Carbohydrates: Structure, Classification, and Reactions

Vocabulary practice flashcards covering carbohydrate structures, stereochemistry, Fischer projections, isomers, and major chemical reactions from lecture notes.

Carbohydrate

The most abundant biomolecule on Earth, composed of carbon, hydrogen, and oxygen typically in a $2:1$ ratio with the empirical formula $(CH_2O)_n$. Chemically defined as a polyhydroxy aldehyde or ketone, or a substance that yields such compounds upon hydrolysis.

Monosaccharide

A simple sugar that cannot be hydrolyzed further into simpler carbohydrates; characterized as a colourless, crystalline solid that is freely soluble in water, insoluble in nonpolar solvents, and composed of an unbranched carbon chain with two or more hydroxyl groups.

Aldose

A monosaccharide whose carbonyl functional group is located at the terminal position of the carbon chain (an aldehyde group).

Ketose

A monosaccharide whose carbonyl functional group occurs at an internal position along the carbon chain (a ketone group).

Glyceraldehyde

The simplest aldose (an aldotriose, $C_3H_6O_3$), containing one chiral carbon center and serving as the reference standard for D- and L- stereochemical configurations.

Dihydroxyacetone

The simplest ketose (a ketotriose, $C_3H_6O_3$), characterized by containing no asymmetric (chiral) carbon atoms.

Fischer Projection

A standardized two-dimensional representation of a chiral carbohydrate introduced in 1891, where the carbon backbone is depicted vertically with C-1 at the top, horizontal bonds project toward the viewer, and vertical bonds project away to the rear.

Enantiomers

Stereoisomers that exist as non-superimposable mirror images of one another, differing in configuration at every single chiral center while sharing identical chemical properties in an achiral environment.

Epimers

Carbohydrate stereoisomers (diastereomers) that differ in configuration around only a single asymmetric (chiral) carbon atom.

Anomers

Cyclic monosaccharide stereoisomers that differ in stereochemical configuration specifically at the anomeric carbon (C-1 in aldoses or C-2 in ketoses), designated as $\alpha$ or $\beta$.

Anomeric Carbon

The former carbonyl carbon atom (C-1 of an aldose or C-2 of a ketose) that becomes a new chiral center upon intramolecular hemiacetal or hemiketal ring formation.

Mutarotation

The spontaneous change in optical rotation accompanying the equilibrium interconversion between $\alpha$ and $\beta$ anomeric forms of a carbohydrate in aqueous solution through an open-chain intermediate.

Alditol

A polyhydroxy alcohol produced when the carbonyl group of a monosaccharide is reduced using reducing agents such as $\text{NaBH}_4$ or $\text{H}_2/\text{Pt}$ (e.g., D-glucitol/D-sorbitol from D-glucose).

Aldonic Acid

A monocarboxylic sugar acid formed by the selective oxidation of the terminal aldehyde group of an aldose using bromine water ($\text{Br}_2$), which leaves ketoses unoxidized.

Aldaric Acid

A dicarboxylic sugar acid formed when both the terminal aldehyde group and the primary alcohol group of an aldose are oxidized by nitric acid ($\text{HNO}_3$).

Uronic Acid

A sugar acid formed through enzyme-catalyzed oxidation of only the terminal primary alcohol group ($-\text{CH}_2\text{OH}$) of a monosaccharide into a carboxylic acid group ($-\text{COOH}$), retaining the aldehyde group.

Kiliani-Fischer Synthesis

A reaction pathway used to lengthen an aldose chain by one carbon, proceeding via cyanide addition ($\text{HCN}$) to form epimeric cyanohydrins, reduction with $\text{H}_2/\text{Pd}$ to form imines, and aqueous acid hydrolysis ($\text{H}_3\text{O}^+$) to give aldohexoses.

Glycoside Formation

A condensation reaction between the cyclic hemiacetal hydroxyl group of a carbohydrate and an alcohol with the loss of water, producing an acetal with an ether linkage that is stable to base.

Osazone

A crystalline carbohydrate derivative formed by reacting a reducing sugar with excess phenylhydrazine ($\text{H}_2\text{N-NH-C}_6\text{H}_5$), yielding distinctive crystal morphologies under microscopic examination.

Glucosazone Crystals

Needle-shaped osazone crystals characterized by a "bundle of hay" microscopic appearance.

Maltosazone Crystals

Osazone crystals characterized by a distinct "sunflower shape" under microscopic view.

Lactosazone Crystals

Osazone crystals characterized by a "cotton ball" or "powder puff/hedgehog" appearance under the microscope.

Galactosazone Crystals

Osazone crystals characterized by forming rhombic plates under microscopic observation.