Leah here from Leah4Sci.com.
And in this video, I will show you how to name ketones.
The ketone functional group can be recognized when you see an R group bound to a carbonyl
carbon and then bound to another R group.
The second R group can be the same as the first for a symmetrical ketone or different
for an asymmetrical ketone.
A carbonyl is simply a carbon double bound to an oxygen and can occur in the beginning,
middle, or end of your chain depending on the functional group in question.
Don't confuse the ketone functional group with that of an ether which is simply RO bound
to R prime without that carbonyl presence.
To name a ketone, you follow the rules for standard IUPAC naming and add the suffix O-N-E
or one to your molecule.
Let's start with a simple example.
My first step is to identify and highlight my parent chain.
In this case, because the molecule is symmetrical, I can choose to number from the right or the
left.
Since I have a total of three carbons, I get a first name of prop.
Since I only have single bonds on my carbon chain, I have the last name of ane.
Since my carbonyl or carbon double bound to oxygen shows up at position 2, I include the
suffix 2-one.
However, since a ketone cannot be on the end of the chain, the number 2 will be understood.
If I try to draw this molecule with a carbonyl on the end, I wound up with an aldehyde rather
than a ketone and therefore the number 2 for ketone will be understood on a 3-carbon chain.
This allows me to drop the 2 and also drop the E given that one starts with a vowel for
a final name of propanone.
A substituted ketone is treated the same way where you first identify and highlight your
parent chain.
You have the option of numbering from the right giving ketone number 2 or numbering
from the left giving methyl number 2.
However, since ketone has a higher priority, it gets the lower number and so I number from
the right.
With four carbons in my parent chain, I have a first name of but.
Having only single bonds on the chain gives me a last name of ane.
My ketone shows up on carbon 2 giving me a suffix of 2-one.
My one carbon substituent at position 3 gives me a prefix of 3-methyl.
When putting the name together, you start with your prefix, first name, last name, and
then your suffix.
However, you can pull 2 in front of the first name allowing you to drop the E in ane for
a final name of 3-methyl-2-butanone.
Let's try a more complex example.
In this case, it appears as if my parent chain is only six carbons long.
However, don't be fooled by what appears to be a straight chain and instead go for your
longest continuous carbon chain.
My parent chain in fact has a total of seven carbons.
I have the option of numbering from bottom right to give methyl number 2 or top left
to give the ketone number 2.
Since ketone is higher priority, I start numbering from the left and get a total of seven carbons
for a first name of pent.
Since I only have single bonds in my parent chain, I get a last name of ane.
My carbonyl shows up on carbon 2 giving me a suffix of 2-one.
My 2-methyl substituents occurring on carbon 5 and 6 gives me the prefix 5,6-dimethyl.
When putting this name together, I have my prefix.
I pulled the number 2 in front of my first name and then last name allowing me to drop
the e for a final name of 5,6-dimethyl-2-pentanone.
When your ketone shows up in cyclic compound, you treat it the same way.
And if it's the only substituent, you don't have to include the number because 1 will
be understood.
In this case, we have six carbons for a first name of hex.
The ring gives me the prefix of cyclo and only single bonds gives me a last name of
ane.
My ketone would be 1-one.
However, the number is understood and therefore omitted for a final name of cyclohexanone.
When your molecule has two ketones, you treat it the same way but simply include the word
di in front of your suffix.
In this case we start by highlighting and identifying your parent chain.
Having five carbons gives me a first name of pent.
The fact that it's in a ring gives me a prefix of cyclo.
Having only single bonds gives me a last name of ane.
Given that I have more than just a single ketone on the molecule, I have to number so
that both functional groups get the overall lowest priority thus giving my ketones number
1 and 3.
Since the ketones occur at both carbons 1 and 3, I get a suffix of 1,3-dione.
The 1 and 3 tell me where each ketone shows up and the di tells me that I have two.
When putting the name together, I pulled the 1 and 3 before the cyclo.
However, I don't drop the E and A given that di is a consonant and separates my two vowels
for a final name of 1,3-cyclopentanedione.
Let's take a look at this example that has both a ketone and the double bond in the ring.
We start by highlighting and identifying the parent chain and the number to give the higher
priority group the lower set of numbers.
Since a carbonyl is higher in priority than a pi bond, the ketone gets the number 1 and
then we continue numbering so that the pi bond gets the next low set of numbers.
Having six carbons in my ring gives me a first name of hex.
The fact that they're in a ring gives me the prefix cyclo.
Since I have a pi bond in my ring, I get the last name of 2-ene.
A carbonyl on number 1 gives me a suffix of 1-one for a final name of cyclohex-2-ene-1-one.
For the last example, we'll look at a molecule that has both the carbonyl and the hydroxyl
occurring at the second carbon in the chain.
Let's start by highlighting and identifying the parent chain and then decide which way
to number.
If I number from the right, I give a high priority hydroxyl number 2, and numbering
from the left gives my ketone number 2.
Since, ketone is a higher priority than an alcohol, the alcohol gets demoted from a functional
group with an ol suffix to a substituent with a hydroxic prefix which means I have to number
from the left.
Numbering from the side of the ketone, I have a total of eight carbons in my ring giving
me a first name of oct.
Having only single bonds gives me a last name of ane.
Since the alcohol is a substituent, I get the prefix 7-hydroxy and the ketone, my functional
group, giving me a suffix of 2-one.
This gives me a final name of 7-hydroxy-2-octanone.
Are you struggling with organic chemistry?
Are you looking for information to guide you through the course and help you succeed?
If so, download my ebook, 10 Secrets to Acing Organic Chemistry using the link below or
visit Leah4Sci.com/OrgoSecrets.
For information regarding online tutoring, visit Leah4Sci.com/OrgoTutor.
If you enjoyed this video, please give it a thumbs up and even share it with a friend
or two.
If you have any questions regarding this video, leave a comment below or contact me through
my Facebook page at Facebook.com/Leah4Sci.
There will be many related videos posted over the course of the semester so go ahead and
click the subscribe button to insure that you don't miss out