Question

Vanillin (4-hydroxy-3-methoxybenzaldehyde), the principal component of vanilla, occurs in vanilla beans and other natural sources as a \(\beta\)-D-glucopyranoside. Draw a structural formula for this glycoside, showing the D-glucose unit as a chair conformation.

Short answer

Based on the given step-by-step solution, provide a short answer explaining how to draw the glycoside of vanillin with the D-glucose unit in its chair conformation. To draw the glycoside of vanillin with the D-glucose unit in its chair conformation, follow these steps: 1. Draw the structure of vanillin, which consists of a benzene ring with a phenol group (OH) at position 4, a methoxy group (OCH3) at position 3, and an aldehyde group (CHO) at position 1. 2. Draw the chair conformation of D-glucose, which has six carbons, hydroxyl groups at positions C1, C2, and C4 in equatorial positions, and a hydroxyl group at C3 in the axial position. The molecule forms a six-membered ring with one oxygen atom. 3. Combine the two structures by forming a glycosidic bond between the anomeric carbon (C1) of D-glucose and the oxygen atom in the hydroxyl group (OH) of vanillin. This will result in the glycoside of vanillin with the D-glucose unit in its chair conformation.

Step-by-step solution

Draw the Structure of Vanillin

Vanillin has the following structure: - A phenol group (OH) at position 4 on the benzene ring - A methoxy group (OCH3) at position 3 on the benzene ring - An aldehyde group (CHO) at position 1 on the benzene ring The structure of vanillin can be drawn as follows: 

Draw the Chair Conformation of D-Glucose

D-glucose has the following structure in its pyranose form: - Six carbons labeled as C1, C2, C3, C4, C5, and C6 - Hydroxyl groups (-OH) at positions C2, C3, and C4 - A six-membered ring formed from carbons C1-C5 and one oxygen atom - Hydrogen atoms bonded to all remaining positions In the chair conformation of D-glucose, the following should be noted: - The hydroxyl groups present at C1, C2 and C4 are on the equatorial positions. - The hydroxyl group present at C3 is in the axial position. The chair conformation of D-glucose is shown below: 

Combine the Structures into a Glycoside

To draw the glycoside of vanillin, we need to join vanillin and D-glucose via a glycosidic bond. This bond forms between the anomeric carbon (C1) of D-glucose and the oxygen atom in the hydroxyl group (OH) of vanillin. The resulting glycoside of vanillin is shown below: 

Key concepts

Vanillin Structure

Vanillin is not only the primary component that gives vanilla its distinctive aroma, but it's also a prime example of how organic compounds are structured. The vanillin molecule consists of a benzene ring, which is a stable structure of six carbon atoms forming a hexagon. Attached to this ring, at different positions, are three functional groups: a phenol group (OH) at position 4, a methoxy group (OCH₃) at position 3, and an aldehyde group (CHO) at position 1.

These functional groups define vanillin's chemical behavior and properties. For instance, the aldehyde group is responsible for its ability to form glycosidic bonds with sugars like D-glucose, creating a glycoside. In organic chemistry, understanding the connectivity and positioning of these groups within a compound is crucial, as they impact the molecule's reactivity and interactions with other compounds.

Chair Conformation

Organic molecules containing rings are often flexible enough to adopt multiple shapes, known as conformations. In carbohydrates like D-glucose, the most stable conformation for the six-membered sugar ring is the chair conformation. This format minimizes the steric strain between hydroxyl groups and hydrogen atoms around the ring, making it energetically favorable. Imagine a lounge chair with a flat seat and a back – the carbon atoms in the sugar take positions analogous to the corners of such a chair.

In the chair conformation of D-glucose, the hydroxyl groups at C2, C3, and C4, as well as the methoxy group at C1, are all positioned to minimize interference with each other, leading to a more stable structure. This insight into the stability of sugar molecules is fundamental in biochemistry, impacting how sugars function in biological processes.

D-Glucose Structure

D-Glucose is a monosaccharide and one of the building blocks of carbohydrates. Each of its carbons is numbered from C1 to C6. In its cyclic form, known as glucopyranose, it forms a six-membered ring with one oxygen atom. The positioning of hydroxyl groups on this ring leads to different isomers of D-glucose. The C1 carbon, known as the anomeric carbon, is vital because its configuration (alpha or beta) determines the isomer's identity and its reactivity.

The structure of D-glucose is key in understanding its role in biology. The arrangement of hydroxyl groups on the carbon backbone is what allows it to interact with other molecules, such as in the formation of glycosidic bonds, a crucial step in building complex sugars and carbohydrates.

Glycosidic Bond

The glycosidic bond is a type of covalent bond that connects a carbohydrate (sugar) molecule to another molecule, which can be another carbohydrate or a different type of organic molecule. This bond forms between the anomeric carbon of the sugar and an oxygen or nitrogen atom of the other molecule. In the case of vanillin's β-D-glucopyranoside, the glycosidic bond occurs between the anomeric carbon (C1) of D-glucose and the oxygen in the hydroxyl group of vanillin.

Glycosidic bonds are essential in biochemistry. They are found in many important biological molecules, such as DNA and RNA, where they link nucleotides, and in polysaccharides like starch and cellulose, where they bind glucose units. The type of glycosidic bond- whether it's alpha or beta- affects the properties and digestibility of the carbohydrate. In the context of the vanillin glycoside, the bond is specifically called a beta-glycosidic bond, reflecting the position of the oxygen atom on the anomeric carbon.