# IUPAC way of writing prefix of alkyl isomers of an ether

Consider this compound:

I am able to identify the base chain as propane. But, I am having trouble naming the other side of the chain. Will it be named as:

1. 2-(isopropoxy)propane,
2. 2-[(propan-2-yl)oxy]propane, or,
3. 2-(2-propoxy)propane

What is the preferred IUPAC way for such a naming of isomeric alkyl groups?

• why is option 2 preferred over "1-methylethyloxy"? – Eashaan Godbole Mar 4 '18 at 19:36
• @EashaanGodbole I think "1-methylethyloxy" is wrong because there is no principal chain (i.e. no "ethane"/"propane"/etc.) – Gaurang Tandon Mar 5 '18 at 1:43
• @GaurangTandon I asked because we used "1-methylethyl" and "1,1-dimethylethyl" for isopropyl and tert-butyl respectively as the point of connection of the side chain is often considered the "1'" carbon. – Eashaan Godbole Mar 5 '18 at 12:15
• @EashaanGodbole As far as I can guess this will lead you to the common name of this compound, diisopropyl ether – Gaurang Tandon Mar 5 '18 at 12:39

According to Nomenclature of Organic Chemistry: IUPAC Recommendations and Preferred Names 2013 (Blue Book) (P-63.2.2.2), the preferred prefix for the substituent $\ce{(CH3)2CH-O\bond{-}}$ is 'propan-2-yloxy'. Both 'isopropoxy' and '1-methylethoxy' remain permissible in general nomenclature.

Correspondingly, the PIN of the symmetrical ether $\ce{[(CH3)2CH]2O}$ is 2-[(propan-2-yl)oxy]propane.

I'm quite sure the double parentheses are required based on other similar examples given in the Blue Book, but am not 100% sure of the rationale for it and would be grateful if somebody could confirm that. I'm thinking one set comes from P-16.5.1.1 as 'propan-2-yloxy' is a compound substituent, and one more comes from P-16.5.1.2 to separate the locant '2' in 'propan-2-yl' from the remainder of the name, but don't quote me on that.

• You may have found another bug, e.g. 2-chloro-4-(5-chloropyridin-2-yloxy)pyridine (P-15.3.2.4.2) was fixed to 2-chloro-4-[(5-chloropyridin-2-yl)oxy]pyridine in the errata. – mykhal Aug 2 '18 at 19:29
• @mykhal Mmhmm, there is a similar erratum on pg704. I’m not sure whether anything else is actually wrong, though. Maybe the prefix should be named ‘(propan-2-yl)oxy’ instead of ‘propan-2-yloxy’. However, the entire section on alkoxy prefixes doesn’t have that set of parentheses (P-63.2.2.1.1), so I’m inclined to believe they’re right. – orthocresol Aug 3 '18 at 4:41

Maybe not preferred officially in this case, very nice IUPAC names are the symmetry-based ones (multiplicative name or ether functional class names):

• 2,2′-oxydipropane
• di(propan-2-yl) ether
• diisopropyl ether

(One might be tempted to replace "di" with "bis", but it should not be the case for this simple substituent.)

2-[(propan-2-yl)oxy]propane PIN name in orthocresol's answer is correct. For symmetrically characteristic-group-disubstituted derivatives, above mentioned name type is used, e.g. $$\ce{HO-C(CH3)2-O-C(CH3)2-OH}$$ 2,2′-oxydi(propan-2-ol).

The backbone has 3 carbons so it is -propane. On the middle carbon (carbon number 2), there is a branch consisting of an oxygen atom and further branching off to three methyl groups. Three is prop- and oxygen is -oxy, so we have propoxy-. So your second option is discarded.

So currently we have $\text{O-CH}_3\text{-CH}_3$ with the $\text{CH}_3$ next to the $\text{O}$ branching off to a methyl group. In other words, this $\text{CH}_3$ is in the middle, with only one branch, so we call it iso-.

As said previously, the carbon number 2 of the backbone has a branch, so the IUPAC name for the compound is 2-isopropoxypropane (your first option) and is more commonly known as diisopropyl ether.

• Note that, according to current (2013) IUPAC recommendations, the prefix ‘isopropoxy’ is retained for use only in general nomenclature. – Faded Giant Feb 2 '18 at 17:44