Kinetics and products of the reactions of selected diols with the OH radical

Article abstract of DOI:10.1002/kin.1025

Using a relative rate method, rate constants been measured at 296 ± 2 K for the gas-phase reactions of OH radicals with 1,2-butanediol, 2,3-butanediol, 1,3-butanediol, and 2-methyl-2,4-pentanediol, with rate constants (in units of 10^-12 cm³ molecule^-1 s^-1) of 27.0 ± 5.6, 23.6 ± 6.3, 33.2 ± 6.8, and 27.7 ± 6.1, respectively, where the error limits include the estimated overall uncertainty of ±20% in the rate constant for the reference compound. Gas chromatographic analyses showed the formation of 1-hydroxy-2-butanone from 1,2-butanediol, 3-hydroxy-2-butanone from 2,3-butanediol, 1-hydroxy-3-butanone from 1,3-butanediol, and 4-hydroxy-4-methyl-2-pentanone from 2-methyl-2,4-pentanediol, with formation yields of 0.66 ± 0.11, 0.89 ± 0.09, 0.50 ± 0.09, and 0.47 ± 0.09, respectively, where the indicated errors are the estimated overall uncertainties. Pathways for the formation of these products are presented, together with a comparison of the measured and estimated rate constants and product yields.

Full text of DOI:10.1002/kin.1025

Kinetics and Products of
the Reactions of Selected
Diols with the OH Radical
HEIDI L. BETHEL, ROGER ATKINSON,1,2 JANET AREY1
Air Pollution Research Center, University of California, Riverside, CA 92521
Received 23 August 2000; accepted 13 December 2000
ABSTRACT: Using a relative rate method, rate constants have been measured at 296 Ϯ 2 K for
the gas-phase reactions of OH radicals with 1,2-butanediol, 2,3-butanediol, 1,3-butanediol,
Ϫ
12
3
Ϫ
1
Ϫ1
and 2-methyl-2,4-pentanediol, with rate constants (in units of 10
cm molecule s ) of
27.0 Ϯ 5.6, 23.6 Ϯ 6.3, 33.2 Ϯ 6.8, and 27.7 Ϯ 6.1, respectively, where the error limits in-
clude the estimated overall uncertainty of Ϯ20% in the rate constant for the reference
compound. Gas chromatographic analyses showed the formation of 1-hydroxy-2-butanone
from 1,2-butanediol, 3-hydroxy-2-butanone from 2,3-butanediol, 1-hydroxy-3-butanone from
1,3-butanediol, and 4-hydroxy-4-methyl-2-pentanone from 2-methyl-2,4-pentanediol, with
formation yields of 0.66 Ϯ 0.11, 0.89 Ϯ 0.09, 0.50 Ϯ 0.09, and 0.47 Ϯ 0.09, respectively,
where the indicated errors are the estimated overall uncertainties. Pathways for the for-
mation of these products are presented, together with a comparison of the measured and
estimated rate constants and product yields. ᭧ 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33:
3
10–316, 2001
INTRODUCTION
measured only for 1,2-ethanediol [6–9] and 1,2-pro-
panediol [6,7,9].
Volatile organic compounds present in the atmosphere
can undergo photolysis and chemical reaction with OH
radicals, NO radicals, and O [1,2], with the OH rad-
In this work, we have measured rate constants for
the gas-phase reactions of the diols 1,2-butanediol,
1,3-butanediol, 2,3-butanediol, and 2-methyl-2,4-pen-
tanediol with OH radicals at 296 Ϯ 2 K and have in-
vestigated selected products formed from these reac-
tions.
3
3
ical reaction being an important, and often dominant,
atmospheric loss process [1,2]. A number of diols are
used as solvents [3], and diols can be formed in the
atmosphere from the OH radical-initiated reactions of
alkenes at sufficiently lowNO concentrations that or-
ganic peroxy ϩ organic peroxy radical reactions are
important [4,5]. It is expected that the dominant at-
mospheric loss process for diols not containing
C"C bonds is by daytime reaction with the
OH radical [1,2]. To date, rate constants for the
reactions of the OH radical with diols have been
EXPERIMENTAL
Experiments were carried out in a 7900-liter Teflon
chamber, equipped with two parallel banks of
Sylvania F40/350BL blacklamps for irradiation,
at 296 Ϯ 2 K and 740 Torr total pressure of purified
air at ϳ5% relative humidity. This chamber is fitted
with a Teflon-coated fan to ensure the rapid mix-
ing of reactants during their introduction into the
chamber.
Correspondence to: R. Atkinson (ratkins@mail.ucr.edu)
1
Also Department of Environmental Sciences.
Also Department of Chemistry.
2
᭧
2001 John Wiley & Sons, Inc.

KINETICS AND PRODUCTS OF THE REACTIONS OF SELECTED DIOLS
311
Kinetic Studies
determined by introducing measured amounts of the
chemicals into the 7900-liter chamber and conducting
several replicate GC-FID analyses [12]. The experi-
mentally measured GC-FID response factors of the
four diols, the four hydroxcarbonyl products observed,
and n-octane agreed with the calculated Effective Car-
bon Numbers [13] to within Ϯ17%, indicating that the
procedures for diol and hydroxycarbonyl introduction
into the chamber and the sampling and analysis tech-
Rate constants for the OH radical reactions were de-
termined using a relative rate method in which the
relative disappearance rates of the diols and a refer-
ence compound, whose OH radical reaction rate con-
stant is reliably known, were measured in the presence
of OH radicals [9,10]. Providing that the diols and the
reference compound reacted only with OH radicals,
then [9,10]
niques were quantitative. NO and initial NO concen-
2
trations were measured using a Thermo Environmental
Instruments, Inc., Model 42 chemiluminescent NO–
[
diol]t0
ln
ͫ
ͬ
[
diol]t
NO analyzer.
x
k1
k2
[reference compound]t0
[reference compound]t
ϭ
ln
(I)
ͫ
ͬ
Product Studies
where [diol] and [reference compound] are the con-
centrations of the diol and reference compound, re-
spectively, at time t , [diol] and [reference compound]
Products were identified and quantified from the re-
actions of the OH radical with the four diols studied,
both during the kinetic experiments (see above) and
t
0
t
0
0
t
t
are the corresponding concentrations at time t, and k1
from additional irradiated CH ONO–NO–diol–air
3
and k are the rate constants for reactions (1) and (2),
respectively.
mixtures, by GC-FID and by combined gas chroma-
tography–mass spectrometry (GC-MS). The initial
2
CH ONO and NO concentrations in the irradiated
3
CH ONO–NO–diol–air mixtures and GC-FID anal-
OH ϩ diol !: products (1)
3
ysis procedures were similar to those employed in the
kinetic experiments described above, and the initial
diol concentrations were in the range (1.51–6.42) ϫ
OH ϩ reference compound !: products (2)
OH radicals were generated by the photolysis of
13
Ϫ3
1
0 molecule cm . To verify the product identities,
methyl nitrite (CH ONO) in air at wavelengths Ͼ300
3
gas samples were collected onto Tenax-TA solid ad-
sorbent for GC-MS analyses, with thermal desorption
onto a 30-m DB-1701 fused silica capillary column in
a HP 5890 GC interfaced to a HP 5971 Mass Selective
Detector operated in the scanning mode.
nm [11], and NO was added to the reactant mixtures
3
to suppress the formation of O and hence of NO3
radicals [11]. The initial reactant concentrations (in
Ϫ
3
14
molecule cm units) were: CH ONO, ϳ2.4 ϫ 10 ;
3
14
13
NO, ϳ2.4 ϫ 10 ; 1,2-butanediol, (2.64–3.01) ϫ 10 ,
,3-butanediol, (2.21–2.36) ϫ 10 , 2,3-butanediol,
2.31–4.47) ϫ 10 , or 2-methyl-2,4-pentanediol,
2.28–2.39) ϫ 10 ; and n-octane (the reference com-
pound), ϳ2.4 ϫ 10 . Irradiations were carried out for
–45 min, resulting in up to 75% consumption of the
13
1
(
(
13
Chemicals
13
The chemicals used, and their stated purities, were:
13
1
,2-butanediol (99%), 1,3-butanediol (99ϩ%), 2,3-bu-
5
tanediol (98%), 1-hydroxy-2-butanone (95%), 3-hy-
droxy-2-butanone, 4-hydroxy-4-methyl-2-pentanone
initially present diol.
The concentrations of the diols and n-octane were
measured during the experiments by gas chromatog-
raphy with flame ionization detection (GC-FID). For
(
(
99%), 2-methyl-2,4-pentanediol (99%), and n-octane
99ϩ%), Aldrich Chemical Company; 1-hydroxy-3-
butanone (95ϩ%), TCI America; and NO (Ն99.0%),
Matheson Gas Products. Methyl nitrite was prepared
and stored as described previously [11].
the analysis of the diols, hydroxycarbonyl products
3
(
see the following) and n-octane, 100-cm volume gas
samples were collected from the chamber onto Tenax-
TA solid adsorbent, with subsequent thermal desorp-
tion at ϳ225ЊC onto a 30-m DB-1701 megabore col-
umn held at 0ЊC and then temperature programmed to
RESULTS
Ϫ
1
2
00ЊC at 8ЊC min . Based on replicate analyses in the
OH Radical Reaction Rate Constants
dark, the GC-FID measurement uncertainties for the
diols were in the range 1–5%. GC-FID response fac-
tors for the diols and hydroxycarbonyl products were
A series of CH ONO–NO–diol–n-octane–air irra-
3
diations were carried out, and the data obtained are

3
12
BETHEL ET AL.
major product from each diol. By comparison of the
GC retention times and the mass spectra with those of
authentic standards, the products were confirmed to be
1
-hydroxy-2-butanone from 1,2-butanediol, 3-hy-
droxy-2-butanone from 2,3-butanediol, 1-hydroxy-3-
butanone from 1,3-butanediol, and 4-hydroxy-4-
methyl-2-pentanone from 2-methyl-2,4-pentanediol.
These hydroxycarbonyl products also react with the
OH radical [10], and their measured concentrations
were corrected for secondary reactions with the OH
radical as discussed previously [15], using the OH re-
action rate constants measured here for the diols and
those of Aschmann et al. [10] for the hydroxycarbonyl
products. The multiplicative correction factors, F, to
account for secondary reactions with the OH radical
increase with increasing rate constant ratio, k(OH ϩ
hydroxycarbonyl product)/k(OH ϩ diol), and with in-
creasing extent of reaction [15]. The maximum values
of F were 1.18 for the 1,2-butanediol reaction, 1.33
for the 2,3-butanediol reaction, 1.21 for the 1,3-buta-
nediol reaction, and 1.13 for the 2-methyl-2,4-penta-
nediol reaction. Plots of the amounts of hydroxycar-
bonyl formed, corrected for reaction with the OH
radical, against the amounts of diol reacted are shown
in Figures 2 and 3. Reasonably good straight-line plots
are observed, and the hydroxycarbonyl formation
yields obtained from least-squares analyses of these
data are given in Table II.
Figure 1 Plots of eq. (I) for the gas-phase reactions of the
OH radical with 2,3-butanediol, 1,2-butanediol, 2-methyl-
2
,4-pentanediol, and 1,3-butanediol, with n-octane as the
reference compound. The data for 1,2-butanediol, 2-methyl-
,4-pentanediol, and 1,3-butanediol have been displaced
2
vertically by 0.4, 0.8, and 1.2 units, respectively, for clarity.
plotted in accordance with eq. (I) in Figure 1. Good
straight-line plots are observed, and the rate constant
ratios k /k obtained from least-squares analyses of the
1
2
data are given in Table I. These rate-constant ratios
are placed on an absolute basis by use of a rate con-
stant, k , for reaction of the OH radical with n-octane
2
Ϫ12
3
Ϫ
1
Ϫ
1
DISCUSSION
at 296 K of 8.67 ϫ 10 cm molecule
s
(Ϯ20%)
[
14]. The resulting rate constants k are also given in
1
Although no literature rate constants for the diols stud-
ied here are available for comparison, rate constants
for the diols can be calculated using the estimation
method proposed by Atkinson [16] and last updated
by Kwok and Atkinson [17]. The OH radical reactions
with the diols studied here proceed by H-atom abstrac-
Table I.
OH Radical Reaction Products
GC-FID analyses of irradiated CH ONO–NO–diol–
n-octane–air mixtures showed the formation of one
3
Table I Rate Constant Ratios k /k and Rate Constants k for the Gas-Phase Reactions of the OH Radical with
1
2
1
Diols at 296 Ϯ 2 K
012 ϫ k (cm molecule s )
3
Ϫ
1
Ϫ1
1
1
Diol
k1/k2a
This Workb
Estimatedc
CH CH CH(OH)CH OH
3.11 Ϯ 0.15
2.72 Ϯ 0.48
3.83 Ϯ 0.12
3.20 Ϯ 0.27
27.0 Ϯ 5.6
23.6 Ϯ 6.3
33.2 Ϯ 6.8
27.7 Ϯ 6.1
15.9 (27.9)
17.3 (30.2)
14.2 (17.2)
10.5 (14.6)
3
2
2
CH CH(OH)CH(OH)CH3
3
CH CH(OH)CH CH OH
3
2
2
(
CH ) C(OH)CH CH(OH)CH
3 2 2 3
a
n-Octane used as the reference compound. The indicated errors are 2 least-squares standard deviations.
b
Ϫ12
3
Ϫ
1
Ϫ1
Placed on an absolute basis by use of a rate constant of k (n-octane) ϭ 8.67 ϫ 10 cm molecule
s
(Ϯ20%) at 296 K [14]. The
2
indicated errors include the estimated overall uncertainty in the rate constant k .
2
c
Calculated using the estimation method of Kwok and Atkinson [17]. The values in parentheses are calculated using revised parameters
for F(9OH) and F(9CH OH) ["F( CHOH)"F(9 COH)] (see text).
2

KINETICS AND PRODUCTS OF THE REACTIONS OF SELECTED DIOLS
313
Figure 2 Plots of the amounts of 4-hydroxy-4-methyl-2-
pentanone and 1-hydroxy-3-butanone formed, corrected for
secondary reactions (see text), against the amounts of 2-
methyl-2,4-pentanediol and 1,3-butanediol reacted with the
OH radical, respectively. The data for 1-hydroxy-3-butanone
Figure 3 Plots of the amounts of 1-hydroxy-2-butanone
and 3-hydroxy-2-butanone formed, corrected for secondary
reactions (see text), against the amounts of 1,2-butanediol
and 2,3-butanediol reacted with the OH radical, respectively.
The data for 3-hydroxy-2-butanone have been displaced ver-
have been displaced vertically by 5.0 ϫ 1012 molecule cm
Ϫ
3
12
Ϫ3
tically by 5.0 ϫ 10 molecule cm for clarity.
for clarity.
k(X9CH(9Y)9Z) ϭ k F(X)F(Y)F(Z)
tert
tion from the various C9H and O9H bonds
1,7,16,17], and the estimation method of Kwok and
[
where kprim, k , and k are the rate constants for H-
sec
tert
Atkinson [17] is based on the calculation of rate con-
stants for H-atom abstraction from CH , CH , CH, and
atom abstraction from CH , CH ,and CH groups, re-
3
2
3
2
spectively, for a “standard” substituent, and F(X),
F(Y), and F(Z) are the substituent factors for the sub-
stituent groups X, Y, and Z, respectively [16,17]. The
standard substituent group is chosen to be X(ϭ Y ϭ Z)
ϭ 9CH , with F(9CH ) ϭ 1.00 [16,17]. At 298 K,
OH groups. The rate constants for H-atom abstraction
from CH , CH , and CH groups is assumed to depend
3
2
on the identity of the substituents attached to these
groups, with
3
3
Ϫ
12
3
the group rate constants are (in units of 10 cm mol-
k(CH 9X) ϭ kprimF(X)
3
Ϫ1
Ϫ1
ecule s ) k
ϭ 0.136, ksec ϭ 0.934, ktert ϭ 1.94,
prim
k(X9CH 9Y) ϭ k F(X)F(Y)
and kOH ϭ 0.14, and the substituent factors are
2
sec
F(9CH 9) ϭ F( CH9) ϭ F(
C
) ϭ 1.23 and
2
and
F(9OH) ϭ 3.5 [17] .
Table II The Formation Yields of Selected Hydroxyketones from the Gas-Phase Reactions of the OH Radical
with Diols at 296 Ϯ 2 K, Compared to Estimated Yields
Molar Formation Yield (%)
Diol
Hydroxyketone
This Worka
Estimatedb
CH CH CH(OH)CH OH
CH CH C(O)CH OH
66 Ϯ 11
89 Ϯ 9
50 Ϯ 9
47 Ϯ 9
65 (64)
96 (97)
59 (40)
79 (47)
3
2
2
3
2
2
CH CH(OH)CH(OH)CH3
CH C(O)CH(OH)CH3
3
3
CH CH(OH)CH CH OH
CH C(O)CH CH OH
3
2
2
3
2
2
(
CH ) C(OH)CH CH(OH)CH
(CH ) C(OH)CH C(O)CH
3
2
2
3
3 2 2 3
a
Indicated errors are 2 least-squares standard deviations combined with estimated overall uncertainties in the GC-FID response
factors for the diols and hydroxyketones of Ϯ5% each.
b
Calculated using the estimation method of Kwok and Atkinson [17]. The values in parentheses are calculated using revised
parameters for F(9OH) and F(9CH OH) ["F( CHOH)"F(9 COH)] (see text).
2

3
14
BETHEL ET AL.
The calculated rate constants for the four diols stud-
ied here are given in Table I, and are factors of 1.4–
.6 lower than the measured values. A similar under-
leads to the calculated rate constants given in paren-
theses in Table I for the diols studied here, and to the
rate constants listed in Table III for the other alcohols
and diols used in the derivation of the group substit-
uent factors. As expected, the revised parametersresult
in closer agreement of the calculated rate constants to
the measured values, although discrepancies of up to
a factor of 1.9 still occur for 1,3-butanediol and
2-methyl-2,4-pentanediol (Table I). Table IV shows
the effect of the revised parameters F(9OH) and
2
estimation of rate constants for the reactions of the OH
radical with 1-hexanol, 1,2-ethanediol, and 1,2-pro-
panediol was observed previously [9] (and shown in
Table III), and our present and previous [9] data sug-
gest that certain parameters in the estimation method
of Kwok and Atkinson [17] need to be revised. Ac-
cordingly, we have used the literature [1,7,18–22] OH
radical reaction rate constants for methanol, ethanol,
F(9CH OH) [ϭ F( CHOH) ϭ F(9 COH)] on
2
1
2
- and 2-propanol, 1- and 2-butanol, 2-methylpropan-
-ol (tert-butyl alcohol), 2,2-dimethylpropan-1-ol, 1-
the calculated versus measured [1,10,22] rate con-
stants for the hydroxycarbonyls for which data are
available (and which were not used in the derivation
of the revised substituent factors). Using the revised
substituent factors, the calculated rate constants agree
approximately as well with the measured values as do
those calculated using the parameters of Kwok and
Atkinson [17] for five of the eight hydroxycarbonyls.
However, the revised parameters lead to significant
disagreements with the measured values for 3-hy-
droxy-3-methyl-2-butanone (by a factor of 3.2) and
glycolaldehyde (by a factor of 4.7, compared to the
previous overestimate of a factor of 2.4 [17]), and it
appears that rate constants for 1,2-hydroxyaldehydes
will be greatly overestimated. Clearly, accurate esti-
mation of OH radical rate constants for hydroxy-con-
taining compounds (to within better than a factor of 2)
does not appear possible using the general approach
of Atkinson [16].
hexanol, 1,2-ethanediol, and 1,2-propanediol, and for
the four diols measured here, to recalculate the sub-
stituent group parameters in the Kwok and Atkinson
[
17] estimation method. In this derivation of revised
parameters for the estimation method, the group rate
constants kprim, k , k , and k and the substituent
sec
tert
OH
factor F(9CH 9) ϭ F(
C
) ϭ F( CH9) ϭ
.23 were unchanged from the values of Kwok and
Atkinson [17]. In contrast to the Kwok and Atkinson
17] study, effects of the OH substituent(s) on H-atom
abstraction at the ␣- and ␤-positions were considered
Kwok and Atkinson [17] only considered effects of
2
1
[
(
OH substituents at the ␣-position, in part because of
the database then available). Because of the limited
database, it was assumed in the present fit that
F(9CH OH) ϭ F( CHOH) ϭ F(9 COH), and a
nonlinear least-squares fit to the rate constants above
2
2
(
minimizing [(kcalc Ϫ kmeas)/kmeas] , where k and kmeas
As noted above, the OH radical reactions proceed
by H-atom abstraction from the various C9H and
O9H bonds. The hydroxyketones formed arise after
calc
are the calculated and measured rate constants,
respectively) resulted in substituent factors of
F(9OH) ϭ 2.9 and F(9CH OH) ϭ F( CHOH) ϭ
H-atom abstraction from the CH(OH) and CH OH
2
2
F(9 COH) ϭ 2.6. Use of these revised parameters
groups, with the H-atoms on these groups being acti-
Table III Comparison of Calculated and Experimentally Measured Room-Temperature Rate Constants for Reaction
of the OH Radical with a Series of Alcohols and Diols
012 ϫ k (cm molecule s )
3
Ϫ
1
Ϫ1
1
Hydroxy Compound
Calc. [17]
Calc. (revised)
Measured
Reference
CH OH
0.62
3.58
5.48
7.27
6.89
9.98
0.64
4.66
9.72
8.32
12.8
0.53
3.20
6.07
6.47
7.78
10.0
1.20
3.97
10.6
14.4
22.3
0.944
3.27
5.53
5.07
8.57
[1,18]
[1,7,18]
[1,18]
[18,19]
[1,18]
[20]
[21]
[22]
[9]
[9]
3
CH CH OH
3
2
CH CH CH OH
3
2
2
CH CH(OH)CH3
3
CH CH CH CH OH
3
2
2
2
a
CH CH(OH)CH CH
8.89
3
2
3
(
CH ) COH
1.08
5.53
15.8
14.7
21.5
3
3
(
CH ) CCH OH
3
3
2
CH (CH ) CH OH
3
2 4
2
HOCH CH OH
2
2
CH CH(OH)CH OH
[9]
3
2
a
Reevaluated to be consistent with the most recent recommendation [14] for the cyclohexane reference compound used.

KINETICS AND PRODUCTS OF THE REACTIONS OF SELECTED DIOLS
315
Table IV Comparison of Calculated and Experimentally Measured Room-Temperature Rate Constants for Reaction
of the OH Radical with a Series of Hydroxycarbonyls
012 ϫ k (cm molecule s )
3
Ϫ
1
Ϫ1
1
Hydroxycarbonyl
Calc. [17]
Calc. (revised)
Measured
Reference
HOCH CHO
23.4
2.69
3.82
5.86
13.9
11.4
1.30
15.3
46.1
2.27
3.40
5.84
12.6
16.2
3.00
15.1
9.9
3.0
7.7
10.3
8.1
15.1
0.94
16.2
[1]
2
CH C(O)CH OH
[1,23]
[10]
[10]
[10]
[10]
[10]
[10]
3
2
CH CH C(O)CH OH
3
2
2
CH C(O)CH(OH)CH3
3
CH C(O)CH CH OH
3
2
2
C H C(O)CH(OH)C H
2
5
2
5
(
CH ) C(OH)C(O)CH
3 2 3
CH C(O)CH(CH )CH OH
3
3
2
6
Ϫ3
vated by the presence of the OH substituent group, as
shown, for example, for the 1,2-butanediol reaction.
10 molecule cm [25,26], the calculated lifetimes of
the four diols studied here are in the range 4–6 h.
OH ϩ CH CH CH(OH)CH OH !: H O
3
2
2
2
ϩ CH CH CB (OH)CH OH (3)
The authors gratefully thank the U.S. Environmental Pro-
tection Agency for support of this research through Grant
No. R826371-01-0 (“Ozone and Fine Particle Formation in
California and in the Northeastern United States”) to the
California Institute of Technology and Grant No. R825252-
3
2
2
followed by reaction of the ␣-hydroxyalkyl radical
with O [1].
2
01-0 (from the U.S. Environmental Protection Agency—
National Center for Environmental Research and Quality
Assurance). Although this research has been funded by fed-
eral funds from the U.S. Environmental Protection Agency,
the results and content of this publication do not necessarily
reflect the views and opinions of the agency or the U.S.
government.
CH CH CB (OH)CH OH
3
2
2
ϩ O !: CH CH C(O)CH OH ϩ HO
2
(4)
2
3
2
2
Note that the hydroxy-aldehyde CH CH CH(OH)CHO
will be formed by an analogous reaction at the 1-po-
3
2
sition CH OH group, but hydroxyaldehydes do not ap-
2
pear to be amenable to analysis by gas chromatogra-
phy without derivatization [24], and hence we only
observe (because of analytical limitations) hydroxy-
ketones. Our observed hydroxyketone formation
yields given in Table II can be compared with the
yields calculated using the estimation method of Kwok
and Atkinson [17] and using the revised parameters
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. Atkinson, R. Atmos Environ 2000 34, 2063.
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(
by calculating the fraction of the overall calculated
OH radical reaction rate constant that is due to H-atom
4
abstraction from the CH(OH) or CH OH group lead-
2
ing to formation of the hydroxyketone observed). Our
measured formation yields agree well with the yields
calculated using the revised substituent group factors,
with a significantly improved agreement between the
estimated and measured formation yield of 4-hydroxy-
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7
8
4
-methyl-2-pentanone from 2-methyl-2,4-pentanediol
1
(
Table II).
Finally, our measured room-temperature rate con-
stants can be combined with an assumed ambient con-
centration of OH radicals to calculate the tropospheric
lifetimes of the diols studied here. Using a 12-h
average daytime OH radical concentration of 2.0 ϫ

3
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