Each carbon atom is then numbered in order through the end of the chain. The L is taken from the Latin word for left, Laever, and the D is taken from the Latin word for right, Dexter.Ĭarbon atoms are numbered beginning from the reactive end of the molecule, the CHO (aldehyde) or “C” double bonded “O” (carbonyl) end of the molecule. To distinguish between the isomers, they are labeled L and D isomers. An L-isomer has the OH on the left of the center carbon:Īnd the D-isomer has the OH on the right of the center carbon. These differences do not affect the physical properties but can affect the biochemical properties due to changing the shape of the molecule. The center C-atom of glycerose is called an asymmetric C-atom because it can be rearranged in space to produce two different structures. Therefore, sugars can exist as pairs of stereoisomers or enantiomers which are mirror images of one another. Some isomers differ only in the way in which the atoms are arranged in 3-D space, that is, the atoms are bonded to each other in the same way, but are arranged differently in 3-D space. These types of compounds are called isomers. As an example both glucose and fructose are hexoses (C 6H 12O 6) but they have different chemical and physical properties. Within each of these groups there are different compounds, each with the same molecular formula. The monosaccharides can be divided into groups based on the number of carbon atoms in the molecules, thus: trioses have 3-C atoms, tetroses have 4-C atoms, pentoses have 5-C atoms, and hexoses have 6-C atoms.
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