7. W. B. De More, H. O. Pritchard, and N. Davidson, J. Am. Chem. Soc., 81, 5874 (1959). 8. M. E. Jacox and D. E. Milligan, J. Am. Chem. Soc., 85, 278 (1963). 9. R. A. Moss and J. R. Przybelam, J. Org. Chem., 33, 3816 (1968); R. A. Moss, J. Org.

Chem., 31, 3296 (1966); R. A. Moss and C. M. Young, J. Am. Chem. Soc., 105, 5859 (1983).

10. T. Weil and M. Cais , J . Org. Chem., 28, 2472 (1963). 11. A. Ledwith andE. C. F r i e d r i c h , J . Chem. Soc . , 504 (1964). 12. A. I. D'yachenko, L. G. Menchikov, and O. M. Nefedov, Izv. Akad. Nauk SSSR, Ser. Khim.,

1664 (1984). 13. J. W. Russel, C. M. Phillips, and T. Davidson, Spectrochim. Acta, 37A, 263 (1981). 14. E. Wasserman, L. Barash, A. M. Trozzolo, et al., J. Am. Chem. Soc., 86, 2304 (!964). 15. R. A. Moss and W. M. Jones, Carbenes, Vol. 2, Wiley, New York (1975).

STUDY OF THE CONFORMATIONS OF SOME ~-HYDROXY

AND ~-METHOXY KETONES

E. Kh. Kazakova, G. R. Davletshina, and A. N. Vereshchagin

UDC 541.63:541.67:547.451.5:547.597

It was shown in a previous communication on the study of cyclic ~-methoxy ketones that in the specific hindrances in the system, the methoxy group is oriented "gauche" to the C-CO bond [i]. It was interesting to determine the conformational situation in the sterically maximally free acyclic analog, ~-methoxy ketone, and to follow the effect of substitution of MeO by HO on the conformation of the oxygen function and ring.

Fig. i.

ml<. i0 -12

2 5 0 -

2 0 0 -

~50 -

Me"c~O Me Me

T A ST

/ ~ sc(sa)

~'0 ~C/GG,

5 ~0 15 20 ~z

Conformation and graph of the dependence D 2 vs m K of methoxyacetone (I).

A. E. Arbuzov Institute of Organic and Physical Chemistry, Kazan Branch, Academy of Scii ences of the USSR. Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. I0, pp. 2208-2212, October, 1987. Original article submitted March 3, 1986.

0568-5230/87/3610-2045512.50 �9 1988 Plenum Publishing Corporation 2045

D 0,66 D

O ~fH ,4D O ,7D /i /

- - C - C / \ , \

H H l hie

Fig. 2. Conformation and direction of the DM in glycolaldehyde and hydroxyacetone (II).

(III) (IV)

I t ~ ~ ~ M e ~ ~ O Me OH

Half-chair

Me OH anti-sofa

o 0

Me OH syn-sofa

Fig. 3. Conformations of carane ketols.

TABLE 1 Additive Bond Parameters

Bond ~t, D BL B T (BV) Bond u, D BL BT (By)

C-C Me Me

\ / / \ C - - C

C cr* -C

0,00

0,00

0,00

0,98

2,3

0,66

0,27

2J7 (3,66)

0,41

C-O 0-H Cef-0 C=O

t,9 1,51 t118 2,96

0,89 0,95 0,89 2,36

0,46 0,49 0,46 1,39(0,25)

cr* -- cyclopropane ring.

~-Methoxy (I) and e-hydroxy (II) ketones and the structural analogs of previously in- vestigated methoxycaranones: $-ketol (Ill) and a-ketol (IV) were examined in the present study.

The methods of dipole moments (DM) and the Kerr effect were used for the conformational studies. The theoretical values of the measured values were calculated with the additive parameters reported in Table i. The results were analyzed by graphic comparison of the ob- served and calculated values in ccoordinates of p2 vs mK~

Conformation (I) is described by the angles of rotation around the C-C (6) and O-C (~). bonds. IR and UV spectroscopy showed that the population of cis- (S) and gauche-conformers (G) on the C-C bond in a nonpolar solvent (CCI~) is 3:7 with predominance of the G-conformers [2]. If we assume that in the S form the values of e = 0 are 120 ~ in the G form* and rota-

*Possible deviations from these values of !15 ~ do not change the conclusions of the analysis of the electrical and electrooptical characteristics.

2046

tion around the O-C bond is analyzed in terms of discrete conformations G, G', T, then it is convenient to compare the experimental and calculated values on a graph (Fig. i). The characteristic found is between the calculated value for the low-polarity GG! form and all of the remaining forms which are more polar (the first index refers to conformers at the C-C bond, and the second refers to conformers at the O-C bond). In considering the spec- troscopically found population at the C-C bond, it is possible to distinctly separate the conformer which participate in the equilibrium: GG' ~ SG (or SG').

The methyl group of the O-Me fragment is thus oriented in the direction of the C=O group in not only cyclic e-methoxy ketones [i], but also in acyclic ~-methoxyacetone, regardless of the conformational state at the C-<] bond.

An attempt was made to reproduce the experimental values for hydroxyacetone (II) with an analogous additive scheme of calculation of the DM and polarizability tensor. It is known that (II) exists in the unique H~bound conformation [3] and its closest homo!og, glycolalde- hyde, was studied by the method of microwave spectroscopy, and the planar structure and value and direction of the DM were determined [4]. The quantum mechanical calculation performed does not confirm the necessity of using the concept of a donor-acceptor H bond [5]. If we assume that the planar form is also realized for (II), the DM and its direction can be found by vector addition of the DM of glycolaldehydeand Csp2-CH 3 bond !-0.55 D). The value of 2.7 D obtained corresponds to the experimentally found value for (II~. However, the theoretical calculation with additive parameters (DM C-O 2.96, 2.8, or 2.7 D) gives neither the polarity nor the experimental value of the polarizability in any of the calculated conformations~

We found the vector difference between the DM obtained with the additive scheme and the DM calculated from the data for glycolaldehyde, which can be considered to correspond to the experimental value with respect to the magnitude and direction (Fig. 2)~ The value of the vector is 0.66 D, it is directed from H to the C-O group at an angle of 120 ~ to the O-H bond, and can be considered effective for the H bond. The introduction of this dipole in the cal- culation with ~ ~ 0 ~ to supplement the additive scheme of calculating the DM results in the coincidence of the experimental and calculated values of the DM and Kerr constants (KC).

In bicyclic ~-ketone (IiI), IR spectroscopy only revealed the H-bound form [6]. This limits the choice of the form of the 6-member ring to half-chair or sofa conformations in which the C-O bond has an equatorial orientation. At the same time, the experimental DM of (III) of 3.31D is higher than for hydroxyacetone, which indicates the absence of a totally flattened structure of the hydroxy ketone fragment in (III)o In calculating the DM and KC with the additive parameters in Table I, values closest to the experimental values are ob- tained for the syn-sofa conformation with angle ~ = 60 ~ (DM 3.64 D and m K = 218"10 -12 , mKexpt 174"10 -:2 ESU). The DM and KC were calculated for the half-chair and two sofa forms with equatorial orientation of the OH group with ~ = 0 ~ with incorporation of the correcting dipole of the H bond found above in the calculation. Relatively good agreement with the ex ~ perimental DM is attained, and with the KC for the anti-sofa conformation (DM 3.1 D, m K = 169"10 -12 ESU). The last structure is consequently the most probable one (Fig. 3).

As for (III), for ~-ketol (IV), the calculation of the electrical and electrooptical characteristics was performed for all possible forms of the ring (nine conformations) [i] and angles of rotation around the C-O bond (with a step of 30~ The experimentally found values are in agreement with the calculated values for the forms of the ring in which the O-C bond is axial, and the range of angles of rotation is ~ = • ~ . This is in good agree- ment with the data in [7], where the observed IR frequencies are either assigned to a bond with a cyclopropane ring or with the v electrons of a carbonyl group.

It is interesting to compare and generalize the results of studying the rotational iso- merism in compounds with possible stabilization due to a H bond (hydroxy ketones) and without it (methoxy ketones) [i].

A complete change in the conformational picture takes place in acetone derivatives (I) and (II): from a distinct cis,cis form in (II) to a predominant gauche;gauche form in (I). in going from B-ketol (III), where there is a H bond with a C=O group (equatorial OH) to the methyl ether (axial OMe), the picture also changes diametrically, which is manifested by as- sumption of the opposite half-chair or sofa conformations by the bicyclic systems. In ~- ketol (IV) and its methyl ether, the orientation of the C-~3 bonds is the same, axial, but the anti-bath form, i.e., different than in (IV), is proposed for the ring in the methyl ether.

2047

TABLE 2. Characteristics of the Compounds Studied

Compound bp, ~ n~ (p. mm Hg) d~o Literature

(~) (ii)

(III) (iv)

t t4-1t6 49-5t(15) 47-50(0,5)

66(0,5)

1,4295 i,4762 t,4840

0,9570 1,0824 0,990 0,990

[8] [8] [91 [lo]

TABLE 3. Coefficients of the Calculation Equations and Experi- mental Values of DM and KC

Compound a~o ~ j 6 ~, D m K' IO~' ESU

(i) (Ii)

(Ill) (IV)

30,19 42,45 27,56 t6,83

-0,396 -0,3t7 -0,375 -0,375

-0,0500 -0,0375

0,0t82 0,0235

122,74 t53,44 142,63 t50,42

2,41 2,71 3133 2148

78,91 82,37

t74,90 190,86

A change in the structure of the polar fragment and conformation of the rings is thus observed in hydroxy ketones in comparison to their methyl ethers. The additive scheme of calculation for describing the electrical properties of the molecules in the H-bound form is inadequate, and for this reason, it can be hypothesized that the H bond in hydroxy ketones is not exhausted by dipole-dipole stabilization alone.

EXPERIMENTAL

The compounds studied were prepared according to [8, 9] (Table 2).

The DM and KC were determined in CCI 4 at 25~ according to [8]. The coefficients of the calculation equations and experimental data are reported in Table 3.

CONCLUSIONS

Using the methods of dipole moments and the Kerr effect, it was found that the methoxy group in ~-methoxyacetone (regardless of the conformational state with respect to the C-C bond) is oriented in the direction of the carbonyl group. The orientation and conformation of the hydroxyl group in ~- and ~-hydroxy-4-caranones were determined and compared with the conformations of the corresponding methoxy derivatives.

LITERATURE CITED

I. E. Kh. Kazakova, G. R. Davletshina, G. A. Bakaleinik, and A. N. Vereshchagin, Izv. Akad. Nauk SSSR, Ser. Khim., 842 (1986).

2. S. A. Cuerrero, J. R. T. Barros, BI. Wladislow, et al., J. Chem. Soc., Perkin Trans. 2, 1053 (1983).

3. M. Oki, H. Jwamura, J. Ainara, and H. Jida, Bull. Chem. Soc. Japan, 41, 176 (1968). 4. K. M. Marstokk and H. M~!lendal, Mol. Struct., 16, 259 (1973). 5. H. H. Jensen, H. M~llendal, and E. W. Nilssen, Mol. Struct., 30, 145 (1976). 6. I. P. Povodyreva, Candidate Dissertation in Chemical Sciences, Kazan' (1973). 7. W. Reppe, Liebigs Ann. Chem., 596, 38 (1955). 8. A. N. Vereshchagin and L. A. Grozina, Teor. Eksp. Khim., i, 361 (1968). 9. M. S. Carson, W. Cocker, D. H. Crauson, and R. V. Shannon, J. Chem. Soc. C, 16, 2220

(1969). i0. H. Schmidt, P. Richter, and M. Muhlstadt, Chem. Ber., 96, 2636 (1963).

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