Stereochemistry and Carbohydrates - Fill in the Blank

A set of fill-in-the-blank flashcards covering key concepts from the notes on stereochemistry and carbohydrates.

The main criterion for optical activity is that the molecule as a whole must be __.

chiral

A plane of symmetry is an imaginary plane that passes through a molecule; if present, the molecule is and optically inactive.

achiral

Two or more chiral centers can give optical inactivity in a form called __ (e.g., meso-tartaric acid).

meso compound

Some compounds lack a chiral center but are optically active due to axial chirality, as seen in biphenyl and allene derivatives; this is called __.

axial chirality

Restricted rotation around a single bond in biphenyls leading to non-superimposable mirror images is referred to as __ (atropisomerism).

atropisomerism

A reaction that yields predominantly one enantiomer of the possible set is called __.

enantioselective reaction

An SN2 substitution at a chiral carbon proceeds with stereochemical , i.e., inversion of configuration.

inversion

In SN2 at a chiral center, the nucleophile attacks from the side, producing inversion.

backside

SN1 reactions proceed via a planar carbocation and typically give (racemization) at the chiral center.

racemization

During E2 elimination the reaction is most favorable when the leaving group and the hydrogen are in an __-periplanar arrangement.

anti

Allenes have the centre carbon in the hybridization and perpendicular π bonds.

sp

The end carbons of allenes are -hybridised and the two π bonds are perpendicular to each other.

sp2

The type of stereoisomerism in biphenyls due to hindered rotation is called __.

atropisomerism

Glycosides are composed of a sugar linked to a non-sugar component called the __.

aglycone

Glycosides are generally non-reducing and do not show __.

mutarotation

The new stereocenter formed during ring closure of a monosaccharide is the carbon, called the anomeric carbon.

anomeric

Disaccharides may be reducing or non-reducing; sucrose is a disaccharide because its linkage uses both reducing ends.

non-reducing

Mutarotation occurs via ring opening to form the -chain form (open-chain form) before re-closure to give α- or β- anomers.

open-chain

Kiliani–Fischer synthesis lengthens the carbon chain of an aldose by forming diastereomeric cyanohydrins which on hydrolysis yield two diastereomeric aldonic acids; these are called acids.

aldonic

Wohl's method shortens the aldose chain to give a aldose (e.g., glucose to arabinose).

lower

Osazones are colored derivatives formed when sugars react with phenylhydrazine; the osazone of glucose is called .

glucosazone

Glycosides derived from a pyranose form are called and those from a furanose are called .

pyranosides

Epimers differ in configuration at only one carbon (usually near the carbonyl).

asymmetric

The six-membered oxide ring in sugars is called a ; the five-membered ring is called a .

pyranose

Epimers differ in configuration at only one carbon (usually near the carbonyl).

asymmetric

The six-membered oxide ring is called a .

pyranose

The five-membered oxide ring is called a .

furanose

Anomeric carbon orientation defines α- and β- anomers: if the -OH on the anomeric carbon is below the plane, it is the -anomer; if above, the -anomer.

alpha, beta

In Haworth projections, substituents on the right of Fischer are drawn on the ring; those on the left are drawn .

below, above

Chair conformation of D-glucopyranose shows that in the β-anomer, all bulky groups prefer the positions (equatorial).

equatorial

Sucrose is a non-reducing sugar because the glycosidic linkage involves both anomeric carbons of glucose and fructose.

non-reducing