Multiplicative names

Have a look at the structure (a).

(a)

N,N-bis(carboxymethyl)glycine (substitutive) N,N,N-tris(carboxymethyl)amine (substitutive) 2,2′,2″-nitrilotriacetic acid (multiplicative)

Its preferred IUPAC name (PIN) is N,N-bis(carboxymethyl)glycine. This is a classical substitutive name based on functional parent glycine (b). However this name fails to convey the structural feature of (a) that is obvious even to a non-chemist, viz. its threefold symmetry. Alternatively, we can think of (a) as a tertiary amine, that is, ammonia in which each hydrogen atom is substituted by a carboxymethyl group: N,N,N-tris(carboxymethyl)amine. This name clearly tells us that there are three identical groups, but it probably will be frowned upon because carboxy group is senior to amino.

It also can be given a name that reflects both symmetry and the fact that it is a carboxylic acid.

Using acetic acid (c) as a functional parent, (a) could be named 2,2′,2″-nitrilotriacetic acid, where ‘nitrilo’ is the trivalent group –N< and locants ‘2,2′,2″’ indicate that all three acetic acids are linked to it via carbon-2^*. Prime and double prime are added to differentiate between the locants of the identical units.

(b)	(c)

glycine (trivial, functional parent) acetic acid (trivial, functional parent)

This naming method is known as multiplicative nomenclature, which, in my opinion, is a bit of a misnomer. Every type of chemical nomenclature uses multiplicative operations where there are two or more identical groups. What is referred to as “multiplicative nomenclature” is a subtype of substitutive nomenclature based on two or more identical parent structures linked by di- or polyvalent substituents [1, p. 69]. (Compare that with conjunctive nomenclature which is based on two different parent structures.)

A typical multiplicative name consists of

1. at least two locants l and m, with at least one of them primed, followed by
2. the di- or polyvalent multiplicative substituent, or linker, followed by
3. the numerical prefix x^†, followed by
4. the name of one of the identical parent structures:

l,...,m′,...-linkerx parent

Within a multiplicative name, the number of locants should match the valency of the linker and the numerical prefix. For example, “2,2′,2″-nitrilotriacetic acid” has three locants (2,2′,2″), trivalent linker (nitrilo) and the numerical prefix ‘tri’. We can say that multiplicative names have built-in redundancy.

The choice between “simple” or “multiplicative” variety of substitutive nomenclature boils down to the choice of the parent.

(d)

triphenylmethane (substitutive) 1,1′,1″-methanetriyltribenzene (multiplicative)

Consider the structure (d). If we think that its parent is methane, we call it triphenylmethane; if we prefer benzene, we can go for a multiplicative name 1,1′,1″-methanetriyltribenzene. Both names tell us that it has three identical parts, but the former one is significantly shorter, so I’d rather stick with triphenylmethane.

In spite of their aforementioned redundancy, multiplicative names are often shorter than their substitutive synonyms. At least, on paper (or computer screen): try saying aloud all these primes, double primes, etc. and you might change your mind.

(e)

DDT (acronym, from dichlorodiphenyltrichloroethane) 1-chloro-4-[2,2,2-trichloro-1-(4-chlorophenyl)ethyl]benzene (substitutive) 1,1′-(2,2,2-trichloroethane-1,1-diyl)bis(4-chlorobenzene) (multiplicative)

The parent structures do not have to be linked to the multiplicative substituent identically:

(f)

1-(naphthalen-2-ylmethyl)naphthalene (substitutive) 1,2′-methylenedinaphthalene (multiplicative)

The linkers do not have to be symmetrical either:

(g)

chlorotrianisene (INN) 1,1′,1″-(2-chloroethene-1,1,2-triyl)tris(4-methoxybenzene) (multiplicative)

Linkers also can be cyclic, although in these cases “caution” is advised [2].

(h)	(i)

POPOP (acronym, from the first letters of phenyl and oxazole) 2,2′-benzene-1,4-diylbis(5-phenyl-1,3-oxazole) (multiplicative) 4,4′,4″,4‴,4⁗-pentarsolane-1,2,3,4,5-pentaylpentakis(2-aminophenol) (multiplicative)

What if one of the identical units gets modified, say by substitution, and thus ceases to be identical — can we still use multiplicative names?

(j)	(k)

2-bromo-4-[2-(4-hydroxyphenyl)propan-2-yl]phenol (substitutive) 2-bromo-4,4′-(propane-2,2-diyl)diphenol (multiplicative + substitutive) bisphenol A (trivial) 4,4′-(propane-2,2-diyl)diphenol (multiplicative)

This is the case of the structure (j) which differs from bisphenol A (k) by the presence of a bromine atom in one of the phenol units. As (k) is named multiplicatively 4,4′-(propane-2,2-diyl)diphenol, (j) can be named 2-bromo-4,4′-(propane-2,2-diyl)diphenol. As you can see, a substitutive modification (‘2-bromo’) of a multiplicative name gives a name that is shorter and more elegant than its “simple substitutive” name, 2-bromo-4-[2-(4-hydroxyphenyl)propan-2-yl]phenol.

Some other times, neither substitutive nor multiplicative names are the shortest.

(l)

3-(prop-2-en-1-yldisulfanyl)prop-1-ene (substitutive) 3,3′-disulfanediylbis(prop-1-ene) (multiplicative) diallyl disulfide (functional class)

For instance, for the structure (l) the shortest unambiguous name is radicofunctional one, diallyl disulfide.

*	It is difficult to think of any other way of attaching nitrogen to acetic acid without changing its name, so we can safely omit the locants and call (a) simply nitrilotriacetic acid. However, in preferred IUPAC multiplicative names locants are always cited [1, p. 30].
†	According to IUPAC rules, the numerical prefixes ‘di’, ‘tri’, ‘tetra’, etc. have to be used unless that could lead to ambiguity; in the latter case, prefixes ‘bis’, ‘tris’, ‘tetrakis’, etc. are employed [1, p. 81], while CAS names always use prefixes ‘bis’, ‘tris’, ‘tetrakis’, etc. [2].

References

1. Favre, H.A. and Powell, W.H. Nomenclature of Organic Chemistry: IUPAC Recommendations 2013 and Preferred IUPAC Names. Royal Society of Chemistry, Cambridge, 2014.
2. Bünzli-Trepp, U. Systematic Nomenclature of Organic, Organometallic and Coordination Chemistry. EPFL Press, 2007, pp. 32—36.