ORGANIC NOMENCLATURE #1 (FOCUS ON ALKANES)
Some easy definitions:
Organic compounds = compounds containing hydrocarbons (hydrogen + carbon)
Compounds = a combination of two or more elements
ALKANE
Alkanes are hydrocarbon compounds that only have single bonds with no functional groups. Below is the chemical formula for any alkane compounds.
Let's take a look at some examples (**you must MEMORIZE the prefixes shown in the table below for the test**):
^The way to name alkanes is to place the appropriate prefix based on the number of carbon atoms present, and end off with "ane". For instance, one carbon atom with four hydrogens attched will have "meth" for its prefix and "ane" combined to form "methane". Two carbon atoms will be assigned "eth" for its prefix and combined with "ane" to form "ethane", so on and so forth.
Notice all of the molecules in the slide fulfill the chemical formula of alkanes.
^Look closely at the sixth rule above: "List substituents alphabeticaally, prefixes are ignored"
Let's take for example that you're stuck between writing 3-ethyl-2-methylhexane vs. 2-methyl-3-ethylhexane (shown below) --> we say that the first one is the correct way because ethyl has an "e" which comes before "m" alphabetically.
Moreover, let's say you have 3,4,4-triethyl-3-methylheptane. You may wonder why the "t" comes before "m"? The answer is we don't count prefixes like di, tri, tetra towards alphabetical order, so we are still keeping the "e" from ethyl to come before the "m" from the methyl group.
^Depending on the arrangement of atoms, the branch or substituent name could change. For instance, we know "butyl" is a 4-carbon substituent, but "sec-butyl" has the carbon bonded to two other carbons whereas "tert-butyl" has the carbon bonded directly to three other carbons.
(**MEMORIZE these branches as well**)
^Halides refer to the Halogen group in our periodic table.
These halides are numbered based on their location and added as a prefix to the alkane chain such as "bromo", "chloro", and "fluoro". If for instance the halide is attached to the first carbon, you assign it a number "1".
^Functional groups are simply a specific arrangement of atoms that display their own distinct properties or characteristics. These functional groups can be added to alkanes and determine their identity.
^Notice:
double bonds --> numbering is done based on its location and "ene" is added to the end of the name
triple bonds --> numbering is done based on its location and "yne" is added to the end
Alcohol (-OH) --> numbering is done based on its location and "ol" is added to the end. The prefix "hydroxy" is also used if there is a higher priority functional group within the alkane structure
Halides --> numbering is done based on its location and halogen names (e.g. bromo) are added at the front
^Note:
Ether --> numbering is done based on its location and "oxy" is added at the front of the name together with the prefix that represents the number of carbons ether is attached to. E.g. methoxy (methyl group is attached to oxygen), ethoxy (ethyl group is attached to oxygen).
Another important thing is you need to select which side (left or right) has a longer carbon chain, because that will determine the name of the alkane chain. For instance, the structure on the left below shows 3 carbons on the left and one carbon on the right. Because 3 carbons are longer, we make that the name of our chain, "propane". Then, we use the remaining one carbon on the right to be added to our "oxy", so it becomes METHoxy. So the name of the structure becomes methoxypropane.
^Note:
All of these functional groups (carboxylic acid, ester, and amide) do not have numbering because they are always located terminally (meaning it is always going to be 1, so we end up not labeling it at all)
Carboxylic acid --> "-oic acid" is added to the end of the name
Ester --> "-oate" is added to the end
Amide --> "amide" is added to the end
^Notice:
Arene refers to aromatic hydrocarbons. Most basic arene we see in this unit is benzene (6 unsaturated carbons) - when naming an aromatic ring (instead of straight alkane chains), we base the name on the specific molecule (e.g. benzene) and add the branch at the front (e.g. ethyl). An example would be as shown above, "ethylbenzene"
When benzene has an (-OH) attached to it, it gets a whole new name, "Phenol". Phenol becomes the base name and whatever branch (e.g. chlorine) is added to the front of the name --> this gives rise to "chlorophenol" as we see above
^Notice:
"-benzyl" has an "yl" at the end meaning this functional group counts as a branch (meaning there is another higher priority functional group that determined the identity of the molecule). Notice "-benzyl" is used when there is the benzene ring with one methyl group!
"-phenyl" is also a branch and is used when there is only the benzene ring with no other substituents. Don't confuse this with "Phenol" which again is the benzene ring with alcohol attached.
SUMMARY CHART
^You should familiarize yourself with the chemical structures of each of the functional groups, be able to identify them in a given molecule, and also be able to name them appropriately. **THAT IS GOING TO BE THE WHOLE TEST FOR THIS SECTION**
PRACTICE Qs ON NAMING ALKANES
PRACTICE Qs ON DRAWING ALKANES
ANSWER KEY - NAMING ALKANES
ANSWER KEY - DRAWING ALKANES
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