| Author | Chemistry nomenclature |
|---|
Whenever naming a organic compound with 3 chain terminating function groups , for example -->
Propane-1 , 2 , 3 -tri-carboxylic acid , why don't we include the carbon on carboxylic acid?
CH2 - CH - CH2
|......|....|
X......X....X
X is CH3COO , the dots are so the structure doenst loses shape
So what my doubt basically is (to make things clear) , why we take
CH2 - CH - CH2 as the word root chain and don't include the carbon in CH3COO (like we can make longest chain of pent yet we choose prop) :3
Thanks in advance)) |
Uff I hope you understand that each CH2 and CH connected with CH3COO
The structure got a bit messy |
| IUPAC nomenclature calls for the parent chain to have naming priority before any functional group attached is named. This is because you would otherwise have to name the oxygens along with butane being the "parent" chain. Also, calling it butane with two oxygens attached would not respect the chemical's properties; it is first and foremost a carboxylic acid in terms of reactivity with other chemicals. It's much easier to just start with the parent chain (propane) and then tell you where the functional group is placed. |
| I slightly misunderstood the drawing. I believe you're thinking of propanoate? |
like we can make longest chain of pent yet we choose prop
Even if you did, longest chain would have 4 carbon not pent like you said; you would choose either of the terminal carboxyl group and the remaining 3 from parent chain. What you are proposing makes things unnecessarily complicated - 3,4-carboxy-1-butanoic acid still tells you that it is a carboxylic acid but here you chose 2 of the 3 main functional groups with same priority as your substituents for naming, and selected the terminal carboxyl group to get the longest chain nomenclature.
I am not an expert on this (rather it would be accurate to say i suck at this) but there seem to be 2 reasons based on common sense;
1. All 3 carboxyl are identical and should carry the same priority so you cannot just select one as main functional group and the remaining two as substituents for the sake of choosing the longest chain.
2. Tricarboxylic acid works better as the identifying nomenclature. It tells you the same information in a less complicated way.
Perhaps unrelated, but when you go on and think about things from a practical standpoint, the number of carboxyl groups has very real significance in describing biological processes and in those cases you cannot argue that tricarboxylic acid should be the preferred nomenclature for the compound rather than the alternative you suggest. To give an example you might have encountered already is when you are trying to determine the quantity of energy released during oxidation of several compounds in our body is a matter of knowing exactly how many carboxyl groups are present in the byproducts. Meaning, whether your products comprise of a number of monocarboxylic acids, dicarboxylic, tri, etc. |
When you first learn naming in chemistry you focus on the longest chain as this is the starting point and when naming simple hydrocarbons or molecules with minimal amounts of functional groups it works. However as molecules become more complicated so do the rules to allow a systematic and therefore consistent approach.
These rules are artificial constructs that have been agreed so as to allow molecules to be identified with clarity and appropriate focus on their chemical characteristics (ie which functional groups are going to be most significant in understanding its action)
Their logic therefore need not be consistent all the way through and will have different clauses for dealing with certain scenarios.
This is one of those where things start deviating to retain clarity and use.
This link may be useful for a specific example
https://chemistry.stackexchange.com/questions/51335/iupac-name-for-citric-acid |
These rules are artificial constructs that have been agreed so as to allow molecules to be identified with clarity and appropriate focus on their chemical characteristics (ie which functional groups are going to be most significant in understanding its action)
Their logic therefore need not be consistent all the way through and will have different clauses for dealing with certain scenarios.
Thats perfectly said, Miles :)
Science is never 100%; never devoid of exceptions. Mostly what you study will always start with a basic rule or a general rule - such as the octet rule for example. Then within no time, you will learn about an exception. And following that, there will be so many of them that explaining these exceptions with information new and old will become what it means to master the subject, not the original so-called rule which held so much importance when you first started ;) |
Thank you everyone and my bad lol , I said CH3COO instead of COOH :3 , but miles and VV got me right :3
Thanks VV , miles , techy ;) |
