Organic Nomenclature question [dioic acid]

[DrTacoElf]

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ok lets say you have hexane dioic acid, and it is subsituted by one methyl group and one propyl group. Each group is on the carbon alpha to the carboxylic acid. Which alkyl group would take precedence. In the kaplan blue book it appears they chose methyl but i'm am unsure to as why, because i thought it was based on size?

I also asked a friend and he said it was based on oxidation?


Thanks again guys 🙂

 

[HBomb]

From my understanding, this is based on a list of precedence by priority (which is highly based on oxidation). But it's difficult to think about the oxidation of a haloalkane, so in this case, you have to know that alkenes are a higher priority group than alkanes. That's the bottom line. (So for clarification, in this case, it is not based on alphabetical order) So we're talking about 2-ethyl-5-methyl hexandioic acid

At least this is what I think. Please let me know if I'm wrong.

 

[1FutureDDS]

First of all, we are dealing with Adipic Acid, easily noted by the 6 carbons, when you're dealing with naming, always follow the alphabetical order. 2-ethyl-5-methyladipic acid.

I would assume this correct being that you have already started that the compound you're dealing with is adipic acid which is even, it can be split and show mirror image. This being said, either way you look at it you will have the same compound 2 ethyl 5 methyl or 2 methyl 5 ethyl, well just do alphabetical order to get the so called "Correct" naming.

Maybe im not understanding correct, you have a Methyl Group and a Propyl group? or a Methyl and Ethyl? if its propyl just name it, 2-isopropyl-5-methyladipic acid

 

[DrTacoElf]

ok lets say you have hexane dioic acid, and it is subsituted by one methyl group and one propyl group. Each group is on the carbon alpha to the carboxylic acid. Which alkyl group would take precedence. In the kaplan blue book it appears they chose methyl but i'm am unsure to as why, because i thought it was based on size?

I also asked a friend and he said it was based on oxidation?


Thanks again guys 🙂

 

[DrTacoElf]

From my understanding, this is based on a list of precedence by priority (which is highly based on oxidation). But it's difficult to think about the oxidation of a haloalkane, so in this case, you have to know that alkenes are a higher priority group than alkanes. That's the bottom line. (So for clarification, in this case, it is not based on alphabetical order) So we're talking about 2-ethyl-5-methyl hexandioic acid

At least this is what I think. Please let me know if I'm wrong.

Why could it NOT be 5-ethyl-2-methyl hexandioic acid

 

[HBomb]

From my understanding, this is based on a list of precedence by priority (which is highly based on oxidation). But it's difficult to think about the oxidation of a haloalkane, so in this case, you have to know that alkenes are a higher priority group than alkanes. That's the bottom line. (So for clarification, in this case, it is not based on alphabetical order) So we're talking about 2-ethyl-5-methyl hexandioic acid

At least this is what I think. Please let me know if I'm wrong.

Yikes!!! Sorry about this previous post. I didn't answer the OP's question, and I didn't even answer the question correctly.

There is a propyl group and a methyl group and NO alkene. So this question is NOT based on oxidation or priority group. It's based on alphabetical order, since the propyl group and methyl group are both alkanes (same priority group). So it would be 2-methyl-5-propyl hexandioic acid.

FYI, I just looked this up, adipic acid is a common name. For IUPAC, use dioic acid.

 

[HBomb]

Why could it NOT be 5-ethyl-2-methyl hexandioic acid

If we had an ethyl group and a methyl group (different from what you originally asked), I think you want to give the ethyl group the lower number. Why? Just because of alphabetical order. I searched and searched my OChem text (Wade) for an example like this one, but had no luck, so my answer is more of a I think than I know. But it's still fun to try to figure it out.

Overall, it's a very nit-picky question, and you're very, very unlikely to encounter it as an actual DAT question. IUPAC nomenclature on the DAT is more straight-forward. The way I see it, why would the ADA need to make IUPAC tricky because there are enough people who already miss these questions as it is.

 

[drat]

Maybe im not understanding correct, you have a Methyl Group and a Propyl group? or a Methyl and Ethyl? if its propyl just name it, 2-isopropyl-5-methyladipic acid

NOOO! 2.) ISOPROPYL is not the same as PROPYL. Isopropyl is branched and propyl is just a straight chain. Like I said before, the correct answer is 2-propyl-5-methyl hexanedioic acid. Forget this nonsense about the apidic acid stuff. IUPAC does not use the "common name." That's why the system is in place. . .so you can figure out the structure without knowing the common name.


drat!

--- I've edited this post just in case someone starts reading this thread but doesn't read to the end. It's very confusing and bottom line, I was wrong...But not wrong that propyl and isopropyl aren't the same thing! That I will bet my life on! 😛

 

[DrTacoElf]

Drat why is 2-propyl-5-methyl hexanedioic acid preferential over 2-methyl-5-propyl hexanedioic acid? That my big question here. What determines the precdenece of alkyl groups. Size, Alphabet, oxidation?

 

[DrTacoElf]

Shoot, my first post didn't make it on this thread. Propyl has the 2 rather than the 5 because it has more carbons and is therefore higher in priority. Let me know if you need more clarification.

drat!

Yes that was my original logic as well until i worked a kaplan problem in the organic chemistry edge. They had hexane dioic acid substituted with an ethyl and a propyl each alpha to a different carbonyl group. I originally name the compuound 2-propyl-5-ethylhexanedioic acid, however their answer was 2-ethyl-5-propylhexanedioic acid which leads me to believe one of two things.

1) based on alphabet
2) error on their part?

 

[drat]

Took this post out 'cause I was wrong. Don't want people confused. 😀

 

[eric275]

The priority isn't assigned based on alphabetical order. I'm sure it was an error on their part...I'm a chemist and I found at least a half dozen errors in the Kaplan blue book, so you're right to go with your gut on this one. I doubled checked this with a PhD chemist a few minutes ago and he said the IUPAC name for your original question is 5-methyl-2-propyl as well for the same reasons we talked about earlier (3 carbons is > than 1 carbon)

Just to make sure that my thinking is correct on this, you number the substituent groups by size, so the longer alkane substituent gets the lowest possible number, but when actually writting down the name you put them in alphabetical order, correct?

 

[HBomb]

Personally, I think it's by alphabetical order and not by the number of carbons in the substituent groups. Both substituent groups are alkanes, so no one group out-ranks the other. You wouldn't use the number of carbons because you use that to determine the base chain (in this case 6 carbons for hexandioic acid).

You would use alphabetical order to name the substituent groups. Then methyl gets the 2 because happens to come before propyl alphabetically. This is an implied step, which is not too well outlined in any of my OChem texts, but if you have the option of ascending/descending numbering, like in this case, you want to use ascending order.

H.

 

[drat]

Wrong AGAIN! Just to clarify:

When the substituents aren't the same, number the carbons so the side chain that comes first alphabetically (in this case methyl before propyl) has the lower # assigned to it.

drat!

 

[HBomb]

..."end of discussion". Yeah, lovely...as if you're the end all, know all. You're a chemist...yada yada yada. I've asked these PhD's yada yada yada. But where's your proof?

Sorry, but I'm a skeptic. I've been searching and searching (through college texts and the web <as if that's super dependable> for an example), trying to do my due diligence, and I've come up with this.
http://www.acdlabs.com/iupac/nomenclature/79/r79_36.htm
Rules 2.3, 2.3(i) and 2.4
It still a little hard to interpret, but I think it points my way. I'm not saying the internet is proof of anything. I certainly wouldn't say it's now "end of discussion". Everything is up to interpretation, and I certainly can be wrong. But in this case, I still think I'm right.

 

[DrTacoElf]

Well based on this you can't really Prove anything because it adheres to alphabetical and what drat said

And even with this you still can't prove anything. But this leads me to believe something. When two alkyl groups have the same number of carbons and are at equivalent positions, the one which is more highly substituted to the attached carbon (to main chain) i.e. t-butyl versus butyl, tert-butyl would be cited first (remember tert isn't included when alphabetizing).

 

[DrTacoElf]

Just something to think about here. Priority to stereocenters is assigned via CIP system described below. So its likely drat is correct (in my view at least)


If two atoms attached to the chiral center have the same atomic number, then the sum of the atomic numbers of the atoms one bond further from the chiral center are totalled, and so on progressing out from the chiral center until one branch or the other originating at the chiral center is found to have higher priority. (If no such difference is found, then the carbon in question is not, indeed, a site of chirality)

 

[HBomb]

I've found more examples.

In my Wade OChem college text, it lists:
cis-1-ethyl-4-isopropylcyclodecane
cis-1-ethyl-3-propylcyclopentane

Only way this happens is because ethyl is listed before propyl or isopropyl by alphabetical order and then assigned numbers because of their equivalent positions.

My references are Wade, 4th ed, p. 129 and OChem Solution Manual to Wade, Simek, 4th ed, p. 52.

 

[DrTacoElf]

At this point i'm just going to assume either alphabet or drat's system and try to eliminate answer choices. My guess is this is totally unlikely to show up anyway, back to studying stuff that counts 😀

 

[HBomb]

...So its likely drat is correct (in my view at least)

Now I know what Marsha Clark and Chris Darden felt like...all the evidence, but the jury still doesn't believe you!!!

 

[DrTacoElf]

Now I know what Marsha Clark and Chris Darden felt like...all the evidence, but the jury still doesn't believe you!!!

Actually the jury might have changed its mind 😀

http://science.csustan.edu/nhuy/chem3010/handouts/HandoutIVNamecyal.htm

Look at 4.

 

[drat]

I was boiling. I was so frustrated you guys didn't believe me...particularly HBomb. But I am not prepared to swallow my pride and admit I'm wrong.

"If the substituents are not identical, they are ordered alphabetically."

From the McMurray text book. I am now on my way to tell everyone I work with the proper way to name chemicals. Up until this point, I thought I knew everything. I stand corrected.

drat!

 

[HBomb]

drat,

Hopefully, we're all taking this in stride and good fun. I too was boiling and frustrated...and I spent at least an hour trying to research a rebuttal. I hold no hard feelings, and I hope you don't either.

Regards,
H.

 

[1FutureDDS]

Um, Of course propyl is three straight carbons and isopropyl is hooked to center of the three, I had no idea what this guy was asking, and where ethyl was even coming from. I enjoy your anger!

By the way, the way I was taught, Adipic Acid was the name we always went by.

 

[drat]

drat,

Hopefully, we're all taking this in stride and good fun. I too was boiling and frustrated...and I spent at least an hour trying to research a rebuttal. I hold no hard feelings, and I hope you don't either.

Regards,
H.

Oh yeah, no hard feelings. I've just been walking around for the past day with a bag over my head.

As an aside, since learning the "truth," I have literally asked a dozen chemists that question -- whether they would label the propyl as 5 or 2...Not one (NOT A SINGLE PERSON!) said "5!" This time, I got to correct them and look like the smarty pants. 😉

Thanks for the education, HBomb and FutureDDS. 👍