For example: two enantiomers of lactic acid can be shown by flying wedge as follows The bonds in the plane are shown by normal lines (-) but the bond above the plane is shown by solid wedge ( ) and the bond below the plane is shown by hashed wedge ( ) or by a broken line (…). Sometimes it may also be used for achiral molecules Two bonds attached to a chiral centre are shown in the plane of the paper and between other two, one is above the plane and another is shown below the plane. This kind of representation is usually done for molecules containing chiral centres. Fischer projection always represent an eclipsed conformation.įlying wedge formula or three-dimensional representations: Exchange of a pair substituents leads to the enantiomeric structure. By rotating the substituents in a group of three keeping the fourth one (e.g. By exchanging two pair of substituents as shown in process ‘A’ onī. Conversion of one Fischer projection formula into an equivalent one with the substituent differently ordered may be done in two ways –Ī. One projection may be rotated 180° within the plane of the paper about an axis perpendicular to the paper, but rotation of 90 0 and 270° are not permitted since such operations exchange horizontal substituents (‘up) with the vertical ones (down) contradicting the convention (iv). Horizontal line represent bonds above plane of paper and vertical lines represent bond below the plane of the paper. The main chain of the molecule is represented by a vertical line from top to bottom (usually with IUPAC numbering) and the carbon chain is usually drawn with the most highly oxidized end carbon atom at the top as in glyceraldehyde. Horizontal lines represent the bonds pointing toward the observer and the vertical bonds point away.
The chiral carbon (s) lye in the plane of paper and is often omitted and it is symbolized by the intersection point of the horizontal and vertical lines.
Fischer projection are not normally used to represent the molecules without chiral centres.Ĭertain convention in Fischer Projection formula: The Fischer projection of one stereoisomer of lactic acid, CH 3CHOHCO 2H is shown below in three different ways in Fischer projection. The point of intersection of these lines is the seat of the chiral centre. In this representation the molecule is so oriented that each chiral carbon remains in the plane of the projection and the four bonds are shown by two vertical and two horizontal lines.
Therefore, several two-dimensional projection formulas have been developed to represent the molecules having three dimensional structures. Since paper and black boards are two dimensional, it is very difficult and inconvenient to represent the three-dimensional molecules in two dimension of paper and black board.
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