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Crystal Structure and Molecular Structure of 3 5 8 10-Tetramethylaceheptylene.

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Crystal Structure and Molecular Structure of
3,5,8,1O-Tetramethylaceheptylene
By E. Carstensen-Oeser and G . Habermehl[*l [**I
3,5,8,1O-Tetramethylaceheptylene,C18H18 (f), a hydrocarbon with a 14 x electron system, was prepared by Hafner
et al."J and has been subjected t o quantum-mechanical
study [21. To test the quantum-mechanical conclusions about
molecular geometry we carried out an X-ray crystal structure
analysis.
ment was effected by further Fourier and difference Fourier
syntheses, as well as by the method of least squares. Finally
we reached an R factor of 7.6%. Anisotropic thermal
motion was taken into account for the carbon atoms in
these calculations.
The calculations show that the molecule is completely planar
except for the hydrogen atoms of the methyl groups. Bond
distances and bond angles can be read from Figures 1 and 2.
The values agree well with the bond lengths calculated for the
parent aceheptylene by Ali and Coulson[21 using the M O
method and by DasGrrpta and Alir2J using the Pople SCF
method. Coulson's relation [41 was used for calculations between bond order and bond length.
[ Z 792 IE]
Received: May 28, 1968
German version: Angew. Chem. 80, 564 (1968)
[*I Priv.-Doz. Dr. G. Habermehl and
3,5,8,10-Tetramethylaceheptyleneforms monoclinic crystals
from benzene but orthorhombic ones from light petroleum.
The lattice constants of the monoclinic modification are a =
8.43 i 0.03 A, b = 13.24 i 0.03 A, c = 12.44 i 0.03 A, p =
107.7 0.1 O. The space group is P 21/c; the unit cell contains four molecules. The orthorhombic form gave the following crystallographic results: a = 17.27 rt 0.03 A, b = 10.98
0.03 A, c = 7.00 i 0.03 A; space group Pna 21, with four
molecules in the unit cell.
We have first worked with the orthorhombic structure. Analysis of the monoclinic modification is in progress.
Measurement of the intensities of 865 symmetry-independent
reflections of the layers hk 0 t o hk 4 was carried out on an
automatic Weissenberg diffractometer with punched-tape
control, system Stoe-Guttinger. We determined the sign of 66
reflections by Sayre, Cochran, and Zachariasen's method [3J.
A Fourier synthesis with the E values of these 66 reflections
as coefficients could be interpreted unambiguously. Refine-
*
*
DipLIng. E. Carstensen-Oeser
Institut fur Organische Chemie und E. Zintl-Institut
fur Anorganische und Physikalische Chernie
der Technischen Hochschule
61 Darmstadt, Schlossgartenstr. 2 (Germany)
I**] We wish to thank DipLIng. 0. Ermer of the Organischchemisches Laboratorium der ETH Zurich for the program used
in the calculation of the E-values and the Deutsche Forschungsgemeinschaft for support of our work.
[l] K . Hafner and G. Hafner-Schneider, unpublished work.
[2] M . A. Ali and C.A. Coulson, Molecular Physics 4, 65 (1961);
N. K. DasGupfa and M . A. Ali, Theoret. chirn. Acta 4,101 (1966);
U.Miiller- Westerhoff, unpublished work.
[3] D . Sayre, Acta crystallogr. 5 , 60 (1952); W . Cochran, &id. 5 ,
65 (1952); W . H. Zachariasen, ibid. 5 , 68 (1952).
141 C. A. Coufson, Proc. Roy. SOC.(London) A 169,413 (1939).
The Absolute Configuration of (-)-thre5-2-Ethyl3-methylsuccinic Acid [*I
By H . Brockmann j r . and D . Muller-Enoch [*I
Fig. 1 . Bond distances in 3,5,8,10-tetramethyIaceheptylene;
niax. error,
iO.008 A
Fig. 2.
+ 10.
By comparison of the molar optical rotations of anhydrides of
mono- and di-alkyl-substituted succinic anhydrides the
( 2 R , 3R)-configuration was recently [ZJ assigned t o (+)threo-2-ethyl-3-methylsuccinic acid ( l ) , and thus the absolute configuration of bacteriochlorophyll was determined.
We have now proved the (28, 3s)-configuration of (-)threo-2-ethyl-3-methylsuccinic acid (2) by a chemical method,
in that we converted (2) by total reduction into (38)-(-)-2,3dimethylpentane (S), whose absolute configuration is
known [31.
(c = 2.5, in
Compound (2) [m.p. 66-68 O C , [a]'," = -17.8
water), corresponding to 68 % optical purity] was reduced by
lithium aluminum hydride in ether t o the diol (3). which was
converted by p-toluenesulfonyl chloride in pyridine at 0 "C
into the ditosylate ( 4 ) ; the yield was 53 % calculated o n (2).
Crystallization of (4) gave several fractions, withivarious
optical activities, [a]'," = -2.1 O to -2.9 ', and various melting
points (56 to 6OoC). A partly oily preparation with [a]',"=
-3.2' (c = 2.5, in chloroform) was used for further reduction. It was treated with lithium aluminum hydride in di-n-
Bond angles in 3,5,8,10-tetramethylaceheptylene;max. error,
Angew. Chem. internat. Edit. Yo!. 7 (1968) I No. 7
543
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