A brief introductionOrganic Chemistry A brief introduction Thursday, April 2, 2009 the study of carbon-containing compounds and their properties Organic Chemistry excluding: CO, CO

Organic Chemistry

A brief introduction

Thursday, April 2, 2009

the study of carbon-containing compounds and their properties

Organic Chemistry

excluding: CO, CO2, CS2, carbonates and cyanides

eight million known organic compounds(and counting!)


Hydrocarbons

compounds composed of hydrogen and carbon


Alkanes

The simplest hydrocarbon


Alkanes

CnH2n+2 where n = 1,2,3...

generic chemical formula

a hydrocarbon containing only single covalent bonds

CH4 C

H

HH

H

Methane

sp3 hybridizationthese molecules are said to be saturated, meaning no more hydrogen atoms can be added to the molecule


Alkanes

CH4Methane

C2H6Ethane CH

HH

CH

HH

CH

HH

H

CH

HH

CH

HCH

HH

C3H8Propane

C4H10Butane Two possible schemes

You must memorize these 1st 4


n-butane

CH

HH

CH

HCH

HCH

HH C

HH

HCH

CH

HH

H CH

H

Structural Isomers:Molecules that have the same molecular formula

but different constitutions/connectivities

Structural Isomers

Exhibit different chemical and physical properties

isobutane


Elemental Composition

Empirical Formula

Molecular FormulaConstitution

Configuration

Conformation

Levels of Structure

√√√

the order in which the atoms are connected


Alkane Nomenclaturethe names of alkanes beyond butane are obtained by

adding the suffix -ane to the Greek root for the number of carbon atoms

(CH2)8 CH3CH3 decane(CH2)7 CH3CH3 nonane(CH2)6 CH3CH3 octane

the longest continuous chain of carbon atoms determines the root name

(CH2)5 CH3CH3 heptane(CH2)4 CH3CH3 hexane(CH2)3 CH3CH3 pentane


Alkane NomenclatureWhen alkane groups appear as substitutents, they are

named by dropping the -ane and adding -yl.

CH2 CH2CH3 PropylCH2CH3 Ethyl

CH3 Methyl

CH CH3CH3 Isopropyl

CH2 CH2CH3 CH2 Butyl


Alkane NomenclatureWhen alkane groups appear as substitutents, they are

named by dropping the -ane and adding -yl.

CH2 CHCH3 CH3 sec- Butyl

C CH2CH3

CH3

H

iso-Butyl

C CH3CH3

CH3tert-Butyl


Alkane NomenclatureThe position of substituent groups are specified by

numbering the longest chain of carbon atoms sequentially, starting at the end closest to the

substituent.

CH3 CH

CH2 CH2

CH3

CH3

1 2 3 4 5

methylpentane

The location and name of each substituent is followed by the root alkane name.

2-


Example

3-methylhexaneCH3 CH

CH2 CH2

CH2

CH3

CH3

CH3 CH2 C CH2 CH3

H

CH3

3-methylpentane


CH3 CH

CH2 CH2

CH2

3-methylhexaneCH3

CH3

Example

CH3 CH2 C CH2 CH3

H

CH3

3-methylpentane


Alkane NomenclatureThe substituents are listed in alphabetical order, and

the prefixes di-, tri-, and so on are used to indicate multiple, identical substituents.

CH3 C CH2 CH2

CH3

CH3

CH3

2,2-Dimethylpentane


Example

2,4-dimethylhexaneCH3 CH

CH2 CHCH2

CH3

CH3

CH CH2 CH2 C CH3

H

2-methylhexane

CH3

CH3

CH3

H


Example

4-ethyl-3,5-dimethylheptane

CH2 CH CH CH

CH2

CH2

CH3

CH3

CH3CH3

CH3

CH2 CH2 CH2 C

CH2

CH2

CH3

CH3

CH3

CH2

CH3

3-ethyl-3-methyloctane


Example

4-ethyl-3,5-dimethylheptane

CH2 CH CH CH

CH2

CH2

CH3

CH3

CH3CH3

CH3

CH2 CH2 CH2 C

CH2

CH2

CH3

CH3

CH3

CH2

CH3

3-ethyl-3-methyloctane


CH3 CH

CH CH2

CH3

CH2

CH2

Alkane NomenclatureIf two chains of equal length are present, choose the one with the larger number of branch points as the

parent.

CH3

CH3

3-ethyl-2-methylhexane


CH3 CH

CH CH2

CH3

CH2

CH2

Alkane NomenclatureIf two chains of equal length are present, choose the one with the larger number of branch points as the

parent.

CH3

CH3

3-isopropyl-hexaneNot


The Chemistry of Alkanes


Physical Properties of Alkanes

as molecular size increases so does the boiling point of the alkane

increased size increased dispersion forces


Alkanes

CH4Methane

C2H6Ethane C

HH

HCH

HH

C3H8Propane

C4H10Butane

CH

HH

H

Boiling Point˚C

-161.6

-88.6

-42.1

-0.5(CH2)2 CH3CH3

(CH2)1 CH3CH3

C5H12Pentane 36.1(CH2)3 CH3CH3

C6H14hexane 68.7(CH2)4 CH3CH3


Chemical Reactions and Alkanes

because the C-C and C-H bonds are relatively strong, the alkanes are fairly unreactive

their inertness makes them valuable as lubricating materials and as backbone material

in the construction of other hydrocarbons


Combustion of Alkanes

these reactions are all highly exothermic

CH4 O2 CO2 2H2O+ +

C4H10 13/2O2 4CO2 5H2O+ +

ΔH˚-890.4 kJ

-3119 kJ

At high temperatures alkanes combust


alkyl halide

An alkane in which one or more hydrogens have been replaced with halogens

CH3Cl


Example

CH3 CH2 CH2 C CH3

H

Cl2-chloropentane

Br CH2 CH2 C CH3

H

Cl1-bromo-3-chlorobutane


A Functional Groupa group of atoms that are largely responsible

for the chemical behavior of the parent molecule

NH2, F, Cl, Br, I, NO2 ,, ,some common

functional groups

Alkyl groups - derived from alkanes



Empirical Formula


Configuration

Conformation

Levels of Structure

√√√√


Stereoisomersisomers that have the same constitution but differ in

the spatial arrangement of their atoms

CH3 CH

CH3

HCH

H CH3

H

H

CH3H

H

saw horse projection


Stereoisomersisomers that have the same constitution but differ in

the spatial arrangement of their atoms

CH3 CH

CH3

HCH

H

saw horse projection

Conformations : different spatial arrangments of a molecule generated by rotation of atoms about single

bonds

CH3

H

HCH3

H

H



Empirical Formula


Configuration

Conformation

Levels of Structure

√√√√√


EnantiomersStereoisomers that are related as an object and

its nonsuperimposable mirror image

ie: being chiral

C

Br

HF

Cl

bromochlorofluoromethane

C

Br

FH

Cl


C

Br

HCl

F

mirror images

C

Br

ClH

F


nonsuperimposable

C

Br

ClH

F

C

Br

HCl

F

amino acids are examples of molecules that have a chiral carbon


Cycloalkanes


Cycloalkanes

Alkanes whose carbon atoms are joined in rings

CnH2n

sp3 hybridization

C5H10cyclopentaneC

CC

C CH

HHH

HH

H

HH

H


Alkane Nomenclaturefollows the same rules as for naming other alkanes except that the root name is preceded by the prefix

cyclo-

The ring is numbered to yield the smallest substitutent number possible.

CH3CH2

CH2CH2

CH2CH2

cyclobutane 1-ethylcyclobutane


Example

1-Ethyl-2-methylcyclohexaneCH3

CH2 CH3

H3C

CH3

1,4-Dimethylcyclohexane


Example

CH3

CH3

1,1-Dimethylcyclohexane


Cyclohexane

CC

C C

H

HCHH

HH

H

H

HH C

HH

to attain tetrahedral bond angles the cyclohexane ring must “pucker”


CyclohexaneTwo stable conformations C6H12

C

C C

C H

HC

H

H

HH

H

H

HH

C

H

H

Boat Thursday, April 2, 2009

CyclohexaneTwo stable conformations C6H12

C

C C

C H

HC

H H

HH

H

H

HH C

H

H

Chair

Cyclohexane assumes the chair conformation 99%

of the time


Fused Ring Cyclic Alkanes - Steroids


Fused-Ring Cyclic Alkanes - Steroids


Alkenes

multiple carbon-carbon double bonds result when hydrogen atoms

are removed from alkanes


CnH2n

Alkenes

sp2 hybridization

hydrocarbons containing at least one carbon-carbon double bond

C2H4

Ethylene C C

H

H

H

HEthene


these molecules are said to be unsaturated

unsaturated: more hydrogen can be added to the molecule

C2H4Ethene C CH

H

H

H

Alkenes


Alkene Nomenclature

The location of the carbon-carbon double bond is indicated by the lowest numbered carbon atom

involved in the double bond.

The root hydocarbon ends in -ene rather than -ane.

1-ButeneCH3CH2 CH2CH2

CH3CH CHCH3 2-Butene


Example

3-methyl-3-hexeneCH3 C CH CH2

CH2

CH3

CH3

CH3 CH2 C CH CH3

H

2-pentene


Conformations of Alkenesrotation around the carbon-carbon double bond is

highly restricted but not impossible

the two H atoms are on the same side

the two H atoms are across from each other

C CH

CH3

H3C

HC C

H

CH3

H

H3C

cis-2-Butenetrans-2-Butene

thus alkenes exhibit cis-trans isomerism


Conformations of Alkenes

less steric strain

C CH

CH3

H3C

HC C

H

CH3

H

H3C

cis-2-Butenetrans-2-Butene

thus alkenes exhibit cis-trans isomerism

rotation around the carbon-carbon double bond is highly restricted but not impossible


Example

C CH

CH2CH3

H3C

H

C CH

CH2

H

CH2

cis-3-hexene

trans-2-pentene

CH3CH3


Some Chemical Reactions involving Alkenes

addition reactions

with hydrogen halides

hydrogenation

with halogens


Hydrogenation of ethylene

Exothermic ΔE˚ = -136 kJ/mol

catalyzed by finely divided Pt,Pd, Rh, Ni

CH

HC

H

HHH CH

HC

H

HH

H

+

Addition Reaction


H HC

H

HC

H

H


CH

HC

H

HH

H

H

H


HH HC C

H

H

H

H

H


HHC C

H

H

H

H

HH


H H

HH HC C

HH

H


Alkynes


CnH n

Alkyneshydrocarbons containing at least one carbon-

carbon triple bond

sp hybridization

C2H2 C C HHEthyne


Alkyne Nomenclature

alkynes involves the use of -yne as a suffix to replace the -ane of the parent molecule

number from the end closer to the carbon bearing the triple

1-ButyneCH3C CH2CHCH3C CCH3 2-Butyne


Chemical Reactions and Ethyne (Acetylene)

Due to its high heat of combustion acetylene has many industrial uses

+ 5O2 4CO2 +CH )( HC 2H2O2

ΔH˚ -2599.2 kJ


Aromatic Hydrocarbons


Benzene

due to benzene’s high carbon to hydrogen ratio it was assumed that it would under go addition

reactions similar to that of alkenes and alkynes

C6H6

Benzene however proved to be relatively inert

Its formula was known relatively early on, but what as its structure???


August Kekulededuced the

structure of benzene to be planar and

cyclicthe properties of benzene can be explained by delocalized

molecular orbitals

CCC C

HC

H

H

H

H CH

CCC C

HC

H

H

H

H CH


Benzene C6H6

CCC C

HCH

H

H

H CH

The circle represents the electrons in the p system.


H

H

H

H

H

H

Benzene C6H6


H

H

H

H

H

H

Benzene C6H6


NomenclatureNaming of monosubstituted benzene

CCC C

HCCl

H

H

H CH

CCC C

HCNO2

H

H

H CH

CCC C

HC

H

H

H CH

CH2 CH3

ethylbenzenechlorobenzenenitrobenzene


NomenclatureIf more than one substituent is present we must indicate

the location of the second group relative to the first

CCC C

ClCCl

H

H

H CH

1,2-dichlorobenzene

CCC C

HCCl

Cl

H

H CH

1,3-dichlorobenzene

CCC C

HCCl

H

H

H CCl

1,4-dichlorobenzeneortho

metapara


NomenclatureIf more than one substituent is present we must indicate

the location of the second group relative to the first

CCC C

ClCCl

H

H

H CH

CCC C

HCCl

Cl

H

H CH

CCC C

HCCl

H

H

H CCl

o-dichlorobenzenem-dichlorobenzene

p-dichlorobenzene


Benzene C6H6

when benzene is used as a substituent, it is called the phenyl Group

CH3CCCH2

1-phenyl-2-butyneThursday, April 2, 2009

NomenclatureAny group that contains one or more fused benzene

rings is called an aryl group

NaphthaleneAnthracene

phenathrene


Graphite - fused aromatic rings in extended sheets held together with van der Waals forces


CCC C

HC

H

H

H

H CH

CCC C

HHC

HH

HH

HH

HH C

HH

+ 3H2Pt

Chemical Reactions involving Aromatics

benzene can be hydrogenated with difficulty


Polymerization

Building large molecules (polymers) from small molecules (monomers).


CH2H2C CH2)(H2C

ethylene polyethylene

From http://www.chemheritage.org/EducationalServices/faces/poly/readings/rec.htm


More Functional Groups


Alcoholscontain at least one hydroxyl group (-OH)

CH

OHH

CH

HH

ethanol

CCC C

HC

OH

H

H

H CH

benzenolphenol


AlcoholsThe systematic name for an alcohol is obtained by

replacing the -e of the parent hydrocarbon with -ol.

The -OH group is specified by a number

OHCH

HH

CH

HCH

HCH

H

CH

CH

HH

CH

OHHH

2-butanol

1-propanol


Ethers

Diethyl ether

CH

HH

O CH

HCH

HH

CH

H

contain the ( R O R ) group

Ethyl methyl ether

CH

HH

OCH

HH

CH

H`


Ethers

Ethyl methyl ether

CH

HH

OCH

HH

CH

H

Diethyl ether

CH

HH

O CH

HCH

HH

CH

H

Names of ethers are derived by listing the two alkyl groups in the general structure ROR’ in alphabetical order as separate words, and then adding ether to the

end.


Aldehydes and Ketones

(formaldehyde)

contain a carbonyl group

Aldehydesat least one hydrogen is bonded

to the carbonyl group C

O

H H

2-butanoneKetones

no hydrogen atoms bonded to the carbonyl group

C

O

CH2CH3H3C

C O

methanal

(methyl propyl ketone)Thursday, April 2, 2009

Carboxylic Acidscontain a carboxyl group C

O

OHR

Acetic acid C

O

OHH3C

C

O

OHHFormic acid

CCC C

HC

H

H

H CH

C

O

OH

Benzoic acid(used in FP Depression lab we did)


EstersHave the general formula R COOR

C

O

OR RC

O

O

Ethyl acetate

CH2CH3CH3

Ethyl benzoate

C

O

O CH2CH2

C

O

O

Methyl propanoate

CH3CH3CH2

`

`


Aminescontain at least one amine group (-NH2)

CH

NH2

HCH

HH

ethylamine

butylamine

CH3CHCH2CH2 NH2

CCC C

HC

NH2

NH2

H

H CH

1,3-benzenediamine


Amino Acids

polymerize to form peptides (a few amino acids long) and proteins (hundreds of amino acids long)

+

+ ???1 2

+ H2O


Documents

A brief introductionOrganic Chemistry A brief introduction Thursday, April 2, 2009 the study of carbon-containing compounds and their properties Organic Chemistry excluding: CO, CO