chemistry

Monosaccharide nomenclature

Monosaccharide nomenclature is a chemistry topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Monosaccharide nomenclature rather than just read about it. In short: Monosaccharide nomenclature is the naming system of the building blocks of carbohydrates, the monosaccharides, which may be monomers or part of a larger polymer. Monosaccharides are subunits that cannot be further hydrolysed in to simpler units.

Key takeaways

Monosaccharide nomenclature belongs to chemistry; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Monosaccharide nomenclature to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Monosaccharide nomenclature from memory before moving on to harder problems.

Reference excerpt

Monosaccharide nomenclature is the naming system of the building blocks of carbohydrates, the monosaccharides, which may be monomers or part of a larger polymer. Monosaccharides are subunits that cannot be further hydrolysed in to simpler units. Depending on the number of carbon atom they are further classified into trioses, tetroses, pentoses, hexoses etc., which is further classified in to aldoses and ketoses depending on the type of functional group present in them.

Systematic name of molecular graph The elementary formula of a simple monosaccharide is CnH2nOn, where the integer n is at least 3 and rarely greater than 7. Simple monosaccharides may be named generically based on the number of carbon atoms n: trioses, tetroses, pentoses, hexoses, etc. Every simple monosaccharide has an acyclic (open chain) form, which can be written as H − ( CH ( OH ) ) x − ( C = O ) − ( CH ( OH ) ) y − H {\displaystyle {\ce {H-(CH(OH))_{\mathit {x}}-(C=O)-(CH(OH))_{\mathit {y}}-H}}} ; that is, a straight chain of carbon atoms, one of which is a carbonyl group, all the others bearing a hydrogen -H and a hydroxyl -OH each, with one extra hydrogen at either end. The carbons of the chain are conventionally numbered from 1 to n, starting from the end which is closest to the carbonyl. If the carbonyl is at the very beginning of the chain (carbon 1), the monosaccharide is said to be an aldose, otherwise it is a ketose. These names can be combined with the chain length prefix, as in aldohexose or ketopentose. Most ketoses found in nature have the carbonyl in position 2; when that is not the case, one uses a numeric prefix to indicate the carbonyl's position. Thus for example, aldohexose means H(C=O)(CHOH)5H, ketopentose means H(CHOH)(C=O)(CHOH)3H, and 3-ketopentose means H(CHOH)2(C=O)(CHOH)2H. An alternative nomenclature uses the suffix '-ose' only for aldoses, and '-ulose' for ketoses. The position of the carbonyl (when it is not 1 or 2) is indicated by a numerical infix. For example, hexose in this nomenclature means H(C=O)(CHOH)5H, pentulose means H(CHOH)(C=O)(CHOH)3H, and hexa-3-ulose means H(CHOH)2(C=O)(CHOH)3H.

Naming of acyclic stereoisomers Open-chain monosaccharides with same molecular graph may exist as two or more stereoisomers. The Fischer projection is a systematic way of drawing the skeletal formula of an open-chain monosaccharide so that each stereoisomer is uniquely identified. Two isomers whose molecules are mirror-images of each other are identified by prefixes 'D-' or 'L-', according to the handedness of the chiral carbon atom that is farthest from the carbonyl. In the Fischer projection, that is the second carbon from the bottom; the prefix is 'D-' or 'L-' according to whether the hydroxyl on that carbon lies to the right or left of the backbone, respectively. If the molecular graph is symmetrical (H(CHOH)x(CO)(CHOH)xH) and the two halves are mirror images of each other, then the molecule is identical to its mirror image, and there is no 'L-' form. A distinct common name, such as "glucose" or "ribose", is traditionally assigned to each pair of mirror-image stereoisomers, and to each achiral stereoisomer. These names have standard three-letter abbreviations, such as 'Glc' for glucose and 'Rib' for ribose. Another nomenclature uses the systematic name of the molecular graph, a 'D-' or 'L-' prefix to indicate the position of the last chiral hydroxyl on the Fischer diagram (as above), and another italic prefix to indicate the positions of the remaining hydroxyls relative to the first one, read from bottom to top in the diagram, skipping the keto group if any. These prefixes are attached to the systematic name of the molecular graph. So for example, D-glucose is D-gluco-hexose, D-ribose is D-ribo-pentose, and D-psicose is D-ribo-hexulose. Note that, in this nomenclature, mirror-image isomers differ only in the 'D'/'L' prefix, even though all their hydroxyls are reversed.

The following tables shows the Fischer projections of selected monosaccharides (in open-chain form), with their conventional names. The table shows all aldoses with 3 to 6 carbon atoms, and a few ketoses. For chiral molecules, only the 'D-' form (with the next-to-last hydroxyl on the right side) is shown; the corresponding forms have mirror-image structures. Some of these monosaccharides are only synthetically prepared in the laboratory and not found in nature.

Names of aldoses

Names of ketoses

Names of 3-ketoses

Cyclic forms For monosaccharides in their cyclic form, an infix is placed before the '-ose', '-ulose', or 'n-ulose' suffix to specify the ring size. The infix is "furan" for a 5-atom ring, "pyran" for 6, "septan" for 7, and so on. Ring closure creates another chiral center at the anomeric carbon (the one with the hemiacetal or acetal functionality), and therefore each open-chain stereoisomer gives rise to two distinct stereoisomers (anomers). These are identified by the prefixes 'α-' and 'β-', which denote the relative configuration of the anomeric carbon to that of the stereocenter at the other end of the carbon chain. If the conformation (R or S) is identical at both the anomeric carbon and the most distant stereocenter, the configuration is 'α-'. If the conformations are different, the configuration is 'β-' Examples

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Illustrations

Worked examples

Example 1 — a first encounter with Monosaccharide nomenclature

Start with the simplest possible case. Write down what Monosaccharide nomenclature claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In chemistry, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Monosaccharide nomenclature before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Monosaccharide nomenclature ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Monosaccharide nomenclature

In research: Monosaccharide nomenclature appears in chemistry research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Monosaccharide nomenclature in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Monosaccharide nomenclature is common in secondary-school and first-year university syllabi. It links to neighbouring topics Carbohydrate chemistry, Carbohydrates, Chemical nomenclature, so understanding it makes those chapters shorter.
In everyday life: Look for Monosaccharide nomenclature outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Monosaccharide nomenclature in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Monosaccharide nomenclature means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Monosaccharide nomenclature out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Monosaccharide nomenclature in simple terms?

Why does Monosaccharide nomenclature matter?

Because it connects several chemistry ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Monosaccharide nomenclature?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Monosaccharide nomenclature.