Atmospheric chemistry of 2-pentanone and 2-heptanone

Article abstract of DOI:10.1021/es9909374

2-Pentanone and 2-heptanone are available for commercial use, which will lead to their possible release into the atmosphere where they are expected to primarily react with the hydroxyl (OH) radical and contribute to the formation of photochemical air pollution in urban and regional areas. We have studied the kinetics and products of the gas-phase reactions of the OH radical with 2-pentanone and 2-heptanone at 298 ± 2 K and atmospheric pressure of air. Using a relative rate method, rate constants for the reactions of the OH radical with 2-pentanone and 2-heptanone of (4.56 ± 0.30) x 10^-12 and (1.17 ± 0.11) x 10^-11 cm³ molecule^-1 s^-1, respectively, were obtained, where the indicated errors are two least-squares standard deviations and do not include the ~10-15% uncertainties associated with the rate constant for the reference compound cyclohexane. Reaction products were analyzed by gas chromatography, in situ Fourier transform infrared spectroscopy, and in situ atmospheric pressure ionization tandem mass spectrometry (API-MS). The products identified and quantified were (with their molar yields) as follows: from 2-pentanone, formaldehyde, 1.03 ± 0.10; acetaldehyde, 0.51 ± 0.11; propanal, 0.19 ± 0.03; 2,4-pentanedione, 0.12 ± 0.03; and molecular weight 147 organic nitrates, 0.12 ± 0.04; and from 2- heptanone, formaldehyde, 0.38 ± 0.08; acetaldehyde, ~0.05; propanal, ~0.05; butanal, 0.07 ± 0.01; pentanal, 0.09 ± 0.01; and molecular weight 175 organic nitrates, 0.18 ± 0.05. API-MS analyses also showed the formation of products of molecular weight 128 and 144 from 2-heptanone, anticipated to be C₇-dicarbonyl(s) and C₇-hydroxydicarbonyl(s), respectively. While 94 ± 13% of the reaction pathways of the 2-pentanone reaction are accounted for, it appears that a substantial fraction (>50%) of the initially formed alkoxy radicals from 2-heptanone undergo isomerization to form products which could not be quantified. 2-Pentanone and 2-heptanone are available for commercial use, which will lead to their possible release into the atmosphere where they are expected to primarily react with the hydroxyl (OH) radical and contribute to the formation of photochemical air pollution in urban and regional areas. We have studied the kinetics and products of the gas-phase reactions of the OH radical with 2-pentanone and 2-heptanone at 298±2 K and atmospheric pressure of air. Using a relative rate method, rate constants for the reactions of the OH radical with 2-pentanone and 2-heptanone of (4.56±0.30)×10^-12 and (1.17±0.11)×10^-11 cm³ molecule^-1 s^-1, respectively, were obtained, where the indicated errors are two least-squares standard deviations and do not include the approximately 10-15% uncertainties associated with the rate constant for the reference compound cyclohexane. Reaction products were analyzed by gas chromatography, in situ Fourier transform infrared spectroscopy, and in situ atmospheric pressure ionization tandem mass spectrometry (API-MS). The products identified and quantified were (with their molar yields) as follows: from 2-pentanone, formaldehyde, 1.03±0.10; acetaldehyde, 0.51±0.11; propanal, 0.19±0.03; 2,4-pentanedione, 0.12±0.03; and molecular weight 147 organic nitrates, 0.12±0.04; and from 2-heptanone, formaldehyde, 0.38±0.08; acetaldehyde, approximately 0.05; propanal, approximately 0.05; butanal, 0.07±0.01; pentanal, 0.09±0.01; and molecular weight 175 organic nitrates, 0.18±0.05. API-MS analyses also showed the formation of products of molecular weight 128 and 144 from 2-heptanone, anticipated to be C₇-dicarbonyl(s) and C₇-hydroxydicarbonyl(s), respectively. While 94±13% of the reaction pathways of the 2-pentanone reaction are accounted for, it appears that a substantial fraction (>50%) of the initially formed alkoxy radicals from 2-heptanone undergo isomerization to form products which could not be quantified.

Full text of DOI:10.1021/es9909374

Environ. Sci. Technol. 2000, 34, 623-631
understanding of the atmospheric chemistry of these and
Atmospheric Chemistry of
other similar ketones (1, 2), it is anticipated that the most
important tropospheric transformation process for these two
ketones is by reaction with the hydroxyl (OH) radical. While
rate constants have been measured for the reactions of the
OH radical with 2-pentanone (4-6) and 2-heptanone (5), to
date no data have been reported concerning the products
and mechanisms of these reactions.
Accordingly, we have investigated the products and
mechanisms of the gas-phase reactions of 2-pentanone and
2-heptanone with the OH radical. There are some discrep-
ancies between the absolute rate study of Wallington and
Kurylo (5) and relative rate studies carried out in this
laboratory (4, 6) concerning the rate constants for the
reactions of the OH radical with 2- and 3-pentanone and
2-hexanone. We have therefore measured rate constants for
the reactions of the OH radical with 2-pentanone and
2-heptanone as part of the present study.
2-Pentanone and 2-Heptanone
R O G E R A T K I N S O N , * , †
E R N E S T O C . T U A Z O N , A N D
S A R A M . A S C H M A N N
Air Pollution Research Center, University of California,
Riverside, California 92521
2-Pentanone and 2-heptanone are available for commercial
use, which will lead to their possible release into the
atmosphere where they are expected to primarily react
with the hydroxyl (OH) radical and contribute to the formation
of photochemical air pollution in urban and regional
areas. We have studied the kinetics and products of the gas-
phase reactions of the OH radical with 2-pentanone and
2-heptanone at 298 ( 2 K and atmospheric pressure of air.
Using a relative rate method, rate constants for the
reactions of the OH radical with 2-pentanone and 2-heptanone
of (4.56 ( 0.30) × 10-12 and (1.17 ( 0.11) × 10-11 cm3
molecule-1 s-1, respectively, were obtained, where the
indicated errors are two least-squares standard deviations
and do not include the ∼10-15% uncertainties associated
with the rate constant for the reference compound
cyclohexane. Reaction products were analyzed by gas
chromatography, in situ Fourier transform infrared
spectroscopy, and in situ atmospheric pressure ionization
tandem mass spectrometry (API-MS). The products
identified and quantified were (with their molar yields) as
follows: from 2-pentanone, formaldehyde, 1.03 ( 0.10;
acetaldehyde, 0.51 ( 0.11; propanal, 0.19 ( 0.03; 2,4-
pentanedione, 0.12 ( 0.03; and molecular weight 147 organic
nitrates, 0.12 ( 0.04; and from 2-heptanone, formaldehyde,
0.38 ( 0.08; acetaldehyde, ∼0.05; propanal, ∼0.05;
butanal, 0.07 ( 0.01; pentanal, 0.09 ( 0.01; and molecular
weight 175 organic nitrates, 0.18 ( 0.05. API-MS analyses
also showed the formation of products of molecular weight
Experimental Methods
Kinetic Studies. The experimental methods were similar to
those we have used previously (7). Experiments were carried
out at 298 ( 2 K and 740 Torr total pressure of purified air
(at ∼5% relative humidity) in a 7900-L all-Teflon chamber
equipped with two parallel banks of blacklamps for irradiation
and a Teflon-coated fan to ensure rapid mixing of reactants
during their introduction into the chamber. In the relative
rate method used, the relative disappearance rates of the
ketones and a reference organic, whose OH radical reaction
rate constant is reliably known, were measured in the
presence of OH radicals. Provided that the ketones and
reference organic were removed solely by reaction with OH
radicals, then
[ketone]t
[reference organic]t
o
k
o
ln
)
1 ln
(I)
{
}
{
}
k2
[ketone]t
[reference organic]t
where [ketone]t and [reference organic]to are the concentra-
o
tions of the ketones and the reference organic at time to,
[ketone]t and [reference organic]t are the corresponding
concentrations at time t, and k1 and k2 are the rate constants
for reactions 1 and 2, respectively:
128 and 144 from 2-heptanone, anticipated to be C -
7
OH + ketone f products
(1)
(2)
dicarbonyl(s) and C -hydroxydicarbonyl(s), respectively.
7
While 94 ( 13% of the reaction pathways of the 2-pentanone
reaction are accounted for, it appears that a substantial
fraction (>50%) of the initially formed alkoxy radicals from
2-heptanone undergo isomerization to form products
which could not be quantified.
OH + reference organic f products
Hydroxyl radicals were produced by the photolysis of
methyl nitrite (CH3ONO) in air at wavelengths >300 nm (8),
and NO was also included in the reactant mixtures to suppress
the formation of O3 and, hence, of NO3 radicals (8). The initial
concentrations of the reactants (in molecule cm-3 units) were
as follows: CH3ONO, ∼2.4 × 1014; NO, ∼2.4 × 1014, and the
ketones and reference organic, ∼2.4 ×1013 each. Cyclohexane
was used as the reference organic because its OH radical
reaction rate constant is similar to those previously reported
for 2-pentanone and 2-heptanone (9) and it could be analyzed
by gas chromatography using the same sampling and analysis
procedures. Irradiations were carried out for 10-45 min at
20% of the maximum light intensity. The concentrations of
the ketones and cyclohexane were measured during the
reactions by gas chromatography with flame ionization
detection (GC-FID). Gas samples of 100 cm3 volume were
collected from the chamber onto Tenax-TA solid adsorbent,
with subsequent thermal desorption at -225 °C onto a 30-m
Introduction
2-Pentanone [methyl propyl ketone, CH3C(O)CH2CH2CH3]
and 2-heptanone [methyl amyl ketone, CH3C(O)CH2CH2CH2-
CH2CH3] are available for commercial use, which will lead
to their possible release into the atmosphere where they will
undergo photolysis and/ or chemical reaction (1, 2) and hence
contribute to the formation of photochemical air pollution
in urban and regional areas (3). On the basis of our current
* Corresponding author phone: (909)787-4191; fax: (909)787-5004;
e-mail: ratkins@mail.ucr.edu.
† Also at the Department of Environmental Sciences and Depart-
ment of Chemistry, University of California, Riverside.
9
10.1021/es9909374 CCC: $19.00
Published on Web 01/13/2000
2000 Am erican Chem ical Society
VOL. 34, NO. 4, 2000 / ENVIRONMENTAL SCIENCE & TECHNOLOGY 6 2 3

DB-1701 megabore column held at -20 °C and then
temperature programmed to 200 °C at 8 °C min-1
.
Product Studies. Experiments were carried out at 298 (
2 K and 740 Torr total pressure of air in three reaction
chambers. These consisted of (i) a 5870-L evacuable, Teflon-
coated chamber containing an in situ multiple reflection
optical system interfaced to a Nicolet 7199 Fourier transform
infrared (FT-IR) spectrometer and with irradiation provided
by a 24-kW xenon arc filtered through a 0.25 in. thick Pyrex
pane (to remove wavelengths <300 nm), (ii) a 7900-L Teflon
chamber with analysis by GC-FID and combined gas chro-
matography-mass spectrometry (GC-MS), with irradiation
provided by two parallel banks of blacklamps, and (iii) a
7500-L Teflon chamber interfaced to a PE SCIEX API III MS/
MS direct air sampling, atmospheric pressure ionization
tandem mass spectrometer (API-MS), again with irradiation
provided by two parallel banks of blacklamps. All three
chambers are fitted with Teflon-coated fans to ensure rapid
mixing of reactants during their introduction into the
chamber.
Hydroxyl radicals were generated in the presence of NO
by the photolysis of methyl nitrite (CH3ONO) or ethyl nitrite
(C2H5ONO) in air at wavelengths >300 nm (8, 10), and NO
was included in the reactant mixtures to suppress the
formation of O3 and hence of NO3 radicals (8). Ethyl nitrite
was used as the OH radical precursor for the in situ FT-IR
analyses of formaldehyde (10) because the photolysis of
methyl nitrite leads to the formation of formaldehyde.
FIGURE 1. Plot of eq I for the gas-phase reactions of 2-pentanone
and 2-heptanone with the OH radical, using cyclohexane as the
reference compound.
Evacuable Chamber Experiments with FT-IR Analysis. For
the experiments carried out in the 5870-L evacuable, Teflon-
coated chamber (at <1% relative humidity), the initial
concentrations (in molecule cm-3 units) were as follows: CH3-
ONO or C2H5ONO, 2.46 × 1014; NO, (1.72-1.85) × 1014; and
2-pentanone or 2-heptanone, (2.37-2.46) × 1014. IR spectra
of the reaction mixtures were recorded prior to and during
irradiation with 64 scans (corresponding to 2.0-min averaging
time) per spectrum, a full-width-at-half-maximum resolution
of 0.7 cm-1, and a path length of 62.9 m. The mixtures were
irradiated intermittently for a number of 4-12-min periods
(with total irradiation times of 15-37 min) or for one
experiment with 2-heptanone continuously for 15 min, with
IR spectra being obtained during the intervening dark periods
or (for the continuous irradiation) during the irradiation.
Chemicals. The chemicals used and their stated purities
were as follows: cyclohexane (HPLC grade), Fisher Scientific;
acetaldehyde (99.5+%), butanal (99%), 2-heptanone (98%),
pentanal (99%), 2,4-pentanedione (99+%), 2-pentanone
(99+%), and propanal (99+%), Aldrich Chemical Co.; and
NO (g99.0%), Matheson Gas Products. Methyl nitrite was
prepared as described by Taylor et al. (13), while ethyl nitrite
was distilled from a commercial 15% solution by weight of
C2H5ONO in ethanol (Aldrich Chemical Co.), and both nitrites
were stored at 77 K under vacuum.
Teflon Chamber with Analysis by GC-FID and GC-MS.
For the experiments carried out in the 7900-L Teflon chamber
(at ∼5% relative humidity), the initial reactant concentrations
(in molecule cm-3 units) were as follows: CH3ONO, (2.2-
2.3) × 1014; NO, (2.1-2.4) × 1014; and 2-pentanone or
2-heptanone, (2.25-2.46) × 1013. Irradiations were carried
out at 20% of the maximum light intensity for 15-45 min,
resulting in up to 33% and 44% reaction of the initial
2-pentanone or 2-heptanone, respectively. GC-FID analyses
of the ketones and their reaction products were carried out
as described above, with the DB-1701 megabore column
being initially held at -40 or -60 °C and then temperature
programmed to 200 °C at 8 °C min-1. Gas samples were also
collected from the chamber onto Tenax-TA solid adsorbent
for thermal desorption with analysis by GC-MS after
preconcentration by an Entech 7000 dehydration precon-
centrator, using a 30-m DB-1701 fused silica capillary column
in a Hewlett-Packard (HP) 5890 GC interfaced to a HP 5971A
mass selective detector operating in the scanning mode. GC-
FID response factors for 2-pentanone, 2-heptanone, acetal-
dehyde, propanal, butanal, pentanal, and 2,4-pentanedione
were determined as described previously (11).
Teflon Chamber with Analysis by API-MS. In the experi-
ments with API-MS analyses, the chamber contents were
sampled through a 25 mm diameter × 75 cm length Pyrex
tube at ∼20 L min-1 directly into the API mass spectrometer
source. The operation of the API-MS in the MS (scanning)
and MS/ MS [with collision activated dissociation (CAD)]
modes has been described elsewhere (12). Use of the MS/
MS mode with CAD allows the “daughter ion” or “parent
ion” spectrum of a given ion peak observed in the MS
scanning mode to be obtained (12). The positive ion mode
was used in these analyses, with protonated water hydrates
[H3O+(H2O)n] being used as the ionizing agent and resulting
in the ions that were mass-analyzed being mainly protonated
molecular ions ([M + H]+) and their protonated homo- and
heterodimers (12). The initial concentrations of CH3ONO,
NO, and 2-pentanone or 2-heptanone were ∼4.8 × 1013
molecule cm-3 each, and irradiations were carried out for 10
(2-heptanone) or 15 min (2-pentanone) at 20% of the
maximum light intensity.
Results
Kinetic Studies. The data obtained from a series of irradiated
CH3ONO-NO-2-pentanone-2-heptanone-cyclohexane-
air mixtures are plotted in accordance with eq I in Figure 1.
Good straight line plots are observed, and the rate constant
ratios k1/ k2 obtained from these plots by least-squares
analyses are given in Table 1. These rate constant ratios k1/ k2
are placed on an absolute basis by use of a rate constant k2
for the reaction of the OH radical with cyclohexane of k2 )
7.21 × 10-12 cm3 molecule-1 s-1 at 298 K (14), and the resulting
rate constants k1 are given in Table 1.
Product Studies. Teflon Chamber with Analysis by GC-
FID. GC-FID and GC-MS analyses of irradiated CH3ONO-
NO-2-pentanone (or 2-heptanone)-air mixtures showed the
formation of acetaldehyde, propanal, and 2,4-pentanedione
[CH3C(O)CH2C(O)CH3] from 2-pentanone and the formation
of acetaldehyde, propanal, butanal, and pentanal from
2-heptanone. These products also react with the OH radical,
9
6 2 4 ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 34, NO. 4, 2000

TABLE 1. Rate Constant Ratios k1/k2 and Rate Constants k1 for the Gas-Phase Reactions of the OH Radical with 2-Pentanone
and 2-Heptanone at Room Temperature
1012 × k1 (cm3 molecule-1 s-1
)
a
ketone
k1/k2
this workb
literature
temp (K)
reference
2-pentanone
0.633 ( 0.041
4.56 ( 0.30
4.53 ( 0.14c
4.00 ( 0.29
4.88 ( 0.25c
8.67 ( 0.84
299 ( 2
296
296 ( 2
296
Atkinson et al. (4)
Wallington and Kurylo (5)
Atkinson and Aschm ann (6)
Wallington and Kurylo (5)
2-heptanone
1.62 ( 0.14
11.7 ( 1.1
a
b
Indicated errors are two least-squares standard deviations. At 298 ( 2 K. Placed on an absolute basis using a rate constant of k2(cyclohexane)
) 7.21 × 10-12 cm 3 m olecule-1 s-1 at 298 K (14). Indicated errors are two least-squares standard deviations and do not take into account the
c
uncertainties associated with the rate constant k2. Relative rate study with cyclohexane as the reference organic. Placed on an absolute basis
using a rate constant of k2 ) 2.88 × 10-17 T2 e309/T cm 3 m olecule-1 s-1 (14).
SCHEME 1
TABLE 2. Products Observed and Their Formation Yields from
the Reactions of the OH Radical with 2-Pentanone and
2-Heptanone in the Presence of NO
formation yield
a
b
product
GC-FID
FT-IR
2-Pentanone Reaction
form aldehyde
acetaldehyde
propanal
2,4-pentanedione
organic nitrates
1.03 ( 0.10
0.51 ( 0.11
0.19 ( 0.03
0.12 ( 0.03
0.12 ( 0.04
0.38 ( 0.08
2-Heptanone Reaction
form aldehyde
acetaldehyde
propanal
butanal
pentanal
0.15 ( 0.03 (0.05)c
0.10 ( 0.02 (0.05)c
0.07 ( 0.01
0.09 ( 0.01
organic nitrates
0.18 ( 0.05
a
Indicated errors are two least-squares standard deviations com -
bined with estim ated uncertainties in the GC-FID response factors for
the carbonyls of (5% each. Estim ated overall uncertainties. Values
in parentheses are the initial form ation yields obtained using second-
order regression analyses (see text and Figure 2).
and their secondary reactions were taken into account as
described previously (15) with rate constants for the reactions
of the OH radical (in units of 10-12 cm3 molecule-1 s-1) as
follows: 2-pentanone, 4.66 (this and previous work from this
laboratory, see below); 2-heptanone, 11.7 (this work, see
below); acetaldehyde, 15.8 (1); propanal, 19.6 (1); butanal,
23.5 (1); pentanal, 28.5 (9); and 2,4-pentanedione, 1.15 (16).
The multiplicative factors F to take into account the secondary
reactions of OH radicals with the carbonyl products increase
with the rate constant ratio k(OH + product)/ k(OH + ketone)
and with the extent of reaction (15). The maximum values
of F were as follows: acetaldehyde, 1.92 (2-pentanone
reactions) and 1.84 (2-heptanone reactions); propanal, 2.20
(2-pentanone reactions) and 2.09 (2-heptanone reactions);
butanal, 2.37 (2-heptanone reactions); pentanal, 2.77 (2-
heptanone reactions); and 2,4-pentanedione, 1.06 (2-pen-
tanone reactions).
Secondary reactions of OH radicals with the aldehyde
products can lead to the formation of the corresponding
aldehyde with one less carbon atom (1, 2); for example,
butanal from pentanal, propanal from butanal, and acetal-
dehyde from propanal by reactions such as those shown in
Scheme 1. Hence the observed concentrations of butanal,
propanal, and acetaldehyde (and especially of acetaldehyde
and propanal) may be influenced by secondary formation
from higher aldehydes. Plots of the amounts of acetaldehyde,
propanal, and 2,4-pentanedione formed (corrected for reac-
tions of the products with the OH radical) against the amounts
of 2-pentanone reacted were good straight lines and the
product formation yields obtained by least-squares analyses
are given in Table 2. Plots of the amounts of aldehydes formed
against the amounts of 2-heptanone reacted, shown in Figure
2, are good straight lines for pentanal (as expected, since
pentanal is not expected to be a secondary product) and
butanal, but there is curvature in the propanal and acetal-
b
c
dehyde plots, with higher formation yields at larger extents
of reaction (Figure 2). Analyses of the data using second-
order regressions results in the fits shown in Figure 2. The
butanal and pentanal concentrations (corrected for secondary
reaction with the OH radical) are clearly fit well by first-
order regressions (the initial slopes of the second-order fits
are indistinguishable from the slopes of the linear least-
squares analyses and the coefficients for the ([2-heptanone]
reacted)2 term are close to zero), while the data for acetal-
dehyde and propanal are better fit by second-order regres-
sions. The initial slopes of the second-order regressions for
acetaldehyde and propanal are also given in Table 2 together
with the least-squares slopes of the first-order regressions.
Teflon Chamber with Analyses by API-MS. API-MS/ MS
daughter ion and parent ion spectra were obtained for ion
peaks observed in the API-MS analyses of irradiated CH3-
ONO-NO-2-pentanone-air and CH3ONO-NO-2-hep-
tanone-air mixtures. Product ion peaks were identified based
on the observation of homo- or heterodimer ions (for
example, [(MP1)2 + H]+, [(MP2)2 + H]+, and [MP1 + MP2 + H]+,
where P1 and P2 are products or the 2-pentanone and
2-heptanone reactants) in the API-MS/ MS parent ion spectra
and consistency of the API-MS/ MS daughter ion spectrum
of a homo- or heterodimer ion with the parent ion spectra
of the various [MP + H]+ ion peaks, as described in detail
previously (12). Water cluster ion peaks of the product ions,
[M + H + H2O]+, were also occasionally observed.
Products of molecular weight 100 (attributed to 2,4-
pentanedione) and 147 were observed from the 2-pentanone
reaction, and products of molecular weight 128, 144, and
9
VOL. 34, NO. 4, 2000 / ENVIRONMENTAL SCIENCE & TECHNOLOGY 6 2 5

FIGURE 4. API-MS/MS CAD “daughter ion” spectrum of the 176 u
FIGURE 2. Plots of the amounts of acetaldehyde, propanal, butanal,
and pentanal formed, corrected for reaction with the OH radical,
against the amounts of 2-heptanone reacted with the OH radical
in the presence of NO using second-order regression analyses (see
text). Analyses by GC-FID. The concentrations of pentanal, propanal,
and acetaldehyde have been displaced vertically by 4 × 1011, 8 ×
1011, and 1.2 × 1012 molecule cm-3, respectively, for clarity.
ion peak observed in the API-MS analyses of irradiated CH ONO-
3
NO-2-heptanone-air mixtures. The 113 u ion peak is attributed to
a loss of HNO , and the 46 u fragment ion is attributed to NO +.
3
2
spectroscopy. Identification and quantification of carbonyl
group-containing species was rendered difficult because
products containing carbonyl groups absorb in the same
∼1740 cm-1 region as do 2-pentanone and 2-heptanone.
Indeed, GC-FID analyses (with sampling modifications to
allow for the higher concentrations involved) were required
to aid in determining the amounts of 2-pentanone and
2-heptanone reacted during the experiments, and analyses
of carbonyl products other than HCHO (for example, those
observed by GC-MS and API-MS analyses and shown in
Table 2) by FT-IR spectroscopy was not possible.
Figure 5A shows a vapor-phase infrared spectrum of
2-pentanone. Figure 5B is the product spectrum obtained
from a CH3ONO-NO-2-pentanone-air mixture after 32 min
of irradiation that resulted in 14.3% consumption of the initial
2.46 × 1014 molecule cm-3 of 2-pentanone. In Figure 5B, the
absorptions by the remaining reactants (the 2-pentanone
concentrations were determined in part by concurrent GC
analyses) and by the products attributed to the photooxi-
dation of methyl nitrite in the presence of NO (HCHO, CH3-
ONO2, HCOOH, NO2, HONO, and HNO3) have been sub-
tracted from the plot. Figure 5C is the residual spectrum
after subtraction from Figure 5B of the absorptions by
peroxyacyl nitrates, specifically 1.4 × 1013 molecule cm-3 of
peroxyacetyl nitrate [CH3C(O)OONO2; PAN] (Figure 5D) and
4.3 × 1012 molecule cm-3 of peroxypropionyl nitrate [CH3-
CH2C(O)OONO2; PPN] (Figure 5E). PAN and PPN are
secondary products arising from the expected products
acetaldehyde and propanal (1, 2), and their apparent yields
increased with the extent of reaction. In Figure 5C, and as
noted above, the acetaldehyde and propanal absorptions
could not be accurately distinguished from each other and
from other possible carbonyl products.
In Figure 5C and in a similar product spectrum obtained
for the case of 2-heptanone, distinct absorption bands near
856, 1285, and 1655 cm-1 indicate the formation of organic
nitrates (RONO2). The specific RONO2 product(s) formed
could not be identified. However, an estimate of the molar
RONO2 concentration was made from the integrated intensity
of the ∼1655 cm-1 absorption band (assigned to the asym-
metric NO2 stretch and which is distinct from that of ROONO2
species) and the average integrated absorption coefficient of
the corresponding bands of other organic nitrates. Thus,
measurements in this laboratory on the corresponding bands
FIGURE 3. API-MS/MS CAD “daughter ion” spectrum of the 148 u
ion peak observed in the API-MS analyses of irradiated CH ONO-
3
NO-2-pentanone-air mixtures. The 85 u ion peak is attributed to
a loss of HNO , and the 46 u fragment ion is attributed to NO +.
3
2
175 were observed from the 2-heptanone reaction. Figures
3 and 4 show the API-MS/ MS CAD daughter ion spectra of
the 148 and 176 u [M + H]+ ions observed in the 2-pentanone
and 2-heptanone reactions, respectively, with these spectra
indicating that these molecular weight 147 and 175 products
are (as expected from their odd molecular weights) organic
nitrates (i.e., from the observations of a loss of HNO3 and the
presence of a 46 u NO2+ fragment ion). The possible identities
of the molecular weight 128 and 144 products from the
2-heptanone reaction are dealt with in the Discussion section
below.
Evacuable Chamber Experiments with FT-IR Analysis.
Analyses of reactants and products during irradiated methyl
(and ethyl) nitrite-NO-2-pentanone (or 2-heptanone)-air
mixtures were carried out by in situ FT-IR absorption
9
6 2 6 ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 34, NO. 4, 2000

Discussion
2-Pentanone Reaction. As shown in Table 1, our present
rate constant for the reaction of the OH radical with
2-pentanone is in excellent agreement (to within 7%) with
those previously measured in this laboratory (4, 6) and is in
good agreement with, being 14% higher than, the absolute
rate constant of Wallington and Kurylo (5). We have used an
average of the three relative rate measurements of the rate
constant of k1(2-pentanone) ) 4.66 × 10-12 cm3 molecule-1
s-1 for the purposes of correcting for secondary reactions of
the products observed (see above).
The OH radical reaction with 2-pentanone can proceed
by four pathways, all involving H-atom abstraction from the
C-H bonds (1).
The empirical estimation method of Kwok and Atkinson (17)
predicts the total OH radical reaction rate constant for
2-pentanone to within 5% of the measured value, and further
predicts that reaction pathways 3a-d account for 2%, 18%,
76%, and 3.5%, respectively, of the total reaction.
In the troposphere, the alkyl radicals formed in reactions
3a-d react solely with O2 to form the corresponding peroxy
radicals (1, 14), as shown for the CH3C(O)CH2C˙ HCH3 radical:
FIGURE 5. Infrared spectra from a CH ONO-NO-2-pentanone-air
3
irradiation. (A) Initial 2-pentanone. (B) Products (except HCHO)
corresponding to 14.3% consumption of the initial 2-pentanone. (C)
From panel B with absorptions by peroxyacetyl nitrate (PAN) and
peroxypropionyl nitrate (PPN) subtracted. (D) PAN reference
spectrum. (E) PPN reference spectrum. Numbers in parentheses
are the concentrations in molecule cm-3. Gaps in the traces of
panels B and C correspond to strong absorptions by NO formed and
2
CH3C(O)CH2C˙ HCH3 + O2 f CH3C(O)CH2CH(OO˙ )CH3
to accumulated NO - ions on the KBr windows.
3
(4)
of methyl nitrate, ethyl nitrate, 1-propyl nitrate, and per-
oxyacetyl nitrate (PAN) showed an average integrated
absorption coefficient (base 10) of (2.5 ( 0.2) × 10-17 cm
molecule-1 (10). Using this value, the average RONO2 yields
obtained from 2-pentanone and 2-heptanone are given in
Table 2, where the cited estimated overall uncertainties
include the uncertainties associated with the absorption
coefficient used.
Under the conditions employed in our experiments, the
organic peroxy radicals then react with NO to form the
corresponding alkoxy radical plus NO2 or the organic nitrate
(RONO2) (1, 2).
The yields of HCHO were determined by FT-IR spec-
troscopy from irradiated C2H5ONO-NO-2-pentanone (or
2-heptanone)-air mixtures, with subtraction of the parent
ketone absorptions again being indexed to the GC-FID
analyses. The product spectra obtained by subtraction of
absorptions by the remaining reactants and byproducts
attributed to ethyl nitrite photolysis in the presence of NO
(CH3CHO, C2H5ONO, NO2, HONO, and HNO3) were similar
to those from experiments that employed methyl nitrite,
except for larger quantities of PAN formed as a secondary
product of ethyl nitrite. The exact subtraction of absorptions
by CH3CHO and other carbonyl products was not necessary
since the analysis of HCHO was based on its sharp Q-branch
feature at 1745 cm-1, which is readily distinguished from the
other, much broader CdO stretch absorption bands. HCHO
measurements were obtained within a 12-min total irradia-
tion period and 12.0% consumption of 2-pentanone and
within a 9-min total irradiation period and 15.2% consump-
tion of 2-heptanone, with an initial concentration of 2.46 ×
1014 molecule cm-3 for each reactant ketone. The measured
HCHO concentrations were corrected for secondary reaction
with the OH radical using an OH radical reaction rate constant
of 9.37 × 10-12 cm3 molecule-1 s-1 (1), with the multiplicative
correction factors to take into account secondary reactions
being <1.17 for the 2-pentanone reactions and <1.11 for the
2-heptanone reactions. The formation yields of HCHO
obtained from least-squares analyses of the data are given
in Table 2.
The organic nitrates formed from the reactions of the peroxy
radicals with NO [CH3C(O)CH2CH2CH2ONO2, CH3C(O)CH2-
CH(ONO2)CH3, CH3C(O)CH(ONO2)CH2CH3, and O2NOCH2-
C(O)CH2CH2CH3] have a molecular weight of 147, and their
formation is consistent with our API-MS and API-MS/ MS
observations of a product(s) of molecular weight 147 (Figure
3) and with the in situ FT-IR analyses discussed above.
The alkoxy radicals then react via a number of pathways,
involving decomposition by C-C bond scission, isomeriza-
tion via a six-membered transition state, and reaction with
O2 (1, 14, 18) [noting that not all of these three reaction
pathways are possible for all four of the alkoxy radicals initially
formed from 2-pentanone]. Scheme 2 shows the possible
reactions of the CH3C(O)CH2CH(O˙ )CH3 radical leading to
first-generation products [the detailed reactions of C˙ H3 and
acyl (RC(O)O) radicals are not shown for clarity, rather the
known products (1, 2) are shown].
O˙ CH2C(O)CH2CH2CH3 Radical. This alkoxy radical can
decompose, isomerize, or react with O2. On the basis of the
reactions of the CH3C(O)CH2O˙ and CH3C(O)CH(O˙ )CH3
radicals of similar structure formed from acetone and
2-butanone, respectively, for which the decomposition
reactions dominate over reaction with O2 (19, 20), the O2
reaction is anticipated to be of negligible importance. The
O˙ CH2C(O)CH2CH2CH3 radical can also isomerize, but it is
9
VOL. 34, NO. 4, 2000 / ENVIRONMENTAL SCIENCE & TECHNOLOGY 6 2 7

(O˙ )(CH3)2 radical being estimated (14, 18) to be ∼4 × 105 s-1
at 298 K. Hence, it is possible that the dominant reactions
of the CH3C(O)CH2CH(O˙ )CH3 radical are by decomposition
and/ or reaction with O2. The decomposition pathway
SCHEME 2
CH3C(O)CH2CH(O˙ )CH3 f CH3CHO + CH3C(O)C˙ H2 (8)
followed by reactions of the CH3C(O)C˙ H2 radical under
tropospheric conditions results in the formation of CH3CHO,
2HCHO, and CO2 (1, 2), while the O2 reaction
CH3C(O)CH2CH(O˙ )CH3 + O2 f
CH3C(O)CH2C(O)CH3 + HO2 (9)
leads to the observed product 2,4-pentanedione.
CH3C(O)CH2CH2CH2O˙ Radical. This alkoxy radical can
decompose or react with O2 (but not isomerize through a
six-membered transition state). The estimation method of
Atkinson (14, 18) predicts that reaction with O2 will dominate
at room temperature and atmospheric pressure of air:
not known, a priori, how important this pathway is. The
decomposition reaction
CH3C(O)CH2CH2CH2O˙ + O2 f
CH3C(O)CH2CH2CHO + HO2 (10)
O˙ CH2C(O)CH2CH2CH3 f HCHO + CH3CH2CH2C˙ O (6)
leading to the formation of the molecular weight 100 keto-
aldehyde CH3C(O)CH2CH2CHO.
leads to the formation of the acyl radical CH3CH2CH2C˙ O,
which will react in the atmosphere (via the intermediary of
the acyl peroxy radical CH3CH2CH2C(O)OO˙ ) to form the
1-propyl radical, which will react to form propanal [plus a
small amount of 1-propyl nitrate] (1, 14).
CH3C(O)CH(O˙ )CH2CH3 Radical. This alkoxy radical can
decompose or react with O2. On the basis of the reactions
of the analogous CH3C(O)CH2O˙ and CH3C(O)CH(O˙ )CH3
radicals (19, 20), the decomposition reaction is anticipated
to totally dominate under our conditions:
Table 3 gives the potential products arising from the four
initially formed peroxy radicals, together with an a priori
estimate of the relative importance of the particular pathways
based on the discussion given in Atkinson and Aschmann
(22) and Atkinson (14, 18). Given the expected low formation
yields of C˙ H2C(O)CH2CH2CH3 and CH3C(O)CH2CH2CH2O˙
radicals, then the expected major products from the OH
radical reaction with 2-pentanone in the presence of NO are
the molecular weight 147 C5H9O(ONO2) nitrates formed from
the RO˙ 2 + NO reactions, CH3C(O)CH2C(O)CH3, CH3CHO +
2HCHO and/ or isomerization products from the CH3C(O)-
CH2CH(O˙ )CH3 radical, and CH3CH2CHO + HCHO from the
CH3C(O)CH(O˙ )CH2CH3 radical. Our experimental data are
in agreement with these expectations, with 19 ( 3% propanal
(plus coproduct HCHO) arising from the CH3C(O)CH(O˙ )CH2-
CH3 radical and 51 ( 11% acetaldehyde (plus coproduct
HCHO with twice the acetaldehyde yield) and 12 ( 3% 2,4-
pentanedione arising from the CH3C(O)CH2CH(O˙ )CH3 radi-
cal. Our observed HCHO yield of 103 (10% agrees reasonably
well with that of 121 ( 23% expected from HCHO being a
coproduct to the acetaldehyde and propanal products. Our
observed products account for 94 ( 13% of the total reaction
pathways and the amounts of products arising from the
CH3C(O)CH(O˙ )CH2CH3 f CH3C˙ O + CH3CH2CHO (7)
The alternative decomposition pathway to CH3C(O)CHO +
CH3C˙ H2 is thermochemically less favorable by ∼11 kcal mol-1
(21) and is therefore expected to be of minor or negligible
importance. The acetyl radical, CH3C˙ O, will react to form
HCHO plus CO2 (1, 2).
CH3C(O)CH2CH(O˙ )CH3 Radical. As shown in Scheme 2,
this alkoxy radical can decompose, isomerize, or react with
O2. For the analogous radical CH3C(O)CH2C(O˙ )(CH3)2 formed
from 4-methyl-2-pentanone, Atkinson and Aschmann (22)
showed that isomerization did not compete with decom-
position, with the decomposition rate of the CH3C(O)CH2C-
TABLE 3. Potential First-Generation Products Arising from the Initially Formed Alkoxy Radicals Formed in the Reaction of the OH
Radical with 2-Pentanone
RO4 radical
reaction pathway
product
O˙ CH2C(O)CH2CH2CH3
(2%)
O2 reactiona
decom position
isom erization
CH3CH2CH2C(O)CHO
HCHO + CH3CH2CHO
HOCH2C(O)CH2C(O)CH3 or CH3CHO +
2HCHO or CH3CH(OH)CH2C(O)CHO
CH3C(O)CH(O˙ )CH2CH3
(18%)
O2 reactiona
CH3C(O)C(O)CH2CH3
CH3C(O)CHO + CH3CHO
CH3CH2CHO + HCHO
decom positionb
decom position
CH3C(O)CH2CH(O˙ )CH3
(76%)
O2 reaction
decom position
isom erization
CH3C(O)CH2C(O)CH3
CH3CHO + 2HCHO
HOCH2C(O)CH2C(O)CH3 or
CH3CHO + 2HCHO
CH3C(O)CH2CH2CH2O˙
(3.5%)
O2 reaction
CH3C(O)CH2CH2CHO
HCHO + CH3C(O)CH2CHO
4HCHO
decom positiona
decom positiona
a˙
b
Reaction pathways expected to be of m inor im portance (1, 14, 18). Expected to be m inor relative to the other decom position pathway.
9
6 2 8 ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 34, NO. 4, 2000

TABLE 4. Potential First-Generation Products Arising from the Initially Formed Alkoxy Radicals from the Reaction of the OH
Radical with 2-Heptanone
RO4 radical
reaction pathway
product
O˙ CH2C(O)CH2CH2CH2CH2CH3
O2 reactiona
CH3CH2CH2CH2CH2C(O)CHO
HCHO + CH3CH2CH2CH2CHO
HOCH2C(O)CH2C(O)CH2CH2CH2OH
CH3CH2CH2CH(OH)CH2C(O)CHO
CH3C(O)C(O)CH2CH2CH2CH3
CH3C(O)CHO + 0.23CH3CH2CH2CHO +
0.77HOCH2CH2CH2CHO
(1%)
decom position
isom erization
isom erization
O2 reactiona
CH3C(O)CH(O˙ )CH2CH2CH2CH3
(11%)
decom positionb
decom position
isom erization
O2 reaction
decom position
decom position
isom erization
O2 reaction
decom position
decom position
O2 reaction
CH3CH2CH2CH2CHO + HCHO
CH3C(O)C(O)CH2CH2CH(OH)CH3
CH3C(O)CH2C(O)CH2CH2CH3
CH3CH2CH2CHO + 2HCHO
CH3C(O)CH2CH(O˙ )CH2CH2CH3
(55%)
CH3C(O)CH2CHO + CH3CH2CHO
CH3C(O)CH2C(O)CH2CH2CH2OH
CH3C(O)CH2CH2C(O)CH2CH3
CH3CHO + CH3C(O)CH2CH2CHO
CH3CH2CHO + CH3C(O)CH2CHO
CH3C(O)CH2CH2CH2C(O)CH3
CH3CHO + CH3C(O)CH2CH2CHO
CH3C(O)CH(OH)CH2CH2C(O)CH3
HCHO + CH3CH(OH)CH2CH2CHO
CH3C(O)CH2CH2CH2CH2CHO
HCHO + CH3C(O)CH2CH2CH2CHO
CH3C(O)CH2CH(OH)CH2CH2CHO
CH3C(O)CH2CH2CH(O˙ )CH2CH3
(17%)
CH3C(O)CH2CH2CH2CH(O˙ )CH3
(14%)
decom position
isom erization
isom erization
O2 reaction
CH3C(O)CH2CH2CH2CH2CH2O˙
(2%)
decom positiona
isom erization
a
b
Reaction pathways expected to be of m inor im portance. This pathway expected to be less im portant than the other decom position pathway.
CH3C(O)CH(O˙ )CH2CH3 and CH3C(O)CH2CH(O˙ )CH3 radicals
(19 ( 3% and 63 ( 12%, respectively) are similar to the
predicted percentages of the alkoxy radicals formed [18%
and 76% formation of their precursor peroxy radicals (17),
with the occurrence of organic nitrate formation from the
RO˙ 2 + NO reactions leading to slightly lower formation yields
of the alkoxy radicals]. It is entirely possible that the products
formed from the CH3C(O)CH2CH2CH2O˙ radical in low overall
yield and any isomerization products of the CH3C(O)CH2-
CH(O˙ )CH3 radical were not identified and quantified and
account in part for the e19% products not presently
accounted for (noting that within the uncertainties our
product yields do account for 100% of the reaction pathways).
2-Heptanone Reaction. As shown in Table 1, our present
rate constant for the reaction of the OH radical with
2-heptanone is 35% higher than the absolute rate constant
determined by Wallington and Kurylo (5). As noted in the
Introduction, there are also discrepancies between the
absolute rate study of Wallington and Kurylo (5) and our
previous relative rate measurements (4, 6) for the reactions
of the OH radical with 2- and 3-pentanone and 2-hexanone.
The absolute rate method used by Wallington and Kurylo (5)
required that the ketone concentrations in the reaction vessel
be known, and these were calculated from the flows of the
various reactant gas streams entering the reaction vessel. It
is possible that in the Wallington and Kurylo (5) study the
larger ketones were subject to wall losses, thereby resulting
in erroneously low measured rate constants.
discussion given in Atkinson and Aschmann (22) and Atkinson
(1, 14, 18). As an example of these reaction pathways, Scheme
3 shows the possible reaction pathways for the alkoxy radical
CH3C(O)CH(O˙ )CH2CH2CH2CH3 [the reactions of the CH3-
CH2CH2C˙ H2 and CH3C˙ O are not shown in detail, because
under atmospheric conditions the CH3CH2CH2C˙ H2 radical
is known to form CH3CH2CH2CHO (23%) plus HOCH2CH2-
CH2CHO (77%) and the CH3C˙ O radical leads to the formation
of HCHO (1, 2, 14, 18)]. Our conclusions concerning the
reactions of the four major initially formed alkoxy radicals
are briefly discussed below.
CH3C(O)CH(O˙ )CH2CH2CH2CH3 Radical. The only route to
formation of pentanal is via decomposition of the CH3C-
(O)CH(O˙ )CH2CH2CH2CH3 radical (Table 4). Furthermore, the
formation yield of pentanal (9 ( 1%) is similar to the
calculated formation yield of the CH3C(O)CH(O˙ )CH2CH2CH2-
CH3 radical of e11% (17) [with the calculated yield of the
CH3C(O)CH(O˙ )CH2CH2CH2CH3 radical depending on the
amount of organic nitrate formed from the reaction of the
CH3C(O)CH(OO˙ )CH2CH2CH2CH3 radical with NO]. Thus, the
dominant reaction of the CH3C(O)CH(O˙ )CH2CH2CH2CH3
radical appears to be decomposition to form pentanal plus
HCHO (Scheme 3).
CH3C(O)CH2CH(O˙ )CH2CH2CH3 Radical. The CH3C(O)CH2-
CH(O˙ )CH2CH2CH3 radical can decompose to form butanal
plus two molecules of HCHO, decompose to form CH3C-
(O)CH2CHO plus propanal, react with O2 to form the
molecular weight 128 dicarbonyl CH3C(O)CH2C(O)CH2CH2-
CH3, and isomerize to form mainly the molecular weight 144
hydroxydicarbonyl CH3C(O)CH2C(O)CH2CH2CH2OH. Be-
cause the butanal formation yield from the 1-butoxy radical
under atmospheric conditions is ∼23% (1, 14) (Scheme 3
and Table 4), most, if not all, of the butanal observed must
arise from decomposition of the CH3C(O)CH2CH(O˙ )CH2CH2-
CH3 radical with the remainder of the CH3C(O)CH2CH(O˙ )-
CH2CH2CH3 radical reacting with O2 to form the molecular
weight 128 dicarbonyl CH3C(O)CH2C(O)CH2CH2CH3 and
isomerizing to form mainly the molecular weight 144
hydroxydicarbonyl CH3C(O)CH2C(O)CH2CH2CH2OH.
CH3C(O)CH2CH2CH(O˙ )CH2CH3 Radical. The CH3C(O)CH2-
CH2CH(O˙ )CH2CH3 radical can react with O2 to form the
molecular weight 128 dicarbonyl CH3C(O)CH2CH2C(O)CH2-
As for 2-pentanone, the OH radical reaction with 2-hep-
tanone proceeds by H-atom abstraction from the various
C-H bonds. The resulting alkyl-type radicals will add O2 to
form organic peroxy (RO˙ ) radicals. These RO˙ 2 radicals then
2
react with NO to form either the molecular weight 175 organic
nitrates observed by API-MS and API-MS/ MS analyses (Figure
4) and consistent with our in situ FT-IR analyses or the
corresponding alkoxy radical plus NO2 as shown in reactions
5a and 5b above for the 2-pentanone reaction. The alkoxy
radicals formed, the estimated percent of the precursor
peroxy radicals formed (17), and the potential first-generation
products formed from their subsequent reactions are given
in Table 4 together with an a priori assessment of the relative
importance of the particular reaction pathways based on the
9
VOL. 34, NO. 4, 2000 / ENVIRONMENTAL SCIENCE & TECHNOLOGY 6 2 9

SCHEME 3
CH3, decompose to form acetaldehyde plus CH3C(O)CH2-
CH2CHO, or decompose to form propanal plus CH3C(O)CH2-
CHO. On the basis of the reactions of alkoxy radicals (e.g.,
2-butoxy and 3-pentoxy radicals) formed from the n-alkanes
(14, 18), reaction with O2 is expected to dominate over
decomposition, and hence we anticipate the formation of
the molecular weight 128 dicarbonyl CH3C(O)CH2CH2C(O)-
CH2CH3 from this radical.
indicate that in general the reactions of the ketones are
analogous to those of the alkanes, in that the intermediate
alkoxy radicals can decompose, isomerize, and react with
O2. Furthermore, the occurrence of the alkoxy radical
isomerization reaction (which proceeds through a six-
membered transition state) becomes important for com-
pounds with a g5-carbon chain (and was observed here for
2-heptanone).
Acknowledgments
The authors thank the Eastman Chemical Company for
supporting this research, and Dr. David A. Morgott (Eastman
Kodak Company) for helpful comments.
CH3C(O)CH2CH2CH2CH(O˙ )CH3 Radical. The CH3C(O)CH2-
CH2CH2CH(O˙ )CH3 radical can react with O2 to form the
molecular weight 128 dicarbonyl CH3C(O)CH2CH2CH2C(O)-
CH3, decompose to form acetaldehyde plus CH3C(O)CH2-
CH2CHO, and isomerize to form HCHO plus CH3CH(OH)-
CH2CH2CHO or the molecular weight 144 hydroxydicarbonyl
CH3C(O)CH(OH)CH2CH2C(O)CH3. We expect that isomer-
ization dominates (see also the discussion below).
Literature Cited
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(2) Atkinson, R. Atmos. Environ., in press.
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Int. J. Chem. Kinet. 1982, 14, 839-847.
As evident from Table 3, the reaction pathways leading
to the formation of pentanal and butanal predict that the
coproduct formaldehyde should have a yield of 23 ( 2% and
suggest that the remaining 15 ( 9% of HCHO arises largely
from the isomerization channel of the CH3C(O)CH2CH2CH2-
CH(O˙ )CH3 radical (HCHO can also be formed as a result of
secondary reactions of the other first-generation products
such as acetaldehyde). Our data analysis therefore suggests
that we have identified ∼60% of the overall reaction pathways,
with the formation of molecular weight 128 dicarbonyls such
as CH3C(O)CH2C(O)CH2CH2CH3, CH3C(O)CH2CH2C(O)CH2-
CH3, and CH3C(O)CH2CH2CH2C(O)CH3 and molecular weight
144 hydroxydicarbonyls such as CH3C(O)CH2C(O)CH2CH2-
CH2OH accounting for the remaining ∼40% of products that
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FT-IR spectroscopy.
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Tropospheric Lifetim es and Products. The reactions of
the OH radical with 2-pentanone and 2-heptanone result in
calculated lifetimes of these two ketones of 2.5 and 1.0 day,
respectively, for a 24-h average OH radical concentration of
1.0 × 106 molecule cm-3 (23, 24). Our product studies indicate
that the reactions of 2-pentanone are relatively straightfor-
ward and involve reactions of the intermediate first-formed
alkoxy radicals with O2 and decomposition, while in the
2-heptanone system the first-formed intermediate alkoxy
radicals also isomerize, with the isomerization reactions
potentially dominating in some cases. Our product analyses
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1695.
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(23) Prinn, R. G.; Weiss, R. F.; Miller, B. R.; Huang, J.; Alyea, F. N.;
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Received for review August 11, 1999. Revised manuscript
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ES9909374
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