What makes a carbon asymmetric

Like isomers, stereoisomers are compounds with the same molecular formula but different molecular structures. Stereoisomers are isomers that differ from each other only in the way the atoms are oriented in space but are like one another with respect to which atoms are joined to which other atoms. Be able to identify an asymmetric carbon atom! A carbon atom is asymmetric if it has four different chemical groups attached. Isomers: The definition of an isomer is not an objective but it may help understand stereoisomers.

Pentoses C 5 H 10 O 5 Three important pentoses are:. D-ribose — a component of RNA, ribonucleic acid, vitamins riboflavin , and coenzymes. In its reduced form, deoxyribose, it is a component of DNA. L-arabinose — occurs in conifer heartwood and is a component of hemicelluloses where it occurs with xylose.

It is also a component of pectin and can be a major component of gums gum Arabic. Bacterial action in making silage can yield free arabinose. Arabans are polymers of arabinose. D-xylose — there are small amounts of D-xylose free in fruits, but it occurs mainly in hemicellulose, as xylans and hetero-xylans. Hemicellulose is a polysaccharide of xylose and arabinose a heteroxylan. The ratio of xylose to arabinose seems to affect digestibility as digestibility is reduced as the proportion of xylose increases.

Hemicelluloses constitute a considerable portion of the cell walls of plants so herbivores eat large amounts of them. These sugars are all aldopentoses. D-glucose — an aldohexose with various common names, including grape sugar, dextrose, corn sugar made from cornstarch. Occurs free in plants, fruits, honey, body fluids, including CSF, blood, lymph.

It is the major end-product of CHO digestion by non-ruminants and is therefore a primary energy form for non-ruminants. It is a major component of many oligosaccharides with galactose forms lactose and polysaccharides such as starch and cellulose. In solution D-glucose exists as an equilibrium mixture of the straight chain form with two pyranose ring forms. Effectively, carbon atom number one reacts with carbon atom number five forming a ring.

In fact two forms of the structure exist, called anomers. If the hydrogen atom is above carbon atom one then it is called an alpha anomer but if the hydrogen atom is below the carbon atom it is called a beta anomer. This structural information is very important because it governs how molecules of glucose join together to form larger molecules. Starch is a polymer of the a- form and is water soluble and digestible by animal enzymes.

Cellulose is a polymer of the b- form, it is not soluble and is not digestible by animal enzymes. Changing from a to b via an open chain structure is called mutarotation, and it requires the O-C bond to be broken to allow the C to swivel the H and OH upside down.

The duality that this produces allows for different structural compositions of carbon based molecules e. By taking the number of asymmetric carbon atoms, one can calculate the possible number of enantiomers for that molecule. Category : Stereochemistry. Read what you need to know about our industry portal chemeurope.

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