Bird-in-the-Hand Method for Determination of Absolute Configuration in Fischer Projections

Abstract

The bird-in-the-hand technique allows for easy visualization and identification of stereogenic centers on Fischer projections. It uses the student’s hand as a molecular model to simplify the stereochemistry of Fischer projections. It can be quickly explained and applied, making it practical for the classroom.All one needs to understand to use this method is (i) vertical lines on Fischer projections go away and horizontal lines project towards the viewer; (ii) the Cahn–Ingold–Prelog R–S notational system; (iii) clockwise from counterclockwise.The substituents are numbered on the Fischer projection (Cahn–Ingold–Prelog system). With palm up (pinkie and ring finger folded), the index finger points away and thumb and middle finger point up (representing the horizontal line of the Fischer projection; the index finger and arm represent the vertical line). Each fingertip is numbered identically to the Fischer projection and the hand is rotated so that the lowest rank points away from the viewer. The rank direction is determined (clockwise or counterclockwise). The absolute configuration is determined: clockwise is R and counterclockwise is S. Unlike other models, the method can be applied by either hand and has few protocols, making it an asset to beginning students of stereochemistry.