexane, and label all the positions as axial or equatorial.

b. Label the higher-energy conformation and the lower-energy conformation.

c. The energy difference in these two conformations has been measured to be about 23 kJ (5.4 kcal) per mole. How much of this energy difference is due to the torsional energy of gauche relationships?

d. How much energy is due to the additional steric strain of the 1,3-diaxial interaction?

The chair conformer of fluorocyclohexane is 0.25 kcal/mol more stable when the fluoro substituent is in an equatorial position than when it is in an axial position. How much more stable is the anti conformer than a gauche conformer of 1-fluoropropane, considering rotation about the C1−C2 bond?