1559r.ch05_70-9010/2/0s20:19Page80 80.Chapter 5 STEREOISOMERS 5-7.Stereochemistry in Chemical Reactions 5-8.Resolution of Enantiomers The most common labo ratory tiomer of a molecule tha ih th your rac ure.The d55 mo with more than one stereocenter) Solutions to Problems 26.Chiral:(b)(c:fan blades are always twisted!).(d).(e).(h).Achiral:(a).(f).(g).(i).(j).(k).(1).All the achiral objects contain a plane of symmetry: yz symmetry plane y symmetry plane 'If you ignore the mounting hinges,then doors are achiral.The plane of a door is a symmetry plane 27.(a)Enantiomers (b)Enantiomers (e)Diastereomers (d)Identical (if one pair is flipped over intact.it becomes superimposable with the other pair) 28.(a)Constitutional (structural)isomers (b)Identical (one is the other turned upside-down) (e)Constitutional isomers (d)Conformers (e)Constitutional(structural)isomers (f)Stereoisomers(enantiomers) (g)Conformers (h)Stereoisomers (enantiomers) If two conformational isomers are cooled to a temperature low enough to prevent their interconversion by or oth notion,then they can be de structures with the same (d) osable miror image model!).Thos n ()they are still ster ome peratu d to stereoisomers.80 • Chapter 5 STEREOISOMERS 5-7. Stereochemistry in Chemical Reactions The apparent complexity of this section is due to the number of situations that are explained in detail. The ma￾terial actually develops very naturally, with no special pitfalls. 5-8. Resolution of Enantiomers The most common laboratory method to separate enantiomers is presented. What is required is a pure enan￾tiomer of a molecule that reacts with the molecules of your racemic mixture. The procedure outlined is a straightforward application of the ideas in Sections 5-2 (properties of chiral molecules) and 5-5 (molecules with more than one stereocenter). Solutions to Problems 26. Chiral: (b)*, (c; fan blades are always twisted!), (d), (e), (h). Achiral: (a), (f), (g), (i), (j), (k), (l). All the achiral objects contain a plane of symmetry: * If you ignore the mounting hinges, then doors are achiral. The plane of a door is a symmetry plane. 27. (a) Enantiomers (b) Enantiomers (c) Diastereomers (d) Identical (if one pair is flipped over intact, it becomes superimposable with the other pair) 28. (a) Constitutional (structural) isomers (b) Identical (one is the other turned upside-down) (c) Constitutional isomers (d) Conformers (e) Constitutional (structural) isomers (f ) Stereoisomers (enantiomers) (g) Conformers (h) Stereoisomers (enantiomers) If two conformational isomers are cooled to a temperature low enough to prevent their interconversion by bond rotation or other motion, then they can be described as stereoisomers: structures with the same connectivity but with different atomic arrangements in three dimensions. For example, the conformers in (d) are nonsuperimposable mirror images (enantiomers) if bond rotation is not allowed to occur (make a model!). Those in (g) are not enantiomers, but they are still stereoisomers. The temperatures required to “freeze out” conformational interconversion are very low: on the order of 200ºC for substituted ethanes and 100ºC for cyclohexanes. Conformers of these types are occasionally referred to as interconvertible stereoisomers. Knife xy symmetry plane y x z Spoon yz symmetry plane y x z 1559T_ch05_70-98 10/22/05 20:19 Page 80