Chemistry 11 Lab #20
Modeling Organic Molecules
Theory:
Organic Chemistry studies the chemical behavior or molecules made from chains of carbon atoms.
Hydrocarbons are organic molecules made solely from carbon and hydrogen.
Alkanes have a backbone of singly bonded carbon atoms. The general formula is CnH2n+2.
Alkane naming
|
Value for n |
Name |
|
1 |
Methane |
|
2 |
Ethane |
|
3 |
Propane |
|
4 |
Butane |
|
5 |
Pentane |
|
6 |
Hexane |
|
7 |
Heptane |
|
8 |
Octane |
|
9 |
Nonane |
|
10 |
Decane |
Alkenes have a backbone of singly bonded carbon atoms AND ONE DOUBLE BOND. The general formula is CnH2n. You can have two molecules of the same formula but with different structure because of where the double bond is. These are called isomers. (See examples below.)
Alkene naming is the same as for alkanes except the “ane” ending is changed to “ene.” Also, the location of the double bond must be specified by way of a number at the front of the name.
Examples
|
1-Butene |
2-Butene |
|
H H H H | | | >C=C-C-C-H H | | | H H H |
H H H H | | | | H-C-C=C-C-H | | H H |
Alkynes have a backbone of singly bonded carbon atoms AND ONE TRIPLE BOND. The general formula is CnH2n-2. You can have two molecules of the same formula but with different structure because of where the double bond is. These are called isomers.
Alkyne naming is the same as for alkanes except the “ane” ending is changed to “yne.” Also, the location of the double bond must be specified by way of a number at the front of the name.
Straight chains have a straight backbone of carbon atoms.
Branched chains differ in that they have branches of smaller hydrocarbon chains added to the base chain (the longest carbon chain you can see).
Naming branched chains Start with the name of the longest chain and add the name of the branched chain with the “ane” ending changed to “yl.” If there is more than one branched chain add the names shortest to longest. If the unit repeats, add bi-, tri, tetra prefixes. You must also note the location of the unit as in the naming of alkenes.
I will show an example on the board.
Cycloalkanes are chains of singly bonded carbon atoms in the form of a ring. They are named as for alkanes but with a cyclo in front. The general formula is CnH2n.
Functional groups are groups of atoms that can take the place of hydrogen. Alcohols (methanol, ethanol, etc.) have the hydroxyl group –O-H. Aldehydes (methanal, ethanal, etc.) have a –C=O group at the END of the chain. Halogenated compounds have hydrogen replaced by elements from the seventh column of the PT (Cl take name chloro-, Br takes bromo-, etc.)
Structural isomers are molecules of the same chemical formula but with different structure. You saw this above for butane, but it can also involve branched isomers.
For more on this
www.absoluteastronomy.com/encyclopedia/I/IU/IUPAC_nomenclature4.htm
Procedure
Get a modeling kit.
1 Which are the carbon, hydrogen and oxygen atoms? How do you know? (Hint: consider the valence number for each of them.) Figure out how you will make a single, double and triple bond.
2 For each of the following straight chain alkanes draw the structural formula, write the chemical formula and build a model.
a) Methane
b) Ethane
c) Propane
d) Butane
e) Pentane
3 Try these alkenes:
a) Ethene
b) Propene
c) All the isomers of Pentene
4 And alkynes:
a) Ethyne
b) Butyne
c) All the isomers of Pentyne
5 Try these branched alkanes
a) 2-methylbutane (what straight chain alkane is this an isomer of)
b) 2,3-dimethylbutane (what straight chain alkane is this an isomer of)
c) 3-ethylpentane
6 Try Cyclopentane
7 Build each of the following functional groups
a) Hydroxyl
b) An aldehyde group
8 Try building
a) Methanol
b) Ethanol
c) Ethanal
d) 1-bromo-2-chlorobutane