Naming Alcohols

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By: khanNotes 1
February 21, 2013 | Chemistry - Khan Academy
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View the video at http://www.youtube.com/embed/nQ7QSV4JRSs

thought it was about time that I actually
made a video on alcohols.
Now, alcohols is the general term for any molecule that
fits the pattern some type of functional group or chain of
carbons OH.
And they use the letter R.
And I've used it before.
R stands for radical.
And I don't want you to confuse
this R with free radical.
It means completely different things.
R in this form really just means a functional group or a
chain of carbons here.
It doesn't mean a free radical.
This just means it could be just something attached to
this OH right there.
Now another point of clarification, do not think
that anything that fits this pattern is drinkable.
Do not associate it with the traditional alcohol that you
may or may not have been exposed to.
Traditional drinking alcohol is actually ethanol.
Alcohol is actually-- let me write out
the molecular formula.
CH3, CH2, and then OH.
This is what is inside of wine and beer and hard liquor, or
whatever you might want.
You do not want to drink and maybe you might not actually
want to drink this either, but you definitely do not want to
drink something like methanol.
It might kill you.
So you do not want to do something like this.
You do not want to ingest that.
Might kill or blind you.
This might do it in a more indirect way.
So I want to get that out of the way and just so that we
get kind of a little bit more comfortable with alcohols, and
we've seen them involved in other reactions.
We've seen hydroxides act as nucleophiles and Sn2
substitution reactions create alcohols.
But I want to do is just learn to get comfortable and really
make sure we know how to name these things.
So let's just name these molecules that I drew right
before I pressed record right over here.
So over here, like everything else, we always want to define
the longest carbon chain.
We have 1, 2, 3, 4, 5 carbons.
So it's going to be pent.
And there's no double bonds.
So it's a pentane.
So I'll just write pentane right then.
And we're not going to just write a pentane because
actually, the fact that makes it an alcohol, that takes
precedence over the fact that it is an alkane.
So it actually, the suffix of the word will involve the
alcohol part.
So it is pentanol.
That tells us that's an alcohol.
And to know where the OH is grouped, we'll start numbering
closest to the OH.
So 1, 2, 3, 4, 5.
Sometimes it'll be called 2-pentanol.
And this is pretty clear because we only have one group
here, only one OH.
So we know that that is what the 2 applies to.
But a lot of times, if people want to be a little bit more
particular, they might write pentan-2-ol.
And this way is more useful, especially if you have
multiple functional groups.
So you know exactly where they sit.
This one is harder to say.
2-pentanol is pretty straightforward.
Now let's try the name this beast right over here.
So we have a couple of things going on.
This is an alkyne.
We have a triple bond.
It's an alkyne.
We have two bromo groups here.
And it's also an alcohol.
And alcohol takes precedence on all of them.
So we want to start numbering closest to the alcohol.
So we want to start numbering from this end
of the carbon chain.
And we have 1, 2, 3, 4, 5, 6, 7, 8 carbons.
We want to call it an octyne.
But because we have an alcohol there, we want to call this an
octyne-- let me make it very clear.
So oct tells us that we have 8 carbons.
Now we have to specify where that triple bond is.
The triple bond is on the 5 carbon.
You always specify the lower number of the carbons on that
triple bond.
So it is oct-5-yn.
That tells us that's where the triple bond is.
And then we have the OH on the 4 carbon.
So 4-ol.
And now we have these two bromo groups
here on the 7 carbon.
So it's 7,7-dibromo oct-5-yn-4-al.
And this would all be one word.
Let me make sure that you realize that
this should be connected.
I just ran out of space.
So that's probably about as messy of a thing you'll have
to name, but just showing you that these
things can be named.
Now let's think about this one over here in green.
So we have 1, 2, 3, 4, 5, 6 carbons.
So it's going to be a hex.
And they're all single bonds, so it's a hexane.
It's a cyclohexane.
But then of course, the hydroxide or the hydroxy group
I should call it, takes dominance.
It's a hexanol.
So this is a cyclohexanol.
And once again, that comes from the OH right there.
And you don't have to number it.
Because no matter what carbon it's on, it's on the same one.
If you had more than one of these OH groups, then we would
have to worry about numbering them.
Let's just do this one right over here.
So once again, what is our carbon chain?
We have 1, 2, 3 carbons.
And we have the hydroxy group attached to
the 1 and the 3 carbon.
Prop is our prefix.
It is an alkane.
So we would call this-- and there's a couple
of ways to do this.
We could call this 1 comma 3 propanediol.
Actually, I don't have to put a dash their.
Propanediol.
And over here, we would add the E because we have the D
right there.
So it's propanediol.
If it wasn't diol, it would be propanal.
You wouldn't have the E, D and the I there.
So this would specify we're at the 1 and the 3 carbons.
We have the hydroxy group.
Or this could also be written as propane- 1, 3- diol.
And once again, the di is telling us that we have two of
the hydroxy groups attached to this thing.
But either of these things are ways that you would see this
molecule named.

 

 

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