Chapter 1 again is the introduction to the
basics of Organic Chemistry from the General
Chemistry perspective. We have this long list
of things that you should know coming into
 
the class. I did send you the emails out periodically
over the summer to make sure that people who
haven't had General Chemistry for a while
could do some background reading so we are
not starting cold here. What I plan to do
today and Monday is to get through that list.
Again on Wednesday what we tried to lay out
was the way you succeed in this class is by
keeping up with it and making sure that you
are progressing day-by-day. Er, it's not a
good idea to be waiting until the last minute
if you are a procrastinator this isn't going
to be much fun but these are things you should
know and we'll find out as we go. Er, we have
the periodic table. This is one of the best,
most brilliant pieces of organization that
humans have ever put together and you look
at all the elements there it's a big, busy
piece of work. Can you memorize this thing?
No. I have no idea what's at the bottom and
I'm not interested in those elements at the
bottom. I probably studied them in high school
but since then I don't care. I'm interested
in the top right-hand side of the periodic
table because that's where carbon is and that's
where most of the elements are that it will
bond with. We do need to worry about some
metals; we will talk about bonding in terms
of electronegativity and how you can predict
the bond in the near future but that periodic
table is there to help you. On every exam
I give, and I think some of the other people
do this too, there's a periodic table on the
front page. So if you need to check it do
so. But what you'll find now is that speed
will be important. If you are spending 5 minutes
trying to find bromine on that periodic table
this isn't going to work. If you roughly know
where bromine is, it's on the right-hand side,
we are on teh way. If you know where the metals
are on the left-hand side then good, because
then we can start to talk about their properties
and why they interact the way they do, why
do they form ionic bonds where atoms in the
middle form covalent bonds? So again, this
is just a sort of gentle introduction to get
started in terms of getting people on the
same page. Now, you should have seen this
along the way. This governs everything. Right?
Having said there are no calculations in this
class, we do have to worry about some numbers;
relative sizes of numbers. We have to worry
about concepts mostly but there will be some
numbers involved as proof and evidence for
chemical reactions and why they work and how
they work. So hopefully you've got the slides
in front of you and feel free to copy down
but don't copy all of that; you've got the
information at home if you need it. This is
really important, this idea of free energy
and how molecules express themselves in terms
of their energetic properties. We have this
combination of what is delta H, enthalpy,
and delta S, which is entropy. And they are
similar and they are related. One is temperature-dependent
and the other one isn't, and we'll over the
next few weeks, get a handle on why this is
important to a chemist and a biochemist. Later
on. We'll see now that enthalpic properties
such as bond energies; we'll have some bonds
that are weak and some bonds that are strong,
which you'll have to learn, and then be able
to use those numbers to be able to predict
what will happen. If you heat a molecule up,
which bond is going to pop first, which one
will break first? It will be the weakest bond
so if you know those ideas it's straighforward.
Erm, we'll talk about entropy and we'll talk
about this idea of organization or disorder
or the expression of energy in a molecule
from an organic perspective. Why are some
reactions entropically favored but enthalpically
disfavored and the other way around. Really
key here, and again I'm saying this in my
way so that you get used to it is this idea
of stability and reactivity and their relationship.
Stable things tend to be unreactive. Reactive
things tend to be unstable. Those ideas then
become really sort of intimately tied together.
When you have to consider a possibility of
one chemical reacting with another. Are they
stable? If yes then they probably won't react.
If they are reactive for some reason you'll
learn, they are going to react and give you
products. That's the very first thing you
have to worry about in terms of a chemical
reaction. So this is just to introduce it,
if you have seen this before great, if you
haven't you need to go back into your gen
chem notes and read the textbook on this and
start to appreciate that everything we do
here is driven by energetics. Erm, we do some
history, we talk about the idea that organic
chemistry means nothing any more. I believe
Berzelius was French and he came up with this
idea that 200 years ago that organic chemistry
was basically compounds isolated from nature
and that meant that only really animals and
plants could make these compounds. And that
was blown away not too long after by Wohler
in 1828 with the seminal experiment where
he mixed chemicals together in the lab, inorganic
chemicals, and he made an organic molecule.
So all of a sudden you didn't need this vital
force, you didn't need something to be alive
to be able to make an organic compound. You
can mix it in a flask and you get an organic
product. So "organic" means nothing; I wish
they'd relabeled it early on because "organic"
now means things like "bananas" and stuff
in the grocery store,, I think "molecular
engineering" is the way to go. That's really
what we do here. So we talked about simplicity
and complexity and how do you go from what
is a fairly sort of solid but certainly lower
level understanding of chemistry to being
able to look at something like that? What
do we need to do along the pathway to get
from one to the other? Everybody should be
able to look at urea and think it is fairly
simple, it doesn't have many atoms. There
are none of these wedges and dashes that will
mean something later in which we have stereochemistry
and direction in space. The atoms there are
pointing in different directions. So how do
you as a beginning organic chemist get your
head around going from the molecule on the
left to the molecule on the right? Well that's
the two semesters. Right, we are going to
see now that it can be done if you learn the
basic rules and you apply them sensibly and
you practice it's very straightforward to
go from the left to the right and to be able
to look at molecules on the right and to be
able to understand them. So, looking at the
sort of historical perspective here the whole
point was that on the left you have an inorganic
molecule, inorganic meaning that it's a rock
or a salt, something like that. Then on the
right you have urea. And this was the first
experiment that was done to show that "organic"
meant nothing anymore. So in itself it's fairly
simple. Urea does typify very simple organic
molecules in which you just have covalent
bonds and elements from the right-hand side
of the periodic table. You have C, N and O.
And you will spend a lot of time this week
learning those three elements, what they look
like, what shapes they adopt, what their electronic
properties are, and how those electronic properties
are expressed in a molecule. Because we will
find very quickly that the atomic structure
from the periodic table often doesn't match
what's happening in a molecule. There has
to be some modification and something we call
a "hybridization model" to explain that along
the way. So we are going to start very quickly
with this idea of valence. You have seen this
before but now we are focusing on a certain
part of the periodic table and the important
part here is carbon; if you understand that
the maximum number or bonds carbon can form
is 4. As we work our way through people like
to put 6 bonds, and 7 bonds and 8 bonds and
that's just wrong. Okay, it only needs 4 bonds
because it only needs 8 electrons, 2 electrons
in each bond and 8 electrons, that's it; 4
bonds. So your typical carbon when it is neutral,
and it isn't missing a bond or isn't missing
any electrons, is 4 valent. We can draw it
as we have drawn it there, which is sort of
a simple first year type depiction, but we'll
see very quickly that this structure is not
correct; the way that is drawn like a cross
is incorrect. We have to put some more detail
in when we talk about electronic properties
in the near future. Nitrogen has 3 bonds.
If you understand NH3, ammonia, from freshman
chemistry you can do an awful lot of organic
chemistry because all we do is swap out some
of those hydrogen atoms and put organic pieces
on. The organic pieces often don't do anything
chemically so if you understand the shape
of NH3 and the chemistry of NH3, the fact
that it's a base and later on we'll call it
a "nucleophile" - if you understand that very
simple molecule you can extrapolate that to
organic chemistry. That's how you start to
learn this stuff and pick it up and it can
become fun. What's the simplest oxygen molecule
that you know that looks like that? Water,
H2O, right? So if you know something about
water you can do ether chemistry you can do
alcohol chemistry in the organic realm. because
those molecules adopt the same shapes, and
they have very similar chemical properties
based on oxygen having 2 lone pairs. So those
are very simple. You should know those coming
in and if you don', go and get comfortable
with them and we'll talk about where lone
pairs go in a minute and if you are okay with
that then we are in good shape. On the right
hand side we'll talk about the halogens. They
tend to have one bond, hydrogen tends to have
one bond and those are very simple things
that you should pick up very quickly. Carbon
doesn't have 5, it can have 3 later, but right
now we are talking about 4 being the maximum.
For nitrogen the maximum is 4 but it has 3
bonds when neutral as right there, and for
oxygen the typical, neutral molecule has 2
bonds. That's as simple as it gets. So, how
do we put these things together? A lot of
this is common sense and again you've all
hopefully passed the freshman class and you've
got some idea and something out of it. The
idea of molecules coming together or atoms
coming together to form molecules based on
the need of something to form an octet, to
get to some stable configuration. but this
organic world gets very big very quickly,
and if you look at that first molecule I gave
you, the Mossaveghi molecule, that's just
got dozens of atoms in it but they've all
got set shape and they are all well understood
shapes. If you come to this and there's a
formula, you are given some sort of formula
to work with and you don't know the arrangement
of those elements. You don't know how thay
are bonded together. Very quickly you should
be comfortable with doing this type of thing.
Okay, Ijust said carbon has a maximum of 4
bonds, hydrogen has a maximum of 1, chlorine
has a maximum of 1. You should be able to
put that molecule together in some form very
quickly to give a sensible molecule in which
all of the bonds have the right valence, all
of the atoms have the right number of electrons,
and that is a stable molecule. The problem
is, people tend to just forget what they know
and they start doing really weird stuff like
this. What's the problem with that? Do we
see a problem with that? H bonded to H bonded
to H, yes, if you don't see a problem then
we need to talk. Yes, if you do see a problem
then we are in good shape. Because that molecule
is absolutely nonsensical because it breaks
the rules. H can only have 2 electrons, in
this molecule I've got a hydrogen with 4 electrons,
that's silly. So very basic stuff as sort
of a starting point. If you are doing stuff
like this we really need to talk, but if you
can put that together we are in good shape
because you understood something from the
freshman classes. Everybody okay? Questions?
Ask questions along the way because I'll just
keep going. We go back a little bit and we
talk about atomic structure. This is old stuff
that you've seen before but it's important
now to be able to understand where we need
to go with organic chemistry becuase we have
to explain the shapes of things soon, we have
to be able to explain shapes and adapt some
of the material that you've seen before. Are
you okay with the idea of 1s2, 2s2, the idea
that orbitals fill up before, they fill up
singly before they double up, and once this
is full we go someplace else, yes?
We go further away. And we talk about energy.
Which is going to have more energy, n = 3
or n = 1? Which one will be further away from
the nucleus? N = 3 right? N = 3 further away,
not held as tightly, easier to give away
and
more energetic.
