COMMUNICATIONS TO THE EDITOR
3374
I
, , I
I
Ill
I, I ,
.
I II II
I
I
I ,I
IIs
I
I
1 II I Id
A .I I ,I I I, I ,,DlI*J I I l l l l l l h I ll,,ll/1lIlI1 Lr,, I t , I , , I I , I . Figure 1. Electron spin resonance spectra of sodium (top) and potassium (bottom) xanthene-9-thione ketyl. The splitting constants given in Table I produce the synthetic line spectrum. The spacing between the largest peaks of the top spectrum due t o sodium splitting is 5 gauss.
splitting in thioketyls reflects a decrease in spin density a t carbons bearing hydrogens and presumably an increase in spin density on the thiocarhonyl function. The most remarkable feature of the esr spectrum of thioketyls is the large metal ion splitting. Whereas in the case of xanthone ketyl, sodium splitting is 0.95 gauss and potassium splitting probably -0.1 gauss: the sodium splitting for xanthone thioketyl is 4.0 gauss and potassium 0.77 gauss. A large metal ion splitting is also undoubtedly part of the spectrum of the other thioketyls since a much larger total line width is observed for sodium than for potassium (Tahle I). The larger metal ion splitting in the thioketyls may be attributed to a higher spin density on the thiocarbonyl function and/or more efficient spin transfer from sulfur to metal ion. These effects may involve sulfur &orbital participation. Molecular orbital cal~~
~
(7) Free radicals with the unpaired electron entirely loodined on aulfur have g value of 2.027: J. J. Windle, A. K.Wiersems, and A. L. Tappel. J . Chem. Phys., 41, 1996 (1964). (8) N. Hirota and S. I. Weieaman, J . Am. Chem. Soc., 86, 2537
(1W). (Sa) NOTEADDED IN PROOP.The wupling wnstants for the &urn ketyl of thiaxanthene&thione in tetrahydrofuran are -3 ( 4 H E Cs). 0.86 (2-H), and 0.50 (2-H) gauea. (9) National Aeronautics and Space Administrstion Traineeship, 1965-1966.
The Journal o/ Ph@d
Chemistry
culations are in progress. Peliminary results have been obtained for other thioketones, e.g., thiohenzophenone and thiofluorenone?' DEPARTMENT OF CHEMISTRY THEUNIVERSITY OF GEORQIA ATHENS.GEORQIA
EDWARD G. JANZEN COITM. DUBOSE,J R . ~
RECEIVED AUQUST15, 1966
Intramolecular Energy Transfer in 7-Irradiated Alkylbenzenes
Sir: Voevodskii,'.'
using epr and Bagdasaryan,* using iodine scavenger techniques, have shown that in phenyl substituted saturated hydrocarbons besides intermolecular energy transfer, intramolecular energy transfer also takes place. Recently, Jones, et aZ.,' (1) Yu. N. Molin, I. I. Chkeidae. N. Ya. Buben. and V. V. Voevodskii. Kinefika i Katolir. 2, 192 (1961). (2) Yu. N. Molin. I. I. Chkeidae, A. A. Petrov, N. Ya. Buben. and V. V. Voevodskii, Dokl. A m . Nauk SSSR, 131, 125 (1960). (3) Kh. S. Bagdsssryan. N. S . Israilevioh, and V. A. Kronpaus. im.. . 141.. 887 (1961). . . (4) I(.H. Jones. W. van Dueen, Jr., and L. M. Theard. RodiOtbn Rea., 23, 128 (1964).
COMMUNICATIONS TO THE EDITOR
3375
studied hydrogen formation in a series of n-alkylbenzenes in an effort to determine the effect of side-chain length on intramolecular energy transfer. They conclude from their experimental results that the extent of alkyl group protection is unaffected by the size of the alkyl side chain. I n this communication, we wish to present further information on this subject because our experimental resuks are not in agreement with the state-
Table 1. n-Alkyibenzene (or alkane-benzene mixture)
-G(H+---Jones, et al.
Toluene Ethylbenzene Propylbenzene Butylbenzene Amylbenzene Amylbenzene 0.5% Iz Hexylbenzene (Hexane-benzene) (Hexane-benzene 0.5% 12) Heptylbenzene Oct ylbenzene Nonylbenzene Nonylbenzene 0.5% It (Nonane-benzene) (Nonane-benzene 0.5% Iz) Dodecylbenzene Tridecylbenzene Tridecylbenzene 0 . 5 % Iz (Tridecane-benzene) (Tridecane-benzene 0.5% Iz) Heptadecylbenzene (Heptadecane-benzene)
0.12 0.16 0.20 0.25 0.25
+
+
+
+
+
+
... 0.29
-@alkyl(Hz)--
This work
Jones. et al.
This work
...
0.49 0.45 0.46 0.51 0.46
0.51 0.55 0.56 0.64
0.18 0.23 0.27 0.34 0.35
...
,..
...
0.40 (0.53) (0.53)
0.50
0.50 0.51
...
0.69 0.75 0.89
...
0.42 0.48 0.59 0.58
...
...
... ...
0.78 (0.83)
...
(1.19)
... ...
0.31 0.33
...
..
,
...
... .
.
I
... *..
...
0.67 0.75 0.73 0.93 0.94
0.95 (1.21)
...
...
..*
...
... ... ....
...
...
...
0.70 (0.94)
...
...
}+
C6H5CnH2n+l f H *kin +C S H S C ~ H * Z~ Hz. +CeH&nH2,+i *
* C G H S C J L +*I C6H5CnH2n+i
+CsHsCnH2n-i
CsHsC,Hz,+i
+ H2
(lb) (2)
--t
+
C12+2nH10+4n Hz
(3)
The reactive species (+) may be an ion or an excited state. Reaction 3 is assumed to contribute the bulk of hydrogen since n-alkylbenzenes show a sharp drop of G(H2) in the solid p h a ~ e . Table ~ ~ ~ I shows the experimental values of G(H2). Furthermore, it contains galkyl(H2) values calculated from the equation G a ~ k benzene y (H2)
ephen y lgpheny I (H2)
+
ea Iky @a l ~ y(Hz) l
(ForgphenYl(H2) the value of 0.038 was used; galkyl (H2) refers to the hydrogen produced per 100 ev absorbed in the alkyl part; ephenyl and e a l k y l are the electron fractions of the phenyl and alkyl part, respectively. The observed differences in G(H2) between the nalkylbenzenes and the equimolar mixtures of alkane and benzene should be due to intramolecular energy transfer, because no scavengable hydrogen could be detected in both systems.
1.5
0.94 1.03
c
i I
I
... (1.28)
... 1.23 (1.56)
Compounds were synthesized using known methods and purified by preparative gas chromatography. Samples (1 ml) were outgassed by freeze-pump-thaw cycles and sealed at lo-* torr. Hz determination was by gas chromatography (see E. J. Weber and H. Heusinger, Radiochim. Acta, 4, 92 (1965)); accuracy better than &5%; irradiation temperature 35 + 5'; total dose 6.85 X lozoev/g; dose rate 0.95 X 1019 ev/g hr.
ment of Jones, et aL4 We investigated the hydrogen formation of n-alkylbenzenes and several equimolar mixtures of alkane and benzene. Addition of iodine up to 0.5% had no effect on G(H2). It is reasonable to assume that the unscavengable hydrogen in alkylbenzenes is produced via CJ&Cn&,+i
+C a H & J L *
Hakin
(la)
Electron fraction alkane.
Figure 1. gslkyl(HZ)as a function of side-chain length: 0, this work (a-alkylbenzenes); this work (1 :1 alkane-benzene mixtures); V, Jones, et aL4
+,
(5) D. Verdin, J . Phys. Chem., 67, 1263 (1963). (6) G. K. Wassiljew and I. I. Chkeidze, Kinetiku i Kutaliz, 5, 802
(1964).
Vohme YO, Number 10
October 1966
COMMUNICATIONS TO THE EDITOR
3376
Contrary to the results of Jones, et u Z . , ~ we find (see Figure 1) that the extent of alkyl group protection by the phenyl group is affected by the length of the alkyl side chain. The protection decreases with increasing distance of the primarily affected portion of the -CH2- chain from the phenyl group. Additional evidence for this statement follows from the hydrogen production of various phenyl-n-nonanes (Table 11). The protection is a maximum when the phenyl group is in the center of the alkane chain, in agreement with earlier results on cross linking of 1- and 6-naphthyldodecane by Alexander and Charlesby.' We feel that the experimental discrepancies may be due to impurities (possibly branched alkylbenzenes) in the commercially available compounds used by Jones, et al. I n order to evaluate in more detail the mechanism of hydrogen formation and the nature of the protection in n-alkylbenzenes, we aae carrying out epr studies and work on deuterated compounds. Table I1
+
Suppose that an association reaction A B = AB occurs in a series of solvents, including the vapor phase. For any two of the solvents, the association constants may be written KAB' = CAB'/CA'CB' and KAB" = CAB"/ CAIICBII,where the superscripts refer to solvents I and I1 and the species concentrations, CA, CB, and CAB, are expressed in units of moles per liter. It is assumed that solute concentrations are sufficiently small so that each species individually obeys Henry's law (in condensed phases) or the ideal gas law (in the vapor phase). The distribution constants KD,A = CAI'/ are deCAI, KD,B= CB"/CBI, and KD,AB= CAB"/CAB' fined in terms of the same concentrations. The association and distribution constants are related by the equality KABIIIKAB'= KD,AB/KD, AKD, B
By making one simple assumption, it is possible to correlate variations in the equilibrium constant and enthalpy of the association reaction occurring in different media. Assume that
+
AFOAB = ~(AFOA AFOB)
Phenylalkane
Q(Hd
Balkyl(Hd
1-Phenylnonane 3-Phenylnonane 5-Phenylnonane
0.59 0.50 0.42
0.89 0.75 0.62
(7) P. Alexander and A. Charlesby, Nature, 173, 578 (1954).
(1)
I+II
I+II
I+II
(2)
where AFOAB represents the change in standard free I+II
energy of the complex upon transfer from phase I to phase I1 (using standard states of 1 mole/l. in each phase), A F O A and A F O B are the corresponding free I+II
Id11
energy changes for transfer of A and B, respectively, and a is a parameter, presumably less than unity and INSTITUT FUR RADIOCHEMIE DER A. ZEMAN TECHNISCHEN HOCHSCHULE MUNCHEN H. HEUSINGER not strongly dependent on either temperature or choice MUNCHEN, GERMANY of solvents. a is related to the fraction of the free RECEIVED AUGUST15, 1966 energy of solvation of the monomers that is retained by the molecular pair after the complex is formed. In general, the complex will not solvate so extensively as the two separated monomers, since the reactive A Method for Predicting the Effect of parts of the monomers are brought closely together in Solvation on Hydrogen-Bonding forming the complex, thus "squeezing out" some solvent molecules. The bulkier and more complicated Association Equilibria the monomers, the more nearly should a approach unity. Furthermore, if a cyclic complex forms, a Sir: A perplexing problem that frequently arises in should be smaller than if only linear aggregates are hydrogen-bonding studies is the prediction of v a r i e present, because a larger percentage of the total tions occurring in the thermodynamic parameters for molecular surface is involved in cyclic as opposed to association reactions as the medium is changed. I n chain complexes. previous investigations of the hydration of polar solutes If eq 2 is valid, with a nearly constant and temperawe have noted that the solubility of water in various ture independent for a range of solvents, several solvents is a good index to relative solvation ability.' interesting conclusions can be drawn. However, reliable methods for calculating solvent effects (1) The relation which is shown in eq. 3 are not presently available. This communication describes a simple technique for predicting the effects (1) J. R. Johnson, Ph.D. Dissertation, The University of Oklaof solvation on the thermodynamic parameters charhoma, 1966; D. D. Mueller, Ph.D. Dissertation, The University of acteristic of hydrogen-bonding reactions. Oklahoma, 1966. The JOUTTMZ~ of Physical Chemistry
