Carbohydrate Chemistry: Isomerization, Structures, and Reactions

Comprehensive practice vocabulary flashcards covering carbohydrate structures, stereoisomerism, cyclization, mutarotation, disaccharides, polysaccharides, and synthetic modifications.

Carbohydrates

Polyhydroxy aldehydes, polyhydroxy ketones, or substances that yield these compounds upon hydrolysis, generally having the empirical formula $C_n(H_2O)_n$ or $(CH_2O)_n$ where $n > 3$.

Monosaccharides

The simplest carbohydrate units (simple sugars) consisting of a single polyhydroxy aldehyde or ketone backbone that cannot be hydrolyzed into simpler sugars.

Oligosaccharides

Carbohydrates that yield between 2 and 10 monosaccharide units upon hydrolysis, with disaccharides being the most abundant naturally occurring group.

Polysaccharides

High-molecular-weight carbohydrates composed of more than 10 monosaccharide units joined by glycosidic bonds, which do not taste sweet and do not exhibit mutarotation.

Stereoisomers

Isomeric compounds that share the exact same molecular formula and atom-to-atom connectivity but possess different three-dimensional spatial arrangements.

Enantiomers

Stereoisomers that are non-superimposable mirror images of each other, displaying identical physical properties in an achiral environment but opposite configurations at all chiral centers.

Diastereomers

Stereoisomers that are not mirror images of one another and possess distinct physical and chemical properties such as differing melting points, boiling points, solubilities, and reactivities.

Epimers

Diastereomers that differ in configuration around only one single chiral center, such as D-glucose and D-mannose at $C\text{-}2$, or D-glucose and D-galactose at $C\text{-}4$.

Anomeric Carbon

The asymmetric carbon atom created upon cyclization from the original carbonyl carbon ($C\text{-}1$ in aldoses and $C\text{-}2$ in ketoses), which is bonded directly to two oxygen atoms.

Anomers

Diastereomeric cyclic monosaccharides that differ specifically in configuration at the anomeric carbon, designated as either $\alpha$ or $\beta$.

Anomeric Effect

The preference of certain electronegative substituents bonded to the anomeric carbon of a pyranoid ring to occupy the axial position rather than the equatorial position.

Mutarotation

The spontaneous change in the optical rotation of a carbohydrate solution over time caused by the interconversion of $\alpha$ and $\beta$ anomers through the open-chain form until equilibrium is established.

Penultimate Carbon

The chiral carbon atom directly adjacent to the terminal primary alcohol carbon ($C\text{-}5$ in aldohexoses), whose $-OH$ orientation determines whether a sugar belongs to the D-series (right) or L-series (left).

Asymmetric Carbon Atom

A chiral center carbon bonded to four distinct atoms or groups; a molecule containing $n$ asymmetric centers can form a maximum of $2^n$ possible stereoisomers.

Racemic Mixture

An equimolar mixture of D- and L-enantiomers that exhibits zero net optical activity because the rotations of the two isomers cancel each other out.

Pyranose

A six-membered cyclic hemiacetal or acetal ring structure of a sugar, named after the six-membered cyclic ether pyran.

Furanose

A five-membered cyclic hemiacetal or acetal ring structure of a sugar, named after the five-membered cyclic ether furan.

Haworth Projection

A standardized representation of cyclic sugars viewed edge-on, in which substituents directed to the right in a Fischer projection are drawn pointing downwards, and those to the left point upwards.

Glycosidic Bond

An acetal or ketal ether linkage formed between the anomeric carbon of a carbohydrate and an alkoxy oxygen from an alcohol or another monosaccharide.

Reducing Sugar

A carbohydrate with a free anomeric hydroxyl group capable of opening into a free aldehyde or ketone in aqueous solution, thereby reducing agents like Tollens' reagent or bromine water.

Non-Reducing Sugar

A sugar whose anomeric carbons are completely locked into glycosidic acetal or ketal bonds, preventing opening to a free carbonyl form, mutarotation, or reduction of mild oxidizing agents.

Maltose

A reducing disaccharide produced by starch hydrolysis, consisting of two D-glucose units linked by an $\alpha\text{-(1,4')}$ glycosidic bond and cleaved by the intestinal enzyme maltase.

Lactose

A reducing disaccharide known as milk sugar, formed by combining $\beta\text{-D-galactose}$ and $\beta\text{-D-glucose}$ via a $\beta\text{-(1,4')}$ glycosidic linkage.

Sucrose

A non-reducing disaccharide composed of $\alpha\text{-D-glucopyranose}$ and $\beta\text{-D-fructofuranose}$ joined by an $\alpha\text{-1,}\beta\text{-2'}$ glycosidic bond, having a specific rotation of $+66.5^\circ$.

Cellobiose

A disaccharide composed of two D-glucose subunits linked together via a $\beta\text{-1,4'}$ glycosidic bond.

Gentiobiose

A disaccharide made up of two glucose units connected through a $\beta\text{-1,6'}$ glycosidic bond.

Amylose

The water-soluble fraction of starch (constituting roughly $20\%$), formed of unbranched helical chains of D-glucose units linked exclusively by $\alpha\text{-1,4'}$ glycosidic bonds.

Amylopectin

The water-insoluble fraction of starch ($80\%$), consisting of D-glucose chains linked by $\alpha\text{-1,4'}$ glycosidic bonds with $\alpha\text{-1,6'}$ branch points occurring approximately every 25 glucose units.

Glycogen

The primary animal storage polysaccharide, composed of D-glucose units linked by $\alpha\text{-1,4'}$ glycosidic bonds with frequent $\alpha\text{-1,6'}$ branch points occurring on average every 10 units.

Cellulose

A structural plant polysaccharide composed of linear D-glucose chains joined by $\beta\text{-1,4'}$ glycosidic bonds, which humans cannot hydrolyze due to the absence of $\beta$-glucosidase.

Alditol

A sugar alcohol formed by reducing the carbonyl group of a monosaccharide with a hydride reducing agent such as $NaBH_4$.

Aldonic Acid

A monocarboxylic sugar acid produced by selectively oxidizing the terminal aldehyde group of an aldose using a mild oxidizing agent like aqueous bromine ($Br_2 / H_2O$).

Aldaric Acid

A dicarboxylic sugar acid formed when both the aldehyde and the terminal primary alcohol carbon ($C\text{-}6$) of an aldose are oxidized by hot nitric acid ($HNO_3$).

Osazone

A crystalline bis-hydrazone derivative formed at $C\text{-}1$ and $C\text{-}2$ when an aldose or ketose reacts with three molar equivalents of phenylhydrazine under acidic conditions.

Ruff Degradation

A reaction pathway for shortening an aldose chain by one carbon via oxidation to a calcium aldonate followed by treatment with $H_2O_2$ and $Fe^{3+}$ catalyst to decarboxylate and generate an aldose.

Kiliani–Fischer Synthesis

A synthetic method used to extend an aldose chain by one carbon through cyanohydrin addition with $HCN/KCN$, reduction over $Pd/BaSO_4$, and acidic hydrolysis, yielding a pair of $C\text{-}2$ epimers.

Enediol Rearrangement

A base-catalyzed isomerization that shifts the carbonyl group of a monosaccharide between $C\text{-}1$ and $C\text{-}2$ via an enediol intermediate, interconverting aldoses and ketoses.

Tollens' Reagent

An ammoniacal silver nitrate solution ($Ag(NH_3)_2^+ OH^-$) that oxidizes aldehydes and reducing sugars to aldonic acids, yielding a characteristic silver mirror deposit.

Cellulose Nitrate

A synthetic cellulose ester prepared with nitric acid; the fully nitrated form ($[C_6H_7O(ONO_2)_3]_n$) is explosive guncotton, while partially nitrated cellulose is pyroxylin.

Viscose Rayon

A regenerated cellulose fiber manufactured by treating cellulose with $NaOH$ and $CS_2$ to produce an alkali-soluble xanthate solution, which is extruded into filaments and precipitated with acid.