Alkanes SCH 102 - University of Nairobi Personal Websites...SCH 102 Dr. Solomon Derese 1 Alkanes are...

SCH 102

Dr. Solomon Derese 1

Alkanes are one of the hydrocarbon families that haveonly sp3 carbons.

Each carbon atom in the molecule is surrounded bysingle covalent bonds.

As a result, the molecules are tetrahedrally shapedand are non-polar molecules since all of the C-H bonddipoles cancel each other.

Alkanes are Saturated hydrocarbons known as acyclicif they are open chain , cycloalkanes if they are cyclic.

Alkanes

SCH 102

Dr. Solomon Derese

The Structure of Alkanes

• The simplest alkane ismethane.

• The molecular formula isCH4.

• Tetrahedral geometry.

• sp3 hybridized carbon.

• Bond angle 109.5°.Tetrahedral

2

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Ethane Propane

C CH

H H

H H

H C CH

H H

H H

C

H

H

H

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C4H10

C CH

H H

H H

C

H

H

C

H

H

H

C CH

H H

H

H

C

H

H

H

CH H

Straight chain (normal)

Branched-chain

n-butane

Isobutane

Two Possible Structures

Compoundswhich havethe sameformula butdifferentstructures arecalledIsomers.

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C5H12 Three possible structures

C CH

H H

H H

C

H

H

C

H

H

C

H

H

H

C CH

H H

H

C

H

H

C

H

H

H

C HH

H

n-Pentane

Neopentane

Isopentane

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Isomers are compounds that have the same numberand kind of atoms but differ in the way the atoms arearranged.

Compounds like butane and isobutene, whose atomsare connected differently, are called ConstitutionalIsomers.

Number of possible isomers increases with number of carbon atoms.

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Step I: Find the parent hydrocarbon

Rules of Naming Alkanes

a) Find the largest continuous chain ofcarbon atoms present in the molecule, anduse the name of that chain as the parentname. The longest chain may not alwaysbe apparent from the manner of writing;you may have to “turn corners”.

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Named as a substituted hexane

Named as a substituted heptane

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b) If two chains of equal length are present, choosethe one with the large number of branches pointsas the parent:

as a hexane withone substituentnot

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Step II: Number the atoms in the main chain

a)Beginning at the end of nearer the first branchpoint, number each carbon atom in the chain:

NOT

12

3

45

6

7 12

3

4 5

6

7

The first branch occurs at C3 in the proper system ofnumbering, not at C4.

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b)If there is branching an equal distance away fromboth ends of the parent chain, begin numbering atthe end nearer the second branch point:

not1

2

3 5

4

6

12

3

4

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Step III Identify and number the substituents

a)Assign a number to each substituent according toits point of attachment to the main chain:

1

234

5

67

8

9

Named as nonane

Substituents: On C3,

CH3

CH3

CH2CH3

On C4,

On C7,

(3-ethyl)

(4-methyl)

(7-methyl)

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b)If there are two substituents on the same carbon,give them both the same number. There must be asmany numbers in the name as there aresubstituents.

123

4

56 Named as hexane

Substituents: On C2,

CH3

CH3

CH2CH3

On C4,

On C4, (4-ethyl)

(4-methyl)

(2-methyl)

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Step IV: Write the name as a single word

Use hyphens to separate the different prefixes, anduse commas to separate numbers. If two or moresubstituents are present, cite them in alphabeticalorder. It two or more identical substituents arepresent, use one of the multiplier prefixes di, tri, tetraand so forth. Do not use these prefixes foralphabetizing purposes, however.

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12

3

4

5

6

12

34

5

67

89

3-Methylhexane

3-Ethyl-4,7-dimethylnonane

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12

34

5

6

7

12

34

56

12

3

456

3-Ethyl-2-methylhexane

4-Ethyl-3-methylheptane

4-Ethyl-2,4-dimethylhexane

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CYCLOALKANES

CH2

CH2

CH

2

CH2

CH2

C

H2

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IntroductionCycloalkanes are hydrocarbons that have the generalformula CnH2n and in which some of the carbon atomsform a ring.

CyclohexaneCyclopropane Cycloheptane

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Nomenclature of Cycloalkanes

The naming of cycloalkanes is basically the same asthat of alkanes, except that where we choose thelongest continuous carbon chain for the base name ofan open-chain alkane, we choose the largest ring forthe base name of a cycloalkane.

3,4,6-Trimethyloctane Propylcyclopentane

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Monocyclic alkanes

The locant of the substituent in cycloalkanes bearingone substituent need not be numbered, sinceconstitutional isomers of a mono-substitutedcycloalkane are not possible.

Unsubstituted/monosubstituted cycloalkanes

Examples

Cyclopropane Ethylcyclohexane Methylcycloheptane

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Multisubstituted cycloalkanes

• However, when a cycloalkane carries more thanone substituent, constitutional isomers are nowpossible and it is important to specify the locantsof the substituents.

• The first alkyl substituent on a cycloalkane alwaystakes the number 1, and then the ring is numberedso that the second substituent gets the lower ofthe two possible locant numbers.

• In other words, start at a point of attachment andnumber the substituents so as to arrive at thelowest sum.

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1,1-Dimethylcyclohexane 1,2-Dimethylcyclohexane

gem-Dimethylcyclohexane vic-Dimethylcyclohexane

Geminal (twins) Vicinal (neighbor)

or or

1,3-Dimethylcyclohexane 1,4-Dimethylcyclohexane

1,5-Dimethylcyclohexanenot

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If the largest ring is larger than the longestcontinuous open chain, the compound is usuallynamed as an alkylcycloalkane, while if the openchain is longer, it will be named as acycloalkylalkane.

1-Ethyl-3,5-dimethylcycloheptane

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(2,2,4-Trimethylpenatan-3-yl)cyclohexane

1

23

54

(1-Isopropyl-2,2-dimethylpropyl)cyclohexane

(1-(Methylethyl)propyl-2,2-dimethylpropyl)cyclohexane

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1-(2-Isopropyl-5-methylcyclohexyl)nonane

1

23

5

4

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17

However, this rule is subject to another restriction:when two (apparently equal) alternative names arepossible for an alkane or a cycloalkane, the correctIUPAC name is the one that gives the higher numberof branches. Thus, if the open chain has moresubstituents than the ring, the cycloalkane is namedas a cycloalkylsubstituent; conversely, when the ringcarries more substituents than the alkylchain, thering is chosen as the base name.

3-Cyclopentyl-3-ethyl-4-propylheptane

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1-Hexyl-3,5-dimethylcyclohexane

1-Cyclohexyl-2,5-Dimethylhexane

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Cis-Trans isomerism in disubstituted cycloalkanes

Free rotation is possible around carbon-carbon bondsin open chain alkanes. However, there is much lessfreedom in cycloalkanes because of their geometricconstraints.

This leads to the possibility of isomerism indisubstituted cycloalkanes.

A

H

A

H

A

H

H

A

Substituent on the sameside of the ring

Substituent on oppositeside of the ring

X Y

X and Yare different compounds

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Both isomers are stable compounds; neither can beconverted in to the other without breaking thecarbon-carbon bond. Compounds that have theircarbon connected in the same order, but differ inthree dimensional orientations are calledstereoisomers.

A

H

A

H

A

H

H

A

Substituent on the sameside of the ring

Substituent on oppositeside of the ring

X Y

CIS TRANS

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Examples

trans-1,2-Dimethylcyclopropanecis-1,2-Dimethylcyclopropane

trans-1,2-dimethylcyclopentanecis-1,2-dimethylcyclopentane

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Conformation and stability of cycloalkanes

H

H

HH

H

H

The normal angle betweenthe carbon bonds in analkane is 109.5°.

However, when the carbon atom forms part of a ring,the angle will be controlled by the requirements ofthe ring.

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Cyclopropane Cyclobutane Cyclopentane

CyclohexaneCycloheptane

n

ngleInternalan

180)2(

Int. angle 60° 90° 108°

Int. angle 120° 129°

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Bäyer (1885) proposed a theory of angle strain forcycloalkanes in which the difference between atetrahedral angle (109.5°) and the internal angle ofthe appropriate polygon is used as a measure ofmolecular stability.

The deviation of bond angles from the tetrahedralangle cause the molecule to be strained and henceunstable compared with molecules in which the bondangles are tetrahedral.

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Stability of cycloalkanes

Ring

size

Heat of combustion

per CH2

(kcal/mol)

Ring

size

Heat of combustion

per CH2

(kcal/mol)

3

4

5

6

166.6

164.0

158.7

157.4

7

8

9

10

158.3

158.6

158.8

157.4

Heat of combustion for an open chain alkane per –CH2-

is 157.4 kcal/mol

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Cycloalkanes, adopt their minimum energy conformation for acombination of three reasons:1. Angle strain: the strain due to expansion or compression

of bond angles. It is an increase in energy when bondangles deviate from the optimum tetrahedral angle of109.5°.

2. Torsional strain: the strain due to the eclipsing of bondson neighboring atoms. It is an increase in energy causedby eclipsing interactions.

3. Steric strain: the strain due to the repulsive interactionswhen atoms approach each other too closely. It is anincrease in energy resulting when atoms are forced tooclose to one another.

The ring strain of a cycloalkane is the total sum of theabove three.

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The various spatial arrangements available to amolecule by rotation about single bonds arecalled conformations. The investigation ofvarious conformations of a molecule and theirrelative stabilities is known as conformationalanalysis.

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Conformations of 3- to 5-membered rings

Cyclopropane

H

H

H

H

H

H

All the 6 H’s are eclipsed and the bond angle is

60. As a result of torsional strain and angle strain

cyclopropane is very unstable.

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Cyclobutane

H

H

H

H

H H

H H

pucker25°H

H

H

HH

H

HH

All 8 H’s areeclipsed and thebond angle is 90°.

Planar cyclobutaneIn the puckeredconformation the bondangles is 88°. This results inincreased angle strain butdecreased torsional strain.

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1.4.1.3 Cyclopentane

H H

HH

H H

H

H

H

HH H

H

HH

H

H

HHpucker

TS No TS

Planar cyclopentane

All 10 H’s areeclipsed and thebond angle is108º.

Envelope

In the envelope conformation fourcarbons are in a plane and the fifth isout of the plane, sort of like the flap ofan envelope. The number eclipsedhydrogens is reduced at the expenseof angle strain, the bond angle is 105º.

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1.4.2 Conformations of cyclohexane

H

H

H

H

H

HH

H

HH

H

H

H H

H

H

HH

H

HH

H

H

All 12 H’s are eclipsedand the bond angle is120º, as a result veryunstable.

pucker

Planar cyclohexaneChair conformer

All 12 H’s are staggeredand the bond angle is109.5°, as a resultcyclohexane is verystable.

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All hydrogens

are staggered!!!

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ax

axax

ax

ax

eq eq

ax

eq

eq

eq

eq

12

3

4

56

Ring axis

Ring equator

Axial and equatorial hydrogens of cyclohexane

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eq

ax

eq

ax

eq

ax

eqax

Me

Me

Me

Me

MeMe

Me

Me

cis-1,2-dimethylcycolohexane

trans-1,2-dimethylcycolohexane

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Me

Me

MeMe

Me

Me

MeMe

eq

axeq

ax

eq

ax

eq

ax

cis-1,3-dimethylcycolohexane

trans-1,3-dimethylcycolohexane

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Monosubstituted cyclohexanes: Conformational analysis

The methyl group can be in an equatorialor axial position.

We might, therefore, expect to find two isomericforms of methylcyclohexane.

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These two compounds are obviouslystereoisomers, and because they are notenantiomers, they must be diastereomers.

H

HH

H

H

HH

HH

H

HH

H

H

H

HH

H

HH

H

H

Equatorial

Axial

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Ring flipping (also known as ring inversion or ringreversal) is a phenomenon involving theinterconversion (by rotation) about single bonds ofcyclic conformers having equivalent ring shapes butnot necessarily equivalent spatial positions ofsubstituent atoms.

H

CH3HH

H

HH

H

HH

H

HH

HHH

H

H CH3

H

HH

H

H

ring flip

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ring flip

push this

carbon up

pull this

carbon down

Ring-flip in cyclohexane

Although cyclohexane rings rapidly flip betweenconformations at room temperature, the twoconformers of a monosubstituted cyclohexane are notequally stable.

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AXIALEQUATORIAL

RING FLIP

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H

CH

H

H

HH

H

HH

H

H

HH

H1

23

4

56 ring flip

H

HH

H

H

HC

H

HH

H

H H

H

H1

23

4 56

van der Walls strain between

hydrogens of the axial CH3

and hydrogens at C-3 and C-

5.

Smaller van der Walls

strain between hydrogens

at C-1 and hydrogens at C-

3 and C-5.

5% 95%

The energy difference between axial and equatorialconformers is due to steric strain caused by 1,3-diaxial interactions.

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In methylcyclohexane for example the equatorialconformer of methyl cyclohexane is more stable than theaxial by 7.6 kJ/mol. Similarly for other monosubstitutedcycloalkanes: “a substituent is almost always stable in anequatorial position that in an axial position”.

The investigation of molecular conformations and theirrelative energies is called Conformational Analysis. Wehave just carried out a conformational analysis ofmethylcyclohexane.

Similar studies with other substituents indicate that thereis generally less repulsive interaction when the groups areequatorial than axial.

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What is true for methylcyclohexane is also true forother monosubstituted cycloalkanes: A substituent isalmost more stable in equatorial position that in anaxial position.

The exact amount of 1,3-diaxial steric strain depends,of course, on the nature and size of the axial group.

The amount of steric strain increases through theseries CH3- < CH3CH2- < (CH3)2CH- < (CH3)3C- in parallelwith increasing bulk of the successively larger alkylgroups.

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H

CH

H

H

HH

H

HH

H

H

CH3CH3

CH31

23

4

56

ring flip

H

HH

H

H

HC

H

HH

H

H CH3

CH3

CH3

12

3

4 56

Severe 1,3-diaxialinteraction involvingt-butyl group.

Decreased van derWalls strain.

< 0.01%99.99%

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Puckered three dimensional

conformations

Minimum Energy Conformation

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Y Strain of one H-Y (1,3-diaxial interaction)

- F 0.5 kJ/mol

- Cl or - Br 1.0 kJ/mol

- OH 2.1 kJ/mol

-CH3 3.8 kJ/mol

-CH2CH3 4.0 kJ/mol

-CH(CH3)2 4.6 kJ/mol

-C(CH3)3 11.4 kJ/mol

-C6H5 6.3 kJ/mol

-CN 0.4 kJ/mol

-COOH 2.9 kJ/mol

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Disubstituted cyclohexanes

Monosubstituted cycloalkanes usually have thesubstituent in an equatorial position.

All steric interactions in both possible chairconformers must be analyzed before deciding whichconformer is favored.

In disubstituted cyclohexanes, however, the situationis more complicated because of the steric effects ofboth substituents must be taken into account.

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Conformational analysis of 1,2-dimethylcyclohexane

cis trans

Which one is more stable cis or trans?

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cis-1,2-Dimethylcyclohexane

H

CH3H

H

H

HH

H

HH

H

CH3 1

23

4

56

H

HH

H

CH3

HCH3

H

HH

H

H

ring flip

One gauche interaction

=3.8 kJ/mol

Two CH3-H 1,3-diaxial

interactions.

2 X 3.8=7.2 kJ/mol

One gauche interaction

=3.8 kJ/mol

Two CH3-H 1,3-diaxial

interactions.

2 X 3.8=7.2 kJ/mol

Total strain = 11.4 kJ/mol Total strain = 11.4 kJ/mol

50% 50%

SCH 102


Gauche butane (3.8 kJ/mol strain)

Gauche interaction

In both chair-conformations of cis-1,2-dimethylcyclohexane, there is one methyl group in anaxial position and one in an equatorial position.Therefore, the energies of these conformations arethe same, 11.4 kJ/mol.

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trans-1,2-dimethylcyclohexane

H

HH

H

H

HCH3

H

HH

H

CH3 1

23

4

56

H

CH3H

H

CH3

HH

H

HH

H

H

ring flip

12

3

4 56

One gauche interaction =3.8 kJ/mol

Four CH3-H 1,3-diaxial interactions.

4 X 3.8=15.2 kJ/mol>99%

The trans-1,2-dimethylcyclohexane with diequatorial methyl substituents is the most stable form.Therefore, trans-1,2-dimethylcyclohexane is morestable than cis-1,2-dimethylcyclohexane.

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Which member of each of the following pairs would you expect to be more stable? Explain your answers.

a) cis or trans-1,2-dimethylcyclohexaneb) cis- or trans-1,3-dimethylcyclohexanec) cis- or trans-1,4-dimethylcyclohexane

Assignment 26

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Dr. Solomon Derese

Overview of Stereochemistry

• The sub-discipline of chemistry dealing with thespatial (i.e., three-dimensional) relationshipsbetween the atoms in a molecule.

• Stereochemistry is the study of the threedimensional shapes of molecules. It is offundamental importance in determining chemicaland physical properties of molecules.

• Accordingly, most studies of organic compoundsinvolve stereochemistry at some level.

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Stereochemistry

The branch of chemistry that dealswith spatial arrangements of atoms inmolecules and the effects of thesearrangements on the physical andchemical as well as biochemicalproperties of substances.

Definition

64

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Effect of stereochemistry on physical property

bp 60°C bp 48°C

C C

H

ClCl

H

C C

Cl

HCl

Hcis-1,2-Dichloroethene trans-1,2-Dichloroethene

Geometric isomers

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only one enantiomer matches chiral enzymes

Think of biological recognition as equivalent to 3-point interaction.

Effect of stereochemistry on biological property

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Lemon Oranges

Mirro

rLevorotatory Dextrorotatory

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b-Blocker of heart disease Contraceptive

Mirro

rN

O

O

N

O

O

DARVON NOVRAD

Mirro

r

Painkiller Anticough68

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Dr. Solomon Derese

Cellulose

one axial, one equatorial bond

two equatorial bonds

Starch

Thus, an apparently minordifference in the three-dimensional arrangementof atoms confers verydifferent properties onstarch and cellulose.

Cotton fabric

Food

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Thalidomide was hailed as a "wonder drug"that provided a "safe, sound sleep". It wasa sedative that was found to be effectivewhen given to pregnant women to combatmany of the symptoms associated withmorning sickness.

The thalidomide tragedy

SedativeTeratogen

Agents that cause malformations in a developing embryo

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Some objects are not the

same as their mirror

images.

A right-hand glove is

different than a left-hand

glove.

Organic molecules (including many drugs) have

handedness that results from substitution

patterns on SP3 hybridized carbon.

This property is commonly

known as “handedness” or

chirality.

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Stereochemistry at Tetrahedral Centres

Handedness is also important in organic andbiological chemistry, where it arises primarily as aconsequence of the tetrahedral stereochemistry ofsp3-hybridized carbon atoms.

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Mirro

r

A B

The mirror images are different, the way aright hand is different from a left hand. As aresult an SP3 hybridized atom bonded to fourdifferent atoms is chiral.

An SP3 hybridized atom bonded to four different atoms.

Sterogenic/Chiral center

A molecule that is not identical to its mirror image is said tobe chiral (ky-ral, from the Greek cheir, meaning “hand”).

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Chiral : four different carbons at C-2.

Achiral : two of the groups at C-2 are the same.

The opposite of chiral is achiral. A molecule that issuperimposable on its mirror image is achiral.

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A molecule having a tetrahedralcarbon with 4 differentattachments may exist as a pairof isomers, stereoisomers.

Tetrahedral (sp3) hybridized carbon.

Stereoisomers are isomers that have same formulaand connectivity but differ in the position of theatoms in space.

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MirrorMirror

Enantiomers are stereoisomers that arenonsuperposable mirror images.

Enantiomers are molecules that are not the sameas their mirror image

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The experimental facts that led van’t Hoff and LeBel to propose that molecules having the sameconstitution could differ in the arrangement oftheir atoms in space concerned the physicalproperty of optical activity.

Optical activity is the ability of a chiral substanceto rotate the plane of plane-polarized light and ismeasured using an instrument called apolarimeter.

How can we experimentally determine whether a

molecule is chiral or achiral?

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Optical Activity

A beam of ordinary light consists of electromagneticwaves that oscillate in an infinite number of planes atright angles to the direction of light travel.

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When a beam of ordinary light is passed through adevice called a polarizer, however, only the light waveoscillating in a single plane pass through-hence thename plane polarized light.

Unpolarized Light Polarized Light

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When a beam of plane polarized light passes througha solution of chiral organic molecules, the plane ofpolarized light is rotated.

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• The ability of chiral molecules to rotate plane ofpolarized light is called optical activity.

• Solutions of chiral compounds rotate plane-polarized light and the molecules are said to beoptically active.

• Plane-polarized light that passes through solutionsof achiral compounds remains in that plane, achiralmolecules are optically inactive.

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Measurement of Optical Rotation

The source passes through a polarizer and then isdetected at a second polarizer. The angle betweenthe entrance and exit planes is the optical rotation.

A polarimeter measures the rotation of plane-polarized that has passed through a solution.

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Specific Rotation

To have a basis for comparison, define specific rotation, []D

for an optically active compound.

Where obs is observed angle of rotationin degrees, l is path length of cell indecimeters, c is concentration ofoptically active compound in grams per100 mL solvent.

Dextrorotatory (+) is an optically active compound thatrotates plane polarized light in a clockwise direction whilelevorotatory (-) rotates it anticlockwise.

Specific rotation is that observed for 1 g/mL in solution in cellwith a 10 cm path using light from sodium metal vapor (589nanometers).

[𝛼]𝐷𝑇=

100𝛼𝑜𝑏𝑠𝑙𝑐

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Specific Rotation and Molecules

Characteristic property of an optically activecompound.

The specific rotation of the enantiomer is equal inmagnitude but opposite in sign.

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Properties of Enantiomers

Enantiomers have identical physical properties:

Melting point, boiling point, density etc.

Enantiomers have different chiral property.

They rotate plane-polarized light in oppositedirections (clockwise or counter clockwise).

+123.8°-123.8°

Stereoisomers of Limonene

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86

Chemists use the letters R and S to indicate theconfiguration about an asymmetric carbon. For anypair of enantiomers with one asymmetric carbon,one will have the R configuration and the other willhave the S configuration. The R,S system wasdevised by Cahn, Ingold, and Prelog (CIP rules).

THE R/S SYSTEM

Each of the four groups attached to the stereocenteris assigned a priority.

Priority is first assigned on the basis of the atomicnumber of the atom that is directly attached to thestereocenter.

SCH 102

Dr. Solomon Derese

The group with the lowest atomic number is given thelowest priority, 3; the group with next higher atomicnumber is given the next higher priority, 2; and so on.

87

• Priority depends on the atomic numbers of the 4atoms attached to the stereocenter; atom withhigher atomic number receives the higher priority.

• If two atoms are isotopes of the same element, theheavier isotope is assigned the higher priority.

Sequence Rule 1

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I

C

BrCl

H

1

2

3

4

Sequence Rule 2

If the relative priority of two groups cannot bedecided by Rule 1, it shall be determined by a similarcomparison of the next atoms in the groups (and soon, if necessary), working outward in ranks from thestereocenter.

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Atoms participating in a double or triple bond areconsidered to be bonded to an equivalent number ofsimilar atoms by single bonds

Sequence Rule 3

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If the order of precedence the three highest rankedsubstituents appears in a clockwise sense then theconfiguration of the chiral carbon is R (Latin Rectus,“Right”)

Look at the molecule with the lowest priority groupfacing away:

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If the order of precedence the three highest rankedsubstituents appears in a an anticlockwise sense,then the configuration of the chiral carbon is S (LatinSinster, “left”)

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I

C

BrCl

H

1

2

3

4

R - Configuration

I

C

Br Cl

H

1

23

4

S - Configuration

MIR

RO

R

SCH 102


Br

C

H3CH2C CH3

H

1

2 3

4

1

23

4

Br

C

CH2CH3H3C

H

S R(S)-2-Bromobutane (R)-2-Bromobutane

SCH 102


Mirro

r

(R)-Butan-2-ol (S)-Butan-2-ol

The sign of optical rotation is not related to the R,Sdesignation. Either of them can be dextrorotatoryor levorotatory.

Their absolute configuration was determinedthrough a series of experiment and it was foundthat (R)-butan-2-ol is levorotatory while (S)-butan-2-ol is dextrorotaory.

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Dr. Solomon Derese

Assignment 27Practice assigning R or S configurations.

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SCH 102

Dr. Solomon Derese

Compounds with two or more Tetrahedral Stereocenters

Many organic compounds have more than oneasymmetric carbon. The more asymmetric carbons acompound has, the more stereoisomers are possiblefor the compound.

If we know how many asymmetric carbons acompound has, we can calculate the maximumnumber of stereoisomers for that compound: acompound can have a 2n maximum of stereoisomers,where n equals the number of asymmetric carbons.

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SCH 102

Dr. Solomon Derese

H

BrCH3

ClCH3

H4

3

21H

CH3Br

CH3Cl

H

H

BrCH3

CH3Cl

H

H

CH3Br

ClCH3

H

I II

III IV

Enantiomers: I and II; III and IVDiasteriomers: I and III; I and IV; II and III; II and IV

Enantiomers

Enantiomers

Dia

ste

riom

ers

Dia

ste

riom

ers

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SCH 102

Dr. Solomon Derese

Stereoisomers that are not enantiomers. Unlike enantiomers,each diastereomer has a unique set of physical and chemicalproperties. Diastereomers are usually encountered inmolecules with multiple stereogenic centers.

Diastereomers

Enantiomers Vs Diastereomers

• Enantiomers are stereoisomers that are non-superimposable mirror images of each other.

• Diastereomers are stereoisomers that are notenantiomers; they are not mirror images of eachother.

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SCH 102

Dr. Solomon Derese

Assignment 28Draw all the stereoisomers that are possible for thecompound given below. Identify the enantiomers anddiastereomers.

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