NOTES
1226
Table 11: Comparison of the Charge Distribution and the Dipole Moment Obtained by the w'-Technique with Those Obtained by Other Methods Method
9%
PA = 48
4s = 41
-0.058
+O. 023
$0,032
-0.043
+0.020
f 0.048
, . I
, . .
...
...
... + O . 130
...
Ql =
Experimental (n.m.r.) Experimental HMO io-Technique; w = 1 . 4 w'-Technique; w = 1 . 4 ; w ' = 0.93 VESCF Pariser-Parr Nonempirical SCF
4s
-0.139 -0.118 -0.115
-0.047 -0.048 +0.008
+ O . 145
+0.095 +o. 119
$0.014 +0.025 -0.048
-0.061 -0.096 -0.049
-0.021 -0,021 0,003
+0.063 +O. 021 +O. 092
-0.009 +O. 049 -0.034
+
a R. D. Brown and M. L. Heffernan, Australian J . Chem., 13, 38 (1960). J . chim. phys., 52, 377 (1955).
qS =
96
+0.084 CO.120
+O. 039 -0,052 $0,062
410
pI
Ref.
D.
-0.027 -0.020 -0.021
0.11 1.08 5.2 4.9 3.3
7 5 3 3
-0.009 -0.013 -0.042
2.3 1.9 1.7
a b
* R. Pariser, J . Chem. Phys., 25, 1112 (1956).
C c
A. Julg,
Table 111: Charge Distribution and Dipole Moments of Fulvene and Heptafulvene Fulvene Method
41 = 94
HMO
qz =
-0.092 -0.055 -0.080
w w'
4s
qs
PI
-0.073 -0,029 -0.019
D.'
Ref.
2.6 2.0 0.9
b
L,
+0.378
-0.047 -0.138 $0.018
+O. 306 $0.181
C
..
Heptafulvene
-
Method
ql = 46
Pa = qs
HMO
+ O . 058
+ O . 038
+ O . 047
w
+O. 032
+0.008 -0.006
+0.021 + O . 027
w
'
f O . 060
pa
q4
Q7
98
c, D.
Ref.
+0.24 +0.094 -0.021
-0.3M -0.216 -0.142
2.6 1.6 0.9
d C
..
a Experimental value is 1.2 D (ref. 5). A. Pullman, B. Pullman, and R. Rumpf, Bull. SOC. chim. France, 15, 757 (1948). A. E. D. Bergmann, E. Fischer, D. Ginsburg, Y. Hirshberg, D. Lavie, M. Manot, Streitwieser, Jr., and P. M. Nair, unpublished results. A. Pullman, and B. Pullman, Bull. SOC. chim. France, 18, 684 (1951).
Table IV : Ionization Potentials
Radical
Methyl Allyl Pentndienvl Benzyl Cycloheptatrienyl Diphenylmethyl a-Saphthylmethyl 6-Naphthy lmethy 1
Crtlcd. by eq. 4, e.v.
10.13 8.50 7.95 7 76 6 82 7 16 7 44 7 55
Obsd., e.v.
9.95" 8.16" 7.736 7 76b 6 60c 7 32d 7 7 56d
deviation of the fit, 0.17 e.v., is not quite as good as in the simple w-technique,* but still represents a rather good performance. We conclude that th/e wf-technique shows significant promise and further tests and applications with this method should be encouraged. (8) A. Streitwieser, Jr., J . Am. Chem. Soc., 82, 4123 (1960).
The C-H Bond Dissociation Energy of Neopentane and Other Hydrocarbons by J. W. Root and F. S. Rowland'
F. P. Lossing, K. 1'. Ingold, and I. H. S. Henderson, J . Chem. Phys., 22, 621 (1954). S. B. Farmer, I. H. S. Henderson, C. A. McDowell. and F. P. Lossina, - ibid., 22, 1948 (1954). c A. G. Harrison, L. R. Honnen, H. J. Dauben, Jr., and F. P. Lossing, J . Am. Chem. SOC.,82, 5593 (1960). a A. G. Harrison and F. P. L-ossing, abid., 82, 1052 (1960). a
The Journal of Physical Chemistry
~ ~ ~ ~ ~ e n " - " n C h e m ~ ~ k ~ ~ ~ Bond dissociation energies of various chemical bonds have been obtained through numerous experimental
NOTES
1227
methods, arid accurate values have been compiled for many m ~ l e c i i l c s . ~ Our ~ ~ experiments with recoil tritium atoms have shown that the hot abstraction of H by reaction 1 is a t least semiquantitatively dependent upoii the bond dissociation energies of the C-H bonds 1 1 1 ~ o l ~ e d . ~ ~ ~ ‘l’*
+ 1tH -+
HT
+R
(1)
The original correlatioii of hot H T yield with bond energy showed a substantial discrepancy5 from the bond dissociation energy for reaction 2 as 95.5 + 2.5 kcal. /mole, measured through a photobromiriation procedure. z6s7 neo-C5H12-+€I
+ CaHIl
(2)
A second measurcmciit, also through the measurement of activation energies of bromination reactions, leads to the value 99.3 k ~ a l . / m o l e . ~ *If~ the latter value is used, no appreciable discrepancy remains and the correlation betwreii hot HT yields and bond dissociation energies is satisfactory within the errors of measurement. This correlatioii is showri in Fig. 1.
2.00
r
the energetics of the reverse of reaction 3 . Further investigatioii of reactioii 1 as a possible measure of bond dissociation energies is being carried out. If the present correlation is borne out t)y succeeding experimeii ts, this approach would have thc merits of ready applicatioii to a wide variety of molecular types. Interpolation of the measured HT yields for cyclopropane and cyclobutaiie leads to estimates of 101 and OB kcal./mole for their respective C I€ bond dissociation energies. (1) This research lies been supported by U. S. .4tornic Energy C‘ommission Contract No.-AT-(11-1)-407 and by a National Science Foundation I’redoctoral Fellowship (J. W. It.). (2) See, for example, T. Cottrell, “The Strengths of Chemical I3orids.” 2nd Ed., Butterworth Publications, London, 1958. (3) It. It. Bernecker and P. A. Long, J . Phys. Chem., 6 5 , 1565 (1861). (4) J. W. Root and F. S. Ilowland, J . A m . Chem. Soc.. 8 5 , 1021 (1063). (5) W. Breckenridge, J. W. Root, and F. S. Ilowland, .I. Chem. Phys., 39, 2374 (1963). (6) E:. I. Hormats and E. It. Vnri Artsdalen, ibid., 19, 778 (1951). (7) B. €1. Eckstein, H. A. Scherrtga. arid E. 11. Van r\rtsdalen, ihid.. 22, 28 (1954). (8) G . C . Fettis, J. 13. Knox, a n d A. F. Trotman-Dickenson, J . Chem. SOC.,4177 (1960). (9) G. C. Fettis and A. P. Trotnian-Dickerison, ibid., 3037 (1961).
n J
w
polarizability of the Closed-Cage
I-
Boron Hydride BloFllo-2
I
by Alexander Karzmarczyk and Gerald 13. Kolskil Department of Chemistry, Dartmouth College, Hanover, New Hampshire ( R e c e i w d .Voi:ember 16, 1.903)
I IO
4.0 BOND
4.5 DISSOCIATION 298’K
KCALIMOLE
5.0 E.V. ENERGY
Figure 1. Correlation of h o t HT yields with bond dissociation energies. HT yields from ref. 5. Bond dissociatJionenergies: 5,ref. 3; 0,ref. 9; B, ref. 6.
The measurement by Trotman-Dickenson, et al., depends upon the evaluation of the activation energies of both the forward and reverse reactions of (3). The reverse reaction has, however, been estimated and not measured. If the correlation of Fig. 1 is assumed to display a valid relationship between hot H T yield and bond dissociation energy, the recoil tritium experiments confirm the accuracy of this estimate of
The very large diamagnetism2 of 1310H,o-2and t,he pseudo-aromatic chemical behavior of this ion3 seem to indicate that the electrons on the cage are extensively delocalized. Preliminary calculations4 suggest that the diamagnetic susceptibility would be compatible with a model in which the ten bororis form a conducting sphere on which t,he 22 cage electrons are relatively free to move under the irifuericc?of an electric or magnetic field. The validity of such a model should also be reflected in other properties such as polarizability. (1) National Seierice Found:ition Cndergrdriate Itesearch Assistant, summer, 1963. (2) It. 11. Dobrott and W . N. Lipscomb, J . Chem., I’hys., 37, 1784 (1962) ; G. Eaton. A. Kacsinarczyk, a n d u‘.N.I,ir)scornb, unpublished results (3) W . H. Knoth. 1%.C. Miller, 11. C. I.;rigland, G . W. I’srshall, and E. b. Muetterties, J . A m . Chem. Soc., 84, 1066 f,l86!2). (4) R. Hoffman, private communication.
