organic chemistry - · pdf filenaming hydrocarbons . root suffix number of carbons in the...

ORGANIC CHEMISTRY

-Organic molecules contain only C, H, O, N and sometimes S and P

-56 204 570 organic substances have been recorded

What allows for the diversity of organic compounds?

-Carbon can make 4 bonds

-The 4 bonds can be a combination of single, double, and triple bonds

methane, CH4 methanal, CH2O

ethanenitrile, CH3CN

Naming Hydrocarbons

root suffix

Number of carbons in the longest chain

Functional group

meth ane Ex:

butan ol Ex:

What’s in a Name

Assembled from components that describe various

features of the molecule.

Root Name = Longest Chain

• The longest continuous chain of carbons containing

the principal functional group defines the root name.

• Other groups attached to this chain are called

substituents.

meth- = 1 carbon

eth- = 2

prop- = 3

but- = 4

pent- = 5

hex- = 6

hept- = 7

oct- = 8

non- = 9

dec- = 10

undec- = 11

dodec- = 12

Longest Carbon Chain Name

Just FYI…

13 trideca- 30 triaconta- 500 pentacta- 7000 heptalia-

14 tetradeca- 40 tetraconta- 600 hexacta 8000 octalia-

15 pentadeca 50 pentaconta- 700 heptacta- 9000 nonalia-

16 hexadeca- 60 hexaconta- 800 octacta-

17 heptadeca 70 heptaconta- 900 nonacta-

18 octadeca- 80 octaconta- 1000 kilia-

19 nonadeca- 90 nonaconta- 2000 dilia-

20 icosa- 100 hecta- 3000 trilia-

21 heneicosa 200 dicta- 4000 tetralia-

22 docosa 300 tricta- 5000 pentalia-

23 tricosa 400 tetracta- 6000 hexalia-

Principal Functional Group =

Suffix • The principal functional group is used to define the

class the compound belongs to e.g. an alkene, alcohol,

etc.

• Refer to ‘Families of Organic Compounds’ handout

• Determines the suffix of molecule’s name

Basic Naming Rules

The IUPAC systematic name of an organic compound can

be constructed based on a series of steps and rules:

1. Identification of the principal functional group and

substituents

2. Identification of the longest continuous chain

containing the principal functional group.

3. Assign locants (i.e. numbers) to the principal

functional group and substituents.

HYDROCARBONS

First Set of Functional Groups:

Hydrocarbons:

When an organic molecule is composed only of hydrogen and carbon, it is called a hydrocarbon:

_________: Hydrocarbons with single bonds

_________: Hydrocarbons with double bond(s)

_______: Hydrocarbons with triple bond(s)

//upload.wikimedia.org/wikipedia/commons/8/8d/Ethene-2D-flat.png

-Characterized by C-C single bonds

-Also known as _________________

-empirical formula = ________

CnH2n+2, n=8

= ______

Properties:

-Hydrophobic (does not mix with water and other polar substances)

-Generally low boiling points (due to weak London Dispersion Forces) - Longer alkane molecules have higher boiling points

Some IUPAC* names of alkanes:

*International Union of Pure and Applied Chemistry

ethane propane butane

All alkanes have the suffix “____”

ALKANES IUPAC naming system:

Molecular

formula Condensed Structural Formula Name

CH4 CH4 methane

C2H6 CH3CH3 ethane

C3H8 CH3CH2CH3 propane

C4H10 CH3CH2CH2CH3 butane

C5H12 CH3CH2CH2CH2CH3 pentane

C6H14 CH3CH2CH2CH2CH2CH3 hexane

C7H16 CH3CH2CH2CH2CH2CH2CH3 heptane

C8H18 CH3CH2CH2CH2CH2CH2CH2CH3 octane

C9H20 CH3CH2CH2CH2CH2CH2CH2CH2CH3 nonane

C10H22 CH3CH2CH2CH2CH2CH2CH2CH2CH2CH3 decane

ALKANES IUPAC naming system:

Name the following alkanes:

1 2 3 4 5 6 1 2 3 4 5 6 7 8 9

Not all alkanes are straight chains. Some alkanes have alkyl side groups (alkyl substituents) attached.

-CH3 methyl

-C2H5 ethyl

-C3H7 propyl

-C4H9 butyl

-C5H11 pentyl

-C6H13 hexyl

-C7H15 heptyl

-C8H17 octyl

Ex:

methyl group

name:

Substituents: Branches in

Chains

IUPAC naming system:

Substituent(s) prefix suffix

Number of carbons in the longest chain

Branches family

For alkanes with side groups…

but ane Ex: 2-methyl

Assigning Locants (i.e.

numbering) • The numbers that define the positions of the principal

functional group and substituents are called locants.

• Compounds are numbered from one end of the longest

continuous chain.

• The locants are assigned such that the principal

functional group gets the lowest possible locant


Name the following branched alkanes

2-methylpentane 3-methylpentane

When there is ambiguity, the substituent must be numbered according to the carbon atom that it is attached to

(aim to get the lowest possible number)

1 2 3 4 5 1 2 3 4 5

First Point of Difference:

Which name is incorrect?

2-methylpentane 4-methylpentane

Aim for the lowest possible number when counting.

1 2 3 4 5 5 4 3 2 1

For alkanes with multiple branches of the same kind attached to the main chain….

hept ane Ex: 4,6-dimethyl

• give each branch a number.

• list the numbers in ascending order.

• give the branch name a multiplying prefix (i.e. di, tri, tetra, etc.) to indicate the number of identical branches.

• put commas between numbers, and hyphens between numbers and letters. No space!


1. Find the longest continuous chain of C atoms (parent chain)

CH3 - CH - CH3

|

CH3 - CH - CH2

|

CH3

Name the following branched alkane

2. Identify any

substitutents


For alkanes with multiple, but different kinds of branched groups…

hept ane Ex: 4-ethyl-6-methyl

• name the branched groups in alphabetical order.

• give the branch name a number to indicate which carbon in the main chain it is bonded with.

• put commas between numbers, and hyphens between numbers and letters.

CH3

|

CH2 - CH2

|

CH2 - CH - CH2 - CH3

|

CH - CH3

|

CH3

Numbering (con’t)

• If numbering a functional group results in a "tie" then the

first point of difference rule. The first time a difference

in numbering occurs, then the method that gives the

lower number at this first difference is used.

• In the event that there is no first point of difference then

alphabetisation is used.


Name the following branched alkane

The order of substituents in the name is based on alphabetical order

Drawing alkanes:

3 types of diagrams—all showing the same molecule

Structural diagram

CH3CH2CH2CH2CH2CH3 Condensed diagram

Line diagram

Drawing alkanes:

Line diagrams:

Every end or point on a line diagram represents a carbon atom. Hydrogen atoms are not shown.

1

2

3

4

5

6

Drawing alkanes:

Draw the following alkanes using line diagrams

2-methylbutane 3-ethyl-3,4-dimethylheptane

Nomenclature of Alkanes

Write the structure of 3-ethyl-2-methylpentane.

No First Point of Difference

• In the event that there is no first point of difference then

alphabetisation is used to determine numbering.

• Name this alkane:

1 2

3

4 5 6 7

8

1

2 3 4 5

6 7

8

• Two branches occur at C-3 and C-6, regardless of how the parent

chain is numbered

3-ethyl-6-methyloctane

NOT

6-ethyl-3-methyloctane

1 2

3

4 5 6 7

8

1

2 3 4 5

6 7

8

This time, there is a first point of difference at C-4

6-ethyl-3,4-dimethyloctane

Condensed Diagrams

• Bonds are (usually) not drawn. Only atoms

are drawn

• Entire molecule is written in one line (even

branches)

• Repeated fragments are simplified with

brackets

• Branches are also indicated with brackets.

CH3CH2CH2CH2CH2CH3

Structural diagram Condensed diagram

CH3(CH2)4CH3

Condensed diagram

CH3

|

CH2 - CH2

|

CH2 - CH - CH2 - CH3

|

CH - CH3

|

CH3

6

6

CH3CH(CH3)CH(CH2CH3)CH2CH2CH2CH3 1 2 3 4 5 7

CH3CH(CH3)CH(CH2CH3)(CH2)3CH3

BE CAREFUL! A bracket to

indicate a branch can be easily

confused with a repeated

fragment. Typically brackets

such as (CH3) indicate a

branch, while brackets such as

(CH2) indicate a repeated

fragment that’s part of a main

chain

OH

O

O

Br

It is common practice to

draw the multiple bond in

the condensed formula, but

the bond can be omitted

when its placement will be

obvious

CYCLOALKANES

-Ring-like structures of alkanes

-empirical formula = CnH2n

CnH2n, n=6

= C6H12



cyclobutane cyclooctane cyclopentane

The prefix “cyclo” is added to the alkane name



propylcyclobutane

CH CH2

CH2 CH2

CH3CH2CH2

Numbering the lcoation is not required, since the number is implied

If two different substituents are present on the ring, they are listed in

alphabetical order, and the first cited substituent is assigned to carbon #1.

If there are several substituents, the numbering of ring carbons then continues

in a direction (clockwise or counter-clockwise) that affords the second

substituent the lower possible location number

1

3

3

1

1

3

3

1

1

2 3

4

5 6

The disubstituted carbon becomes #1 because the total locator

numbers are thereby kept to a minimum. The methyl substituent is

then located on carbon #2 (clockwise numbering), and the ethyl

group is located on #4


Draw the following alkanes using line structures:

1,1-dipropylcyclopropane 1-ethyl-1,2,5-trimethylcyclopentane

HALOALKANES

-Alkanes with halogen atoms

-Also known as alkyl halides


Halogen groups:

Just like alkyl substituents, the halogens are placed at the beginning of the name, and are ordered alphabetically.

-F fluoro

-Cl chloro

-Br bromo

-I iodo


Name the following haloalkanes:

STRUCTURAL ISOMERS

Compounds with the same molecular formula but with different bonding arrangements are structural isomers.

Butane isomers Pentane isomers

Ex: Structural isomers of hexane + boiling points

Changing the structure affects the boiling point

This structure can easily stack and form more London Dispersion Forces with neighbouring hexane molecules

Draw all of the structural isomers of heptane using line structures:

Number of Carbon Atoms

4 5 6 7 8 9

10 12 15

Number of Isomers

2 3 5 9 18 35 75 355 4347

The longer the chain, the greater the number of structural isomers

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