1559T_ch05_70-9810/22/0520:19Pa9e77 EQA Keyso the Chopter·7刀 immediately visualize the mirror plane between them,and recognize them as mers.Similarly. CH H- Br- and H Br- H clearly lack Br without very thoroughly.The one important precaution here is never operate on more than one stereocenterat a time when interconverting Fischer projections. Examole:What is the relationship between the following structures:identical.enantiomeric.or diastereomeric? Br CH:- -Br and C1- CH: c- Procedure 1.Operate on the top stereocenter Br CHCICH CHCICH CHCICH Same as Structure 2 Twoswitches made the top stereocenr of1 identical to that of 2:therefore these carbons are identical in configuration. Keys to the Chapter • 77 immediately visualize the mirror plane between them, and recognize them as enantiomers. Similarly, clearly lack a mirror-image relationship and must be diastereomers. The hard part is determining, for example, the relationship between without getting all messed up (or taking forever to do it, and then getting all messed up). In short, you need to be able to move quickly and accurately among Newman, dashed-wedged line, and Fischer structures. This capability takes practice at visualizing three-dimensional structures from flat drawings and requires applica￾tion of a couple of specific techniques. The text covers comparison and interconversion of Fischer projections very thoroughly. The one important precaution here is never operate on more than one stereocenter at a time when interconverting Fischer projections. Example: What is the relationship between the following structures: identical, enantiomeric, or diastereomeric? Procedure: 1. Operate on the top stereocenter. Two switches made the top stereocenter of 1 identical to that of 2; therefore these carbons are identical in configuration. Cl CHClCH3 CH3 Br Structure 1 CH3 CHClCH3 Cl Br Br CHClCH3 Cl CH3 Same as Structure 2 Switch Cl, CH3 Switch CH3, Br Cl CH3 CH3 Br H Structure 1 Structure 2 and Cl Br H CH3 CH3 Cl Cl Cl Br CH3 H H CH3 Br C C and H H CH3 CH3 Cl CH3 CH3 H Cl H and CH3 CH3 H H Cl Br Br 1559T_ch05_70-98 10/22/05 20:19 Page 77