double.... h-atom transfer, and of alkoxy radicals from isoprene prompt chemistry intramolecular......
TRANSCRIPT
Double . . . .H-atom Transfer, and of Alkoxy Radicals
from Isoprene
Prompt Chemistry
Intramolecular. . . Hydrogen Bonding,
T. S. DibbleChemistry Department, SUNY-ESF
OH O2
OH O2, NO O3
HOOH
Global Organic compound emissionsCH4 530 Tg/yearIsoprene 500 Tg/yearOther 650 Tg/year
Importance of Isoprene in the Atmosphere
(Oxidizes SO2 to sulfuric acid)
(Health Hazard)
(“Vacuum cleaner of the atmosphere”)
OH..
O2
OH
OO.OH.
OH
.OH
OH
OH
O.OHOH
.OH
OH
.O2
NO
.
OHOH
OO iso
*
(E)-1 (Z)-1
(Z)-V.
OHOH
ONO
Chemistry Forming Second Generation Radicals(Paulson and Seinfeld, 1992)
Note many branching pathways are not shown above!!
VIIO VIIOO VII
Second Generation Alkoxy Radicals Expected to Decompose(Paulson and Seinfeld, 1992)
(Dibble, 2002)
OH
O
+ CH2OHVIIO
OHOH
O.
.
But double hydrogen bonding of (Z) isomerinhibits decomposition, unlike single H-bond (Dibble 1999) in first generation alkoxy radicals.
0 Kcal/mole
(4)
-19 Kcal/mole
Unexpected Chemistry
Double H-atom Transfer
Unexpected ChemistryUnexpected ChemistryUnexpected Chemistry
OH
OH
O.
OH
O
OH
.
OH
O
OH
.
NomenclatureWe identify oxygen atoms by the number (in isoprene) of the
carbon atom to which it is bound. The O atom acting as ahydrogen bond donor is to the left of an arrow, the acceptor
is to the right.
(Z) VIIO(14, 4 3)
1
3
4
(Z) VII’OH (34, 4 1)
1
3
4
Multiple Hydrogen bonding Arrangements(zero, one, or two hydrogen bonds)
(Z)-VII’OH (41)
(Z)-VII’OH (43,31)
(Z)-VII’OH (43) (Z)-VII’OH (none)
(Z)-VII’OH (31) (Z) VII’OH (34, 4 1)
1
3
4
5
-10
-15
10
0
-5
-20
(Z)-VII’OH (none) (Z)-VII’OH
(3 4)(Z)-VII’OH (4 3)
(Z)-VII’OH (4 3,3 1)(Z)-VII’OH (3 4,4 1)
(Z)-VII’OH (4 1) (Z)-VII’OH (3 1)
(Z)-VIIO (1 4,4 3)
(Z)-VIIO (1 3)’
Kca
l/m
ol
Relative Energies, H-atom transfer, and H-bonding
5
-10
-15
10
0
-5
-20
OHO
+CH2OH
OH
O
+ CH2OH
(Z)-VII’OH (none) (Z)-VII’OH
(3 4)(Z)-VII’OH (4 3)
(Z)-VII’OH (4 3,3 1)(Z)-VII’OH (3 4,4 1)
(Z)-VII’OH (4 1) (Z)-VII’OH (3 1)
(Z)-VIIO (1 4,4 3)
(Z)-VIIO (1 3)’
Kca
l/m
ol
Part of the Potential Energy ProfileThermal Decomposition of VII’OH is slow...
0 5 10 15 20 250.00
0.25
0.50
0.75
1.00
F
ract
ion
Pro
mpt
Dec
ompo
tion
Initial Energy (Kcal/mol)
10 Torr
760 Torr
298 K
… But Prompt Decomposition of VII’OH is Extensive!
OOH
+ CH2OH
OHO
OH.
OHO
OH. M
*
* OHO
OH.
Consequences for Atmospheric Chemistry?
OH
O
+VIIO
OHOH
O.
CH2OH.
CH2OH.
OHO
OH.VII'OH
O
OH
+
OHO
OH.
O2,NO
OHO
OHO.
O
O.
OH
OH
+
MGLY
O2
OH
O
+ HO2VII'OH
*
Decomposition of VIIO same as Prompt Decomposition of VII’OH!
But quenched VII’OH results in different chemistry
Theodore S. [email protected]
Chemistry DepartmentState University of New York - Environmental Science and Forestry
Syracuse, NY 13210http://www.esf.edu/chemistry/faculty/dibble.htm
AcknowledgementsNSF-Atmospheric SciencesNCSA - University of KentuckyWei Deng, Katherine Kitney, Lei Zhang
J. Phys. Chem A, (2004) 108, 2199 and 2208.