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Optically Active 2 2-Dimethylbiphenyl the Simplest Atropisomeric Hydrocarbon.

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cellulose (liquid phase: butan-1-ol/propan-1-ol/water=
1 : 1 :1 v/v). Dimeric uridine (RF = 0.13) appeared as third
fraction, after uridine and 5,6-dihydro-6-hydroxyuridine,
was obtained analytically pure: colorless crystals, m.p.
178-179 "C (from ethanol); Mol. wt. (cryoscopically and
osmometrically in water) 480 (calc. 488).
By degradation of the dimeric uridine (2) with concentrated
hydrochloric acid [80 mg (0.16 mmole) in 10 ml conc. HCI,
4 h reflux] and thin-layer chromatographic separation we
obtained uridine and uracil [fission of the cyclobutane ring
of (2)],as well as the dimeric uracil ( 3 ) of known structure[4]
(identified by comparison of I R data with data for a sample
of (3) prepared by UV irradiation of uracil; and by chromatographic data: thin-layer chromatography on silica gel
(n-propanol!water, 7 :3 viv) RF = 0.47, (n-butanollwater
(saturated)) RF = 0.18).
Since (3) is unchanged under the conditions used (as proved
by boiling a solution of ( 3 ) in conc. HCI for 4 h) the dimeric
uridine has structure (2).
Contrary to expectation, the irradiation of uridine in an
ice matrix leads to a dimer [51 in which the sugar residues are
oriented next t o one another.
Received: January 13th, 1967
[Z 415 IE]
German version: Angew. Chem. 79, 235 (1967)
[*I Prof. Dr. E. Fahr, cand. chem. G. Fiirst, Dr.
G . Dorhofer,
and cand. rer. nat. H. Popp
Institut fur Organische Chemie der Universitat
Rontgenring 11
87 Wurzburg (Germany)
[l] Part VIII of "Effect of Radiation o n Nucleic AcidComponents"; Part VII: 141.
[2] Cf. A. Wacker, D. Weinblurn, L. Trriger, and Z. H. Moustafa,
J. molecular Biol. 3, 790 (1961).
[3] Irradiation data: 10-2 mol. aqueous solution, frozen in a
layer of 1-2 mm, time of irradiation: 30 min, distance from the
UV source: 5 cm.
141 G . Dorhofer and E. Fuhr, Tetrahedron Letters 1966, 4511;
where further references are given.
IS] Four isomeric dimers are possible; see D. L. Wui@ and
G. Fruenkel, Biochim. biophysica Acta 51, 332 (1964).
Optically Active 2,2'-DimethylbiphenyI,
the Simplest Atropisomeric Hydrocarbon
For the preparation of optically active 2,2'-dimethylbiphenyl
we therefore started from optically stable (+)- or (-)-2,2'-dimethylbiphenyl-6,6'-diamine [31 (2). We diazotized this in
hydrochloric acid solution a t -10 "C and deaminated it with
hypophosphorous acid and copper(1) oxide/copper(tr) sulfate
at approximately -35 "C. The solution was extracted with
isobutene at -50 " C , the extract poured through aluminum
oxide at -50 "C, and the isobutene evaporated at -78 "C.
The optically active 2,2'-dimethylbipheny1(3) obtained in this
way was dissolved in dimethylformamide at -55 OC, and the
optical rotation of this solution was measured after various
times at temperatures between -30 "C and -36 "C.
The following data were obtained for the racemization:
1 -35.46 1 -34.42 I -33.04 1 -32.28 1 -30.94
kra,x 103 Is-11
EA = 15.1 f 0.4 kcal mole-1; A H * = 14.6 i 0.4 kcal mole-1;
AS* = -11.6 : 1.8 cal mole-1 deg-1 (calc. for inversion);
AG* = 17.4 kcal mole-1 at -35 " C ,18.1 kcal mole-' at + 25 ".
The half-reaction time for racemization at -32 O C is 7 min;
that calculated for +25 O C is 1.1 sec.
Since the absolute configuration of (2) is knownf41 and
configuration is not reversed on deamination, the absolute
configuration of (3) is also established. (+)-(2) ([a];:: =
+ 53.8'; c = 1.13; ethanol) receives the chirality symbol
( R ) 191; the (-)-form of (3) (maximum value: [a];:: = -26 O ;
c = 2.7, dimethylformamide) resulting therefrom receives
the same chirality symbol.
Received: January 13th, 1967
[Z 416 IE]
German version: Angew. Chem. 79, 232 (1967)
[ * ] Prof. Dr. W. Theilacker and Dip1.-Chem. H. Bohm
Institut fur organische Chemie der Technischen Hochschule
Callinstr. 46
3 Hannover (Germany)
[l] W.Theilacker and R. Hopp, Chem. Ber. 92, 2293 (1959);
R . Hopp, Dissertation, Technische Hochschule Hannover, 1961.
[2] W. Theilacker and R. Hopp, unpublished.
[3] J. Meisenheirner and M . Horing, Ber. dtsch. chem. Ges. 60,
1425 (1927).
141 F. A. McGinn, A . K . Lazarus, M . Siegel, J. E. Ricci, and
K. Mislow, J. Amer. chem. SOC.80, 476 (1958).
151 R . S.Cuhn, C. K . Ingold, and V. Prelog, Angew. Chem. 78,
413 (1966); Angew. Chem. internat. Edit. 5, 385 (1966).
By W.Theilacker and Horst Bohm [*I
2,2',3,3'-Tetramethylbenzidine (la) can be obtained relatively
easily in optically active form [I], and optically active
2,2',3,3'-tetramethylbiphenyl ( I b ) can be obtained from it by
deamination [21. Both compounds have considerable optical
stability although the atropisomerism is caused only by two
relatively small ortho-substituents in the biphenyl molecule.
This stability is caused on the one hand by the support
x x
(buttressing effect) given by the methyl groups in the 3,3'positions to the 2,2'-substituents and o n the other to the fact
that these compounds have a relatively large negative
racemization entropy. If the buttressing substituents are
removed, the optical stability decreases appreciably; earlier
unsuccessful attempts to obtain optically active 2,2'-dimethylbenzidine confirmed this.
Angew. Chem. internat. Edit.
Vol. 6 (1967)
No. 3
Anion Radicals from 1-Nitroolefins
By A . Berndt [*I
Independently of recent papers 21 concerning radicals of
unproved or, in the light of our results, incorrectly assigned
structure 121, that were formed o n reduction of I-nitroalkenes,
we have studied electrolytic one-electron reduction [31 of
substituted I-nitroalkenes ( I ) in acetonitrile. We have thus
obtained the first anion radicals from 1-nitroolefins that have
been conclusively characterized as radicals of type (2) by
electron spin resonance (ESR) spectra (41. The radicals were
generated at a platinum cathode in acetonitrile containing
10-3 mole/l of ( I ) and 10-1 rnole/l tetra-n-propylammonium
perchlorate as supporting electrolyte, within the ESR spectrometer cavity.
The lifetimes of the new radicals lie between a few minutes
and some hours, according to the substituents, the nature
of R1 being of little influence. Substituents R* and R3 that
25 1
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optically, simplest, hydrocarbonic, activ, atropisomerism, dimethylbiphenyl
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