According to the IUPAC rules of nomenclature, alkenes have higher priority over rings but what if the ring also contains a double or a triple bond?

For eg:

Organic compound

Is this compound going to be named as 1-(2-chlorocycloprop-2-enoxy)propene or 1-chloro-3-propenoxycyclopropene?

  • 1
    $\begingroup$ "According to the IUPAC rules of nomenclature, alkenes have higher priority over rings" – where did you find this rule? It's not in the current IUPAC recommendations. $\endgroup$ – Loong May 6 at 16:21
  • $\begingroup$ @Loong Check this nomenclature for eg images.app.goo.gl/C4EEzNMs5zoy2BmV6 $\endgroup$ – Neha May 6 at 16:56
  • $\begingroup$ or this one images.app.goo.gl/FhmRDtSUG8wZ72LY7 they clearly exhibit that rings have lesser priority than alkenes (in my question I asked about the unsaturated rings) $\endgroup$ – Neha May 6 at 16:58
  • 1
    $\begingroup$ Both examples "1,2-dicyclopropylethene" and "2-cyclopropylpropene" are not preferred IUPAC names. $\endgroup$ – Loong May 6 at 17:33
  • $\begingroup$ I'm unaware then but in all my books the nomenclatures are done in a similar way. $\endgroup$ – Neha May 7 at 2:39

The name given by ChemDraw is: (E)-1-chloro-3-(prop-1-en-1-yloxy)cycloprop-1-ene.

The ring is determined to be the parent structure. This is rationalised in the 2013 edition of the IUPAC Blue Book on organic nomenclature by the following rules (pg 451):

P- Systems composed of rings and chains (exclusive of linear phanes)

Two methods are recognized to name systems composed of rings and chains (exclusive of linear phanes).

(1) Within the same class, a ring or ring system has seniority over a chain. When a ring and a chain contain the same senior element, the ring is chosen as parent. Rings and chains are chosen regardless of their degree of hydrogenation. As a consequence, this approach prefers the choice of a ring over a chain in systems composed of cyclic and acyclic hydrocarbons

(2) The context may favor the ring or the chain, so that, for example, substituents may be treated alike or an unsaturated a cyclic structure may be recognised, or the one chosen has the greater number of skeletal atoms in the ring or in the principal chain of the acyclic structure.

So either the chain or ring may be used as the parent for the name, but the ring will define the preferred IUPAC name.

The preference of ring over chain is further clarified in the following rule (pg 596):

P-52.2.8 Selection between a ring and a chain as parent hydride

Within the same heteroatom class and for tha same number of characteristic groups cited as the principal characteristic group, a ring is always selected as the parent hydride to construct a prefered IUPAC name. In general nomenclature, a ring or a chain can be a parent hydride (see P-

All emphasis added.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.