8357
J. Phys. Chem. 1992,96, 8357-8363
Molecular Structures and Conformatlons of 1,I,3,3-Tetrachloropropene, CIS- and trans-l,2,3,3-Tetrachloropropene, 1,1,2,3,3-PentachIoropropene, and 1,1,2-Trlchloro-3,3-dHluoropropene According to Gas-Phase Electron Dlffractlon Humayun Kaleem> Astrid L ~ n d S. , ~ Helene Schei,t Armin de Meijerqt Kolbjram Hagen,*pt and Reidar Stralevikt Department of Chemistry, A VH, University of Trondheim, N- 7055 Trondheim, Norway, and Institut fiir Organische Chemie, Georg-August- Universitiit Gbttingen, Tammanstrasse 2, 0-3400 Gbttingen, Federal Republic of Germany (Received: June 15, 1992)
Four chloro-substituted propenes have been investigated at about 330 K by gas-phase electron diffraction, and the ED data for 1,1,2-trichloro-3,3d~uoropropene have been reanalyzed. For 1,1,3,3-tetrachloropropeneonly one conformer was observed in which the carbon-hydrogen bond eclipses the carbon-carbon double bond. This is also the predominating form of trans- 1,2,3,3-tetrachIoropropeneand 1,1,2,3,3-pentachloropropene,but for these two compounds small amounts of a second conformer with the C3-H bond anti to c-.C are probably also present in the gas phase. For cis-l,2,3,3-tetrachloropropene we found substantial fractions of two conformers, namely, 41 (12)% of a form with C3-H syn to C1-2 (H-C-C=C torsional angle 4 = 0') and 59 (12)% of a form with C3-H gauche to C 1 4 2 (4 = 133 (4)'). On the assumption that ASoequals R In 2, this corresponds to an energy difference AEo = Eopuchc- E', = 0.9 (7) W mol-'. Reanalyzing the ED data from an earlier investigation for 1,1,2-trichloro-3,3-difluoropropene, we have found the molecules to be a mixture of two conformers, both with C, symmetry. The majority (82 (8)%) of the molecules have a syn conformation with a C 4 - C - H torsional angle of 41 = O', while the rest (18 (8)%) have an anti conformation with 42 = 180'.
Introduction Several halogen-substituted propenes have been investigated by electron diffraction, and their structure and conformational composition have been determined.'-" Our continuing interest in the structures of substituted propenes has led us to investigate four chloro-substituted propenes that all contain a CHClz group. Additional incentive to look at these compounds was generated by the observation of a strikingly different chemical behavior of 1,1,2-trichloro-3,3-difluoropropene(TCDFP), 1,1,3,3-tetrachloropropene (TCP), and cis-l,2,3,3-tetrachloropropene(CTCP) on one side and trans-l,2,3,3-tetrachloropropene (TTCP) and 1,1,2,3,3-pentachloropropene(PCP) on the other side.12 While TCDFP, TCP, and CTCP upon treatment with a proton-specific base such as lithium diisopropylamide all give, at least to a certain degree, rise to formation of the corresponding halogen-substituted vinylcarbene, which can be trapped by an alkene to yield 1halo- l-ethenylcyclopropane derivatives, TTCP and PCP undergo only &elimination to yield tri- and tetrachloroallene. The difference especially between CTCP and TTCP was conceived to arise from a difference in conformational properties,l2 whereas the preferred a-elimination in TCDFP could also be caused by the hard relationship between lithium and fluorine.
3
Figure 1. 1,1,3,3-Tetrachloropropene: average experimental intensity curves (El, E2) shown together with the theoretical curve (Z') calculated from the parameter values in Table I. Difference curves are D = E T.
ExperimeaW Methods and Data Reduction
1,1,3,3-Tetrachl-e (TCP), 1,1,2,3,3-pentachlmpropene (PCP), trans- 1,2,3,3-tetrachloropropene (TTCP), and cis1,2,3,3-tetrachloropropene(CTCP) were synthesized as reported earlier.I2 Sample punty was checked by GC before use. Electron diffraction photographs were recorded with the Oslo electron diffraction unit" on Kodak Electron Image plates. Voltage/ distance calibration was made with benzene as reference. The nozzle-tip temperature was nearly the same for all experiments (TCP, 329 K PCP, 331 K 'ITCP, 338 K CTCP, 333 K). Data were obtained at two different nozzle-to-plate distances (226.53 and 467.53 mm) and 4-6 plates were recorded at each distance. 'University of Trondheim. tUniversity of G6ttingen.
-
D1
- -
A _ _
--
0
5
/
io
"
"
1
.
"
'
,
$5
.
a0
I
/
V
I
25
,
,
'
I
I , ' ' , I , 30 35
I
%A''
I
,
'
3
Figure 2. truns- 1,2,3,3-Tetrachloropropene: average experimental intensity curves ( E l , E2) shown together with the theoretical curve (Z') calculated from the parameter values in Table 11. Difference curvts are D=E-T.
0022-3654/92/2096-8357$03.00/00 1992 American Chemical Society
Kaleem et al.
8358 The Journal of Physical Chemistry, Vol. 96, No. 21, 1992
1
Flgm 3. cis- 1,2,3,3-Tetrachloropropene: average experimental intensity curves (El, E2) shown together with the theoretical curve (7')calculated from the parameter values in Table 111. Difference curves are D = E
- T.
i
Figure 4. 1,1,2,3,3-Pentachloropropene: average experimental intensity curve? (El, E2) shown together with the theoretical curve (T)calculated from the parameter values in Table IV. Difference curves are D = E -
T.
TABLE I: Final Parameter Values for 1,1,3,3-Tetmcidoropropese (TCP) Darameter" fJL I r(C-H) 1.075 (40) 0.078 C=C) 1.336 (11) 0.044 r(C-C) 1.483 (14) 0.049 (4C-Cl)) 1.752 (3) b(C-Cl) 0.054 (8) Lc-c=c 125.0 (18) Lc2=cl-a4 123.1 (13) LC2=Cl-C15 120.2 (17) LC3-C2-H6 11111 LCZ-C3-C1 111.8 (12) LCkC3-CI 108.0 (17) LC 2-C 3-H 7 [io91
PI
db C syn
100
Selected Dependent Parameters LC14-Cl-C15 116.8 (18) r(C1-Cl) 1.725 (5) 0.048 r(C3-C1) 1.779 (5) 0.048 r(C 1.. 423) 2.498 (17) 0.060 r(C2. ..CIS) 2.705 (16) 0.067 0.055 (7) r(C2. 434) 2.696 (18) r(C2. * .CIS) 2.658 (20) 0.054 r(C3- * C14) 3.134 (28) 0.09 1 r(C3. * .CIS) 4.075 (17) 0.061 r(Cl8. * 4219) 2.877 (32) (20) r(C14. .CIS) 2.936 (31) r(C1. *.CIS) 3.759 (22) 0.149 (30) r(H7. C14) 2.585 (44) 0.163 r(C18. C14) 4.409 (26) 0.307 (88) r(C18.s CIS) 5.150 (18) 0.144 (15)
1
-
:g;}
Distances (r,) and vibrational amplitudes are in angstroms, angles (L,) are in degrees. Parenthesized values are 20 and include estimates
of uncertainties in voltage/nozzle heights and of correlation in the experimental data. Quantities in square brackets were kept constant in the final refinement. b~ is the H7-C3-C241 torsion angle.
Optical densities were measured using a Joyce Loeble doublebeam microdensitometer, and the data were reduced in a way reported el sew her^.^^^' The range of data were 2.00 I s/A-' I 19.50 and 6.50 I s/A-l I35.00. The average experimental intensity curves in the form sZ,,,(s) for the five m o l d e s are shown in Figures 1-5. Data for the individual curves and backgrounds are available on request. The atomic scattering and phase factors used were obtained from tables.16 The ED experiment for 1,1,2-trichloro3,3-difluoropropene (TCDFP) has been reported earlier." The nozzle-tip temperature was 295 K.
TABLE U Find Parameter V d t m for M - l , 2 , 3 , 3 - T ~ ~ (TTCP) & ~ parameter" f.IL r(C-H) 1.047 (36) r(C=C) 1.340 (1 1) r(C-C) 1.489 (12) (r(C--CI)) 1.751 (2) b(C--a) 0.046 (9) LC-C=C 125.7 (15) LCZ=Cl--C14 124.4 (19) K 2 - C 1-H5 [1181 LC3-C2--CM 116.6 (23) LC2-C3--C1 111.8 (20) LCI-C3--CI 110.3 (7) LC2-C3-H7 [io71
1 0.078 0.048 0.051
PI
$Ib
426
% syn % anti
1801 87 (13) 13 (13)
Selected Dependent Parameters LC 1=C2--C16 117.7 (15) r(C 1-C1) 1.728 (5) 0.050 r(C3-CI) 1.774 (5) 0.048 r(C1.. .C3) 2.514 (19) 0.061 r(C 1. * C16) 2.627 (19) 0.063 r(C2-.*C18) 2.702 (28) 0.068) 2.715 (22) 0.061 (9) r(C2. * 434) r(C3...C16) 2.732 (38) 0.064 3.187 (44) 0.127 (58) r(C3- C14) 2.914 (10) 0.071 (5) r(C18. ..C19) r(C14*.*H5) 2.386 (37) 0.098 r(C14. 4216) 4.284 (8) 0.062 (6) r(H5. **Cl6) 2.700 (34) 0.111 2.581 (10 0.135 3.748 (24) 0.1 11 r(Cl** C18) r(C14. * -H7) 2.645 (59) 0.189 4.422 (48) 0.224 (56) r(H5. .-C18) 4.533 (42) 0.135 3.344 (26) 0.177 (26) 0.109 3.594 (40) r(C1. * *H7) 3.297 (34) 0.103 3.280 (69) 0.138 r(C14. * aH7) 4.184 (54) 0.130 3.370 (88) 0.280 4.205 (77) 0.153 r(C16. -CIS) 3.989 (21) 0.146 2.628 (59) 0.163
-
-
ODistances (r,) and vibrational amplitudes (I) are in angstroms, angles (L,) are in degrees. Paranthesized values are 2u and include estimates of uncertainty in voltage/nozzle heights and of correlation in the experimental data. Quantities in square brackets were kept constant in l O2 are the H 7 - C 3 - C 2 4 1 torsion the final refinement. b ~ and angles for the syn and anti conformers, respectively.
Molecular Structures and Conformations
The Journal of Physical Chemistry, Vol. 96, No. 21, 1992 8359
t
f
A -.
40
45
20
25
dA-1
=O
Figure 5. 1,1,2-Trichloro-3,3-difluoropropene:average experimental intensity curves (El, E2) shown together with the theoretical curve ( r ) calculated from the parameter values in Table V. Difference curves are DIE-T.
TABLE III: Final Parameter Values for 1
rBILa
1.023 (38) 1.333 (9)' 1.492 (11) 1.746 (3) 0.062 (7) 123.4 (9) [I181 123.1 (23) 113.4 (18) 114.2 (12) 110.4 (6) [lo91
--
-
A
c b 1,2,3,3-Tetrachloro~ro~ene (CI'CP)
parametef rIC-H) r i c ej r(C-C) (r(C-Cl)) Af(C-CI) LC-C-C L C 2 4 1-H4 L C 2 4 1-C15 LC3-C2-C16 LC2-C3-C1 LCl-C3-CI LC2-C3-H7
DIFF.
, ~ ~ ' " ' " ' I ' ~ ' ' " ~ " I " ' ' ~ ' " I ' ' " ' ' ' " I ' ~ ' ' " ' ~ ~
0
4
0.078 0.047 0.051
PI
4Ib
$26
133 (4) 41 (12) 59 (12)
% syn % gauche
syn
Selected Dependent Parameters LC142-Cl6 123.2 (22) r (C 1-C1) 1.715 (4) 0.050 r(C3-CI) 1.777 (4) 0.048 r(C 1. * 423) 2.482 (1 5 ) 0.062 r(Cl*--C16) 2.690 (29) 0.056 r(C2. 438) 2.746 (19) 0.062 (9) r(C2- -CIS) 2.680 (26) 0.057 r(C3. **Cl6) 0.062 2.680 (27) r(C3. * *CIS) 4.077 (20) 0.057 (16) r(C18. * CIS) 2.919 (9) 0.072 (6) r(H4. 435) 2.368 (36) 0.098 r(H4. *.C16) 3.597 (39) 0.088 r(C15***C16) 3.205 (18) 0.094 (20) r(C 1 *H7) 2.563 (21) 0.136 r(Cl.**C18) 3.747 (16) 0.109 (47) r(H4-. C18) syn 3.925 (25) 0.218 r(C15***C18) 5.191 (15) 0.167 (48) r(C16. * 438) 3.359 (23) 0.111 (42) r(C 1* *H7) 3.170 (38) 0.116 3.018 (41) 0.1 18 3.712 (34) 0.111 r( H4. 438) 2.568 (60) 0.197 3.866 (57) 0.191 r(C15. * C18) 4.695 (42) 0.129 r(C15-*-CIS) 5.165 (29) 0.125 r(C16. * 438) 4.271 (19) 0.082 r(C16. C19) 3.409 (51) 0.164
anti
1
--
1
'Distances (r,) and vibrational amplitudes (I) are in angstroms, angles ( L a ) are in degrees. Parenthesized values are 2a and include estimates of uncertainty in voltage/nozzle heights and of correlation in the experimental data. Quantities in square brackets were kept constant in the final refinement. b # , and b2 are the H7-C3-C2=C1 torsion angles for the syn and gauche conformers, respectively.
'V F 1
8 1 % oyn +
138 anti
"
1
DIPF.
0
1
2
3
4
5
r/A
6
Figure 7. Radial distribution curves for trans- 1,2,3,3-tetrachIoropropene, together with molecular models for the syn and anti conformers. The theoretical curves were calculated for 100% anti conformer, 100% syn conformer, and a mixture of 87% syn and 13% anti conformers. Difference curves are experimental minus theoretical curves.
Kaleem et al.
8360 The Journal of Physical Chemistry, Vol. 96, No, 21, 1992
gauchc SYn
+ 100% gauche
DIFI’.
DIPF.
I
2
3
4
0
5 rlh
I
2
3
4
5
6 r/A
Figure 8. Radial distribution curves for cis-1,2,3,3-tetrachloropropene, together with molecular models for the syn and gauche conformers. The theoretical curves were calculated for 10096 syn conformer, 10096 gauche conformer, and a mixture of 41% syn and 59% gauche conformers. Difference curves are experimental minus theoretical curves.
Structure Analysis
Radial distribution (RD) curves were calculated in the usual way by Fourier transformation of the function Z’(s) = SI,&) X ZJ<&-l exp(-Bs2) with B = 0.0020 AZ. The A’s are electron scattering amplitudes multiplied by s2. Data from the unobserved region 0 I s/A-’ I1.75 were at first omitted and in later calculations taken from models close to the final one. The gametry of four of the molecules (TCP, PCP, TTCP, and CTCP) may be described by 14 parameters, 5 distance parameters (r(C-H), r(C--C), r(C-C), ( r ( C - C l ) ) = OS(r(C3-Cl) r(Cl-Cl)), A r ( C 4 1 ) = r(C3-Cl) - r(C1-Cl)) and 9 angle parameters (LC-C-C, LC2-C3-C1, LC 18-C3-C 19, LC2-C3-H7, LC241-X4, LC241-X5, LC3--C2-X6, X = H or C1, (the C142-C3-H7 torsion angle for the syn conformer), and & (the Cl=C2-C3-H7 torsion angle for the anti or gauche conformer). Corresponding parameters were also used in TCDFP except that here r(C-F) and r(C-Cl) were used as carbon-halogen distance parameters. Molecular models which give the atomic numbering arc shown together with the RD curves in Figures 6-10. Comparing experimental with theoretical RD curves for different conformational compositions (Figures 6-10). we found that four of the compounds exist primarily as one conformer. For CTCP, however, no single conformer gave a theoretical RD c w e with a good fit to the experimental curve. Good fit was obtained for a theoretical curve calculated with about 40% syn and 60% gauche conformers (see Figure 8).
+
Figure 9. Radial distribution curves for 1,1,2,3,3-pentachloropropene, together with molecular models for the syn and anti conformers. The theoretical curves were calculated for 100% anti conformer, 1 0 % syn conformer, and a mixture of 89% syn and 11% anti conformers. Difference curves are experimental minus theoretical curves.
For each of the five molecules, structural refmements were made by the method of least squares,19adjusting a single theoretical curve to the two experimental ones, one for each of the two nozzle-wplate distances,using a unit weight matrix. The different conformers for each molecule were assumed to have the same geometry except for the C-C torsional angle 4. The C-H distances were assumed to be equal and r(C1-Cl) was assumed to be equal to r(C2-Cl). Conversion of the structurally consistent set of r, distances to r,, and r, for use in the scattered intensity formula was done by using values of centrifugal distortion constants (dr), perpendicular amplitude corrections (K), and root-mean-square amplitudes of vibration (0calculated from harmonic force fields (ra = r, - P / r K dr = r - P / r ) . The force fields were based on a force with the field developed for 1,1,2-trichloro-3,3-difl~oropropene~ necessary modifications for the substitution of F by C1, and in some molecules C1 by H. A torsional force constant of 0.12 mdyn A rad-2 was used.I’ The possibility of more than one conformer being present was also tested for TCP, PCP, TTCP, and TCDFP. Inclusion of a gauche conformer in the refinements, as was observed in CTCP, gave no improvements in the fit between experimental and theoretical RD curves and no lowering of the R factor. In TCDFP a significant improvement in the fit was observed if about 20% of a second conformer with C3-H anti to C=C was included in the model. This possibility was therefore also tested for TCP, TTCP, and PCP. Least-squares refinements for TCP gave a slightly negative amount of this anti form, and no improvement in the fit between experimental and theoretical RD curves was
+ +
The Journal of Physical Chemistry, Vol. 96, No. 21, 1992 8361
Molecular Structures and Conformations
TABLE I V Find Parameter Values for 1,1,2,3,3-Pemtrchloropropem WP) parametef r(C-H) r(C=C) r(C-C) W-Cl)) Ar(C-CI) LC-C-C LC2=a-C14 LC2-Cl-Cl5 LC3-C2-C16 LC2-C3-C1 LCI-C3-CI LC2-C3-H7
hb
[ 1801 89 (11) 11 (11)
% syn % anti
Selected Dependent Parameters 121.0 (17) LCl=C2-C16 115.3 (24) Lc14-c 1-c15 1.724 (5) r( C 1-CI) 1.765 (7) r(C3-CI) 2.510 (19) 0.060 r(C1. * C 3 ) 2.672 (20) 0.059 r(CI*.*CI6) 2.718 (25) 0.070 r(C2. 4218) 0.059 (4) 2.678 (21) r(C2. 434) 0.057 2.700 (18) r(C2. .CIS) 0.062 2.707 (30) r(C3.e C16) 3.097 (56) 0.092 r(C3. C14) 4.115 (20) 0.062 r(C3. 435) 2.880 (41) r(C18- * CIS) 0.068) (10) 0.069 2.911 (41) r(C14. * .CIS) 0.060 (10) 4.294 (8) r(C14**4!16) 0.107 (22) 3.170 (33) r(C15***C16) 0.133 2.613 (26) r(Cl..*H7) 0.101 3.761 (23) r(Cl***C18) 0.164 2.533 (74) r(H7-.*C14) 0.226 (61) 4.344 (44) r(C18- C14) syn 0.141 (23) 5.201 (22) r(C18***CI5) 0.194 (51) 3.325 (33) r(C18. * C16) 0.108 3.644 (22) r(H7. * C16) 0.120 3.366 (15) r(C1. * *H7) 0.108 3.287 (49) 0.161 4.165 (53) r(H7** C14) 0.168 3.280 (93) 0.121 4.880 (49) 0.122 3.973 (22) r(C18. * 436) 0.162 2.619 (42) r(H7.s 436)
I
-
0
I
2
3
4
5
Figure 10. Radial distribution curves for 1,1,2-trichloro-3,3-difluoropropene, together with molecular models for the syn and anti conformers. The theoretical curves were calculated for 100% anti conformer, 100% syn conformer, and for a mixture of 82% syn and 18% anti conformers. Difference curves are experimental minus thearetical curves.
obtained by including some of the anti conformer in the theoretical model. For PCP, however, the refinements gave the lowest R factor for a model with 89 (1 1)% of the form with C3-H syn to C-C and 11 (11)% of the anti form. For TTCP the best result was obtained with 13 (13)% anti conformer. Figures 7, 9, and 10 show theoretical RD curves calculated for 'ITCP, PCP, and TCDFP for 100%anti, 100% syn, and the best mixtures, together with the experimental and difference curves. Tables I-V list final results for the five molecules.
MscuaPion All five molecules studied here have been found to have a conformer in which C3-H eclipses the carbon-carbon double bond. For TCP no indication of a second form was observed. In TTCP and PCP small fractions of a second form with C3-H anti to c=-C may be present, and in TCDFP it is very likely that such a form is present. The reason that this second form is anti and not gauche, as is found in CTCP and also in 3-chloropropene4and trans- 1,3-dichloropropene,' is the large steric repulsion to be expected in such a conformer between one of the halogen atoms on C3 and the chlorine atoms cis to C3 on C1. CTCP contains a hydrogen atom in the cis position, and that makes it possible for CTCP to adopt a conformation in which C 3 4 1 eclipses C 4 . These results are supported by our investigation of hexachloropropene where we have found only one conformer in which one C 3 4 1 bond is anti with respect to C=C2I
1
0.078 0.045 0.049
[OI
62b
DIFF.
rJLn [ 1.0951 1.341 (10) 1.497 (13) 1.745 (3) 0.041 (11) 124.6 (1 3) 121.5 (17) 123.2 (12) 114.4 (18) 112.7 (17) 109.4 (22) [io91
-
1
"Distances (rs) and vibrational amplitudes (I) are in angstroms, angles (L,) are in degrees. Parenthesized values are 2u and include estimates of uncertainty in voltage/nozzle heights and of correlation in the experimental data. Quantities in square brackets were kept constant in the final refinement. *&, and c$* are the H 7 - C 3 - C 2 = C l torsion angles for the syn and anti conformers, respectively.
The probable reason for finding the anti form in TCDFP, TTCP, and PCP but not in TCP is that the steric repulsion between X8/X9 and C16 in TCDFP, TTCP, and PCP will increase the energy of the syn form enough to make it less favorable with respect to the anti conformer. TCP has a hydrogen atom (H6) on C2 and therefore experiences a much smaller repulsion. However, the energy difference between conformers is still large enough, especially for TTCP and PCP, to only give a very small amount of this second form. Conformationally it is therefore CTCP which shows a large difference from the other molecules, and where we can say with certainty that two different conformers must be present in the gas phase. The fact that the gauche conformer is the predominating form must cause its different behavior toward lithium diisopropylamidementioned above.12 A trans-&elimination cannot take place in this preferred conformation; consequently the molecule has a better chance than 'ITCP and PCP to a-eliminate hydrogen chloride and form a carbene. 8-elimination to an allene is not the preferred reaction mode for
8362 The Journal of Physical Chemistry. Vol. 96, No. 21, 1992
TABLE V Final Parameter Values for
Comparing TTCP and PCP, we can see that the conformational effect of a chlorine atom trans to C3 is very small, if at all present. This was also observed in the investigations of 3-chl~ropropene~ and trans- 1,3-dichloropropene.’ If we assume ASoequal to zero for TTCP, TCDFP, and PCP and ASo = R In 2 for CTCP (two equivalent gauche forms may exist), we can use the observed conformational composition to calculate the difference in energy between the conformers. For =-0.9 (u = 0.7) kJ CTCP the result is AEo = Eogaucbc mol-’. For TTCP the result is AEo = anti E’s? = 5 ( 0 = - Eosyn 4 (u = 2) 2) kJ mol-’, for TCDFP it is AEo = Eoanti kJ mol-’, and for PCP the conformational composition corresponds - Eosyn= 6 (u = 2) kJ mol-’. to AEo = Eoanti In Table VI the geometries for the five molecules studied in this work are summarized. The observed bond distances and valence angles have normal values for molecules like these. r(C3-Cl) is somewhat shorter in these molecules than in 3chlor~propene~ (1.803 ( 5 ) A), cis-1,3-dichloro ropene5 (1.805 (3) A), trans-l,3-dichl~ropropene~ (1.801 (6) ), or trans-1,2,3trichloropropene* (1.800 (9) A), but this is as expected since the molecules in our investigation all have two chlorine atoms on C3, while the other molecules only have one chlorine atom on C3. The values observed for r(C2-Cl) (1.713-1.728 A) are, as expected, close to those observed in cis-l,2-dichloropropene (1.726 (3) A), trans-l,2-dichloropropene(1.716 ( 5 ) A), and trans-1,2,3-trichloropropene (1.733 (25) A). In TCP we found that &=CC14 > L C - c - C l 5 while the opposite is observed for PCP. The differences may not be significant, but the trend is as expected since TCP has a hydrogen atom on C2 while PCP has a much larger chlorine atom in this position.
1,1,2-T~chloro-3.3-difluoro~rowne’ parametef r(C-H) r(C=C) r(C-C) r(C-F) r(C-CI) LCl=C2-C3 LC2=C 1-C14 Lc2=c l-CI5 LC3-C2-C16 LC2-C3-F LF-C3-F LC2-C3-H7
41b CZb % syn
I
rg/4
1.087 (45) 1.361 (i4j 1.499 (11) 1.354 (7) 1.713 (2) 124.4 (7) 122.2 (6) 123.7 (4) 113.8 (6) 111.4 (7) 107.4 (7) [109.5] [OI [1801 82 (8)
0.078 0.047 0.048 0.050 0.049 (3)
-
w
Selected Dependent Parameters LCl=C2-C16 121.8 (5) r(C 1* * *C3) 2.522 (14) 0.073 r(C2.s.F) 2.350 (8) 0.064 r(F. .F) 2.185 (9) 0.063 r(C3. ~216) 2.686 (12) 0.066 r(C1.s C16) 2.685 (7) 0.059 r(C2. G 4 ) 2.691 (7) 0.058 r(C2. * .CIS) 2.709 (12) 0.058 r(C14. **CIS) 2.870 (9) 0.053 (1 1) r(C15. C16) 3.205 (12) 0.080 (17) 4.292 (16) 0.057 ( 5 ) r(C14. 4216) r(C3. * 434) 3.120 (22) 0.112 r(C3...C15) 4.115 (11) 0.053 (14) r(C 1* * *F) 3.429 (12) 0.085 (23) r(C14.q eH7) 2.588 (30) 0.199 r(Cl4. .F) syn 4.049 (8) 0.201 (38) r(C15.s .F) 4.894 (1 1) 0.107 (13) r(C16. .F) 3.034 (14) 0.084 (27) r(CI...F) 2.999 (26) 0.128 r(C14. sH7) 4.167 (53) 0.129 r(C14...F) anti 3.121 (40) 0.240 r(C15.. .F) 4.609 (24) 0.123 r(C16*-.F) 3.617 (14) 0.124
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Kaleem et al.
I
Acknowledgment. We are grateful to A. Almenningen for carrying out the electron diffraction experiments, to S.Gundersen for technical assistence, and to the Norwegian Research Council for Science and the Humanities (NAVF) as well as the Deutsche Forschungsgemeinschaft for financial support of this work.
1
RWW NO. TCP, 18611-43-3; CTCP, 34495-85-7; TTCP, 3449584-6; PCP, 1600-37-9; TCDFP, 433-59-0.
Distances (rp)and root-mean-square amplitudes of vibration (I) in angstroms, angles (La)in degrees. Parenthesized quantities are 20 and include estimates of the uncertainty in voltage/nozzle heights and of correlation in the experimental data. Quantities in square brackets were kept constant in the final refinement. b ~ and l 42 are the H7C3-C2=C1 torsional angles in the syn and anti conformers, respectively.
References and Notes (1) Trongmo, 0.;Shen, Q.;Hagen, K.; Seip, R. J. Mol. Srruct. 1981,71, 185. (2) Savik, 0. I.; Shen, Q.;Schei, S.H.; Stolevik, R.; Hagen, K. J. Mol. Struct. 1984. 116. 239. (3) Sevik,’O. I.’;Trongmo,0.;Shen, Q.;Hagen, K.; Schei, S.H.; Stolevik, R. J . Mol. Struct. 1984,118, 1. (4) Schei, S.H.; Shcn, Q ,J. Mol. Struct. 1985,128, 161. ( 5 ) Shen, Q. J. Mol. Strucr. 1981,75, 303. (6) Schei, S.H.:Shen. 0.J. Mol. Struct. 1982.81. 269. (7) Shen, Q.;Nunn, C. 1.Mol. Struct. 1989,212, 143. (8) Shen, Q.J. Mol. Strucr. 1989,212, 151. (9) Schei, S.H.; Hagen, K.J. Mol. Struct. 1984, 116, 249.
TCP anyway, because it cannot occur when the most acidic C-H bond at C3 is attacked by the base. And the observed or-elimination in TCDFP must have to do with the hard/hard relationship of lithium and fluorine, as the preferred conformation (82% syn) at least does not preclude trans-@-elimination.
TABLE VI: Parameter Values Obtained for Halogen-Substituted Prownes” TCP (C12HC-CH=CCIZ) r(C=C) 1.336 (11) r(C-C) 1.483 (14) 1.725 ( 5 ) r(C1-CI) r(C3-X) 1.779 ( 5 ) LC=C-C 125.0 (18) 111.8 (12) LC 2-c 3-x LX-C3-X 108.0 (17) LC3-C2-C16/H6 [1111 LC2-C 1-C14/H4 123.1 (13) 120.2 (17) LC2=C 1-C15 /H5 CI 0 42 180 ’% syn 100 ’% anti ’% gauche “Distances (r,) are in angstroms, angles
TTCP (C12HC-CCI4CIH) 1.340 (11) 1.489 (12) 1.728 ( 5 ) 1.774 ( 5 ) 125.7 (15) 111.8 (20) 110.3 (7) 116.6 (23) 124.4 (19) [I181 0 180 87 (13) 13 (13) (La) in
CTCP (CI,HC-CCI--CCIH) 1.333 (9) 1.492 (11) 1.715 (4) 1.777 (4) 123.4 (9) 114.2 (12) 110.4 (6) 113.4 (18) [I181 123.1 (23)
PCP (CI2HC--CCI=CC12) 1.341 (10) 1.497 (13) 1.724 ( 5 ) 1.765 (7) 124.6 (13) 112.7 (17) 109.4 (22) 114.4 (18) 121.5 (17) 123.2 (12)
0
0
133 (4) 41 (12)
180 89 (1 1) 11 (11)
59 (12)
degrees. For definition of symbols etc. see footnotes on Table V.
TCDFP (F2HC-CCI4C12) 1.361 (14) 1.499 (11) 1.713 (2) 1.354 (7) 124.4 (7) 111.4 (7) 107.4 (7) 113.8 (6) 122.2 (6) 123.7 (4) 0 180 82 (8) 18 (8)
8363
J. Phys. Chem. 1992,96, 8363-8367
(16) Andersen, B.; Seip, H. M.; Strand, T.; Stelevik, R. Acta Chem.
(10) Samdal, S.;Seip, H. M.; Torgrimsen, T. J. Mol. S t r u t . 1977, 42, 153. (11) Schei, S. H.; S i p , R. Acta Chem. Scad. 1984, A38, 345. (12) (a) Keyaniyan, S.; Gbthling, W.; de Meijere, A. Chem. Ber. 1984, 120,395 and references therein. (b) Keyaniyan, S.;Gathling, W.; de Meijere, A. Tetrahedron Lett. 1984, 25,4105. (13) Bastiansen, 0.; Hassel, 0.;Risberg, E. Acta Chem. S c a d . 1955, 9, 232. (14) Hagen, K.; Hedberg, K. J . Am. Chem. Soc. 1973, 95, 1003. (15) Gundersen, G.; Hedberg, K. J . Chem. Phys. 1969, 51, 2500.
Scad. 1969, 23, 3224.
(17) Hedberg, L. Abstracts of Papers, 5th Austin Symposium on GasPhase Molecular Structure, Austin, TX, March 1974; p 37. (18) Internutiom1 Tables of X-ray Crystallography; Vol. 111, to be pub lished. (19) Hedberg, K.; Iwasaki, M. Acta Crystallogr. 1964, 17, 529. (20) Klaeboe, P.; Neerland, G.; Schei, S. H. Spectrochim. Acta 1982, 338A, 1025. (21) Kaleem, H.; Stelevik, R.; Hagen, K., to be published.
WalCJet Electrode Linear Sweep Voltammetry Richard C. Compton,* Adrian C. Fisher, Mark H. Latham, Physical Chemistry Laboratory, South Parks Road, Oxford OX1 3QZ, United Kingdom
Christopher M. A. Brett, and Ana Maria C,F. Oliveira Brett Departamento de Quimica, Universidade de Coimbra. 3049 Coimbra, Portugal (Received: July 31, 1991)
Theory is presented which predicts the linear sweep voltammetry behavior at the wall-jet electrode for a reversible couple. The scan rate and electrode geometry dependences are established, and hence the requirements for the measurement of true “steady state”hydrodynamic voltammograms are defmed. Theory is found to be in good agreement with experiments conducted on the oxidation of the ferrocyanide anion in aqueous solution.
Introduction The wall-jet electrode (WJE) is a well-characterized hydrodynamic electrode in which the flow is due to a (submerged) fluid jet which strikes a planar electrode at right angles and spreads out radially over that surface, the fluid outside the jet being at rest.’ The mass transport experienced by the electrode is dependent on its size relative to the impinging jet, and two extremes are recognized. The term “wall jet” is understood to pertain to the case where the electrode is substantially larger than the jet,I” whereas the other limit, in which the relatively tiny electrode is within a stagnant flow region, is defined as of “wall-tube” geometry.’ The description “impinging jet” finds occasional usage and may relate to either the wall jet or wall tube.8-’0 In this paper we are copwmed with the wall jet as described above and the mass transport characteristics of this system are outlined below.’” WJES are finding increasing use in analysis, e.g. ref 11, primarily due to the advantages of on-line detection and fast sample throughput. Moreover, in the context of the mechanistic investigation of electrode processes, the wall-jet geometry has been shown to psscss considerable advantages most notably due to its highly nonuniform primary current distribution.12 Further merits arise first from the flow-through nature of the device which means that the constant supply of fresh solution prevents the buildup of intermediates and products of the electrode reaction which might otherwise alter the course of the electrode process (chemostatic conditions) and second from the high sensitivity of the wall jet (as compared to, say, the rotating disc electrode) to variations in the rate of mass transport. The use of wall-jet electrodes in flow analysis has been recently reviewed.” In this paper we establish theory which predicts the current/voltage response resulting from a potential sweep, at the wall-jet electrode. The problem is of interest since it effectively defmes the “response time” of the electrode and, additionally, such simulations can define the range of scan rates for which an effective steady-state current/voltage curve can be recorded. Experiments are reported which quantitatively confii the theoretical predictions.
a potential at which no current flows to one that corresponds to the transport limited reduction/oxidation of species A. The convective diffusion equation describing the concentration of A in time (t) and space is
-~1-
- D -a- 2 [ ~ 1 0
AI ’ 7
-V
A AI Z
F
(1)
at az2 where D is the diffusion coefficient of A, v, is the radial solution velocity (r direction), and vz is the velocity in the direction normal to the electrode surface ( z direction). Expressions for u, and u, for wall-jet flow are given in ref 12. Note that in writing eq 1 radial diffusion has been neglected: the basis of this approximation has been developed e1~ewhere.l~We also assume the presence of sufficient supporting electrolyte that migration effects are negligible. The elcctrode potential E, is swept linearly with time at a rate u V s-l (where u is either positive or negative) through the reduction/oxidation wave of A, starting from an initial potential E1 * E, = E1 - vt The relevant boundary conditions to the problem, as defmed above, may be formulated as 7 = 0,Z L 0,O < r < R [A] [A]bulk [B] = O (2) (3)
r>O,z=O,O
