Rule 2: Sequence rules assign priorities to substituents. each 8csgelnag2etatemcnwmtor.hdrogom HH cedence over is the same as CHCH-CH. CHCH. K)-I-Bro erify these two examples C(CHh a CH.CH,b "c-c (-2-lod (S)-3-Ethyl-2.2,4-trimcthylpentan CH-ci 5-4 Fischer Projections There is more than one correct way to draw a Fischer projectio coftet the CH:CH,Br bon by vertical 4 4 Sequence rules assign priorities to substituents. Rule 1: Look first at the atoms directly attached to the stereocenter. Precedence is in order of highest atomic number. Hydrogen is always the lowest precedence. A higher-mass isotope takes precedence over a lower-mass isotope. Rule 2: If two atoms are of the same precedence using rule 1, proceed along the two respective substituent chains until you reach a point of difference. Verify these two examples: Rule 3: Double and triple bonds are treated as if they are single and the atoms in them are duplicated or triplicated at each end by the respective atoms at the other end of the multiple bond. Verify these assignments: 5-4 Fischer Projections Fischer projection formulas represent 3-D tetrahedral carbon atoms and their substituents in two dimensions. The molecule is drawn in the form of a cross. •The tetrahedral carbon is in the plane of the paper at the center of the cross. •Atoms connected to the tetrahedral carbon by horizontal bonds are behind the plane of the paper. •Atoms connected to the tetrahedral carbon by vertical bonds are in front of the plane of the paper. There is more than one correct way to draw a Fischer projection: