Vol. 24, No. 6
the Revised Red and Blue Books and Preparing for IUPAC Preferred Names
2001 IUPAC General Assembly in Brisbane, Australia, the former Commissions
on Nomenclature of Organic and Inorganic Chemistry (CNOC and CNIC, respectively)
began discussions on a project to avoid conflict between the preferred
names for organic nomenclature and the revision of inorganic nomenclature.
The project arose from the fact that CNOC was working on a revision
of the "Blue Book" and its supplemental Guideto
become one revised Blue Bookand CNIC was working on a revision
of the "Red Book." (See box below.)
of Inorganic Chemistry (Recommendations
1990), Leigh, G. J. (Blackwell Science, 1990, ISBN 0-63202-4941)
Nomenclature of Organic
Chemistry, Rigaudy, J. and Klesney, S. P. (Pergamon, 1979,
to IUPAC Nomenclature of Organic Compounds (Recommendations
1993), Panico, R.; Powell, W.H.; and Richer, J-C. (Blackwell
Science, 1994, ISBN 0-63203-4882)
revisions of these books should be completed in 2003.
for alignment of these two areas of nomenclature was clear given that
the revised Blue Book had as a main feature the introduction of preferred
names. That is, among the various names that can often be constructed
for a given compound using the nomenclature principles endorsed by IUPAC,
one name was to be designated the preferred one, ready to offer to users
who would like to have always just one name. It turned out that a number
of inorganic compounds were also represented with preferred names in
the drafts of the revised Blue Book. This requires a bit more of an
principle of organic nomenclature as laid out in the Blue Book is that
of naming compounds on the basis of parent compounds by applying standard
operations, mainly substitution, whereby the parents are modified in
order to arrive at the structure of the compound being named. This is
substitutive nomenclature. (Examples include 'trichloroacetic
acid', where the numerical prefix 'tri' together with the prefix 'chloro'
indicates substitution of the three methyl group hydrogen atoms in acetic
acid by chlorine, and 'butan-2-ol', obtained by modifying the parent
name 'butane' by introducing the 'ol' suffix and the locant '2'.)
compounds are hydrides, such as butane and naphthalene, and a number
of them are inorganic hydrides, i.e., they do not contain carbon, such
as gallane (GaH3) and selane (SeH2). Other parent
compounds are organic or inorganic oxoacids, such as acetic acid, CH3COOH,
and phosphonic acid, PH(O)(OH)2. The parent names are important
for the naming of organic derivatives and thus had a prominent plae
in the drafts of the revised Blue Book. However, the former Commission
on Nomenclature of Inorganic Chemistry felt that it was premature to
designate the inorganic parent names themselves as preferred. The revised
Red Book will not contain preferred names for the simple reason that
the working group does not think the chemistry community is ready to
select preferred names for inorganic compounds at large. The choice
will often be difficult for inorganic compounds; compare examples given
problem of selecting parent structures and the desire to extend the
naming principles of coordination chemistry to broader areas of inorganic
chemistry had led inorganic chemists to favor additive nomenclature
over substitutive nomenclature. Additive names specify compounds
according to the way they are formally assembled from particular building
blocks (central atoms and ligands).
example may illustrate the general points made above. Take a neutral
molecular compound like PCl5. Traditionally, it would be
named 'phosphorus pentachloride'. This type of name will be called a
compositional name (of binary type) in the revised Red Book.
By systematic additive nomenclature, its name is 'pentachloridophosphorus'.
(In the revised Red Book, ligands in additive names now carry the 'ido'
ending rather than just the 'o' ending used before.) By substitutive
nomenclature, starting from the parent hydride PH5, its name becomes
which of the three names does one want to choose as the preferred one?
The first name is what everybody uses. The next two belong to two different
systematic approaches, one of which prevails in inorganic chemistry,
the other in organic chemistry. Neither of the two systems can be extended
to all of chemistry without creating sometimes extremely cumbersome
and unfamiliar-looking names. Division lines have to be drawn through
chemistry and most probably also through inorganic chemistry, and this
will require more careful thinking than the Red Book group presently
has time for. It is generally anticipated in IUPAC that a new project
will be set up to address the issue of inorganic preferred names once
the Red Book revision has been finished.
compounds (compounds with a bond from a carbon atom to a metal atom),
the question arises whether to use substitutive or additive nomenclature.
Consider Pb(C2H5)4 . By substitutive
nomenclature, the name is 'tetraethylplumbane', with reference to the
parent hydride plumbane, PbH4, and the additive name is 'tetraethyllead'
(or tetraethanidolead). Which one should be preferred? In the alignment
project, there was support for a proposal made by W. H. Powell that
prescribes where to draw the line between organometallic compounds that
will have preferred substitutive names and those that will have preferred
additive names. This proposal is being discussed among members of the
Chemical Nomenclature and Structure Representation Division (Div. VIII)
Advisory Committee and will probably be incorporated into the Blue Book
and Red Book more or less in its present form.
the 'ane' hydride names are needed for a number of preferred organometallic
names and, within inorganic chemistry, for constructing substitutive
names that may or may not end up being preferred names in the future,
depending on where the borderline is drawn between substitutive and
additive nomenclature. Therefore, those parent hydride names will be
given both in the Red Book and Blue Book. As an interesting aside, there
was a problem in giving an 'ane' name to indium trihydride, InH3.
The name 'indane' is occupied for a particular parent ring system in
organic chemistry. The name 'indiane' would present problems when derived
names containing the sequence ' indiene' could be misinterpreted as
indicating the presence of two double bonds. The latter is maybe less
of a problem, but nevertheless, the proposal being considered at present
is the name 'indigane', which should not lead to confusion and which
is in accord with the historical origin of the word 'indium' as related
to an indigo-blue spectral line.
are organic derivatives of inorganic parents that present a particular
problem. Consider a compound like C2H5As(Cl)(OH)S.
It could be named substitutively on the basis of the parent hydride
AsH5, l5-arsane. It
could also be named additively. However, neither of these options is
chosen in practice. There is an extensive system of names for derivatives
of certain inorganic oxoacids whereby this compound would be named 'ethylarsonochloridothioic
acid'. This name is based on the substitution of a hydrogen atom by
an ethyl group, and the replacement of the oxo group and one hydroxy
group in the parent arsonic acid, HAs(O)(OH) 2, by sulfur
and chloride, respectively. There are related oxoacids called
arsenic acid or arsoric acid
arsenous acid, arsorous acid
- AsH2(OH) arsinous acid
are all needed as parents when naming various organic derivatives according
to this particular type of nomenclature called functional replacement
nomenclature. The problem with these oxoacid names from the inorganic
point of view is that they stem from an antiquated system for indicating
oxidation states using the endings 'ous' and 'ic'. Compare with names
like 'ferrous' and 'ferric', which were officially abandoned about 50
years ago (although they are difficult to get entirely rid of!) in favor
of indications of oxidation state by Stock numbers (iron(II) oxide,
etc.) or by charge numbers (iron(2+) oxide, etc.), because the 'ous'
and 'ic' names were ambiguous. (The name 'ferric' only says it is a
higher oxidation state than 'ferrous', but not which oxidation
state.) There is no way to know what 'arsinous acid' is unless you are
given a table of formulas to memorize it from, whereas the additive
name 'dihydridohydroxidoarsenic', although a bit longer, immediately
tells you that the structure is AsH2(OH). (But the latter
name cannot be used as a parent name in functional replacement nomenclature.)
therefore not acceptable to institute the 'ous' and 'ic' names as preferred
names for the oxoacids themselves. The agreement was made in the alignment
project that these names are kept available as parent names for giving
preferred names to the organic derivatives, but no decision was made
regarding the status of the parent names themselves. Having said this,
a number of names are of course in daily use all over chemistry (e.g.,
sulfuric acid, arsenic acid) and the Red Book team has no intention
to prohibit the use of those well-entrenched names. They will be given
in the revised Red Book alongside systematic additive names (which may
or may not end up being the preferred ones later).
Book chapter on substitutive nomenclature, in a draft form, was also
reviewed in the alignment project. The process here consisted not just
in naming specific compounds, but in inspecting the rules and ensuring
they were consistent with the rules for substitutive nomenclature given
in the Blue Book. And finally, a number of names of organic ligands
needed for the Red Book were checked for consistency with the (new)
Blue Book rules.
name of this
project, #2001-031-1-800, is "Alignment of nomenclature in
areas of overlap between the preferred names for organic nomenclature
and the revision of the nomenclature of inorganic chemistry." The
project task group consisted of Henri Favre and Warren H. Powell, who
represented the task group revising the Blue Book that will replace
the 1979 Blue Book and the 1993 Guide; Gerry P. Moss, who represented
the IUBMB-IUPAC Joint Commission on Biochemical Nomenclature; and Richard
Hartshorn and myself (task group chairman), who represented the team
working on a revision of the Red Book that will replace the 1990 version.
At its meetings, the group also had participation from Neil G. Connelly,
editor in chief of the revised Red Book; Herbert D. Kaesz, the last
chairman of the former Commission on Nomenclature of Inorganic Chemistry
where the Red Book revision project was initiated; and Alan D. McNaught
(ADM), president of Division VIII on Chemical Nomenclature and Structure
Representation. ADM also hosted the meetings at the facilities of The
Royal Society of Chemistry in Cambridge.
like to thank Warren H. Powell and Alan McNaught for helpful comments
on a draft of this article.
Damhus <[email protected]> is the former secretary of CNIC
(2000-1001), a current member of Division VIII Advisory Committee, and
also a member of the Interdivisional Committee on Terminology, Nomenclature,
and Symbols. He works at Novozymes A/S, Denmark.