Conventions
All bonds are depicted as horizontal or vertical lines. The carbon chain is depicted vertically, with carbon atoms represented by the center of crossing lines. The orientation of the carbon chain is so that the C1 carbon is at the top. In an aldose, the carbon of the aldehyde group is C1; in a ketose the carbon of the ketone group has the lowest possible number (usually C2).
A Fischer projection is used to differentiate between L- and D- molecules. On a Fischer projection, the penultimate carbon of D sugars are depicted with hydrogen on the left and hydroxide on the right. L sugars will be shown with the hydrogen on the right and the hydroxide on the left.
In a Fischer projection, all horizontal bonds project toward the viewer, while vertical bonds project away from the viewer. Therefore, a Fischer projection cannot be rotated by 90° or 270° in the plane of the page or the screen, as the orientation of bonds relative to one another can change, converting a molecule to its enantiomer. According to IUPAC rules all hydrogen atoms should preferably be drawn explicitly. Especially the hydrogen atoms of the end group of carbohydrates should be present.
Read more about this topic: Fischer Projection
Famous quotes containing the word conventions:
“Art, it seems to me, should simplify. That, indeed, is very nearly the whole of the higher artistic process; finding what conventions of form and what detail one can do without and yet preserve the spirit of the whole—so that all that one has suppressed and cut away is there to the reader’s consciousness as much as if it were in type on the page.”
—Willa Cather (1873–1947)
“I find nothing healthful or exalting in the smooth conventions of society. I do not like the close air of saloons. I begin to suspect myself to be a prisoner, though treated with all this courtesy and luxury. I pay a destructive tax in my conformity.”
—Ralph Waldo Emerson (1803–1882)
“Why does almost everything seem to me like its own parody? Why must I think that almost all, no, all the methods and conventions of art today are good for parody only?”
—Thomas Mann (1875–1955)