Volume 3, No. 2
A chemist-turned-translator, Dr. Claff earned his B.S. and Ph.D. degrees in Organic Chemistry at
M.I.T. in 1950 and 1953. His academic and industrial research experience included the fields of
organosodium chemistry, synthetic rubber, leather tanning and finishing, acrylic and vinyl
polymerization, adhesives for coated abrasives, and flexographic printing inks. His career later
evolved into corporate administration and management in metalworking, heart-lung machines,
biological instrumentation, printing, personnel administration, and paper box manufacturing. His
exposure to such diverse disciplines has been a valuable resource in his career as a freelance
technical translator since 1974.
Dr. Claff and his wife Eleanor make their home in Brockton, Massachusetts, with their Maine coon
cats, DownE and Baxter.
Dr. Claff can be reached at email@example.com
A Translators Guide to Organic Chemical
by Chester E. Claff, Jr., Ph.
Download the zipped version of the first installments of this series, originally published in the Sci-Tech Translation Journal, of the American Translators Association. The file is approximately 87 KB.
Previous installments of this series appeared in the July
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1998, April 1998, July
1998, October 1998, and January 1999 issues of the Translation
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The orderly diversity of organic chemical nomenclature
Reference has been made repeatedly to different systems of
nomenclature (radicofunctional, substitutive, trivial, etc.) and to
the fact that multiple names are often acceptable for the same
compound. This situation is pointedly recognized in the following
advertisement from a recent issue of Chemical and Engineering News:
VII. Alicyclic Compounds (continued)
The concept of chirality is of such current importance in organic
chemistry and medicine that it will be worthwhile to explore the
subject a little further before returning to specific chemical
J.R. Biot in 1815 discovered that many naturally occurring organic
compounds were optically active, i.e. they rotated the plane of
polarized light. The extent of this rotation was expressed in terms
of specific rotation [a]; for example the expression [a]D25 = +n°
means that a (hypothetical) solution of 1 gram of a substance in 1
ml of solution in a tube 10 cm long would rotate polarized light
from incandescent sodium (its so-called D line) by n° to the right
In 1848 Louis Pasteur noticed that certain salts of racemic tartaric
acid crystallized from water in two different mirror-image forms.
When meticulously separated with tweezers, one form proved to be
dextrorotatory and the other levorotatory, with the same but
opposite values of [a]. He called the two isomers d-tartaric acid
and l-tartaric acid, and their racemic mixture dl-tartaric acid.
Some confusion began to reign when the configuration of chiral
centers was sometimes designated by a small capital D or L,
depending on how the configuration of the compound was related to d-
or l-glyceraldehyde. These descriptors no longer always correlated
with the direction of rotation of polarized light, so that D-(+)-,
D-(-)-, L-(+)-, and L-(-)- descriptors were added to indicate this
Cahn, Ingold, and Prelog in 1956 brought some order out of this
chaos by proposing the R,S descriptors discussed in the preceding
part of this series.
We have already shown graphically the three configurations of
1,2-dichlorocyclopentane. Another, more up-to-date depiction of
these three isomers would be:
In these illustrations, the solid wedges indicate bonds that rise
above the plane of the page, and the shaded ones dip below it. This
convention is now universal, and is applied also to fused ring
systems and achiral compounds:
|With this (admittedly tedious) coverage of stereoisomerism behind
us, let's now return to elements other than C, H, O, S, and halides
commonly found in organic compounds.
VIII. Organic Nitrogen Compounds
While the halides are monovalent, oxygen and sulfur are divalent,
and carbon is tetravalent, nitrogen is trivalent; the saturated
compounds of these elements with hydrogen reflect this:
HCl || Hydrogen chloride|
H2S|| Hydrogen sulfide|
The reason why hydrogen precedes the other element in some of these
formulas and follows it in others is neither known nor significant,
but this order is nevertheless conventional.
The nitrogen atom of ammonia has a free, unbonded electron pair and
therefore has great affinity for protons or other positively charged
entities. Such compounds are said to be nucleophilic, while their
willing positive partners are electrophilic. Ammonia readily
abstracts a proton from water or hydrogen chloride to give ammonium
hydroxide or ammonium chloride:
NH3 + H2O --> NH4+OH-
NH3 + HCl --> NH4+Cl-
A dramatic demonstration of the latter reaction consists of placing
a beaker of ammonia solution next to a beaker of hydrochloric acid
solution and blowing across the top. When the invisible NH3 and HCl
gases unite, a dense cloud of solid NH4Cl particles is formed.
Nucleophilicity in action!
The hydrogen atoms of ammonia can readily be replaced by alkyl
groups to give primary, secondary, or tertiary amines:
CH3NH2||Methylamine (a primary amine)
(CH3)2NH||Dimethylamine (a secondary amine)
(CH3)3N||Trimethylamine (a tertiary amine)
When the alkyl groups of a secondary or tertiary amine differ, all
of the alkyl groups are named in sequence, with no spaces between
CH3NHC2H5||Methylethylamine (or N-methylethylamine) |
Dimethylpropylamine (or N,N-dimethylpropylamine)|
It may be confusing (but again prescribed by convention) that the
terms primary, secondary, and tertiary have different meanings when
applied to amines than when applied to alcohols or halides. A
primary alcohol is a compound with a hydroxyl group bonded to a
carbon atom that carries two hydrogen atoms (RCH2OH). A primary
amine, on the other hand, can be bonded to any carbon atom, but
there must be two hydrogen atoms on the nitrogen atom (RNH2). A
secondary alcohol is R2CHOH, while a secondary amine is R2NH, and
the tertiary compounds are R3COH and R3N. Therefore, tert-butylamine
is a primary amine (CH3)3CNH2. Strange but true!
Amines, like ammonia, are nucleophilic and form salts with acids:
|C4H9NH3+Cl- or C4H9NH2.HCl ||Butylammonium chloride (or butylamine
Quaternary ammonium compounds
Tertiary amines also react with alkylating agents including alkyl
halides or alkyl sulfates (such as methyl iodide or dimethyl
sulfate) to give quaternary ammonium salts:
(C2H5)3N + C2H5Br --> |
(CH3)3N + CH3OSO2OCH3 --> |
Long-chain quaternary ammonium chlorides are marketed in very large
volume as fabric softeners.
Quaternary ammonium hydroxides also exist. They are very strong
Part XVI will address amino acids and proteins.
Readers are urged to e-mail questions, comments, or suggestions for further topics in the field of
organic nomenclature to the author at:
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