1.1 Alkanes

A hydrocarbon is formed from carbon and hydrogen.

Alkanes are hydrocarbons that are joined by single covalent bonds only. They are the
simplest of hydrocarbons

Since each carbon is bonded to the maximum possible number of atoms, these carbons are
often referred to as saturated hydrocarbons (saturated with hydrogen)

The chemical formula for the number of hydrogens in an alkane is given by CnH2n+2, where n
is the number of carbon atoms
Structural Diagrams
Complete structural diagram – shows all the atoms in a
structure and the way they are bonded to one another.
Condensed structural diagram – shows the bonds between the
carbon atoms but not those between the carbon and hydrogen atoms
Line structural diagram - shows only lines representing bonds
between carbon atoms (it gives us a better sense of 3-D shapes of the
molecules).
Rules for Naming Alkanes:
1. Find the longest carbon chain, called the main chain
2. Number the carbons such that the branches are on the lowest position #
3. If the there is more than one of the same branch, use a prefix to indicate this (di, tri,
tetra, etc)
4. Write branches in alphabetical order, ignoring any prefixes, including a number to
indicate position
5. separates #’s and letters with a hyphen, separates #’s with a comma
Alkanes:
Name
# of carbon
atoms
Name
# of carbon
atoms
methane
1
hexane
6
ethane
2
heptane
7
propane
3
octane
8
butane
4
nonane
9
pentane
5
decane
10
Alkyl Branches:
Ex)
Name the following compounds:
CH3 – CH2 – CH2 – CH3
Ex) Draw the condensed structural diagram for 3-ethyl-2,2-dimethylhexane
Ex) Draw the line diagram for 6-ethyl-2,5-dimethyl-4-propylnonane
Structural Isomers
•
•
compounds that have the same molecular formula but different structures
different shape and bonding therefore different properties
Eg.
C6H14 can be:
Cycloalkanes
•
•
•
Not all alkanes are based on straight chains. Their carbon atoms can form rings. A cyclic
alkane is a closed loop.
When naming these molecules, the cyclic structure is always the main chain
Number the carbons, in either direction, so that the branches have the lowest possible
position number
Ex) Name the following:
Ex) Draw 2-ethyl-1,4-dimethylcyclohexane
Alkyl Halides
•
•
•
one or more hydrogen atoms have been substituted with halogen atoms (F, Cl, Br, I)
use prefix fluoro-, chloro-, bromo- or iodo- with a position #
name in alphabetical order
Self Check
How prepared am I to start my homework? Can I …
… draw structural isomers for a hydrocarbon
… name branched and cyclic alkanes
… draw branches and cyclic alkanes
0
0
0
1
1
1
2
2
2
3
3
3