Mr. E’s Organic Chemistry

Some organic chemicals

DNA

Essential oils

Medicines•Active Pharmaceutical Ingredients•Excipients

Materials

Fuels

Pigments

•Organic molecules = Carbon-based molecules•Organic chemistry = Chemistry of carbon-based molecules

Some properties of organic molecules

•Stability: composed of stable C-C covalent bonds

•Defined molecular structures

•Defined three-dimensional shapes

Carbon:• e.x. Methane • Four single covalent bonds:• Shape = tetrahedral.

CH

H HH

2 electrons = 1 bond

Alkanes: Saturated Hydrocarbons• Hydrocarbons are molecules composed of carbon & hydrogen

– Each carbon atom forms 4 chemical bonds– A saturated hydrocarbon is one where all C - C bonds are “single”

bonds & the molecule contains the maximum number of H-atoms– Saturated hydrocarbons are called ALKANES

‘Meth…’ = 1 Carbon

‘Eth…’ = 2 Carbons

‘Prop…’ = 3 Carbons

‘But…’ = 4 Carbons

‘Pent…’ = 5 Carbons

‘Hex…’ = 6 Carbons

‘Hept…’ = 7 Carbons

‘Oct…’ = 8 Carbons

‘Non…’ = 9 Carbons

‘Dodec…’ = 12 Carbons

‘Undec…’ = 11 Carbons

‘Dec…’ = 10 Carbons

Heptane CH3CH2CH2CH2CH2CH2CH3

‘Hept…’ implies 7 Carbons ‘…ane’ implies compound is an alkane

n

1

2

3

4

5

6

MolecularFormula

CH4

C2H6

C3H8

C4H10

C5H12

C6H14

Structuralformula

HCH

CCH

HH

H

HH

HCH

CH

HH

CH

HH

HCH

CCH

HC

H

HH

HCH

CCH

HC

H

HH

HCH

CCH

HC

H

HH

H

H

H

HH

H

HCH

HH

H

HCH

HCH

HH

Name

methane

ethane

propane

butane

pentane

hexane

Condensedstructural

formulaCH4

CH3CH3

CH3CH2CH3

CH3CH2CH2CH3

CH3CH2CH2CH2CH3

CH3CH2CH2CH2CH2CH3

Further members of the series

Heptane (7) CH3CH2CH2CH2CH2CH2CH3

Octane (8) CH3CH2CH2CH2CH2CH2CH2CH3

Nonane (9) CH3CH2CH2CH2CH2CH2CH2CH2CH3

Decane (10) CH3CH2CH2CH2CH2CH2CH2CH2CH2CH3

Undecane (11) CH3CH2CH2CH2CH2CH2CH2CH2CH2CH2CH3

Dodecane (12) CH3CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH3

Etc., etc.

Normal vs Branched Alkanes• NORMAL alkanes consist of

continuous chains of carbon atoms

• Alkanes that are NOT continuous chains of carbon atoms contain branches

• The longest continuous chain of carbons is called the parent chain

CH3

CH2CH2

CH2CH3

CH3

CH2CH

CH3

CH3

Structural Isomerism• Structural isomers are

molecules with the same chemical formulas but different molecular structures - different “connectivity”.

• They arise because of the many ways to create branched hydrocarbons.

CH3

CH2CH2

CH2CH3

CH3

CH2CH

CH3

CH3

n-pentane, C5H12

2-methlbutane, C5H12

IUPAC Rules for Naming Branched Alkanes– Find and name the parent chain in the hydrocarbon - this is

the chain with containing the most # of C atoms.– Number the carbon atoms in the parent chain starting at the

end closest to the branching– Name alkane branches by dropping the “ane” from the

names and adding “yl”. A one-carbon branch is called “methyl”, a two-carbon branch is “ethyl”, etc…

– Name Halogen branches by dropping the “ine” and adding a ”o”. Bromine Bromo

– When there are more than one type of branch (ethyl and methyl, for example), they are named alphabetically

– Finally, use prefixes to indicate multiple branches

A Little Practice

Alkane Alkyl group

Methane Methyl (CH3-)

Ethane Ethyl (CH3CH2-)

Propane Propyl (CH3CH2CH2-)

Butane Butyl (CH3CH2CH2CH2-)

Etc.

CH3 CH2 CHCH3

CH31234

2-Methylbutane

[Straight chain numbered so as to give the lower branch number]

Example 1: 2,2-dimethylpentane• The parent chain is indicated by

the ROOT of the name -“pentane”. This means there are 5 carbons in the parent chain.

CH3

CH2CH2

CH2CH3

• “dimethyl” tells us that there are TWO methyl branches on the parent chain. A methyl branch is made of a single carbon atom.

• “2,2-” tell us that BOTH methyl branches are on the second carbon atom in the parent chain.

CH31

CCH23

CH2

4

CH35

CH3

CH3

1

2

34

5

Example 2: 3-ethyl-2,4-dimethylheptane• The parent chain is indicated by

the ROOT of the name -“heptane”. This means there are 7 carbons in the parent chain.

CH3

CH2CH2

CH2CH2

CH2CH3

• “2,4-dimethyl” tells us there are TWO methyl branches on the parent chain, at carbons #2 and #4.

• “3-ethyl-” tell us there is an ethyl branch (2-carbon branch) on carbon #3 of the parent chain.

1

2

34

5

76

CH3

CHCH

CHCH2

CH2CH3

CH2CH3

CH3 CH3

Example 3: 2,3,3-trimethyl-4-propyloctane• The parent chain is indicated by

the ROOT of the name -“octane”. This means there are 8 carbons in the parent chain.

• “2,3,3-trimethyl” tells us there are THREE methyl branches - one on carbon #2 and two on carbon #3.

• “4-propyl-” tell us there is a propyl branch (3-carbon branch) on carbon #4 of the parent chain.

1

2

34

5

7

6

8

1

23

45

7

6

8

CHC

CHCH2

CH2

CH2CH3

CH3

CH3

CH3

CH3CH2

CH2

CH3

Example 4: Name the molecules shown!• parent chain has 5 carbons -

“pentane”• two methyl branches - start

counting from the right - #2 and #3• 2,3-dimethylpentane

CH3

CH2CH

CHCH3

CH3

CH3

• parent chain has 8 carbons - “octane”• two methyl branches - start counting

from the left - #3 and #4• one ethyl branch - #5• name branches alphabetically

3,4-dimethyl

43

octane

5

5-ethyl-

Alkanes Review - Cycloalkanes• A cycloalkane is made of a hydrocarbon chain

that has been joined to make a “ring”.

CH3

CH2CH3 CH2

CH2

CH2

n-propaneC3H8

cyclopropaneC3H6

60° bond angleunstable!!

109.5° bond angle

•Note that two hydrogen atoms were lost in forming the ring!•What is the general formula for a cycloalkane?

Other CycloalkanescyclobutaneC4H8 - ~90° bond angles

cylcopentaneC5H10 ~109.5° bond angles

cyclohexaneC6H12 = 109.5° bond angles

Angle (ring) Strain - results from compression of the internal bond angles. Cyclopropane has the greatest angle strain (60° bond angles) while the strain is eliminated in cyclohexane.

Alkenes & Alkynes• Alkenes are

hydrocarbons that contain at least one carbon-carbon double bond

• Alkynes are hydrocarbons that contain at least one carbon-carbon triple bond

• The suffix for the parent chains are changed from “ane” to “ene” for double bonds and “yne” for triple bonds.– e.g. ethene, propyne

• We start numbering the carbons closest to the multiple bond.

Alkenes & Alkynes: Examples

CH2 CH2 CHCH CH2 C

H

CH3

C16

CH

CH3 CH2 CH

CH2

CH3 C C CH2CH3

CH3

ethene ethyne propene

propyne 1-butene 2-pentyne

Hydrocarbons

1

2

3

4

5

6

7

8

9

10

Number ofCarbon Atoms

AlkanesCnH2n + 2

AlkynesCnH2n-2

AlkenesCnH2n

_______

Ethyne

Propyne

Butyne

Pentyne

Hexyne

Heptyne

Octyne

Nonyne

Decyne

____

C2H2

C3H4

C4H6

C5H8

C6H10

C7H12

C8H14

C9H16

C10H18

Methane

Ethane

Propane

Butane

Pentane

Hexane

Heptane

Octane

Nonane

Decane

CH4

C2H6

C3H8

C4H10

C5H12

C6H14

C7H16

C8H18

C9H20

C10H22

_______

Ethene

Propene

Butene

Pentene

Hexene

Heptene

Octene

Nonene

Decene

____

C2H4

C3H6

C4H8

C5H10

C6H12

C7H14

C8H16

C9H18

C10H20

Name those alkenes...CH

CH

CH3 CH CH3

CH3

CH

CH

CH2

CH2

CH2

Br

4-methyl-2-pentene 2-methyl-2-hexene

cyclopentene3-heptene

2-bromo-3-methyl-2-pentene

Cis-Trans Isomerism…Again!• Like rings, alkenes and alkynes show

restricted rotation - this time about the multiple bonds

• Because of the 120° bond angles in alkenes, cis-trans isomerism is possible– If one of the carbons in the double bond

have two of the same substituents, there is NO cis-trans isomerism!

– Remember that “trans” means opposite sides of the double bond and “cis” means the same side of the bond!

– Use molar mass to prioritize the substituents to decide cis-trans isomerism