Optical Activity The direction of rotation of the polarized light is indicated in the names of the enantiomers by placing (+)or(-)as prefixes to their names eg (+)-glyceraldehyde (-)-2-methylbutanoic acid Rotation,in degrees,is a specific rotation,[a]p for an optically active compound is the angle observed for 1 g/mL in solution in cell with a 10 cm path using sodium D line (ie light of 589 nanometers) [a]p observed rotation/(pathlength x concentration) =al(Ix C)=degrees/(dm x g/mL)Optical Activity „ The direction of rotation of the polarized light is indicated in the names of the enantiomers by placing (+) or (-) as prefixes to their names eg (+) - glyceraldehyde ( – ) - 2-methylbutanoic acid „ Rotation, in degrees, is α „ specific rotation, [ α ] D for an optically active compound is the angle observed for 1 g/mL in solution in cell with a 10 cm path using sodium D line (ie light of 589 nanometers) „ [ α ] D = observed rotation/(pathlength x concentration) = α/(l x C) = degrees/(dm x g/mL)