Organic Chemistry

Chapter 12

Organic Chemistry

• Organic chemistry:Organic chemistry: the study of the compounds of carbon– organic compounds are made up of carbon and

only a few other elements– chief among these are hydrogen, oxygen, and

nitrogen– also present are sulfur, phosphorus, and a

halogen (fluorine, chlorine, bromine, or iodine)

Organic Chemistry

– the experiment of Wöhler in 1828 was the first in a series of experiments that led to the demise of the vital force theory

NH4Cl AgNCO H2N-C-NH2

OAgCl+ heat +

Ammoniumchloride

Silvercyanate

Urea Silverchloride

Organic Chemistry

• The link to biochemistryThe link to biochemistry– carbohydrates, lipids, proteins, enzymes,

nucleic acids, hormones, vitamins, and almost all other chemicals in living systems are organic compounds

Organic Structure– Make a model of each of these structures:Make a model of each of these structures:

H-C-C-H

H

H H

H H

HC C

H

HH-C C-H

H-C-O-H

H

H

HC O

HH-C-N-HH

HH

HN

H HC

H-C-C-Cl

H

H H

H

Ethane(bond angles

109.5°)

Ethylene(bond angles

120°)

Acetylene(bond angles

180°)

Methanol(bond angles

109.5°)

Formaldehyde(bond angles

120°)

Methanamine(bond angles

109.5°)

Methyleneimine(bond angles 120°)

Chloroethane(bond angles

109.5°)

::

::::

::

:

Organic Structure– VSEPR model:VSEPR model: the most common bond angles

are 109.5°, 120°, and 180°

H-C-C-H

H

H H

H H

HC C

H

HH-C C-H

H-C-O-H

H

H

HC O

HH-C-N-HH

HH

HN

H HC

H-C-C-Cl

H

H H

H

Ethane(bond angles

109.5°)

Ethylene(bond angles

120°)

Acetylene(bond angles

180°)

Methanol(bond angles

109.5°)

Formaldehyde(bond angles

120°)

Methanamine(bond angles

109.5°)

Methyleneimine(bond angles 120°)

Chloroethane(bond angles

109.5°)

::

::::

::

:

Functional Groups

• Functional group:Functional group: anything other than just C-C, or C-H bonds!

• Functional groups are important because– they undergo the same types of chemical reactions no

matter in which molecule they are found– to a large measure they determine the chemical and

physical properties of a molecule– Naming is based on FG.

Functional Groups

• Why are they FUNCTIONAL?

Functional Groups• Five important functional groups

-OH

-NH2

-C-HO

-C-O

CH3CH2OH

CH3CH2NH2

CH3CHO

CH3CCH3

O

CH3COHO

-C-OHO

Example

Alcohol

Amine

Aldehyde

Ketone

Carboxylic acid

Ethanol

Ethanamine

Ethanal

Acetone

Acetic acid

NameFamilyFunctionalgroup

Alkanes

• Alkanes:Alkanes: hydrocarbons containing only carbon-carbon single bonds– the first two alkanes are methane and ethane

H-C-HH

HH-C-C-HH

H

H

H

Methane Ethane

Alkanes• line-angle formula:line-angle formula:

– a line represents a carbon-carbon bond and an angle represents a carbon atom

– a line ending in space represents a -CH3 group– hydrogen atoms are not shown in line-angle formulas

CH3CH2CH2CH3CH3CH2CH3 CH3CH2CH2CH2CH3CH3CH2CH2CH3CH3CH2CH3 CH3CH2CH2CH2CH3PentaneButanePropane PentaneButanePropane

Condensedstructural

formula

Line-angleformula

Ball-and-stick model

Alkanes

– the first 10 alkanes with unbranched chains

CH4 CH4C2H6 CH3CH3C3H8 CH3CH2CH3C4H10 CH3(CH2)2CH3C5H12 CH3(CH2)3CH3

C6H14 CH3(CH2)4CH3C7H16 CH3(CH2)5CH3C8H18 CH3(CH2)6CH3C9H20 CH3(CH2)7CH3C10H22 CH3(CH2)8CH3

CH4 CH4C2H6 CH3CH3C3H8 CH3CH2CH3C4H10 CH3(CH2)2CH3C5H12 CH3(CH2)3CH3

C6H14 CH3(CH2)4CH3C7H16 CH3(CH2)5CH3C8H18C9H20C10H22

CondensedStructural Formula

MolecularFormulaName

decane

nonane

octane

heptane

hexane

pentane

butane

propane

ethanemethane

CondensedStructural Formula

MolecularFormulaName

CondensedStructural Formula

MolecularFormulaName

decane

nonane

octane

heptane

hexane

pentane

butane

propane

ethanemethane

CondensedStructural FormulaName

Constitutional Isomerism• Constitutional isomers:Constitutional isomers: compounds that

have the same molecular formula but different structural formulas– for the molecular formulas CH4, C2H6, and

C3H8, only one structural formula is possible. – for the molecular formula C4H10, two

constitutional isomers are possible

CH3CH2CH2CH3 CH3CHCH3

CH3

Butane(bp -0.5°C)

2-Methylpropane(bp -11.6°C)

Constitutional Isomerism– Problem:Problem: do the structural formulas in each set

represent the same compound or constitutional isomers?

CH3CH2CH2CH2CH2CH3 CH3CH2CH2CH2CH2CH3

CH3CHCH2CHCH3

CH3

CH3

CH3CH2CHCHCH3

CH3

CH3

(a) and (each is C6H14)

(b) and (each is C7H16)

Constitutional Isomerism– Solution:Solution: (a) they represent the same compound

– Solution:Solution: (b) they represent constitutional isomers

CH3CHCH2CH

CH3

CH3

CH3CH3CH2CHCHCH3

CH3

CH35

1 12 23 3

4

455

2 5 4 3

2 1

431 and

CH3CH2CH2CH2CH2CH3 CH3CH2CH2

CH2CH2CH3

654321

654

321

and

21

12

3 3

4

45

5

6

6

Constitutional Isomerism

– Problem:Problem: draw structural formulas for the five constitutional isomers of molecular formula C6H14

Constitutional Isomerism

– Problem:Problem: draw structural formulas for the five constitutional isomers of molecular formula C6H14

– Solution:Solution:

Six carbons in an unbranched chain

Five carbons in a chain; one carbon as a branch

1 32 4

56

1 12

23 3

4 4

5 5

Four carbons in a chain; two carbons as branches

1 12 2

3 34 4

IUPAC Names• The IUPAC name of an alkane with an

unbranched chain of carbon atoms consists of two parts: – (1) a prefix: the number of carbon atoms in the chain– (2) the suffix -ane-ane: shows that the compound is a

saturated hydrocarbon

Prefixmeth-eth-prop-but-pent-

hex-

oct-non-dec-

12345

67hept-8910

Number ofCarbon Atoms

Number ofCarbon AtomsPrefix

IUPAC Names• The name of an alkane with a branched

chain of carbon atom consists of – a parent name: the longest chain of carbon

atoms– substituent names: the groups bonded to the

parent chain

CH3

CH3CH2CH2CHCH2CH2CH2CH38

substituent

4-Methyloctane

1 2 3 4 5 6 7 8

parent chain

12

34

5

6

7

IUPAC Names• Alkyl group:Alkyl group: a substituent group

– named by dropping the -aneane from the name of the parent alkane and adding the suffix -ylyl

-CH2CH3

-CH3

-CH2CH2CH3

-CHCH3CH3

-CH2CH2CH2CH3

-CH2CHCH3CH3

-CHCH2CH3CH3

-CCH3

CH3

CH3

tert-butyl

sec-butyl

isobutyl

butyl

isopropyl

propyl

ethyl

methylName

CondensedStructural Formula

CondensedStructural FormulaName

IUPAC Names-Review1. The name for an alkane with an unbranched chain

of carbon atoms consists of a prefix showing the number of carbon atoms and the ending -aneane

2. For branched-chain alkanes, longest chain of carbon atoms is the parent chain

3. Name and number each substituent on the parent chain; use a hyphen to connect the number to the name

CH3CHCH3

CH3

2-Methylpropane

12

3

IUPAC Names-Details

4. If there is one substituent, number the parent chain from the end that gives the substituent the lower number

CH3

CH3CH2CH2CHCH35

2-Methylpentane(not 4-methylpentane)

123

4

IUPAC Names-Details5. If the same substituent occurs more than

once,– indicate the number of times the substituent

occurs by a prefix di-, tri-, tetra-, penta-, hexa-, and so on

– use a comma to separate position numbers

CH3CH2CHCH2CHCH3

CH3 CH3

2,4-Dimethylhexane(not 3,5-dimethylhexane)

12

34

56

IUPAC Names- Details6. If there are two or more different substituents

– list them in alphabetical order

– number the chain from the end that gives the lower number to the substituent encountered first

– if numbering is the same in both directions, give the substituent of lower alphabetical order the lower number

CH3CH2CHCH2CHCH2CH3

CH3

CH2CH3

12

34

56

7

3-Ethyl-5-methylheptane(not 3-methyl-5-ethylheptane)

IUPAC Names-Details7. Do not include the prefixes di-, tri-, tetra-, and so

on, or the hyphenated prefixes sec- and tert- in alphabetizing; – alphabetize the names of substituents first, and then

insert these prefixes

CH2CH3

CH3CCH2CHCH2CH3

CH3

CH34-Ethyl-2,2-dimethylhexane

(not 2,2-dimethyl-4-ethylhexane)

23

45

61

Common Names

• Common names- older system

– use the IUPAC system for our class!

CH3CHCH3

CH3

CH3CH2CHCH3

CH3

IsopentaneIsobutane

24.2

Cycloalkanes

Alkanes whose carbon atoms are joined in rings are called cycloalkanes. They have the general formula CnH2n where n = 3,4,…

Cycloalkanes• Cyclic hydrocarbon: Cyclic hydrocarbon: a hydrocarbon that contains

carbon atoms joined to form a ring• Cycloalkane:Cycloalkane: a cyclic hydrocarbon in which all

carbons of the ring are saturated – cycloalkanes of ring sizes ranging from 3 to over 30

carbon atoms are found in nature– five-membered (cyclopentane) and six-membered

(cyclohexane) rings are especially abundant in nature

Cyclopentane Cyclohexane

Cycloalkanes• Nomenclature

– Prefix cyclo-,cyclo-,– if only one substituent, no location number– if there are two substituents, number the ring

beginning with the substituent of lower alphabetical order.

Name These Cycloalkanes

Conformations - Alkanes– Molecules move a lot … each movement result in a

different conformation … each conformation has an associated energy … some conformations are more stable than others!

– following are three conformations for a butane molecule

Most crowdedconformation

rotate by 120°

rotate by 60°

Least crowdedconformation

Intermediatecrowding

Cycloalkanes cis and trans

If a ring has two substituents on it, they can be on the same side (cis) or the opposite side (trans).

H3C CH3

H3C

CH3

CH3CH3

CH3

CH3

cis-1,2-dimethylcyclopropane

trans-1,2-dimethylcyclopropane

cis-1,2-dimthylcyclobutane

trans-1,2-dimthylcyclobutane

Cis-Trans Isomers– alternatively, we can view it from above

CH3trans-1,2-Dimethyl-

cyclopentanecis-1,2-Dimethyl-

cyclopentane

H3C CH3 H3C

Cis-Trans Isomers– to determine cis-trans isomers if cis-trans isomers

are possible, we can view a cyclohexane ring as a planar hexagon

– because cis-trans isomers differ in the orientation of their atoms in space, they are stereoisomersstereoisomers

– cis-trans isomers are one type of stereoisomers

trans-1,4-Dimethylcyclohexane cis-1,4-Dimethylcyclohexane

H

H3C

CH3

H

H

H3C

H

CH3

or or

CH3

CH3

CH3

CH3

24.2

Alkane Nomenclature-Review

1. Find the longest continuous chain of carbon atoms in the molecule. This is the “parent” name. … or the ring is the parent.

2. Branched are named as an alkyl group.

3. Substituents are numbered in the direction that gives the smaller numbers for the locations of the branches.

4. Use prefixes di-, tri-, tetra-, when there is more than one alkyl branch of the same kind.

5. Use previous rules for other types of substituents. Write them in alphabetical order.

Alkane ChemistryKey reactions:1) Burning

• CH4 + O2 CO2 + H20 + Heat

2) Chlorination• CH3CH3 + Cl2 CH3CH2Cl + HCl

• Note that multiple chlorination reactions can occur in uncontrolled environments.

Monochlorinate Butane1) When butane is chlorinated, the C1 and C2

products are different.

2 structural isomers

Cl

Cl

1-chlorobutane 2-chlorobutane

*

•A chiral carbon•See CH 15

Formation of 2-chlorobutane

Mechanism of formationCl Cl

H H

H

Cl

2 Cl

+ Cl .+ HCl

.+ Cl

Both mirror images0ptically different

PlanerIntermediate

Chapter 12 End

Cyclopropane

Hydrogen's move to alleviate eclipsing energies

Cyclobutane

Cyclopentane

Cyclopentane

• The most stable conformation of a cyclopentane ring is an envelope conformation

Cyclohexane

H

H

H

H

H

H

Axial hydrogens shown

Cyclohexane

• The most stable conformation of a cyclohexane ring is the chair conformation– all bond angles are approximately 109.5°

Cyclohexane• In a chair conformation,

– six C-H bonds are equatorialequatorial– six C-H bonds are axialaxial

HH

H

HHH

(a) Ball-and-stick modelshowing all 12 hydrogens

axis through thecenter of the ring

H H

H

H

H

H

(b) The six equatorialC-H bonds

(c) The six axial C-H bonds

Draw the Chair

Cyclohexane– the more stable conformation of a substituted

cyclohexane ring has substituent group(s) equatorial rather than axial

CH3

Equatorial methylcyclohexane

CH3

Axial methylcyclohexane

Axial vs. Equatorial

Cl

Cl

vs.

Which is more stable?