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Organic chemistry
Course: Organic chemistry > Unit 7
Lesson 1: Alcohol nomenclature and propertiesAlcohol nomenclature
Rules for naming alcohols. Created by Jay.
Want to join the conversation?
- instead of 2-heptanol can we write it as hept-2-ol ?(11 votes)
- Yes, you can. You don't need to add "ane" to anything with a functional group because that wouldn't be an alkane anymore. However, you do need to add "ene" and "yne" for alkenes and alkynes because you otherwise don't know that they have those extra bonds.(4 votes)
- would you write 2-bromo phenol or 2-bromo-phenol? When do you put a hyphen and when not?(12 votes)
- 2-Bromophenol, without hyphen, without space.
See:
http://www.sigmaaldrich.com/catalog/product/aldrich/130915
https://en.wikipedia.org/wiki/Bromophenol_blue
etc.(9 votes)
- Theres an 8 carbon chain man! ahhh
3, chloro- 3 ethyl - 5 isopropanol - octane
i know thats not right but i tried help me out please(10 votes)- Athe says: 3:11
"you want to find the longest carbon chain that INCLUDES THE ALCOHOL GROUP"(18 votes)
- Suppose we have double bond in the starting of the chain and an alcohol group in the end ..then from where would we start numbering our chain....?(5 votes)
- Alcohols are higher in priority than alkenes, therefore the molecule must be numbered at the end giving the hydroxyl the lowest numbering possible.(16 votes)
- At about, why didn't we assign R/S to the 1 and 4 carbons? 10:40(6 votes)
- Because carbon atoms 1 and 4 are not chiral. The molecule has an internal plane of symmetry: The 1,2,3,4 side of he ring is identical to the 1,6,5,4 side.(9 votes)
- Instead of writing 1-propanol, would it still be correct to write just propanol (without the 1-)?(2 votes)
- If it is 1-propanol then YES!, Because it is understood that Alcohol is in the first position.
HOPE THAT HELPS :)(4 votes)
- For the last example, the 2- Bromophenol, shouldn't there have been a number to indicate which carbon the -OH group is bonded to? I ask because this was the case with other examples. Is this an exception to that rule, because the phenol ring has a halogen attached?(2 votes)
- In case of aromatic (benzene derivatives) compounds, the IUPAC rules are a little bit relaxed. The ideal name should have been 2-Bromo Benzen-1-ol or 2-Bromo 1-Phenol. But, the main reason of writing the numbers is to avoid ambiguity. By writing a compound as a phenol derivative, it is assumed that the numbering of the side chains is done in such a way that the firsty number, 1, goes to the hydroxyl group of the compound, as it should considering the functional priority order. This means, that saying it is a phenol, means hydroxyl is at position 1. You could also call this (although this naming is wrong, it is only for understanding "implied" numbers) 2-hydroxy bromobenzene, where calling it a bromobenzene derivative means bromine atom is at position 1.(3 votes)
- If i have a molecule with an E/Z conformation as well as chiral centers, do I put the E/Z before or after the R/S in the name and are they in the same brackets or not?(1 vote)
- You put them all in the same parentheses in numerical order. For example,
(2Z,4E,6R)-6-chloro-6-methylocta-2,4-diene.(4 votes)
- How do you determine not only the functional groups, but also whether they are primary, secondary or tertiary of a compound made up of more than two cyclics?(2 votes)
- The functional groups are the same as in noncyclic compounds: alcohol, aldehyde, ketone, carboxylic acid, etc.
For each carbon atom, you look at the number of directly-attached carbon atoms:
1° — one directly-attached carbon atom.
2° — two directly-attached carbon atoms.
3° — three directly-attached carbon atoms.(2 votes)
- AtShouldn't the molecule be 3-chloro 3-methyl 5-(ethan-1-ol) octane? 4:46(2 votes)
- No, the OH group is the highest priority group here so the main carbon chain HAS to include it, even though there is a longer carbon chain possible. The name Jay gives is correct.(2 votes)
Video transcript
In this video, we'll look at the
classification and nomenclature of alcohols. So here I have my generic
alcohol up at the top. And I have an alkyl group
over here on the left. And I have an O-H
on the right, which is called a hydroxyl group. Let's look at the
classification our alcohol. So if I have a carbon
bonded to an O-H, and that carbon is bonded
to one other carbon in this alkyl group here, that's
said to be a primary alcohol. This carbon over here is bonded
to two carbons in those two alkyl groups. So it is therefore
a secondary alcohol. And then this carbon
over here on the right is bonded to three
other carbons. So therefore, it is said
to be a tertiary alcohol. Let's take a look at the
nomenclature of alcohols. And we'll start with some
real simple molecules here. So if I had a molecule
that looked like that, and I wanted to name it
using IUPAC nomenclature, I want to number my carbon chain
to give that O-H the lowest number possible. So therefore, this carbon
would get a number one. This carbon would
get a number two. And this carbon would
get a number three. Now, if that O-H
weren't there, then we'd have just a three carbon alkane,
which we would call propane. But since we have our O-H there,
this is actually an alcohol. Alcohol is going to
have the -ol ending. So this is called propanol. So let's go ahead and
write propanol here. And the O-H group is
coming off of carbon one. So we're going to say that's
one propanol like that. How would we classify
this alcohol? Well, the carbon right here
that is bonded to the O-H, that carbon is bonded to
one other carbon right here. So this would be
a primary alcohol. So one propanol is
a primary alcohol in terms of its classification. Let's look at a
similar-looking molecule. Still three carbons,
but this time we put the O-H on the carbon
in the middle there. So once again, you're going
to go ahead and number it. Right. This is carbon one, this carbon
two, this is carbon three. This is a three-carbon alcohol. So it's also called propanol. The difference is the hydroxl
group is on a different carbon, right? It's now on carbon two. So we're going to write
two-propanol here, which is the IUPAC name. This is also called
isopropanol, rubbing alcohol, it's all the same stuff. But two-propanol would be the
proper IUPAC nomenclature. How would you
classify two-propanol? So once again, we find the
carbon attached to the O-H. That's this one. How many carbons is
that carbon attached to? It's attached to one
and two other carbons. So therefore, this is
a secondary alcohol. So we have an example
of a primary alcohol, and an example of a
secondary alcohol here. Let's do a little
bit more complicated nomenclature question. And so let's go
ahead and draw out a larger molecule with
more substituents. So let's put an O-H here. And let's do
something like that. And then let's go ahead
and do that as well. So give the full IUPAC
name for this molecule. So you want to find
the longest carbon chain that includes the O-H. OK
so you have to find the longest carbon chain that
includes the O-H, and you want to give the O-H
the lowest number possible. So that's going to
mean that you're going to start over here. And make this carbon
number one like that. So if that's carbon
number one, this must be carbon number two,
three, four, five, six, and seven. So we have a
seven-carbon alcohol. So seven-carbon alcohol
would be heptanol. So we can go and
start naming this. Make sure to give us
plenty of space here. So we have heptanol. And we know that the O-H is
coming off of carbon two. So we can go ahead and write
two-heptanol like that. Let's look at the other
substituents that we have. Well, what do we have right
here coming off of our ring? That's a three-carbon
alkyl group. So that would be propyl. So we have three-propyl. So go ahead and write
three-propyl in here. And what else do we have? At carbon five, we
have two substituents. So we have a chloro
group right here. And we have a methyl
group right here. And remember your alphabet. Right, so C comes
before M. So we can go ahead and put
our methyl in there. All right, coming
off of carbon five, so that would be
five-methyl, like that. And then also coming off
five, we have chloro. So five-chloro. Right in here. And that should do it. Everything follows
the alphabet rule. So we have five-chloro,
five-methyl, three-propyl, two-heptanol for this molecule. What about a problem that
includes some stereochemistry? So let's say they
give us one where we have to worry
about stereochemistry. So let's go ahead and draw
another chain out here. So let's see,
something like that. And let's make an O-H
group going away from us. And then let's go ahead and
make this one coming out at us like that. So give the full IUPAC
name for this molecule, and you have to include
stereochemistry. So once again, find your
longest carbon chain that includes your O-H group. And you want to give that O-H
the lowest number possible so it takes precedence over
things like alkyl groups, and halogens, and double bonds. So we're going to
start from the left. So one, two, three, four,
five, six, seven, eight, nine like that. So we have a
nine-carbon alcohol. So that would be nonanol. And the alcohol is coming
off of carbon three. The O-H is coming
off of carbon three. So we have three-nonanol. Like that. So three-nonanol. And let's see, what's
our other substituent? Well at carbon six here, we
have a two-carbon substituent. So that would be an ethyl group. So let's go ahead and
put in our six-ethyl. Go and put that dash in there. So far, we have this
six-ethyl, three-nonanol. And we have to worry
about stereochemistry. So if they put in wedges
and dashes on the problem, you need to think
about stereochemistry. And you put those
absolute configurations at the beginning
of the IUPAC name. So let's figure out the
stereochemistry of carbon three, first of all. So this is our chirality
center right here, this carbon. And again, you go to the
atoms that are directly connected to your
chirality center. So that's carbon,
carbon, oxygen. Coming off of our
chirality center, we also have a hydrogen, which
is coming out at us like that. So that would be
the lowest priority. So that would get
a number four here. So the oxygen has the
highest atomic number. So it's going to
get a number one. And then we have a
longer chain over here for this carbon on the right. So that's going to get a number
two, we have a number three. And then the hydrogen
would be a number four. So there's a little trick that
I covered in an earlier video. So if you ignore
the hydrogen, it looks like you're
going around this way, it looks like you're going
around counterclockwise. So it looks like it's S. But
you have this lowest priority group is actually
coming out at you. So remember the trick
was, if it looks like it's S with those
three, just reverse it. And so it must be R. It must
have an absolute configuration of R at carbon three. So we'll go ahead and
put in here a three R. And then we have to worry about
the absolute configuration at carbon six. So at carbon six here, this
is another chirality center. Four different substituents
attached to it. There's also a hydrogen
attached to this carbon, going away from us like that. And let's think about
the highest priority. Well, this chain
over here on the left is going to get the
highest priority. It has the most carbons,
it has an oxygen over here. So it's definitely going to
be highest priority There are more carbons this one
over here on the right. So again, when you
assign priority, this is going to
get highest one. And then this is going
to get a third up here. So this time, you're going
around one, two, three, you're going around counterclockwise. But your lowest priority group,
which is this hydrogen back here, is going away from you. So this actually is going to
be S. So it's counterclockwise. So it's S. Three R, six S. And I went through
those kind of fast. So you need to go back and
watch some of the earlier videos on absolute configurations
if that was a little bit too fast for you. All right. Let's look at cyclic alcohol. So ring systems. Let's look at an alcohol
with six carbons in a ring. And then there's an O-H
coming off of it like that. So six carbons without the O-H,
we would call that cyclohexane. And since this is an
alcohol, we would just change that to cyclohexanol. So that's very
simple nomenclature. You don't really need a number. But you could write a one there. It's implied if
you don't put in. So that would be cyclohexanol. What about something
that has a ring system with two hydroxyl groups? So let's say we'll put in
some stereochemistry, too. So let's say we have an
O-H coming out at us. And let's say we have an O-H
going away from us like that. So when you have a
situation like this, when you have two alcohols
in the same molecule, your prefixes be di. So this is actually a diol. And the nomenclature is based
off the cyclohexane molecule. So you would write cyclohexane. And then right after
the cyclohexane is where you put the diol. So di meaning
two-- two alcohols. You have to specify where those
two alcohols are on the ring. So we need to go ahead
and number our ring. Let's say this is carbon one. That would make this carbon two,
carbon three, and carbon four. So we have alcohols at the
one and four positions. So go ahead and write
one and four here. And those two alcohols
are trans to each other. One is coming out at you. And one is going away from you. So you could go ahead and write
trans-one-four-cyclohexanediol. And that's a good IUPAC name. So other types of alcohols. Well, instead of a
cyclohexane ring, we could have an alcohol
based off of a benzene ring. So we put in our
pi bonds like that. And if we have an O-H here,
this is a special type of alcohol called a phenol. This molecule is called phenol. And also you'll see this
hydroxybenzene portion of the molecule in lots
of natural products. So this is actually a
very important molecule to recognize, the phenols. Right, let's go ahead and
put something on that ring. So let's go ahead and we have
our phenol as our base here. And let's go ahead and
put a bromine right here. So how would we
name that molecule? Well, the base part
of the molecule is the phenol molecule. So go ahead and put
phenol like that. And then we'll go
ahead and number it. So the O-H, this
must be carbon one. We want to give our substituent
the lowest number possible. So we're going to give
this carbon number two. So a bromine coming off
of carbon number two. So it's very simple. All you have to do
is write two-bromo. So we have
two-bromophenol, like that. So that's nomenclature
for alcohols, and a special type of
alcohol called a phenol.