CHEM1102 Lecture Notes 4-5

1Chemistry 1102Charlie BondMCS Rm 4.16/[email protected]

What is Organic Chemistry?Organic Reactions I IIAlkanes (Ch 21)Conformational Analysis (Ch 21)Stereochemistry I II III (Ch 22)Alkyl Halides I II (Ch 24)Alcohols and Ether I II (Ch 24)

2Problems to do in Brown&LeMay

21.1- 21.37 except 21.4, 21.15, 21.16 21.19, 21.20

Online self-help study at www.masteringchemistry.com

3Organic Chemistry

H-C C-HH-C-C-HH

H

H

H HC C

H

H H

Hydrocarbons

Alkanes(Chapter3)

Alkenes(Chapters45)

Alkynes(Chapter4)

Arenes(Chapter9)

Onlycarboncarbonsingle

bonds

Oneormorecarboncarbondoublebonds

Oneormorecarboncarbontriplebonds

Oneormorebenzenelike

rings

Class

Example

Carboncarbonbonding

Name Ethane Ethylene Acetylene Benzene

Saturated Unsaturated

ethene ethyne

4Structure

Hydrocarbon:Hydrocarbon: a compound composed only of carbon and hydrogen

Saturated hydrocarbon:Saturated hydrocarbon: a hydrocarbon containing only single bonds

Alkane:Alkane: a saturated hydrocarbon whose carbons are arranged in a open chain

Aliphatic hydrocarbon:Aliphatic hydrocarbon: another name for an alkane

5Nomenclature Alkanes have the general formula CnH2n+2

names of unbranched chain alkanes

MolecularFormulaName

heptane

hexane

pentane

butane

propaneethanemethane CH4

C2H6C3H8C4H10C5H12C6H14C7H16

tetradecane

hexadecane

octadecane

eicosane

decanenonane

octane C8H18

C9H20C10H22

C14H30C16H34C18H38C20H42

dodecane C12H26

MolecularFormulaName

6IUPAC Nomenclature Common alkyl groups

-CH2CH3

-CH3

-CH2CH2CH3-CHCH3CH3-CH2CH2CH2CH3

-CH2CHCH3CH3

-CHCH2CH3CH3

-CCH3CH3

CH3tertbutyl

secbutyl

isobutyl

butyl

isopropyl

propyl

ethylmethyl

NameCondensedStructuralFormula

CondensedStructuralFormulaName

7IUPAC Nomenclature1.The name of an alkane with an unbranched chain

consists of a prefix and the suffix aneane2. For branched alkanes, the parent chain is the longest

chain of carbon atoms3. Each substituent is given a name and a number

4. If there is one substituent, number the chain from the end that gives it the lower number

CH3CH3CH2CH2CHCH32Methylpentane

14 3 2

5

CH3CHCH3CH3

2Methylpropane1

23

8Classification of Carbons Primary (1):Primary (1): a C bonded to one other carbon Secondary (2):Secondary (2): a C bonded to two other carbons Tertiary (3):Tertiary (3): a C bonded to three other carbons Quaternary (4)Quaternary (4): a C bonded to four other carbons

a4carbon a3carbon

a2carbon

CH3-C-CH2-CH-CH3

2,2,4Trimethylpentane

CH3

CH3

CH3a1carbon a1carbon

9Constitutional Isomers Constitutional isomers: compounds with the same

molecular formula but a different connectivity of their atoms there are two constitutional isomers with molecular

formula C4H10

CH3CH2CH2CH3 CH3CHCH3CH3

Butane(bp0.5C)

2Methylpropane(bp11.6C)

10

Constitutional Isomerism the potential for constitutional isomerism is

enormous

4,111,846,763

4,3477531

ConstitutionalIsomers

MolecularFormula

CH4C5H12C10H22C15H32

C30H6236,797,588C25H52

World populationWorld populationisis

>6,000,000,000>6,000,000,000

11

Physical Properties Alkanes are nonpolar compounds and have only

weak interactions between their molecules Dispersion forces:Dispersion forces: weak intermolecular forces of

attraction resulting from interaction of temporary induced dipoles

At Room Temperature:1-4C are gases (e.g. butane), 5-17C are liquids (e.g.

hexane, kerosene), 18+C are solids/waxes (e.g. parafin wax).

average density is about 0.7 g/mLliquid and solid alkanes float on water

12

Physical Properties Constitutional isomers are different compounds and

have different physical propertiesMeltingPoint(C)

BoilingPoint(C)Name

hexane

2methylpentane3methylpentane

2,3dimethylbutane2,2dimethylbutane

69

6264

5850

Density(g/mL)

95

236

129100

0.659

0.6530.664

0.6620.649

Hexane

2,2Dimethylbutane

Melting point goes up with branching less flexibility, molecules can pack together more easilyBoiling point goes down with branching less available surface area for interactions (e.g. compare spaghetti with spaghetti hoops)

13

Reactions of Alkanes Oxidation is the basis for the use of

alkanes as energy sources for heat and power heat of combustion:heat of combustion: heat released when

one mole of a substance is oxidized to carbon dioxide and water

CH4 2O2

CH3CH2CH3 5O2

CO2

3CO2

2H2O

4H2O

Methane++

++Propane

H=212kcal/mol

H=530kcal/mol

-886 kJ/mol

-2215 kJ/molC2H6 + 3.5O2 2CO2 + 3H2O Ho = -1427 kJ/mol

14

Conformations of EthaneConformations of Ethane

Staggered Conformation

C C

H HH H

H HEthane

H

HH

H

H

H

Newman projection

60

Each carbon-hydrogen bond bisects the angle between two carbon-hydrogen bonds on the other carbon

Each hydrogen on the front carbon is perfectly staggered between two hydrogens on the back carbon

ConformationConformation: any three-dimensional arrangement of atoms in a molecule that results from rotation about a single bond

15

Conformations of EthaneConformations of Ethane Eclipsed Conformation

Each carbon-hydrogen bond on one carbon of the eclipsed conformation of ethane is directly in line with a carbon-hydrogen

bond on the other carbon The back carbon-hydrogen bonds lie directly behind the front

carbon-hydrogen bonds The front hydrogens eclipse the back hydrogens

C C

H HH H

H HEthane

H

HH

H

H H

Newman projection

17

Conformations of ButaneConformations of Butane

C C

C C

H HH H

Butane

H HH H

H H1

2 3

4

Conformation analysis about C2-C3 bond of butane is more complex, because each carbon has a methyl group and two hydrogens bonded to it

HH

C

C

H H

C

H H

C

H H

H H

HHH H

HH

H

H

HH

18

Conformations of ButaneConformations of Butane

CH3

HH

H

H3C

H

staggered conformer

H3CH

H

H

CH3

H

eclipsed conformer

H3C

H

H

H

CH3

H

staggered conformer

CH3

HHH

CH3

H

eclipsed conformer

C C

H3C CH3

H HH H

12 3

4

C C

H3C

CH3

HH

12 3

4

HH

Newman projectionsNewman projections

19

Conformations of ButaneConformations of Butane Staggered Conformations

The methyl groups are said to be anti if the angle between them is 180

Is the most stable because is staggered and has the two methyl groups as far apart as possible

CH3

HH

H

H3C

H

conformer 1

H3C

H

H

H

CH3

H

conformer 2

We can predict that conformer 1 will be of lower energy than alternative staggered conformer 2

20

Conformations of ButaneConformations of Butane Eclipsed Conformations

The eclipsed conformation is 19 kJ/mol higher in energy than anti, due to a H with H and CH3 with CH3 eclipsing interactions

CH3

HH H

H3C

H

conformer 1

conformer 2

H3CH

H

H

CH3

H

21

The energy difference between the low-energy staggered anti conformer and the highest energy eclipsed conformer is about 19 kJ/mol

22

Physical Properties Constitutional isomers are different compounds and

have different physical propertiesMeltingPoint(C)

BoilingPoint(C)Name

hexane

2methylpentane3methylpentane

2,3dimethylbutane2,2dimethylbutane

69

6264

5850

Density(g/mL)

95

236

129100

0.659

0.6530.664

0.6620.649

Hexane

2,2Dimethylbutane

Melting point goes up with branching less flexibility, molecules can pack together more easilyBoiling point goes down with branching less available surface area for interactions (e.g. compare spaghetti with spaghetti hoops)

23

Cycloalkanes General formula CCnnHH2n2n

five- and six-membered rings are the most common

Cyclopentane, cyclohexane

24

Cyclic Molecules in NatureCyclic Molecules in Nature

Steroids are an important class of compounds occurring in all animals and plants and have many important functions;

hormones, anabolic steroids

OH

H HHH H H

OCH3

HO OEstradiol Progesterone

25

Conformations of CyclohexaneConformations of Cyclohexane This is a chair conformation The view along C1 C5 shows that there

are no eclipsing C H

All bonds are fully staggered, giving the lowest energy possible

This is why cyclohexane is strain free

26

Conformations of CyclohexaneConformations of Cyclohexane

Staggered Conformation of Butane

C C

C C

H HH H

Butane

H HH H

H H1

2 3

4

This is a chair conformation of cyclohexane

H3C

H

H

H

CH3

H

conformer 2

27

Conformations of CyclohexaneConformations of Cyclohexane This is a boat conformation Now all the C H bonds are eclipsed

Boat conformation is 25 kJ/mol

higher in energy than chair conformation

28


CH3

HH H

H3C

H

Newman projection

C C

C C

H HH H

Butane

H HH H

H H1

2 3

4

Eclipsed Conformation of Butane

This is a boat conformation of cyclohexane

29

Eclipsed conformation of butane


CH3

HH

H

H3C

H

Newman projection

CH3

HH H

H3C

H

Newman projection

Staggered conformation of butane

30

Drawing CyclohexaneDrawing Cyclohexane1. Draw two parallel lines, slanted

downward and slightly offset from each other. This means that four of the cyclohexane carbon atoms lie in plane.

3. Locate the top most carbon above and to the right of the plane of the other four atoms and connect the bonds.

5. Locate the bottom most carbon atom below and to the left of the plane of the middle four and connect the bonds.

7. Note that the bonds to the bottom most carbon are parallel to the bonds to the top most carbon.

31

Drawing CyclohexaneDrawing Cyclohexane1. Start off with one end. Locate

the top carbon on the left.

2. Next draw the two parallel lines of equal lengths. At this stage,

the top of the new line should be level with the top of the original pair.

6. Finally, the last lines should be parallel to the first pair of lines

shown, and the lowest points should also be level.

these lines should be parallel

these lines should be parallel

Level

32

How How Not Not to Draw Cyclohexaneto Draw Cyclohexane

33

AxialAxial and and EquatorialEquatorial Bonds in Cyclohexane Bonds in Cyclohexane The chair conformation has two kinds of positions for substituents

on the ring: axial positions and equatorial positions Chair cyclohexane has six axial hydrogens perpendicular to the

ring (parallel to the ring axis) and six equatorial hydrogens near the plane of the ring

34

AxialAxial and and Equatorial Equatorial BondsBonds

35

Conformational Mobility of Cyclohexane Conformational Mobility of Cyclohexane

The chair conformations readily interconvert, resulting in the exchange of axial and equatorial positions by a ring-flip

36

Ring flippingRing flippingFor an animation, look athttp://www.chem.calgary.ca/courses/351/Carey5th/Ch03/ch3-06.html

37

NH

N

OO

OHOH

OHHOH2C

OHHO

H NH

Tetrodotoxin

The Poisonous PufferfishThe Poisonous Pufferfish

25 milligrams of tetrodotoxin would be expected to kill a 75 kg person

FuguFugu- is the Japanese word for pufferfish and is also a Japanese dish prepared from the meat of pufferfish."I want to eat fugu, but I don't want to die" "I want to eat fugu, but I don't want to die" Fugu wa kuitashii, inochi wa oshishii

38

Conformation of Methylcyclohexane Conformation of Methylcyclohexane CH3

The two conformers of methylcyclohexane are not equal in energy

HHH3C

HH

H

123

4 561

234

5 6

chairequatorial 95%

chairaxial 5%

boat

CH3

H

H

HH

H

H

H

CH3

HH

H

H

HH

H

H

H

H

H

39

The equatorial conformer of methyl cyclohexane is more stable than the axial conformer by 7.6 kJ/mol

Conformation of Methylcyclohexane Conformation of Methylcyclohexane

40

CH3

Cl CH3Cl

CH3

Cl

I II III

CH3

IV

Cl

Problem:Problem: Which of the following cyclohexanes has the highest highest energy?

Problem:Problem: Which of the following cyclohexanes has the lowestlowest energy?

C

Cl

I II III IV

H3C

CH3

CH3C

CCH3CH3H3C

Cl

H3CCH3

CH3Cl

CCH3CH3H3CCl

41


H

H

1

234

5 6

H

HH

H

H

HH

H

H

H

these H atoms are allup relative to their partnerson the same C carbon

these H atoms are alldown relative to their partnerson the same C carbon

H H

OH OH

HOH

H

e

a

42

What happens with more than one substituent on the cyclohexane ring? Problem:Problem: Draw the conformations of the two isomers of cis and trans 1,2-cyclohexanediol.

OH

H

both OH groups occupy positions on the upper side of the ring

cis - 1,2-cyclohexanediol both H atoms occupy positions on the lower side of the ring

e

a e aOH

OH OH

H

OH

HHO

H1

22 1

OH

Hea e

aH

OH

H

OHHO

H1

22 1

conformer with bothOH axial

the more stableconformer with bothOH equatorial

trans - 1,2-cyclohexanediol

OH

OH

43

Problem:Problem: Draw the conformations of the two isomers of cis and trans 1,4-cyclohexanediol.

OH OH

HOH

HOH OH

H

H

HO

conformer with bothOH axial

the more stableconformer with bothOH equatorial

trans - 1,4-cyclohexanediol

a

a

ee

OH H

OHH

OHOH OH

H

H

HO

both H atoms occupy positions on the upper side of the ring

cis - 1,4-cyclohexanediol both OH groups occupy positions on the lower side of the ring

e

a

e

a

1

4

4

1

44

Draw the preferred conformations of the two isomers of 1,3,5-trimethylcyclohexane

CH3CH3

CH3

H

H

H

axialequatorial

13

5

axialequatorial

13

5CH3

HCH3

H

H3C

H

1

3

5

1

3

5

CH3

H

H

CH3

H3C

H 13

5

CH3

H

H3C

H

H3C

H 13

5

Slide 1Slide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26Slide 27Slide 28Slide 29Slide 30Slide 31Slide 32Slide 33Slide 34Slide 35Slide 36Slide 37Slide 38Slide 39Slide 40Slide 41Slide 42Slide 43Slide 44

Documents

CHEM1102 Lecture Notes 4-5