C2 in All Its GuisesRoaldHoffmannI love the chemistry that of its own subverts(推翻) theclassicalcompartmentalization(划分）of themolecularscience into organic, inorganic, biological, physical andanalytical subdisciplines.Here's an example.C2 is a simple diatiomic molecule. Just two carbonatoms. It's not very stable, quite unlike the familiar O2, N2orF2.Butwhenever anarcisstruckbetween twocarbonatoms,one gets a little C2(and a little soccer-ball shapedC6o, buckminsterfullerene. But that's another, marvelous,story). There is also a good bit of C2 in comets. And C, isresponsibleforthebluelight we seeinflames
1 C2 in All Its Guises I love the chemistry that of its own subverts(推翻) the classical compartmentalization( 划 分 ) of the molecular science into organic, inorganic, biological, physical and analytical subdisciplines. Here’s an example. C2 is a simple diatiomic molecule. Just two carbon atoms. It’s not very stable, quite unlike the familiar O2 , N2 or F2 . But whenever an arc is struck between two carbon atoms, one gets a little C2 (and a little soccer-ball shaped C60, buckminsterfullerene. But that’s another, marvelous, story). There is also a good bit of C2 in comets. And C2 is responsible for the blue light we see in flames
like aThe C, molecule looksfreedumbbell,andtheonlygeometrical variable it has’ is thedistance between the two carbons.That distance is 1.2425 angstroms inthe ground state, the stable form ofthe molecule.Any molecule, C, as well, alsoexists transiently in excited states.These result from absorption of lightby the molecule, or from the input ofenergy in other way.2
2 The C2 molecule looks like a dumbbell, and the only free geometrical variable it has is the distance between the two carbons. That distance is 1.2425 angstroms in the ground state, the stable form of the molecule. Any molecule, C2 as well, also exists transiently in excited states. These result from absorption of light by the molecule, or from the input of energy in other way
The C, molecule looks like a dumbbell,and the only free geometrical variable ithas is the distance between the twoThat distanceis1.2425carbons.angstroms in the ground state, the stableform of the molecule.Any molecule, C2 as well, also existstransiently in excited states. These resultfrom absorption of light by the molecule,or from the input of energy in other way.C分子看起来象哑铃，它具有的唯一的自由几何变量是两个碳原子间的距离。在基态，即分子的稳定状态该距离为1.2425埃。任何分子，包括C2，也短暂地处于激发态。激发态是由于分子吸收了光或通过其它途径获得了能量而形成的。3
3 C2 分子看起来象哑铃，它具有的唯一的自由几何变 量是两个碳原子间的距离。在基态，即分子的稳定状态， 该距离为1.2425埃。任何分子，包括C2, 也短暂地处于 激发态。激发态是由于分子吸收了光或通过其它途径获 得了能量而形成的。 The C2 molecule looks like a dumbbell, and the only free geometrical variable it has is the distance between the two carbons. That distance is 1.2425 angstroms in the ground state, the stable form of the molecule. Any molecule, C2 as well, also exists transiently in excited states. These result from absorption of light by the molecule, or from the input of energy in other way
C-CDistancesStateofCz(inangstroms)1.2425WLWIWIWWAE(ground state)1.3119,1.3184m1.3693S1.2661,1.25521.23,1.23801.5351Pha1.25291.3931.3579Figure Z:The archetypicalorganic moleculestethane,ethylene,acetylene.C-Cdistances in angstroms10-cen1.307C-Cdistance (angstroms)neters are indicatedcntheboeemIsRsACmputedpotential energycurvesforCCHTheoreticalOrganicPhysicalOganometallic271SlversurfanFigure6:TheGdoCClzstructureimcarbidsurfaceInorganicSolid state1995July-August309AmericanScientist,Volume83
4 Organic Oganometallic Inorganic Solid state surface Physical Theoretical
Theinthisyou'vestructuresseenMarginalium come from different parts of themolecular enterprise: physical, theoretical, organicorganometallic, inorganic, solid state, surfacechemistry. I think what nature is saying to us, asclearly as possible through this dazzling richness,is “You guys may chop up chemistry as you wish,but I'm telling you the world is one. There are C2molecular units in each of these structures, actingout a dance of varying distances."I think this is beautiful. And seeing the unitytakes nothingaway form the diversity5
5 The structures you’ve seen in this Marginalium come from different parts of the molecular enterprise: physical, theoretical, organic, organometallic, inorganic, solid state, surface chemistry. I think what nature is saying to us, as clearly as possible through this dazzling richness, is ‘‘You guys may chop up chemistry as you wish, but I’m telling you the world is one. There are C2 molecular units in each of these structures, acting out a dance of varying distances.” I think this is beautiful. And seeing the unity takes nothing away form the diversity