Question 11 of 17 > Macmillan Learning Given the planar trisubstituted cyclohexane, fill in the missing substituents (with H, Cl or Br) to complete the two possible cyclohexane chair conformations. Then, determine the more stable conformer. You might find it helpful to make a model of the cyclohexane to help visualize the chair conformations. CI Br H H H H H Chair 1 Which is the more stable conformer? Chair 2 Chair 1 H H chair flip H H H H Answer Bank Chair 2 H Br

Gibbs free energy differences between axial-substituted and equatorial-substituted chair conformations of cyclohexane were given in Table 2.4. (a) Calculate the ratio of equatorial to axial tert-butylcyclohexane at 25C. (b) Explain why the conformational equilibria for methyl, ethyl, and isopropyl substituents are comparable but the conformational equilibrium for tert-butylcyclohexane lies considerably farther toward the equatorial conformation.

Following is a chair conformation of cyclohexane with the carbon atoms numbered 1 through 6. (a) Draw hydrogen atoms that are above the plane of the ring on carbons 1 and 2 and below the plane of the ring on carbon 4. (b) Which of these hydrogens are equatorial? Which are axial? (c) Draw the alternative chair conformation. Which hydrogens are equatorial? Which are axial? Which are above the plane of the ring? Which are below it?

Draw the most stable conformation of 1,4-dichlorobutane, using wedges and dashes to represent bonds coming out of the paper and going behind the paper, respectively.

Following are structural formulas for 1,4-dioxane and piperidine. 1,4-Dioxane is a widely used solvent for organic compounds. Piperidine is found in small amounts in black pepper (Piper nigrum). (a) Complete the Lewis structure of each compound by showing all unshared electron pairs. (b) Predict bond angles about each carbon, oxygen, and nitrogen atom. (c) Describe the most stable conformation of each ring and compare these conformations with the chair conformation of cyclohexane.

11. s) Draw the most stable conformation of 1,3-dichloro-2,4-difluorocyclohexane: 12. Which of the following represents the most stable conformation of 1,2,4,5- tetramethyleyclohexane? (one correct answer) CH b) CH HC H- H- CH HC CH, CH 6. Give IUPAC name for the following molecule. Include "cis" and "trans" designations if applicable. H2C-CH3 H -CH2 H- H Br

5. Draw the two chair conformations ("ring filips") of trans –1- ethyl-4-methylcyclohexane to show the axial and equatorial substituents (including all hydrogens). Then determine which of the two conformations is more stable and why.

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Construct the chair structures with the molecular models for trans-1-ethyl-3-methylcyclohexane. Find the energy of each conformer, the equilibrium constant Keq, and the percentage of each conformer at 25oC. Indicate which conformer is more stable.

Cyclohexane derivatives exist primarily in the most stable of the available chair conformations. Give the position, axial or equatorial, of each of the three groups shown when the ring is in the most stable chair conformation. If a group divides its time equally between axial and equatorial positions, indicate this with ax/eq.