Chemistry
“Methylenebis(oxy)” vs. “oxymethyleneoxy” or similar divalent group names used when bound to single moiety
Step-by-step chemistry solution: “Methylenebis(oxy)” vs. “oxymethyleneoxy” or similar divalent group names used when bound to single moiety
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1. What the question is asking (in plain language)
The student wants to know:
- When we have the –O‑CH₂‑O‑ fragment (two oxygen atoms linked by a methylene carbon), can we call it “methylenebis(oxy)” only when the fragment bridges two different parts of the same molecule (e.g. a 1,2‑substituted benzene)?
- Or can the same fragment also be called “oxymethyleneoxy” (or a similar name) when it is attached once to a single parent structure?
- In other words – what are the IUPAC‑approved ways of naming this fragment in the two different situations, and why does the Wikipedia entry 1,2‑[methylenebis(oxy)]benzene look acceptable?
2. Step‑by‑step answer
Step 1 – Identify the fragment and the two possible connection patterns
O–CH2–O
- Bridging (bidentate) connection – the two O atoms are each bonded to a different atom of the parent (e.g. two adjacent carbons of a benzene ring).
- Monodentate (substituent) connection – only one of the O atoms is bonded to the parent; the other O is “inside” the substituent.
The IUPAC “Blue Book” treats these two cases differently.
Step 2 – IUPAC name for the bridging case
Rule (Blue Book 2013, P‑15.3.1.2.2.1):
When the same multiplicative group occurs more than once in a single substituent, the group is written once and preceded by a multiplicative prefix (bis, tris, …). The whole group is placed in parentheses and the locants of the attachment points are written before the parentheses.
The fragment –O‑CH₂‑O‑ is the *bis(oxy) of a methylene bridge, therefore the systematic name of the fragment itself is methylenebis(oxy).*
Putting it on a parent:
parent‑locant1,parent‑locant2‑(methylenebis(oxy))
Example – benzene with the fragment joining C‑1 and C‑2:
1,2-(methylenebis(oxy))benzene
The same structure is also known as the fused‑ring system 1,2‑benzodioxole (the preferred IUPAC name for the heterocycle). Both names are correct; the “‑(methylenebis(oxy))‑” version follows the substitutive‑nomenclature rules and is therefore allowed.
Step 3 – IUPAC name for the monodentate (single‑attachment) case
When the fragment is attached through one of its oxygens, the IUPAC “substituent” name is built from the parent of the fragment (oxymethylene) and the atom by which it is attached (oxygen). The result is the oxymethyleneoxy prefix.
- Construction:
| fragment part | IUPAC term | Reason |
|---|---|---|
| –CH₂– attached to O | oxymethylene | carbon attached to oxygen, the carbon bearing the two oxygens is the “oxymethylene” unit |
| the external O that bonds to the parent | ‑oxy | indicates that the point of attachment is an oxygen atom |
Thus the whole substituent is oxymethyleneoxy‑.
Putting it on a parent:
parent‑locant‑(oxymethyleneoxy)
Example – a C₆₀ fullerene bearing the fragment through one oxygen:
1,9-(oxymethyleneoxy)[C60‑Ih][5,6]fullerene
Here the locants (1,9) refer to the two carbon atoms of the fullerene that are linked indirectly through the oxygen of the substituent; the fragment itself is attached only once (through an O).
Step 4 – Why the two names are not interchangeable
| Situation | Correct prefix | Reason |
|---|---|---|
| Bridging (two separate attachment points on the same parent) | methylenebis(oxy) | The multiplicative prefix “bis” tells the reader that the same –O‑CH₂‑O‑ unit is used twice, each time to connect a different atom of the parent. |
| Monodentate (only one attachment to the parent) | oxymethyleneoxy | No multiplicative prefix is needed; the name describes the internal constitution of the substituent (oxymethylene) and the atom that makes the bond to the parent (oxy). |
If you used “methylenebis(oxy)” for a monodentate substituent, the name would incorrectly suggest a second attachment point that does not exist. Conversely, using “oxymethyleneoxy” for a bridging fragment would hide the fact that the fragment links two positions.
Step 5 – Summary of the answer to the original question
- Yes, “1,2‑[methylenebis(oxy)]benzene” (or more formally 1,2-(methylenebis(oxy))benzene) is a perfectly valid IUPAC name for the benzodioxole ring when the –O‑CH₂‑O‑ group bridges two adjacent carbons of benzene.
- The name “oxymethyleneoxy” is not a synonym for “methylenebis(oxy)”; it is the monodentate substituent name that is used only when the fragment is attached through a single oxygen atom.
- Therefore, “methylenebis(oxy)” is suitable only for bridging (bidentate) situations, whereas “oxymethyleneoxy” (or analogous constructions) is used when the fragment is a single‑attachment substituent.
3. Final answer (concise)
- Bridging (two‑point) attachment → methylenebis(oxy), written as locant‑(methylenebis(oxy)) (e.g. 1,2-(methylenebis(oxy))benzene).
- Monodentate (single‑point) attachment → oxymethyleneoxy, written as locant‑(oxymethyleneoxy) (e.g. 1,9-(oxymethyleneoxy)[C₆₀‑Ih][5,6]fullerene).
Thus, “methylenebis(oxy)” is not used for a substituent that is bound to only one moiety; for that case the correct IUPAC prefix is “oxymethyleneoxy”.
4. Common mistakes to avoid
| Mistake | Why it’s wrong | How to fix it |
|---|---|---|
| Using “methylenebis(oxy)” for a monodentate substituent | “bis” implies two identical attachment points; the name would suggest a second, non‑existent bond. | Use the monodentate prefix oxymethyleneoxy (or another appropriate substituent name). |
| Omitting the parentheses (e.g. writing “1,2‑methylenebis(oxy)benzene”) | The parentheses signal that methylenebis(oxy) is a single substituent; without them the name is ambiguous. | Always write locant‑(methylenebis(oxy)) for a bridging group. |
| Swapping the order of the locants and the prefix (e.g. “methylenebis(oxy)‑1,2‑benzene”) | IUPAC requires the locants before the parent name, not after the substituent name. | Write 1,2‑(methylenebis(oxy))benzene. |
| Calling the fused heterocycle “methylenebis(oxy)benzene” without the locants | The fused ring system has its own preferred name (1,3‑benzodioxole); omitting locants loses structural information. | Use the systematic name **1 |
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