Dr. Wolf's CHM 201 & 202 3-1

Chapter 3Chapter 3Conformations of Alkanes Conformations of Alkanes

and Cycloalkanesand Cycloalkanes

Dr. Wolf's CHM 201 & 202 3-2

Conformational Analysis of EthaneConformational Analysis of Ethane

Conformations are different spatial Conformations are different spatial arrangements of a molecule that are arrangements of a molecule that are

generated by rotation about single bonds.generated by rotation about single bonds.

Dr. Wolf's CHM 201 & 202 3-3

Eclipsed conformationEclipsed conformation

EthaneEthane

Dr. Wolf's CHM 201 & 202 3-4

Eclipsed conformationEclipsed conformation

EthaneEthane

Dr. Wolf's CHM 201 & 202 3-5

Staggered conformationStaggered conformation

EthaneEthane

Dr. Wolf's CHM 201 & 202 3-6

Staggered conformationStaggered conformation

EthaneEthane

Dr. Wolf's CHM 201 & 202 3-7

Projection formulas of the staggeredProjection formulas of the staggeredconformation of ethaneconformation of ethane

NewmanNewman SawhorseSawhorse

HH

HHHH HH

HH HH

HH

HH HHHH

HH

HH

Dr. Wolf's CHM 201 & 202 3-8

Anti relationshipsAnti relationships

HH

HHHH HH

HH HH

HH

HH HHHH

HH

HH

Two bonds are anti when the angle between them is 180°. Two bonds are anti when the angle between them is 180°.

180°180°

Dr. Wolf's CHM 201 & 202 3-9

Gauche relationshipsGauche relationships

HH

HHHH HH

HH HH

HH

HH HHHH

HH

HH

Two bonds are gauche when the angle between them is 60°. Two bonds are gauche when the angle between them is 60°.

60°60°

Dr. Wolf's CHM 201 & 202 3-10

An important point:An important point:The terms anti and gauche applyThe terms anti and gauche apply

only to bonds (or groups) on only to bonds (or groups) on adjacentadjacentcarbonscarbons, and only to , and only to staggeredstaggeredconformations.conformations.

Dr. Wolf's CHM 201 & 202 3-11

0°0° 60° 60° 120° 120° 180° 240° 180° 240° 300°300° 360°360°

12 kJ/mol12 kJ/mol

Dr. Wolf's CHM 201 & 202 3-12

• The eclipsed conformation of ethane is 12 kJ/molThe eclipsed conformation of ethane is 12 kJ/molless stable (higher energy) than the staggered.less stable (higher energy) than the staggered.

• The eclipsed conformation is destabilized byThe eclipsed conformation is destabilized bytorsional strain.torsional strain.

• Torsional strain is the destabilization that resultsTorsional strain is the destabilization that resultsfrom eclipsed bonds.from eclipsed bonds.

Torsional strainTorsional strain

Dr. Wolf's CHM 201 & 202 3-13

Conformational Analysis of ButaneConformational Analysis of Butane

Dr. Wolf's CHM 201 & 202 3-14

Conformational Analysis of Butane: C2-C3 Rotation

Dr. Wolf's CHM 201 & 202 3-15

0°0° 60° 60° 120° 120° 180° 240° 180° 240° 300°300° 360°360°

3 kJ/mol3 kJ/mol

14 kJ/mol14 kJ/mol

Dr. Wolf's CHM 201 & 202 3-16

• The The gauchegauche conformation of butane is 3 kJ/mol conformation of butane is 3 kJ/molless stable than the less stable than the antianti..

• The The gauchegauche conformation is destabilized by conformation is destabilized byvan der Waals strain (also called steric strain) van der Waals strain (also called steric strain) which results from atoms being too close together.which results from atoms being too close together.

van der Waals strainvan der Waals strain

gauchegauche antianti

Dr. Wolf's CHM 201 & 202 3-17

• The conformation of butane in which the twoThe conformation of butane in which the twomethyl groups are eclipsed with each other ismethyl groups are eclipsed with each other isis the least stable of all the conformations.is the least stable of all the conformations.

• It is destabilized by both torsional strainIt is destabilized by both torsional strain(eclipsed bonds) and van der Waals strain.(eclipsed bonds) and van der Waals strain.

van der Waals strainvan der Waals strain

eclipsedeclipsed

Dr. Wolf's CHM 201 & 202 3-18

Conformational Analysis of Conformational Analysis of Higher AlkanesHigher Alkanes

Dr. Wolf's CHM 201 & 202 3-19

The most stable conformation of unbranchedThe most stable conformation of unbranchedalkanes has anti relationships between carbonsalkanes has anti relationships between carbons

HexaneHexane

Dr. Wolf's CHM 201 & 202 3-20

The Shapes of Cycloalkanes:The Shapes of Cycloalkanes:Planar or Nonplanar?Planar or Nonplanar?

Dr. Wolf's CHM 201 & 202 3-21

Adolf von Baeyer (19th century)Adolf von Baeyer (19th century)

• assumed cycloalkanes are planar polygonsassumed cycloalkanes are planar polygons

• distortion of bond angles from 109.5° givesdistortion of bond angles from 109.5° givesangle strain to cycloalkanes with rings eitherangle strain to cycloalkanes with rings eithersmaller or larger than cyclopentanesmaller or larger than cyclopentane

• Baeyer deserves credit for advancing the ideaBaeyer deserves credit for advancing the ideaof angle strain as a destabilizing factor.of angle strain as a destabilizing factor.

• But Baeyer was incorrect in his belief that But Baeyer was incorrect in his belief that cycloalkanes were planar.cycloalkanes were planar.

Dr. Wolf's CHM 201 & 202 3-22

Types of StrainTypes of Strain

•• Torsional strainTorsional strainstrain that results from eclipsed bondsstrain that results from eclipsed bonds

•• van der Waals strain (steric strain)van der Waals strain (steric strain)strain that results from atoms being too closestrain that results from atoms being too closetogethertogether

•• angle strainangle strainstrain that results from distortion of bondstrain that results from distortion of bondangles from normal valuesangles from normal values

Dr. Wolf's CHM 201 & 202 3-23

Measuring Strain in CycloalkanesMeasuring Strain in Cycloalkanes

• Heats of combustion can be used to compareHeats of combustion can be used to comparestabilities of isomers.stabilities of isomers.

• But cyclopropane, cyclobutane, etc. are not isomers.But cyclopropane, cyclobutane, etc. are not isomers.

• All heats of combustion increase as the numberAll heats of combustion increase as the numberof carbon atoms increase.of carbon atoms increase.

Dr. Wolf's CHM 201 & 202 3-24

Measuring Strain in CycloalkanesMeasuring Strain in Cycloalkanes

• Therefore, divide heats of combustion by numberTherefore, divide heats of combustion by number of carbons and compare heats of combustion of carbons and compare heats of combustion on a "per CHon a "per CH22 group" basis. group" basis.

Dr. Wolf's CHM 201 & 202 3-25

Heats of Combustion of CycloalkanesHeats of Combustion of Cycloalkanes

CycloalkaneCycloalkane kJ/molkJ/mol Per CHPer CH22

CyclopropaneCyclopropane 2,0912,091 697697CyclobutaneCyclobutane 2,7212,721 681681CyclopentaneCyclopentane 3,2913,291 658658CyclohexaneCyclohexane 3,9203,920 653653CycloheptaneCycloheptane 4,5994,599 657657CyclooctaneCyclooctane 5,2675,267 658658CyclononaneCyclononane 5,9335,933 659659CyclodecaneCyclodecane 6,5876,587 659659

Dr. Wolf's CHM 201 & 202 3-26

Heats of Combustion of CycloalkanesHeats of Combustion of Cycloalkanes

CycloalkaneCycloalkane kJ/molkJ/mol Per CHPer CH22

According to Baeyer, cyclopentane shouldAccording to Baeyer, cyclopentane shouldhave less angle strain than cyclohexane.have less angle strain than cyclohexane.CyclopentaneCyclopentane 3,2913,291 658658CyclohexaneCyclohexane 3,9203,920 653653The heat of combustion per CHThe heat of combustion per CH22 group is group is

less for cyclohexane than for cyclopentane.less for cyclohexane than for cyclopentane.Therefore, cyclohexane has less strain thanTherefore, cyclohexane has less strain thancyclopentane.cyclopentane.

Dr. Wolf's CHM 201 & 202 3-27

Adolf von Baeyer (19th century)Adolf von Baeyer (19th century)

• assumed cycloalkanes are planar polygonsassumed cycloalkanes are planar polygons

• distortion of bond angles from 109.5° givesdistortion of bond angles from 109.5° givesangle strain to cycloalkanes with rings eitherangle strain to cycloalkanes with rings eithersmaller or larger than cyclopentanesmaller or larger than cyclopentane

• Baeyer deserves credit for advancing the ideaBaeyer deserves credit for advancing the ideaof angle strain as a destabilizing factor.of angle strain as a destabilizing factor.

• But Baeyer was incorrect in his belief that But Baeyer was incorrect in his belief that cycloalkanes were planar.cycloalkanes were planar.

Dr. Wolf's CHM 201 & 202 3-28

Small RingsSmall Rings

Cyclopropane Cyclopropane

Cyclobutane Cyclobutane

Dr. Wolf's CHM 201 & 202 3-29

CyclopropaneCyclopropane

sources of strain:sources of strain:

torsional straintorsional strain

angle strainangle strain

Dr. Wolf's CHM 201 & 202 3-30

CyclobutaneCyclobutane

nonplanar conformation relieves some torsional strainnonplanar conformation relieves some torsional strain

angle strain presentangle strain present

Dr. Wolf's CHM 201 & 202 3-31

CyclopentaneCyclopentane

Dr. Wolf's CHM 201 & 202 3-32

CyclopentaneCyclopentane

all bonds are eclipsedall bonds are eclipsed

planar conformation destabilizedplanar conformation destabilizedby torsional strainby torsional strain

Dr. Wolf's CHM 201 & 202 3-33

Nonplanar conformations of cyclopentaneNonplanar conformations of cyclopentane

EnvelopeEnvelope Half-chairHalf-chair

Relieve some, but not all, of the torsional strain.Relieve some, but not all, of the torsional strain.

Envelope and half-chair are of similar stabilityEnvelope and half-chair are of similar stabilityand interconvert rapidly.and interconvert rapidly.

Dr. Wolf's CHM 201 & 202 3-34

Conformations of CyclohexaneConformations of Cyclohexane

heat of combustion suggests that angleheat of combustion suggests that anglestrain is unimportant in cyclohexanestrain is unimportant in cyclohexane

tetrahedral bond angles require tetrahedral bond angles require nonplanar geometriesnonplanar geometries

Dr. Wolf's CHM 201 & 202 3-35

Chair is the most stable conformation of cyclohexaneChair is the most stable conformation of cyclohexane

All of the bonds are staggered and the bond All of the bonds are staggered and the bond angles at carbon are close to tetrahedral.angles at carbon are close to tetrahedral.

Dr. Wolf's CHM 201 & 202 3-36

Boat conformation is less stable than the chairBoat conformation is less stable than the chair

All of the bond angles are close to tetrahedralAll of the bond angles are close to tetrahedralbut close contact between flagpole hydrogensbut close contact between flagpole hydrogenscauses van der Waals strain in boat.causes van der Waals strain in boat.

180 pm180 pm

Dr. Wolf's CHM 201 & 202 3-37

Boat conformation is less stable than the chairBoat conformation is less stable than the chair

Eclipsed bonds bonds gives torsional strain toEclipsed bonds bonds gives torsional strain toboat.boat.

Dr. Wolf's CHM 201 & 202 3-38

Skew boat is slightly more stable than boatSkew boat is slightly more stable than boat

Less van der Waals strain and less torsional Less van der Waals strain and less torsional strain in skew boat.strain in skew boat.

BoatBoat Skew boatSkew boat

Dr. Wolf's CHM 201 & 202 3-39

The chair conformation of cyclohexane is theThe chair conformation of cyclohexane is themost stable conformation and derivativesmost stable conformation and derivativesof cyclohexane almost always exist in the of cyclohexane almost always exist in the chair conformationchair conformation

Dr. Wolf's CHM 201 & 202 3-40

Axial and Equatorial BondsAxial and Equatorial Bondsin Cyclohexanein Cyclohexane

Dr. Wolf's CHM 201 & 202 3-41

The 12 bonds to the ring can be divided intoThe 12 bonds to the ring can be divided intotwo sets of 6.two sets of 6.

Dr. Wolf's CHM 201 & 202 3-42

Axial bonds point "north and south"Axial bonds point "north and south"

6 bonds are axial6 bonds are axial

Dr. Wolf's CHM 201 & 202 3-43

Equatorial bonds lie along the equatorEquatorial bonds lie along the equator

6 bonds are equatorial6 bonds are equatorial

Dr. Wolf's CHM 201 & 202 3-44

Conformational Inversion Conformational Inversion (Ring-Flipping) in Cyclohexane(Ring-Flipping) in Cyclohexane

Dr. Wolf's CHM 201 & 202 3-45

Conformational InversionConformational Inversion

chair-chair interconversion (ring-flipping)chair-chair interconversion (ring-flipping)

rapid process (activation energy = 45 kJ/mol)rapid process (activation energy = 45 kJ/mol)

all axial bonds become equatorial and vice versaall axial bonds become equatorial and vice versa

Dr. Wolf's CHM 201 & 202 3-46

Dr. Wolf's CHM 201 & 202 3-47

Half-Half-chairchair

Dr. Wolf's CHM 201 & 202 3-48

Half-Half-chairchair

SkewSkewboatboat

Dr. Wolf's CHM 201 & 202 3-49

Half-Half-chairchair

SkewSkewboatboat

Dr. Wolf's CHM 201 & 202 3-50

Half-Half-chairchair

SkewSkewboatboat

Dr. Wolf's CHM 201 & 202 3-51

45 45 kJ/molkJ/mol

45 45 kJ/molkJ/mol

23 23 kJ/molkJ/mol

Dr. Wolf's CHM 201 & 202 3-52

Conformational Analysis ofConformational Analysis ofMonosubstituted CyclohexanesMonosubstituted Cyclohexanes

most stable conformation is chairmost stable conformation is chair

substituent is more stable when equatorialsubstituent is more stable when equatorial

Dr. Wolf's CHM 201 & 202 3-53

MethylcyclohexaneMethylcyclohexane

5%5% 95%95%

Chair chair interconversion occurs, but at any instant 95% Chair chair interconversion occurs, but at any instant 95% of the molecules have their methyl group equatorial.of the molecules have their methyl group equatorial.Axial methyl group is more crowded than an equatorial one.Axial methyl group is more crowded than an equatorial one.

CHCH33

CHCH33

Dr. Wolf's CHM 201 & 202 3-54

MethylcyclohexaneMethylcyclohexane

5%5% 95%95%

Source of crowding is close approach to axial Source of crowding is close approach to axial hydrogens on same side of ring. hydrogens on same side of ring. Crowding is called a "1,3-diaxial repulsion" Crowding is called a "1,3-diaxial repulsion" and is a type of van der Waals strain.and is a type of van der Waals strain.

Dr. Wolf's CHM 201 & 202 3-55

FluorocyclohexaneFluorocyclohexane

40%40% 60%60%

Crowding is less pronounced with a "small" Crowding is less pronounced with a "small" substituent such as fluorine.substituent such as fluorine.Size of substituent is related to its branching.Size of substituent is related to its branching.

FF

FF

Dr. Wolf's CHM 201 & 202 3-56

terttert-Butylcyclohexane-Butylcyclohexane

Less than 0.01%Less than 0.01% Greater than 99.99%Greater than 99.99%

Crowding is more pronounced with a "bulky" Crowding is more pronounced with a "bulky" substituent such as substituent such as terttert-butyl.-butyl.terttert-Butyl is highly branched.-Butyl is highly branched.

C(CHC(CH33))33

C(CHC(CH33))33

Dr. Wolf's CHM 201 & 202 3-57

terttert-Butylcyclohexane-Butylcyclohexane

van der Waalsvan der Waalsstrain due tostrain due to1,3-diaxial1,3-diaxialrepulsionsrepulsions

Dr. Wolf's CHM 201 & 202 3-58

Disubstituted Cycloalkanes:Disubstituted Cycloalkanes:StereoisomersStereoisomers

Stereoisomers are isomers that have Stereoisomers are isomers that have same constitution but different same constitution but different arrangement of atoms in spacearrangement of atoms in space

Dr. Wolf's CHM 201 & 202 3-59

Isomers Isomers

Constitutional isomersConstitutional isomers StereoisomersStereoisomers

Dr. Wolf's CHM 201 & 202 3-60

1,2-Dimethylcyclopropane1,2-Dimethylcyclopropane

There are two stereoisomers of There are two stereoisomers of 1,2-dimethylcyclopropane.1,2-dimethylcyclopropane.

They differ in spatial arrangement of atoms.They differ in spatial arrangement of atoms.

Dr. Wolf's CHM 201 & 202 3-61

1,2-Dimethylcyclopropane1,2-Dimethylcyclopropane

ciscis-1,2-Dimethylcyclopropane has methyl groups-1,2-Dimethylcyclopropane has methyl groupson same side of ring. on same side of ring.

transtrans-1,2-Dimethylcyclopropane has methyl groups-1,2-Dimethylcyclopropane has methyl groupson opposite sides.on opposite sides.

Dr. Wolf's CHM 201 & 202 3-62

Relative stabilities of stereoisomers may beRelative stabilities of stereoisomers may bedetermined from heats of combustion.determined from heats of combustion.

Dr. Wolf's CHM 201 & 202 3-63

3371 kJ/mol3371 kJ/mol

3366 kJ/mol3366 kJ/mol

van der Waals strain makes cisstereoisomer less stable than trans

Dr. Wolf's CHM 201 & 202 3-64

Conformational Analysis ofConformational Analysis ofDisubstituted CyclohexanesDisubstituted Cyclohexanes

Dr. Wolf's CHM 201 & 202 3-65

1,4-Dimethylcyclohexane stereoisomers1,4-Dimethylcyclohexane stereoisomers

ciscis transtrans

CHCH33

5219 kJ/mol5219 kJ/mol 5212 kJ/mol5212 kJ/mol

less stableless stable more stablemore stable

Trans stereoisomer is more stable than cis, but Trans stereoisomer is more stable than cis, but methyl groups are too far apart to crowd each other.methyl groups are too far apart to crowd each other.

HH33CC

HH HH

HH33CC

CHCH33HH

HH

Dr. Wolf's CHM 201 & 202 3-66

Conformational analysis of Conformational analysis of cis-cis-1,4-dimethylcyclohexane1,4-dimethylcyclohexane

CHCH33

Two equivalent conformations; each has one axial Two equivalent conformations; each has one axial methyl group and one equatorial methyl groupmethyl group and one equatorial methyl group

HH33CC

HH HH

HH

CHCH33

HHCHCH33

HH

HH33CC

HH

CHCH33

Dr. Wolf's CHM 201 & 202 3-67

Conformational analysis of Conformational analysis of trans-trans-1,4-dimethylcyclohexane1,4-dimethylcyclohexane

Two conformations are not equivalent; most stableTwo conformations are not equivalent; most stableconformation has both methyl groups equatorial.conformation has both methyl groups equatorial.

CHCH33

HH33CC

HH

HH

HH

HH33CC

HH

CHCH33

HH

HH33CC

HH

CHCH33

Dr. Wolf's CHM 201 & 202 3-68

1,2-Dimethylcyclohexane stereoisomers1,2-Dimethylcyclohexane stereoisomers

ciscis transtrans

5223 kJ/mol5223 kJ/mol 5217 kJ/mol5217 kJ/mol

less stableless stable more stablemore stable

Analogous to 1,4 in that trans is more stableAnalogous to 1,4 in that trans is more stablethan cis.than cis.

CHCH33

CHCH33HH

HHHH33CC

CHCH33

HH

HH

Dr. Wolf's CHM 201 & 202 3-69

Conformational analysis of Conformational analysis of cis-cis-1,2-dimethylcyclohexane1,2-dimethylcyclohexane

Two equivalent conformations; each has one axial Two equivalent conformations; each has one axial methyl group and one equatorial methyl groupmethyl group and one equatorial methyl group

CHCH33

CHCH33HH

HH

HHCHCH33

HH

CHCH33 HH

CHCH33

HH

CHCH33

Dr. Wolf's CHM 201 & 202 3-70

Conformational analysis of Conformational analysis of trans-trans-1,2-dimethylcyclohexane1,2-dimethylcyclohexane

Two conformations are not equivalent; most stableTwo conformations are not equivalent; most stableconformation has both methyl groups equatorial.conformation has both methyl groups equatorial.

CHCH33

HH33CC HH

HH

HH

CHCH33

HH

CHCH33

HH

HH33CC

HH

CHCH33

Dr. Wolf's CHM 201 & 202 3-71

1,3-Dimethylcyclohexane stereoisomers1,3-Dimethylcyclohexane stereoisomers

ciscis transtrans

5212 kJ/mol5212 kJ/mol 5219 kJ/mol5219 kJ/mol

more stablemore stable less stableless stable

Unlike 1,2 and 1,4; cis-1,3 is more stable than trans.Unlike 1,2 and 1,4; cis-1,3 is more stable than trans.

HH33CC

CHCH33

HH

HH

CHCH33

HH33CCHH HH

Dr. Wolf's CHM 201 & 202 3-72

Conformational analysis of Conformational analysis of cis-cis-1,3-dimethylcyclohexane1,3-dimethylcyclohexane

Two conformations are not equivalent; most stableTwo conformations are not equivalent; most stableconformation has both methyl groups equatorial.conformation has both methyl groups equatorial.

HH33CC

HHHH

CHCH33

CHCH33

HH33CCHH HH

HH

CHCH33

HH

CHCH33

Dr. Wolf's CHM 201 & 202 3-73

Conformational analysis of Conformational analysis of trans-trans-1,3-dimethylcyclohexane1,3-dimethylcyclohexane

Two equivalent conformations; each has one axialTwo equivalent conformations; each has one axialand one equatorial methyl group.and one equatorial methyl group.

HH33CC HH

HH CHCH33

HH

HH33CC

HHCHCH33

HH33CC

CHCH33

HH

HH

Dr. Wolf's CHM 201 & 202 3-74

Table 3.2 Heats of Combustion of Table 3.2 Heats of Combustion of Isomeric DimethylcyclohexanesIsomeric Dimethylcyclohexanes

CompoundCompound OrientationOrientation --H°H°

ciscis-1,2-dimethyl-1,2-dimethyl ax-eqax-eq 52235223transtrans-1,2-dimethyl-1,2-dimethyl eq-eqeq-eq 5217*5217*

ciscis-1,3-dimethyl-1,3-dimethyl eq-eqeq-eq 5212*5212*transtrans-1,3-dimethyl-1,3-dimethyl ax-eqax-eq 52195219

ciscis-1,4-dimethyl-1,4-dimethyl ax-eqax-eq 52195219transtrans-1,4-dimethyl-1,4-dimethyl eq-eqeq-eq 5212*5212*

*more stable stereoisomer of pair*more stable stereoisomer of pair

Dr. Wolf's CHM 201 & 202 3-75

Medium and Large RingsMedium and Large Rings

Dr. Wolf's CHM 201 & 202 3-76

Cycloheptane and Larger RingsCycloheptane and Larger Rings

More complicated than cyclohexane.More complicated than cyclohexane.

Common for several conformations to be of Common for several conformations to be of similar energy.similar energy.

Principles are the same, however.Principles are the same, however.Minimize total strain.Minimize total strain.

Dr. Wolf's CHM 201 & 202 3-77

Polycyclic Ring SystemsPolycyclic Ring Systems

Contain more than one ring…..Contain more than one ring…..

bicyclic, tricyclic, tetracyclic, etc.bicyclic, tricyclic, tetracyclic, etc.

Dr. Wolf's CHM 201 & 202 3-78

Number of ringsNumber of rings

equals minimum number of bond disconnectionsequals minimum number of bond disconnections

required to give a noncyclic speciesrequired to give a noncyclic species

Dr. Wolf's CHM 201 & 202 3-79

MonocyclicMonocyclic

requires one bond disconnectionrequires one bond disconnection

Dr. Wolf's CHM 201 & 202 3-80

BicyclicBicyclic

requires two bond disconnectionsrequires two bond disconnections

Dr. Wolf's CHM 201 & 202 3-81

BicyclicBicyclic

requires two bond disconnectionsrequires two bond disconnections

Dr. Wolf's CHM 201 & 202 3-82

Types of ring systemsTypes of ring systems

spirocyclicspirocyclic

fused ringfused ring

bridged ringbridged ring

Dr. Wolf's CHM 201 & 202 3-83

SpirocyclicSpirocyclic

one atom common to two ringsone atom common to two rings Spiro[4.5]decaneSpiro[4.5]decane

Dr. Wolf's CHM 201 & 202 3-84

Fused ringFused ring

adjacent atoms common to two ringsadjacent atoms common to two rings

two rings share a common sidetwo rings share a common side Bicyclo[4.3.0]nonaneBicyclo[4.3.0]nonane

Dr. Wolf's CHM 201 & 202 3-85

Bridged ringBridged ring

nonadjacent atoms common to two ringsnonadjacent atoms common to two rings

Bicyclo[3.2.1]octaneBicyclo[3.2.1]octane

Dr. Wolf's CHM 201 & 202 3-86

SteroidsSteroids

carbon skeleton is tetracycliccarbon skeleton is tetracyclic

Dr. Wolf's CHM 201 & 202 3-87

Heterocyclic CompoundsHeterocyclic Compounds

Dr. Wolf's CHM 201 & 202 3-88

Heterocyclic CompoundHeterocyclic Compound

a cyclic compound that contains an atom other a cyclic compound that contains an atom other

than carbon in the ringthan carbon in the ring

(such atoms are called heteroatoms)(such atoms are called heteroatoms)

typical heteroatoms are N, O, and Stypical heteroatoms are N, O, and S

Dr. Wolf's CHM 201 & 202 3-89

Oxygen-containing heterocyclesOxygen-containing heterocycles

OO

Ethylene Ethylene oxideoxide

OO

TetrahydrofuranTetrahydrofuran

TetrahydropyranTetrahydropyran

OO

OO

Dr. Wolf's CHM 201 & 202 3-90

Nitrogen-containing heterocyclesNitrogen-containing heterocycles

PyrrolidinePyrrolidine PiperidinePiperidine

NNHH

NN

HH

Dr. Wolf's CHM 201 & 202 3-91

Sulfur-containing heterocyclesSulfur-containing heterocycles

SSSS

SSSS

SS

SSSS

CHCH22CHCH22CHCH22CHCH22COHCOH

OOLipoic acidLipoic acid

LenthionineLenthionine

Dr. Wolf's CHM 201 & 202 3-92

End of Chapter 3