Leah here from leah4sci.com and in this video, we're going to look at a quick introduction
to alcohol including an overview and structure so that we can move on to physical properties
acids, bases, and of course reactions in the remainder of this series.
You can find the alcohol series along with the practice quiz and cheat sheets by visiting
my website leah4sci.com/alcohol.
Alcohols are very important in Organic Chemistry.
Alcohols can participate in many reactions either when you're creating an alcohol like
you learn from substitution.
When you're using an alcohol to create something else, or as an inbetween in longer multi-steps
synthesis and reactions.
Let's backtrack to the basics.
When you hear alcohol you should immediately think of an Oxygen bound to a Hydrogen.
This is the alcohol functional group.
Just oxygen bound to a Hydrogen.
For example, if you see a molecule that has an OH on a carbon but that same carbon also
has a carbonyl, that's not an alcohol.
This is a carboxylic acid which you should have studied when you look at functional groups.
Methanol is the smallest alcohol and it has a CH3 bound to an Oxygen, bound to a Hydrogen.
This is the simple fluid structure so we can see all the bonds and atoms.
The oxygen atom has 4 groups attached to it.
We have the Hydrogen, the methyl group, and 2 lone pairs.
4 groups means that it's sp3 hybridized.
With the bond angle of approximately 109.5 but it's slightly smaller.
That's because if we look at this alcohol as a 3d structure we'll have the 2 lone pairs
in a plane of the page, we'll show the CH3 coming out of the page and the hydrogen going
into the page.
The electron density is greater at the lone pair compared to the two electrons that make
up a bond between oxygen carbon for oxygen hydrogen and that means these electrons are
bulging out pushing slightly on the carbon and hydrogen bringing them closer together
for a bond angle that is slightly less than 109.5.
Oxygen is a highly electronegative atom and when bound to hydrogen which is less electronegative
you're going to have an unequal sharing of electrons in that covalent bond making it
a polar covalent bond where the hydrogen has the positive and oxygen, negative.
We can represent this with a delta negative at the oxygen, delta positive at the hydrogen.
This will be very important when we look at things like hydrogen bonding, solubility,
and boiling point in the physical properties video.
Alcohols can be classified as primary, secondary, or tertiary, depending on what is attached
to the alpha carbon or the carbon holding the alcohol.
Methanol does not have anything attached to the carbon so it doesn't fit this classification
but the rest will use the pencil trick which I teach in the tutorial link below.
The alcohol on ethanol sits on the carbon that has just one bond coming out of it making
it a primary alcohol.
In ethanol, the oxygen sits on a carbon with two bonds to carbon making it a secondary
alcohol, and in tert-butyl alcohol, the carbon is bound to 1,2,3 carbon atoms making it a
tertiary alcohol.
Many students gets scared when a ring is brought into the picture.
So let's see the same thing.
The alcohol sits on a primary carbon, once again giving us a primary alcohol.
This alcohol sits on a carbon with two bonds to carbon making it a secondary alcohol.
And finally the alcohol sits on a carbon bound to 3 carbon atoms making it a tertiary alcohol.
You should also recognize a molecule that has an alcohol sitting on the very same carbon
as a pi-bond.
This is both an alkene and an alcohol which we call the enol and you should recognize
this from your alkyne reactions and of course you'll see many more in your advanced Orgo
2 reactions.
One more alcohol that's very important to recognize is phenol.
When you have an OH sitting directly on a benzene ring, this is called a phenol, not
to be confused with phenyl which is benzene as a substituent on a carbon atom.
When it comes to naming alcohols, you simply drop the e at the end of the name and add
"ol" for the ol in alcohol.
This is discussed in detail in the Alcohol Naming video linked below.
But let's look at a few.
We've already seen methanol, it gets the name meth from having one carbon, ane from just
being an alkane, then we drop the e, add an ol from methanol.
Ethanol has two carbons giving us a first name of eth, last name of ane, add the ol,
and we get ethanol.
We don't need a number 1 because it's self understood as being the carbon holding the
OH, For this molecule we have 3 carbons atoms for a first name of prop, no double bonds
for a last name of ane, and ol on carbon 2 for 2O, bring the two out to the front for
2 propane, drop the e, ol for 2-propanol.
What about this one, what do we have?
2 carbons for a first name of eth, only single bonds last name of ane, 2 alcohols on carbons
1 and 2 so we specify 1,2 and specify that it's a diol.
Bring the numbers out to the front, and that gives us 1 comma 2, ethanediol.
The reason we don't drop the e is because we have d which is a consonant following the
vowel, we only drop the e when it would've been a vowel following another vowel, o following
p.
And what about, this one?
We have 3 carbons for a first name of prop, only single bonds in the chain for a last
name of ane, alcohols on carbon 1, 2, and 3 giving is a triol.
Bring the numbers out to the front, giving us 1 comma 2, comma 3, propanetriol.
The reason I chose these molecules is you should recognize them beyond their IUPAC names.
Methanol is wood alcohol.
You'll see this a lot in reactions.
Ethanol is grain alcohol or drinking alcohol, you'll also see this as a common solvent in
reactions.
2-propanol or isopropyl alcohol or isopropanol which is your standard rubbing alcohol.
1,2 ethyldiol is ethylene glycol and this a carbonyl protecting groups that you'll see
very soon.
And finally, 1,2,3 propanetriol is also glycerol, this is the backbone that you use for fatty
acid formation.
Be sure to join me in the next video where we look at physical properties of alcohol,
including hydrogen bonding, solubility, and boiling point.
You can find this entire series along with the alcohol practice quiz and cheat sheet
by visiting my website leah4sci.com/alcohol.