Chapter 5

Draw the staggered conformations of each of the following compounds using the indicated convention: a. 2,3 -dimethylbutane (sawhorse) b. 1,2 -dibromo-1,1,2,2-tetrafluoroethane (Newman) c. the \(d, l\) isomers of 1 -chloro-1-fluoroethane (Newman)

Draw the conformation of 2,2,5,5-tetramethylhexane that you expect to be of lowest energy.

Write structures for all the configurations possible for 2,4-dibromopentane. Which stereoisomers are enantiomers? Which are diastereomers? What combination of isomers would give a racemic mixture? Which isomer is achiral?

From the compounds listed select all those that may have achiral meso configurations and draw the configurations for each of them. a. 1,2-dichlorocyclopropane b. 1,4 -dichlorocyclohexane c. 1,3 -dichlorocyclohexane d. 2,3-dichloropentane e. \(2,3,4\) -trichloropentane f. \(2,3,4,5\) -tetrachlorohexane

Which of the following compounds could exist as cis-trans configurational isomers? a. 1,2 -dibromoethane b. 2,3-dibromopropene c. dibromoethyne d. 1,3-dibromopropene

Which of the following compounds can exist as (1) a pair of enantiomers, (2) a pair of cis-trans isomers, and (3) as a cis pair of enantiomers and a trans pair of enantiomers? a. 3-chloro-1-butyne b. 4 -chloro-1-butyne c. 1 -chloro-1,3-butadiene d. 2 -chloro-1,3-butadiene e. 4 -chloro-2-pentene f. 5-chloro-2-pentene

Write structural formulas showing configuration for all of the possible cis- trans isomers of the following compounds: a. 1,2,3-trimethylcyclopropane b. 1,3-dichlorocyclopentane c. 3-methyl-2,4-hexadiene d. 1 -(3-methylcyclobutyl)-3-methylcyclobutane

Would you expect cis- or trans-1,2-dimethylcyclopropane to be the more stable? Explain.

Draw suitable formulas for all of the position and configurational isomers possible (include optical isomers but not conformational isomers) for the following compounds of molecular formula: a. \(\mathrm{C}_{3} \mathrm{H}_{5} \mathrm{Cl}\) (five) b. \(\mathrm{C}_{5} \mathrm{H}_{10}\) (thirteen) c. \(\mathrm{C}_{4} \mathrm{H}_{7} \mathrm{Cl}\) (nineteen)

Determine which of the following compounds are chiral and which are achiral. Indicate each chiral atom with an asterisk \(\left(^{*}\right)\), noting that more than one may be present in some examples. a. 2,3-dimethylpentane b. 2,3 -dimethyl-2-pentene c. 2 -bromo-3-chlorobutane

Write structures that fit the following descriptions: a. An achiral isomer of dimethylcyclohexane that has the methyl groups on different carbons. b. All the chiral isomers of formula \(\mathrm{C}_{5} \mathrm{H}_{12} \mathrm{O}\). c. A compound of formula \(\mathrm{C}_{4} \mathrm{H}_{5}\) Cl that has just one double bond and is chiral. d.* The conformation of 2,5-dimethylhexane you would anticipate to be the most stable.

Draw structures for all the possible configurational isomers of the following compounds. In Part a, D stands for deuterium, the hydrogen isotope of mass 2 . a. ethene- \(1,2-\mathrm{D}_{2}\) (1,2-dideuterioethene) b. 3-phenoxy-1-butene c. 4 -iodo- 2 -pentene d. 2 -chloro-3-phenylbutane e. 2,3 -diphenylbutane f. 3-chlorocyclohexene g. 3-chlorocyclooctene (use models) h. 4-chloromethylcyclohexane i. 3-chloromethylcyclohexane j. 1 -methyl-4-(1-propenyl)cyclohexane k. 1 -methyl-3-(1-propenyl)cyclohexane

This problem is designed to illustrate chirality, asymmetry, and dissymmetry with simple models or common objects. a. Bend three pieces of wire into a hair-pin shape with equal legs. Now take one piece and make a \(90^{\circ}\) bend in one of the legs in the middle to give (1). Bend up both legs equally of another piece to give (2), and one up and the other down to give (3). Determine whether (1), (2), and (3) are chiral or achiral, and asymmetric, dissymmetric, or symmetric. b. Classify each of the following as chiral, achiral, asymmetric, dissymmetric, or symmetric: a cup, a shirt, a bicycle, a tennis racket, an automobile, a penny, a pair of scissors, a flat spiral (4), and a conical spring (5). Indicate any ambiguities that may be involved.