CHEMISTRY COMMUNITY

Posted: **Tue Feb 28, 2017 2:16 pm**

How do you determine where to put the dashes within the name of the organic compound? I think there are several instances where you would use one, but I just wanted some clarification.

Posted: **Tue Feb 28, 2017 2:20 pm**

I think dashes are typically used to separate numbers from words but I'm not completely sure.

Posted: **Tue Feb 28, 2017 2:40 pm**

I believe you use dashes not just to separate numbers but also prefixes/suffixes. e.g. 3-ethyl-5-methyl-octane

Posted: **Tue Feb 28, 2017 6:55 pm**

Yes, you use the dashes to separate words from numbers, but the example 3-ethyl-5-methyl-octane would not need a dash between methyl and octane so it would essentially be written 3-ethyl-5-methyloctane

Posted: **Tue Feb 28, 2017 8:52 pm**

What do the numbers represent?

Posted: **Wed Mar 01, 2017 7:51 am**

I think they represent which carbon is the group attached to. For instance, In 3-ethyl-2-methylhexane. Hexan shows a 6 carbon chain and since there are two
different alkyl groups attached, we put an ethyl group on the number 3 carbon atom and a methyl group on the number 2 carbon atom.

Posted: **Wed Mar 01, 2017 10:09 am**

emilie liu 3G wrote:Yes, you use the dashes to separate words from numbers, but the example 3-ethyl-5-methyl-octane would not need a dash between methyl and octane so it would essentially be written 3-ethyl-5-methyloctane

Correct.

In class I often add a dash to separate the substituent from the main chain word to make it easier for students to identify the different parts of the name. For example: 3-ethyl-5-methyl-octane

However the way it would be printed in a book or science journal is: 3-ethyl-5-methyloctane

We will accept both.

Posted: **Thu Mar 02, 2017 12:33 am**

nikita bhat 2D wrote:What do the numbers represent?

The numbers are used to represent which Carbon in the parent chain the substituent is attached to. For example, in 4-methyl-octane, the methyl substituent is attached to the 4th carbon in the octane parent chain. Counting carbons from the left, you will get that the substituent is on the 4th carbon; counting from the right, you will get that the substituent is on the 5th carbon. In all cases, you will choose the lowest number, so 4-methyl is written instead of 5-methyl.

Posted: **Thu Mar 02, 2017 2:21 pm**

What does it mean when it has "#,#" before the name? Which number means which thing?

Posted: **Thu Mar 02, 2017 2:36 pm**

With #,# do you mean something like 2,3 dimethyl octane? If yes, then I think the numbers are to indicate which carbon the methyl is placed on. So if its 2,3 it means that on the second and third carbon, there is a methyl branch

Posted: **Thu Mar 02, 2017 6:25 pm**

How do we know in what order we should put the numbers? (because we can start counting from either side of the molecule)

Posted: **Thu Mar 02, 2017 8:53 pm**

Caleb Lim 2M wrote:How do we know in what order we should put the numbers? (because we can start counting from either side of the molecule)

You number the substituents based off the lowest number/location on the parent chain.

Posted: **Fri Mar 03, 2017 7:56 pm**

It should be the smallest number - from either end of the chain.

Posted: **Sat Mar 04, 2017 1:12 pm**

we use the dashes to separate numbers from words.
For example, 3-methyl-2-ethylpropane
Note that we do not use the dashes when separating two numbers; instead, we use a comma.
Like this, 2,3-dimethylbutane

Also, the name of our last substituent and the name of our longest carbon chain (the parent chain) will be connected (no space in between)

Posted: **Sat Mar 04, 2017 3:53 pm**

There was also a thing Lavelle mentioned about not using a dash sometimes for the second to last term? It's in our course reader but was different on the powerpoint or something like that.

Posted: **Sun Mar 05, 2017 3:14 pm**

NinaSheridan wrote:There was also a thing Lavelle mentioned about not using a dash sometimes for the second to last term? It's in our course reader but was different on the powerpoint or something like that.

Yeah the last carbon group doesn't need a dash, it just combines with the parent group, for example 3-ethyl-2,3-dimethylpentane or something.

Posted: **Sun Mar 05, 2017 8:19 pm**

I'm not sure if this is an obvious answer but on page 93 of the course reader what do the numbers (1,2,2) in 1-Bromobutane, 2-Chlorobutane, &
2-Iodobutane mean?

Posted: **Sun Mar 05, 2017 8:31 pm**

Those numbers refer to the carbon to which the halogen is attached, numbering follows the same rules, so the lowest numbering scheme is chosen.

Posted: **Sun Mar 05, 2017 9:53 pm**

nikita bhat 2D wrote:What do the numbers represent?

The numbers represent which carbon the substituents are added to. You number the carbons on the longest chain and it could start on the right or left side, but in the end, you number it so that the substituent is bonded to the lowest number carbon.

Posted: **Sun Mar 05, 2017 10:10 pm**

Will the order always be in alphabetical order when naming the structures ?

Posted: **Sun Mar 05, 2017 10:14 pm**

For substituents do we use common or systematic naming??

Posted: **Sun Mar 05, 2017 10:21 pm**

On page 93 of the course reader, we choose 4-ethyl-2,2-dimethyl-hexane as the correct name of the molecule instead of 3-ethyl-5,5-dimethyl-hexane. We are always supposed to choose the name with the lowest number, so why do we choose 4-ethyl instead of the 3-ethyl? Is it dependent on the dimethyl only?

Posted: **Sun Mar 05, 2017 11:00 pm**

104781135 wrote:On page 93 of the course reader, we choose 4-ethyl-2,2-dimethyl-hexane as the correct name of the molecule instead of 3-ethyl-5,5-dimethyl-hexane. We are always supposed to choose the name with the lowest number, so why do we choose 4-ethyl instead of the 3-ethyl? Is it dependent on the dimethyl only?

Just whichever has the lowest number overall, which in this case is dimethyl.

Posted: **Sun Mar 05, 2017 11:06 pm**

KarinaOropeza_2L wrote:Will the order always be in alphabetical order when naming the structures ?

Yes, the order is always in alphabetical order when naming the structures, based on the substiuents.

Posted: **Sun Mar 05, 2017 11:09 pm**

Leo_Navejas_3B wrote:For substituents do we use common or systematic naming??

I believe that Professor Lavelle said that either is acceptable but they'd specify if they want the IUPAC name.

Posted: **Mon Mar 06, 2017 1:27 pm**

Why is there a 2 in pentanone for CH3COCH2CH2CH3

Posted: **Mon Mar 06, 2017 1:45 pm**

AonyaMontoya2B wrote:Why is there a 2 in pentanone for CH3COCH2CH2CH3

It is a ketone which means there is a double bond attached to a carbon in the parent carbon chain which is bonded to two other carbons and since this is your functional group and you want to have the lowest possible number you start counting from whichever end gives you the lower number and in this case it is 2, and the longest carbon chain has 5 carbons which makes it 2-pentanone.

Posted: **Tue Mar 07, 2017 12:25 am**

On page 3 of the OChem textbook at the bottom, how do you get the "-diene" at the end of the molecule 2-Methyl-1,3-butadiene? Also, I'm confused on how to start the numbering for this example. Which Carbon is 1, and what order/direction do you go from there?

Posted: **Tue Mar 07, 2017 1:09 am**

Are the pentyl and amyl in the course reader the same thing? If so, which one should we use for common naming, or does it matter?

Posted: **Tue Mar 07, 2017 9:07 am**

Pentyl is the IUPAC naming and amyl is the common naming

Posted: **Tue Mar 07, 2017 10:03 pm**

When we name an alkene or alkyne with a functional group, do we put the number for the double/triple bond inside the word or in front of the word? For example, is it 2-pentene or pent-2-ene.

Posted: **Tue Mar 07, 2017 10:06 pm**

I believe that its not necessary in between names, but it is for in between numbers and names. Lavelle mentioned that the dashes in between names were meant to avoid confusion and promote better understanding of the different parts when teaching the material.

Posted: **Tue Mar 07, 2017 11:11 pm**

Would a prefix, such as "di" in dimethyl, affect the order when naming alphabetically?

Posted: **Wed Mar 08, 2017 11:02 am**

KarinaOropeza_2L wrote:Will the order always be in alphabetical order when naming the structures ?

Sometimes it can vary if there's a "substituent in a substituent" type of situation (i.e. IUPAC naming for isopropyl branch would be 2-methylpropyl which would be included amongst other substituents if applicable). The propyl could be in front of another substituent name like nonyl even though it is not alphabetically first since it is part of the branch.

Posted: **Wed Mar 08, 2017 11:04 am**

Bryan Vega 2E wrote:Would a prefix, such as "di" in dimethyl, affect the order when naming alphabetically?

no!

Posted: **Wed Mar 08, 2017 2:42 pm**

When you add the numbers to the name, I know that the position is the first number, but what is the number after the name? Ex. 3-methyl-5,5-pentanehexane or whatever it would be. Thank you.

Posted: **Wed Mar 08, 2017 5:44 pm**

In one of the course reader examples for cycloalkanes (around pg. 93 of the course reader), it shows 1-tert-butyl-4methylcyclohexane. Why is there a "tert" before the butyl? I don't understand why it isn't just called "butyl"

Posted: **Wed Mar 08, 2017 8:06 pm**

The "tert" is before "butyl" to show that the 4 carbon substituent comes from 1 carbon being connected to 3 other carbons rather than it just being a chain of 4 carbons associated with "butyl" by itself. Hope that helps!

Posted: **Wed Mar 08, 2017 8:08 pm**

What counts when using the alphabetical reference when naming?

I thought Neo- and Iso- counted, while Tert- didn't? Or is it the opposite? Is there a reason for it?

Thanks in advance.

Posted: **Wed Mar 08, 2017 8:09 pm**

Leo_Navejas_3B wrote:For substituents do we use common or systematic naming??

I was told common and systematic naming are the same thing.

Posted: **Wed Mar 08, 2017 9:13 pm**

What do "Z" and "E" mean?

Posted: **Thu Mar 09, 2017 1:53 am**

You can think of Z as having the higher priority groups on the same side of the molecule (also known as "cis" and hence the mnemonic "Zee Zame Zide") and E as having the higher priority groups on the opposite sides of the molecule (also known as "trans"). When looking at the groups bonded to the same carbon, higher priority is determined by whichever group has the higher atomic number (for example: Br has priority over H because atomic number of Br is 35 and H is 1). Without using Z or E, there will be two possible structures that would have the same name, thus Z and E are necessary.

Posted: **Thu Mar 09, 2017 9:24 pm**

I have a question about page 94 in the course reader from yesterday's lecture. We went over pentyl and isopentyl, but I thought you use neo instead of iso for pentane and beyond. Shouldn't the name be neopentyl instead of isopentyl?

Posted: **Thu Mar 09, 2017 9:48 pm**

If there are 2 substituents on the same Carbon do we use "di" or just 2?

Posted: **Fri Mar 10, 2017 2:20 pm**

If there are two methyls, for example, on Carbon number 2; then you would write it as 2-dimethyl. Similarly, if it was on Carbon #3, it would be 3-dimethyl.

Posted: **Sat Mar 11, 2017 9:40 pm**

Rodri_Karla_1J wrote:I have a question about page 94 in the course reader from yesterday's lecture. We went over pentyl and isopentyl, but I thought you use neo instead of iso for pentane and beyond. Shouldn't the name be neopentyl instead of isopentyl?

Neo is used for substituents that have the formula C(CH3)3 while iso is used for those with CH(CH3)2. I hope it helps!

Posted: **Sat Mar 11, 2017 10:17 pm**

You separate numbers form words with dashes (i.e. 3-ethyl)

Posted: **Sun Mar 12, 2017 12:38 am**

Dashes are used to separate not only numbers of the location of the substituents, bonds, etc., but also substituents. For example, for 2-methyl-pentane, we know that on the second carbon of the carbon chain of pentane, there is a methyl substituent located.

Hope this helps!

Posted: **Sun Mar 12, 2017 10:56 am**

If there is multiple functional groups which group gets the highest priority?

Posted: **Sun Mar 12, 2017 11:53 am**

Bryan Vega 2E wrote:If there is multiple functional groups which group gets the highest priority?

As I discussed in class Chem 14B syllabus does not cover multiple functional groups. This is covered in Chem 14C/CL/D.

Posted: **Sun Mar 12, 2017 3:27 pm**

When naming should we always include if a compound is cis/trans, or will a question specifically ask us for that information?

Posted: **Sun Mar 12, 2017 3:44 pm**

PriscillaMariscal_3F wrote:When naming should we always include if a compound is cis/trans, or will a question specifically ask us for that information?

If the molecule can exist in the cis or trans form, you must specify which one it is.

Posted: **Sun Mar 12, 2017 5:14 pm**

It seems like there are a lot of structures in the Introduction to Organic Chemistry book that could be named using either -neo and -iso or sec, tert, etc. Is there a specific time and place for using one form versus the other, or are both acceptable forms of the name?

Posted: **Mon Mar 13, 2017 1:23 am**

I think generally iso and neo are for alkyl groups and sec and tert are used for carbon atoms which have functional groups

Posted: **Mon Mar 13, 2017 1:07 pm**

Also what about bis?

Ethan_Wilson_1E wrote:It seems like there are a lot of structures in the Introduction to Organic Chemistry book that could be named using either -neo and -iso or sec, tert, etc. Is there a specific time and place for using one form versus the other, or are both acceptable forms of the name?

Posted: **Mon Mar 13, 2017 8:29 pm**

I'm still a little confused on the difference between IUPAC and common names. Can someone please explain.

Posted: **Mon Mar 13, 2017 10:04 pm**

When theres both a double bond and a functional group group which gets priority?

Posted: **Mon Mar 13, 2017 10:07 pm**

Still having trouble with knowing where to start counting the carbons when there is a double bond, any clarification

Posted: **Tue Mar 14, 2017 12:10 am**

Does using common names (for substituents like isopropyl, for example) make a difference in the use of dashes?

Posted: **Tue Mar 14, 2017 6:33 pm**

Jaime_Chamberlain_3G wrote:When you add the numbers to the name, I know that the position is the first number, but what is the number after the name? Ex. 3-methyl-5,5-pentanehexane or whatever it would be. Thank you.

The second number (-5) is not in regards to the methyl, it is talking about the pentanehexane.

Posted: **Tue Mar 14, 2017 7:18 pm**

A question: Is the functional group given preference over a double or triple bond during naming? Or is the double or triple bond given preference over the functional group?

Posted: **Tue Mar 14, 2017 8:08 pm**

If i am trying to add -oxy onto the end of isopropyl, would it become or isopropylanoxy or just isopropyloxy?

Posted: **Tue Mar 14, 2017 8:16 pm**

Andrea Medina 1A wrote:When theres both a double bond and a functional group group which gets priority?

the functional group gets priority.

Posted: **Tue Mar 14, 2017 8:16 pm**

shreya_mantri_3I wrote:A question: Is the functional group given preference over a double or triple bond during naming? Or is the double or triple bond given preference over the functional group?

the functional group is given priority.

Posted: **Wed Mar 15, 2017 12:07 am**

Do you prefer us to write the number on the outside of the name, or embedded in the functional group (but-1-amine for example)?

Posted: **Wed Mar 15, 2017 1:52 pm**

I know substituents must be written alphabetically but when there are halides with additional alkyl substituents, do they halides always come first (alphabetically) followed by all the alkyl groups (alphabetically)? For example would it be 3-iodo-4-ethyl... Or 4-ethyl-3-iodo... ?

Posted: **Wed Mar 15, 2017 8:48 pm**

Not quite sure how 3-5,Dimethylbenzene-1ylium is the lowest number for self test4.2A????

Posted: **Wed Mar 15, 2017 8:56 pm**

In Class we went over Cis and Trans molecules in a hexane when the substituents where on carbon 1 and 4. If say the substituents were on 1 and 3, would we still be determining cis and trans?

Posted: **Thu Mar 16, 2017 2:14 pm**

Jaret Nishikawa wrote:Do you prefer us to write the number on the outside of the name, or embedded in the functional group (but-1-amine for example)?

I believe on the outside.

Posted: **Thu Mar 16, 2017 10:26 pm**

Andrea Medina 1A wrote:Still having trouble with knowing where to start counting the carbons when there is a double bond, any clarification

If there is only a double bond in the molecule then you start counting on the side which gives it the lowest number. If there is a functional group and a double bond, then you give the lowest number to the functional group because it has priority.

Posted: **Fri Mar 17, 2017 12:35 am**

I'm a little confused on what cases to use prefixes like iso and neo rather than the normal numbering

Posted: **Fri Mar 17, 2017 1:30 am**

In Q6A of the 2013 practice Final Exam, the answer is either 1,5,5,6-tetramethylcyclohex-1-ene or 1,5,5,6- tetramethylcyclo-1-hexene or 1,5,5,6- tetramethylcyclohexene in the solution.... But, I would like to know if 1,5,5,6- tetrameythyl- 1- cyclohexene would also be accepted.

Posted: **Fri Mar 17, 2017 2:57 pm**

Can someone please explain when you are supposed to use numbers in the middle of a word? For example, prop-2-en-1ol / 2-propen-1-ol.

Thank you!

Posted: **Fri Mar 17, 2017 5:24 pm**

I believe you only do that when it involves alkenes or alkynes in order to distinguish where the second or third bond is.

Posted: **Fri Mar 17, 2017 9:36 pm**

Can someone explain what "sec" is?

Posted: **Sat Mar 18, 2017 1:49 pm**

Divya Kumar 3I wrote:I'm a little confused on what cases to use prefixes like iso and neo rather than the normal numbering

I also have this question - although I understand that you use iso- and neo- when you see specific groups, I can't quite understand how to identify them and when to use iso- or neo- as opposed to other naming strategies. Any help would be much appreciated, thanks!

Posted: **Sat Mar 18, 2017 2:57 pm**

why is there sometimes a number in between the name like hexadecan-1-ol?

Posted: **Sat Mar 18, 2017 2:59 pm**

So cis- trans- and E, Z are always interchangeable?

Posted: **Sat Mar 18, 2017 3:00 pm**

904621096 wrote:why is there sometimes a number in between the name like hexadecan-1-ol?

I believe it is there because the OH (alcohol) group is attached to the 1st carbon

Posted: **Sat Mar 18, 2017 8:15 pm**

Will we be penalized for not including 1 in naming? For example can we just write 2-methyloct-4-enol instead of 2methyloct-4-en-1ol?

Posted: **Sat Mar 18, 2017 8:18 pm**

Would you put a dash inbetween naming with groups when one ending has a vowel and the start has a vowel? For example, would it be bromooctane or bromo-octane?

Posted: **Sat Mar 18, 2017 8:27 pm**

If it were something like 1-bromooctane I believe you still can write it like that or you can write 1-bromo-octane. Same would apply to 1-bromoethane. I dont think vowels change the naming of the organic molecule

Posted: **Sat Mar 18, 2017 11:10 pm**

Michael_Phillipi_1I wrote:Will we be penalized for not including 1 in naming? For example can we just write 2-methyloct-4-enol instead of 2methyloct-4-en-1ol?

Because there are other substituents, it is important to describe the location of the alcohol group

Posted: **Sun Mar 19, 2017 12:32 am**

tpat14 wrote:So cis- trans- and E, Z are always interchangeable?

They are interchangeable but the Z and the E must have parenthesis around them, while cis and trans do not need parenthesis

Posted: **Sun Mar 19, 2017 12:42 am**

how do you name substituents on a ring if there are more than 2 substituents?

Posted: **Sun Mar 19, 2017 1:03 am**

Alexma 3A wrote:how do you name substituents on a ring if there are more than 2 substituents?

Compare each number and select the name with lowest number.

Posted: **Sun Mar 19, 2017 1:00 pm**

tpat14 wrote:So cis- trans- and E, Z are always interchangeable?

No, cis/trans is comparing identical groups or the longest chain, but E/Z is based on a priority system. The question will probably ask to label something as either cis/trans OR E/Z. But if it doesn't specify, it's suggested to always use E/Z because it will never fail.

Posted: **Sun Mar 19, 2017 1:34 pm**

When you name something with an ether substituent in it how do you name it?

Posted: **Sun Mar 19, 2017 1:42 pm**

Aiden_Hsu_1M wrote:When you name something with an ether substituent in it how do you name it?

Because we know that ether is a substituent, you replace the -yl at the end of the subsituent with -oxy. For example, if we have an ethyl substituent with an Oxygen molecule (i.e. -OCH₂CH₃) we name it ethoxy instead.

Hope this helps!

Posted: **Sun Mar 19, 2017 6:33 pm**

FaithPigeon_1E wrote:
Michael_Phillipi_1I wrote:Will we be penalized for not including 1 in naming? For example can we just write 2-methyloct-4-enol instead of 2methyloct-4-en-1ol?

Because there are other substituents, it is important to describe the location of the alcohol group

But isn't that implied? Dr. Lavelle said that you can omit the 1 on other examples.

Posted: **Sun Mar 19, 2017 6:43 pm**

nikita bhat 2D wrote:What do the numbers represent?

where the specific functional group or constituent is

Posted: **Sun Mar 19, 2017 6:43 pm**

nikita bhat 2D wrote:What do the numbers represent?

where the specific functional group or constituent is

Posted: **Sun Mar 19, 2017 6:45 pm**

You would use dashes to separate the position of the substituents or functional group from the type of substituent or functional group. Also, we use them to separate the position of a double bond or triple bond. For Example:
3,2-dimethylbutane
2-ethylpent-1-ene --------> 1 represents the carbon that the double bond is on.

Posted: **Thu Mar 10, 2022 1:15 pm**

The dashes are used to separate the numbers from the names.

CHEMISTRY COMMUNITY

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