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SUMMARY:Timescales of chemical reactions - Prof Michael Pilling\, Universi
 ty of Leeds
DTSTART:20111025T151500Z
DTEND:20111025T161500Z
UID:TALK32448@talks.cam.ac.uk
CONTACT:Dr Alex Archibald
DESCRIPTION:*Timescales of chemical reactions\nM J Pilling\, School of Che
 mistry\, University of Leeds\, Leeds\, LS2 9JT*\n\n Chemical reactions occ
 ur on timescales from femtoseconds to many years. Some reactions occur bef
 ore the energy can be randomly distributed in the reacting molecule\; the 
 reaction between cyclopentyne and ethene\, for example\, [1] requires a dy
 namical description in order to understand the mechanism. For many other r
 eactions\, occurring on longer timescales\, energy is randomly distributed
  in the reacting molecule\, but not equilibrated with the bath gas\, and i
 t is necessary to consider the interaction between collisional energy tran
 sfer and reaction\, using a master equation approach. [2]Such an approach 
 may be necessary even in solution phase reactions\, despite the high colli
 sional frequency\, as illustrated by the reaction between propene and BH3.
 [3]\n \nGas phase reactions following the association of two molecules can
  lead\, on a single chemical timescale\, to the association product. In ot
 her cases\, such as the reaction between an organic radical and O2\, the r
 eaction may involve several isomers\, and can lead to dissociation to form
  bimolecular products. There are now several chemical timescales\, which d
 epend on the details of the isomerisation\, dissociation and energy transf
 er processes occurring in the reacting system. Examples will be drawn from
  combustion and atmospheric chemistry.  Solution of the master equation is
  the key to understanding these timescales and interpreting experimental r
 esults to obtain the underlying chemical kinetics and mechanism.[4]\n\nTim
 escales of complex sequences of chemical reactions can be interpreted in a
  similar way\, but now using the Jacobian of the system. There is a distin
 ction between the chemical lifetime – the reciprocal of the reactant’s
  overall pseudo first-order rate constant for loss – and the system time
 scales\, as has been appreciated for many years for methane in the atmosph
 ere.[5] Other examples will be briefly discussed.\n \n[1] D. R. Glowacki \
 , S. Marsden\, M.J. Pilling\, Significance of Nonstatistical Dynamics in O
 rganic Reaction Mechanisms: Time-Dependent Stereoselectivity in Cyclopenty
 ne"Alkene Cycloadditions\,’J. Am. Chem. Soc.\, 2009\, 131 (39)\, pp 1389
 6–13897 \n[2] S. H. Robertson\, M. J. Pilling\, L. C. Jitariu and I. H. 
 Hillier\, Master equation methods for multiple well systems: application t
 o the 1-\,2-pentyl system\, \nPhys. Chem. Chem. Phys.\, 2007\, 9\, \n4085 
 - 4097\n[3] D. R. Glowacki\, C.H. Liang\, S. Marsden\, J. N. Harvey\, and 
 M.J. Pilling\, ‘Alkene Hydroboration: Hot Intermediates That React While
  They are Cooling\,’ J. Am. Chem. Soc.\, 2010\, 132(39)\, 13621-1362\n[4
 ]D. R. Glowacki and M.J. Pilling\, ‘Unimolecular reactions of peroxy rad
 icals in atmospheric chemistry and combustion\,’ ChemPhysChem \, 2010\, 
 11(18)\, 3836–3843\n[5]Prather\, M.J.\, Lifetimes and eigenstates in atm
 ospheric chemistry. Geophysical Research Letters 1994\, 21\, 801–804. Na
 tural modes and time scales in atmospheric chemistry: theory\, GWPs for CH
 4 and CO\, and runaway growth. Geophysical Research Letters 1996\, 23\,259
 7–2600.\n
LOCATION:Pfizer  Lecture Theatre\,  Department of Chemistry
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