Organic 7: Stereochemistry

Question 1

Stereoisomers

Answer 1

isomers that have the same constitution but differ in the spatial arrangement of their atoms

Question 2

Chiral

Answer 2

object not superimposable on its mirror image; a molecule is this if its 2 mirror-image forms are not superimposable in 3 dimensions

Question 3

Achiral

Answer 3

a molecule that is superimposable on its mirror image

Question 4

Enantiomers

Answer 4

stereoisomers that are related as an object and its nonsuperimposable mirror image; describes a particular relationship between 2 objects; a chiral molecule can have only one of these

Question 5

Chirality center

Answer 5

an atom that has 4 nonequivalent atoms or groups attached to it; at various times, these have been called asymmetric centers or stereogenic centers

Question 6

Plane of symmetry

Answer 6

bisects a molecule so that one half of the molecules is the mirror image of the other half

Question 7

Center of symmetry

Answer 7

a point in the center of a molecule is this if any line drawn from it to some element of the structure will, when extended an equal distance in the opposite direction, encounter an identical element

Question 8

Optical activity

Answer 8

ability of a chiral substance to rotate the plane of plane-polarized light

Question 9

Polarimeter

Answer 9

instrument that measures optical activity

Question 10

Racemic mixtures

Answer 10

mixtures containing equal quantities of enantiomers; optically inactive

Question 11

Optically pure

Answer 11

at the limit, where all the molecules are of the same handedness

Question 12

Enantiomeric excess

Answer 12

optical purity; percent of major enantiomer - percent of minor enantiomer

Question 13

Specific rotation

Answer 13

effects of path length and concentration symbolized by alpha; a physical property; optical purity can be calculated [(___ of sample/___ of pure enantiomer) x 100]

Question 14

Absolute configuration

Answer 14

the exact 3D spatial arrangement of substituents at a chirality center

Question 15

Relative configurations

Answer 15

stereochemical configuration on a comparative, rather than an absolute, basis; terms such as D, L, erythro, threo, alpha, and beta describe relative configuration

Question 16

Cahn-Ingold-Prelog System

Answer 16

AKA the sequence rules; system that deals with the problem of the absolute configuration at a chirality center

Question 17

Fischer Projections

Answer 17

always generated the same way - the molecule is oriented so that the vertical bonds at the chirality center are directed away from you and the horizontal bonds point toward you; a projection onto the page is a cross; the chirality center lies at the center of the cross but is not explicitly shown

Question 18

Prochiral

Answer 18

addition to either face converts an achiral reactant to a chiral product

Question 19

Enantiotopic

Answer 19

product from reaction at 1 face is the enantiomer of the product from reaction at the other

Question 20

Prochirality center

Answer 20

an atom of a molecule that becomes a chirality center when 1 of its attached atoms or groups is replaced by a different atom or group

Question 21

Diastereomers

Answer 21

stereoisomers that are not mirror images; cis & trans isomers of a particular compound are ___ of each other

Question 22

Erythro

Answer 22

when the carbon chain is vertical and like substituents are on the same side of the Fischer projection, the molecule is described as this type of diastereomer

Question 23

Threo

Answer 23

when like substituents are on opposite sides of the Fischer projection, the molecules is described as this type of diastereomer

Question 24

Meso forms

Answer 24

achiral molecules that have chirality centers

Question 25

Conformational enantiomers

Answer 25

enantiomers interconvertible by a conformational change

Question 26

Stereospecific reaction

Answer 26

reaction in which stereoisomeric starting materials yield products that are stereoisomers of each other

Question 27

Diastereotopic

Answer 27

describing 2 atoms or groups in a molecule that are attached to the same atom but are in stereochemically different environments that are not mirror images of each other

Question 28

Resolution

Answer 28

the separation of a racemic mixture into its enantiomeric components

Question 29

Kinetic resolution

Answer 29

separation of enantiomers based on their unequal rates of reaction with a chiral reactant

Question 30

Enzymatic resolution

Answer 30

resolution of a mixture of enantiomers based on the selective reaction of one of them under conditions of enzyme catalysis