lllustratlng Newman Projection Formulas in Large Classes Newman projection formulas are used to illustrate conformational isomers. Upon their first introduction to these formulas. many students invariably ask "Where is the other carbon?' If Studems are shown a molecular model of the compound whose conformatianal isomers are beino examined. thav. can oenerallv graspthe tact lnat the circle 01 the heuman projection represents two caroons. a trontanda rear caroon however, h a large class it is a1111c~It 0, even impDrSio e to orient lne model so Inat each student can view directly down the carbon-carbon bond being examined. In such situations, an overhead projector solves the problem. If a model of ethane is placed directly on the overhead pmiector surface with one carbon directly above the other (a) the image mat appears on the screen looks very much like the apprapriate Newman projection, (b) and (c). The hydrogens on the carbon closer to the projectorsulfaceare in sharper focus than the hydrogens on the mwe distant carbon, so the identity of the hydrogen can be readily ascertained. Rotation about the carboncarbon bond shows clearly staggered (b) end eclipsed (c) conformational isomers. Bail and stick molecular models from SargentWelch 15-61815) are a convenient size to use.
Stella D. Elakovlch Universihlof Southern Mississbpi
570
Journal of Chemical Education
