Organic Chemistry Organic Chemistry: The chemistry of carbon and carbon-based compounds Organic Chemistry in everyday life: Smells & tastes: fruits, chocolate,

Organic Chemistry

Organic Chemistry: The chemistry of carbon and carbon-based compounds

Organic Chemistry in everyday life:Smells & tastes: fruits, chocolate, fish, mint

Medications: Aspirin, Tylenol, Decongestants, Sedatives

Addictive substances: Caffeine, Nicotine, Alcohol, Narcotics

Hormones/Neurotransmitters: Adrenaline, Epinephrine

Food/Nutrients: Carbohydrates, Protein, Fat, Vitamins

Genetics: DNA, RNA

Consumer products: Plastics, Nylon, Rayon, Polyester

Simplest class of organic compounds

Consist entirely of carbon and hydrogen

Four major classes of hydrocarbons:1. Alkanes — contain only carbon-hydrogen and carbon-

carbon single bonds2. Alkenes — contain at least one carbon-carbon double

bond3. Alkynes — contain a least one carbon-carbon triple bond4. Aromatics — contain rings of six carbon atoms that can be

drawn with alternating single and double bonds

Alkanes are saturated hydrocarbons; alkenes, alkynes, and aromatics are unsaturated hydrocarbons

Hydrocarbons

Copyright 2007 Pearson Benjamin Cummings. All rights reserved.

Alkanes

– Names of all alkanes end in –ane, and their boiling points increase with more carbon atoms present.

– The simplest alkane is methane. – In larger alkanes, carbon atoms are joined in an unbranched

chain (straight-chain alkanes) where each carbon atom is bonded to two other carbon atoms.

– Alkanes with four or more carbon atoms can have more than one arrangement of atoms. Carbon atoms can form a single, unbranched chain, or the primary chain of carbon atoms

can have one or more shorter chains that form branches. – The systematic name for branched hydrocarbons uses the lowest

possible number to indicate the position of the branch along the longest straight carbon chain in the structure.

Hydrocarbons

Copyright 2007 Pearson Benjamin Cummings. All rights reserved.

Alkenes

– The simplest alkenes are ethylene and propylene. – Names of alkenes that have more than three carbon atoms

use the same stems as the names of alkanes but end in –ene.

– More than one structure is possible for alkenes that contain four or more carbons.

– The number in the name of an alkene specifies the position of the first carbon atom of the double bond. The

name is based on the lowest possible number starting from either end of the carbon chain.

Hydrocarbons

Copyright 2007 Pearson Benjamin Cummings. All rights reserved.

Alkynes

– The simplest alkyne is acetylene.

– The names of alkynes are similar to those of the corresponding alkanes but end in –yne.

Hydrocarbons

Copyright 2007 Pearson Benjamin Cummings. All rights reserved.

Cyclic hydrocarbons

– The ends of a hydrocarbon chain are connected to form a ring of covalently bonded carbon atoms.

– Cyclic hydrocarbons are named by attaching the prefix cyclo- to the name of the alkane, alkene, or alkyne.

– The simplest cyclic alkanes are cyclopropane and cyclobutane

– Draw structures of cyclic alkanes by sketching a polygon with the same number of vertices as there are

carbon atoms in the ring with each vertex representing a CH2 unit.

Hydrocarbons

Copyright 2007 Pearson Benjamin Cummings. All rights reserved.

Hydrocarbons

Copyright © 2007 Pearson Benjamin Cummings. All rights reserved.

Aromatic Hydrocarbons

– Alkanes, alkenes, alkynes, and cyclic hydrocarbons are called aliphatic hydrocarbons.

– Aromatic hydrocarbons are also called arenes and are obtained by the distillation and degradation of highly scented resins from tropical trees.

– The simplest aromatic hydrocarbon is benzene. – The chemical behavior of aromatic compounds differs from the

behavior of aliphatic compounds. – The general name for a group of atoms derived from an alkane is

an alkyl group, and the name of the alkyl group is derived from the name of the alkane by adding the suffix –yl.

– Groups of atoms derived from aromatic hydrocarbons are aryl groups.

– In general formulas and structures, alkyl and aryl groups are abbreviated as R.

Hydrocarbons

Copyright © 2007 Pearson Benjamin Cummings. All rights reserved.

Hydrocarbons

Copyright © 2007 Pearson Benjamin Cummings. All rights reserved.

• Alcohols

– Replacing one or more hydrogen atom of a hydrocarbon with an –OH group gives an alcohol and is

represented as R-OH.

– The simplest alcohol is methanol (systematic name) or methyl alcohol (common name).

– The simplest alcohol derived from an aromatic hydrocarbon is phenol.

Hydrocarbons

Copyright © 2007 Pearson Benjamin Cummings. All rights reserved.

Drawing Organic Structures

Butane: C4H10

C C C C

H

H

H

H

H

H

H

H

H

H

CH3 CH2 CH2 CH3

CH3CH2CH2CH3

CH3(CH2)2CH3

Shortcuts make structures easier & faster to draw

Line Structure• Only shows bonds• C atoms assumed at each end

and intersection of bonds• H atoms not shown• Assume 4 bonds to each C• Fulfill C’s 4 bonds by adding H’s

Lewis Structure

Condensed Structures

Carbon Atoms

Types of Organic CompoundsClassified according to functional group

Alkane

Alkene

Alkyne

Haloalkane

Alcohol

Ether

Ketone

Aldehyde

Carboxylic acid

Amine

Amino acid

AmideO

H

O

NH2

O

OH

O

H2NOH

O

OH

Cl

Br

NH2

C C

O

Big Idea in Organic Chemistry

Structure controls Function

Each functional group has predictable reactivity

Alkanes or Paraffin• All C atoms are tetrahedral and sp3 hybridized

(only C-C single bonds)

• General formula = CnH2n+2 (CH4, C2H6, C3H8, C4H10, etc.)

• Can have linear or branched alkanes

C5H12

• Same molecular formula, different structure: structural isomers

• Branches are called substituents

Primary (1°) carbon atom: bound to one other C atom

Secondary (2°) C atom: bound to 2 other C atoms

Tertiary (3°) C atom: ” 3 ”

Quaternary (4°) C atom: ” 4 ”

C CH2H3C

H

CH3

CH33° 1°

2°

Names of Linear Alkanes and Alkyl Substituents

Alkane Alkyl substituents# of

C atoms

CH4

CH3CH3

CH3CH2CH3

CH3CH2CH2CH3

-CH3

-CH2CH3

-CH2CH2CH3

methyl

ethyl

propyl

etc.

methane

ethane

propane

butane

pentane

hexane

heptane

octane

nonane

decane

Root: number of C atomsSuffix: functional group (-ane for alkanes) (-yl for alkyl groups)

1

2

3

4

5

6

7

8

9

10

C H

H

H

H

Methane CH4

H

CC C C

H H H

H

HHHH

H

Butane C4H10

Butyl -C4H9

Methyl-CH3

C H

H

H

?R

H

CC C C

H H H

H

HHHH

?

Where R = any other C atom or arrangement of C atoms

R

First Ten Hydrocarbons: Properties

Name

Methane

Ethane

Propane

Butane

Pentane

Hexane

Heptane

Octane

Nonane

Decane

1

2

3

4

5

6

7

8

9

10

CH4

C2H6

C3H8

C4H10

C5H12

C6H14

C7H16

C8H18

C9H20

C10H22

Number ofCarbon Atoms

Molecular Formula

Melting Point, oC

# of Isomers

Boiling Point, oC

-182.5

-183.2

-187.7

-138.3

-129.7

- 95.3

- 90.6

- 56.8

- 53.6

- 29.7

-161.5

-88.6

-42.1

-0.5

36.1

68.7

98.4

125.7

150.8

174.0

1

1

1

2

3

5

9

18

35

75

Properties of Alkanes

Compound

Methane

Ethane

Propane

Butane

Pentane

MW

16

30

44

58

72

Boiling point (°C)

-164

-88.6

-42.1

-0.5

+36.0

Linear Alkanes:1 - 4 C atoms: gas at room temp

5 - 15 C atoms: liquid at room temp>15 C atoms: solid at room temp

Larger molecular weight → Stronger London dispersion forces

Nonpolar → only London Dispersion Forces IMF

Formula

CH4

C2H6

C3H8

C4H10

C5H12

Fractional Distillation of

Crude Oil

Kelter, Carr, Scott, Chemistry A World of Choices 1999, page 429

Naming Branched Alkanes (IUPAC)

1. Root name: name of longest continuous C chain (parent chain)Two equally long? Choose the one with more branches

2. Number C atoms in chain, starting at end with first branch

3. Identify substituents, give each a number (C it is connected to)Two or more identical substituents: use prefixes (di-, tri-, tetra-, etc.)

4. List substituents alphabetically before root nameDo not alphabetize prefixes

5. Punctuation: commas separate numbers from each other

hyphens separate numbers from namesno space between last substituent & root name

4-ethyl-3,5-dimethyloctane1

2

3

65

8

74

4-ethyl

3-methyl and 5-methyl = 3,5-dimethyl

Octane

Common Names of other Alkyl Substituents

isopropyl

isobutyl

sec-butyl

tert-butyl

alphabetized as “i”

alphabetized as “i”

alphabetized as “b”

alphabetized as “b”

CH CH2 CH3

CH3

C CH3

CH3

CH3

CH CH3CH2

CH3

CH CH3

CH3R

R

R

R

R

R

R

R

Remember that R = any carbon chain

“iso” indicates symmetry

3 carbons

4 carbons

2o

2o

Secondary carbon

Tertiary carbon

3o 3o

H

C H

H

H CC C

H H

HHH

C

H

HH

2 - methylbutanebutane

Naming Practice

Expanded Structure Line Structure

H C

C C C

H

H

CH3

CH3HH

H

C

C

H

H

H

H

H

hexane3,3-dimethyl

1 2 3

4

5

61

2

3

456

hexane4,4-dimethyl

Lowest sum of numbers is correct

Naming Practice

Line Structure

IsomersThe fat dog shook himself, and then rolled over on the wet rug.

The dog shook the fat rug, then rolled over and wet on himself.

These two statements use the same words...but have very different meanings!

OR

Likewise, isomers may have the same formula, but have very different structures…

Structural Isomers of C4H10

2-methylpropane

or

Structural Isomer Practice• On piece of your own paper, draw AND name

ALL of the isomers for the following alkanes:

Formulas # isomers

If you complete that, try to draw and name all of the isomers for octane (C8H18). There are 18 of them!

Some of your drawings may look different, but they are only different structures (isomers) if they also have different names

Pentane

Hexane

Heptane

C5H12

C6H14

C7H16

359

Structural Isomers: Pentane (C5H12)

pentane

2-methylbutane

2,2-dimethylpropane

Structural Isomers: Hexane (C6H14)

hexane

2-methylpentane

3-methylpentane

2,3-dimethylbutane

2,2-dimethylbutane

Structural Isomers: Heptane (C7H16)

heptane

2-methylhexane

3-methylhexane

2,2-dimethylpentane

2,3-dimethylpentane

Structural Isomers: Heptane C7H16

2,4-dimethylpentane

3,3-dimethylpentane

3-ethylpentane

2,2,3-trimethylbutane

Comparing Structural Isomers

C5H12

(Same formula, different structure)

More branching → weaker London dispersion forces

36.0pentane

27.92-methylbutane

9.52,2-dimethylpropane

Boiling point (°C)NameStructure

BP/MP of Linear alkanes > BP/MP of branched alkanes

Reactions of Alkanes

Combustion• exothermic reaction• alkanes used as fuel source

C4H10 + ___ O2 ___ CO2 + ___ H2O4 513/2

Incomplete Combustion with insufficient O2 produces CO• Poor ventilation, cigarettes

C4H10 + ___ O2 ___ CO + ___ H2O4 59/2

CO is poisonous because it binds to the hemoglobin in the blood, preventing the absorption

of O2

Radical Halogenation Terms

Mechanism

How the reaction occurs through multiple steps (most reactions actually occur in many steps)

Chain Reaction

Reactions that occur on their own after some initiating event

Free Radicals

Atoms that have one free electron—highly reactive

Radical Halogenation Terms• Initiation Step

– Step where a bond is split by heat/light, producing free radicals

• Propagation Step– Step where free radicals react with non-

radicals, producing more free radicals and continuing the “chain reaction”

• Termination Step– Step where free radicals react with each

other, producing non-radicals and terminating the “chain reaction”

Initiation

Propagation

Propagation

Termination

Reactions of Alkanes

Radical Halogenation of Alkanes

Mechanism (chain reaction):

Step 1 Cl2 ⇌ 2 Cl·

Step 2 Cl· + CH4 CH3· + HCl

Step 3 CH3· + Cl2 CH3Cl + Cl·

Step 4 Cl· + Cl· Cl2Overall reaction: CH4 + Cl2 CH3Cl + HCl

Halogenated product is a haloalkane

Naming: halogen atom is a substituent, replace –ine ending with –o

-F fluoro -Cl chloro -Br bromo -I iodo

chloromethane

h(Free Radicals)

Why not 1-chloromethane?

Type of Step

Radical Halogenation of AlkanesHalogen substitutes for hydrogen in alkane →multiple results

CH4 CH3Cl CH2Cl2 CHCl3 CCl4

Cl2

Cl2

Cl2

Cl2

Compound

CH3Cl

CH2Cl2

CHCl3

CCl4

IUPAC Name

chloromethane

dichloromethane

trichloromethane

tetrachloromethane

Common Name

methyl chloride

methylene chloride

chloroform

carbon tetrachloride

All are liquids at room temperature• Heavy Cl atoms increase LDF• Polar C-Cl bonds – can have polar molecules