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The conformational analysis of acrolein
Tetrahedron Letters No. 12,
pp 951 - 934, 1973.
Pergamon Press.
Printed in Great Britain.
TIE CONFORMATIONAL ANALYSIS OF ACROLEW Robert L. Lipnicd Department of Chemistry, University of Minnesota Minneapolis, Minnesota 55455 (Received in USA 18 August 1972; received in UK for Publication 6 February 1973) Studies by microwave,
1
ultrasonic relaxation,
2
X-ray,3 nmr,4 and raman and infrared5
indicate that acrolein exists as a mixture of -trans and cis conformers, with the former predominating at room temperature. While the major trans conformer is coplanar (,&), it is not known whether the minor conformer is coplanar (a)
or skewed (&,
x).
(1)
In this study, the temperature-dependences been measured for acrolein-A2
of the averaged conformer nmr parameters have
(2) at 13 temperatures over a range of 175.6', and these param-
eters related to changes in conformer population. Acrolein-A2 was prepared according to the scheme outlined in Figure 1. propionate of Ingold,
(2) was prepared from sodium ethoxide and ethyl propiolate b.p. 93'117 nrm (lit. 93'122 mm).
Ethyl 3,3-diethoxy-
(Aldrich) using the method
Reduction of $ with LiAlD4 in ether gave 3,3-di-
ethoxypropanol-g2
(2) in 69% yield, b.p. 99-102'/18 mm (lit. 98*/20 mm),7
p-toluenesulfonyl
chloride in anhydrous pyridine afforded 3,3-diethoxypropanol-g2
an uncrystallizable
oil, in 84% yield.
Tosylation of 2 with tosylate ($),
The tosylate (4) underwent facile elimination with
potassium t-butoxide (100% molar excess) in anhydrous dimethyl sulfoxide at room temperature to 3,3-diethoxypropene-A2
(J), b.p. 121-123' (lit. 123.5").8
by acetal exchange in n-heptaldehyde
Acrolein-A2
(6) was prepared from
containing a catalytic amount of p-toluenesulfonic
931
2
acid.'
932
No. 12
NaOEt EtOH p
CH=C-CO2Et
LiAlD4 (gtO)2CHCH2CO2Et
Et20 '
(EtO)2CHCH2CD20H
.,
c
3 'L
TsCl CH3(CH2)5CHO CRO-CH=CD2
<
TsOH
Py I
tBuOK 'DMSO
(Et0)2CBCH=CD2
(Et0)2CHCH2CD20Ts
FIGURE I
All spectra were obtained from a sealed 5 mm sample tube containing 1.07% (m/m) acrolein-A2 (RMDS) (> 99% by glpc) in Reagent CS2,
(> 99% by glpc) and 0.48% (m/m) hexamethyldisilane
stabilized by the addition of a small crystal of hydroquinone. The deuterium-decoupled
spectrum of ,Q consists of two'equally-spaced
sponding to the aldehyde (HA) and olefinic (HB) protons. sideband-calibrated
doublets, corre-
At each temperature, 16-22 BMDS 10 yielding line frequencies
spectra were recorded for each doublet,
relative to BMDS, whose standard deviations ranged 0.02-0.06 Hz, with an average value of 0.03 Hz.
At all temperatures, the two doublets were well-separated,
were obtained from a direct first-order analysis. from the average of the two doublet separations.
and all nmr parameters
The vicinal coupling, JAB, was derived Table 1 shows the experimental values for
vA, uB, and JAR at 13 temperatures. Table 1
Temperaturea 69.8 54.5 39.5 38.5 29.5 15.6 -0.9 -17.5 -37.8 -60.0 -72.5 -82.5 -105.2
b
b
JABC
"A
"B
568.80 568.67 568.47 568.55 568.48 568.32 568.02 567.92 567.55 567.12 566.79 566.56 565.82
374.28 374.35 374.45 374.49 374.54 374.63 374.79 374.86 375.01 375.25 375.37 375.53 375.81
7.37 7.46 7.58 7.56 7.60 7.68 7.76 7.78 7.88 7.94 7.99 8.06 8.06
In Hz from HMDS.
c) In Hz.
a) In 'C; accurate to fl'.
b)
These parameters, in addition to the derived parameters in an attempt to determine AH for the equilibrium 4. e
(vA - vB) and (vA + v,), were used
@, (&,
,&$) by iterative solution of
lo.
eq.
12
933
2 where P -al
respectively;
$
Solution eters.
is
of
eq.
at either
(j.k),
2 varying
enantiomers led
of
to reduce
for
and lb,
11 T -li’ the above param-
for
any of
the number of unknowns by one by holding
the minor 2 for
solution
&
th at the 1. of & temperatures,
corresponding
of eq.
error
the others
in A! of
discarded.
been accurately
only
sign
conformers
the unknowns was not achieved
i$)
yielded
in algebraic
of
to either
AZ
one planar
conformer.
three
values
qualitatively
parameter
sets:
of M_ which
vA,
differ
(vA
-
appreciably
VB),
and
from liter-
one&d whose percent probable errors were greater 14 than expected from similar measurements. As JAR yielded a solution value of AH (Table 2) in lb accord with previous measurements (1.7,5a 2.06,2 kcal./mole) and gave rise to a and 2.5
probable
(even
($,
parsmeters
parameters
e.u.,
to solution
and (vA - vS)
vB
values
all
it was necessary
treatment
Roth
JAB’ ature
of _L intensive
0 or R &n 2 (1.~76)~
or two e This
th
of .& observed
the ith
Consequently,
fixed
are the 1
and 3!A
6.5$,
The values
for
this
parameter
was retained are
of AlJ and &),
for
further
insensitive
consideration
and
to Ag, and therefore
have
determined.
Table 2 Solution
Solution
Parametersa of Equation J+R at Fixed Values
1 Using Temperature-dependence6 of AZ for Equation 2
of
Agb (Fixed)
1
0
l&U122
8.11f0.02
2
1.376
1942H15
8. mto.ce
-3.67a.85
0.021
1.24+o.g8
O.CQ2
a) All nmr parameters are given in Hz. Subscripts 2 and a denote nmr parameters calculated for the trans and cis conformers, respectively. f figures denote probable errors. b)cal/(ae deg). c) In Cal/mole. The value formation, acrolein. 1.376,
,lk, l5
(&R)b
is
in poor
However,
corresponding
estimate. solution
of
Figure 2.
(-3.67
f
1.85
agreement
the solution
Hz) found
with value
for
the best (+1.24
f 0.98
to two skewed enantiomers, 2 shoes
The apparent
steric,
and/or
similar
to the result
electrostatic
the experimental nonplanarity energy
found for
AS = 0 corresponding
theoretical
is
Hz) found if
in good agreement
and calculated
of acrolein
to one planar (2.4
Es)
AZ is held with
this
temperature-dependence6
can be explained
contributions to the total 14a
-cis-butadiene.
estimate
by large
torsional
con-
for sconstant
at
theoretical of &
for
torsional, 5c and is potential,
934
No. 12
z Acknowledgment:
77 -
z
The author is grateful to the
National Science Foundation for Grant No. ~~-9815
-. 7s
which provided support for this work, and to Dr. Edgar W. Garbisch, Jr. for helpful discussions.
FIGURE 2. The experimental (*) and tileoretical (solid line) temperature dependence of JAB. The theoretical dependence is derived from solution 2 of eq. 2.
References and Footnotes * Correspondence may be directed to R.L.L., 53 Winthrop Road, Brookline, Massachusetts
~146.
1.
(a) C. E. Cherniak and C. C. Costain, J. Chem. Phys., $2, l& (1966); (b) R. Wagner, J. Fine, J. W. Sirmsons, and J. H. Goldstein, J. &em. Phys., g$, 634 (1957).
2.
M. S. De Groot and J. Lamb, Proc. Roy. Sot. (London), A2$2, 36 (1957).
3.
K. Kuchitsu, T. Fukuyama, and Y. Morino, J. Mol. Struct., 2, 463 (1967-68).
4.
(a) A. W. Douglas and J. H. Goldstein, J. Mol. Spectros., _1_6,1 (1965); (b) J. E. D. Davies, J. Mol. Spectros., 22, 499 (1969).
5.
(a) S. Dzhessati, V. I. Tyulin, and V. M. Tatevskii, Vestr. Mosk. Univ., Ser. II 22 (2), 14-19 (1967), see C.A. 68, 109587b; (b) R. K. Harris, Spectrochim. Acta, 20, 112$71964); (c) W. G. Fateley,rKTUHarris, F. A. Miller, and R. E. Witkowsky, Spect?&him. Acta, ,2,1,231 (1965).
6.
E. H. Ingold, J. Chem. Sot.,
$?J, 1199 (1925).
7.
A. Wohl and W. Emnerich, &.,
22, 2760 (1900).
8.
A. wohl, E.,
9.
All of the synthetic intermediates and their nondeuterated analogs gave nmr spectra that were in agreement with the assigned structures.
10.
The modified ~-60 nmr spectrometer and experimental method have been described previously in reference 13-a.
11.
For a detailed discussion of the scope and limitations of this method, see E. W. Garbisch, Jr., B. L. Hawkins, and K. D. MacKay, in "Conformational Analysis: Scope and Present Limitations", E. Chiurdogu, Ed., pp. 93-110, Academic Press, New York, 1971.
12.
The entropy of mixing is normally used for such a case.
13.
22, 1796 (1898).
Solution values at AS = 0 : AH = 691 f 66 Cal/mole (vg) and -62 f 87 Cal/mole (VA-vB)The unreliability of-solution-values of AH obtained from chemical shift data is consistent with the erratic concentration-dependence of chemical shift reported for acrolein in reference 4a and ascribed to head to tail dimer equilibrium.
14.
(a) The Conformational Analysis of 1,3-butadiene, R. L. Lipnick and E. W. Garbisch, Jr., (b) the Conformational Analysis of 4,43. Amer. Chem. Sot., 95, 0000 (1973). Dimethyl-1-pentene, P.-x. Weller and E. W. Garbisch, Jr., J. Amer. Chem. Sot., 94, 0000 __ (1972).
15.
A. A. Bothner-By and R. K. Harris, J. Org. Chem., 30, 254 (1965). __
pp 951 - 934, 1973.
Pergamon Press.
Printed in Great Britain.
TIE CONFORMATIONAL ANALYSIS OF ACROLEW Robert L. Lipnicd Department of Chemistry, University of Minnesota Minneapolis, Minnesota 55455 (Received in USA 18 August 1972; received in UK for Publication 6 February 1973) Studies by microwave,
1
ultrasonic relaxation,
2
X-ray,3 nmr,4 and raman and infrared5
indicate that acrolein exists as a mixture of -trans and cis conformers, with the former predominating at room temperature. While the major trans conformer is coplanar (,&), it is not known whether the minor conformer is coplanar (a)
or skewed (&,
x).
(1)
In this study, the temperature-dependences been measured for acrolein-A2
of the averaged conformer nmr parameters have
(2) at 13 temperatures over a range of 175.6', and these param-
eters related to changes in conformer population. Acrolein-A2 was prepared according to the scheme outlined in Figure 1. propionate of Ingold,
(2) was prepared from sodium ethoxide and ethyl propiolate b.p. 93'117 nrm (lit. 93'122 mm).
Ethyl 3,3-diethoxy-
(Aldrich) using the method
Reduction of $ with LiAlD4 in ether gave 3,3-di-
ethoxypropanol-g2
(2) in 69% yield, b.p. 99-102'/18 mm (lit. 98*/20 mm),7
p-toluenesulfonyl
chloride in anhydrous pyridine afforded 3,3-diethoxypropanol-g2
an uncrystallizable
oil, in 84% yield.
Tosylation of 2 with tosylate ($),
The tosylate (4) underwent facile elimination with
potassium t-butoxide (100% molar excess) in anhydrous dimethyl sulfoxide at room temperature to 3,3-diethoxypropene-A2
(J), b.p. 121-123' (lit. 123.5").8
by acetal exchange in n-heptaldehyde
Acrolein-A2
(6) was prepared from
containing a catalytic amount of p-toluenesulfonic
931
2
acid.'
932
No. 12
NaOEt EtOH p
CH=C-CO2Et
LiAlD4 (gtO)2CHCH2CO2Et
Et20 '
(EtO)2CHCH2CD20H
.,
c
3 'L
TsCl CH3(CH2)5CHO CRO-CH=CD2
<
TsOH
Py I
tBuOK 'DMSO
(Et0)2CBCH=CD2
(Et0)2CHCH2CD20Ts
FIGURE I
All spectra were obtained from a sealed 5 mm sample tube containing 1.07% (m/m) acrolein-A2 (RMDS) (> 99% by glpc) in Reagent CS2,
(> 99% by glpc) and 0.48% (m/m) hexamethyldisilane
stabilized by the addition of a small crystal of hydroquinone. The deuterium-decoupled
spectrum of ,Q consists of two'equally-spaced
sponding to the aldehyde (HA) and olefinic (HB) protons. sideband-calibrated
doublets, corre-
At each temperature, 16-22 BMDS 10 yielding line frequencies
spectra were recorded for each doublet,
relative to BMDS, whose standard deviations ranged 0.02-0.06 Hz, with an average value of 0.03 Hz.
At all temperatures, the two doublets were well-separated,
were obtained from a direct first-order analysis. from the average of the two doublet separations.
and all nmr parameters
The vicinal coupling, JAB, was derived Table 1 shows the experimental values for
vA, uB, and JAR at 13 temperatures. Table 1
Temperaturea 69.8 54.5 39.5 38.5 29.5 15.6 -0.9 -17.5 -37.8 -60.0 -72.5 -82.5 -105.2
b
b
JABC
"A
"B
568.80 568.67 568.47 568.55 568.48 568.32 568.02 567.92 567.55 567.12 566.79 566.56 565.82
374.28 374.35 374.45 374.49 374.54 374.63 374.79 374.86 375.01 375.25 375.37 375.53 375.81
7.37 7.46 7.58 7.56 7.60 7.68 7.76 7.78 7.88 7.94 7.99 8.06 8.06
In Hz from HMDS.
c) In Hz.
a) In 'C; accurate to fl'.
b)
These parameters, in addition to the derived parameters in an attempt to determine AH for the equilibrium 4. e
(vA - vB) and (vA + v,), were used
@, (&,
,&$) by iterative solution of
lo.
eq.
12
933
2 where P -al
respectively;
$
Solution eters.
is
of
eq.
at either
(j.k),
2 varying
enantiomers led
of
to reduce
for
and lb,
11 T -li’ the above param-
for
any of
the number of unknowns by one by holding
the minor 2 for
solution
&
th at the 1. of & temperatures,
corresponding
of eq.
error
the others
in A! of
discarded.
been accurately
only
sign
conformers
the unknowns was not achieved
i$)
yielded
in algebraic
of
to either
AZ
one planar
conformer.
three
values
qualitatively
parameter
sets:
of M_ which
vA,
differ
(vA
-
appreciably
VB),
and
from liter-
one&d whose percent probable errors were greater 14 than expected from similar measurements. As JAR yielded a solution value of AH (Table 2) in lb accord with previous measurements (1.7,5a 2.06,2 kcal./mole) and gave rise to a and 2.5
probable
(even
($,
parsmeters
parameters
e.u.,
to solution
and (vA - vS)
vB
values
all
it was necessary
treatment
Roth
JAB’ ature
of _L intensive
0 or R &n 2 (1.~76)~
or two e This
th
of .& observed
the ith
Consequently,
fixed
are the 1
and 3!A
6.5$,
The values
for
this
parameter
was retained are
of AlJ and &),
for
further
insensitive
consideration
and
to Ag, and therefore
have
determined.
Table 2 Solution
Solution
Parametersa of Equation J+R at Fixed Values
1 Using Temperature-dependence6 of AZ for Equation 2
of
Agb (Fixed)
1
0
l&U122
8.11f0.02
2
1.376
1942H15
8. mto.ce
-3.67a.85
0.021
1.24+o.g8
O.CQ2
a) All nmr parameters are given in Hz. Subscripts 2 and a denote nmr parameters calculated for the trans and cis conformers, respectively. f figures denote probable errors. b)cal/(ae deg). c) In Cal/mole. The value formation, acrolein. 1.376,
,lk, l5
(&R)b
is
in poor
However,
corresponding
estimate. solution
of
Figure 2.
(-3.67
f
1.85
agreement
the solution
Hz) found
with value
for
the best (+1.24
f 0.98
to two skewed enantiomers, 2 shoes
The apparent
steric,
and/or
similar
to the result
electrostatic
the experimental nonplanarity energy
found for
AS = 0 corresponding
theoretical
is
Hz) found if
in good agreement
and calculated
of acrolein
to one planar (2.4
Es)
AZ is held with
this
temperature-dependence6
can be explained
contributions to the total 14a
-cis-butadiene.
estimate
by large
torsional
con-
for sconstant
at
theoretical of &
for
torsional, 5c and is potential,
934
No. 12
z Acknowledgment:
77 -
z
The author is grateful to the
National Science Foundation for Grant No. ~~-9815
-. 7s
which provided support for this work, and to Dr. Edgar W. Garbisch, Jr. for helpful discussions.
FIGURE 2. The experimental (*) and tileoretical (solid line) temperature dependence of JAB. The theoretical dependence is derived from solution 2 of eq. 2.
References and Footnotes * Correspondence may be directed to R.L.L., 53 Winthrop Road, Brookline, Massachusetts
~146.
1.
(a) C. E. Cherniak and C. C. Costain, J. Chem. Phys., $2, l& (1966); (b) R. Wagner, J. Fine, J. W. Sirmsons, and J. H. Goldstein, J. &em. Phys., g$, 634 (1957).
2.
M. S. De Groot and J. Lamb, Proc. Roy. Sot. (London), A2$2, 36 (1957).
3.
K. Kuchitsu, T. Fukuyama, and Y. Morino, J. Mol. Struct., 2, 463 (1967-68).
4.
(a) A. W. Douglas and J. H. Goldstein, J. Mol. Spectros., _1_6,1 (1965); (b) J. E. D. Davies, J. Mol. Spectros., 22, 499 (1969).
5.
(a) S. Dzhessati, V. I. Tyulin, and V. M. Tatevskii, Vestr. Mosk. Univ., Ser. II 22 (2), 14-19 (1967), see C.A. 68, 109587b; (b) R. K. Harris, Spectrochim. Acta, 20, 112$71964); (c) W. G. Fateley,rKTUHarris, F. A. Miller, and R. E. Witkowsky, Spect?&him. Acta, ,2,1,231 (1965).
6.
E. H. Ingold, J. Chem. Sot.,
$?J, 1199 (1925).
7.
A. Wohl and W. Emnerich, &.,
22, 2760 (1900).
8.
A. wohl, E.,
9.
All of the synthetic intermediates and their nondeuterated analogs gave nmr spectra that were in agreement with the assigned structures.
10.
The modified ~-60 nmr spectrometer and experimental method have been described previously in reference 13-a.
11.
For a detailed discussion of the scope and limitations of this method, see E. W. Garbisch, Jr., B. L. Hawkins, and K. D. MacKay, in "Conformational Analysis: Scope and Present Limitations", E. Chiurdogu, Ed., pp. 93-110, Academic Press, New York, 1971.
12.
The entropy of mixing is normally used for such a case.
13.
22, 1796 (1898).
Solution values at AS = 0 : AH = 691 f 66 Cal/mole (vg) and -62 f 87 Cal/mole (VA-vB)The unreliability of-solution-values of AH obtained from chemical shift data is consistent with the erratic concentration-dependence of chemical shift reported for acrolein in reference 4a and ascribed to head to tail dimer equilibrium.
14.
(a) The Conformational Analysis of 1,3-butadiene, R. L. Lipnick and E. W. Garbisch, Jr., (b) the Conformational Analysis of 4,43. Amer. Chem. Sot., 95, 0000 (1973). Dimethyl-1-pentene, P.-x. Weller and E. W. Garbisch, Jr., J. Amer. Chem. Sot., 94, 0000 __ (1972).
15.
A. A. Bothner-By and R. K. Harris, J. Org. Chem., 30, 254 (1965). __