Aug., 1942
ELECTRON DIFFRACTION OF ~ R O P A R G YHALIDES L
[CONTRIBUTION FROM
THE
1753
GATESAND CRELLIN LABORATORIES OF CHEMISTRY, CALIFORNIA INSTITUTE OF TECHNOLOGY, No. 8781
The Electron Diffraction Investigation of Propargyl Chloride, Bromide, and Iodide BY LINUSPAULING, WALTERGORDY,~ AND
The surprising discovery that the carbon-carbon single-bond distance in methyla~etylene~ and some related substancesb is less than the normal value suggested that the study of the propargyl halides would be of interest. We have carried out this study, and have found that the carboncarbon triple-bond and single-bond distances are the same in these molecules as in methylacetylene, and that the carbon-halogen bond distances are somewhat larger than normal. Experimental Methods The propargyl halides were prepared in these Laboratories by Mr. Allan Grossberg from achloroallyl alcohol (H2C=CC1CH20H) kindly furnished by the Shell Development Company. This substance was converted into propargyl alcohol by the method described by Henry.3 Propargyl chloride and propargyl bromide were then prepared by treating the alcohol with phosphorus trichloride and phosphorus tribromide, respectively.* Propargyl iodide was prepared from propargyl bromide and sodium iodide.6 The electron diffraction photographs were made in the usual way, with film distance 10.85 cm. and electron wave length 0.0613 A. For each substance the ring diameters were measured separately by two observers on about ten photographs and the resultant values of &bs = 40 (sin 0/2)/A were averaged. Estimates were made of the intensities of the apparent maxima and minima, and in addition cumes were sketched reproducing the appearance of the photographs. Radial distribution curves were calculated by the equation Ck sin P
lD(1) = k
10 (Ik1
with use of coefficients c k obtained from the estimated intensities by multiplication by the damping factor e-aq'. (1) National Research Fellow in Physics. (2) (a) G. Herzberg. F. Patat, and H. Verleger, J . Phys. Chem., 41, 123 (1937);(b) R.M.Badger and S . H. Bauer, J . Chem. Phys., 6,599 (1937); (c) L. Pauling, H. D. Springall, and K. J. Palmer, THIS JOURNAL, 61, 927 (1939). (3) L. Henry, Bcr., 6, 453,569 (1872); 6,729 (1873). (4) L. Henry, ibid., 7, 761 (1874); 8, 398 (1875); A. Kirsmann, Bull. EOC. chim. [iv], 8% 698 (1926). (6)LL.penry. Bcr., 17, 1132 (1884)
JOHN
H. SAYLOR
The simplified theoretical intensity curves were calculated by the equation
The scattering powers J. were taken proportional to the atomic numbers of the atoms. The values C3-H = 1.06 A. and C1-H = 1.09 k. were assumed, and as the bond angle C2-Cl-X was varied the other five angles of Clwere kept equal in value. The atoms HC3C2C1were assumed to be collinear, as indicated by the bonds in the model H-CEC-C-H /H 3 2 l\X
All calculations were made with use of punched cards and International Business Machines. Interpretation of the Data Propargyl Chloride.-The photographs of propargyl chloride, showing about thirteen maxima and thirteen minima, have the appearance indicated by curve Chloride Obs. in Fig. 2. The radial distribution curve calculated from the data of Table I is given in Fig. 1. The peaks of this curve are a t 1.18, 1.48, 1.81, 2.72, and 3.72 A. The jame values, to within 0.01 A., were found for the three principal peaks for other curves calculated with somewhat changed values of the coefficients C. These distances correspond, respectively, to C,-C2. C2-CI, C,-Cl, G-CI (plus C,-C,), and C3-CI. We make the following assumptions: 1. The distance C3-CZ has the tiple-bond value 1.20 A. 2. The carbon chain is linear. 3. The three carbon-chlorine distances have approximately (to within about 0.02 A.) the values 1.81, 2.72. and 3.72 A. given by the three principal peaks of the radial distribution curve. These assumptions determine the structure completely, except for the uncertainty resulting from the possible small deviations from the radial distribution values. The bond angle a = C2CI-Cl is indicated to be near 112". If the distance C2-Cl weie equal to 1.47 or 1.48 A., as indicated by the radial distribution curve and by the values for methylacetylene and related molecules, and the three carbon-chlorine distances were to
LINUSPAULING, WALTERGOKDYAND JOHN H. SAYLOK
1754
Vol. 64
TABLE I In Fig. 2 calculated intensity curves are given ELECTRON DIFFRACTION DATAFOR PROPARGYL CHLORIDE for models with CY = 109" 30', 111", and 112" 30' Max
Min
I
C
gobs
&?B
aB/Poba
and with the above assumptions satisfied (Table IV). These curves, A, B, and C, agree well with + the appearance of the photographs; the agreement is best for the curve with CY = 11l0,in particular with respect to the relative intensities of maxima 7 and 8, and we accept the value of this angle as OL = 111° * 2". Curves for various other models for which interatomic distances differ from those for this model by ad much as 0.03 A.,such as those for models D and E (Fig. 2, Table IV). were found to be less satisfactory, and those for models with larger deviations were unsatisfactory . The quantitative comparison of values of gob and gcalcd for model B given in Table I leads to the average ratio qB/qobs = 1.006. Giving equal + weight to this and the radial distribution values, -+ we accept as the final values for propargyl chlo+ ride the following: C3-CZ = 1.20 8.(not varied), C? -C1 = 1.48 * 0.02 CI--Cl = 1.82 * 0.02 A.,angle C2-C1-C1 = 111 * 2 0 , C2-CI = 2.72 * 0.03 A, C~--CI = 3.73 * 0.03 A. Propargyl Bromide.-The data for propargyl show the minimum deviations from the abol-e bromide given in Table I1 lead to a radial disvalues, the bond angle would be 111'. tributiori curve (Fig. 1) with the two carbon-carbon peaks unresolved and with well-defined carbon-bromine peaks a t 1.95, 2.84, and 3.85 A. The three intensity curves F, G, and H of Fig. 2 are calculated for the assumed values C3---C2 = 1.20 and CI-Br = 1.95 A.,the angle CY and C.-Cl distance being varied in such a way as to give the longer carbon-bromine distances approximately the radial distribution values. It is seen that all BROMIDE three curves are in good agreement with the appearance of the photographs as represented by the curve shown in Fig. 2 ; the Cl-C2 distance and bond angle accordingly cannot be determined directly. We assume that the CI-C~ distance has the value 1.47 8.,the average of those found in methylacetylene (1.46 8.) and the chloride (1.48 * 0.02 A.) ; the correI I I 1 sponding curve, G, is a little better 1 2 3 4 A. than the other two, of which F makes Interatomic distance. the 8th maximum too weak and H Fig. 1.-Radial distribution curves for the propargyl halides. T h e makes the 5th too weak. vertical lines correspond to the finally accepted structures. 8 . 9 (1 14) 11.4 (1.07) 1 1.007 13.9 2 2 +63 16.97 1 7 . 1 1.007 -+-7 -51 20.25 20.2 0.997 -6 3 1 006 23.% 23.7 +*57 3 f'i 28.53 29.9 4a 0 0 33.6 (1.036) 4 +20 32.42 +3 1 000 35.61 35.6 0 0 0 0.995 38.5 0 +34 38.69 +6 0,991 42.38 42.0 -7 -35 6 1. 003 45.6 6 +32 45.43 +7 -, 1.022 -2 - 8 50.19 51.3 1.021 i 54.03 55.2 +16 +5 1.003 67.33 57.5 0 0 8 0.997 60.09 59.Y 8 +la +5 " 1.000 63.93 63.9 --( -13 9 1 017 68.50 69.7 9 412 +7 1 015 75.18 76.3 5 10 +4.5 1 011 11 $0 1 81.48 82.4 12 -+(i H 88.17 91.3 (1.023) l.OO(i Average Average deviatioii 0 008 a A small apparent maximum could be seen between maxima 3 and 4. 1
-2 1-0.5 -2.5
-20 5 -23
7.83 10.66 13.81
-
a,
ELECTRON DIFFRACTION OF PROPARGYL HALIDES
Aug., 1942
TABLR I1 ELECTRON DIFFRACTION DATAFOR Max.
Min.
1 2 2
C
I
+ 1.3 -3 +8
10.35 11.0 -26 13.23 13.8 +60 16.55 16.4 -68 19.45 19.1 $75 22.45 22.8 -48 27.20 28.0 +30 30.85 32.3 7 33.75 35.2 +15 37.04 37.0 -20 40.54 39.9 +25 43.19 43.3 -12 48.22 47.5 7 51.82 53.1 2 54.1 55.7 57.7 4 57.1 64.1 4 63.6 73.4 2 70.6 Average Average deviation
-
4
+ +
4 5 5
-
+ -
6 6 7 7
8
+ + + +
+ + +
8 9 10
qG
+10
-10 $12 8 6 1.5 4 6.5 +10 6.5 5 2 4 7 7
3
3
PROPARCYL
gabs
1755
BROMIDE PG/'?obs
(1.06) (1.04) 0.991 0.982 1.015 (1.029) (1.046) (1.043) 0,999 0.984 1.003 0.985 1.024 1.029 1.011 1.008 (1 .039) 1.003 0.003
Various other models were found to be unsatisfactory; for example, models I and J (Fig. 2), with C1--Br given the value 1.91 equal to the sum of the single bond radii and the C-C-C1 angle chosen so as to make the long C-Br distances close to the radial distribution values, fail to give the observed relative intensities of maxima 6, 7 , and 8. The quantitative comparison of gobs and qcslcd for model G leads to the average ratio @/qobs = 1.003 (omitting values which seem less reliable than the others). We accept the following parameter values: c3-C~ = 1.20 A., C2-C1 = 1.47 * TABLE I11 ELECTRON DIFFRACTION DATAFOR PROPARCYL Max.
Min.
1 2 2
3 3 4 4
5
5
6 6"
7 7 8 9
a A shelf this ring.
c
I
+3 -4 +2
4oba
Qcalod
IODIDE
Poslcd/Pob
10.8 (1.10) 13.6 (1.09) 15.9 1.004 6 18.2 0.983 21.5 1.000 +11 8 25.0 0.978 7 30.7 (1.037) 6 34.1 (1.035) 2 36.5 1.001 3 38.0 1.003 4- 9 41.1 1.013 9 44.5 (0.962) 9 48.3 0.984 6 56.0 1.022 6 61.4 0.984 Average 0.997 Average deviation 0.012 at q = 44.7 could be seen on the outer edge of
+ + -
+ + +
$28 -40 +16 -46 f77 -48 4-35 -26 7 -10 4-25 -18 4-14 6 3
+
+ +
9.80 12.47 15.83 18.51 21.49 25.56 29.60 32.93 36.45 37.85 40.55 46.29 49.07 54.8 62.4
0
20
60
40
80
4. Fig. 2.-Curves (marked Chloride Obs., Bromide Obs., Iodide Obs.) drawn to represent the appearance of electron diffraction photographs, and calculated intensity curves for the propargyl halides.
0.02 A,, CI-Br = 1.95 * 0.02 A., angle C2C1-Br = 112' * 2O, C2-Br = 2.85 * 0.03 A., C3--Br = 3.85 * 0.03 A. Propargyl Iodide.-The photographs of propargyl iodide were not so good as those of the bromide, which were themselves inferior to those of the chloride. The radial distribution curve of Fig. 1, corresponding to the data in Table 111, has well-defined maxima at 2.13 and 2.96 A., and poorer ones a t 1.2, 1.5, and 4.1 A.
Vol. 64
LINUSPAULING, WALTERGORDYAND JOHN H. SAYLOR
1756
TABLEIT' carbon-halogen bond distances are larger than DISTANCES AND BONDANGLES FOR PROPARCYL HALIDE those usually observed. Each of the values found, MODELS C-CI = 1.83 8., C-Br = 1.95 A., and C-I = Model X = CI
A R
C D 1;
Ci-X
C8-G
C
1.81 1.81 1.81 1.81 1.76
1.20 1.20 1.20 1.20 1.20
1 .50 1.47 1.44 1.50 1.47
~
1.9.5 1.95 1.95 1.91 1.91
1.20 1.20 1.20 1.20 1.20
1.47 1.42 1.47 1.47
Ansls I e
CPCI
Cs-C1
2.71 111" 2.71 112"30' 2.72 111" 2.69 2.71 113'40'
3.72 3.72 3.72 3.72 3.72
2.85 2.85 2.84 2.81 2.86
3.85 3.85 3.85 3.82 3,SR
109"30'
X = Rr
F G
H I
J
1.3% 110"
112" 114" 112" 115"
M N 0
>x : H-CT=C=CH2
(in addition to the usual ionic
:x:-
4-
structure H-C=C-CHt
X = I
K L
2.13 A.,exceeds the normal single-bond value (1.76, 1.91, and 2.10 A,,rezpectively) by a significant amount, the difference being largest (0.07 A.)for the chloride and smallest for the iodide. A plausible ad hoc explanation for this is that there occurs resonance between the normal structure H-C=C-CHe and an ionic structure
2.13
2.13 2.13 2.13 2.10
1.20 1.20 1.20 1.20 1.20
1.47 1.47 1.47 1.47 1.47
108" 110" 112" 114" LlO"30'
2.95 2.98 3.01 3.05 2.95
3.90 3.95 4.00 4.05 3.94
There is no possibility of evaluating the carboncarbon distances from the data. We assume the values C1-C2 = 1.47 A. and Cz-Ca = 1.20 k. With these, the two C-I distances 2.13 and 2.96 A.lead to the value 109' for the C-C-I bond angle. Curves K, L, M, and S of Fig. 2 are calculated for models with C---I = 2.13 h. and with bond angle lOS, 110, 112, and 114', respectively (Table I V ) ; of these K and ;1- are unsatisfactory, especially with respect to the intensities of maxima S and 9. The best agreement is obtained for the curve interpolated between L and RI ; because of the poor quality of the photographs, however, this cannot be given much significance. Various other models also give unsatisfactory curves, such as that for model 0 (with Cl-I = 2.111 A,, angle l10°:30') shown ir: Fig. 2 . The quantitative comparison in Table 111 is for the model with angle 111O, intermediate between L and M. It leads to the ratio qcalcdjqobs = 0.99'7. We accept for this molecule the values C3-Cz = 1.20 A,, C2-C1 = 1.47 A., '21-1 = 2.13 = 0.03 A., angle C2-CI-I = 111' * fjo, C2-I = 3.00 * 0.05 A.,(21-1 = 3.98 * 0.07 A. Discussion of the Structures There is only one surprising feature of the structures found for these molecules; this is that the
which confers ionic :X:-
character on the C-CI bond). This explanation accounts for the decrease in magnitude of the deviation in the sequence chloride, bromide, iodide, for which the electronegativity of the halogen decreases6 A much greater deviation, about 0.30 A., of nitrogen-halogen interatomic distances from the single-bond values was observed for nitrosyl chloride and nitrosyl bromide by Ketelaar and Palmer,' who offered a similar explanation, based on resonance with the ionic structure : O+=N : :X:-
We are indebted to Dr. IT.Schomaker for valuable help in this work.
Summary The electron diffraction investigation of the propargyl halides has teen carried out, leading to the interatomic distances C=C = 1.20 8. (assurxed), C-C = 1.47 * 0.02 A.,C-C1 = 1.83 * O.Oi!A.,C-Br = 1.95 * O.O%A.,andC-I = 2.13 * 0.03 h. and the angles C-C-CI = 111 * ?", C-C-Rr = 112 * 2",andC-C-I = 111 * 3". PASADENA, CALIFORNIA
RECEIVED MAS 1, 1942
(ti) I t w a s suggested by Dr. S. Winstein [Dissertation, California Institute of Technology (1930)l t h a t the large values of the mole refraction of the allyl halides could he explained us resulting from large polarizabilities of the molecirles due t o resonance of the type discusscd i n t h e text above. This would lead t o large values ol t h e molt rcfraction for the propargyl halides also. 17) J . A. A. Kcti-laar and K. .T. Palmer, THISJ O U R N A L , 59, 2G20 (1037).
