Organic Nomenclature: Naming Organic Molecules …vancew/chem281/nomenclature.pdfOrganic...

Organic Nomenclature:Naming Organic Molecules

What’s in a name?

Reguline Caustic

Russian Pot Ash

K2CO3Potassium Carbonate

Pearl AshOil of Tartar Mild Vegetable Alkali

Mild Vegetable AlkaliAerated Alkali

Alkahest of Reapour

Alkahest of Van HelmotFixed Vegetable Alkali

Alkali of T

artar

Cendres Gravellees

Cineres Clavellati

Fixed Alkali Salt

German Ash

Sal Alkanus Vegetablis

Sal Gentianae

Sal Guaiaci ex Ligno

Sal Juniperi

Sal TartariSalt of Tachenius

Salt of Wormwood

Tartarin

Wood Ash Alkali of Wine Lees

Glauber's Alkahest

IUPAC Rules for naming organic molecules

3

International Union of Pure and Applied Chemists

Alkanes

4

Name Molecular Formula

Prefix

Methane CH4 Meth

Ethane C2H6 Eth

Propane C3H8 Prop

Butane C4H10 But

Pentane C5H12 Pent

Hexane C6H14 Hex

Heptane C7H16 Hept

Octane C8H18 Oct

Nonane C9H20 Non

Decane C10H22 Dec

CnH2n+2

Structure of linear alkanes

5

propane butane pentane hexane

heptane octane

nonane decane

Constitutional Isomers: molecules with same molecular formula but differ in the way in which the atoms are connected to each other

6

Physical properties of constiutional

isomers

7

Isomers

8

n # of isomers 1 1 2 1 3 1 4 2 5 3 6 5 7 9 8 18 9 35 10 75 15 4,347 25 36,797,588

The more carbons in a molecule, the more possible ways to put them together.

Naming more complex molecules

9

C6H14

hexane

Naming more complex molecules

10

Step 1: identify the longest continuous linear chain: this will be the root name: this is the root name

1

2

3

4

5

6 longest chain = 6 (hexane)

1 2 3

4

51

2 34

51

2 34

incorrectcorrectlongest chain = 5 (pentane) longest chain = 5 (pentane)

12

3

4

12 3

4

longest chain = 4 (butane) longest chain = 4 (butane)

Naming more complex molecules

11

Step 2: identify all functional group (the groups not part of the “main chain”)

1 2 3

4

51

2 34

5

main chain: pentane main chain: pentane

12

3

4

12 3

4

main chain: butane main chain: butane

CH3

CH3

CH3CH3 CH3

CH3

Alkyl groups: fragments of alkanes

12

methane methyl

CH4 CH3

empty space (point where it attaches to something else)H C

H

H

HC

H

H

H

More generally...

13

H C C C

H

H

H

H

H

H

H C C

H

H

H

H

CC

H

H

H H

H

C

H

C

H

H

H

ethyl propyl butylC2H5 C3H7 C4H9

CnH2n+1

Naming more complex molecules

14

1 2 3

4

51

2 34

5

main chain: pentanegroup: methyl (x1)

main chain: pentanegroup: methyl (x1)

12

3

4

12 3

4

main chain: butanegroup: methyl (x2)

main chain: butanegroup: methyl (x2)

CH3

CH3

CH3CH3 CH3

CH3

Naming more complex molecules

15

1 2 3

4

5

1

2 34

5

Step 3: position of the group denoted by number of carbon of main chain that it is attached to.

2-methylpentane

3-methylpentane

position of group

name of group

main chain

5 4 3

2

1

4-methylpentane

incorrect: start numbering from the end that gives groups the lowest number

Multiple groups

16

12

3

4

12 3

4

2,2-dimethylbutane 2,3-dimethylbutane

there are 2 methyl groups

group prefixdi=2tri=3

tetra=4penta=5hexa=6

Common Problems

17

1

23

45

67

1 2 3 45

6

4-ethylheptanenot

3-propylhexane

Be careful to choose the longest chain!

Numbering and priorities

18

Always start numbering to give the lowest number for the first substituent:

2,3-dimethylpentanenot 3,4-dimethylpentane

3,5,7-trimethyldecanenot 3,6,8-trimethyldecane

19

3/6

3-ethyl-6-methyloctanenot 3-methyl-6-ethyloctane

ignore “di-”, “tri-” etc. for

alphabetical ordering

5-ethyl-3-methyloctanenot 4-ethyl-6-methyloctanenot 3-methyl-5-ethyloctane

4-ethyl-2,8-dimethylnonanenot 2,8-dimethyl-4-ethylnonane

if same #s obtained in both directions, first

group listed gets lower number

groups listed in alphabetical

order

Groups within groups

20

What happens when the alkyl group isn’t a straight chain?

“isopropyl” (common name)

“t-butyl” or “tert-butyl” (common name)

“s-butyl” or “sec-butyl” (common name)

21

Treat branched side chains as groups with groups on them. Start numbering chain from point of attachment to main chain.

12

34

56

7

12

1-methylethyl group

4-(1-methylethyl)heptane

4-(1,1-dimethylethyl)heptane

5-(1-methylpropyl)nonane

Beyond alkanes

22

Alkyl halides: compounds containing F, Cl, Br, I

Br

1-bromobutaneCl

2-chloropentane

Fl

4-(1-fluoroethyl)heptaneI

I

1,1-diiodopropane

Alcohols

23

OH

1-propanolor

propan-1-ol

OH

ethanol

name of alkane--> replace “e” with “ol”

OH

2-propanolor

propan-2-ol

HOOH

1,4-dihydoxybutane