MAGNETOELECTRIC CHARACTERISTICS AND STEREOCHEMICAL

STRUCTURE OF I,I-DIPHENYL-I,2-DIHALOGENOETHANES

S. G. Vul'fson, O. M. Dianova, V. E. Kataev, and A. N. Vereshchagin

UDC 541.67:541.63:547.636'121

In the previous communication [i] we showed that the molecules of ~,$-dichloro- and a,B-dibromoethylbenzenes (I) and (II) in carbon tetrachloride exist in an equilibrium mix- ture of the staggered trans and gauche conformers; in both forms the plane of the phenyl group eclipses the C-H bond. The introduction of a second geminal phenyl group into (I) and (II) complicates the conformational problem. The stereochemical structure of l,l-diphenyl- 1,2-dichloro- and l,l-diphenyl-l,2-dibromoethanes (III) and (IV) can be characterized by the ratio of the three discrete rotational isomers, i.e., the trans (n T) and the two degen- erate (disregarding optical isomerism) gauche (n G) isomers, and also the four torsion angles of rotation of the planes of the phenyl groups (Fig. i), which in the general case are not equal to each other (~I)T ~ (~2)T ~ (~I)G ~ (~2)G.

We used the dipole moment method to determine the composition of the equilibrium mixture. The conformations of the phenyl groups were determined by means of the Kerr and Cotton- Mouton effects. The molecular geometry was taken as standard; the bond angles of the satur- ated carbon atoms were tetrahedral, and the torsion angles at the Ca-~ B bonds were staggered. As the reference point for the rotation of the phenyl group (~i = 0~ we used the eclipsing of the C~-~$ bond by the plane of the phenyl group; conrotatory rotation was taken as posi- tive, so that when ~i = 60~ the phenyl group eclipses the C sp2-C sp3 bond and when ~2 = 60 ~ it eclipses the Ca-Hal bond. During calculation of the polarities of the C-Hal bonds we used the experimental dipole moments of C2H5CI (1.96 D), C=H~Br (1.93 D), i-C3HTCI (2.04 D), and i-C3HTBr (2.04 D) [2], and we took account of the inductive interaction of the vicinal substituents C~-CI 1.42 D, C~-CI 1.50, C~-Br 1.40 and C~-Br 1.54 D. The dipole moment of the Csp2-H bond was taken as equal to -0.28 D [2]. The contribution from the di- phenylmethyl radical was not included, since the dipole moment of diphenylmethane is zero [2]. The polarizability and magnetic susceptibility ellipsoids of the C-Hal bonds at the C a atom were taken from the data for i-C3HTHal, those for C~ were taken from the data for C2H5Hal [3, 4], and those for the C6Hs-C-fragment were taken from the data for toluene [5-7].

The calculated molecular dipole moments for the trans and gauche conformers amount to 0.08 and 2.84 D respectively for (III) and 0.14 and 2.86 D for (IV). Comparing them with the experimental values [1.71D for (III) and 1.72 D for (IV)] and solving the set of equations

2 mT2~T ~ ~G2~G ~ mexpt

nT/na = 2exp (--AH/kT)

we o b t a i n t h e mole f r a c t i o n s and t h e d i f f e r e n c e s i n t h e f r e e e n e r g i e s (hHT_G) o f t h e r c t a m e r s : n T = 0 . 6 4 , n G = 0 . 3 5 , AHT_ G = - 0 . 7 5 k c a l / m o l e , i r r e s p e c t i v e o f t h e n a t u r e o f t h e h a l o g e n . The o b t a i n e d 5H v a l u e s c o r r e s p o n d t o t h e d i f f e r e n c e i n t h e e n e r g i e s o f t h e P h . . . H a t and H a l . . . H a l i n t e r a c t i o n : hE ( I I I ) , ( IV) = 2 ( P h . . . H a l ) - ( P h . . . H a l ) - ( H a l . . . H a l ) . I t was i n t e r e s t i n g t o s e e w h e t h e r t h e a d d i t i v i t y o f hE was p r e s e r v e d i n t h e t r a n s i t i o n f rom ( I ) and ( I I ) t o ( I I I ) and ( I V ) . E a r l i e r we showed by means o f t h e d a t a f rom PMR s p e c t r o s c o p y [1] t h a t t h e m o l e c u l e s o f ( I ) and ( I I ) i n c a r b o n t e t r a c h l o r i d e e x i s t i n t h e fo rm o f t h e t r a n s con - f o r m e r ( i n r e l a t i o n t o t h e C-Hal b o n d s ) t o t h e e x t e n t o f 85% and i n t h e s t e r i c a l l y l e s s h i n d e r e d g a u c h e form t o t h e e x t e n t o f 15%. C a l c u l a t i o n on t h e b a s i s o f t h e s e d a t a g i v e s h E [ ( P h . . . H a l ) - ( H a l . . . H a l ) ] = - 1 . 0 k c a l / m o l e , wh ich i s c l o s e t o 5E ( I I I ) , ( I V ) . Some d e -

A. E. Arbuzov Institute of Organic and Physical Chemistry, Kazan' Branch, Academy of Sciences of the USSR. Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. i0, pp. 2212-2217, October, 1987. Original article submitted March 3, 1986.

0568-5230/87/3610-2049512.50 �9 1988 Plenum Publishing Corporation 2049

~ Hal 7" G

Fig. i. The conformations of the l,l-diphenyl-l,2-dihalogenoethane molecules.

fSO

IZO

80

~0

0 0

/ �9 \

o zlO 80 iZO i60 ~Z

f ) l l j z~ J L / . - < J.~z <,~,*<,d

~~ " b

i I I I

0 40 00 iZO i~O ~a ~

I I

0 *0 e0 ,z0 len,~ a ~0 e0 ,za ,e0~f

Fig. 2. Maps of the conformational energies of the trans conformer of l,l-diphenyl-l,2-dichloroethane (a), the gauche conformer of l,l-diphenyl- 1,2-dichloroethane (b), the trans conformer of l,l-diphenyl-l,2-dibromo- ethane (d), and the gauche conformer of l,l-diphenyl-l,2-dibromoethane (c).

crease in the difference between the conformational energies (~0.25 kcal/mole) is evidently due to change in the conformation of the phenyl group, which leads to a change in their steric demands.

In order to check this proposal we calculated the conformational relationships for the Kerr constants (KC) and Cotton-Mouton constants (CMC) of compounds (III, IV). Compari- son of the calculated values with the experimental constants (see the experimental section) shows that multiple combinations of the ~i angles correspond to the experimental values even if the conformational equilibrium is disregarded. The number of possible variants is greatly reduced if only the sterically "permitted" structures are analyzed. For this purpose, in terms of the mechanical model of atom-atom potentials (MAP) with the inclusion of the contributions from the unshared electron pairs of the halogens* we calculated the

*The calculations were performed by analogy with [8] using the MAP-3 program, which was written and kindly supplied by A. Kh. Plyamovatyi.

2050

rnlf "fO

?00 -

f60

lZO

~0

qO

12 7 B g fO ~1 ,~Z gauche - -- , -- ,-,

a

xpt

] 0

mK.lO 12

/ 'ZO~ gauche 6 7 8 g ~'0 t'~' - - o �9 - - t , ~ . . - ~ o

lq IJ CZ

8O

O0

t tram ~ , - ~ - o - - ~ o L ~ JI 2

0 1 z

trans h ~ 5

Z $ mG.fO 15

d mC" lD 15

Fig. 3. The mK-m C relation for l,l-diphenyl-l,2-dichloro- ethane (a) and l,l-diphenyl-l,2-dibromoethane (b). The angles of rotation of the phenyl groups (@i, @2)T and (@l, @2)G (deg) are as follows: a) i) i0, 80; 2) i0, 90; 3) i0, i00; 4) 20, 80; 5) 20, 90; 6) 30, 80; 7) 0, 60; 8) i0, 60; 9) 20, 65; I0) 30, 65; Ii) 50, 60; 12) 60, 60; b) i) i0, 90; 2) i0, i00; 3) 20, 80; 4) 20, 90; 5) 30, 90; 6) 0, 40; 7) i0, 40; 8) 20, 45; 9) 40, 45; i0) 50, 45; ii) 60, 40; 12) 70, 40; 13) 80, 35; 14) 90, 30.

energies of the trans and gauche rotamers (Iii) and (IV) in relation to the angles @! and @2 and constructed the corresponding contour maps.

As can be seen (Fig. 2a-d), the minima of the conformational energies for (III) corre- spond to torsion angles @i = 20, @2 = 90~ in the trans form and @i = 0, @2 = 80-90~ in the gauche form; for (iV) they correspond to (@I)T = 20, (@2)T = 90~ (@L)G = 0, (@2)G = 80~ However, these values are approximate, since the minimization of the molecular energies was performed exclusively for the @i angles and did not include the change in the torsion angles with respect to the ethane bond (they were assumed to be staggered), the bond angles (they were considered to be tetrahedral), and bond lengths, which were assumed to have standard values: ~ (C~-C~) = 1.54 ~, ~ (Cs~2-Csn3) = 1.51, s (Car-Car) = 1.39, ~ (Csp3-Cl) = 1.77, s (Csp3-Br) = 1.94,~s (Csp3-H) = 1.08~ s (~sp2-H) = 1.07 ~ [9]. In this connection, in the region of "permitted" conformations we included structures whose energy characteris- tics differed from the minimum by 15-19"i0 -12 esu. Consequently, using the data on the conformational composition of (III) and (IV) obtained on the basis of the dipole moment method and assuming that mKtrans (III), (IV) ~ 17-i0 -12 esu with the experimental values mKexpt(III) = 89-10 -12 and mKexpt(IV) = 55"10 -12 esuwe can determine the Kerr constant of the gauche form mKG according to the equation:

nTmKT + na,~K~=,~Kexpt

f o r ( I I I ) mEG = 2 2 0 " 1 0 -12 , a n d f o r ( IV)mK G = 120"10 -12 e s u .

The o b t a i n e d v a l u e s o f m K t r a n s a n d mKG c o r r e s p o n d t o a s e r i e s o f p e r m i t t e d s t r u c t u r e s with angles @i and @2 which vary in the ranges of (@I)T = 10-30~ (@2)T = 80-I00~ (@l)G = 0-60~ (@2)G = 60-65~ for (III) and (@~)T = I0-30~ (@2)T = 80-100~ (@~)G = 0-90~ (@2)G = 30-45 ~ for (IV). The values of the @i angles can be refined if the data on the Cotton-

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TABLE i. The Experimental Dipole Moments (m, D), Kerr Constants (mKCCI~, esu), and Cotton-Mouton

Constants (mCCCI4, esu)

Compound m ] mKcCl.to~ I rnCCC14.101~

([I1) 1,71 89 2,t3-+0,09 (IV) 1,72 55 1,5i-+0,07

Mouton constants calculated for the above-mentioned conformations together with the obtained Kerr constants and the experimental values are set out in the form of mK-m C graphical re- lationships by analogy with [i, i0]. The section with the shoulder ratio (0.64:0.36) pass- ing through the experimental point in the case of (IV) (Fig. 3b) connects the points corre- sponding to thetrans and gauche structures with angles (~I)T = i0~ (~2)T = 90, (~)G = 0, and (@2)G = 40~ For (III) with the same shoulder ratio, as follows from Fig. 3a, the sec- tions isolate the regions which describe the magnetoelectric characteristics in a narrow range of angles, i.e., the trans conformation (~i = 10-20~ ~P2 = 80-90~ and the gauche conformation (~i = 0-20~ ~2 = 60-650) �9 Together, the data from experimental and theoretical conformational analyses make it possible to suppose that the molecules of (III) and (IV) in carbon tetrachloride are present in the form of an equilibrium mixture of the trans and gauche rotamers in a ratio of 2:1, irrespective of the nature of the halogen. In the conformers with the trans orientation of the C-Hal bonds the plane of one of the phenyl groups eclipses the C~-C~ ethane bond, and the plane of the second phenyl group is ortho- gonol to it. In the gauche conformers, as in the trans conformers, one of the phenyl groups and the C~-C~ bond lie in a common plane. As far as the second phenyl group is concerned, it is deflected from the orthogonal conformation under the influence of the steric repulsion from the ortho-C-H bond and the C-Hal bond, and the size of the deflection is related to the size of the halogen atoms.

It can also be seen that fundamental change in the conformation of one of the phenyl groups compared with (I) and (II) (eclipsing of the Ca-C~ bond) increases its steric demands with respect to the C$-Hal bond, and this in the final count reduces the AH value of the rotational isomers compared with the value expected from the data for the monophenyl deriva- tives.

EXPERIMENTAL

l,l-Diphenyl-l,2-dichloroethane (III) was obtained by the chlorination of l,l-diphenyl- ethylene; mp 52-53~ Found %: C 66.82; H 4.74; CI 28.31. C14H12CI 2. Calculated %: C 66.93; H 4.78; CI 28.28.

l,l-Diphenyl-l,2-dibromoethane (IV) was obtained by the bromination of l,l-diphenyl- ethylene [ii]; mp 62-63~ The dipole moments, Kerr constants, and Cotton-Mouton constants were measured in carbon tetrachloride at 25~ by analogy with [2, 3, 7] (Table i).

CONCLUSIONS

i. In carbon tetrachloride the molecules of l,l-diphenyl-l,2-dichloro- and l,l-diphenyl- 1,2-dibromoethanes coexist in the form of a mixture of rotational isomers with two-thirds of the form having the trans arrangement of the C-Hal bonds.

2. In both compounds one of the phenyl rings eclipses the ethane C-C bond, irrespective of the nature of the halogen and the mutual orientation of the C-Hal bonds; the second ring in the trans isomer is orthogonal to it, while in the gauche isomer it is close to eclipsing the geminal C-Hal bond.

LITERATURE CITED

i. S. G. Vul'fson, O. M. Dianova, V. E. Kataev, and A. N. Vereshchagin, Izv. Akad. Nauk SSSR. Ser. Khim., i00 (1987).

2. O. V. Osipov, V. I. Minkin, and A. D. Garnovskii, Manual of Dipole Moments [in Russian], Vysshaya Shkola, Moscow (1971).

3. A. N. Vereshchagin, Polarizability of Molecules [in Russian], Nauka, Moscow (1980).

2052

4. S. G. Vul'fson and O. M. Dianova, Izv. Akad. Nauk SSSR. Ser. Khim., 2269 (1984). 5. B. A. Arbuzov, S. G. Vul'fson, I. M. Khamatullina, and A. N. Vereshchagin, Izv. Akad.

Nauk SSSR. Ser. Khim., 2474 (1975). 6. B. A. Arbuzov, S. G. Vul'fson, A. N. Vereshchagin, and I. M. Khamatullina, Izv. Akad.

Nauk SSSR. Ser. Khim., 601 (1977). 7. S. G. Vul'fson, V. F. Nikolaev, and A. N. Vereshchagin, Izv. Akad. Nauk SSSR. Ser.

Khim., 2296 (1983). 8. V. G. Dashevskii, Conformational Analysis of Organic Molecules [in Russian], Khimiya,

Moscow (1982). 9. Interatomic Distances Supplement. Special Publication, Chemical Society, Burlington

House, London (1965), No. 18. i0. S. G. Vul'fson, O. M. Dianova, V. E. Kataev, and A. N. Vereshchagin, Izv. Akad. Nauk

SSSR. Ser. Khim., 1312 (1987). ii. P. Lipp, Chem. Ber., 56, 567 (1923).

ANISOTROPY OF MAGNETIC SUSCEPTIBILITY AND MOLAR COTTON-

MOUTON CONSTANTS OF SIX ANILINES AND 1,3,5-TRIMETHYL-

HEXAHYDRO-I,3,5-TRIAZINE

A. P. Timosheva, S. G. Vul'fson, I. A. Kushnikovskii, and A. N. Vereshchagin

UDC 541.67:547.551:547.87

The amino and dimethylamino groups are the most electron-donating substituents in the aromatic series, and the interaction between the dimethylamino group and the benzene ring is somewhat stronger than in unsubstituted aniline. Thus, the Hammett constant of the NMe 2 group is more negative than that of the NH 2 group [i]. Structural investigations have shown that the pyramid of the N atom in the dimethylaniline molecule is flattened, i.e., there is greater possibility for conjugation with the aromatic system [2, 3]. During investigation of the electric polarizability it was found that the mobility of the electrons along the b I axis (along the C-N bond) is higher than the additive value, decreasing accord- ingly in the direction perpendicular to the plane of the ring, and this is typical of di- methylaniline to a much greater degree [4].

It seemed of interest to see how the conjugation effects show up in the magnetic charac- teristics. Whereas donor-acceptor interactions show up fairly clearly in the electric polarizability characteristics (the mobility of the electron cloud along the chain of conjuga- tion increases with interaction of the conjugation effects), the corresponding pattern in the magnetic susceptibility is more complicated. The magnetic susceptibility of diamag- netic molecules consists of two parts, i.e., paramagnetic (kp) and diamagnetic (kd):

= + kp = - (ef/6mc )} + M B I J': i 12,/ J - - ( 1 )

The d i a m a g n e t i c component i s c h a r a c t e r i z e d by t h e a r e a o f t h e o r b i t a l in which t h e e l e c t r o n s move and by t h e number o f t h e s e e l e c t r o n s . The p a r a m a g n e t i c component i s d e t e r m i n e d by t h e mix ing o f t h e l o w - l y i n g u n o c c u p i e d l e v e l s ( J ' ) t h a t d i s t o r t t h e symmetry o f t h e m o l e c u l a r o r b i t a l s ( J ) in which t h e e l e c t r o n s c i r c u l a t e . The o v e r a l l m a g n e t i c s u s c e p t i b i l i t y (MS) i s d e t e r m i n e d by t h e b a l a n c e o f t h e s e q u a n t i t i e s , which a r e o p p o s i t e in s i g n . On t h e one hand, t h e i n c l u s i o n o f t h e u n s h a r e d p a i r o f t h e n i t r o g e n atom in t h e g e n e r a l c h a i n o f con- j u g a t i o n must i n c r e a s e t h e d i a m a g n e t i c c o n t r i b u t i o n , s i n c e t h e a r e a o f t h e o r b i t a l and t he number o f e l e c t r o n s i n c r e a s e and, on t h e o t h e r , t h e r e i s d i s t o r t i o n in t h e r i n g form o f t h e ~ - o r b i t a l , which must l e a d t o an i n c r e a s e in t h e p a r a m a g n e t i s m d i r e c t e d , a c c o r d i n g t o [ 5 ] , a l o n g t h e normal o f t h e a r o m a t i c r i n g .

A. E. Arbuzov Institute of Organic and Physical Chemistry, Kazan' Branch, Academy of Sciences of the USSR. Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. i0, pp. 2217-2221, October, 1987. Original article submitted March 3, 1986.

0568-5230/87/3610-2053512.50 �9 1988 Plenum Publishing Corporation 2053