The$Molecular$Elusive$Time$and$Aesthe5cs$in$Chemistry$

$$$$$

Tami$I.$Spector$University$of$San$Francisco,$Dept.$of$Chemistry$

(spector@usfca.edu)$

“The%huge%variety%of%chemical%species,%types%of%reac6ons,%and%the%accompanying%poten6al%energy%surfaces%involved%means%that%the%6mescale%over%which%chemical%reac6ons%occur%covers%many%orders%of%magnitude”%(Claire%Vallance,%“Reac6on%Kine6cs”)%$

Very$Slow$Reac5ons$$

Cai$Guo$Qiang,!Restrained!Violence:!Rainbow:!Project!for!Extraterrestrials!No.!25,%2002%Johannesburg%Biennial,%Johannesburg,%South%Africa%%Gunpowder:%5%kg,%fuse:%500%meters,%Photo:%Kochi%Watari%$$%

Extremely$Fast$Reac5ons$

Reac5ons$That$Occur$on$a$Percep5ble$Time$Scale$

BriggsNRauscher%“Oscilla6ng%Clock%Reac6on”%

•  Reac6ons%materially%appear%to%go%from%star6ng%material%to%product%

•  Along%the%path%from%star6ng%material%to%product%various%transient%(very%short%lived)%molecular%species%are%formed%

%

Oxida6on%of%Iron%to%Fe%(II)%Oxida6on%of%Fe%(II)%%to%Fe%(III)%in%presence%of%water%Fe%III%combine%with%Oxygen%to%form%Fe%(III)%oxide%Fe%(III)%oxide)%is%hydrated%with%water%

•  Dis5nc5on$between$slow$and$fast$reac5ons$is$based$on$how$oNen$the$reac5ons$occur$on$a$molecular$level,$not$how$quickly$$

•  Given$enough$energy,$all$reac5ons$on$the$molecular$level$proceed$very$quickly$through$transient$molecular$species$

•  Time$in$Transi5on$State:$femtosecond$(fs)$5me$scale$(10T15$sec)$•  Time$as$Intermediate$(Minima):$(10T10$T$10T6$sec)$$

Stable$(low$energy)$/Persistent$(long$life5me)$$

“The$transi5on$state$is$neither$one$thing,$namely,$chemical$reagents,$nor$the$other,$reac5on$products.$Instead$it$illustrates$the$mys5cal$event$of$transTsubstan5a5on.”$%%(John%C.%%Polanyi%and%Ahmed%H.%Zewail,%“Direct%Observa6on%of%the%Transi6on%State,”%1995)%%

The$Transi5on$State$(fs$5mescale)*$$

*One%femtosecond%is%10N15%seconds,%that%is,%0.000000000000001%seconds,%which%is%to%a%second%as%a%second%is%to%32%million%years.%%

“Cyclobutadiene,%(CH)4,%is%the%Mona%Lisa%of%organic%chemistry%in%its%ability%to%elicit%wonder,%s6mulate%the%imagina6on,%and%challenge%interpre6ve%ins6ncts.%No%other%organic%compound%combines%such$a$flee5ng$existence$and%so%many%different%syntheses,%with%such%a%propensity%for%different%chemical%reac6ons,%and%with%the%variety%of%calcula6ons%of%its%structure.”%%(Donald%J.%Cram,%et!al.!“The%Taming%of%Cyclobutadiene”,%1991)%%%

The$Intermediate$(10T10$T$10T6$sec$5mescale)$$$

FeCOCOOC

Ce(IV)

E

$Femtochemistry%has%fundamentally%changed%our%view%of%chemical%reac6ons.%From%a%phenomenon%described%in%rela6vely%vague%metaphors%such%as%'ac6va6on'%and%'transi6on%state',%we%can%now%see%the%movements%of%individual%atoms%as%we%imagine%them.%They%are%no%longer%invisible.%%%%%%%%Press%release%for$Ahmed%Zewail,%awarded%the%1999%Nobel%Prize%in%Chemistry%“For!his!studies!of!the!transi?on!states!of!chemical!reac?ons!using!femtosecond!spectroscopy”$

�...it%is%the%molecules,%and%only%the%molecules,%for%which%claims%of%beauty%and%ar6s6c%crea6vity%are%jus6fied,%no%mader%what%sensual%quali6es%the%corresponding%materials%have.�%%(Joachim%Schummer,%“Aesthe6cs%of%Chemical%Products,”%2003)%

The$Transi5on$State$$$

The$Transi5on$State$$$

Time%Snapshot%

The$Transi5on$State$$$

Time%Snapshot%

Twisted%TS%

PE%Surface%

Time%Snapshot%

Twisted%TS%

PE%Surface%

“Transi6on%state%theory%allows%the%chemist%in%a%sense%to%visualize%?me!itself…6me%that%is%completely%tethered%to%space”%(Stephen%Weininger,%2000)%%

Aesthe5cs$of$Transient$Molecular$Systems$%

“To%be%concentrated%is%to%be%symbolically%powerful”(Barbara%Maria%Stafford,%Echo!Objects,%2007)%

Sta5c$Structures$of$Transi5on$States$and$Intermediates$Compress$5me,$space$and$energy$into$a$single$structure$

Aesthe5cs$of$Transient$Molecular$Systems$%

%.30!Bullet!Piercing!an!Apple%(Harold%Edgerton,%1964)%

“…we%may%also%think%of%sta5c$pictures$which%only%implicitly$have$a$narra5ve$func5on.%That%is,%where%a%frozen%scene%in%a%tacit%ac6on%sequence%has%been%chosen,%from%which%what%has%preceded%and%will%follow%has%to%be%inferred%by%the%beholder.”%(Michael%Ranta,%“Narra6vity%and%Time%in%Sta6c%Pictures”,%2001)%%%

“In%the%experience%of%any%change%we%may%iden6fy%a%par6cularly%salient%point,%such%as%the%moment%a%longNdistance%runner%crosses%the%finishing%line.%We%might%represent%this%as%a%6meNslice%of%the%ac6on,%but%in%fact%(since%we%perceived%it)%it%has%a%nonNzero%dura6on.%This,%then,%is%what%sta6c%images%are%capable%of%depic6ng:%specious!instants!which%are%parts%of%a%larger%movement%represented%by%the%image.%Images%can%thus%represent%a%movement%by%depic6ng%perceptually%minimum%parts%of%it.”%(“Time%and%the%Sta6c%Image,”%Robin%Le%Poidevin,%1997)%%%

Instants$have$no$dura5on$and$therefore$are$impercep5ble$Specious$instant$=$the$smallest$perceivable$part$of$an$instant$Timeframes$of$Transi5on$States$and$Intermediates$=$specious$instants$Depic5ons$of$Transi5on$States$and$Intermediates$express$the$impercep5bility$of$5me$%

Fin