alkana - website staff uistaff.ui.ac.id/system/files/users/rita.arbianti/material/alkana.pdf ·...

AlkanaAlkanaDept Teknik KimiaFTUIDept Dept TeknikTeknik KimiaKimiaFTUIFTUI

CCnnHH22nn+2+2

HydrocarbonsHydrocarbonsHydrocarbons

AromaticAromaticAromaticAliphaticAliphaticAliphatic


AromaticAromaticAromaticAliphaticAliphaticAliphatic

AlkanaAlkanaAlkana AlkunaAlkunaAlkunaAlkenaAlkenaAlkena


AliphaticAliphaticAliphatic

AlkanaAlkanaAlkana

Alkanes are hydrocarbons in which all of the bonds are single bonds.

CC CCHH HH

HH HH

HH HH

etana



AlkenaAlkenaAlkena

Alkenes are hydrocarbons that contain a carbon-carbon double bond.

CC CC

HH HH

HH HH

Etena



AlkunaAlkunaAlkuna

Alkuna are hydrocarbons that contain a carbon-carbon triple bond.

HCHC CHCH

Asetilen


AromaticAromaticAromatic

The most common aromatic hydrocarbons are those that contain a benzene ring.

HH

HH

HH

HH

HH

HH

StrukturStruktur alkanaalkana

tetrahedral about carbon all bond angles are approximately 109.5°

PenggambaranPenggambaran AlkanaAlkana

CH3 CH2 CH2 CH3CH3 CH2 CH3 CH3CH2CH2 CH2 CH3

PentaneButanePropane PentanePropane

Structuralformula

Line-angleformula

Ball-and-stickmodel

PenamaanPenamaan AlkanaAlkana

Suffix -anaana specifies an alkanaana Prefix tells the number of carbon atoms

undec-dodec-

tetradec-pentadec-hexadec-heptadec-

nonadec-eicos-

tridec-

11121314151617

octadec- 181920

Prefixmeth-eth-prop-but-pent-hex-

oct-non-dec-

1234567hept-89

10

Carbons CarbonsPrefix

PenamaanPenamaan AlkanaAlkana Parent name:Parent name: the longest carbon chain Substituent:Substituent: a group bonded to the parent

chain alkyl group:alkyl group: given the symbol R-

Alkane Alkyl group

CH4

Name Name

Methane CH3 - Methyl group

CH3 CH3 Ethane CH3 CH2 - Ethyl group


Each substituent is given a name and a number

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

CH3 CHCH3

CH3

2-Methylpropane

12 3

2-metilpropana

CH3 CH2 CH2 CHCH3

CH3

2-Methylpentane123

45 543

21

(not 4-methylpentane)2-metilpentana


If there are two or more identical substituents, number the chain from the end that gives the lower number to the substituent encountered first• indicate the number of times the

substituent appears by a prefix di-, tri-, tetra-, etc.

• use commas to separate position numbers

2,4-Dimethylhexane1

23

456

65

43

21

(not 3,5-dimethylhexane)2,4-dimetilheksana


If there are two or more different substituents,• list them in alphabetical order• number from the end of the chain that

gives the substituent encountered first the lower number

3-Ethyl-5-methylheptane

12

34

5 67 7

65

43 2

1

(not 3-methyl-5-ethylheptane)3-etil-5-metilheptana


The prefixes di-, tri-, tetra-, etc. are not included in alphabetization

alphabetize the names of substituents first and then insert these prefixes

4-Ethyl-2,2-dimethylhexane(not 2,2-dimethyl-4-ethylhexane)

1 2 34 5

6

4-etil-2,2-dimetilheksana

Physical PropertiesPhysical Properties

Boiling points: increase with increasing number of carbonsdecrease with chain brainching

Alkanes are non-polar, soluble in nonpolar or slightly polar solvents, insoluble in water

Intermolecular forces are van der Waals forces Less dense than water

Chemical PropertiesChemical Properties

All alkanes burn in air to give CO2 and H2O Halogenation Pyrolysis (cracking): decomposition of a compound by

the action of heat alone

HalogenationHalogenation(mekanisme radikal bebas)

Alkanes can react with halogens to form alkyl halides via free radical substitution pathways.

A radical is…………………………………………

HalogenationHalogenation(mekanisme radikal bebas)

Carbon radicals are formed by homolytic cleavage of covalent bonds using either:

(1) Light ( h)

(2) Heat (Δ)

(3) Radical Initiators (ROOR i.e. peroxides)

HalogenationHalogenation

The mechanism has three distinct stages.

Stage I

Stage II

Stage III

Initiation( formation of the halogen radicals)

Propagation( formation of product and anotherhalogen radical)

Termination( multiple pathways to extinguishall radicals)


Initiation:

The reaction begins with an initiation stage, which is the separation of the halogen (X2) into two radicals (atoms with a single unpaired electron) by the addition of uv light.

HalogenationHalogenationPropogation:

The initiation stage, or the formation of the chlorine radicals, is immediately followed by the propogation stages--stages directly involved in the formation of the product.

In the last stage, the tertiary radical then reacts with anotherone of the chlorine molecules to form the product.

HalogenationHalogenationTermination:

Side reactions that can stop the chain reaction are called termination stages.


monohalogenation

excess halogen is used

The most important steps of radical halogenation are those that lead to product formation—the propagation steps

Radical Reactions—Mechanism

Sources of AlkanesSources of Alkanes

Natural gas 90-95% methane

Petroleum gases (bp below 20°C) naphthas, including gasoline (bp 20 - 200°C) kerosene (bp 175 - 275°C) fuel oil (bp 250 - 400°C) lubricating oils (bp above 350°C) asphalt (residue after distillation)

Coal Biomass ??????????

CycloalkanesCycloalkanes

General formula CCnnHH2n2n five- and six-membered rings are the most

common Structure and nomenclature

to name, prefix the name of the corresponding open-chain alkane with cyclocyclo--,, and name each substituent on the ring

if only one substituent, no need to give it a number

if two substituents, number from the substituent of lower alphabetical order

if three or more substituents, number to give them the lowest set of numbers and then list substituents in alphabetical order

Cycloalkanes

Line-angle drawings each line represents a C-C bond each vertex and line ending represents a C

CC C

CC

CC

C H2 C

H2 C CH2

CH

CH2

CH

CH3

CH3

C8 H1 6

Cycloalkanes

Example:Example: name these cycloalkanes

(a) (b)

(c) (d)

Bicycloalkanes

Bicycloalkane:Bicycloalkane: an alkane that contains two rings that share two carbons

Bicyclo[4.4.0]decane(Decalin)

Bicyclo[4.3.0]nonane(Hydrindane)

Bicyclo[2.2.1]heptane(Norbornane)(camphor)

monoterpenes

odorous components of plants

1,7,7-trimethylbicyclo[2.2.1]heptan-2-one

Bicycloalkanes

Nomenclature parent is the alkane of the same number of carbons as

are in the rings number from a bridgehead, along longest bridge back

to the bridgehead, then along the next longest bridge, etc.

show the lengths of bridges in brackets, from longest to shortest

Bicyclo[2.2.1]heptane

1

2

3

4

5

67bridgehead two C’s

one C

Isomers relationships among isomers

Cis,Trans Isomerism(Geometric isomers)

Cis,transCis,trans isomersisomers stereoisomers that are the result of the presence of

either a ring or a carbon-carbon double bond

Cis,Trans Isomers

1,2-Dimethylcyclopentane

CH3

trans-1,2-Dimethyl-cyclopentane

cis-1,2-Dimethyl-cyclopentane

H3 CH3 C CH3

CH3

H

CH3

HH

HH

H

HH

HH

CH3

H3 C

H

HH

HH

H

Cis,Trans Isomerism

1,4-Dimethylcyclohexane

t rans-1,4-Dimethyl-cyclohexane

cis-1,4-Dimethyl-cyclohexane

H

H3 C

CH3

H

H

H3 C

H

CH3CH3

H3 C H3 C

CH3

Cis,Trans Isomerism trans-1,4-Dimethylcyclohexane

the diequatorial-methyl chair conformation is more stable by approximately 2 x (7.28) = 14.56 kJ/mol

CH3H

HCH3

HH3 C

CH3H

(more stable)(less stable)

Cis,Trans Isomerism

cis-1,4-Dimethylcyclohexane

conformations are of equal s tability

H

CH3

H

CH3

H

H3 CH

CH3

Cis,Trans Isomerism The decalins

H

H

H

H

B

H

H

A

B

H

H

A

trans-Decalin

cis-Decalin

Conformations

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

Newman projection:Newman projection: a way to view a molecule by looking along a carbon-carbon single bond

Conformations

Staggered conformation:Staggered conformation: a conformation about a carbon-carbon single bond in which the atoms or groups on one carbon are as far apart as possible from the atoms or groups on an adjacent carbon

H

H H

H H

H

Conformations

Eclipsed conformation:Eclipsed conformation: a conformation about a carbon-carbon single bond in which the atoms or groups of atoms on one carbon are as close as possible to the atoms or groups of atoms on an adjacent carbon

H

H H

H

HH

Conformations Torsional strain Torsional strain

also called eclipsed interaction straineclipsed interaction strain strain that arises when nonbonded atoms separated

by three bonds are forced from a staggered conformation to an eclipsed conformation

the torsional strain between eclipsed and staggered ethane is approximately 12.6 kJ (3.0 kcal)/mol

+12.6 kJ/mol

Conformations

Dihedral angle (Q)Dihedral angle (Q): the angle created by two intersecting planes

Conformations

Ethane as a function of dihedral angle

Conformations

conformations of butane as a function of dihedral angle

Anti Butane

Energy-minimized anti conformation the C-C-C bond angle is 111.9° and all

H-C-H bond angles are between 107.4 and 107.9°

Eclipsed Butane

Cyclopropane

angle strain:angle strain: the C-C-C bond angles are compressed from 109.5° to 60°

torsional strain:torsional strain: there are 6 sets of eclipsed hydrogen interactions

strain energy is about 116 kJ (27.7 kcal)/mol

H

H

H

H

H

H

Cyclobutane

puckering from planar cyclobutane reduces torsional strain but increases angle strain

the conformation of minimum energy is a puckered “butterfly” conformation


Cyclopentane

puckering from planar cyclopentane reduces torsional strain, but increases angle stain

the conformation of minimum energy is a puckered “envelope” conformation


Cyclohexane

Chair conformation:Chair conformation: the most stable puckered conformation of a cyclohexane ring all bond C-C-C bond angles are 110.9° all bonds on adjacent carbons are

staggered

Cyclohexane

In a chair conformation, six H are equatorial and six are axial

Cyclohexane

For cyclohexane, there are two equivalent chair conformations all C-H bonds equatorial in one chair

are axial in the alternative chair, and vice versa

Cyclohexane Boat conformation:Boat conformation: a puckered conformation of a

cyclohexane ring in which carbons 1 and 4 are bent toward each other there are four sets of eclipsed C-H

interactions and one flagpole interaction a boat conformation is less stable than a

chair conformation by 27 kJ (6.5 kcal)/mol

Cyclohexane

TwistTwist--boat conformationboat conformation approximately 41.8 kJ (5.5 kcal)/mol

less stable than a chair conformation approximately 6.3 kJ (1.5 kcal)/mol

more stable than a boat conformation

Cyclohexane

Equatorial and axial methyl conformations

Methylcyclohexane

CH3

CH3

+7.28 kJ/mol

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