[BIOCHEM LEC MIDTERMS] CHIRALITY AND STEREOCHEMISTRY

Chirality

Property describing molecular handedness, where two forms are mirror images that cannot be perfectly superimposed

Chiral molecule

A molecule whose mirror image cannot be superimposed on the original molecule

Achiral molecule

A molecule that does not possess handedness and whose mirror image can be superimposed

Chiral center

A carbon atom attached to four different groups in a three-dimensional arrangement

Handedness

The existence of left-handed and right-handed forms of a molecule, analogous to human hands

Superimposable

Describes two structures that can be placed exactly on top of each other so that corresponding parts match

Mirror image

A structure that is the reflected version of another structure, like a left hand and right hand

3D

The arrangement of carbohydrate atoms that produces different stereochemical forms

Glucose

A carbohydrate with the molecular formula C₆H₁₂O₆ shown in the lesson as an example of a monosaccharide

Galactose

A carbohydrate with the molecular formula C₆H₁₂O₆ shown alongside glucose as an example of molecules with the same formula but different arrangement

Chiral carbon

A carbon with four attached groups that are all different

T

A ring carbon that can be chiral when it has four single bonds, different substituents, and different directions around the ring. t/f

T

The ring carbon must have different two directions or halves of the ring for it to qualify as a chiral center. T/F

Stereoisomerism

The existence of molecules with the same connectivity but different three-dimensional arrangements

Isomer

Molecules having the same molecular formula but differing in how their atoms are arranged

Stereoisomer

Molecules with the same molecular and structural formulas but different three-dimensional arrangements

Enantiomers

Stereoisomers that are mirror images of each other but cannot be perfectly superimposed

Diastereomers

Stereoisomers that are not mirror images of one another

Fischer projection

A two-dimensional representation of the three-dimensional arrangement of groups around chiral centers

Hermann Emil Fischer

The scientist associated with the development of Fischer projection formulas

Central atom

The chiral center considered to be in the plane of the paper

Vertical bonds

Bonds considered to point into the printed page

Horizontal bonds

Bonds considered to point out of the printed page

Fischer projection vertical rule

The vertical lines represent groups directed away from the viewer

Fischer projection horizontal rule

The horizontal lines represent groups directed toward the viewer

Glyceraldehyde

The three-carbon carbohydrate also called 2,3-dihydroxypropanal, used to illustrate D and L forms

2,3-Dihydroxypropanal

The chemical name of glyceraldehyde

D-glyceraldehyde

The glyceraldehyde stereoisomer with the OH on the right in its Fischer projection

L-glyceraldehyde

The glyceraldehyde stereoisomer with the OH on the left in its Fischer projection

D sugar

A sugar whose relevant configuration in a Fischer projection has the OH on the right

L sugar

A sugar whose relevant configuration in a Fischer projection has the OH on the left

D/L designation

A system describing the orientation of carbohydrate stereoisomers relative to D- and L-glyceraldehyde

Dextro

A term from Latin associated with right in the historical D/L naming system

Levo

A term from Latin associated with left in the historical D/L naming system

2,3,4-Trihydroxybutanal

The chemical name of the four-carbon aldose used to demonstrate erythrose and threose

D-erythrose

A D-form tetrose whose Fischer projection has its two OH groups on the same side

L-erythrose

The L-form enantiomer of erythrose with the two OH groups on the same side

D-threose

A D-form tetrose whose two OH groups are on opposite sides in the Fischer projection

L-threose

The L-form enantiomer of threose with the two OH groups on opposite sides

Spearmint and caraway flavor

The lesson's example of a natural flavor associated with enantiomeric molecules

Epinephrine

The hormone also called adrenaline, used to illustrate the biological importance of molecular shape

Adrenaline

The common name for epinephrine, whose stereochemical form can affect biological activity

Open-chain form

The non-cyclic form of a monosaccharide containing its carbonyl group

cyclic forms of monosaccharides

monosaccharides with 5 or more carbon atoms usually do not stay in the open-chain form

Carbonyl group

A functional group containing a C=O bond

Intramolecular reaction

A reaction occurring between functional groups within the same molecule

Ring formation

The process in which a monosaccharide's carbonyl group reacts with an internal OH group to produce a cyclic structure

Cyclic hemiacetal

The ring structure produced when an aldose carbonyl group reacts with an internal OH group

Dominant cyclic form

The form of a monosaccharide that is present in the greatest amount in solution

Anomeric carbon

The new chiral center formed at carbon 1 when glucose cyclizes

Anomer

A cyclic carbohydrate stereoisomer that differs at the anomeric carbon

a form

The carbohydrate configuration in which the anomeric OH and CH₂OH point in opposite directions

b form

The carbohydrate configuration in which the anomeric OH and CH₂OH point in the same direction

a-glucose

One cyclic form of glucose distinguished by the configuration of the anomeric OH group

b-glucose

One cyclic form of glucose distinguished by the configuration of the anomeric OH group and identified in the lesson as the most abundant form in water

Interconversion

The continuous change between α, β, and open-chain forms of glucose in water

Haworth projection

A two-dimensional notation specifying the three-dimensional structure of a cyclic monosaccharide

Walter Norman Haworth

The British carbohydrate chemist associated with Haworth projection formulas

T

The purpose of a Haworth projection for showing the structure of a ring-form carbohydrate T/F

D-form

A carbohydrate whose terminal CH₂OH group is above the ring

L-form

A carbohydrate whose terminal CH₂OH group is below the ring

D/L Haworth rule

The CH₂OH position above or below the ring determines the D or L form

Same direction

Relationship between anomeric OH and CH₂OH that identifies the β configuration

Opposite direction

Relationship between anomeric OH and CH₂OH that identifies the α configuration

a-D-glucose

The D-glucose form with the anomeric OH opposite the CH₂OH group

b-D-glucose

The D-glucose form with the anomeric OH in the same direction as CH₂OH

Starch and glycogen

A major energy-storage carbohydrate formed from α-D-glucose

Cellulose

An important structural component of plant cell walls formed from β-D-glucose

Carbohydrate stereochemistry

The study of how different spatial arrangements produce different carbohydrate forms

Fischer and Haworth projections

The two projection methods used to represent and identify carbohydrate structures

D/L configuration

A designation describing a carbohydrate's specific stereochemical arrangement

α/β configuration

A designation describing the specific arrangement at the anomeric carbon

Chirality and biological function

The connection between molecular handedness and biological activity

Stereoisomer biological effect

The phenomenon in which different stereoisomers can have different biological activities

Carbohydrate stereochemistry synthesis

The lesson's overall concept that spatial arrangement determines carbohydrate form and function