Naming Alcohols Using IUPAC Rules for Nomenclature

By Brian Lemay 51 comments


Leah here from www.Leah4Sci.com and in this
video I will show you how to name alcohols. An alcohol is a molecule that has an OH as
its functional group. This is typically shown as R-OH where R means the rest of the molecule
and OH is your alcohol functional group. Since alcohol is a high priority functional
group, you will add the letters “ol” as a suffix to your molecule. Starting with this
example, we highlight the parent chain and number so that the OH gets the lowest possible
number. In this case we have five carbons giving me
a first name of “pent”. We have only single bonds giving me a last name of “ane”. Since
the alcohol occurs on carbon 2, we add the prefix “2-ol”. When putting the name together,
you can bring the 2 to the front of the name and that means “ol” will directly follow “ane”
and so you drop the E. This gives me a final name of 2-pentanol where it’s A-N, instead
of A-N-E, O-L. When you have a substituent on your alcohol,
you still follow the same rules where your substituent becomes the prefix and the alcohol
is your suffix. You may recognize this molecule as having
the common name tert-butyl alcohol but let’s see how to name it using the IUPAC rules.
We will start by identifying and highlighting our longest carbon chain. In this case, there
are three carbons and numbering so that alcohol gets the lowest number. We have the option of numbering both from
the right and the left, each giving oxygen a number 2. So I will start numbering from
the left. Having three carbons in my parent chain gives me a first name of “prop”. Having
only single bonds gives me a last name of “ane”. Since the alcohol is on carbon 2, I
have a suffix of “2-ol” and since the methyl is also on carbon 2, I get a prefix of “2-methyl”. Putting the name together, remember that the
prefix goes first, then the first name, then the last name and the suffix. Remember to
drop the E from “ane” for a final name of 2-methyl-2-propanol. The rules for naming a cyclic alcohol are
just like straight chain alcohols. We start by identifying the parent chain, in this case
a total of five carbons for a first name of “pent”. Given that the molecule is a ring,
I add the prefix “cyclo”. Only single bonds gives me a last name of “ane”. Since alcohol is the only group on the molecule,
I give it a number 1 and then choose to go clockwise or counterclockwise for a total
of five. The alcohol would give me a suffix of “1-ol”. However, since it’s the only group
on the molecule, the number 1 is understood and does not have to be included. This gives
me a final name of cyclopentanol. A diol is a compound that has 2 OH groups
on the same molecule and we will use this as an example. My parent chain has a total
of six carbons in a ring. That gives me a first name of “hex” and a prefix of “cyclo”.
Only single bonds gives me a last name of “ane”. Since this is a symmetrical molecule,
I can choose to number from either direction as long as one OH group gets number one and
the second one gets number two. I will write 1, 2 to show which carbons the
OH groups show up on and then I will put “di” in front of the “ol” to show that I have two
alcohols. Putting the name together, I get 1, 2-cyclohexanediol. Notice that I did not drop my E in this case
given that I have the consonant D in between two vowels. Let’s try an example with the pi bond. Identifying
my parent chain, I see that I have a total of five carbons. If I number from the right,
I give my pi bond the number 2. If I number from the left, I give the alcohol a 2. Since
the alcohol is higher priority than the pi bond, I number from the right for a total
of five carbons giving me a first name of “pent”. Having a pi bond on carbon 3 gives
me a last name of “3-ene”. Having an OH on carbon 2 gives me a suffix of “2-ol”. Putting the name together, I get 3-pentene-2-ol.
Notice again that I did not drop the E and that’s because I have the number 2 separating
the two vowels. Let’s try something tricky for the final problem.
In this case I have two rings fused together. So I have to go back to the rules of naming
bicyclic compounds. I start numbering from the bridge head closest to the OH group since
that’s my highest priority giving it a number 1 and then follow my way around the ring that
has the OH. Continuing around the ring that has the bromine
and then jumping to the bridge carbon that has nothing on it. Having seven carbons in
my parent chain gives me a first name of “hept”. Having only single bonds gives me a last name
of “ane”. Since I have two fused rings, I have to precede
with the word “bicyclo,” and then I have to include how many carbons are unique to each
ring in the brackets. I have two carbons unique to the ring portion with the OH giving me
2. I have two unique carbons to the portion with Br giving me dot 2 and one carbon on
the bridge giving me dot one. Bromine is my prefix which gives me “5-bromo”
and OH is my suffix giving me “2-ol”. Putting the name together, we start with the prefix,
then we have the name and finally we have the suffix. Putting the entire name together, I get 5-bromobicyclo
[2.2.1] heptane-2-ol. When you have a name this complicated, it helps to use your puzzle
pieces as a checklist to ensure you didn’t miss anything. I have my prefix “5-bromo”. I have the start
to my bicyclic compound. I have my first name and last name and finally I have my suffix

51 Comments

Ama Mbonu

May 5, 2013, 7:38 pm Reply

thank you so much
you are way better than my chemistry teacher
everyone in my lecture watches your video xx

Shrubbs

Jul 7, 2013, 1:02 am Reply

Question! As far as the order of numbering the parent chain goes, 1. Substituents, 2. alcohols, 3. double (-ene) 4. triple bonds (-yne) are all given priority before halogens?

Siva Prasad

Jan 1, 2014, 3:09 pm Reply

thankyou so so much mam… you are the best teacher out there…

ho ka

Mar 3, 2014, 5:55 pm Reply

thank u very much <3

Abz

Apr 4, 2014, 11:18 pm Reply

When do you give the OH number 1 priority in a carbon chain is it when there is another functional group present with less priority

Abz

Apr 4, 2014, 11:23 pm Reply

For example you only gave the OH number 1 priority when you showed the cyclopentane why didnt you give it priority in a straight carbon chain, instead you gave it a number 2.

kikkirow

May 5, 2014, 7:27 pm Reply

Wow you used way too much noise removal in this. The sound is too tinny. But thanks for the help. 

F M

Jun 6, 2014, 1:52 am Reply

for the one where you got 3-pentene-2-ol, can you also write pent-3-ene-2-ol and also can u elaborate on when to drop e and when not to? Thanks

hootie017

Aug 8, 2014, 2:40 am Reply

love the call back to previous videos – thanks. 

Ahmed Musa

Sep 9, 2014, 8:09 pm Reply

thank you so much Leah, its very helpful to watch these videos.

Yoon Weon Suh

Nov 11, 2014, 7:37 am Reply

For the tert-butyl alcohol, can we name it 1,1-dimethyl ethanol? I learned in class that the IUPAC name for tert-butyl functional group is 1,1-dimethyl ethyl.

Maame Efua

Nov 11, 2014, 11:19 am Reply

Thanx Leah..u d best

汽水橘子

Dec 12, 2014, 4:50 am Reply

thanks for sharing this, i found it very helpful! i begin to like chemistry and i never feel like it!! thank you very much!!

Waheed360

Feb 2, 2015, 2:27 am Reply

is it true that the Carbon with the OH has to be saturated? it has to have only single bonds?

Relanie Jalandra

Mar 3, 2015, 5:57 am Reply

Thankk You so much Ma'am. 🙂 

Mohamed Kh

Mar 3, 2015, 6:49 am Reply

Helpfull …….. Ty

Tamara

Apr 4, 2015, 2:11 am Reply

did you do any videos in regards to alcohol reactions ?

Daniel Duran

Sep 9, 2015, 11:57 pm Reply

Thank you!!! This helps out tremendously!!! 🙂

Glam by Mahsa

Sep 9, 2015, 5:38 pm Reply

useful………..thanks

Nor Hamizah

Oct 10, 2015, 8:58 am Reply

It really help me.thanks you very much

Adam Thomas

Oct 10, 2015, 4:59 am Reply

For the molecule you named 3-pentene-2-ol why did you not add the prefix trans or (E) to make it (trans) or (E) 3-pentene-2-ol? A pi bond at carbon 3 signifies the bond must remain in place and has another way of being illistrated, does it not?

SC92

Oct 10, 2015, 6:04 am Reply

Priority numbering is difficult. Sometimes double bond is higher sometimes substituent is higher?

Saira Roshnaye

Oct 10, 2015, 11:25 am Reply

What if there's another functional group besides OH on the cyclo alcohol?

Sarthak Vijay

Nov 11, 2015, 5:53 pm Reply

Leah, wouldn't it be 3-penten-2-ol, instead of 3-pentene-2-ol; you may google it!

daric nd

Jan 1, 2016, 12:02 am Reply

Hi Leah I have a question. When a molecule has a methyl as a substituent and a double/triple bond then the double/triple bond gets the highest priority. But in this case, are you implying that the alcohol substituent gets the highest priority overall? I remember reading this in my textbook last semester. I just wanted to confirm this with you. Your response will be kindly appreciated. Thank you.

vector addition

Mar 3, 2016, 3:15 pm Reply

In the fused rings example if the ring with Br had more carbons than the ring with OH would the order of numbering reverse following the fused rings rule or would it remain the same due to OH priority?

Shihong Zhang

Apr 4, 2016, 9:07 pm Reply

you make such a complex chemistry simple and easy to understand. thanks a lot.

Naga Epic videos

May 5, 2016, 2:01 am Reply

hy….i wana know abot Two oh grp attchd…

Naga Epic videos

May 5, 2016, 2:05 am Reply

ohh..i got it now…..Wen ders 2 OH ..we dnt remove 'E'…. ya..i got…..but my teacher dint tell me abot dat….

Naga Epic videos

May 5, 2016, 1:14 am Reply

Do u kik accnt??

Y CP

Jun 6, 2016, 7:33 am Reply

so useful. I found naming organic compound boring before, but after watching your video, my interest has been greatly arounsed. Thank You!!!!

Omar Totonji

Jun 6, 2016, 10:36 am Reply

hi
if we have cycloalkane we can name it either clockwise or counter C.W. according to which gives the branches lowest number ?
and in case of cycloalcohol it is the same too ??

thanks

Shubham Shinde

Sep 9, 2016, 6:49 pm Reply

When do we use hydroxy as prefix for OH

John Yim

Oct 10, 2016, 2:19 pm Reply

I apologize if this has already been asked, but in previous videos the di- and tri- are prefixes and apart of the substituent group which you said was before the "First" and "Last" names, however in the example of 1,2-cyclohexanediol the di- is after. Why is this?

John Yim

Oct 10, 2016, 2:23 pm Reply

Sorry I posted before deciding to post a couple other questions, maybe it might help others as well. Thank you for putting these videos together and taking the time to answer our questions. Organic has been the toughest class I've encountered in my first three years.

Can isopropyl also be called secpropyl?

Are pi bonds always a higher priority than substituents?

Priority substituents: does the greater number of substituents or the first letter more of a priority?

I find an example contradicting: it was said that substituents (C substituent) have priority over pi bond (triple bond in example), however later a double bond was given priority over a halogen substituent. Does the double bond vs. triple bond the cause of the different result or did the type of substituent make this difference?

Brigette Paulo

Nov 11, 2016, 11:55 am Reply

where is your video about phenol? can I have the link please?

iGreatSpartan

May 5, 2017, 1:43 pm Reply

in the second example , why cant we start numbering from the carbon closest to OH , making the parent chain the right line(starting from top right).

Merièm Houche

Aug 8, 2017, 10:21 am Reply

great job.would you please tell me why the halogens are low priority then the double bound while the alcohols are higher ?

Jerby Cristo

Sep 9, 2017, 6:44 am Reply

In 3:46 can it also be named as cyclohexan-1,2-diol?

haroon miah

Sep 9, 2017, 5:44 pm Reply

fuuucking hell did this on second lesson of A level chem im lost…i still am lol

Robin Delilah

Oct 10, 2017, 1:27 pm Reply

At 5:12 you start describing the unique carbons on each of the rings. Why are carbons numbers 3, 6, and 7 considered unique?

DJ Scottic

Feb 2, 2018, 3:29 am Reply

You Should have added spiro too..Overall good! Keep it going

ZULU ZERO

Mar 3, 2018, 6:06 pm Reply

Urgh this is so hard

Zafar Iqbal Ghural

Apr 4, 2018, 8:24 am Reply

Thank you

AnjewelApples

Aug 8, 2018, 9:04 am Reply

(5:09) how did you determine the information that would go in the brackets? I was slightly confused how you determined the number of unique carbons on the chain.

Asma Arshad

Dec 12, 2018, 5:54 am Reply

What ?…if OH is not preffered group

دانية اناناس

Dec 12, 2018, 10:13 pm Reply

Huh?

Chemist Me

Jan 1, 2019, 11:05 am Reply

you sound like Samantha from 'Her'

winter forest

Mar 3, 2019, 2:54 am Reply

thanks

Fahim Safi

Mar 3, 2019, 7:06 am Reply

I just can say Thank you so much for brilliant explanation.

sebastian alvarez

Apr 4, 2019, 4:54 am Reply

An ayuwoki!!!! Run!!!!

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