Organic Nomenclature: Naming Organic Molecules

Organic Nomenclature: Naming Organic Molecules

Aerated Alkali

What’s in a name?

Mild Vegeta

ble Alkali

Tartarin

Glauber's Alka

hest

t o lm e H n a V f o t s e Alkah

Fixed Vegetable Alkali R ussian Pot Ash

es e l l e v a r G s e Cendr lkali A e l b a t r e g e Mild V ta r a T f o K2CO3 li a k Al Sal Juniperi

Alkahest of Reapour

Potassium Carbonate Salt of Tachenius

Sal Ta Salt o

rtari

dA xe

Sal Gentia nae

Reguline Caustic sh A d Woo

Fi

Alkali of Wine Lees German Ash

Oil of Tartar Pearl Ash

alt

li S

lka

f Wor o n g mwo Li i t a l x l e e v od a i l c C s a e i r e a n i u C Sal Alkanus Vegetablis Sal G

IUPAC Rules for naming organic molecules

International Union of Pure and Applied Chemists

3

Name

Alkanes CnH2n+2

Prefix

Methane

Molecular Formula CH4

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

Meth

4

Structure of linear alkanes propane

butane

heptane

nonane

pentane

hexane

octane

decane 5

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

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

n 1 2 3 4 5 6 7 8 9 10 15 25

# of isomers 1 1 1 2 3 5 9 18 35 75 4,347 36,797,588 8

Naming more complex molecules hexane

C6H14

9

Naming more complex molecules Step 1: identify the longest continuous linear chain: this will be the root name: this is the root name 2 1

1

4

6

3

2

longest chain = 6 (hexane)

5 2

4 3

5

2

4

1

longest chain = 5 (pentane)

1

3

3

5

correct longest chain = 5 (pentane)

1 4

longest chain = 4 (butane)

2

2

3

1

3 4 incorrect

4

longest chain = 4 (butane) 10

Naming more complex molecules Step 2: identify all functional group (the groups not part of the “main chain”) CH3 2

1

2

4 3

5

main chain: pentane

4

3

1

5

CH3 main chain: pentane

CH3 1

2

3

1 4

CH3

CH3

main chain: butane

2

3

4

CH3 main chain: butane 11

Alkyl groups: fragments of alkanes H H

C

H

H

H

C

H

H

methane

methyl

CH4

CH3

empty space (point where it attaches to something else)

12

More generally...

H

H

H

C

C

H

H

ethyl C2H5

H

H

H

H

C

C

C

H

H

H

propyl C3H7

CnH2n+1

H

H

H

H

H

C

C

C

C

H

H

H

H

butyl C4H9

13

Naming more complex molecules CH3 2

1

2

4 3

5

main chain: pentane group: methyl (x1)

4

3

1

5

CH3 main chain: pentane group: methyl (x1)

CH3 1

2

3

1 4

CH3

CH3

main chain: butane group: methyl (x2)

2

3

4

CH3 main chain: butane group: methyl (x2) 14

Naming more complex molecules Step 3: position of the group denoted by number of carbon of main chain that it is attached to. 4

2

1

3

5

2-methylpentane position of group

name of group

2 1

3

main chain

5

4

2 3

1

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

4 5

3-methylpentane 15

Multiple groups 1

2

3

1 4

2,2-dimethylbutane

2

3

4

2,3-dimethylbutane

there are 2 methyl groups group prefix di=2 tri=3 tetra=4 penta=5 hexa=6 16

Common Problems Be careful to choose the longest chain! 1 2 1

3

3 2 4 4 5

5 6

6

4-ethylheptane not 3-propylhexane

7

17

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

2,3-dimethylpentane not 3,4-dimethylpentane

3,5,7-trimethyldecane not 3,6,8-trimethyldecane

18

5-ethyl-3-methyloctane not 4-ethyl-6-methyloctane not 3-methyl-5-ethyloctane

3/6

groups listed in alphabetical order

4-ethyl-2,8-dimethylnonane not 2,8-dimethyl-4-ethylnonane

ignore “di-”, “tri-” etc. for alphabetical ordering

3-ethyl-6-methyloctane not 3-methyl-6-ethyloctane

if same #s obtained in both directions, first group listed gets lower number 19

Groups within groups 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) 20

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

2

1-methylethyl group

1

4-(1-methylethyl)heptane

1

2

3

4

5

6

7

4-(1,1-dimethylethyl)heptane

5-(1-methylpropyl)nonane 21

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

Br

1-bromobutane

I

I

1,1-diiodopropane

Cl

2-chloropentane

Fl

4-(1-fluoroethyl)heptane 22

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

OH

ethanol

OH

1-propanol or propan-1-ol

2-propanol or propan-2-ol

OH HO

1,4-dihydoxybutane 23