NEWS OF THE WEEK
BOND-SPECIFIC CHEMISTRY: Triatomic molecule selectively split Chemists at Stanford University have demonstrated, for the first time, selective cleavage at will of either of two bonds in a triatomic molecule. This accomplishment is seen as fundamentally very important, although its practical implications remain unclear, according to several sources. If this newfound capability can be extended to other molecules, it may bring chemists closer to an important long-range goal: the ability to make polyatomic molecules react at a specific bond, yielding a single desired product. The work was carried out by Stanford physical chemistry professor Richard N. Zare and his coworkers: graduate students Michael J. Bronikowski and William R. Simpson, and former postdoctoral researcher Bertrand Girard. It is described in the Dec. 1 issue of the Journal of Chemical Physics [95, 8647 (1991)]. The bond-specific chemistry was performed on HOD, a water molecule that is substituted with one deuterium atom. This molecule can react with an energetic hydrogen atom in one of two ways: If the O-H bond is cleaved, the products are the radical OD and H 2 . If the O-D bond is cleaved, the reaction yields the radical OH and HD. Normally, all four products would be produced, because both bonds in HOD have an about equal chance of breaking. To control the course of the reaction, the Stanford team used a tunable infrared laser to selectively excite only one of the bonds, causing it to stretch and break more readily. Depending on which bond is excited, the reaction yields exclusively either OD and H 2 , or OH and HD. Zare's achievement goes a step further than work reported last year by physical chemistry professor F. Fleming Crim of the University of Wis6
December 2, 1991 C&EN
| stretched the bond much more than in the Stanford work. 2 Zare's results are especially inter8 esting because they show that just a little stretching, achieved with the barest minimum of excitation energy, affords flexible control over the reaction. Both Crim and Zare succeeded where many others failed in the past because they chose vibrational excitations that remain localized on the chosen bond long enough for a collision with a hydrogen atom to occur. Whether such bond-specific chemistry can be performed on other, potentially more interesting or more useful molecules remains to be seen. "It would be great if this finding Zare: laser cleavage of HOD can be generalized to other molecules/' notes Frank J. Wodarczyk, consin, Madison. Crim and his co- program director for experimental workers, Amitabha Sinha and Mark physical chemistry at the National C. Hsiao, used a laser to produce Science Foundation, which funded HOD with a vibrationally excited Zare's work. Zare, he explains, O-H bond. When this molecule react- worked with water, a small moleed with a hydrogen atom, the excited cule with few vibrations. "And the O-H bond was cleaved preferentially, vibrations it has are at frequencies producing at least 100 times more that are far enough apart from one OD than OH [/. Chem. Phys.f 92, 6333 another that he could separate the (1990)]. Until that experiment, Crim motion in one bond from all the says, no one had selectively cleaved a other motions in the molecule/' Exciting a single bond in a more combond in a bimolecular reaction. Zare tells C&EN that as far as he plex molecule having many more knows, his group is the first to excite vibrational motions may be much two different bonds in one molecule more difficult, Wodarczyk says. and observe two different sets of "These vibrational motions can couproducts. Even more important, he ple with one another, and as soon as adds, is that his group excited the you put energy into one, it could lowest vibrational state of the hy- leak into the others very quickly. droxyl bond (the fundamental), us- That's been a problem all along." ing the minimum amount of infraZare is hopeful—though he canred energy (one quantum, or about not be confident—that bond-specific 45 kilojoules per mole for the O-H chemistry can be achieved with othbond). Crim's group, by contrast, ex- er molecules. Success will depend cited a higher energy overtone—the on finding other localized vibrafourth excited vibrational state of tions that will stretch a specific bond the O-H bond—by blasting it with to the point of rupture, he says. four quanta from a visible laser. This Although the Stanford experi-
ment was performed in the gas phase, Zare is optimistic it can be extended to the liquid phase. One possibility, he speculates, would be to use an infrared laser to control redox chemistry at an electrode. Such an electrochemical system might actually be simpler than the gas-phase HOD reaction, in terms of its laser requirements. The gas-phase experiment requires three pulsed lasers— one to generate the high-velocity hydrogen atoms, one to excite the hydroxyl bond, and one to detect the reaction products. Zare does not want to oversell his group's accomplishment. "This is just one step along; the way" to the Holy Grail of bond-specific chemistry, he says. It's still very far from applicable to an industrial process, he stresses. "But in terms of intellectual understanding of chemistry, I'm pretty excited about what we've done." Ron Dagani
White House council raises Democratic ire In what has become a very partisan issue, Congressional Democrats are aiming intense fire at the White House Council on Competitiveness, charging it with actions they believe are at best too secretive, and at worst illegal. A specific target of their attacks is the council's executive director, Allan B. Hubbard, who has strong ties to the chemical industry. The council was set up by President Bush in 1989, under the chairm a n s h i p of Vice President Dan Quayle, to ensure that federal regulations are not overly burdensome to industry. For example, it has modified—some say weakened—Environmental Protection Agency rules implementing the Clean Air Act, and EPA's definition of what constitutes wetlands. More recently, the council revamped the Food & Drug Administration's new drug review process, an action some call detrimental to the public's health (C&EN, Nov. 25, page 4). Sen. Albert Gore Jr. (D.-Tenn.) is calling for Hubbard's resignation as council executive director. Gore
charges that Hubbard—a co-owner mitting him to consider issues that of a small Indianapolis chemical may in fact benefit his substantial company who also has financial in- business interests. From World Wide terests in 30 other businesses—is a alone, Hubbard received $786,000 in 1990. By granting the waiver, Quayle fox guarding the hen house. Gore notes that Indiana environ- signals that he is not concerned Hubmental officials have cited Hub- bard's judgment will be comprobard's company, World Wide Chem- mised by his interests. Hubbard has refused to appear ical, for polluting the environment. Yet, Gore says, Hubbard "is put in before Congressional committees. charge of the regulations governing And the competitiveness council has pollution, is acting behind closed refused Freedom of Information Act doors, refusing to answer questions requests from public interest groups, from Congress or anyone else, refus- citing executive privilege. Nancy ing to abide by the safeguards estab- Watzman, an analyst with Public lished in the laws which delegate Citizen's Congress Watch, says this authority to the Environmental Pro- claim will be tenuous if a federal court decision in September—which tection Agency." Democratic members of the House the White House has appealed—is also express concern. In a letter to upheld. That decision says White Hubbard, Rep. John Conyers Jr. (D.- House review panels, like the counMich.), chairman of the House Com- cil, are not shielded by executive mittee on Government Operations, privilege and must supply requested has written that his committee "is information. The council's stonewalling actions concerned that your activities may involve a serious conflict of interest." also are irking Sen. John Glenn (D.Rep. Henry A. Waxman (D.-Calif.), Ohio), who chairs the Senate Govchairman of the House Subcommit- ernmental Affairs Committee. Last tee on Health & the Environment, week, his committee voted out a also is investigating the conflict-of- "sunshine" bill (S. 1942) that requires the White House to docuinterest question. To put these concerns to rest or es- ment its reviews of agency-proposed tablish a foundation for future hear- rules or process changes, and to supings, Conyers asks Hubbard to an- port any alterations to them. The bill swer questions regarding his in- also requires a public record of communications between volvement in council the review body and decisions, and his conagencies or outside tacts with agency officontacts. cials and industry repGlenn's bill applies resentatives. Hubbard to the council's work. previously did not anHe supports existence swer some committee of some Administraquestions, so Conyers tion review body to pointedly asks him to coordinate federally let t h e c o m m i t t e e issued rules. But he know early "whether believes the council's you will in fact volunadvice is b e c o m i n g tarily supply by Dec. the "marching orders" 10 all the information for federal agencies, requested." and thus exceeds palH u b b a r d is also atable limits. Quayle's deputy chief Republican Senators of staff, and the Vice disagree. A group of President's office runs 24 Senators that is led the council. Hubbard by Don Nickles (R.has recused himself Okla.) has sent Presifrom matters related dent Bush a letter of to his business holdsupport for the counings. Still, Quayle has cil and Quayle. They granted him a waiver from federal conflict- Hubbard: conflict of interest write: " T h e council provides an appropriof-interest laws, per in chemical ties charged December 2, 1991 C&EN
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