# IUPAC Nomenclature of a dioic acid

I have to name the following organic cpd according to IUPAC.

My attempt: I am unable to select a parent carbon chain as there are 2 carbon chains possible and I don’t know how do we proceed in such a type of compound.

According to the key the answer should be 3,3’ -[oxy bis(ethyleneoxy)]dipropanoic acid Now, this seems certainly wrong to me as there is no double bond in the carbon chain so ‘ene’ must not be there, or am I missing out on something.

PubChem gives the name of the cpd as 3,3'-((Oxybis(ethane-2,1-diyl))bis(oxy))dipropanoic acid I would be glad if somebody could explain the reason behind this nomenclature.

Thank You!

• Note that the retained name “ethylene” for $\ce{-CH2-CH2-{}}$ was still included in the 1998 Guide to IUPAC Recommendations. According to the current (2013) IUPAC Recommendations, the preferred prefix is “ethane-1,2-diyl”. – user7951 Sep 21 at 14:58
• okay i get it now why ethylene is used. But i still don’t understand the nomenclature of the ether part. Could you please explain that along with the choice of parent carbon chain? – rockin numbers Sep 21 at 15:06

According to the current version of Nomenclature of Organic Chemistry – IUPAC Recommendations and Preferred Names 2013 (Blue Book), a structure with two or more identical units that are linked by di- or polyvalent groups can be named in two ways:

• by ordinary substitutive nomenclature, in which one of the parent structures is chosen as the senior parent structure and the remainder of the structure is expressed by substituent prefixes
• by multiplicative nomenclature, in which two or more parent structures are connected by symmetrical or unsymmetrical single or concatenated substituent groups

Both methods yield correct names, which may be used in general nomenclature. However, the IUPAC recommendations define a preferred IUPAC name (PIN), which is the name preferred among two or more names generated from two or more IUPAC recommendations.

P-45.1 MULTIPLICATION OF IDENTICAL SENIOR PARENT STRUCTURES

P-45.1.1 Multiplicative nomenclature is senior to substitutive nomenclature for generating preferred IUPAC names to express multiple occurrences of identical senior parent structures, other than alkanes, in the name of the parent structure (see P-51.3.1). In most cases multiplicative names are shorter than regular substitutive names. A preferred IUPAC name is generated by multiplicative nomenclature when the following criteria for its use are met (see P-51.2.3).
(1) the linking bonds (single or multiple) between the central substituent group of the multiplicative group and all subsequent structural units are identical; and
(2) the multiplicative groups, other than the central multiplicative group, are symmetrically substituted; and
(3) the locants of all substituent groups on the identical parent structures, including suffix groups, are identical.

When these conditions are not met, substitutive nomenclature generates preferred IUPAC names.

The given structure fulfils these requirements; therefore, the preferred IUPAC name is generated by multiplicative nomenclature as follows.

P-15.3.1.3 Multiplicative name formation
Multiplicative names are formed in accordance with the number of occurrences of identical structural units as defined in P-15.3.1.1 and the relationship of the linking multiplicative substituent group to the identical structural units.
When a compound contains identical structural units as defined in P-15.3.1.1 linked by a symmetrical simple, compound, complex, or concatenated multiplicative group (a di- or polyvalent substituent group), it is named by stating successively:

(a) the locants for the positions of substitution of the linking multiplicative substituent atom or group to the identical parent structural unit (the locant 1 is omitted when alone in the name of a mononuclear parent hydride);

Here: 3,3'

(b) the name of the linking multiplicative substituent atom or group;

Here: oxybis(ethane-2,1-diyloxy) for $$\ce{-O-CH2-CH2-O-CH2-CH2-O-{}}$$

(c) the numerical prefix ‘di’, ‘tri’, etc.; and/or ‘bis-‘, ‘tris-‘, etc., with no elision of the final vowel before the name of the identical parent structural unit;

Here: di

(d) the name of one of the identical structural units including the principal characteristic group and substituents, if any, enclosed in appropriate enclosing marks (see P-16.5).

Here: propanoic acid

The numbering of the identical parent structural unit is retained and, when there is a choice, the locants of the point of substitution by the linking multiplicative substituent groups on the identical parent structure are as low as possible.

Here: 3,3'-(…)dipropanoic acid

Therefore, the preferred IUPAC name is 3,3'-[oxybis(ethane-2,1-diyloxy)]dipropanoic acid.

By way of comparison, the Blue Book contains the similar example 2,2'-[oxybis(ethane-2,1-diyloxy)]diacetic acid.