Organic Chemistry

Chapter 22

Organic Chemistry

The study of carbon-containing compounds and their properties.

The vast majority of organic compounds contain chains or rings of carbon atoms.

Organic & Inorganic Compounds

Originally the distinction between inorganic and organic substances was based on whether or not they were produced by living systems.

In 1828, German chemist Friedrich Wohler prepared urea from the inorganic salt ammonium cyanate by simple heating:

heat

NH4OCN ---> NH2CONH2

Hydrocarbons

. . . compounds composed of carbon and hydrogen.

Saturated: carbon-carbon bonds are all single - alkanes [CnH2n+2]

H C

H

H

C

H

H

H

Hydrocarbons(continued)

Unsaturated: contains carbon-carbon multiple bonds.

H C

H

H

C

H

CH

H

Hydrogen Addition

C2H4(g) + H2(g) ---> C2H6(g)

unsaturated saturated

22_492

C

sp3

sp3sp3

sp3

H1s

H1s

H1s

H1s

The carbon-hydrogen bonds in methane.

22_493

C

H

H

C

H

H

H H

(a) (b)

The Lewis structure, space-filling, and ball-and-stick models for ethane.

22_494

(a) (b)

The structures of propane and butane with 109.5o

bond angles.

Structural Isomerism

-- isomers contain the same atoms but one or more different bonds.

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(a)

(b)

Normal butane (n-butane) and the branched isomer, isobutane.

Isomers of Pentane

What are the three isomers of pentane?

1) n-pentane -- straight-chain

2) isopentane -- one branch from 2nd carbon

3) neopentane -- two branches from central carbon

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CH3 CH2 CH2 CH2 CH3

n-Pentane

The straight-chain isomer, n-pentane.

Rules for Naming Alkanes

1. For alkanes beyond butane, add -ane to the Greek root for the number of carbons.

C-C-C-C-C-C = hexane

2. Alkyl substituents: drop the -ane and add -yl.

-C2H5 is ethyl

Rules for Naming Alkanes3. Positions of substituent groups are specified

by numbering the longest chain sequentially. C

C-C-C-C-C-C

3-methylhexane

4. Location and name are followed by root alkane name. Substituents in alphabetical order and use di-, tri-, etc.

See Sample Exercise 22.2 on pages 1062-1064.

Combustion Reactions of Alkanes

C3H8(g) + 5O2(g) ----> 3CO2(g) + 4HOH(g)

2C4H10(g) + 13 O2(g) ----> 8CO2(g) + 10HOH(g)

Substitution Reactions for Alkanes

Primarily where halogen atoms replace hydrogen atoms.

CHCl Cl CCl HClh3 2 4

Dehydrogenation Reactions

Cr2O3

CH3CH3 ----> CH2=CH2 + H2

500oC

ethane ethylene

Cyclic AlkanesCarbon atoms can form rings containing only carbon-carbon single bonds.

C3H6, C4H8, C6H12

Shorthand notation for the cyclic alkanes.

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C C

C

109.5

60

No "head-on"overlap of atomic orbitals

(b)(a)

The molecular structure of cyclopropane andthe overlap of the sp3 orbitals that form the C-C bonds.

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Boat

(b)

These two Hatoms repeleach other

Chair

(a)

The chair and boat forms of cyclohexane.

Alkenes and Alkynes

Alkenes: hydrocarbons that contain a carbon-carbon double bond. [CnH2n]

CC=C propene

Alkynes: hydrocarbons containing a carbon-carbon triple bond. [CnH2n-2]

CCCCC 2-pentyne

Nomenclature for Alkenes

1. Root hydrocarbon name ends in -ene

C2H4 is ethene

2. With more than 3 carbons, double bond is indicated by the lowest numbered carbon atom in the bond.

C=CCC is 1-butene

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H1s

sp2

sp2

sp2

sp2

H1s

2p

C C

sp2

sp2

The bonding in ethylene.

The two stereoisomers of 2-butene. a) cis-2-butene b) trans-2-butene

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H

H

H H

H

H

CC

The bonding in ethane allows rotation and nocis-trans isomerism.

22_504

2p

2pH1s

H

sp

2p

2p

C

sp 2p

2p

2p

C H

H1s

2p

sp

The bonding in acetylene.

Addition Reactions

. . . in which (weaker) bonds are broken and new (stronger) bonds are formed to atoms being added.

CH CHCH H CH CH CHcatalyst2 3 2 3 2 3

propene propane

Halogenation

CH2=CHCH2CH2CH3 + Br2 --->

CH2BrCHBrCH2CH2CH3

1-pentene 1,2-dibromopentane

Aromatic Hydrocarbons

A special class of cyclic unsaturated hydrocarbons.

+ Cl2

FeCl3

Cl

+ HCl

benzene Chlorobenzene

Aromatic Hydrocarbons

phenyl group

Ortho (o-) -- two adjacent substituents.

meta (m-) -- two substituents with one carbon between them.

para (p-) -- two substituents opposite each other.

Refinery Processes

Cracking: large molecules broken down to smaller ones by breaking carbon-carbon bonds.

Pyrolysis (thermal cracking): The process that produces cracking at high temperatures.

Catalytic Cracking: Cracking at lower temperatures.

Catalytic reforming: Alkanes and cycloalkanes converted to aromatic compounds.

The Common Functional Groups

Class General Formula

Halohydrocarbons RX

Alcohols ROH

Ethers ROR

Aldehydes

CRO

H

The Common Functional Groups

Class General Formula

Ketones

Carboxylic Acids

Esters

Amines RNH2

Amides R-C=ONH2

CRO

R'

CRO

OH

CRO

O R'

22_05TTable 22.5 The Common Functional Groups

Functional GeneralClass Group Formula* Example

Halohydrocarbons X (F,Cl,Br,I) R X CH3IIodomethane

(methyl iodide)

Alcohols OH R OH CH3OHMethanol

(methyl alcohol)

Ethers O R O R' CH3OCH3Dimethyl ether

CH2OAldehydes Methanal

(formaldehyde)

CH3COCH3Ketones Propanone

(dimethyl ketoneor acetone)

CH3COOHCarboxylic acids Ethanoic acid

(acetic acid)

CH3COOCH2CH3Ethyl acetateEsters

Amines CH3NH2Aminomethane (methylamine)

C H R C H

O O

C R C R'

O O

C OH R C OH

O O

C O R C O R'

O O

NH2 R NH2

*R and R' represent hydrocarbon fragments.

Alcohols

contain the hydroxyl group (-OH).

Aldehydes & Ketones

contain the carbonyl group ( C=O ).

In ketones the carbonyl group is bonded to two carbon atoms -- CH3C=OCH3.

In aldehydes the carbonyl group is bonded to at least one hydrogen atom -- HCHO.

Carboxylic Acids & Esters

Carboxylic acids contain the carboxyl group

O (-C-OH).

OEsters contain the -C-O- group.

Amines & Ethers

Amines contain -NH2 group.

If one hydrogen is removed and replaced with a hydrocarbon group, it is a primary amine.

If two hydrogen are replaced, it is a secondary amine.

If all three hydrogens are replaced, it is a tertiary amine.

Ethers contain the -O- group.

Polymers

. . . are large, usually chainlike molecules that are built from small molecules called monomers.

Monomer PolymerEthylene PolyethyleneVinyl chloride Polyvinyl

chlorideTetrafluoroethylene Teflon

Types of Polymerization

Addition Polymerization: monomers “add together” to form the polymer, with no other products. (Teflon)

Condensation Polymerization: A small molecule, such as water, is formed for each extension of the polymer chain. (Nylon)