5
86
ATKINSON, TUAZON, AND ASCHMANN
two yield determinations are averaged, resulting in a
formation yield of 2-methylpropanal of 0.58 Ϯ 0.08.
Consistent with the reaction pathways shown in Re-
action Schemes I–III, formation of 2-methylpropanal
plus HCHO, acetone plus glycolaldehyde, and meth-
acrolein plus HCHO account for 58 Ϯ 8%, 18 Ϯ
tion pathway accounts for 91 Ϯ 12% of the overall
OH radical reaction with 3-methyl-1-butene. Taking
into
account
the
possible
formation
of
HOCH C(CH )"CHCHO [or possibly CH "
2
3
2
C(CH )C(O)CH OH; see Reaction Scheme III] as sug-
3
2
gested by our API-MS data and noting our upper limits
to the formation of methyl vinyl ketone and 3-methyl-
2-butenal of Ͻ1% each, a reasonable estimate of the
H-atom abstraction pathway in the reaction of the OH
radical with 3-methyl-1-butene is 5–10%. Combined
with previous literature data [4,8,9,11], this suggests
that H-atom abstraction from the allylic C9H bonds
of alkenes during the OH radical reactions is of minor
importance, accounting for only a few percent of the
overall reactions under tropospheric conditions.
3
%, and 3.3 Ϯ 0.7% of the overall reaction products,
with the molar HCHO yield of 0.70 Ϯ 0.06 being in
reasonable agreement with the sum of the 2-methyl-
propanal and methacrolein yields (0.61 Ϯ 0.09). To-
gether with the estimated yield of “organic nitrates” of
ca. 0.15 during the initial portions of the experiments,
9
4% of the total reaction products and reaction path-
ways of the OH radical-initiated reaction of 3-methyl-
-butene in the presence of NO are accounted for. Fur-
thermore, as shown by the estimated reaction rates
32] of the major alkoxy radicals involved in the OH
1
[
radical-initiated reaction of 3-methyl-1-butene in the
presence of NO, the observed products are consistent
with the calculated dominant reaction pathways of
these alkoxy radicals. No evidence for the formation
of methyl vinyl ketone or 3-methyl-2-butenal was ob-
tained, and conservative upper limits to the formation
yields of these two potential H-atom abstraction path-
way products (Reaction Scheme III) are given in Table
I. The formation of organic nitrates during the early
stages of the reaction is anticipated to arise from the
reaction of the organic peroxy radicals [including
The authors gratefully thank the U.S. Environmental Pro-
tection Agency, Office of Research and Development (As-
sistance Agreement R-825252-01-0) for supporting this re-
search, and thank the National Science Foundation (Grant
No. ATM-9015361) and the University of California, Riv-
erside, for funds for the purchase of the SCIEX API III MS/
MS instrument. While this research has been supported by
the U.S. Environmental Protection Agency, it has not been
subjected to Agency review and, therefore, does not neces-
sarily reflect the views of the Agency, and no official en-
dorsement should be inferred.
(
CH ) CHCH(OOB )CH OH, (CH ) CHCH(OH)CH OB ,
3
2
2
3 2
2
2
(CH ) C(OOB )CH"CH , and (CH ) C"CHCH OB ]
BIBLIOGRAPHY
3
2
2
3 2
2
2
with NO (Reaction (6a) and analogous reactions). The
approximate organic nitrate formation yield of 0.15 is
reasonably consistent with organic nitrate formation
yield measurements for the OH radical-initiated reac-
tions of C 9C alkenes in the presence of NO [36–
1. R. L. Seila, W. A. Lonneman, and S. A. Meeks, Deter-
mination of C to C12 Ambient Air Hydrocarbons in 39
2
U.S. Cities, from 1984 through 1986, U.S. Environmen-
tal Protection Agency Report EPA/600/3-89/058, At-
mospheric Research and Exposure Assessment Labo-
ratory, Research Triangle Park, North Carolina,
September 1989.
. F. W. Lurmann and H. H. Main, Analysis of the Ambient
VOC Data Collected in the Southern California Air
Quality Study, Final Report to California Air Resources
Board Contract No. A832-130, Sacramento, CA, Feb-
ruary 1992.
4
6
3
0
8], with reported organic nitrate yields of 0.037 Ϯ
.009 for the cis-2-butene reaction [37] and ca. 0.15
for the 2,3-dimethyl-2-butene reaction [36,38].
The API-MS and API-MS/MS analyses are
consistent with the GC-FID and FT-IR analyses,
with the major products being attributed to acetone,
2
2
-methylpropanal
and
the
-hydroxynitrates
(
(
CH ) CHCH(ONO )CH OH
and/or
3. W. L. Chameides, F. Fehsenfeld, M. O. Rodgers, C.
Cardelino, J. Martinez, D. Parrish, W. Lonneman, D. R.
Lawson, R. A. Rasmussen, P. Zimmerman, J. Green-
berg, P. Middleton, and T. Wang, J. Geophys. Res., 97,
3
2
2
2
CH ) CHCH(OH)CH ONO . The API-MS analyses
3
2
2
2
also suggest the presence of a product (or products) of
molecular weight 100, possibly HOCH C(CH )"
CHCHO and/or CH "C(CH )C(O)CH OH formed
subsequent to the H-atom abstraction pathway (Re-
action Scheme III).
Therefore, our data show that at room temperature
and atmospheric pressure, OH radical addition domi-
nates for 3-methyl-1-butene, with H-atom abstraction
accounting for a minimum of 3.3% (based on the for-
mation yield of methacrolein). The OH radical addi-
2
3
6
037 (1992).
. R. Atkinson, J. Phys. Chem. Ref. Data, Monograph 2,
(1994).
2
3
2
4
1
5
6
. R. Atkinson, J. Phys. Chem. Ref. Data, 26, 215 (1997).
. N. J. Blake, S. A. Penkett, K. C. Clemitshaw, P. Anwyl,
P. Lightman, A. R. W. Marsh, and G. Butcher, J. Geo-
phys. Res., 98, 2851 (1993).
7. R. Atkinson, Gas Phase Tropospheric Chemistry of Or-
ganic Compounds, In Volatile Organic Compounds in