Sub-module 5A, chem lesson, page 1

A little organic chemistry

Organic chemistry is the study of carbon compounds. Since life on earth is built of carbon compounds, the field of organic chemistry is very broad. What follows is a brief sketch of some organic chemistry terms that I have been using.

The simplest organic compounds are the hydrocarbons that consist of only carbon and hydrogen.

Here is one that has two carbons:

Here is one with six carbons:

Go here and read the top of this page to see the names of other hydrocarbons in this series (you don't need to download anything) .Parafins

Now it gets tiring writing all those C's and H's, and there's no need to if you observe that each C has four sticks from it. Each stick connects to another atom. Each H has one stick from it. (The stick represents a shared pair of electrons, but that's not important for our purposes.) That results in each interior carbon atom having two hydrogen atoms connected to it and each end carbon having three.

Now we can write hexane as:

This line representation means that there is a carbon at each apex plus one at each end. And we know the arrangement of the hydrogen atoms from the stick rule.

How about this?

How many carbons does it have . And what is its name

Not all hydrocarbons with eight carbons are octane. The carbons can be linked differently:


The upper molecule is 2-methylheptane

The lower is 3-ethylhexane

All three arrangements of eight carbons are isomers of each other. Such isomers have the exact same atomic formula and molecular weight, but have slightly different chemical and physical properties. For example their boiling points might be slightly different.

It is also possible for the end carbons to link to each other, as in:

The same rule about the number of hydrogen atoms applies, each carbon has two, but since there are not any end carbons, there are 12 hydrogen atoms attached to cyclohexane. Go back to the web site above and glance at the lower portion of the page. It has lots of examples about how isomers are numbered. Don't bother memorizing from this page, but if you have some familiarity with the naming process, you will be less intimidated by some of the complicated names of environmental contaminants. Here it is again Isomers (Note the page uses a convention to illustrate molecular structure, with wedge shaped lines to indicate if the atoms are in front of or behind the page.)

The scientific name for hydrocarbons like those we described above is alkanes. The trade name for them is aliphatics.


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