Absolute rates of the solution-phase addition of atomic hydrogen to a vinyl ether and a vinyl ester: Effect of oxygen substitution on hydrogen atom reactivity with olefins

Article abstract of DOI:10.1021/jp021963i

The reactions of vinyl butyl ether and vinyl butyrate with atomic hydrogen and deuterium lead to addition at the terminal position of the olefins. This observation is consistent with the reactions carried out earlier with other olefins. Both of the absolute rates of addition to vinylbutyl ether and vinyl butyrate, in acetone and hexane, were measured at several temperatures. The relative rates are consistent with only modest stabilization of the transition state of the radical adduct by the α-O substituent compared with that of hydrogen atom addition to 1-octene. The relative rates measured in acetone and hexane indicate no significant differential solvation of the ground state relative to the transition structures of the hydrogen atom addition. The kinetics reveal that the early transition states for hydrogen atom addition exhibit little selectivity (vinyl ether versus simple olefin) in either the abstraction of hydrogen a to the oxygen or by terminal addition to the olefinic ether and reflects the modest influence of the increased enthalpy of reaction associated with resonance stabilization by the oxygen substituent at the developing radical site.

Full text of DOI:10.1021/jp021963i

3054
J. Phys. Chem. A 2003, 107, 3054-3063
Absolute Rates of the Solution-Phase Addition of Atomic Hydrogen to a Vinyl Ether and a
Vinyl Ester: Effect of Oxygen Substitution on Hydrogen Atom Reactivity with Olefins
D. D. Tanner,*,† P. Kandanarachchi,†,‡ N. C. Das,§ and J. A. Franz*,‡
Department of Chemistry, UniVersity of Alberta, Edmonton, AB T6G 2G2 Canada, and
Pacific Northwest National Laboratory, 902 Battelle BouleVard, Richland, Washington 99352
ReceiVed: August 27, 2002; In Final Form: February 12, 2003
The reactions of vinyl butyl ether and vinyl butyrate with atomic hydrogen and deuterium lead to addition at
the terminal position of the olefins. This observation is consistent with the reactions carried out earlier with
other olefins. Both of the absolute rates of addition to vinylbutyl ether and vinyl butyrate, in acetone and
hexane, were measured at several temperatures. The relative rates are consistent with only modest stabilization
of the transition state of the radical adduct by the R-O substituent compared with that of hydrogen atom
addition to 1-octene. The relative rates measured in acetone and hexane indicate no significant differential
solvation of the ground state relative to the transition structures of the hydrogen atom addition. The kinetics
reveal that the early transition states for hydrogen atom addition exhibit little selectivity (vinyl ether versus
simple olefin) in either the abstraction of hydrogen R to the oxygen or by terminal addition to the olefinic
ether and reflects the modest influence of the increased enthalpy of reaction associated with resonance
stabilization by the oxygen substituent at the developing radical site.
Introduction
addition of a hydrogen atom to methyl vinyl ether (∆Hadd )
-40 kcal/mol) would be expected to exhibit a gas-phase rate
constant of ca. 2 × 109 M-1 s-1, only about a factor of 4 faster
than that of ethylene or propylene. Clearly, the very high
exothermicity of hydrogen addition to olefins will result in a
very narrow range of addition rate constants. The thermochem-
istry of the addition of hydrogen atoms to olefins relevant to
this work can be roughly calculated.4-6 Past work on hydrogen
atom addition to olefins shows that addition exhibits little
sensitivity to adduct radical structure.
However, little work has been carried out to determine the
absolute rates of reaction of the hydrogen atom in solution. The
reactivity of atomic hydrogen with an olefin, which leads to a
carbon-centered radical R to an oxygen substituent, will be
enhanced if the transition state for addition develops a higher
dipole moment than the starting material. The resonance
stabilization of the product radical has been suggested to involve
a polar structure.7
Recently, we reported a method for obtaining the absolute
rate constants for the liquid-phase reaction of the addition of
atomic hydrogen to an olefin.1b The reaction of 1-octene was
reported to be very close to diffusion-controlled k2a5°C ) 4.6 ×
109 M-1 s-1. The same kinetic method can be used to evaluate
the stabilizing effect of a radical having a geminal oxygen
substituent. The addition of hydrogen to a terminal olefin was
found to be regioselective, giving addition to form only the most
stable secondary or tertiary radical.1a It remained to be estab-
lished that addition to the vinyl ether or ester also underwent
regioselective addition to give a radical center on carbon
containing a geminal oxygen substituent. The effect of a
substituent on the enthalpy of addition should also be estab-
lished.
The addition of hydrogen atoms to olefins has been exten-
sively studied in the gas phase. Activation barriers for the
addition to olefins range from 1 to 3 kcal/mol, and Arrhenius
A factors are typically 1010-1011.2 The enthalpy of the addition
of atomic hydrogen also correlates with the rate constants for
addition.3 The large rate constants, k2a5°C ) 4.6 × 109 M-1s-1
,
reported for the solution-phase addition reactions are supported
by the observation that the activation parameters (Ea ) 5.3 (
2.9 kcal/mol and log A ) 14 ( 3.5 M-1 s-1) are consistent
with the values expected for this fast reaction. The values
reported for the solution-phase reactions are within the experi-
mental error of those reported for the vapor-phase reactions.2
The gas-phase addition rate constants for hydrogen to olefins
The importance of this resonance form has been substantiated
by the observation that the EPR spectrum of the radical shows
a γ-hydrogen hyperfine coupling constant larger than that of
the R hydrogen.8 Although such an argument may be suggestive
of the polar characteristics of oxygen-substituted radicals, it does
not address the question of whether the transition structure is
more polar than the ground-state olefin and hydrogen atom.
Indeed, theoretical calculations suggest that hydrogen atom
addition to an olefin increases the dipole moment from the
starting olefin to the transition state only slightly, with most of
the polarization of the product radical developing after the
transition state has been transited. For example, vinyl alcohol
is predicted to exhibit a dipole moment of 1.2 D compared to
1.3 D for the TS of H atom addition and 1.8 D for the product
vary from 5 × 108 M-1 s-1 for addition to ethylene (∆Hadd
)
-36 kcal/mol) to 5 × 109 M-1s-1 for addition to butadiene
(∆Hadd ) -44 kcal/mol), or (very roughly) log kadd,H ≈ 4.5-
0.12 ∆Hadd. For a case of intermediate exothermicity, the
* Corresponding authors. E-mail: dennis.tanner@ualberta.ca.
† University of Alberta.
‡ Pacific Northwest National Laboratory.
§ Postdoctoral Fellow, University of Alberta, 1996.
10.1021/jp021963i CCC: $25.00 © 2003 American Chemical Society
Published on Web 04/08/2003

Absolute Rates of Atomic Hydrogen Addition
J. Phys. Chem. A, Vol. 107, No. 17, 2003 3055
TABLE 1: Product Distribution from the Reaction of Atomic Hydrogen with Vinyl Butyl Ether in Acetone at -72 °C
a Proportionation was calculated using atomic deuterium product distributions; see Table 2. b Product from 1,2-hydrogen addition. c Traces of
1,3-dibutane were also observed.
hydroxyethyl radical.9 It is clear that whereas the radical product
is more polar than the olefin the polarity is not developed in
the transition state. The qualitative importance of the stability
of the radical was demonstrated by Fischer, who placed oxygen,
as a substituent, on a scale of substituents that show radical
stabilization by resonance.10 As indicated above, carbon-centered
radicals are stabilized by 5-7 kcal/mol by oxygen substi-
tution.
The effect of this type of resonance stabilization predicts that
a large solvent effect will stabilize or destabilize the contribution
of a charge-separated species. If the transition structure for
hydrogen atom addition to a vinyl ether exhibits a higher dipole
moment than the ground-state olefin, then the free energy of
solvation of the transition state will be greater than that of the
starting olefin and hydrogen atom. In the present work, the
reactions were carried out in both polar (acetone) and nonpolar
(hexane) solvents.
Numerous studies of the reactivity of substrates that upon
reaction form carbon-centered radicals R to an oxygen atom
have been described as being governed by stereoelectronic
control.11
To probe the importance of this type of resonance stabiliza-
tion, the reactivity of an olefin that formed a radical R to oxygen
was compared to that of an olefin that adds hydrogen to form
a secondary radical. In the present study, the R radicals formed
upon the addition of a hydrogen atom in the â position to the
oxygen substituent are favored by resonance stabilization over
addition R to the oxygen substituent.
solution of the reactive substrate. The products formed in these
highly chemospecific reactions are analyzed, and the solution-
phase structure-reactivity relationships for the reactions of
atomic hydrogen are obtained.
Regioselective Addition. When atomic hydrogen (0.25-2.5
mmol) is passed over neat vinyl butyl ether (-72 °C), the
products of the reaction are ethyl butyl ether (B), dl- and meso-
2,3-dibutoxy butane (C), and traces of 1,3-dibutoxybutane. See
Table 1.
Some insight is obtained concerning the mechanism of the
formation of these products by carrying out the reduction with
deuterium atoms (-78 °C). The distributions of the products
from these reactions are listed in Table 2. By comparing the
1
2
mass spectra and H and H NMR spectra of the protiated to
deuterated products of the reaction mixture, it is obvious that
in each of the products, monomers or dimers, at least one
deuterium is attached to a terminal position attributable to the
original olefin. See Table 2.
The mass spectra of the products show vinyl butyl ether (A,
Ad1, and Ad2), ethyl butyl ether (B, Bd2, and Bd3), and dl- and
meso-2,3-dibutoxy butane (Cd2). All of the olefins previously
studied underwent regioselective addition of atomic hydrogen
to generate the most stable radical.1a If one assumes that the
vinyl ether likewise undergoes addition to give a secondary
radical (eq 1), then the formation of the products listed in Tables
1 and 2 are those formed by this primary reaction.
In principle, the rate constant for a second substrate (s2) can
be obtained by competition kinetics using a mixture of olefins
(s1 and s2). However, in the heterogeneous gas-liquid kinetic
method employed in this and previous studies, absolute rate
constants (ka) were not found to be independent of the
concentration of the olefin.1 The absolute rate constants for
substrates s1 and s2 must be determined independently. As shown
below, when the relative rate constants were determined using
mixtures of substrates at [s1], [s2] = 0, the results converged to
the ratio of individually determined absolute rate constants.
The effects of the stability of the radical geminal to oxygen
can likewise be investigated by comparing the rate of abstraction
of hydrogen from an ether relative to the known rate constant
for allylic abstraction. Thus, in this study, we present absolute
and relative reactivities and solvent effects in hydrogen addition
to olefins and in hydrogen abstraction by atomic hydrogen from
allylic hydrocarbons or oxygen-substituted alkanes.
The 2H NMR shows absorptions with intensities (In) at δ 1.10
(DCH2-; I1), 1.17, 1.20 (DCH2-; I2 (Cd2)), 3.49 (-CDH-,
I3), and 4.04, 4.27 (DCHdCH-, I4). These intensities are
proportional to the concentrations of the products; see Table 1.
The proportionality constant ×c41 is obtained from the equation
I1 + I2 ) ([Bd] + [Bd2] + 2[Cd2])/×c4, and the unknown
product concentrations are obtained from the following relation-
ships: [Ad] ) ×c4I4; [Bd2] ) ×c4I3; [Bd] ) [B]tot - [Bd2];
[Ad] + [Ad2] ) ×c4I4. The [Ad]/[Ad2] ratio was estimated from
GC/MS spectra by using M+ and M+ + 1 peaks after making
corrections for natural abundances.
When the secondary radical encounters a deuterium atom,
1,2-dideuterio-2-butoxyethane (Bd2) is formed (eq 2).1b
Results and Discussion
Using the procedure reported previously,1 hydrogen atoms
generated in a microwave discharge are passed over a stirred
The major saturated or unsaturated products, however, contain
only one deuterium atom. The incorporation of protium into

3056 J. Phys. Chem. A, Vol. 107, No. 17, 2003
Tanner et al.
TABLE 2: Product Distribution from the Reaction of Atomic Deuterium with an Acetone Solution of Vinyl Butyl Ethera
2
a Five milliliters of 0.20 mol L-1 solutions in acetone. D2 flow rate ) 6 mL/min. b Deuterium distribution was quantitated by H NMR and
GC/MS. c Monodeuterated alkanes (FMDA) to monodeuterated olefins (FMDO) ratio was corrected for secondary reactions. (FMDA/FMDO ) Bd1/(Ad1
+ Ad2 + Bd3)). d Disproportionation (kd) to combination (kc) ratio (kd/kc ) (Ad1 + Ad2 + Bd1 + Bd3)/2 × Cd2). e A value of 0.54 ( 0.05 was
obtained in reactions carried out at several concentrations (1.0-0.20) of the starting material.
the saturated ether can be attributed to disproportionation (eq
3).
The observation that the ratio of monodeuterated ethyl butyl
ether to monodeuterated vinyl butyl ether (FMDAE/FMDOE) is
essentially equal to 1 (1.02 ( 0.05) is consistent with the
disproportionation pathway (eq 3).
Hydrogen abstraction R to the vinyl ether can be ruled out
since no secondary deutero vinyl ether nor unsaturated dimer
could be detected.
Figure 1. Plot of log(kd/kc) at several temperatures for reactions carried
out in acetone.
Since the products of disproportionation can be identified,
the disproportionation-to-combination ratio is easily determined.
The value determined for the reaction carried out to low
conversion (13-26% reaction) is 0.68 ( 0.001 (-72 °C). When
the reaction is carried out at several temperatures, -63, -84,
of olefin, [olefin]0, approaches zero). Under these conditions,
an estimate of ka can be obtained from eq 4.
∆P
∆t total
) ka[H•][olefin]0
(4)
(
)
and -94 °C, a plot of ln kd/kc vs 1/T gives a slope of Ea(dis)
-
Ea(comb) that is equal to 0.4 kcal/mol. (See Figure 1.)
The ratio of rate constants kd/kc calculated from the plot at
25 °C is 1.01 and is essentially identical to the value (kd/kc/H
) 1.01, 1.00) reported for the sec-butyl radical.12
Since the relative rates of the formation of combination (C) and
disproportionation (D) are diffusion-controlled, the concentration
of radicals formed from addition can be calculated from those
products if one determines the time dependence of the products
formed from their reactions:
The rate of formation of the total products resulting from
the initial addition of a hydrogen atom to a olefin in a given
time, (∆P/∆t)total, is proportional to the concentration of the
reactants. In the case of a nonhomogeneous reaction, only the
first molecules that react obey these kinetics. Under nonhomo-
geneous conditions, reaction occurs only upon the encounter
of the reactants in the volume of the reaction zone (i.e., the
true concentration is achieved only when the initial concentration
∆P
∆t c,d
) kR•[R•]2
(5)
(
)
The diffusion rate constant, kR•, can be estimated using the
Stokes-Einstein equation by assuming slip conditions and

Absolute Rates of Atomic Hydrogen Addition
J. Phys. Chem. A, Vol. 107, No. 17, 2003 3057
TABLE 3: Absolute Rate Constants (f 1/2ka) for the Addition of Deuterium Atoms to Vinyl Butyl Ether at -72 °C in Acetone
104(∆p/∆t) tboutlk
104(∆p/∆t)c,d
107[R-]b
mol L-1
104(∆p/∆t)RD
108[H•]c
10-3f 1/2kad
a
[olefin]
mol L-1
2
mol L-1 s-1
mol L-1 s-1
mol L-1 s-1
mol L-1
M-1 s-1
1.12
0.45
0.09
0.045
0.034
0.022
6.19
7.36
1.90
1.01
0.58
0.52
5.37
5.60
1.33
0.81
0.19
7.84
8.43
3.90
3.05
1.47
0.82
1.13
0.34
0.19
0.16
11.9
15.2
9.92
6.42
2.69
(2.35)
4.09
11.2
30.6
40.8
63.5
127
a Experimentally measured as the change in the concentration of vinyl butyl ether with time. b Calculated by using eq 5. c Calculated by using
eq 7. d Calculated by using eq 9.
TABLE 4: Absolute Rate Constants (f 1/2ka) for the Addition of Deuterium Atoms to Vinyl Butyl Ether at -72 °C in Hexane
104(∆p/∆t) tboutlk
104(∆p/∆t)c,d
107[R-]b
mol L-1
104(∆p/∆t)RD
108[H•]c
10-3f 1/2kad
a
a
a
[olefin]
mol L-1
2
mol L-1 s-1
mol L-1 s-1
mol L-1 s-1
mol L-1
M-1 s-1
1.00
0.50
0.17
0.067
0.033
0.017
0.0084
4.90
6.34
4.77
2.40
1.23
0.66
0.36
4.50
5.85
4.33
1.57
0.91
0.42
6.86
7.82
6.73
4.05
3.09
2.10
0.40
0.49
0.44
0.16
0.06
0.04
6.10
6.60
6.80
4.10
2.86
8.03
19.2
41.3
87.4
150
185
261
2.10
(1.62)e
a Experimentally measured as the change in the concentration of vinyl butyl ether with time. b Calculated by using eq 5. c Calculated by using
eq 7. d Calculated by using eq 9. e Calculated from a plot of (H•) vs (∆p/∆t) btoutlk
.
applying a spin statistic correction:1
(8RT)103
kR•
)
3
(6)
3η
The concentration of [R•] can then be calculated from eq 5.
The products from the reaction of hydrogen atoms with the
alkyl radicals, also diffusion-controlled, (i.e., the capping
reaction (eq 7)), can be determined from the products resulting
from 1,2 addition:
∆P
∆t RH2
) kH•[R•][H•]
(7)
(
)
Figure 2. Variation of the apparent rate constant log(f1/2 ka) of vinyl
butyl ether with the concentration of the olefin in (O) acetone and (b)
hexane.
Since this radical-radical coupling will also be diffusion-
controlled, an estimation of the hydrogen atom concentration
can be made. Because the hydrogen atom concentration has now
been determined, the addition of hydrogen to a primary olefin
can likewise be determined (eq 4) if the time-dependent
concentrations of the reactants and the products formed in the
reaction zone, {(∆n/V)/∆t)}RZ, are known. Since the volume
of the reaction zone is only a fraction, f, of the bulk volume,
the kinetic expressions that are listed (eqs 4, 5, and 7) are valid
only at extremely low concentrations (eq 8).
By using the data in Tables 3 and 4, a plot of the calculated
values of f 1/2ka versus their olefin concentrations was constructed
(Figure 2).
The data were fit to an equation of the form log f 1/2ka )
a[olefin]b + c. The function is monotonic and steeply dependent
upon the concentration of the substrate. The radical concentra-
tions and rate constants for the addition reactions are also listed
in Tables 3 and 4. Since stabilization of an oxygenated substrate,
by resonance, infers that the intermediate radical should exhibit
polar charge-separated characteristics, carrying out the reaction
in a polar solvent should stabilize the oxygenated intermediate
compared to the intermediate formed from addition to the alkene.
The rate constants obtained from the extrapolated values in
hexane and in acetone are listed in Table 5.
∆n/V RZ
∆t
∆n/V bulk
∆t
=
(8)
(
)
(
)
An expression (eq 9) that defines the rate constant for addition,
ka, can be derived by combining eqs 4-7:
(∆P/∆t)total(kdiff(∆P/∆t)c,d)1/2
ka ) f -1/2
(9)
The accuracy of the values of the relative rates determined
by dividing the absolute rate constants for the addition of atomic
hydrogen to 1-octene and vinyl butyl ether was compared to
that of the values obtained by competition kinetics. The values
obtained were compared at several concentrations; see Figure
3. To support the suggestion that the intermediates are solvated,
the rates of the abstraction of hydrogen from two oxygenated
substrates and from a dialkyl ether and the addition to vinyl
butyrate were compared in both solvents. As a standard, the
[
]
[olefin](∆P/∆t)RH
2
Absolute Rate of Addition of H• to Vinyl Butyl Ether.
The experimental data (Tables 1 and 2) were used to calculate
the concentrations of the reactants ([olefin], [R•], [H•]) and the
rate constant for each reaction at each concentration of olefin.
The apparent rate constants (f 1/2ka) of the substrates in their
reaction zone are listed in Tables 3 and 4.13

3058 J. Phys. Chem. A, Vol. 107, No. 17, 2003
Tanner et al.
TABLE 5: Absolute Rate Constants for Addition and Abstraction by Atomic Deuterium at -72 °C
a Measured from the extrapolated values at zero olefin concentrations in Figure 2a and b and Figure 3. b Calculated from the relative rate constants
in Table 7 and the absolute rate constants of addition to vinylbutyrate.
TABLE 6: Relative Rates for the Addition of Atomic
Deuterium to Vinyl Butyl Ether and Vinyl Butyrate at
-72 °C
[substrate
a
solvent mol L-1
]
(ke/ko)b
0.71 ( .05 0.19
0.56 ( .01 0.24 ( .02 2.42 ( .03 0.67 ( .20
0.33 ( .03 0.81 ( .17
(kes/ko)c
(ke/kes)d
(ke/kes)e
acetone
acetone
acetone
acetone
acetone
acetone
hexane
hexane
hexane
hexane
hexane
hexane
1.00
0.60
0.40
0.20
0.05
0.02
0.50
0.20
0.10
0.05
0.02
0.01
3.74 ( .05 0.56 ( .20
0.79 ( .07 0.30 ( .03 2.63 ( .10 1.02 ( .03
0.99 ( .05 0.50 ( .02 1.98 ( .07 1.48 ( .04
1.05 ( .07 0.61 ( .07 1.72 ( .14 1.99 ( .25
1.45 ( .13 0.74 ( .03 1.96 ( .16 1.29 ( .01
1.44 ( .27 0.76 ( .03 1.89 ( .30 1.41 ( .07
1.46 ( .20 0.79 ( .05 1.85 ( .25 1.51 ( .001
1.35 ( .21 0.72 ( .01 1.86 ( .22 1.58 ( .02
1.11 ( .16 0.83 ( .06 1.35 ( .22 1.70 ( .12
1.30 ( .12
1.74 ( .05
Figure 3. Variation of the relative rate for (O) vinyl butyl ether (ke/
ko) and (b) vinyl butyrate (kes/ko) with the concentration of the sub-
strate.
a Mixtures (1:1, M/M) of the ether or ester and 1-octene. b Relative
rate constant of vinyl butyl ether compared to that of 1-octene. c Relative
rate constant of vinyl butyrate compared to that of 1-octene (M/M).
d Calculated relative rate constant between vinyl butyl ether and vinyl
butyrate using (ke/ko) and (kes/ko). e Calculated relative rate constant
using f 1/2ka values from Figures 2 and 4.
abstraction reaction of the ether was compared to the addition
to the vinyl ester. If solvation was important for both of the
oxygenated substrates, then it was expected that the relative rates
in acetone (both substrates solvated) and hexane (both substrates
nonsolvated) would show very little extra stabilization; see Table
7.
in activation energy for reactions carried out in acetone and in
hexane using the data in Table 7 and the values previously
determined for allylic abstraction from 1-octene.1b
As expected, the relative rate ratios in both solvents were,
within the experimental accuracy, the same.
∆∆Ea ) Ea(allyl) - Ea(R-O) ) -0.76 ( 0.9 kcal/mol
The intermediate radical geminal to oxygen could also be
formed by R abstraction from a dialkyl ether. The relative rate
constant for abstraction was obtained by competition kinetics
using as a competitive substrate the addition to the slowest of
the olefins studied, vinyl butyrate; see Table 7. Because the
absolute rate constant for allylic abstraction had previously been
determined1b and the absolute rate of addition of atomic
hydrogen to 1-octene and now vinyl butyl ether has also been
determined, the relative ratios of allylic abstraction could be
compared to that for abstraction of the R hydrogen from a dialkyl
ether, Table 7. The products from the abstraction of hydrogen
were calculated from the reactions of the mixture of the two
substrates with atomic deuterium. Under these conditions, only
mono-R-d and cross dimeric products resulting from the
reactions of the ether (Table 7) could be detected. No correction
for disproportionation or addition needed to be made for the R
radical formed from the ether.
∆ log A ) log A(allyl) - log A(R-O) ) 1.8 ( 2.3
Ea(allyl) ) 7.64 ( 2.9
Eaab(R-O) ) 8.4 ( 3.8
log Aab(R-O) ) 12.2 ( 2.3
In hexane,
∆∆Ea ) Ea(allyl) - Ea(R-O) ) -1.0 ( 1.4 kcal/mol
∆ log A ) log A(allyl) - log A(R-O) ) 2.1 ( 3.7
The determined activation parameters allowed the calcula-
tion of the rate constants for the abstraction of R hydrogen from
R-O
ab
Stabilization of the radical by a geminal oxygen relative to
allylic abstraction was estimated by calculating the difference
an ether; see Table 5. The abstraction rate constant k
is
within experimental error the same as that for allylic abstraction

Absolute Rates of Atomic Hydrogen Addition
J. Phys. Chem. A, Vol. 107, No. 17, 2003 3059
TABLE 7: Product Distribution from the Reaction of Atomic Deuterium with a Mixture of Vinylbutyrate and n-Butyl Ethera
a R ) C4H9, R′′ ) C3H7. b Calculated from the disappearance of starting material. c Deuterium distribution of the products was calculated by
2
GC/MS and H NMR spectra. d Ratio of rate constants for the abstraction of hydrogen from n-butyl ether (kbe) by atomic deuterium to the rate
constant of the addition of atomic deuterium to vinyl butyrate (kes). e Calculated rate constant ratio using measured values (kbe/kes) and (kes/ko).
acetone(hexane)
23°C
f Calculated from data in ref 3b, (kall/kR-o
)
) 3.0 (2.1).
TABLE 8: Product Distribution from the Reaction of Atomic Deuterium with Vinyl Butyrate in Acetone at -72 °Ca
a Products from disproportionation were calculated on the basis of the reactions of atomic deuterium; see Table 9. b Product from 1,2 radical
addition. c Ratio (1:1) of d,l- to meso isomers. Traces of a dimer from radical addition to the vinyl ester was also detected.
but is substantially slower (25-50 times) than addition to
from the competing relative rates between the ether or ester
and 1-octene, in both solvents, are consistent with the absolute
rate constants (i.e. the ether is marginally faster than the olefin,
and the ester is slower than the ether and the olefin; see Figure
5).
1-octene.
A similar study was carried out for the reactions of vinyl
butyrate, Tables 8 and 9.
The absolute rates were calculated for reactions carried out
in acetone and hexane; see Tables 10 and 11.
Experimental Section
The mechanism for addition, disproportionation, and com-
bination is the same as that for all of the other terminal olefins.
The absolute rate constant (see Figure 4 and Table 5) is within
experimental error the same as was found for the ether. The
relative rates for addition, as expected, are measurably slower
than those for the ether for reactions carried out in both acetone
and hexane; see Table 6. Arrhenius plots for the data constructed
Materials. 1-Octene (98%), butyl ether (99+%), chlorohep-
tane (99%), butyl ethyl ether (99%), and ethyl butyrate (99%,
Aldrich) were checked for purity by GC and used as received.
Butyl vinyl ether (98%) and vinyl butyrate (Eastman) were
fractionally distilled before use. Acetone (99.5%) and hexane
(99%, Aldrich) were distilled before use.

3060 J. Phys. Chem. A, Vol. 107, No. 17, 2003
Tanner et al.
TABLE 9. Product Distribution of the Reaction of Atomic Deuterium with an Acetone Solution of Vinyl Butyratea
2
a 0.20 mold M-3 solutions in acetone. D2 flow rate 6 mL/min; R ) C3H7. b Deuterium distributions were calculated by H NMR and GC/MS
spectra. c Monodeuterated alkanes (FMDA) to monodeuterated olefins (FMDO) ratio, which was corrected for secondary reactions. (FMDA/FMDO
Ld/(Kd + Kd2 + Ld3)). d Disproportionation (kd) to radical combination (kc) ratio (kd/kc ) (Kd + Kd2 + Ld + Ld3)/2Md2).
)
TABLE 10: Absolute Rate Constants (f 1/2ka) for the Addition of Deuterium Atoms to Vinyl Butyrate at -72 °C in Acetone
104(∆p/∆t) tboutlk
104(∆p/∆t)c,d
107[R-]b
mol L-1
104(∆p/∆t)RD
108[H•]c
mol L-1
10-3f 1/2kad
a
a
a
[olefin]
mol L-1
2
mol L-1 s-1
mol L-1 s-1
mol L-1 s-1
M-1 s-1
1.12
0.22
0.09
0.056
0.033
0.022
0.011
0.0056
6.58
2.75
0.89
0.92
0.44
0.40
0.18
0.12
5.89
2.46
0.81
0.82
0.39
0.33
8.21
5.31
3.04
3.06
2.11
1.94
0.69
0.29
0.08
0.10
0.05
0.07
9.62
6.25
3.56
3.70
2.71
6.11
20.0
27.8
44.4
49.2
67.2
72.4
100.1
2.67
(2.26)e
(2.14)e
a Experimentally measured as the change in the concentration of vinyl butyrate with time. b Calculated by using eq 5. c Calculated by using eq
7. d Calculated by using eq 9. e Calculated from a plot of (H•) vs (∆p/∆t) btoutlk
.
TABLE 11: Absolute Rate Constants (f 1/2ka) for the Addition of Deuterium Atoms to Vinyl Butyrate at -72 °C in Hexane
104(∆p/∆t) tboutlk
104(∆p/∆t)c,d
107[R-]b
mol L-1
104(∆p/∆t)RD
108[H•]c
mol L-1
10-3f 1/2kad
a
[olefin]
mol L-1
2
mol L-1 s-1
mol L-1 s-1
mol L-1 s-1
M-1 s-1
1.00
0.50
0.17
0.067
0.033
0.017
0.0084
5.54
4.68
3.91
2.40
1.17
0.52
0.21
4.98
4.20
3.37
1.97
0.92
7.22
6.63
5.94
4.54
3.10
0.56
0.48
0.42
0.29
0.12
8.11
7.57
7.39
6.84
12.32
30.96
52.78
88.09
109.3
150.0
6.68
4.05
(2.26)e
(1.00)e
a Experimentally measured as the change in the concentration of vinyl butyrate with time. b Calculated by using eq 5. c Calculated by using eq
7. d Calculated by using eq 9. e Calculated from a plot of (H•) vs (∆p/∆t) btoutlk
.
Identification and Characterization of the Reaction Prod-
ucts. The products from the reactions of hydrogen atoms were
identified by comparing their GC retention times and GC/IR
and GC/MS spectra with those of authentic samples. The dimeric
products were isolated from the reaction mixture by reduced-
pressure distillation, and the dimers were separated by prepara-
tive gas chromatography. The products from the reactions of
deuterium atoms were identified by their GC/MS spectra and2H
NMR spectroscopy.
The 1H, 2H, and 13C NMR spectra were obtained using either
a Bruker AM-400 (400 MHz) or a Bruker AM-300 (300 MHz)
NMR spectrometer. The 1H NMR spectra are referenced to TMS
as an internal standard at 0.00 ppm unless otherwise noted. The
13C spectra were studied by APT (attached proton test) to
determine the number of protons attached to each carbon. GC/
IR spectra were obtained using an HP 5965A IRD GC/FTIR
interfaced to an HP 5890 gas chromatograph fitted with a DB-5
(30 m × 0.25 mm) glass capillary column. GC/MS data were

Absolute Rates of Atomic Hydrogen Addition
J. Phys. Chem. A, Vol. 107, No. 17, 2003 3061
gel. 1H NMR (400 MHz, CD3COCD3): δ 0.90 (t, 6H), 1.20 (t,
6H), 1.60 (m, 4H), 2.40 (m, 4H), 4.95 (m, 2H). 13C NMR (300
MHz, CD3COCD3): δ 13.8, 15.2, 16.2, 19.0, 36.6, 71.5, 71.6,
172.8. The APT spectrum was consistent with the above
structure. IR (vapor phase) ν: 2981, 2889, 1753, 1458, 1379,
1253, 1174, 1095 cm-1. Anal. Calcd for C12H22O4: C, 62.62;
H, 9.56. Found: C, 62.60; H, 9.71; m/z+ 230.
2-Butenoxy-3-methyl-nonane. This compound was separated
from the reaction mixture by preparative GC on a packed
column (15% Apiezon L on 60/80 chromosorb W: 10 ft × 0.25
1
in). H NMR (400 MHz, CD3COCD3): δ 0.90 (m, 6H), 1.10
(m, 6H), 1.30 (m, 8H), 1.60 (m, 4H), 2.30 (t, 2H), 2.80 (m,
1H), 4.80 (m, 1H). 13C NMR (300 MHz, CD3COCD3): δ 13.8,
14.3, 15.0, 16.3, 17.3, 19.2, 23.2, 27.7, 30.6, 33.3, 38.3, 73.7,
74.1, 175.0. The APT spectrum was consistent with the above
structure. IR (vapor phase) ν: 2938, 1749, 1462, 1377, 1255,
1184, 1096, 947 cm-1. Anal. Calcd for C14H28O2: C, 73.68;
H, 12.28. Found: C, 73.45; H, 12.15; m/z+ 228.
Figure 4. Variation of the apparent rate constant log(f1/2 ka) with the
concentration of vinyl butyrate in (O) acetone and (b) hexane at -72
°C.
Reactions with Hydrogen (Deuterium) Atoms. The ap-
paratus for the microwave discharge was as described previously.1a
A solution of the substrate (10 mL, 1 M) in acetone or hexane
with an added standard (1-chloroheptane) was placed in the “U”-
shaped reactor, and hydrogen or deuterium atoms generated by
the H2/He or D2/He plasma (H2/D2 flow rate 5 mL/min, pressure
3-4 Torr) were swept over the stirred solution from -42 to
-94 °C for 10-60 min. The reaction mixtures were analyzed
2
by GC, GC/MS, GC/IR, and H and 13C NMR spectroscopy.
Determination of Absolute Rates. Solutions of substrates
(vinyl butyl ether or vinyl butyrate) and the internal standard
(1-chloroheptane) were subjected to D2/He or H2/He plasma as
described above, and the disappearance of the starting material
and appearance of the products were measured for a given time.
The rate constant f 1/2ka was calculated using eqs 3-7. The
concentrations and viscosities of solutions were corrected for
temperature. Some cross dimers with the solvents and substrates
were observed at low substrate concentrations. These were taken
into account when the appearance of products was calculated.
Determination of the Relative Rates. A 1:1 mixture of vinyl
ethers or esters and 1-octene was prepared in acetone or hexane
in the presence of an unreactive internal standard (1-chloro-
heptane) and allowed to react with hydrogen or deuterium atoms.
The relative rates were calculated by the GC analysis of initial
and final reaction mixtures according to eqs 10 and 11.
The relative rate of disappearance of the vinyl ether was
determined by competition kinetics from mixtures of 1-octene
and vinyl butyl ether using the relationship given in eqs 10 and
11; see Table 2:
Figure 5. Arrhenius plot for the relative rate of vinyl butyl ether in
(O) acetone and (b) hexane and for vinyl butyrate in ([) hexane and
(0) acetone. (4) Extrapolated values at 23 °C.
obtained by using a VG-70E EI+ spectrometer fitted with a
Varian Vista 6000 gas chromatograph having a glass capillary
column (DB-5 30 m × 0.25 mm, J & W Scientific).
dl and meso-2,3-Dibutoxybutane. These were separated from
the product mixture resulting from the addition of atomic
hydrogen to n-butyl vinyl ether by column chromatography
(silica gel column, eluted with 10% methylene chloride in
1
hexane). H NMR (400 MHz, CD3COCD3): δ 0.90 (t, 6H),
1.00 (d, 3H), 1.10 (d, 3H), 1.40 (m, 4H), 1.5 (m, 4H), 3.00 (t,
4H), 3.50 (m, 2H). 13C NMR (300 MHz, CD3COCD3): δ 14.1,
14.5, 16.3, 29.5, 33.1, 69.4, 77.7, 79.2. The APT spectrum was
consistent with the above structure. IR (vapor phase) ν: 2942,
2882, 1466, 1381, 1114 cm-1. Anal. Calcd for C12H26O2: C,
71.29; H, 12.90. Found: C, 71.01; H, 13.07; m/z+ 202.
2-Butoxy-3-methyl-nonane. This compound was separated
from the product mixture resulting from the addition of atomic
hydrogen to a mixture of 1-octene and n-butyl vinyl ether by
preparative GC on a packed column (15% Apiezon on 60/80
chromosorb W: 10 ft × 0.25 in). 1H NMR (400 MHz,
CD3COCD3): δ 0.88 (m, 6H), 1.00 (d, 3H), 1.10 (d, 3H), 1.30
(m, 14H), 2.80 (m, 1H), 3.20 (m, 2H), 3.50 (m, 1H). 13C NMR
(300 MHz, CD3COCD3): δ 14.2, 15.4, 15.6, 16.5, 20.1, 23.3,
28.0, 30.4, 32.6, 38.9, 33.2, 33.7, 68.8, 79.2, 79.4. The APT
spectrum was consistent with the above structure. IR (vapor
phase) ν: 2937, 2877, 1464, 1381, 1106 cm-1. Anal. Calcd for
C14H30O: C, 78.50; H, 14.02. Found: C, 78.30; H, 13.60; m/z+
214.
log(Cet /Ceo)
keadd ) koadd
(10)
e
e
{
}
log(Ct /Co)
The concentrations of the ether or octene that had undergone
reaction were corrected for reformation by disproportionation
and for disappearance by radical addition. The area ratios (A)
were calibrated using an unreactive internal standard (S).
log[((Ae - A(Ad) + A(D))/As)t/(Ae/Ads)o]
keadd ) koadd
(11)
o
(Ad)
(I)
s
e
{
}
log[((A - A
+ A )/A )t/(A /As)t]
where superscript o is 1-octene, superscript e is vinyl ether;
subscript t is the reaction time, and subscript o is the initial
area or concentration. The superscript capital letters in eq 11
refer to the compounds in Table 12.
dl and meso-2,3-Dibutenoxybutane. These were separated
from the product mixture resulting from the addition of atomic
hydrogen to vinylbutyrate by column chromatography on silica

3062 J. Phys. Chem. A, Vol. 107, No. 17, 2003
Tanner et al.
TABLE 12: Product Distribution from the Reaction of Atomic Deuterium with a Mixture of 1-Octene and Vinyl Butyl Ether in
Acetone Solutionsa
a R ) C4H7, R′ ) C6H13, R′′ ) C5H11. b Numbers in parentheses indicate the average values of two independent reactions carried out for the
c
same times. FMDO ) monodeuterated octene and vinyl butyl ether, FMDA ) monodeuterated octane and ethyl butyl ether. d Rates corrected for the
addition and disproportionation products. e kd/kc is the disproportionation/combination ratio.
Reactions of Vinyl Butyl Ether with Atomic Deuterium.
The H spectra of the reaction mixture showed absorptions at
δ 0.75, 0.83, 0.86, and 1.09 (DCH2-), 3.12 (-DCH-O-), and
3.66, 3.88 (DCHdCH-O-), indicating that the products are
formed from the deuterium atom addition to the terminal
position of the double bond.
Acknowledgment. This work was supported in part by the
Office of Science, Office of Basic Energy Science, U.S.
Department of Energy under Contract DE-AC06-76 RLO 1830.
2
References and Notes
(1) (a) Tanner, D. D.; Zhang, L. J. Am. Chem. Soc. 1994, 116, 6683.
(b) Tanner, D. D.; Zhang, L.; Kandanarachchi, P. J. Phys. Chem. 1996,
100, 11319. (c) Tanner, D. D.; Zhang, L.; Kandanarachchi, P. J. Phys. Chem.
A 1997, 101, 9327.
(2) EValuated Kinetic Data on Gas-Phase Addition Reactions: Reac-
tions of Atoms and Radicals with Alkenes, Alkynes and Aromatic Com-
pounds; Kerr, J. A., Parsonage, M. J., Eds.; Butterworths: London, 1972.
Weissman, M.; Benson, S. W. Int. J. Chem. Kinet. 1984, 16, 307. Benson,
S. W. Thermochemical Kinetics Methods for the Estimation of Thermo-
Reactions of Vinyl Butyrate with Atomic Deuterium. The
2H spectra of the reaction mixture showed absorptions at δ 1.19,
1.24 (DCH2-), 4.00, 4.10 (-DCH-O-), and 4.50, 4.60, 4.80,
4.90 (DCHdCH-O-), indicating that the products are formed
from the deuterium atom addition to the terminal position of
the double bond.

Absolute Rates of Atomic Hydrogen Addition
J. Phys. Chem. A, Vol. 107, No. 17, 2003 3063
chemical Data and Rate Parameters, 2nd ed.; Wiley-Interscience: New
York, 1976; pp 95-96 and references therein.
10b). Geometries were calculated at the all-electron MP2/6-31G(d, p) level
of theory, ground and transition states were verified by vibrational
calculations, and electronic properties were calculated at the QCISD(T)/6-
311G((d, p)//MP2)FU/6-31G(d, p) level of theory. The hydrogen atom
adduct (hydroxyethyl radical) exhibited a dipole moment of 1.8 D, the
transition state exhibited a dipole moment of 1.3 D, and vinyl alcohol
exhibited a dipole moment of 1.2 D. (b) Frisch, M. J.; Trucks, G. W.;
Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Zakrzewski,
V. G.; Montgomery, J. A., Jr.; Stratmann, R. E.; Burant, J. C.; Dapprich,
S.; Millam, J. M.; Daniels, A. D.; Kudin, K. N.; Strain, M. C.; Farkas, O.;
Tomasi, J.; Barone, V.; Cossi, M.; Cammi, R.; Mennucci, B.; Pomelli, C.;
Adamo, C.; Clifford, S.; Ochterski, J.; Petersson, G. A.; Ayala, P. Y.; Cui,
Q.; Morokuma, K.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.;
Foresman, J. B.; Cioslowski, J.; Ortiz, J. V.; Stefanov, B. B.; Liu, G.;
Liashenko, A.; Piskorz, P.; Komaromi, I.; Gomperts, R.; Martin, R. L.;
Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.;
Gonzalez, C.; Challacombe, M.; Gill, P. M. W.; Johnson, B. G.; Chen, W.;
Wong, M. W.; Andres, J. L.; Head-Gordon, M.; Replogle, E. S.; Pople, J.
A. Gaussian 98, revision A.7; Gaussian, Inc.: Pittsburgh, PA, 1998.
(3) Zytowski, T.; Fischer, H. J. Am. Chem. Soc. 1996, 118, 437-439
and references therein.
(4) Heats of formation of methyl, sec-butyl, and isopropyl radicals:
Tsang, W. In Energetics of Organic Free Radicals; Simoes, J. A. M.,
Greenberg, A., Liebman, J. F., Eds.; Blackie Academic & Professional:
New York, 1996; pp 22-58 and references therein.
The R-O substituted radicals are estimated from the parent hydrocarbons
using a bond dissociation energy of 92-93 kcal/mol. The value of 92-93
kcal/mol is in good agreement with limited available experimental values.5
This value of 93 kcal/mol for a secondary C-H bond with R-O substitution
is in agreement with high-level ab initio isodesmic calculations (Gaussian
98, G2MP2 level of theory) of the enthalpy of reaction, 5.4 kcal/mol, for
the reaction CH3CH2CH2CH3 (-28.9) + CH3OCH•CH3 (-9.05) f
CH3CH2CH•CH3 (19.7) + CH3CH2OCH3 (-52.3) from the experimental
bond dissociation of secondary alkyl radical, 98.4 kcal/mol. Values in
parentheses are G2MP2 enthalpies of formation at 298 K. The C-H bond
dissociation energy of methanol is 98 kcal/mol, compared to 105 kcal/mol
for methane. Thus, oxygen substitution of an alkane carbon reduces the
bond dissociation energy by 5-7 kcal/mol.6
(10) Fischer, H. Z. Naturforsch., A: Phys. Sci. 1965, 20, 428.
(11) (a) Haydag, K.; McKelvey, R. D. J. Org. Chem. 1976, 41, 2222.
(b) Malatesta, V.; Ingold, K. U. J. Am. Chem. Soc. 1981, 103, 609. (c)
Beckwith, A. L. J.; Easton, C. J. J. Am. Chem. Soc. 1981, 103, 615. (d)
Griller, D.; Howard, J. A.; Marriott, P. R.; Scaiano, J. C. J. Am. Chem.
Soc. 1981, 103, 619.
(12) Gibian, M. J.; Corley, P. C. Chem. ReV. 1973, 73, 448.
(13) A small error is introduced (∼6%) in the overall reaction rate
constant from the values of 1,2-dideutero olefin since disproportionation
from the monodeutero radical may also transfer a deuterium to yield the
1,2-dideutero product and undeuterated olefin. This process causes a
maximum error in the value of ∼6% in (p/t)RH2, which is moderated by a
deuterium isotope effect of 1.2-2; see eq 9 and data from Tables 3 and 4.
This error may account for the small deviation (within experimental error)
in the 1:1 ratio of monodeutero olefin to alkane. An estimate of the error
(∼6%) could be made by using the values in eq 9. The reproducibility of
each value determined from two or more reactions at several olefin
concentrations at varying percentages of reaction yielded only ka, which
differed by ∼6%.
(5) Laarhoven, L. J. J.; Mulder, P. J. Phys. Chem. B 1997, 101, 73-
77.
(6) Thermochemical values for other structures in the illustration are
from Lias, S. G.; Bartmess, J. E.; Liebman, J. F.; Holmes, J. L.; Levin, R.
D.; Mallard, W. G. J. Phys. Chem. Ref. Data 1988, 17, suppl. 1.
(7) Elad, D. The Chemistry of the Ether Linkage; Interscience Publish-
ers: New York, 1967; Chapter 8, p 355.
(8) (a) Wertz, J. E.; Bolton, J. R. Electron Spin Resonance; Chapman
& Hall: New York, 1986; pp 112-114. (b) Dobbs, A. J.; Gilbert, B. C.;
Norman, R. O. C. J. Chem. Soc. A 1971, 124.
(9) (a) The potential surface for the addition of a hydrogen atom to
vinyl alcohol was examined using the Gaussian 98 set of programs (ref