chemistry

Glycal

Glycal 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 Glycal rather than just read about it. In short: Glycal is a name for cyclic enol ether derivatives of sugars having a double bond between carbon atoms 1 and 2 of the ring. The term "glycal" should not be used for an unsaturated sugar that has a double bond in any position other than between carbon atoms 1 and 2.

Key takeaways

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

Reference excerpt

Glycal is a name for cyclic enol ether derivatives of sugars having a double bond between carbon atoms 1 and 2 of the ring. The term "glycal" should not be used for an unsaturated sugar that has a double bond in any position other than between carbon atoms 1 and 2.

History The first glycal was synthesized by Hermann Emil Fischer and Karl Zach in 1913. They synthesized this 1,2-unsaturated sugar from D-glucose and named their product D-glucal. Fischer believed he had synthesized an aldehyde, and therefore he gave the product a name that suggested this. By the time he discovered his mistake, the name "glycal" was adopted as a general name for all sugars with a double bond between carbon atoms 1 and 2.

Conformation

Glycals can be formed as pyranose (six-membered) or furanose (five-membered) rings, depending on the monosaccharide used as a starting material to synthesize the glycal. Glycals can also be classified as endo-glycals or exo-glycals. A glycal is an endo-glycal when the double bond is within the ring. If the hydroxyl group on carbon 1 has been replaced with another carbon atom, a double bond can also form outside the ring between carbon 1 and this new carbon. In this case, the product is called an exo-glycal. The glycal conformation that has been studied in most depth is that of the pyranose endo-glycal. The favoured conformation of this glycal is the half-chair, a result which has been confirmed by quantum mechanical calculations.

Synthesis The original Fischer glycal synthesis was the reductive elimination with zinc of a glycosyl halide. This glycosyl halide was formed from a monosaccharide starting material. Some other synthetic routes include:

Ring-closing metathesis Reaction of thioglycosides with lithium naphthalenide. Mesylation of the anomeric hydroxyl and formation of the anomeric palladium complex, which undergoes beta-elimination A general example of each synthetic route is given below (drawn with first discussed synthesis bottom right, moving clockwise):

Reactions and uses The double bond of a glycal allows many other functional groups to be introduced into a monosaccharide. Like an alkene, a glycal can undergo electrophilic addition across the double bond to add in these new atoms such as halogens, epoxides, and nitrogen. The glycal double bond also allows a deoxy position (carbon in the ring that doesn’t have an oxygen bonded to it) to be easily introduced. Glycals have many uses in synthetic carbohydrate chemistry. They are commonly used as glycosylation donors, meaning that they can react with other monosaccharides to form a longer chain of monosaccharides called an oligosaccharide. Glycals can also have interesting applications in studying biological systems, particularly enzymes. D-glucal and radiolabelled D-galactal have been used to selectively bind with amino acids in the active sites of several enzymes. These enzyme-glycal complexes allow these amino acids that are essential for catalysis to be identified and allow for a better understanding of how these enzymes function.

References

See also Ferrier rearrangement Chemical glycosylation

Illustrations

Worked examples

Example 1 — a first encounter with Glycal

Start with the simplest possible case. Write down what Glycal 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 Glycal 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 Glycal 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 Glycal

In research: Glycal 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 Glycal 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: Glycal is common in secondary-school and first-year university syllabi. It links to neighbouring topics Carbohydrate chemistry, Carbohydrates, so understanding it makes those chapters shorter.
In everyday life: Look for Glycal 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 Glycal in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Glycal 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 Glycal out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Glycal in simple terms?

Why does Glycal 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 Glycal?

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 Glycal.