December 01, 2015
Naming Organic Molecules
Organic chemistry has its own naming system that is very different from inorganic chemistry (which is the naming system that you are familiar with). Because carbon can form so many structures, the name has to indicate not only how many of each atom in the compound, but also how the atoms are connected together.
A few things to keep in mind:
• every carbon atom must have exactly four bonds, and every hydrogen can only have one bond, oxygen atoms have two bonds
• the backbone of an organic molecule is carbon atoms joined together, and the naming system is based on the longest continuous chain of carbon atoms
• carbon atoms in the longest continuous chain are numbered, which is like an address for a molecule
December 01, 2015
There are three parts to the name of an organic molecule
Prefix
Root
-indicates the
-gives the name
longest continous
and position of any carbon chain in the
branches or side
molecule
groups
Prefix
-gives the name
and position of any
branches or side
groups
Methyl
Ethyl
Propyl
Suffix
-indicates the
organic family that
the molecule
belongs to
December 01, 2015
Root
-indicates the
longest continous
carbon chain in the
molecule
Carbon Atoms
1
2
3
4
5
6
7
8
9
10
Root Name
meth
eth
prop
but
pent
hex
hept
oct
non
dec
What are the root names and branches in the following molecules?
December 01, 2015
Functional Group
General Formula
Suffix
alkane
Rules for Naming
See below
Physical Properties
non-­‐polar (London forces only)
-­‐not soluble in water
-­‐soluble in non-­‐polar solvents such as hexane or benzene
-­‐boiling point increases as carbon chain length increases
December 01, 2015
Alkanes
-­‐a family of organic compounds where all of the carbon atoms are connected by single bonds
1. Determine the suffix – for alkanes the suffix is -­‐ane
2. Find the longest continuous chain of carbon atoms. This longest chain may not be written in a straight line.
3. Name that longest chain with the appropriate root.
4. Find the substituents, or branches, and name each of them with the appropriate group name.
5. Number the carbons in the chain such that the lowest number is given to the group nearest one end of the chain. Numbering can be from the left or right.
6. List the groups alphabetically in front of the longest chain name.
7. Precede each group name with a prefix indicating how many of them are present in the molecule. In front of the prefix, list the carbon number that each group is attached to in the molecule and separate the numbers with a hyphen. (there is no prefix if there is only one branch)
December 01, 2015
December 01, 2015
December 01, 2015
Draw 3-­‐ethyl-­‐4-­‐methylheptane
Why is 2-­‐ethylpentane not a correct name? December 01, 2015
Assignment: Page 549 1-­‐3, Page 550 4-­‐7 (answers are in the back of the textbook)