NOTES
iE predicted t o be 5% or less. On the assumption of 5% d character and for the observed values of eQq,, (-73.94 c/sec) and eQqstomic (-109.74 Mc/sec), eq 3 shows that the s character of the chlorine bond orbital is nearly 25%.
Aclmowledgment. The author expresses his gratitude and thanks to Professor Krishnaji for his kind supervision of the work.
Experimental Determination of the Electron Affinity of Several Aromatic
Aldehydes and Ketones
1929
of AB, k~ is a pseudo-first-order rate constant representing the loss of electrons due to processes other than attachment to AB, k~ is a pseudo-first-order rate constant representing the loss of AB- due to ail processes other than detachment or dissociation, kl is the rate constant for the attachment of electrons to AB, k-1 is the rate constant for the detachment of electrons from AB-, and K is the electron-capture coefficient. For some compounds, there is one region, designated p, at lower temperatures where k~ >> k-1, so that K = kl/kD
(2)
and K is relatively insensitive to temperature. I n another region, designated a, k-1 >> k~ and, assuming the statistical thermodynamic expression for an ideal gas
by W. E. Wentworth and Edward Chen' Department of Chemistry, University of Houston, Houston, Texas 77004 (Received December 19, 1966)
Recently, Wentworth, Chen, and Lovelock2 have proposed a kinetic model for the processes occurring within the electron-capture detector operated in the pulse-sampling mode and have demonstrated its validity for several aromatic hydrocarbons. Earlier Wentworth and Beckera calculated the electron affinities of some aromatic hydrocarbons using the electroncapture detector data and correlated these electron affinities with their half-wave reduction potentialsSand the energy of their 0-0 tran~ition.~The experimental electron affinities were also compared with several theoretical calculations of the electron affinitie~.~ However, thus far only aromatic hydrocarbons have been studied, although the technique for the calculation of the electron affinities originally given in ref 3 and later modified by the kinetic model2 is applicable to any molecule which forms a stable negative ion. Therefore, the electron-capture detector response to a series of aromatic aldehydes and ketones has been studied as a function of temperature in order to test the validity of the interpretation for a different type of molecule which apparently forms a stable negative ion with respect to electron attachment. For the kinetic model, the following expression can be derived for the response2
where b is the electron concentration before the addition of the test molecule, AB, [e-] is the electron concentration in the presence of AB, a is the initial concentration
A/T'/' exp(EA/kT)kL/kD
(3)
A is a constant which can be calculated from fundamental parameters, EA is the electron affinity, and IC is the Boltzmann constant. In the a region, the electron affinity can be obtained from the slope of a In KT"' vs. 1/T graph.
Experimental Section The procedure and equipment used in this study have been described earlier. The naphthaldehyde-1, benzaldehyde, and acetophenone were Eastman White Label. The phenanthrenealdehyde-9 and naphthaldehyde-2 were obtained from the Aldrich Chemical Co. The solvent used was Eastman's Spectroquality benzene.
Results and Discussion The capture coefficients for the compounds studied are plotted in Figure 1 as In KT"' vs. 1/T. All of the compounds except cinnamaldehyde exhibit an a region. Acetophenone and benzaldehyde do not have a /3 region. From the data in the a region, the electron affinities have been calculated from the slopes using an average intercept2v5and a variable intercept. The average value for the intercept from the aromatic hydrocarbons and the compounds used in this study was used and is equal to 14.8. The average intercept (1) This work was used for partial fulfillment of the requirements for the Ph.D. degree at the University of Houston, Houston, Texas. (2) W. E.Wentworth, E. Chen, and J. E. Lovelock, J . Phys. Chem., 70,445 (1966). (3) W. E.Wentworth and R. S. Beoker, J . A m . Chem. SOC.,84,4263 (1962). (4) R. S. Becker and W. E. Wentworth, ibid., 85, 2210 (1963). (5) W. E. Wentworth, W. Hirsch, and E. Chen, J. Phys. Chem., 71, 218 (1967).
Volume 71, Number 6
M a y 1967
NOTES
1930
Table I : Electron Affinities and Half-Wave Reduction Potentials Compound
Acetophenone Benzaldehyde Naphthaldehyde-2 Naphthaldehyde-1 Phenanthrenealdehyde-9 Cinnamaldehyde Anthracenealdehyde-9
Electron affinity, ev (variable intercept)
Intercept
0.334 f 0.004 0.421 f 0.010 0.620 f 0.040 0.745 f 0.070 0.655f0.142
14.70 f 0.15 15.89 f 0 . 3 0 14.46f0.99 1 2 . 6 1 f 1.60 14.92 f 3.34
Electron affinity, ev (common intercept)
...
...
(ref 7)
...
0.334f0.004 0.448f0.006 0.615f0.014 0.669 320.022 0.712f0.009 0.823f0.043 (1.02)
...
...
Eli2
1.592 1.505 1.476 1.447 1.335 1.207
Table I1 hi, l./mole sec
Compound
Naphthaldehyde-2 Naphthaldehyde-1 Phenanthrenealdehyde-9 Cinnamaldehyde
6.7 5.7 3.7 3.4
k-1,
f 3.2 X 10'9
2.7 f 1.2 X 2.2 rt 1 . 3 X 4.9 f 3.0 X 5.2 f 3.2 X
f 3.4 x 10'8 f 2.3 X 1018 f 2.2 x lo'*
seo-1
107Ta/zexp(-0.615f 0.014/kT) 107T*/2exp(-0.669f 0.022/kT) 10V"/zexp(-0.712 f 0.009/kT) 107T'~zexp(-0.823f 0.043/kT)
perature dependency in both the a and p regions was carried out. This is obtained by substituting eq 3 into eq 1 giving
I
I
1.0
2.0
I
3.0
flo5m-') Figure 1. Ln KT8/l us. 1/T; 1, acetophenone; 2, benzaldehyde ; 3, naphthaldehyde-2; 4, naphthaldehyde-1 ; 5, phenanthrenealdehyde-9; 6, cinnamaldehyde.
was used in two ways. For acetophenone and benzaldehyde, only the slope and hence the electron affinity using eq 3 was determined. For the other compounds, a least-squares fit to an equation expressing the temThe Journal of Physical Chemistry
Three parameters, the electron affinity and the ratios of kl/kL and kL/kD, were determined using a nonlinear least-squares adjustment.6 The average intercept was derived from the aromatic hydrocarbons2J and the compounds in this study. The results of the leastsquares data reduction procedure are given in Table I. The electron affinities are plotted against the half-wave reduction potentials8 in Figure 2. There is a rather good linear correlation between the two, but the slope is greater than unity (approximately 1.5). This is in contrast to the slope for the similar correlation for the aromatic hydrocarbons, which is less than unity.2 Recently the correlation for the aromatic hydrocarbons has been reexamined with additional electron affinity data and the following equations have been obtained.
EA
=
0.681
f 0.09Ei/,
+ 1.95 A 0.20, @(la =
-0.019
(5)
(6) W. E. Wentworth, J . Chem. Educ., 42, 96, 162 (1965). (7) R. S. Becker and E. Chen, J . Chem. Phys., 45, 2403 (1966). (8) R. W. Schmidt and E. Heilbronner, Helv. Chim. Acta, 37, 1453 (1954).
NOTES
1931
.80
-
+70
-
.60
-
.50
-
tt0
-
Wtv)
1 - 30 1 '1.20
In conclusion, the results of the temperature study of the capture coefficients of the aromatic aldehydes and ketones are in agreement with the kinetic model proposed earlier.2 The linear correlation of the electron affinities calculated using this model with the half-wave reduction potentials supports the interpretation of the electron-capture response in terms of the electron affinities for compounds which form stable negative ions. The absolute values of electron affinities for five aromatic aldehydes and acetophenone are given. Acknowledgments. This work was financially supported by the Robert A. Welch Foundation. Edward Chen was also a NASA predoctoral fellow.
130
1.40
1.60
1.50
E (ev)
h
Carbon Monoxide Solubilities in Sea Water
Figure 2. Electron affinity us. half-wave reduction potential for the aromatic aldehydes. The compounds are, reading from left to right: cinnamaldehyde, phenantbenealdehyde-9, naphthaldehydel, naphthaldehyde-2, and benzaldehyde. The values obtained from the average intercept are indicated by rectangles, the height at the rectangle - being- a measure of the standard error. The circles are the data obtained by using a variable intercept with the horizontal lines indicating the standard error limits.
for the polarographic data in dioxane and
EA
=
0.705
f O.lOEi/,
+ 1.67
f
0.17, (Tab
=
-0.018
(6)
in 2-methoxyethanol. (Tab is the covariance term associated with the two parameters shown in the linear equations, eq 5 and 6. In ref 3 it was pointed out that the formation of a solvated charge-transfer complex could not be used to explain a slope which was less than unity. However, of the aromatic aldehydes, the slope is in the greater than unity and would be in agreement with the postulate of complex formation. The affinity Of anthracenea1dehyde-9 can be in Figure and is given in estimated from the Table I in parentheses. From the least-squares estimate of kl/kL and a value for kL, the rate constant, kl, can be determined. The value for k L can be determined from the average intercept and a value for kD. The value of kD is 2.4 X lo3 sec-' SO that the value of kL is 2.4 X lo4 sec-l. With these values and assuming a preexponential temperature dependency for k-1 of Tal/',IC-1 can be determined. The results of this analysis for the compounds exhibiting both an a and fi region are given in Table 11.
by Everett Douglas scripps Institution of Oceanography, La Jolla, California191 (Received October 1.4, 1966)
Carbon monoxide was first reported in the brown alga Nereocystis in 191L3 Since then it has been observed in other algael4v6some other plants,6 and a few of the siphonophores such as the surface-floating Physalia,?P8 a bathypelagic N a n ~ m i a ,and ~ ~ a~ ~benthic form.11 The concentration of this gas in the siphonophore floats has been found to be as high as 93%" of the total gas while in the algae upward to 12% has been r e p ~ r t e d . ~ With this rising interest in the occurrence and utilization of CO, generally considered toxic in biological systems, it has become desirable to measure some of the (1) Contribution from the Scripps Institution of Oceanography, University of California, Ban Diego, Calif. (2) This investigation was supported by Public Health Service Research Grant NO.GM-10521 from the National Institutes of Health and was performed under contract for the United States Navy Electronics Laboratory, San Diego, Calif. (3) S. E.Langdon, J . Am, Chm. Sot,, 39, 149 (1917). (4) M. W. Loewus and C. C. Delwicke, Plant Physiol., 38, No. 4 , 371 (1963). (5) D. J. Chapman and R. 0. Tocher, Can. J. Botany, 44, 1438 (1966). (6) S. M. Siegel, G. Renwick, and L. A. Rosen, Science, 137, 683 (1962). (7) J. B. Wittenberg, BWl. Bull., 115, 371 (1958). (8) J. B. Wittenberg, J . Ezptl. Biol., 37, 698 (1960). (9) G. V. Pickwell, E. G. Barhan, and J. W. Wilton, Science, 144, 860 (1964). (10) G. V. Pickwell, U. S. Navy Electronics Laboratory, Report N ~ 1369, . 1966, (11) E. Douglas, unpublished data. .
I
Volume 71, Number 6 May 1967
