K. HIROTA,I. FUJITA, M. YAMAMOTO, AND Y. NIWA
410 Since this equals V(Q,+ Q2)
b exp(--yb) - a exp(-TU)] ~ x P ( - - Y ~-) exp(-w)
+ Fz[-1Y
-
or
square well potential. There is even some quantitative agreement as one proceeds to the right in Figure 3. However, the critical volume predicted (C’) is displaced considerably from the true value (C). The critical pressure and temperature achieved in Figure 3 are, of course, exactly correct because they were used to estimate two of the parameters of the square well model. The point marked (A) is also correct because of the arbitrary way the liquid volume at 1 atm was related to (a b ) / 2 in eq 71. The lack of quantitative agreement in the upper left portion of the figure can possibly be attributed to the abnormally high compressibilities predicted by the square well potential. The results obtained encourage further study in (1) the use of more realistic potential functions; (2) the consideration of interactions with more than one neighbor; and (3) the justification of a uniform measure on v space, or the derivation of the true measure.
+
The parametric values used for nitrogen in Figure 3 are
P, = 33.5 atm“ T, = 126.1’K“ VI = 0.3465 l./mol a t 77.34’K and 1 atm”
N E = 1082 cal/mol a t 77.34’K and 1 atmI2 Discussion The theory presented gives a respectable qualitative prediction of the critical phenomenon even with a crude
(11) “Handbook of Chemistry and Physics,” Chemical Rubber Publishing Co., Cleveland, Ohio, 1960. (12) “Selected Values of Chemical Thermodynamic Properties,” National Bureau of Standards, Circular 600, U. S. Government Printing Office, Washington, D. C., 1962.
Electron Distribution of Electron-Bombarded Alkylamines and Its Correlation with the Probability of Bond Scission in Their Mass Spectral by Kozo Hirota, Iwao Fujita, Masao Yamamoto, and Yoshio Niwa Department of Chemistry, Faculty of Science, Osaka University, T o y o n a h , Osaka, Japan (Received M a y 80, 1060)
Electron distribution of n-propylamine and ethylamine is calculated by means of the CNDO method to study the probability of bond scission in their mass spectra. Electron density of the highest occupied orbital in the skeletal bonds of both amines is found to be the largest on the a-CC bond adjacent to the CN bond. This is in sharp contrast to the equivalent orbital calculation, in which electron density is the largest on the CN bond. The order of scission probability of each bond determined from the mass spectra of propylamine (a-CC bond > CN bond > pCC bond) can be explained by the MO theory, based on the above electron density. Under the assumption that there exist fast and slow processes in fragmentation of alkylamines, change of scission probability a t low energy of the bombarding electron can be explained also. Reliability of the calculated values can be supported by the agreement of the calculated dipole moment with the observed.
Introduction As far as the mass spectra of the aliphatic and cyclic alkanes are concerned, the correlation2that the scission Drobabilitv of their skeletal bonds is Droportional to the positive charge distribution of the highest occupied (Ho) Orbital at’the corresponding bond Of the molecular ions seems now to be accepted generally.a *
The Journal of Physical Chemistry
-
However, the use of this correlation to predict the mass spectra of other compounds is not regarded credit(1) Report XX on molecular orbital theory for mass spectra. (2) (a) K. Fueki and K. Hirota, Nippon Kagaku Zasshi, 81, 212 (1960); (b) K. Hirota and Y. Niwa, J. Phya. Chem., 7 2 , 5 (1968). (3) J. C. Lorquet, ibid., 73,463 (1969); K. Hirota, Y. Niwa, and M. Yamamoto, ibid., 73,464 (1969).
ELECTRON DISTRIBUTION OF ELECTRON-BOMBARDED ALKYLAMINES able yet. For instance, Lorquet, et u L , ~heavily criticized our attempt to extend this line of research over normal alkyl amine^.^ Their criticism against our attempt is due to the calculated result of alkylamines based on the LCBO approximation; i e . , though the charge densities at the C N bond and lone pair are 16 and 71% of the total charge, respectively, we took only the charge distribution of the CC bonds into account in discussing relative scission probability. The above criticism was already expected by us when the research was started. However, because of the following reason, we dared to adopt the above assumption. I n our LCBO calculation, charge distribution of the lone pair is included implicitly in that of the CN bond, and the net charge distribution at the CN bond might occupy only a small fraction of the total and even be smaller than that at the a-CC bond adjacent to it. Nevertheless, such a presumption seems not to have been justified by Lorquet's simple calculation, even though details are not shown by them. Final decision of the applicability of the correlation, therefore, has to be postponed until the charge distribution is calculated by a more elaborate MO method than they used. This is the reason why we began to investigate the problem by adopting the complete neglect of differential overlap (CNDO) method proposed by Pople, et aL6 As the compounds to be studied, ethylamine and npropylamine are adopted in the calculation, and the correlation of the charge density of the HO orbital a t each bond with its scission probability is compared with the experiment which is carried out on n-propylamine under such a condition as to satisfy the purpose of theoretical discussion. The result obtained is found favorable for our standpoint; ie., the experimental scission probabilities of the CK bond and 8-CC bond as well as of the e-CC bond can be predicted by our calculation. Besides, if the NIO theory is extended more generally than the original theory," effect of ionizing voltage on the mass spectra can be explained.
Method of Calculation As is well known, the CNDO method is a semiempirical SCF method of calculating molecular orbitals and is known to be able with success to treat T electrons and lone-pair electrons as well as u electrons. Therefore, this method is much more elaborate than the LCBO method, which was adopted by Hirota and Itoh.5 Before entering into the details of calculation, it has to be pointed out that the electron distribution of neutral amines is Calculated, but the charge distribution of the corresponding ions is not calculated as Lorquet, et aL,4 did, owing to the reason that both absolute values would be practically the same as already discussed.2b I n the calculation, two stable conformations (Le., trans and gauche form with respect to the CC bond and lone pair along the CN bond) are adopted as the repre-
411
HH
!20
I 1
H (a)
trans-form
H
H H:20
19
*/ N
17 3\\0
H (b)
gauche-forv
Figure 1. Numbering of atomic orbitals of n-propylamine used in the calculation.
sentative ones of all the possible conformations. They are explained by Figure 1, taking n-propylamine as an example. Since the 1s electrons of carbon and nitrogen atoms are amalgamated to the cores, only the orbitals in problem for each amine are numbered in Figure 1, where the lone-pair orbital is numbered to be the first in both forms. Atomic distances o,f both amineso are adopted as follows: C-C, 1.540 A; C-N, 1.474 A; C-H, 1.085 A; N-H, 1.012 8. All the bond angles are taken to be 109" 28'. Atomic integrals necessary in the calculation were the same as in the papers of Pople and Segal." For instance, see Table I where the matrix elements U,, concerning the pth orbital are assumed to be equal to - (ionization potential electron affinity). (V,,
+
Table I: Matrix Elements U p , (in electron volts)
s orbital p orbital
H
C
N
-7.176
- 14.051
...
-5.572
-19.316 -7.275
(4) J. C. Lorquet, A. J. Lorquet, and J. C. Leolerc, Aduan. Ma68 Spectrom., 4,569 (1968). Jap., 39, 1406 (1966). (5) K.Hirota and M. Itoh, Bull Chem. SOC. (6) (a) J. A. Pople, D. P. Santry, and G. A. Segal, J . Chem. Phus., 43, 5129 (1965); (b) J. A. Pople and G. A. Segal, ibid., 43,8136 (1965); (0) J. A. Pople and G. A. Segal, ibid.,44,3289 (1966). Volume 74,Number 2 Januaru 83, IQYO
K. HIROTA,I. FUJITA, M. YAMAMOTO, AND Y. NIWA
412 = ( p / - I/,V2 - Z A / T ~ , A Iwhere ~ ) , p denotes an atomic orbital on atom A, T ~ Ais the distance between the electron and nucleus A, and ZA is the core charge.) I n actual calculation of electron densities, 2s, 2p,, 2p,, 2p, orbitals of nitrogen and carbon atoms are adopted as the basis set of orbitals, and they are transformed into sp3-hybrid orbitals after the calculation. Then, their values are summed up in both atoms forming the bond, for the convenience of predicting the scission probability of the bond by use of the values. The calculation has been carried out on the KEAC2200 Model 500 computer at the Computer Center of Osaka University.
Experimental Section Even though mass spectra of n-propylamine measured a t various ionizing voltages Vi were reported in our previous paper,' they are measured again a t the repeller voltage Vr of 3 or 0 V, to investigate its effect, because Vr was 10 V in the previous paper. The same spectrometer of high-resolution type is used, which is installed in our department (Hitachi RMU-7HR). Several mass patterns are shown in Table 11, where unpublished spectra measured a t Vr = 10 V are included. Table I1 : Pattern Coefficients of Mass Spectra of n-Propylamine m/e
15
Bb 26 270
28c 29" 30 31 38 39 40c 410 420 43 44 52 54 56 58
59p 60 6
----Effect 80Va
50V
of ionizing voltage ( V , = 10 V)30 V 20Va 15V
1.2 1.1 2.1 1.9 1.9 1.5 5.3 5.1 9.6 10.0 2.6 2.6 100.0 100.0 1.8 1.7 0.5 0.3 2.4 2.7 0.9 0.8 6.0 6.4 3.4 3.8 2.6 2.7 1.2 1.3 0.4 (5.3 0.4 0.5 1.1 1.4 2.2 2.6 11.1 13.4 0.4 0.3
a Published data (ref 7). Doublet.
0.5 2.0
1.6
1.1
3.0 6.3 2.5 100.0 1.9
0.8 1.8 0.9 100.0 1.5
100.0 1.5
5.5 3.9 2.6 1.2
3.9 1.7 1.4 1.2
2.5 1.0 0.6 1.0
1.6
0.7 2.7 16.0 0.6
3.1 23.1 1.0
1OV
100.0
1.7
3.0
14.0 0.3 b
1.5 26.3
Contribution of HzO+ is omitted.
There was no intense metastable peak worthy to be mentioned. The metastable peaks are not shown a t all in Table 11. This neglect is due to our view of the role of metastable peaks in the fragmentation scheme of the The Journal of Physical Chemistry
'8.0r
,5.0to\
mle JO(CNH&=
vi = 8 0
LO.Ol0
100
Volts
l fA -
;
;
2 3 4 5 6 8 9 10 Repeller Voltage ( v o l t s )
Figure 2. Dependence of main peaks on repeller voltage.
mass spectra, because the metastable peaks correspond only to a part of the fragmentation successively produced. It is expected that if V r is too low, the ion initially produced should again decompose in the ion source. To investigate this possibility, dependence of main peaks on Vr is shown in Figure 2. From the shape of the curve of the parent ion (m/e 59), successive fragmentation would not occur in the ion source if V , lies between 3 and 10 V a t Vi = 80 V. Results I n calculation, the SCF procedure is repeated until self-consistence is achieved on all coefficients with a tolerance of 0.0001. The results thus obtained are shown in Table I11 (ethylamine) and Table IV (npropylamine), where the electron densities in each atomic orbital at the HO level are tabulated as are the total densities at each orbital for the reference. Thereby, the relation between atomic orbitals and relating bond as indicated by Figure 1 is also listed for the next use; also it has to be noted that the same orbital number is given to lone pair in both trans and gauche forms. Tables I11 and I V indicate that about half of the electron density localizes at lone-pair orbitals, irrespective of trans and gauche forms. This tendency may be generally true in higher alkylamines. Now from the tables, the electron densities of the HO orbital at the skeletal bonds are calculated from those of the atomic orbitals by the procedure already described. Their normalized values of both amines are shown at the corresponding bonds in Figure 3. Figure 3 indicates that if the lone pair is put aside from consideration, electron density at the a-CC bond is larger than that a t the CN bond. The conclusion (7) M. Itoh, M. Yamamoto, and K. Hirota, Nippon Kagaku Zasshi, 8 9 , 443 (1968).
413
ELECTRON DISTRIBUTION OF ELECTRON-BOMBARDED ALKYLAMINES
I 1.7 ethylamine (trans)
88.3 C-C-N
Table I11 : Electron Density of the Higher Occupied Orbitals (HO) and the Total Electron Density of Ethylamhe" .---Atomic Numbering
N
1
orbitals---trans Relating bond HO, %
form-Total
F o a u o h e formTotal HO,%
Lone pair CN NH NH
59.1 1.3 1.1 1.1
1.979 1* 080 1.077 1.077
52.7 0.5 1.0 1.1
1.973 1.083 1.078 1 075
5 6 7 8
CN
1.6 8.3 0.8 0.8
0.923 0.992 0.993 0.993
0.9 7.7 1.2 1.3
0.920 0.995 0.988 0.992
c-2 9 10 11 12
cc CH CH CH
13.4 1.4 0.0 0.0
1.017 1.003 1,005 1.005
2.3 0.0 0.2 1.5
1.008 1.003 1.006 1 008
H
NH NH CH CH CH CH CH
2.6 2.6 1.7 1.7 0.0 0.0 2.4
0.923 0.923 1.012 1.012 0.994 0.994 0.999
2.6 2.6 17.3 3.3 0.6 3.1 0.1
0.922 0.929 1.028 1.012 0.993 0.991 0.997
2 3 4
c-1
13 14 15 16 17 18 19
cc
CH CH
C-
72.0~ 280
-N
ethylamine (gauche)
C- 13.6 c 75.4 c I I .ON
I
propylamine (trans)
c 0.1 ~
8 9 . IO 7 2~ -N propylamine (gauche)
Figure 3. Electron distribution in the highest occupied orbital on skeletal bonds excluding the lone pair.
I
0 All the orbitals of Table I11 and IV are regarded to be spa hybrid ones for N and C atoms, and their numbering is illustrated in Figure l.
Table V : Scission Probability of the Skeletal Bonds C8-CZ-C1-N
Theoretical values trans form mean value LCBO (old method) LCBO (new method)
Table IV : Electron Density of the Highest Occupied
Observed values
Orbitals (HO) and the Total Electron Density of n-Propylamine 80 Y A t o m i o orbitalsNumbering Relating bond
N
c-1
1 2 3 4 5 6 7 8
Lone pair CN NH NH CN
a-cc CH CH
H r a n e form-
-0aUChe
HO,%
Total
KO, %
48.9 1.9 0.8 0.8
1.979 1.084 1.076 1.076
49.2 0.2 0.8 1.6
formTotal
1.973 1.088 1.077 1.074
1.8 10.9 0.6 0.6
0.922 0.993 0.994 0.994
0.6
7.0 0.8 3.0
0.920 0 996 0.990 0.994
1.011 0.996 0.996 0.996
4.1 0.0 0.1 1.9
1.001 0.997 0.996 0.999
a-cc 8-cc CH CH
14.7 1.9 0.1 0.1
C-3 13 14 15 16
p-cc CH CH CH
2.7 0.1 0.1 2.1
1.003 1.003 1.003 1.001
0.0 0.2 0.0 0.4
1 001 1.004 1.004 1.002
17 18
NH
2.0 2.0
19
CH CH CH CH CH CH CH
0.924 0.924 1.011 1.011 1.002 1.002 0.998 0.998 1.003
3.5 2.0 16.1 2.5 0.3 4.1 0.6 0.0 0.9
0,923 0.930 1.027 1.012 1.001 0.999 0.997 0.997 1.002
20 21 22 23 24 25
NH
1.2
1.2 0.2 0.2 0.3 0.3 4.4
-
2 (a-CC)
11.0 10.2 10.6 (0.0) 8.0
75.4 89.7 82.6 86.5 80.8
13.6 0.1 6.8 13.5 11.2
1:;
7.2b
86.9 86.0 85.8
4.7 5.7 7.0
8.4"
85.7
5.9
Ref3 erenoe (8-CC)
30
{7'':
86.8 89.3
6.0 4.3
20
4.4" 13.9 3.2b
91.8 94.0 95.1
3.8 2.1 1.7
15
{y:: O.Ob
94.2 96.9 100.0
2.9 1.3 0.0
10.0" 0.0
100.0 100.0
0.0 0.0
Ionizing voltage"
5 7
I
c-2 9 10 11 12
H
50
no,-
-Bond 1 (CN)
I
5 Measured a t V , = 10 V. data measured a t V , = 3 V.
b
Measured a t 0 V.
0
All new
is applicable to both trans and gauche form of n-propylamine. This is in sharp contrast to the Lorquet's result based on the LCBO appro~imation.~The above electron distribution, however, is favorable for the MO theory because this CNDO method can predict the scission probability of the CN bond also so t>hatthe range of its applicability can be extended more than the case when the simple LCBO approximation was adopted. Volume 74, Number 9 January 99, 1970
414
NOW,experimental scission probabilities of the skeletal bonds of n-propylamine are evaluated from the spectra shown in Table 11. They are summarized in the lower part of Table V. I n the upper part of the table, theoretical scission probabilities are described for comparison with the observed. The calculated scission probabilities obtained by two kinds of the LCBO methods are also compared in Table V. The parameters used in the new LCBO calculation are the empirical ones which give plausible results for several monoamines and dianiines.7~8 Even though two gauche forms are possible to n-propylamine, simple mean values of both forms are shown in the table, considering the situation that both conformations are not reported to be stable at room temperature.
Discussion Generally speaking, mean theoretical values agree qualitatively well with the observed above Vi = 30 V, irrespective of V,. It is noteworthy that the agreement is even better than that of the new LCBO method, because the order of bond scission, bond 2 > bond 1 > bond 3, can be given by the present method. The above satisfactory result gives us an answer to the criticism against our attempt to apply the XI0 theory to the prediction of the skeletal bond scission of alkylamines. However, explanation of the reason why the scission of bond 2 is larger than the theoretical values a t very low Vi would be very desirable, to estimate the range of applicability of the MO theory. This apparent discrepancy can be explained by the possibility that the electron energy at low Vi is too small to elevate the bombarded molecule to the highly excited (or superexcited) state,2b so that it does not have sufficient energy to rupture a bond instantly. Besides, even if the highly excited species would be produced, the most abundant ion in the initial fragmentation process would produce the parent ion CHsCHzCH2NH2+, because the electron at the HO orbital exists a t the lone pair with the probability of about 50%. I n either case, the parent ion includes some excess energy, so that slow fragmentation of the initial ions can occur successively, according to the scheme of the statistical theory. Considering the shape of the potential energy hypersurface of molecular ethylamine ion,g fragment ions may be produced overwhelmingly by scission of bond 2. Therefore, because of superposition of this slow fragmentation process on the fast one, the discrepancy between theory and experiment a t low Vi can be explained; Le., scission probability of bond 2 becomes larger as Vi is lowered. Of course, the above successive fragmentation may occur a t high Vi, but it does not proceed actually, judging from the analysis of ions in mass spectra. Only the initial fragmentation seems to occur even a t high Vi. This possibility is reasonable also from the fact that sufficient energy is given to the bombarded moleThe Journal of Physical Chemistry
K. HIROTA,I. FUJITA, M. YAMAMOTO, AND Y. NIWA cule so as t o reach very highly excited state, and most of the fragmentations proceed very fast via such species. By introducing the slow process which occurs more easily as Vi is lowered, existence of the correlation between charge and fragmentation in the fast process may be very plausible as far as n-propylamine is concerned. On the other hand, the agreement was also satisfactory when the new LCBO method was adopted in the mass spectra of n-butyl-, n-pentyl-, n-hexyl-, and n-heptylamine7 and several diamines.* Considering the situation, the A40 theory may be applicable more generally to the alkylnmines, at least as a useful tool in the study of mass spectra. Finally, it has to be mentioned why the theoretical value agrees well with the calculated irrespective of V , above Vi = 30 V. This can be explained by the possibility that V , plays a role of Vi, especially when Vi is low; i.e., such a role becomes negligibly small a t high Vi in comparison to Vr. Physical Picture of the M O Theory. The above successful results favor the MO theory, but the fundamental assumption on the correlation of charge distribution with the scission probability and the approximation adopted in the actual calculation are not given any firm physical picture. This point cannot reduce the plausibility of the theory, considering that the present knowledge of the electronic state of the molecules a t the moment of electron bombardment is still limited. It has to be mentioned here on the approximation that the positive charge distribution of the molecular ion can be substituted for the electron distribution at the HO orbital of the stable neutral molecule. This approximation may not be a pure assumption, because it may have some connection to the nature of highly excited species, which can be regarded as a positive ion loosely coupled with an electron. Since such species can decompose spontaneously through a kind of autoinizing process, its life is very short. Then, an alternative attempt to calculate the electron density of the ionized molecule instead of the neutral molecule is not necessarily required, though such a proposition can be suggested. I n short, the physical picture of the present theory explained above is not a final model but is a preliminary one. Nevertheless, the approximation to calculate the electron distribution of the neutral molecule instead of its ion may be allowed under the fundamental assumption. Evaluation of Dipole Moment. To estimate the reliability of the present calculation, the dipole moment of ethylamine is evaluated by use of the total electron density shown in Table 111. The calculated results are 1.77 and 1.67 D for trans (8) M.Yamamoto, M. Itoh, I. Fujita, and K. Hirota, Nippon Kagaku Zasshi., 89, 752(1968). (9) J. C.Leclerc and J. C. Lorquet, J . Phys. Chem., 71,787 (1967).
GROUND-AND EXCITED-STATE GEOMETRIES OF BENZOPHENONE and gauche forms, respectively. Their mean value, 1.72 D, agrees fairly well with the observed 1.39 D in benzene solution.'0 Therefore, the electron density C%lculated by the CNDO method may be reliable and can be used as the basis of our research. This conclusion, in turn, suggests the possibility Of apply-
415
ing the LCBO-MO theory as a semiempirical one to the compounds other than alkanes.
AcJ.nowle,.&ment, The authors express their sincere thanks to Dr. Keiji Kuwata for his discussions, (io)P. Trunel, Compt. Rend., 203, 563 (1936).
Ground- and Excited-State Geometries of Benzophenone by Roald Hoffmann and Jerrald R. Swenson Department of Chemistry, Cornell University, Ithaca, New York 14860
(Received August 6, 1969)
The equilibrium geometries of benzophenone and benzaldehyde in ground and (n,n*) excited states are calculated using the extended Huckel and C N D 0 / 2 methods. The ground state of benzophenone has both phenyl rings twisted out of plane to a CZgeometry by 38'. The excited state has a considerably steeper potential well for a similar geometry in which the angles of twist are 32'. It appears that the carbonyl group remains locally planar in the excited state. Potential surfaces for the interconversion of enantiomeric minima are reported. Introduction Among photochemists benzophenone (1) is a most popular molecule. Careful and elegant studies have clarified the mechanism of the classic photochemical reduction of benzophenone to benzpinacol in the presence of hydrogen donors.' Benzophenone participates in a
I
+
number of photochemical 2 2 cycloadditions yielding oxetanes,2 but perhaps the greatest utility of benzophenone is found in its application as an agent for efficient triplet state energy t r a n ~ f e r . ~Equilibrium geometry changes in the excited states of molecules play a most significant role in determining their photochemical behavior. I n this contribution we examine possible geometry changes in the (n,r*) excited state of benzophenone. The ground-state equilibrium geometry of benzophenone is determined by a balance of steric and conjugative effects. Conjugation of the carbonyl group with the phenyl rings would favor a planar conformation. Steric repulsion between the Hz and H2' hydrogen atoms prevents the attainment of coplanarity. Each of the phenyl rings must then be rotated by some angle, a and P (see structure l),out of the plane formed by the carbonyl group and the adjacent phenyl carbon
atoms. The mode of rotation which most eficiently relieves the steric problems of the planar geometry is a conrotatory one, Le., a and p as defined in structure 1 both positive and probably of similar magnitude. This was clearly pointed out by ad am^,^ Rodebush,6 and Jones6 though the steric prohibition to coplanarity was no doubt apparent to many researchers as soon as the structure of optically active biphenyls was clarified.' (1) G. Ciamician and P. Silber, Ber., 33, 2911 (1900); 34, 1530 (1901); C. Weirmann, E. Bergmann, and Y. Hirschberg, J . Amer. Chem. SOC.,60, 1530 (1938); H. L. J. Backstrom, 2. Phys. Chem., B25, 99 (1934); H. L. J. Backstrom and K. Sandros, Acta Chim. Scand., 14,48 (1960);A. Schonberg and A. Mustafa, Chem. Rev., 40, 181 (1947); G. Porter and F. Wilkinson, Trans. Faraday Soc., 57, 1686 (1961);A. Beckett and G. Porter, ibid., 59, 2039,2051 (1963); W. M. Moore, G. S. Hammond, and R. P. Foss, J . Amer. Chem. SOC.,83, 2789 (1961); G. S. Hammond, W. P. Baker, and W. M. Moore, ibid., 83, 2795 (1961); J. N. Pitts, Jr., H. W. Johnson, and T. Kuwana, J . Phys. Chem., 66, 2471 (1962); J. A. Bell and H. A. Linschitz, J. Amer. Chem. Soc., 85, 528 (1963). (2) E. Paterno and G. Chieffi, Gazz. Chim. Ital., 39, 341 (1909); D. Scharf and F. Korte, Tetrahedron Lett., 821 (1963); G. 0.Schenck, W. Hartmann, and R. Steinmetz, Ber., 96,498 (1963);R.Steinmetr, W. Hartmann, and G. 0. Schenck, ibid., 98, 3864 (1965); J. S. Bradshaw, J . Org. Chem., 31,237 (1966); J. W. Hanifin and E. Cohen, Tetrahedron Lett., 1419 (1966); D. R, Arnold, R. L. Hinman, and A. H. Glick, ibid., 1425 (1964); N. C. Yang, Pure Appl. Chem., 9, 591 (1965); D.R. Arnold, Advan. Phofochem., 6, 301 (1968),and
references therein. (3) Reviewed by A. Terenin in "Recent Progress in Photobiologv," E. J. Bowen, Ed., Blackwells, London, 1965, p 3; V. L. Ermolaev,
Usp. Fiz. Nauk, 80, 3 (1963). (4) J. F. Hyde and R. Adams, J. Amer. Chem. Soc., 50, 2499 (1928); M.E.Maclean and R. Adams, ibid., 55,4683 (1933). ( 6 ) M.T.O'Shaughnessy and W. H. Rodebush, ibid., 62,2906(1940). (6) R. N. Jones, ibid., 67, 2127 (1945). Volume 74* Number W January $8, 1970
