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Hydrocarbons are any molecules that are composed strictly
of just carbon and hydrogen, hence
hydrocarbon. Yes, organic chemists have senses of humor, too.
Here's an example at the hydrocarbon: nothing but carbon
and hydrogen. And you'll notice we've got lines representing
single covalent bonds. Now these covalent bonds
are nonpolar because there's no oxygen,
no nitrogen. This is your basic
organic molecule. In this case
it's forming a line or a chain. They can also flip around the form circles.
Now, in this case you'll notice that I've left out
the hydrogens. If I were to put all the hydrogens in there it would get kinda
messy.
In fact, often times organic chemists
will abbreviate it still further and just draw the shape of the molecule.
Here you're given to understand that each point
there's a carbon. Now the question arises,
how I know how many hydrogens there are, how do I
know that there's a carbon there?
Remember that carbon needs four
electrons to share, so it can form four bonds.
So if I only show one bond, you'd . . .
well, excuse me . . . one bond, one bond here, this carbon is show with only
two bonds, so we know that there's
hydrogen sticking of here. And with the abbreviation where I'm showing you just
a shape
the points are showing where the carbons are and I'm going to
actually draw out the parts that are actually of interest.
Now, back to organic molecules. Carbon is considered
the foundation of life because it can form these four bonds.
Because it can form four bonds, it can form any shape you like
by hooking up with a variety of different molecules. Now hydrogen is
important
in organic chemistry but it can only form one bond.
So you'll notice with each of these hydrogens there's only one line going
from each H. Four from carbon,
one from hydrogen. Now oxygen can form two bonds,
so you're gonna see just two lines coming from oxygen.
Nitrogen can form three, sulfur can form two,
phosphorus can form five. As you look at these
various hydrocarbons you'll notice that they're all hydrophobic.
They can't dissolve in water because they don't have any oxygen,
they don't have the nitrogen. They, all of the
covalent bonds are nonpolar and so
there's no charge. Now, from here we're going to be talking about some
functional groups.
These are groups of molecules that you can add to your basic hydrocarbon
to change its nature. Most of them
make that part of the molecule hydrophilic. So, let's go
and talk about the functional groups.
The way that I remember things is by remembering
what's different. Of the different functional groups there's one that's
hydrophobic.
All the rest are hydrophilic so all I have to remember is the one the
hydrophobic one.
There's also two acidic functional groups.
All I have you watch for them. And one basic
functional group. So let's look at the methyl group.
It is a carbon attached two 3 hydrogens.
When it is drawn out it looks like this. Now over here
would be the rest a hydrocarbon. So if you had to make a guess, would you consider
this one to be
hydrophilic or hydrophobic? It is hydrophobic.
There's no oxygen, no nitrogen. Now, the next one is the hydroxyl group or
alcohol group. It's an oxygen bonded to hydrogen.
Now because this goes as a grou,p we generally leave out
the covalent bond between the oxygen and hydrogen
but it's a polar covalent bond. Remember,
the oxygen is stealing, um,
the electrons partially from the hydrogen so
the electrons are going "woo, woo" over here once, "woo" over here once,
and so we get a little bit of a charge. Now with this,
when you add this to a hydrocarbon,
it makes this part of the hydrocarbon hydrophilic have makes it so it can
hydrogen bond
with water. The book talks about ethers.
Those are bonds, it's not a functional group, but it's where you take two
hydrocarbons and have come together
by means of an oxygen. Now the carbonyl group
is a double bonded oxygen that you put on
to a hydrocarbon. Now it doesn't have a hydrogen attached to it,
so it can't really hydrogen bond but it does make the molecule more
hydrophilic because of this double bond, the oxygen as stealing those
electrons
part of the time from the carbon,
so you get just a little bit of a negative charge, enough the water will interact with it.
Now when this is in the middle of a molecule, we call
and a keytone. If it's on the end, we call a molecule an aldehyde.
Later on in Chapter 5 you're going to see what keytones and lots of aldehydes.
Now let's talk about the carboxyl group.
We call it this because it's kind of a combination of
a carbonyl group where you have a double bonded oxygen
and a hydroxy group. Okay. So we call it
a carbonxyl and this is what it looks like.
this is how it's going to be abbreviated in your te,xt COOH,
this is what it looks like when it's drawn out. Here you can see
you've got your double bonded oxygen, you've got your hydroxy group.
Now this oxygen doesn't have a real good hold on this hydrogen
so this hydrogen has a tendency to leave its electrons with
the oxygen and take off in the solution. So this is an acidic
group and loses that hydrogen.
and it becomes . . . this part of the molecule develops a full
negative charge because the oxygen has the
electron, and so it's an acid. If you're looking at a molecule and you're
looking to see if it's an acid,
you look for that negative charge. This next one that the book mentions
is an ester. Once again, it's not really
a functional group, it's a bond, but this time you have two oxygen hooking
together. Now let's talk about the amino group.
Escuse me, this is what the ester group looks like
where you have a carbon with a double bonded oxygen and then we have another
oxygen there.
NOW let's talk about the amino group. This is a nitrogen with two hydrogens.
Remember,
nitrogens can form three bonds.
This is what it looks like one is drawn out.
Now, this nitrogen has a tendency
to pick up hydrogen ions from solutions.
So it comes along and so this nitrogen
has one extra proton in association with it that has electrons,
so this gives it a positive charge. This also makes it
our basic functional group.
So if you're looking at a molecule you're trying to decide whether it's a
acid or a base,
if you see a positive on it then you know it's a base,
and in biology it's generally gonna be the amino group.
Now let's look at the phosphate group. Remember, phosphates can form 5 bonds.
So we can stick all sorts of stuff on a phosphate. This is how you're gonna see
it
in your textbook when its abbreviated. This is what it looks like one
when it's drawn
out. So you've got the rest of your organic molecule, here you've got your phosphate
with four oxygens,
one of which is double bonded. Now it has a tendency to lose the hydrogens off of
these oxygens.
It is just like the carboxyl group or the other acid group,
and those hydrogens leave their electrons with the oxygens
and head off into the solution,
usually looking for an amino group. So this is our
other acidic functional group.
And our last one is the sulfhydryl. This is a sulfur attached
to a hydrogen. Now, this becomes important when we talk about proteins
because if you get two sulfhydryl groups together, they're gonna lose
their hydrogens and they're going to form a bond between it, and
that has a tendency to stabilize proteins.
So those are all of our functional groups.