Welcome to part 1 of the organic
chemistry introduction. I'm Melissa Maribel your personal tutor and the most
important element for organic chemistry
is carbon. Remember carbon has four valence electrons which means it could
have four bonds knowing this let's go
over the four different ways a molecule can be represented. The first way is the
typical molecular formula. The second way
is the structural formula which looks
like a typical lewis structure. The third way is called a condensed structural
formula. To write this formula we looked at the structural formula where on the
first carbon to the left there are three hydrogen's attached this is why we have
CH3. Next, the middle carbon only has two hydrogens so CH2 and the last carbon to
the right has three hydrogens so CH3. The fourth way is what you will most
commonly see throughout the entire semester, it is the skeletal formula also
referred to as a line diagram where each point represents a carbon and the
hydrogens are not shown. This is where knowing that carbon wants four bonds is
going to be very important. This is what the structure would look like if we drew
in the hydrogens. At this carbon we already have one bond so we are missing
three more bonds which must be three hydrogens. Next, the middle carbon
already has two bonds so we need two more so we have two hydrogens and this
last carbon already has one bond so we need three more bonds so three more
hydrogens to make sure you get this down and don't miss anything on your
exam make sure to pause the video and try this question out and we'll go over
the answers together.
Okay here are the answers the structural formula consists of four carbons and 10
hydrogens. So this first carbon needs 3 hydrogens, next carbon has two bonds so
it needs 2 hydrogens, same goes for this carbon and this last
carbon has one bond so it needs 3 hydrogens so this is our structural
formula. Using the structural formula we'll write the condensed structural
formula where this first carbon has three hydrogens so CH3 the next carbon
has two hydrogens so CH2 same for the next carbon so CH2 and the last carbon
has three hydrogens so CH3 this is our condensed structural formula. Now for the
skeletal formula since there are four carbons we need four points there is a
trick to drawing this right each time if you were to count 1 2 3 4 we actually
drew too many carbons we drew 1, 2, 3, 4, 5 but we just wanted four, so if you count
to one less carbon than what you're originally looking for then you will
draw the correct amount of carbons each time. So in our case we will count to 3
when drawing the lines so 1, 2, 3 and we really have 1, 2, 3, 4 carbons
this is the correct skeletal formula. These molecules that we are working with
are called hydrocarbons, a hydrocarbon consists of only hydrogens and carbons
there are different types of hydrocarbons this is based on the type
of bonds that are between the carbon atoms, alkanes have single bonds, alkenes
have at least one double bond and alkynes have at least one triple bond.
You will later get into naming different types of structures so know that the
ending is very important if something ends in ane it's an alkane meaning
it only has single bonds. The ending ene means it's an alkene which has a
double bond and the ending of yne makes it an alkyne which means it's a triple
bond this all is talking about the major carbon chain or longest carbon chain but
we can also have something known as a substituent which is an atom or groups
of atoms that replaces a hydrogen and gets attached to the carbon in the
longest carbon chain. Think of it this way the longest carbon chain is like the
body of a person and the substituents are the arms or legs because that's
what's sticking out of the body. Here's a list of the most common substituents you
will first see. These specific substituents are also referred to as
alkyl groups an alkyl group is made up of only carbons and hydrogens it is
also defined as an alkane that is missing one hydrogen
the first alkyl group is methyl this has only one carbon next is ethyl this has
two carbons, then propyl has three carbons and butyl has four carbons
you will definitely be tested on functional group switches what I'll be
covering in part 2 you can find that right over here
and remember stay determined you can do this!