Sawhorse diagrams

Recalling that the addition of Br2 to alkenes occurs with anti stereochemistry, rotate the sawhorse diagram so that the bromines are anti to each other ... 

In addition to Fischer and perspective diagrams, physical organic chemists use Newman and sawhorse diagrams to show conformations as well as configurations of two-centre compounds. 

Saccharic acids. See Aldaric acids Saccharin, 997 Salicylic acid, 737 acetylation of, 952 acidity of, 953 synthesis of, 952-954 Samuelsson, Bengt, 1025 Sandmeyer reactions, 892, 894, 906—907, 919 Sanger, Frederick, 1070—1074, 1101—1102 Sanger s reagent. See l-Fluoro-2,4-dinitrobenzene a-Santonin, 1046 Saponification, 794—799 Sawhorse diagrams, 90—91 Saytzeff. See Zaitsev, Alexander M. Schiemann reaction, 892, 893, 905 Schiff s base, 673, 689. See also Imines Schrbdinger, Erwin, 7 Schrbdinger equation. See Wave equation Scientific method, 217... 

In the sawhorse diagram used in Figure 8.2, a focus on 1 and 3 shows the molecule is tilted at an angle to show both carbon atoms as well as the groups... 

Figure 8,2 Rotation about the carbon-carbon bond in ethane using sawhorse diagrams.

In contrast to 3 or 9, sawhorse diagram 4 and Newman projection 10 show a rotamer where the hydrogen atoms (and the bonds attaching them to the carbons) eclipse each other. The hydrogen atom on the front and top (red H) and the hydrogen atom on the rear and top in 10 line up one behind the other... 

Draw the sawhorse diagram of syn- and anti-2,2,5,5-tetramethylhexane sighting down the C3-C4 bond. If you have access to a computer modehng program, convert this structure to its 3D structure (both a ball and a stick drawing and a space-filling model). Comment on the steric hindrence found in each rotamer. 

Draw a sawhorse diagram of what you believe to be the low-energy and the high-energy conformation for each of the following, using the red bond as a focus ... 

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