Chapter 5 Stereochemistry: Chiral Molecules

Question 1

What are the subdivision of isomers?

Answer 1

isomers to constitutional isomers and stereoisomers to enantiomers and diastereomers

Question 2

isomers with the same molecular
formula and same connectivity of atoms but different arrangement of atoms in space

Answer 2

Stereoisomers

Question 3

Different compounds with same molecular formula

Answer 3

Stereoisomers

Question 4

isomers whose atoms have a different connectivity

Answer 4

Constitutional isomers

Question 5

isomers that have the same connectivity but that differ in the same arrangement of their atoms in space

Answer 5

stereoisomers

Question 6

stereoisomers that are non superposable mirror images of each other

Answer 6

enantiomers

Question 7

The ability for an isomers to be placed over another isomers, usually in such a way that both will be visible

Answer 7

superposable

Question 8

Not superposable on its mirror image and can exist as a pair of enantiomers

Answer 8

chiral molecules

Question 9

A chiral molecule and its mirror image

Answer 9

Pair of enantiomers

Question 10

Superposable on its mirror image

Answer 10

Achiral molecule

Question 11

A molecule with a _________ bonded to four different groups will always be chiral

Answer 11

single tetrahedral carbon

Question 12

A molecule with ______________ bonded to four different groups is not always chiral

Answer 12

more than one tetrahedral carbon

Question 13

Switching two groups at the tetrahedral center leads to the ______ in a molecule with one tetrahedral carbon

Answer 13

enantiomeric molecule

Question 14

An atom bearing groups of such nature that an interchange of any two groups will produce a stereoisomer

Answer 14

Stereogenic center

Question 15

Carbons at a tetrahedral stereogenic center are designated with an _________

Answer 15

asterisk(*)

Question 16

The binding specificity of a chiral receptor site for a chiral molecule is usually only favorable in one way

Answer 16

The Biological Importance of Chirality

Question 17

consider this when testing for chirality

Answer 17

planes of symmetry

Question 18

An imaginary plane that bisects a molecule in such a way that the two halves of the molecule are mirror images of each other

Answer 18

Plane of symmetry

Question 19

A molecule with a plane of symmetry cannot be _____

Answer 19

chiral

Question 20

Nomenclature of Enantiomers

Answer 20

R,S System

Question 21

The R,S System is also called

Answer 21

Cahn-Ingold-Prelog system

Question 22

The four groups attached to the stereogenic carbon are assigned priorities from ___________

Answer 22

highest to lowest

Question 23

Priorities are assigned as follows:
1. Atoms directly attached to the _____ are compared
2. Atoms with _______ are given higher priority

Answer 23

1. stereogenic center
2. higher atomic number

Question 24

If priority cannot be assigned based on directly attached atoms, the _________ of atoms is examined

Answer 24

next layer

Question 25

The molecule is rotated to put the lowest priority group at the_____

Answer 25

back

Question 26

If the groups descend in priority (a,b then c) in clockwise direction the enantiomer is ____

Answer 26

R

Question 27

If the groups descend in priority in counterclockwise direction the enantiomer is ____

Answer 27

S

Question 28

Groups with double or triple bonds are assigned priorities as if their atoms were ________ or _______

Answer 28

duplicated or triplicated

Question 29

_________ have almost all identical physical properties (melting point, boiling point, density)

Answer 29

enantiomers

Question 30

An empty sample tube or one containing an achiral molecule will not rotate the plane-polarized light

Answer 30

Specific Rotation

Question 31

The amount the analyzer needs to be turned to permit light through is called ______

Answer 31

observed rotation (a)

Question 32

If the analyzer is rotated clockwise the rotation is (+) and the molecule is _________

Answer 32

dextrorotatory

Question 33

If the analyzer is rotated counterclockwise the rotation is (-) and the molecule is ________

Answer 33

levorotatory

Question 34

what is the formula for specific rotation

Answer 34

[a] = a/c*l

Question 35

[a]

Answer 35

specific rotation

Question 36

a

Answer 36

the observed rotation

Question 37

c

Answer 37

concentration of the solution in g/ml

Question 38

l

Answer 38

length of the tube in decimeters

Question 39

= A 1:1 mixture of enantiomers = No net optical rotation = Often designated as (+)

Answer 39

Racemic mixture

Question 40

Often a mixture of enantiomers will be enriched in one enantiomer

Answer 40

Enantiomeric Excess

Question 41

formula for %enantiomeric excess

Answer 41

1. % enantiomeric excess = moles of one enantiomer - moles of other enantiomer/ total moles of both enantiomers * 100 2. % enantiomeric excess* = observed specific rotation/ specific rotation of the pure enantiomer * 100

Question 42

The optical rotation of a sample of 2-butanol is +6.76o. What is the enantiomeric excess? its [a] = +13.52o

Answer 42

50%

Question 43

The maximum number of stereoisomers available will not exceed ____, where n is equal to the number of tetrahedral stereogenic centers

Answer 43

2^n

Question 44

achiral despite the presence of stereogenic centers

Answer 44

Meso compound

Question 45

= Not optically active = Superposable on its mirror image = Has a plane of symmetry

Answer 45

meso compound

Question 46

A 2-dimensional representation of chiral molecules

Answer 46

Fischer Projection Formulas

Question 47

______ represent bonds that project behind the plane of the paper

Answer 47

vertical lines

Question 48

_________ represent bonds that project out of the plane of the paper

Answer 48

horizontal lines

Question 49

A reaction which takes place in a way that no bonds to the stereogenic carbon are broken is said to proceed with _______

Answer 49

retention of configuration

Question 50

the relationship between comparable stereogenic centers in two different molecules

Answer 50

Relative configuration

Question 51

the actual 3-dimensional orientation of the atoms in a chiral molecule

Answer 51

Absolute configuration

Question 52

absolute configuratoon can be determined by ______

Answer 52

x-ray crystallography

Question 53

Chiral Molecules that Do Not Possess a Tetrahedral Atom with Four Different Groups

Answer 53

1. atropoisomer 2. allenes

Question 54

conformational isomers that are stable

Answer 54

Atropoisomer

Question 55

contain two consecutive double bonds

Answer 55

Allenes