Question

The sugar glucose could conceivably be given the name 2,3,4,5,6 -pentahydroxyhexanal (though this name is never used because the actual sugar glucose is only one possible isomer having this name). Draw the structure implied by this name.

Short answer

The structure of 2,3,4,5,6-pentahydroxyhexanal is represented as \(CH(=O)-CH(OH)-CH(OH)-CH(OH)-CH(OH)-CH_2(OH)\), containing 6 carbon atoms, 5 OH groups, and an aldehyde group. The molecule consists of a carbon backbone with an aldehyde group at one end and hydroxy groups at positions 2, 3, 4, 5, and 6.

Step-by-step solution

Drawing the carbon backbone

First, draw the carbon backbone of the molecule, which consists of 6 carbon atoms connected by single bonds. We will number the carbons from 1 to 6 starting from the aldehyde end, so that carbon 1 is where the aldehyde group will be attached.

Adding the aldehyde group

Attach the aldehyde group to carbon 1. An aldehyde group consists of a carbon atom double bonded to an oxygen atom, with carbon 1 becoming part of the aldehyde group, the structure would now be C=O connected to carbon 2.

Attaching the hydroxy groups

Now, we need to attach the hydroxy groups (OH) to carbon atoms 2, 3, 4, 5, and 6. To do this, simply draw an OH group at each of the carbon positions. Make sure that each carbon atom forms 4 bonds in total, so in addition to the OH groups and carbon-carbon bonds, add hydrogen atoms to each carbon to complete their bonding requirements.

Final structure

After completing all the necessary steps, the final structure of 2,3,4,5,6-pentahydroxyhexanal will look like this: \( \displaystyle \/CH(=O)-CH(OH)-CH(OH)-CH(OH)-CH(OH)-CH_2(OH) \) As a note, glucose belongs to a subgroup of hexanal sugars called hexoses, which have this general structure but in different isomers (specific arrangement of atoms).

Key concepts

Glucose Structure

The glucose molecule is a fundamental carbohydrate and an essential source of energy for cells. It is a hexose, meaning it has six carbon atoms, and classified as an aldohexose because it contains an aldehyde group. The accurate structural representation of glucose is critical to understanding its role in biology and chemistry. Each carbon atom, except the first, is attached to a hydroxyl group (OH), and the orientation of these groups determines its specific isomer. Carbon 1 has an aldehyde group represented by \( C=O \), which is a defining feature of aldoses.

For glucose, particularly, it exists primarily in two major forms: the 'D-glucose' and 'L-glucose' isomers. The 'D' and 'L' denote the orientation of the hydroxyl group on carbon 5, which is farthest from the aldehyde group. In D-glucose, the hydroxyl group on this carbon is on the right in a Fischer projection. This is the naturally occurring isomer and the one most often found in cells and biological systems. The structural depiction of D-glucose shows a chain of six carbon atoms, with hydroxyl groups and hydrogen atoms bonded in such a way that they fulfill the four bonds required for carbon. Understanding the 3-dimensional chair form representation is also crucial, which shows D-glucose as it predominantly exists in solution.

Organic Chemistry Nomenclature

The nomenclature in organic chemistry provides a systematic way to name molecules according to their structure. The IUPAC system is the most widely used method for naming and it involves several steps to determine the correct name. First, the longest continuous chain of carbon atoms is identified to determine the root name. Then, groups attached to this chain, such as aldehydes, ketones, and alcohols, are indicated in the name through specific prefixes and suffixes.

The molecule in our exercise is named 2,3,4,5,6-pentahydroxyhexanal. 'Hex' indicates the presence of six carbon atoms, 'anal' denotes the aldehyde group at the end of the carbon chain, and 'pentahydroxy' specifies that there are five hydroxyl (OH) groups present. The numbering 2,3,4,5,6 indicates the position of the hydroxyl groups on the carbon chain. Naming complex organic molecules like this involves meticulous attention to the placement and orientation of each functional group to deduce the correct name.

Drawing Organic Molecules

Drawing organic molecules is a fundamental skill in chemistry that aids in visualizing and understanding molecular structure and reactivity. To accurately draw a molecule like 2,3,4,5,6-pentahydroxyhexanal, one must start with a carbon backbone. Each carbon atom bonds with four other atoms; any remaining valences are satisfied with hydrogen atoms.

When drawing, consider the arrangement of atoms in space – for hydroxy groups, they can be on either side of the carbon plane, leading to different stereoisomers. Hydrogens are often omitted for clarity when the molecule is represented in line-angle (skeletal) format. It's essential to ensure that the functional groups, such as the aldehyde in carbon 1, are correctly placed. The use of wedges and dashes to represent bonds coming towards or away from the observer can denote the three-dimensional aspect of molecules.