Question #5: Conformations of trans- and cis-1,4-dimethylcyclohexane A. Using your molecular modeling kit, construct trans-1,4-dimethylcyclohexane. In the space below, draw one of the chair conformations. Label the methyl groups as either axial (a) or equatorial (e). Number the carbons of the cyclohexane ring, perform a chair flip and draw the new chair conformation. B. Construct trans-1,4-dimethylcyclohexane in Avogadro using the steps listed. In Avogadro, construct cyclohexane. Optimize the geometry so that the ring is in the chair conformation. It may take a few attempts to obtain the chair cyclohexane. Place a methyl group in the axial position on carbon-1 of the ring. Next, place a methyl group on carbon-4 of the ring, making sure that the trans conformation is represented. Is this group axial or equatorial? Calculate the energy of the compound and record the value in the table. Delete the methyl groups, and optimize the cyclohexane again. Now place a methyl group in an equatorial position on carbon-1 of the ring. Place a second methyl group on carbon-4 of the ring, making sure the trans conformation is represented. Optimize the geometry and calculate the energy of the compound. Record the energy of this trans conformation in the table. Which chair is higher in energy? Carbon-1 methyl position Carbon-4 methyl position axial equatorial C. Using your molecular modeling kit, construct cis-1,4-dimethylcyclohexane. In the space below, draw one of the chair conformations. Label the methyl groups as either axial (a) or equatorial (e). Number the carbons of the cyclohexane ring, perform a chair flip and draw the new chair conformation. D. Using Avogadro, construct cis-1,4-methylcyclohexane In Avogadro, construct cyclohexane. Optimize the geometry so that the ring is in the chair conformation. It may take a few attempts to obtain the chair cyclohexane Place a methyl group in the axial position on carbon-1 of the ring. Next, place a methyl group on carbon-4 of the ring, making sure that the cis conformation is represented. Calculate the energy of the compound and record the value in the table. Delete the methyl groups, and optimize the cyclohexane again. Energy (kJ/mol) Now place a methyl group in an equatorial position on carbon-1 of the ring. Place a second methyl group on carbon-4 of the ring, making sure the cis conformation is represented. Optimize the geometry and calculate the energy of the compound. Record the energy of this trans conformation in the table. Which chair is higher in energy? Carbon-1 methyl position axial equatorial Carbon-4 methyl position 53 Energy (kJ/mol) E. Of all the chair conformations from question #5, which is the lowest in potential energy? Which is more stable, the cis or the trans isomer? Explain.