Carbohydrate Isomerism: Epimers, Anomers, Enantiomers, and Diastereomers

Vocabulary flashcards covering epimers, anomers, enantiomers, diastereomers, D/L designations, and key carbohydrate terms (glucose, fructose, starch, cellulose, lactose).

Epimer

A diastereomer that differs in configuration at exactly one chiral center (not a mirror image).

Diastereomer

A stereoisomer that is not a mirror image and differs at some but not all chiral centers.

Enantiomer

A non-superimposable mirror-image pair of stereoisomers that differ at every chiral center.

Anomer

A type of stereoisomer in cyclic sugars that differs at the anomeric carbon.

Anomeric Carbon

The carbon that becomes a new chiral center during ring closure; C-1 in aldoses and C-2 in ketoses.

Alpha (α) Anomer

Anomer in which the OH on the anomeric carbon is opposite to the CH2OH group.

Beta (β) Anomer

Anomer in which the OH on the anomeric carbon is on the same side as the CH2OH group.

Aldose

A sugar with an aldehyde group; in aldoses the anomeric carbon is C-1.

Ketose

A sugar with a ketone group; in ketoses the anomeric carbon is C-2.

D-Form (Dextrorotatory)

Sugars with the highest-numbered chiral carbon's OH on the right in Fischer projection.

L-Form (Levorotatory)

Sugars with the highest-numbered chiral carbon's OH on the left in Fischer projection.

D-Glucose

A common energy-yielding hexose in the D-family; OH on the right at the highest-numbered chiral carbon in Fischer projection.

L-Glucose

Mirror image of D-glucose; rarely metabolized by human enzymes.

Fructose

A ketohexose; forms ring structures with the anomeric carbon at C-2.

Fructofuranose

Five-membered ring form of fructose; anomeric carbon is C-2.

Glucopyranose

Six-membered ring (pyranose) form of glucose.

Pyranose

Six-membered ring form of a sugar.

Furanose

Five-membered ring form of a sugar (e.g., fructose).

Glycosidic Bond

Bond linking two sugar units (or a sugar to a non-sugar) via the anomeric carbon.

Starch

Polysaccharide of glucose with α-1,4 linkages; digestible by humans.

Cellulose

Polysaccharide of glucose with β-1,4 linkages; not digestible by humans.

α-1,4 linkage

Glycosidic bond between glucose units at the 1 and 4 positions in starch.

β-1,4 linkage

Glycosidic bond between glucose units at the 1 and 4 positions in cellulose.

Lactose

Disaccharide of glucose and galactose; glucose unit can be α- or β-, affecting digestion and sweetness.

D- vs L- designation

Designations based on orientation of OH at the highest-numbered chiral carbon in Fischer projection (D right, L left).

Chiral Center

Carbon atom bonded to four different groups; determines stereochemistry.

Haworth Projection

A planar representation of cyclic sugars showing ring form and substituents.

Isomer

Molecules with the same formula but different arrangement of atoms, leading to different properties.

Monosaccharide

The simplest carbohydrate unit; cannot be hydrolyzed into smaller sugars.

Epimer at C-2 (Glucose vs Mannose)

An epimer differing at carbon 2, changing configuration at exactly one chiral center.

Epimer at C-4 (Glucose vs Galactose)

An epimer differing at carbon 4, changing configuration at exactly one chiral center.

D-Galactose

A common epimer of glucose differing at C-4; part of many disaccharides.