tus quo." Indeed, the report notes, "Unless trends are reversed, tragic changes could occur in just the next two decades. The longer society waits, the more radical and draconian the needed responses will be." There are no "quick fixes" for this problem, Brown and his coauthors stress. It will require "fundamental reordering of national energy priorities within the next decade." However, "If energy policymaking continues to be the domain of short-term thinking and narrow political considerations, there can be little hope." Improved energy efficiency in transportation, electric appliances, lighting systems, and other areas is the most economical method, the team notes, with the largest and most immediate impact on carbon emissions and global warming. One step recommended is a global fuel efficiency standard for new cars of 50 miles a gal by the year 2000.
An effective response to the grow ing environmental threats will re quire people to cross a "perceptual threshold," learning to relate to Earth's natural systems in a new way and to recognize the world's growing interdependence. "The dif ficult choices that lie ahead will challenge our social institutions and personal values as never before. Lit tle precedent exists for the scale of action needed over the next dec ade." Indeed, Brown notes, "We face difficult questions of individual rights and responsibilities. A per son may be able to afford a large, energy-consumptive automobile, but can the planet afford it? A couple may desire and be able to support several children, but can the planet afford several children per family? The old business of pursuing nar row economic and political selfinterest falls away, anachronistic and plainly untenable." Richard Seltzer
Cuprous ions serve as templates to tie the knot...
v—iOV\ Bis (phenanthroline) segments
\
/
Helical chelate Knotted chelate
...and knotted ring remains after demetallation
Cuprous ions route to knotted-ring compound Chemists at the Université Louis Pasteur, Strasbourg, have made the first compound whose molecules are tied in cloverleaf knots [Angew. Chem., 101,192 (1989)]. Says the journal editor of this accomplishment, "Compounds with knot topologies are of considerable theoretical interest and have always lent wings to chemists' fantasies." Research associate Christiane O. Dietrich-Buchecker and chemistry professor Jean-Pierre Sauvage devised a strategy in which two cuprous ions served as templates to hold two bis(phenanthroline) segments in place. In some of these chelates, the bis(phenanthroline) segments were coiled in double helices about the cuprous ions. Using two long, bifunctional chains to tie these double helices together into one single molecule formed knotted rings. The phenanthroline nuclei each bore a ^-hydroxyphenyl group. The French workers reacted the tetrakis(hydroxyphenyl) chelates with an α,ω-diiodo compound made from hexaethylene glycol to tie the knots. In some of the chelates, however, the bis(phenanthroline) segments
were not bound as double helices, and tying these together gave only large unknotted rings. Also, the diiodo compound sometimes reacted to close rings internally within each bis(phenanthroline) segment, yield ing smaller, unknotted rings. Chromatography and cyanide de metallation afforded samples of com pounds corresponding to all these possibilities—large knotted rings and large and small unknotted ones. Mass spectra of large knotted-ring and large unknotted-ring compounds were very similar, with parent ions at the calculated 1690 mass units. Proton nuclear magnetic reso nance spectra of small and large unknotted-ring compounds were well resolved and almost superim posable. NMR spectra of the large knotted-ring compound were very different from those of the unknotted compounds, however, with broad, poorly resolved aromatic proton sig nals. Addition of potassium hexafluorophosphate sharpened the res olution of these spectra, possibly by complexation of potassium by ether oxygen atoms. The Strasbourg chemists deter mined the knotted-ring structure by
reasoning that the compound must be a racemic mixture. This is be cause the knotted-ring compound was formed from a chelate that was a double helix. The chelate thus would have been a mixture of rightand left-handed helices. The researchers established the racemic nature of the compound from NMR spectra with both potas sium hexafluorophosphate and (S)(+)-2,2,2-trifluoro-l-(9-anthryl)ethanol added. This chiral ethanol was introduced by chemistry professor William H. Pirkle of the University of Illinois, Urbana-Champaign, in 1976. It solvates each enantiomer in a racemic mixture differently, lead ing to differentiation of the pro tons of each. Indeed, addition of Pirkle's re agent led to splitting of NMR sig nals in two, especially those of the hexaethylene glycol and aromatic groups. By contrast, addition of even large amounts of Pirkle's reagent left NMR spectra of large and small un knotted-ring compounds unaffected. Stephen Stinson March 6, 1989 C&EN
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