Organic ChemistryChapter 22

Vocabulary • Organic Chemistry• Hydrocarbons• Saturated• Unsaturated• Alkanes• Alkenes• Alkynes• Cis-trans isomerism

• Carbonyl group• Ketones• Aldehydes• Carboxylic acids• Carboxyl group• Ester• Ether• Amine

Saturated vs. UnsaturatedHydrocarbons

• Hydrocarbons are molecules composed of carbon & hydrogen– Each carbon atom forms 4 chemical bonds– A saturated hydrocarbon is one where all C - C

bonds are “single” bonds & the molecule contains the maximum number of H-atoms

– An unsaturated hydrocarbon is one where at least 1 C=C bond is double.

Prefixes for # of CarbonsPrefixes for # of Carbons

11 MethMeth 66 HexHex

22 EthEth 77 HeptHept

33 PropProp 88 OctOct

44 ButBut 99 NonNon

55 PentPent 1010 DecDec

AlkanesAlkanes• Hydrocarbon chains where all the bonds between Hydrocarbon chains where all the bonds between

carbons are SINGLE bondscarbons are SINGLE bonds• Name uses the ending –Name uses the ending –aneane• Examples: MethExamples: Methaneane, Prop, Propaneane, But, Butaneane, Oct, Octaneane

• Formula: (CnH2n+2)

Straight-Chain Alkanes• Straight-chain alkanes contain any

number of carbon atoms, one after the other, in a chain pattern - meaning one linked to the next (not always straight)C-C-C C-C-C-C etc.

Writing/drawing compounds

Line formula

Normal vs Branched Alkanes• NORMAL alkanes consist of

continuous chains of carbon atoms

• Alkanes that are NOT continuous chains of carbon atoms contain branches

• The longest continuous chain of carbons is called the parent chain

CH3

CH2CH2

CH2CH3

CH3

CH2CH

CH3

CH3

EndingsEndings• Attached carbon groups (substituents) end in Attached carbon groups (substituents) end in

–yl–yl– MethMethylyl CH CH33 - -– EthEthylyl CHCH33CHCH22--– PropPropylyl CH CH33CHCH22CHCH2 2 – –

3-ethylpentane

Names of branchesNames of branches

• Carbon (alkCarbon (alkylyl) groups) groups– MethMethylyl CH CH33 - -– EthEthylyl CHCH33CHCH22--– PropPropylyl CH CH33CHCH22CHCH2 2 ––

Branched-Chain Alkanes• Rules for naming –1. Longest C-C chain is parent2. Number so branches have lowest #3. Give position number to branch4. Prefix (di, tri) more than one branch5. Alphabetize branches (not prefix)6. Use proper punctuation ( - and , )

Designate the LocationDesignate the Location

• Designate the location (number of the carbon on the parent chain) for each attached group

1 2 3 4 5

2-methyl

Name this compound

• 3,3-dimethylhexane

Some Simple AlkanesSome Simple Alkanes

• 2-methylpentane2-methylpentane

• 3-ethylhexane3-ethylhexane

• 2,2-dimethylbutane2,2-dimethylbutane

• 2,3-dimethylbutane2,3-dimethylbutane

Branched-Chain Alkanes• From the name, draw the structure, in a

right-to-left manner:1. Find the parent, with the -ane2. Number carbons on parent3. Identify substituent groups (give lowest

number); attach4. Add remaining hydrogens

Example 1: 2,2-dimethylpentane2,2-dimethylpentane• The parent chain is indicated by

the ROOT of the name - “pentanepentane”. This means there are 5 carbons in the parent chain.

CH3

CH2CH2

CH2CH3

• “dimethyldimethyl” tells us that there are TWO methyl branches on the parent chain. A methyl branch is made of a single carbon atom.

• “2,22,2-” tell us that BOTH methyl branches are on the second carbon atom in the parent chain.

CH31

CCH23

CH2

4

CH35

CH3

CH3

1

2

3

4

5

Example 2: 3-ethyl-2,4-dimethylheptane3-ethyl-2,4-dimethylheptane• The parent chain is indicated by

the ROOT of the name - “heptaneheptane”. This means there are 7 carbons in the parent chain.

CH3

CH2CH2

CH2CH2

CH2CH3

• “2,4-dimethyl2,4-dimethyl” tells us there are TWO methyl branches on the parent chain, at carbons #2 and #4.

• “3-ethyl3-ethyl-” tell us there is an ethyl branch (2-carbon branch) on carbon #3 of the parent chain.

1

2

3

4

5

76

CH3

CHCH

CHCH2

CH2CH3

CH2

CH3

CH3 CH3

Example 3: 2,3,3-trimethyl-4-propyloctane2,3,3-trimethyl-4-propyloctane• The parent chain is indicated by

the ROOT of the name - “octaneoctane”. This means there are 8 carbons in the parent chain.

• “2,3,3-trimethyl2,3,3-trimethyl” tells us there are THREE methyl branches - one on carbon #2 and two on carbon #3.

• “4-propyl4-propyl-” tell us there is a propyl branch (3-carbon branch) on carbon #4 of the parent chain.

1

2

34

5

7

6

8

1

23

45

7

6

8

CHC

CHCH2

CH2

CH2CH3

CH3

CH3

CH3

CH3CH2

CH2

CH3

Example 4: Name the molecules shown!

• parent chain has 5 carbons - “pentane”

• two methyl branches - start counting from the right - #2 and #3

• 2,3-dimethylpentane2,3-dimethylpentane

CH3

CH2

CHCH

CH3

CH3

CH3

• parent chain has 8 carbons - “octane”• two methyl branches - start counting

from the left - #3 and #4• one ethyl branch - #5• name branches alphabetically

3,4-dimethyl3,4-dimethyl

4433

octaneoctane

55

5-ethyl-5-ethyl-

Draw 2,2,4-trimethylpentane

Structural Isomerism• Structural isomers are

molecules with the same chemical formulas but different molecular structures

CH3

CH2CH2

CH2CH3

CH3

CH2CH

CH3

CH3

n-pentane, C5H12

2-methlbutane, C5H12

• However, carbons in butane (CHowever, carbons in butane (C44HH1010) can be ) can be arranged in two ways; four carbons in a row (linear arranged in two ways; four carbons in a row (linear alkane) or a branching (branched alkane). These alkane) or a branching (branched alkane). These two structures are two isomers for butane.two structures are two isomers for butane.

Your TurnYour Turn• Draw all possible structural isomers of C5H12

Practice

IUPAC Rules for Naming Branched Alkanes

– Find and name the parent chainFind and name the parent chain in the hydrocarbon - this forms the root of the hydrocarbon name

– Number the carbon atoms in the parent chainNumber the carbon atoms in the parent chain starting at the end closest to the branching

– Name alkane branchesName alkane branches by dropping the “ane” from the names and adding “yl”. A one-carbon branch is called “methyl”, a two-carbon branch is “ethyl”, etc…

– When there are more than one type of branch (ethyl and methyl, for example), they are named alphabeticallyalphabetically

– Finally, use prefixesuse prefixes to indicate multiple branches

CLASSWORK ASSIGNMENTCLASSWORK ASSIGNMENT• Review section 22-1Review section 22-1

– make notes on NONMENCLATURE OF ALKANES and CYCLIC ALKANES

– Pay attention to sample exercises!

Alkenes & AlkynesAlkenes & Alkynes• Alkenes are

hydrocarbons that contain at least one carbon-carbon double double bondbond

• Alkynes are hydrocarbons that contain at least one carbon-carbon triple triple bondbond

• The suffix for the parent chains are changed from “ane” to “ene” and “yne”– e.g. ethene, propyne

• the BONDS are numbered like branches so that the location of the multiple bond may be indicated

Alkenes & Alkynes: Examples

CH2 CH2 CHCH CH2 C

H

CH3

C16

CH

CH3 CH2 CH

CH2

CH3C C CH2CH3

CH3

ethene ethyne propene

propyne butene 2-pentyne

Aromatic Hydrocarbons Aromatic Hydrocarbons CycloalkanesCycloalkanes

• A cycloalkane is made of a hydrocarbon chain that has been joined to make a “ring”.

CH3

CH2

CH3 CH2

CH2

CH2

n-propaneC3H8

cyclopropaneC3H6

60° bond angleunstable!!

109.5° bond angle

•Note that two hydrogen atoms were lost in forming the ring!

Aromatic Hydrocarbons Aromatic Hydrocarbons CycloalkanesCycloalkanes

• The two ends of the carbon chain are attached in a ring in a cyclic hydrocarbon– named as “cyclo- ____”

Aromatic Compounds and BenzeneAromatic Compounds and Benzene

Aromatic compounds contain benzene.

Benzene, C6H6 , is represented as a six carbon ring with 3 double bonds.

Two possible resonance structures can be drawn to show benzene in this form.

H

H

H

H

H

H

HH

H

H

H

H

Aromatic HydrocarbonsAromatic Hydrocarbons• Benzene derivatives can have two or more

substituents:– 1,2-dimethylbenzene– 1,3-dimethylbenzene– 1,4-dimethylbenzene

• Can use ortho for 1,2; meta for 1,3; and para for 1,4 (page 711)

C

C

CC

IsomersIsomersWith organic compounds

Isomers• There is a lack of rotation around a carbon

to carbon multiple bond– Two possible arrangements:

1. trans configuration - substituted groups on opposite sides of double bond

2. cis configuration - same side

Substituted groups are on opposite sides of the double bond (in this case, one is above, the other is below)

Substituted groups are on the same side of the double bond (in this case, both are above)

Geometric Isomers

Trans-2-butene

Cis-2-butene

Cis-Trans Isomers - Examples

Cl Cl

CH1

CH2

2

CH3

CH34CH25

CH3

6

cis-1,3-dimethylcyclobutanecis-1,3-dimethylcyclobutane

cis-1,2-dichlorocyclohexanecis-1,2-dichlorocyclohexane

trans-1-ethyl-2-methylcyclopropanetrans-1-ethyl-2-methylcyclopropane

ReactionsReactionsWith organic compoundsWith organic compounds

AlkanesAlkanes1. Combustion Combustion reactions

2C2H6(g) + 7O2(g) 4CO2(g) + 6H2O(g)

2. SubstitutionSubstitution reactionsCH4 + Cl2 CH3Cl + HCl

Methane chloromethane

3. DehydrogenationDehydrogenation reactionsCH3CH3 CH2=CH2 + H2

Ethane ethene

hv

500C

Alkenes & AlkynesAlkenes & Alkynes1. Addition Addition reactions

a. Hydrogenationa. Hydrogenation

CH2 =CHCH3+ H2 CH3CH2CH3Propene Propane

b. Halogenation b. Halogenation CH2 =CHCH2CH2CH3 + Br2 CH2 BrCHBrCH2CH2CH3

Pentene 1,2-dibromopentene

c. Polymerizationc. PolymerizationSmall molecules = large molecules

Catalyst

AromaticAromatic1. Substitution Substitution reactions

+ Cl2 + HClCatalyst = FeCl3

Functional GroupsFunctional GroupsWith organic compoundsWith organic compounds

Functional GroupsFunctional Groups

Functional group:Functional group: an atom or group of atoms within a molecule

Functional Groups

AlcoholsAlcohols

contain an -OH (hydroxylhydroxyl) group

H-C-C-O-H

H

H

H

H::-C-O-H

Ethanol(an alcohol)

Functionalgroup

CH3-CH2-OH CH3CH2OHor

Halides & Carboxylic AcidsHalides & Carboxylic Acids

contain an -X (HalogenHalogen) groupF, Cl, Br, I, At

contain a carboxyl (-COOH) groupcarboxyl (-COOH) group

C O

O

H CH3-C-O-HO

CH3COOH CH3CO2H

: ::: or or

Acetic acid(a carboxylic acid)

Functionalgroup

Aldehydes and KetonesAldehydes and Ketones

contain a carbonyl (C=O) groupcarbonyl (C=O) group

C H

O

CH3-C-H

O

CH3-C-CH3

O

C

O

Functionalgroup

Acetaldehyde(an aldehyde)

Acetone(a ketone)

Functionalgroup

AminesAmines contain an amino groupamino group; nitrogen bonded to

one, two, or three carbon atoms– an amine may by 1°, 2°, or 3°

CH3 N H

H

CH3 N H

CH3

CH3 N CH3

CH3

Methylamine(a 1° amine)

Dimethylamine(a 2° amine)

Trimethylamine(a 3° amine)

: : :

Esters & EthersEsters & Ethers Ester:Ester: trapped carboxylic acid

Ether: Ether: Trapped oxygen

C O

O

Functionalgroup

CH3-C-O-CH2-CH3

Ethyl acetate(an ester)

::

: :O

BranchesCnH2n+2 Alkane CnH2n+1 Alkyl group

CH4 methane CH3 Methyl

C2H6 ethane C2H5 ethyl

C3H8 propane –C3H7 propyl

CH3CHCH3 methylethyl

Functional Group

General Formula

Name Examples

saturated ring CnH2n cycloalkane cyclohexane

-X -RX haloalkane chloroethane

R-O-R’ ether ethoxyethane

-OHROH

alkanol ethanol

(-CHO) 

RCHO

 alkanal ethanal

-NH2 RNH2 amine methylamine

 alkanone butan-2-one

-COOH RCOOH alkanoic acid ethanoic acid

-COOR’ RCOOR’ ester methyl ethanoate

C

O

C R'R

O

Naming

Naming

Naming