Organic ChemistryOrganic ChemistryUnit 10Unit 10

What is Organic chemistry?What is Organic chemistry?• What does organic mean to you?• The name organic was given to molecules

found in living organisms• Now, organic chemistry refers to the chemistry

of carbon compounds– Carbon is important to life because of its ability to

form an endless number of molecules• CH4 – methane gas• Proteins• Cotton, wool, silk• CH3CH2OH - Ethanol

Organic CompoundsOrganic Compounds

Typically, organic compounds

Contain carbon.

Have covalent bonds.

Have low melting points.

Have low boiling points.

Are flammable.

Are soluble in nonpolar solvents..

Bonding in Organic CompoundsBonding in Organic Compounds• Carbon has 4 valence electrons (lone

electrons)

C • This means there are four places for it to

bound to other atoms in order for carbon to achieve an octet

C

•

• •

•

•••

•1

3

24

Bonding with HydrogenBonding with Hydrogen Carbon has 4 lone electrons; hydrogen has 1.Carbon has 4 lone electrons; hydrogen has 1.

••

•• C C • • H H •• ••

To achieve an octet, carbon forms four bonds. To achieve an octet, carbon forms four bonds. HH H H

• • • • ||H H C C H H H H——CC——HH CH CH4 4 , , methanemethane

• •• • || HH H H

Tetrahedral Nature of CarbonTetrahedral Nature of Carbon

• When carbon forms four bonds to other atoms, the bonds are situated 109.5o apart from each other.

• This arrangement is a

tetrahedral arrangement.

Organic MoleculesOrganic Molecules• In organic molecules, valence electrons form

covalent bonds between carbon atoms• Molecules consisting of only carbon and

hydrogen are call hydrocarbons H H H H

• • • • | |

H C C H H—C—C—H Ethane,CH3CH3

• • • • | | H H H H

Other ElementsOther Elements

• Carbon in organic compounds also commonly forms covalent bonds with N, O, S, and halogens (Cl, Br)

Learning CheckLearning Check

• Complete the structure of the organic molecule by adding the correct number of hydrogen atoms.

C—C—C

Learning CheckLearning Check• Complete the structure of the organic

molecule by adding the correct number of hydrogen atoms.

H H H | | | H—C—C—C—H | | |

H H H

AlkanesAlkanes• Hydrocarbons that contain only carbon-carbon single bonds

• General formula = CnH2n+2

– n = number of carbons

Uses of AlkanesUses of Alkanes• Small number of carbons (1 – 4

carbons)– gases– Heating fuels – propane, butane

• 5 – 8 carbons– Liquids– Fuels – gasoline, kerosene, diesel,

jet fuel• 18 + carbons

– Waxy solids– Waxes (paraffins), Vaseline

Conformation of AlkanesConformation of Alkanes• Because of the tetrahedral shape of carbon bonds,

carbon bonds are in a zigzag pattern

• Atoms can rotate around a single carbon-carbon bond– Different arrangements that can occur because of this

are called conformations

Expanded and Condensed Expanded and Condensed FormulasFormulas

• Expanded structural formula = all individual bonds (indicated with dashes) and atoms are drawn

• Condensed structural formula =each carbon atom is grouped with its bonded hydrogen atoms. Subscripts are used to indicate number of H’s and bonds are indicated with dashes

• Skeletal Formula= only carbons and bonds(as dashes) are represented- Hydrogens are implied

Expanded and Condensed Expanded and Condensed FormulasFormulas

• Line bond formulas = lines represent carbon-carbon bonds. No individual atom is indicated. Hydrogens and Carbons are implied.

• Molecular Formula= Atoms are represented and subscripts are used to indicate the number of each atom. No bonds are drawn.

• Geometric Formula= Similar to line bond formulas, but used for cyclic compounds.

IUPACIUPAC• International Union of Pure and Applied

Chemistry• Determined protocol for naming organic

compounds• Pentane

– Prefix states number of carbons• Pent - = five carbons

– Suffix shows kind of compound• -ane = alkane, only single carbon bonds

Prefixes (Table 11.2)Prefixes (Table 11.2)

CycloalkanesCycloalkanes• Hydrocarbons do not need to be in a chain, they

can also form circular structures

CycloalkanesCycloalkanes

• Cycloalkanes: • Are rings of carbons that can be drawn as

geometric figures. • Have a general formula of CnH2n or 2 H less than

the alkane. • propane C3H8 cyclopropane C3H6. • butane C4H10 cyclobutane C4H8. • Are named with the prefix cyclo- in front of the

corresponding alkane name.

Table 11.4Table 11.4

Cyclopropane CyclohexaneCyclopentaneCyclobutane

LINE BOND FORMULAS FOR SOME CYCLOALKANES

C3H6 C4H8 C5H10 C6H12

Naming AlkanesNaming Alkanes• Molecular formulas do not tell us the structure

– constitutional isomers

• Carbon compounds can be continuous-chain or branched-chained

SubstituentsSubstituents

• Substituents are groups of atoms that replace a hydrogen on a carbon chain– Blue flashcards! *need to know!!*

• If the substituent is a hydrocarbon, it is called an alkyl group– The alkyl group is named by replacing the –

ane with -yl

Some of these included in Table 11.5

Steps for naming alkanesSteps for naming alkanes1. Name the longest continuous chain of

carbons as the main chain2. Number the carbon atoms in the main

chain starting on the end nearest a substituent

-Where there are 2 or more substituents, the main chain should be numbered to give the lowest possible number set

Naming Alkanes Cont. Naming Alkanes Cont. 3. Give the location and name of each alkyl

group in front of the name of the main chain- use prefixes (di-, tri-) if a group appears more than once

4. List the substituents in alphabetical order

NamingNaming

• 1. Name Longest Chain First= hexane

• 2. Number Carbons from the end with the nearest substituent.

CH3-CH-CH2-CH-CH2-CH3

CH3 CH2CH3

1 2 3 4 5 6 CH3-CH-CH2-CH-CH2-CH3

CH3 CH2CH3

3. Give the location and name of each alkyl group in front of the name of the main chain2-methyl-4-ethylhexane

4. List substituents in alphabetical order. 4-ethyl-2-methylhexane

NamingNaming

• 1. Name Longest Chain First= heptane

• 2. Number Carbons from the end with the nearest substituent.

1 2 3 4 5 CH3-CH-CH2-CH2-CH-CH3

CH3 6 CH2CH3

7

CH3-CH-CH2-CH2-CH-CH3

CH3 CH2CH3

3. Give the location and name of each alkyl group in front of the name of the main chain2,5-dimethylheptane

4. List substituents in alphabetical order. Fine as is!

Try a Few!Try a Few!

• On board exercise!

Drawing Structural FormulasDrawing Structural Formulas

Step 1 – Draw the main chain of carbon atoms

Step 2 – Draw the substituents on the main chain in the positions indicated by the location numbers

Step 3 – Fill in the correct number of hydrogen atoms to give four bonds to each carbon atom

Draw 2,3-dimethylpentaneDraw 2,3-dimethylpentane

1. Draw Main Chain of Carbon atoms

C-C-C-C-CC-C-C-C-C

2. Draw the substituents on the main chain in the positions indicated by the location numbers

C-C-C-C-C

C C

3. Fill in the correct number of hydrogen atoms to give four bonds to each carbon atom

CH3-CH-CH-CH2-CH3

CH3 CH3

Try a few!Try a few!

• 2,3,5-trimethylhexane

• 3-ethylpentane

• 4-isopropyloctane

IsomersIsomers

• Molecules with the same molecular formula but different structural formula

• Example: C5H12

CH3-CH2-CH2-CH2-CH3

CH3-CH-CH2-CH3

CH3

Constitutional IsomersConstitutional Isomers

• Most organic compounds have structural isomers and their number increases as the number of atoms increases

Physical Properties of Constitutional Isomers

Different structural arrangement can result in very different physical properties

Drawing IsomersDrawing Isomers

• Step 1 – Draw the longest continuous chain

• Step 2 – Remove one carbon from the chain and attach it as a methyl group in as many locations as possible

• Step 3 – Remove another carbon atom from the main chain and attach as another alkyl group

Try SomeTry Some

• Draw isomers for C4H10

– Practice Naming!!

HaloalkanesHaloalkanes• An alkane in which halogen atoms replace

one or more hydrogens• Used as solvents and anesthetics• CFC’s (chlorofluorocarbons) were used a

propellants in aerosols– React with ozone in the upper atmosphere– Resulted in ozone depletionover the Antarctic

Naming HaloalkanesNaming Haloalkanes

• IUPAC names for halogen substituents are:

• Fluorine = fluoro-• Chlorine = chloro-• Bromine = bromo-• Iodine = iodo-

• The halo-substituents are numbered and arranged alphabetically, like we did before

Other substituents

• Use the same naming rules– Number position on the parent chain– Put in alphabetical order

CH3-CH-CH2-CH3

Cl

Naming Cycloalkanes

A cycloalkane with: One substituent is named by placing the

name of the substituent in front of the cycloalkane name.

Two or more substituents is named by numbering the ring in the direction that gives the lower numbers to the substituents.

Cycloalkanes with Side Groups

CH3

CH3

CH3

CH3

CH3

CH3

methylcyclopentane

1,2-dimethylcyclopentane

1,2,4-trimethylcyclohexane

Try Some!Try Some!

• On Board Exercise

Worksheet 1Worksheet 1• You can now complete worksheet 1.

Alkanes are typically not very reactive due to strong C-C single bonds.

The most typical reaction is combustion, where an alkane reacts with oxygen to produce carbon dioxide, water, and energy.

alkane + O2 CO2 + H2O + energy

Chemical Properties of Alkanes

Combustion

A fuel such as propane reacts with oxygen and burns, producing CO2 and H2O.

Propane is burned to obtain energy and heat for cooking or warming a room.

C3H8 + 5O2 3CO2 + 4H2O

Incomplete combustionIncomplete combustion

• It is dangerous to burn fuels in a closed room

• With limited amounts of oxygen, incomplete combustion occurs– This produced carbon monoxide, which is a toxic

gas

2CH4(g) + 3O2(g) 2CO(g) + 4H2O(g) + heat

Classifying Carbon AtomsClassifying Carbon Atoms

• Primary Carbons (1o)- Bonded to only one other carbon atom

• Secondary Carbons (2o)- Bonded to two other carbon atoms

• Tertiary Carbons (3o)- Bonded to three other carbons

Functional GroupsFunctional Groups• Millions of compounds possible• However, certain structures behave in

similar manners• These are called functional groups• For now: • Alkanes

– Saturated Hydrocarbons

• Alkenes, Alkynes, Aromatics– Unsaturated Hydrocarbons

Background: Double BondsBackground: Double Bonds

• Two nonmetal atoms can share more than one set of electrons

• Sharing four electrons = double bond

H H

C C

H H••• ••

•••• ••

•

Background: Triple BondsBackground: Triple Bonds

• Two nonmetals can also form triple bonds = sharing 6 electrons

Alkenes, Alkynes and AromaticsAlkenes, Alkynes and Aromatics• Alkanes contain only single bonds

• Alkenes contain one or more double bonds

• Alkynes contain one or more triple bonds

• Aromatic ring (benzene) is 6 carbons cyclized with alternating double bonds

Unsaturated hydrocarbons:

Have fewer hydrogen atoms attached to the carbon chain than alkanes.

Are alkenes with double bonds or alkynes with triple bonds.

Ch. 12-Unsaturated Hydrocarbons

AlkenesAlkenes• Contain at least one

double bonds• Important in

manufacturing and in human and plant functioning– Hormones– Ripening fruit– Ethene used to make

polymers

In the IUPAC system, the –ane ending of the corresponding alkane is changed to –ene for alkenes and to –yne for alkynes.

Naming Alkenes and Alkynes

When the carbon chain has 4 or more C atoms, the chain is numbered to give the lowest number to the double or triple bond.

1

CH2=CH—CH2—CH3 1-butene 2

CH3—CH=CH—CH2—CH3 2-pentene 3

CH3—CH2—CC—CH2—CH3 3 -hexyne

Naming Alkenes and Alkynes

More NamingMore Naming

• If you have more than 1 double or triple bond:– Name them as dienes or diynes

• CH2=CH—CH2—CH2=CH3 1, 4 - pentadiene

1 2 3 4 5

• CHC—CH2—CC—CH2—CH3 ????

More NamingMore Naming• If you have more than 1 double or triple bond:

– Name them as dienes or diynes

• CH2=CH—CH2—CH2=CH3 1, 4 - pentadiene

1 2 3 4 5

• CHC—CH2—CC—CH2—CH3

1, 4 - heptadiyne

Alkenes and Alkynes with Alkenes and Alkynes with SubstituentsSubstituents

• 1. Name the longest carbon chain that contains the double or triple bond

• 2. Number the chain starting at the end nearest the double or triple bond.

4-methyl-1-pentene

Try One!Try One!

Naming Cyclic Alkenes and Naming Cyclic Alkenes and AlkynesAlkynes

• Use –ene instead of -ane

• The double bond of a cycloalkene is understood to be between Carbon 1 and Carbon 2. Number from there to get the lowest possible number set.

Practice!Practice!

• On Board Exercise

Cis-Trans IsomersCis-Trans IsomersDouble Bonds do not rotate freely!Introducing a new type of isomer!

Cis-Trans IsomersCis-Trans Isomers Two isomers are possible

when groups are attached to the double bond.

In a cis isomer, groups are attached on the same side of the double bond. symmetrical

In the trans isomer, the groups are attached on opposite sides. unsymmetrical

Naming Cis-Trans Isomers

The prefixes cis or trans are placed in front of the alkene name when there are cis-trans isomers.

cis-1,2-dibromoethene trans-1,2-dibromoethene

C C

Br H

BrH

C C

Br Br

H H

Worksheet 2Worksheet 2• You can now complete worksheet 2.

Addition ReactionsAddition Reactions

Double and triple bonds are weaker than single bonds More reactive

In the addition reaction, reactants are added to the carbon atoms in the double or triple bond.

Addition ReactionsAddition Reactions

• H2C=CH2 + A—B H2C—CH2

A B

HydrogenationHydrogenation In hydrogenation, hydrogen atoms add to the

carbon atoms of a double bond or triple bond. A catalyst such as Pt or Ni is used to speed up

the reaction.

HC CH + 2H2Ni

HC CH

H H

H H

H2C CH2

H HPt

H2H2C CH2 +

Hydrogenation of OilsHydrogenation of Oils

When hydrogen adds to the double bonds in vegetable oils, the products are solids at room temperature.

HalogenationHalogenation

• In halogenation, halogen atoms add to the carbon atoms of a double bond or triple bond.

+ HC C CH3 2Cl2 C C

Cl Cl

Cl Cl

CH3H

H2C CH2

Br Br

Br2H2C CH2 +

Testing for Double and Triple Testing for Double and Triple BondsBonds

• When bromine (Br2) is added to an alkane, the red color of bromine persists.

• When bromine (Br2) is added to an alkene or alkyne, the red color of bromine disappears immediately.

HydrohalogenationHydrohalogenation

• In hydrohalogenation, the atoms of a hydrogen halide add to the carbon atoms of a double bond or triple bond.

CH3 CH CH CH3

H Cl

+ HClCH3 CH CH CH3

H

Br

+ HBr

Markovnikov’s RuleMarkovnikov’s Rule

• When an unsymmetrical alkene undergoes hydrohalogenation, the H in HX adds to the carbon in the double bond that has the greater number of H.

CH3 CH CH2

Cl H

CH3 CH CH2 + HCl

CH3 CH CH2

H Cl

Does not form

C with the most H

Product that forms

Hydration Adds WaterHydration Adds Water

• In hydration, H and OH from water add to the carbon atoms of a double bond or triple bond to form alcohols (OH).

• The reaction is catalyzed by acid H+.

+ HOHH

OH

CH3 CH CH2 + HOH

CH3 CH CH2

OH H

H+

H+

Worksheet 3Worksheet 3• You can now complete worksheet 3.

Aromatic CompoundsAromatic CompoundsBenzene is An aromatic compound.

A ring of 6 C atoms and 6 H atoms. Alternating single and double bonds Aromatic compounds often have fragrant

odors

Aromatic Compounds in Nature and Medicine

A benzene with a single substituent is often named as a benzene derivative.

Methylbenzene Chlorobenzene A benzene ring as a substituent is called a phenyl-

group

Naming Aromatic Compounds

ClCH3

Some substituted benzene rings have common names that have been in use for many years.

Also, know naphthalene (2 fused rings)

Some Common Names

CH3 NH2 OH

Toluene Aniline Phenol(Methylbenzene) (Benzenamine) (Hydroxybenzene)

A benzene ring with two or more substituents is numbered to give the lowest numbers to the side groups.

Common names use the prefixes ortho- (1,2-), meta- (1,3-) and para- (1,4-).

Naming Aromatic Compounds

Br

Br

Cl

Cl

CH3

Cl

1,2-dimethylbenzene 1,3-dichlorobenzene 4-chloromethylbenzene(o-dibromobenzene) (m-dichlorobenzene) (p-chlorotoluene)