hello and welcome to a primer on organic chemistry
There is something very interesting about all the different
molecules that exist on earth which is that the vast majority of them contain carbon
something extremely important to remember is that we call
compounds that contain carbon organic compounds
all of which will answer our overarching question
One of the first tenets of understanding organic structure is that carbon always
has four bonds, something you will notice throughout this video.
carbons amazing versatility is that it bonds to a large variety of other elements,
Including iteself!
Let's see how many different compounds we can make by bonding various
atoms around just two carbon atoms. When all bonds are saturated with hydrogen,
We have ethane a common component of natural gas.
Here with ethene, we demonstrate carbon's
further bonding versatility with double bonding, and the
polymerization of ethane gives us a huge variety of plastics made from polyethylene.
And carbon can also triple bond.
This is ethyne, the gas used in acetylene torches used in welding and other
applications requiring a lot of heat.
An important point to consider here is our
earlier statement that carbon always has four bonds.
Each dash represents a bond a pair of electrons
and so whether carbon is entirely single bonded or has a
double bond, or a triple bond,
there are still a total of four bonds,
four electron pairs around the carbon.
Let's go back to ethane and see what else we
can get with just two carbons. We can keep adding fluorines,
each time creating a new molecule with new properties.
Or chlorine, and here we have a class of compounds
called chlorofluorocarbons which have a variety of uses
including refrigerants and aerosols, but which are also the source
of much pollution.
back to ethane again to demonstrate something very interesting.
We can substitute groups of atoms for a hydrogen which vastly
extends the properties we can get from our two carbon example. Any alcohol has
the OH or hydroxyl group which makes ethanol something that people actually
put in their bodies. And here we see the simplicity of naming schemes in organic chemistry.
For ethanol the first part of the name comes from the ethane that we
attached the OH group to and the o-l comes from the classification of this
type of molecule. It is an alcohol. This is the aldehyde group. You may have heard
of the preservative formaldehyde, this molecule is called acetaldehyde.
Organic acids also known as carboxylic acids are attached to a very wide range of carbon structures.
This one is acetic acid which is the acid found in vinegar.
NO2 is the nitro group found in most explosives, and here is the amine group which when
coupled to an organic acid group on the other side creates the amino acid glycine.
I hope you can see from the structure where the term amino acid derives.
All amino acids have this basic structure only differing by what groups
of atoms are displacing one of the hydrogen's which are designated with the letter R.
And thiols play a large part in protein folding when they are present in peptide chains.
OK so we've made 18 different organic compounds at this point
just by changing
I hope you can see this is just the tip
this is just the tip of the iceberg for only two carbons.
let's go back to our original molecule
to see the many other things that carbon can do and how we can
represent increasing complexity by creating what are called skeletal structures.
Carbon can keep adding to itself and this property is called
the ability to create long chains.
carbon can also branch off of itself
and this is called--can you guess?
And carbon can close those chains into ring structures.
As our molecules become more complex it is extremely important to understand the
shorthand called skeletal structures used to represent these molecules.
Before we get to skeletal structures however we have to remember that carbon forms bonds
at approximately 109 degrees. By showing that here we can now see from where the
zigzag line of the skeletal structure derives, which is simply a line that
marks where all the carbons would be if shown. The zigzag line, as the carbon
chain itself, would exist in the plane of the screen for any carbon at any vertex
of the skeletal structure, two of the four bonds are shown, which are in the
plane of the screen, and for the implied hydrogen's one would be bonded above the
plane of the screen as shown by the solid triangle, the other hydrogen bonded
below the plane of the screen, shown by the bond made of dashes. The skeletal
structure assumes the presence of these hydrogen's but for convenience they are
not shown. The addition of a parallel line indicates a double bond and ring
structures can be easily shown.
Let's see some examples of molecules using a
skeletal structure, which hopefully will give you a better idea of the enormous
range of organic molecules. Let's start with butane. Each vertex and endpoint
represents a carbon and hydrogens are implied but not shown but this is where
they would be given our understanding that each carbon has four bonds.
Butane is a common fuel found in lighters. This is the vitamin A molecule and the
skeletal structure gives us access to the arrangement of a large amount of atoms.
Oleic acid is oil found in olives, and it is an acid due to the organic
acid groups shown here.
The structures of one of the estrogens, estradiol, and
testosterone can be easily compared using skeletal structures they are
almost identical with the exception of those atoms seen here in blue and red.
Both of these molecules are synthesized from cholesterol in the bodies of both
sexes. We can also begin to see here the process of naming organic compounds.
There are two alcohol side groups designated with the suffix 0-l, thus the
derivation dial. Testosterone has the organic ketone side group, which is
reflected in the name testosterone.
Ring structures hugely extend carbon's versatility.
A six carbon ring gives us cyclohexane, benzene, phenol, and toluene
for starters. If we add three nitro groups to the toluene we get
trinitrotoluene otherwise known as TNT a powerful explosive.
Five carbon rings are also prevalent,
and if we substitute nitrogen at four of the carbons vertices
we get this extremely ancient structure called purine. Purines have been around
since the earliest life-forms on earth and it is the precursor to many other
molecules such as the DNA base guanine, which incidentally is a component of
guano or seabird poop and thus its name guanine. Caffeine is another example of
many purines that are biologically synthesized. Carbon's versatility in
bonding means it can be used to build extremely large molecules such as the
protein insulin with 778 atoms, or the protein hemoglobin with 9336 atoms.
Bonding with metals again expands carbons versatility such as heme, where
iron binds to nitrogen in a carbon-based structure used to bind oxygen in
hemoglobin. Or dimethyl zinc in which carbon bonds directly to the metal.
DNA is the largest known molecule with more than a billion atoms in the DNA of a
single human chromosome.
So why are most compounds organic?
Just think of how large that number grows with more than 50 atoms.