Quiz - Carbohydrates - 2 | Carbohydrates

While carbohydrates are generally soluble in water and can form both straight-chain and cyclic structures due to the presence of multiple hydroxyl groups, and they exhibit chirality, they are not typically insoluble in organic solvents. Some carbohydrates can dissolve in organic solvents, particularly if the solvent can form hydrogen bonds.

The Fischer projection is used to distinguish between D- and L-isomers of sugars. In glucose, the configuration of carbon-5 (the highest-numbered chiral carbon) determines the classification. If the hydroxyl group is on the right, it is D-glucose; if on the left, it is L-glucose.

The main difference between aldoses and ketoses lies in the location of the carbonyl group. Aldoses have the carbonyl group at the first carbon (aldehyde group), which can be oxidized to form an aldonic acid. Ketoses have the carbonyl group at the second carbon (ketone group) and can form ketonic acids upon oxidation.

Haworth projections are used to represent the cyclic structures of sugars, specifically the hemiacetal or the hemiketal forms. They provide a more accurate depiction of the spatial arrangement of the hydroxyl groups around the ring, which is important for understanding the chemical reactivity and properties of the sugars.

The reduction of a monosaccharide involves the addition of hydrogen, typically converting the carbonyl group (aldehyde or ketone) to an alcohol. When an aldose is reduced, it forms an alditol (sugar alcohol), not an acid or isomer.

The Kiliani-Fischer synthesis is a chemical reaction that allows for the lengthening of the carbon chain of monosaccharides. This involves the addition of a carbon atom by cyanohydrin formation followed by hydrolysis, thereby increasing the chain length of the sugar.

The main difference between starch and cellulose lies in the type of glycosidic bond. Starch consists of α-1,4 and α-1,6 glycosidic bonds allowing for branching and a helical structure, while cellulose consists of β-1,4 glycosidic bonds, leading to straight chains that can form strong fibers due to hydrogen bonding.

When monosaccharides react with alcohols in the presence of an acid catalyst, they form glycosides. This reaction involves the substitution of the hydroxyl group of the monosaccharide by an alkoxy group from the alcohol, leading to the formation of a glycosidic bond. Glycosides are important compounds found in many natural products and can serve as storage forms of carbohydrates in plants.

In the cyclic form of D-glucose, a hemiacetal is formed when the aldehyde group on carbon 1 reacts with a hydroxyl group to form a ring. The open-chain form does not have this hemiacetal linkage, but it does have a primary alcohol group, can rotate plane-polarized light, and has an aldehyde carbon which becomes the anomeric carbon in the cyclic form.

The Wohl degradation is a chemical reaction used in carbohydrate chemistry to shorten the carbon chain length of a carbohydrate molecule. This reaction involves the conversion of a carbohydrate into a shorter-chain carbohydrate by breaking glycosidic bonds. It is a valuable tool for structural elucidation and synthesis of complex carbohydrates.