DIPOLEMOMENTS AND SPECTRA OF O-BENZOQU~NONE
Feb. 20, 1954
TABLE VI1 CHARACTERISTIC FREQUENCIES OF BORANES Motion
BHz stretch BH stretch
BH* stretch
BH, bend BH bend B-B stretch BH*zB stretch BH * bend
BzHs"
BzHz(CHa)d's
2610 2520
.. ..
BoHe
..
..
..
2102 19S2 1847 1180 1173 1010 970
2137 1987
2610 2598 1844 1802
..
..
..
..
..
..
799 370
844 365
1621 1449 1413 1126 799 605 568
stretching frequency near 800 cm.-' which exhibits considerable boron isotopic structure and for B6H9 shifts on deuteration by a factor around 1.25. The low frequency bands of B6"J a t 568 and 605 cm.-l show unexpectedly large isotopic shifts on deuteration. It is interesting that there is a corresponding mode of BzHB a t 370 cm.-' which shifts by a factor close to 1 / 2 on deuteration. These
1003
bands must correspond to bridge hydrogen motions and they provide the basis for the estimate of the frequency of one of the A2 vibrational modes of B6H9 a t 500 ern.-'. Thermodynamic Properties of Pentaborme.Since several fundamental vibrations were selected enly by consideration of expected vibrational type, it does not seem appropriate to include detailed calculations of thermodynamic functions. However, the entroyy of gaseous B6H9 a t 296'K., measured by Johnston, Kerr, Clarke and Hallett6 together with the accurate values of the moments of inertia from the microwave s t u d i e ~provide ~ ~ ~ ~one check upon the present assignment. The calculated entropy of B6H9 a t 296'K., 65.73 cal./deg. mole, may be ccmFared to the experimental value, 65.75 cal./deg. mole.6 This agreement is fortuitous since the uncertainty in each of the numbers is of the order of a few tenths of an entropy unit (the experimental entropy includes a - 2.68 cal/deg. mole ideal gas correction based upon Berthelot's equation) but it probably does substantiate the conclusion that there is one unobserved, low frequency fundamental (assigned here as an Az mode a t about 500 cm.-l). (14) A report by H. J. Hrostowski and R. Myers on the microwave study of BsHp and BaDi is in press (. Chcm. I P h y s ). They give (he product of the principal momenls of inertia for Ba"Hi, 2 460 X 10-114 g.Scm 8.
BERKELEY4, CALIF.
-
[CONTRIBUTION FROM THE INSTITUTE O F SCIENCE AND
TECHNOLOGY, UNIVERSITY O F TOKYO]
Dipole Moments and Absorption Spectra of o-Benzoquinone and its Related Substances BY SABURO NAGAKURA AND AKIRAKUBOYAMA RECEIVED APRIL 3, 1953 Dipole moments of o-benzoquinone and 1,2-naphthoquinone were determined in benzene solutions as 5.1 and 5.67 D, respectively. These high moments can be explained on the basis of the 7-electron distribution calculated by the molecular orbital method. The solvent effects on the electronic absorptions were measured with o-, p-benzoquinone, 1,2- and 1,4naphthoquinone. As a result of the measurement, it was found that the absorptions of these quinones appearing in the visible region shift t o the side of shorter wave lengths with the increasing dielectric constant of the solvent. This probably shows t h a t these absorptions are due t o the n-**-transition.
I t is known that quinones have many interesting properties. They absorb visible light; they form a group of molecular compounds' ; their oxidationreduction potentials are generally high and positive2; further, a certain quinone has an abnormally high dipole moments3 Of these properties oxidation-reduction potential appears to be an unique example of being fully studied; viz., Evans, et a1.,2 have discussed this property in detail with reference to 7-electrons. (1) P. Pfeiffer, "Organische Molekulverbindungen," Ferdinand Bnke. Stuttgart. 1927; G. Weiss, J. Chem. SOC.,245 (1942),and 462 (1943); H. M. Powell, G. Huse and P. M. Cooke, i b i d . , 153 (1943), and 435 (1943); L. Michaelis and S. Granick, THISJOURNAL, 86, 1023
(1944). (2) G. E. K. Branch and M. Calvin, "The Theory of Organic Chemistry," P r e n t i c t H a l l , Inc., New York, N. Y.,1941, p. 303; E. Berliner, T H I SJ O U R N A L , 68,49 (1946): M . G. Evans, Trans. Forad a y Soc., 42, 113 (1946); M. G. Evans, J. Gergely and J. de Heer, i b i d . , 46, 312 (1949). (3) C. C. Caldwell and R. J. W. Le Fevre. J . Chcm. SOC.,1614 (1939). T h e dipole moment of phenanthrenequinone was determined b y them as 5.6 D.
The work in the present paper was undertaken to study the problem somewhat in a wider scope. First, the dipole moments and visible and near ultraviolet absorption spectra measured for several quinones will be reported. Second, the experimental result on the dipole moment will be compared with the theoretical value obtained by the use of the molecular orbital method. Experimental Materials.-o-Renzoquinone4 was prepared by oxidation of catechol and recrystallized from ether. The dark-red crystalline product melted at 60-70" with decomposition. p-Benzoquinone was prepared by oxidation of commercial hydroquinone and purified by repeated sublimation, m.p. 116'. 1,4-Naphthoquinone6 was obtained by oxidation of 1,4(4) R. Willstatter and A. Pfannenstiel, BPr , 41, 2580 (1908) S. Goldschrridt and F Graef, ibrd., 61, 1858 (1928). R. Kuhn and I Hammer, ;bid., 89, 413 (1950). o-Benzoquinone is unstable, so the measurement with this substance has been made within six hours after preparation ( 5 ) Org. Synlhrsic, 17,4, 24 (1P07).
aininonaphthol which was prepared by reduction of Orange 1. The product was crystallized from ether, m.p. 125'. 1 ,2-Naphthoquinoiie6 was obtained according t o the nirthod of L . F. Fieser, m . p . 147-148". Ilrn7ene, Iwtroleiiin beuzirie, niethanol and chloroform
-0.51 , , , , 200 250 300 350 400 450 500 550 600 650 700 1
1
I
I
I
1
A, m r .
Fig. 1.-Absorption spectra of 0- and p-benzoquinone in various solvents: -, o-benzoquinone in benzene; - - -, a-benzoquinone in chloroform; , p-benzoquinone in petroleum benzine; . - - . , p-benzoquinone in benzene; . . , , p-benzoquinone in chloroform; -'-, p-benzoquinone in water. ,
p =
i
M
2.0
2'5 1.5 1.0
P?, = -11[30!Z1i)'(€if 2)' the dipole moment
p
+ + 0)(€1 (Z'1
1)/(€1
+ 2)]
was obtained by t h e usual equation
0.01273d(/(Pzm - f5fRn)T
I n the above equation, the molecular refraction for the sodium D-line, . 1 f R ~was evaluated as the sum of the atomic refractions.
4.5 5.0 4.0 . 3.5 ' 3.0 '
-
used as the solvent were purified by the methods described in "Organic Solvents".6 Methods and Results.-The absorption spectra were measured with a Beckman quartz spectrophotometer model DU. The results obtained in the present experiment are shown in Figs. 1-3. In these figures, the logarithm of the molar extinction coefficient (EM) is plotted against the wave length in millimicrons. T h e absorptions of o-benzoquinone7 in hexane, ether and chloroform, p-benzoquinone8 in n-hexm e and chloroform, 1,2-naphthoquinone in ether, chloroform and alcohol, and 1,4-naphthoquinoneg in alcohol have already been measured by several investigators. In the present experiment, absorption spectra were measured with o-benzoquinone in benzene and chloroform; p-benzoquinone in petroleum benzine, benzene, chloroform and water; 1,2-naphthoquinone in benzene, chloroform and methanol; 1,4-naphthoquinone in petroleum benzine, benzene and chloroform. Comparing present experimental results with those obtained by other investigators in the same solvent, it is seen t h a t there is good accordance between them. T h e dielectric constant was measured with the apparatus described previously.'o All the measurements of the dielectric constant and the specific volume &#were made in benzeiie solutions a t 25". T h e measured values of these two quantities are given in Table I, ivhere w is the weight fraction of the solute. Using these experimental results, the molecular polarization at infinite dilution, P 2 , was calculated by the ITalverstadt and Kumler method.ll From the value of P2-,
TABLE I DIELECTRIC COSSTASTSAND SPECIFICVOLUMESI N BENZENE S O L G T I O S S O F O-BENZOQVIXONE A N D 1, % N A P T H O -
I1
QrISOSE
(A) o-Benzoquinone; temp., 25.0' w
U
6
; 0
-0.5 -1.0 O': 200 250 300 350 400 450 500 550 600 650
A, mp. Fig. 2.-Absorptiori spectra of 1,2-naphthoquinone in various solvents: -, in benzene; ---, in chlorofornl: -_ - -, in methanol.
4.5 t
i1
3.5 4.0 3.0 2.5 . 2.0 '
t~,
1,14728 1.34676 1,14671 1,14686 = 1.147. Pz, =
(B) 1,2-Saphthoquinone; temp., 25.0' 0 2.270 I . 14715 0.001494 2.301 1,14662 2.311 1,14634 .002002 2.320 1,14639 .(I02266 2,325 1 14605 .002512 2 3.55 1 14581 ,003880 ry = 22.2, B = -0.:13, €1 = 2.270, = 1.147, Prim 701 c c . , J I R , , = *36.0c c . , p = 7.67 D.
=
Theoretical The calculation of the rr-electron density has been carried out with 0 - and +benzoquinone by use of the same molecular orbital method as we pre-
-
-
-0.5 l o t -1.0 .-I 200
.000567 000877 .001Iacbeth, ibid , 327 f l y 3 5 1 ( l o ) S. Xagakura and A . K u b o y a m a R e p l s . I n s / . Cii. I ' e c h n , Cnir, T o k y o , 4 , 242 (1950). (11) I. F. Halverstadt and TV. D. Kumler, THISJ O U R K A I . , 64, 2988 (194%). hccording t o their method, PgLo is obtained b y t h e e q u a t i i i n where .lf i 9 t h e molecular weiaht of t h e s o l u t e T h e values o f a 8 . t ;ind 7 , nec'eswry firr t h P c,tl,,!!ldti
