Organic ChemistryOrganic Chemistry

AlkanesAlkanes &&AlkanesAlkanes & & cycloalkanescycloalkanes

AlkAlkanes

general formula CnH2n+2general formula CnH2n+2

alkanes are saturatedalkanes are saturated(each C is bound to 4 other atoms)

AlkanesAlkanesAlkanesAlkanes•• Hydrocarbon chains where all the bonds Hydrocarbon chains where all the bonds

b t b SINGLE b db t b SINGLE b dbetween carbons are SINGLE bondsbetween carbons are SINGLE bonds•• Name uses the ending Name uses the ending ––aneane•• Examples: MethExamples: Methaneane, Prop, Propaneane, But, Butaneane, Oct, Octaneane, ,

22--methylpentmethylpentaneane

Summary: IUPAC Rules for Alkane Summary: IUPAC Rules for Alkane NomenclatureNomenclature

1.1. Find and name the longest continuous carbon chain. Find and name the longest continuous carbon chain. This is called the This is called the parent chainparent chain. (Examples: methane, . (Examples: methane, s s ca ed es s ca ed e pa e t c apa e t c a ( a p es e a e,( a p es e a e,propane, etc.)propane, etc.)

2.2. Number the chain consecutively, starting at the end Number the chain consecutively, starting at the end nearest an attached group (nearest an attached group (substituentsubstituent). ). g p (g p ( ))

3.3. Identify and name groups attached to this chain. Identify and name groups attached to this chain. (Examples: methyl(Examples: methyl--, bromo, bromo--, etc.), etc.)

4.4. Designate the location of each substituent group withDesignate the location of each substituent group with4.4. Designate the location of each substituent group with Designate the location of each substituent group with the number of the carbon parent chain on which the the number of the carbon parent chain on which the group is attached. Place a dash between numbers and group is attached. Place a dash between numbers and letters. (Example: 3letters. (Example: 3--chloropentane)chloropentane)

5.5. Assemble the name, listing groups in alphabetical order. Assemble the name, listing groups in alphabetical order. The prefixes di, tri, tetra etc., used to designate several The prefixes di, tri, tetra etc., used to designate several groups of the same kind, are not considered when groups of the same kind, are not considered when l h b ti i Pl b t lti ll h b ti i Pl b t lti lalphabetizing. Place a comma between multiple alphabetizing. Place a comma between multiple

numbers. (Example: 2,3numbers. (Example: 2,3--dichloropropane)dichloropropane)

Step 1 Find the parent chainStep 1 Find the parent chainStep 1. Find the parent chain.Step 1. Find the parent chain.

•• Where is the longest continuous chain ofWhere is the longest continuous chain ofWhere is the longest continuous chain of Where is the longest continuous chain of carbons?carbons?

Prefixes for # of CarbonsPrefixes for # of CarbonsPrefixes for # of CarbonsPrefixes for # of Carbons

11 MethMeth 66 HexHex11 MethMeth 66 HexHex

22 EthEth 77 HeptHeptpp

33 PropProp 88 OctOct

44 ButBut 99 NonNon

55 PentPent 1010 DecDec

IUPAC Names for AlkanesIUPAC Names for Alkanes

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EndingsEndings•• AlkanesAlkanes (all C(all C--C single bonded parent chain) C single bonded parent chain)

end in end in ––aneane–– MethMethaneane CHCH44–– EthEthaneane CC22HH66–– PropPropaneane CC33HH88

Att h d b (Att h d b ( b tit tb tit t ) d i) d i ll•• Attached carbon groups (Attached carbon groups (substituentssubstituents) end in ) end in ––ylyl–– MethMethylyl CHCH33 --

EthEth ll CHCH CHCH–– EthEthylyl CHCH33CHCH22--–– PropPropylyl CHCH33CHCH22CHCH2 2 ––

3-ethylpentane

Step 2. Number the parent chain.Step 2. Number the parent chain.• Number the parent chain so that the attached

groups are on the lowest numbersgroups are on the lowest numbers

Methyl is on carbon #2 of the parent chain

Methyl is on carbon #4 of the parent chain

1 2 3 4 5

4 3 2 1

Methyl is on carbon #4 of the parent chain

GREEN is the right way for this one!5 4 3 2 1 way for this one!

1 2

3 7 8

4 5 6

8 7

6 2 1

5 4 31 2 3 4 5 6

77 6 5 4 3 24 5 65 4 3

Groups on 2, 3, and 5Groups on 4, 6, and 7

7Groups on 2 and 5

7 6 5 4 3 2 1

Groups on 3 and 6

Step 3 Name the attached groupsStep 3 Name the attached groupsStep 3. Name the attached groups.Step 3. Name the attached groups.

•• Carbon (alkCarbon (alkylyl) groups) groups(( yy ) g p) g p–– MethMethylyl CHCH33 --–– EthEthylyl CHCH33CHCH22--yy 33 22–– PropPropylyl CHCH33CHCH22CHCH2 2 ––

•• HalogensHalogens–– FluoroFluoro (F(F--))–– ChloroChloro ((ClCl--))–– BromoBromo (Br(Br--))–– IodoIodo (I(I--))

Step 4. Designate where the group Step 4. Designate where the group i h d h h ii h d h h iis attached to the parent chain.is attached to the parent chain.

• Use the numbers of the parent chain from step 2Use the numbers of the parent chain from step 2 to designate the location of the attached groups to the parent chain.

2-methyl

1 2 3 4 51 2 3 4 5

Step 5. Alphabetize the groups, Step 5. Alphabetize the groups, bi lik d blbi lik d blcombine like groups, and assemble.combine like groups, and assemble.

•• The prefixesThe prefixes didi, tri, tetra, tri, tetraThe prefixes The prefixes didi, tri, tetra , tri, tetra etc., used to designate etc., used to designate several groups of the same several groups of the same ki dki dkindkind

•• Prefixes are not considered Prefixes are not considered when alphabetizingwhen alphabetizingwhen alphabetizing when alphabetizing (Example: (Example: dimethyldimethyl = m for = m for alphabetizing)alphabetizing)

1,1,1-trichloro-1-fluoromethane

1,1-dichloro-1,1-difluoromethane

•• Parent chain goes LASTParent chain goes LAST

Draw Some Simple AlkanesDraw Some Simple AlkanesDraw Some Simple AlkanesDraw Some Simple Alkanes

•• 22--methylpentanemethylpentane22 methylpentanemethylpentane

33 th lhth lh•• 33--ethylhexaneethylhexane

•• 2,22,2--dimethylbutanedimethylbutane

•• 2,32,3--dimethylbutanedimethylbutane

Order of PriorityOrder of PriorityOrder of PriorityOrder of Priority

•• IN A TIE halogens get the lower numberIN A TIE halogens get the lower numberIN A TIE, halogens get the lower number IN A TIE, halogens get the lower number before alkyl groupsbefore alkyl groups

44--chlorochloro--22--methylpentane ormethylpentane or44 chlorochloro 22 methylpentane ormethylpentane or22--chlorochloro--44--methylpentane?methylpentane?

Order of PriorityOrder of PriorityOrder of PriorityOrder of Priority

•• IN A TIE between SIMILAR GROUPS theIN A TIE between SIMILAR GROUPS theIN A TIE between SIMILAR GROUPS, the IN A TIE between SIMILAR GROUPS, the group lower ALPHABETICALLY gets the group lower ALPHABETICALLY gets the lower numberlower numberlower numberlower number

4-bromo-2-chloropentane or4 bromo 2 chloropentane or 2-bromo-4-chloropentane ?

IsomersIsomersIsomersIsomers

St i htSt i ht h ih i lklk AA lklk•• StraightStraight chainchain alkanesalkanes:: AnAn alkanealkanethatthat hashas allall itsits carbonscarbons connectedconnected inin aarowrow..•• BranchedBranched chainchain alkanesalkanes:: AnAn alkanealkanethatthat hashas aa branchingbranching connectionconnection ofofcarbonscarbons..•• IsomersIsomers:: CompoundsCompounds withwith samesamemolecularmolecular formulaformula butbut differentdifferentmolecularmolecular formulaformula butbut differentdifferentstructuresstructures..

•• ThereThere isis onlyonly oneone possiblepossible wayway thatthat thethecarbonscarbons inin methanemethane (CH(CH44),), ethaneethane (C(C22HH66),),andand propanepropane (C(C33HH88)) cancan bebe arrangedarranged..

HoweverHowever carbonscarbons inin butanebutane (C(C HH )) cancan bebeHowever,However, carbonscarbons inin butanebutane (C(C44HH1010)) cancan bebearrangedarranged inin twotwo waysways;; fourfour carbonscarbons inin aa rowrow(linear(linear alkanealkane)) oror aa branchingbranching (branched(branchedalkanealkane)) TheseThese twotwo structuresstructures areare twotwoalkanealkane)).. TheseThese twotwo structuresstructures areare twotwoisomersisomers forfor butanebutane..

IsomersIsomers

methane1 isomer

ethane1 isomer

propane1 isomer

Isomers

normal butane(n butane) isobutane(n-butane)

DifferentDifferent isomersisomers areare completelycompletely differentdifferentDifferentDifferent isomersisomers areare completelycompletely differentdifferentcompoundscompounds.. TheyThey havehave differentdifferent structures,structures,differentdifferent physicalphysical propertiesproperties suchsuch asas meltingmeltingp yp y p pp p ggpointpoint andand boilingboiling point,point, andand maymay havehave differentdifferentphysiologicalphysiological propertiesproperties..

Learning CheckLearning CheckLearning CheckLearning Check

• Draw all possible structural isomers of C5H12Draw all possible structural isomers of C5H12

Types of Carbon AtomsTypes of Carbon AtomsTypes of Carbon AtomsTypes of Carbon Atoms•• Primary carbon (1Primary carbon (1oo)) HHy (y ( ))

–– a carbon bonded to a carbon bonded to one other carbonone other carbon

C CH

HC CH

H

•• Secondary carbon (2Secondary carbon (2oo))

HH

H

–– a carbon bonded to a carbon bonded to two other carbonstwo other carbons

C C CH H

•• Tertiary carbon (3Tertiary carbon (3oo))–– a carbon bonded toa carbon bonded to

H

C C CH

a carbon bonded to a carbon bonded to three other carbonsthree other carbons C

AlkanesAlkanesAlkanesAlkanes

Example: Name the following compounds:Example: Name the following compounds:Example: Name the following compounds:Example: Name the following compounds:

CHCHCH3

CHCH3

CH3

CH3 C CH2 CH2BrCHCH3

CH3 CH CH CH2 CH CH3

CH2CH3C

CH3

CH3CH3

CH2CH3

2 33

CH3

3

Structural FormulasAlkanes are written with structural formulas that are• Expanded to show each bond• Expanded to show each bond.• Condensed to show each carbon atom and its

attached hydrogen atomsattached hydrogen atoms. • Line to show bonds as lines and omit hydrogens

C C C H

H

H

H H

H3CH2C CH3

H H H

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Expanded and Condensed St tStructures

TABLE 11.3

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Line-Bond FormulasLine Bond Formulas

• Because each C atom has a tetrahedral arrangement, the order of atoms is not a straight line, but a zigzag pattern.

• A line-bond formula abbreviates the carbon atoms and shows only the zigzag pattern of b d f b t t b tbonds from carbon atom to carbon atom.

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AlkanesAlkanes

Example: Write the condensed Example: Write the condensed t t f th f ll i dt t f th f ll i dstructure for the following compounds:structure for the following compounds:

3,33,3--dimethylpentanedimethylpentane

22--methylmethyl--44--secsec--butyloctanebutyloctanee ye y secsec bu y oc a ebu y oc a e

1,21,2--dichlorodichloro--33--methylheptanemethylheptane

CycloalkanesCycloalkanes

Are cyclic alkanesAre cyclic alkanes.Have 2H fewer than the open chain.Are named by using the prefix cyclo beforeAre named by using the prefix cyclo- before the name of the alkane chain with the same number of carbon atoms.

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CycloalkanesCycloalkanesThe structural formulas of cycloalkanes are usually y yrepresented by geometric figures,

Cyclopropane CH2

CH2 CH2CH2 CH2

CyclobutaneCH2 CH2

CH2 CH2

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CycloalkanesCycloalkanes

=

cyclopropanecyclopropane

CycloalkanesCycloalkanes

cyclobutane

cyclopentane

cyclohexanecyclohexane

CycloalkanesCycloalkanes

Naming Cycloalkanes with S b tit tSubstituents

The name of a substituent is placed in frontThe name of a substituent is placed in front of the cycloalkane name.

CH3CH3

methylcyclobutane

Number ring with two substituents1 bromo 2 chlorocyclopentane B1-bromo-2-chlorocyclopentane Br

Cl

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Nomenclature of CycloalkanesNomenclature of Cycloalkanes

Name each of the following :Name each of the following :

Name each of the following :Name each of the following :

Name each of the following :Name each of the following :

Name each of the following :Name each of the following :

Some Properties of AlkanesSome Properties of Alkanes

The properties of alkanes includeThe properties of alkanes includebeing

N l• Nonpolar.• Insoluble in water.

L d th t• Less dense than water• Flammable in air.• Relatively unreactive. Copyright © 2007 by Pearson Education, Inc.

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Alkanes with 1-4 Carbon AtomsAlkanes with 1 4 Carbon Atoms

Alkanes with 1-4 carbon atoms areAlkanes with 1 4 carbon atoms are• Methane, ethane, propane, and

butane.• Gases at room temperature.• Used as heating fuelsUsed as heating fuels.

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Alkanes with 5-17 Carbon Atoms

Alkanes with 5-8 carbon atoms are• Liquids at room temperature.• Pentane, hexane, heptane, and octane.• Very volatile.• Used to make gasoline.

Alkanes with 9-17 carbon atoms • Are liquids at room temperature• Have higher boiling points.

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g g p• Are found in kerosene, diesel, and jet fuels.

Alkanes with 18 or more Carbon AtomsAlkanes with 18 or more Carbon Atoms

Alkanes with 18 or more carbon atomsAlkanes with 18 or more carbon atoms• Have high molar masses.• Are waxy solids at room temperatureAre waxy solids at room temperature.• Used in waxy coatings of fruits and

vegetablesvegetables.

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Crude OilCrude OilThe hydrocarbons incrude oil are• Separated by boiling

points.points.• Heated to higher

temperatures to prod ce gases thatproduce gases that can be removed and cooled.

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Alkane Reactions

1. CombustionTh b ti f b d i ll h d b h b thThe combustion of carbon compounds, especially hydrocarbons, has been the most important source of heat energy for human civilizations throughout recorded history.

CH3-CH2-CH3 + 5 O2 ——> 3 CO2 + 4 H2O + heat

Two points concerning this reaction are important:Two points concerning this reaction are important: 1. Since all the covalent bonds in the reactant molecules are broken,

the quantity of heat evolved in this reaction is related to the strength of these bonds (and of course the strength of the bonds formed inof these bonds (and, of course, the strength of the bonds formed in the products).

2. The stoichiometry of the reactants is important. If insufficient oxygen is supplied some of the products will consist of carbon monoxide, a pp p ,highly toxic gas.

Combustion of Alkanes

Alkanes • Undergo combustion by

reacting with oxygen to produce carbon dioxide, p ,water, and energy.

• Are typically not very ti d t t Creactive due to strong C-

C single bonds.

alkane + O2 CO2 + H2O + energy

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52

2 2 2 gy

Balancing A Combustion Equation

Write the equation

Balancing A Combustion Equation

Write the equationC5H12 + O2 CO2 + H2O

Balance CBalance CC5H12 + O2 5CO2 + H2O

Balance HC5H12 + O2 5CO2 + 6H2O

Balance O with O2

C5H12 + 8O2 5CO2 + 6H2O balanced

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2. Halogenation

Halogenation is the replacement of one or more hydrogen atoms in an organic compound by a halogen (fluorine, chlorine, bromine or g p y g ( , ,iodine).

CH4 + Cl2 + energy ——> CH3Cl + HCl

When alkanes react with halogens:• One or more hydrogens will be replaced with halogensy g p g• Halogens prefer to go to the more substituted (location

with more surrounding carbons) location• Tertiary is more reactive than secondary which is more• Tertiary is more reactive than secondary which is more

reactive than primary• Light or heat is required to form the radicals• Radicals have unpaired electrons and violate the octet

rule (reactive)

Free Radical Halogenation M h iMechanism

Li htX X

LightX X1.

2 X H+

+

2. R H + X R X H+

R + X X R X + X3.

X = shorthand for a halogen atom

used to indicate an unpaired electron (free radical)

X = shorthand for a halogen atom

R = shorthand for an organic compound or group

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Free Radical Halogenation

1 inisiation

gMechanism

1. inisiation,

2. propagation

radical reaction with Cl :radical reaction with Cl2:

3. termination;

Predicting the Major Product of Free R di l H l tiRadical Halogenation

• Halogens prefer more substituted location on moleculeg p• Tertiary is more reactive than secondary which is more

reactive than primary• Reactivity depends on ease of forming radical• Below radicals listed from easiest to form to hardest

C

C

C C

H

C C

H

H C

H

HCC

C

CC

C

CH

C

CH

H

59tertiary secondary primary methyl

Predict the Major ProductPredict the Major ProductHH H

H C C C H

HHH

+ Cl2

H2C CH

CH3

+ BCH2H2C

+ Br2

+ Br2

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Predict the Major ProductPredict the Major ProductHH H ClH H

H C C C H

HHH

+ Cl2 H C C C H

HHH

+ HCl

H2C CH

CH3

+ BrH2C C

CH3

+ HBr

Br

CH2H2C+ Br2

CH2H2C+ HBr

+ Br2 + HBrBr

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