... (13) For an interesting account of the early history of the isoprene rule, see: Ruzicka, L. in Perspectives in Organic Chemistry; Todd, A ... 4050 J. Org. ... Q (100/120 mesh for ana- lytical, 60/80 mesh for preparative, Applied Sciences) with 3% OV-1 or 3% Carbowax 20M (Pierce Chem. ...