IUPAC Nomenclature

Organic Compounds

(Part 1)

of

I. Introduction

Carbon is special because a single carbon atom is capable of combining with up to four other atoms (valence of four = maximum of four bonds).

Carbon can combine with many other carbon atoms making large molecules. This means that carbon atoms can form chains and rings onto which other atoms can be attached.

In Chemistry, an organic compound is one containing carbon atoms.

I. Chains of Carbon AtomsThe simplest Organic compounds are made up of only carbon and hydrogen atoms only and are called hydrocarbons.

Names of simple chains of hydrocarbons are given names based on the number of carbon atoms in the molecule. Prefixes are used to denote the number carbon atoms.

Alkane hydrocarbons consist of carbon and hydrogen atoms linked together with single bonds.

C methane

C-C ethane

C-C-C propane

C-C-C-C butane

C-C-C-C-C pentane

C-C-C-C-C-C hexane

C-C-C-C-C-C-C heptane

I. Alkane Hydrocarbons

C-C-C-C-C-C-C-C octane

C-C-C-C-C-C-C-C-C nonane

C-C-C-C-C-C-C-C-C-C decane

C-C-C-C-C-C-C-C-C-C-C undecane

C-C-C-C-C-C-C-C-C-C-C-C dodecane

I. Alkyl Groups Attached to Chain

methyl

ethyl

propyl

butyl

CH3

CH2CH2 CH3

CH2 CH3

CH2CH2 CH3CH2

II. Structural IsomersTwo or more compounds are structural isomers if they have the same formula but different connected structures. Structural isomers will have different IUPAC names (covered later).

The alkane, C4H10 , has two structural isomers.

Question #1:

Try to build two different molecules with 4 carbons and 10 hydrogens (using only single bonds), then draw it.

Hint: Use branching alkyl groups!!!!!!!!

C4H10

C4H10 has the following two structural isomers:

CCH3 CH3

CH3

CH2CH3 CH2 CH3

H

Note: Both molecules look different but have the same number of carbon and hydrogen atoms.

The following two molecules are exactly the same:

CCH3 CH3

CH3

H

CCH3 CH3

H

CH3

They are not different isomers! Build both molecules and try rotating one to match the other one.

Question #2:

Try to build three different molecules with 5 carbons and 12 hydrogens (using only single bonds), then draw it.

Hint: Use branching alkyl groups!!!!!!!!

The alkane, C5H12 , has three structural isomers.

C5H12

C5H12 has the following three structural isomers:

CCH3 CH2

CH3

CH2CH3 CH2 CH2

H

Note: All molecules look different but have the same number of carbon and hydrogen atoms.

CH3

CH3

CCH3 CH3

CH3

CH3

CCH3 CH2

CH3

CH2CH3 CH2 CH2

H

All of these compounds have the formula, C5H12. We can only distinguish them by giving them different names.

CH3

CH3

CCH3 CH3

CH3

CH3

III. Naming & Drawing Alkanes

Parent Name = longest continuous chain of carbon atoms

Name of branching group or substitute

(if any)

Parent name+

General Formula: CnH2n+2

Use Greek prefixes to indicate the presence of multiple identical branching groups.

C C C C

C

C

C

What is the parent name?

C C C C

C

C

C

What is the parent name?

Hexane

(Longest chain is 6 carbons)

C C C C

C

C

C

What is the parent name?

Hexane

(Longest chain is 6 carbons)

C C C C

C

C

C

What is the parent name?

Hexane

(Longest chain is 6 carbons)

What is the branching group? Methyl -CH3

C C C C

C

C

C

What is the position of the methyl group?

Must number carbon atoms so that the methyl group is attached to the carbon with the lowest number.

C C C C

C

C

C

What is the position of the methyl group?

Must number carbon atoms so that the methyl group is attached to the carbon with the lowest number.

1234

5

6 1

2

3

4 5 6

C C C C

C

C

C

What is the name of the compound?

3-methylhexane

1234

5

6 1

2

3

4 5 6

Indicates position of alkyl group (substituent)

C C C C

C

C

What if there are 2 or more of the same substituent?

Use Greek prefixes to tell how many. E.g di, tri, tetra

C

C 1

2

34 5 6

3,3-dimethylhexane

Must use 3 twice because there are 2 methyl groups

C C C CC

C

C C

C

What is the longest chain?

What are the substituents?

C C C CC

C

C C

C

What is the longest chain?

Hexane

What are the substituents?

Methyl -CH3 and Ethyl -CH2 -CH3

C C C CC

C

C C

C

What is the longest chain?

Hexane

What are the substituents?

Methyl -CH3 and Ethyl -CH2 -CH3

C C C CC

C

C C

C

Which substituent is named first?

Answer: alpha order or by increasing size

If by alpha order: Ethyl -CH2 -CH3 first

If by size: Methyl -CH3 first (smaller than ethyl)

C C C CC

C

C C

C

If by alpha order:

3-ethyl-3-methylhexane

If by size:

3-methyl-3-ethylhexane

3

12

456

Practice Questions

C C CC

Question 1: What is the correct IUPAC name?

C C CC

Question 1: What is the correct IUPAC name?

Answer: butane

CH2CH3

Question 2: What is the correct IUPAC name?

CH3

CH2CH3

Question 2: What is the correct IUPAC name?

Answer: propane

CH3

C C C

C

C

Question 3: What is the correct IUPAC name?

C

C C C

C

C

Question 3: What is the correct IUPAC name?

C

Answer: 2, 2-dimethylbutane

CCH3

Question 4: What is the correct IUPAC name?

CH2

CH3

CH2CH3

CH CH2 CH3

CH2 CH2 CH3

CCH3

Question 4: What is the correct IUPAC name?

CH2

CH3

CH2CH3

CH CH2 CH3

CH2 CH2 CH3

Answer: 3,3–dimethyl-5-ethyloctane

3 5

Question 5: Draw the correct structural formula?

2-methylbutane

CHCH3

Question 5: Draw the correct structural formula?

CH2

CH3

CH3

Answer:

2

2-methylbutane

or

CH2CH3 CH CH3

CH3

2

IV. Naming & Drawing Cyclic Alkanes

Parent Name = longest continuous chain of carbon atoms

Cyclo = parent chain forms a ring

Name of branching group

or substitute

(if any)

Parent name+

General Formula: CnH2n+2

+Use

Prefix

“cyclo”

H2C CH2

CH2

What is the parent name?

H2C CH2

CH2

What is the parent name?Propane(Longest chain is 3 carbons) Is the parent chain in a ring?

H2C CH2

CH2

What is the parent name?Propane(Longest chain is 3 carbons) Is the parent chain in a ring? Yes

Correct name is:

H2C CH2

CH2

What is the parent name?Propane(Longest chain is 3 carbons) Is the parent chain in a ring? Yes

Correct name is: cyclopropane

H2C CH

CH2

CH3

Parent name is cyclopropane.What is the branching group? Methyl –CH3

Correct name is: methylcyclopropaneNote: The number (1) is not needed to identify the place of the substituent if only one is present in the molecule.

H2C CH

H2C

CH3

CH CH3

Parent name is cyclobutane.What is the branching group? Methyl –CH3

Correct name is: 1, 2-dimethylcyclobutaneNote: The first named substituent is arbitrarily given the number one (1) position

1

23

4

There are several ways to draw structural formulae of cyclic compounds:

H2C CH2

H2C CH2

C C

C C

Each corner represents a carbon atom

Assignment #1: Multimedia Organic Chemistry Program

Quiz – Introduction to OrganicAlkanes

Cycloalkanes