Chapter 12

Write expanded structures showing the \(C-C\) bonds for each of the following condensed formulas. Name each substance by the IUPAC system. a. \(\left(\mathrm{CH}_{2}\right)_{10}\) b. \(\left(\mathrm{CH}_{2}\right)_{5} \mathrm{CHCH}_{3}\) c. \(\left(\mathrm{CH}_{3}\right)_{2} \mathrm{C}\left(\mathrm{CH}_{2}\right)_{6} \mathrm{CHCH}_{2} \mathrm{H}_{5}\) d. the position and configurational isomers of trimethylcyclobutane e. \(\left(\mathrm{CH}_{2}\right)_{6} \mathrm{CHCH}_{2} \mathrm{C}\left(\mathrm{CH}_{3}\right)_{2} \mathrm{CH}_{2} \mathrm{Cl}\) f. \(\left[\left(\mathrm{CH}_{2}\right)_{2} \mathrm{CH}\right]_{2} \mathrm{C}\left(\mathrm{CH}_{3}\right) \mathrm{C}_{2} \mathrm{H}_{5}\)

Using the sawhorse convention, draw the possible conformations of chlorocyclohexane with the ring carbons in the planar, in the chair, and in the extreme boat forms. Arrange these in order of expected stability. Show your reasoning.

Draw the preferred conformation of each of the following: a. isopropylcyclohexane b. cyclohexylcyclohexane

Draw the possible chair conformations of trans- and cis-1,3-dimethylcyclohexane. Is the cis or the trans isomer more likely to be the more stable? Explain.

Investigate the thermodynamic feasibility of the following propagation steps for opening the rings of cycloalkanes with \(n=2\) to \(n=6\) by a radical-chain mechanism: $$ \begin{array}{c} \left(\mathrm{CH}_{2}\right)_{n}+\mathrm{Br} \cdot \rightarrow \mathrm{BrCH}_{2}-\left(\mathrm{CH}_{2}\right)_{n-2}-\mathrm{CH}_{2} \\ \mathrm{BrCH}_{2}-\left(\mathrm{CH}_{2}\right)_{n-2}-\mathrm{CH}_{2} \cdot+\mathrm{Br}_{2} \rightarrow\left(\mathrm{CH}_{2}\right)_{n-2}\left(\mathrm{CH}_{2} \mathrm{Br}\right)_{2}+\mathrm{Br} \end{array} $$ Use 83 kcal \(\mathrm{mol}^{-1}\) for the bond-dissociation energy of a normal \(\mathrm{C}-\mathrm{C}\) bond and \(68 \mathrm{kcal} \mathrm{mol}^{-1}\) for the bond-dissociation energy of a \(\mathrm{C}-\mathrm{Br}\) bond. (An easy way to solve a problem of this type is first to calculate \(\Delta H\) of each step for cyclohexane, for which there is no strain, then to make suitable corrections for the strain that is present for smaller values of \(n .\) )

Space-filling models (Section \(2-2 B\) ) indicate that the chiral forms of trans-cyclopentadecene are likely to be readily interconverted at room temperature. How and where might trans-cyclopentadecene be substituted to give stable chiral forms that possess a chiral center but no chiral carbon atoms?

Draw a sawhorse-style formula for bicyclo[1.1.0]butane and formulas for all of the eight possible dichlorobicyclo[1.1.0]butanes (including chiral forms).

How could you phrase Bredt's rule so it could distinguish between the lack of stability of 16 and the stability of bicyclo[5.5.0]-1,2-decene, both compounds having a double-bonded carbon at a ring junction?

Write structural formulas for substances (one for each part) that fit the following descriptions. Make sawhorse drawings of the substances for which conformational problems are involved. a. a compound of formula \(\mathrm{C}_{4} \mathrm{H}_{8}\) that reacts slowly with sulfuric acid and also with bromine (light induced) b. the most highly strained isomer of \(\mathrm{C}_{5} \mathrm{H}_{10}\) c. the possible products from treatment of 1 -ethyl-2-methylcyclopropane with bromine (light-induced) d. the least-stable chair and the least-stable boat conformations of cis \(-1,4\) -dichlorocyclohexane e. the most stable geometrical isomer of 1,3 -di-tert-butylcyclobutane f. a compound with a six-membered ring that is most stable with the ring in a boat form g. trans-bicyclo[7.1.0]decane h. the most stable conformation of trans \(-1,3\) -di-tert-butylcyclohexane i. the most stable conformation of cis-2-tert-butyl-cis-decalin j. a boat-boat conformation of cis-decalin k. trans, trans,trans-tricyclo[8.4.0.0^{2,7} ] tetradecane

Draw structural formulas in reasonable perspective for each of the following substances: a. the cis and trans isomers of bicyclo[3.3.0]octane b. trans-tricyclo \(\left[3.1 .0 .0^{2,6}\right]\) hexane c. tricyclo[ \(3.1 .0^{2,6}\) ]hexane d. trans \(-2,6\) -dichlorobicyclo[2.2.2] octane e. quinquecyclo \(\left[4.4 .0 .0^{2,5} .0^{3,9} .0^{4,8}\right]\) decane

Draw each of the following compounds in perspective to show the preferred conformation. Construct models if in doubt. a. 2 -tert-butyl-trans-decalin b. bicyclo[2.2.2] octane c. spiro[5.4]decane d. trans-3-phenyl-1-methylcyclohexane