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Conformations of ortho-Disubstituted Aniline and Toluene Derivatives. Proton Magnetic Resonance and Semiempirical Energy Calculation

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plane of the dienyl carbon atoms, is not consistent with the
N M R data[9,111.
Received: July 20, 1970
[Z 263 IEI
German version: Angew. Chem. 82, 838 (1970)
gies. Compounds of types ( I ) and (2) are suited to experimental study of the possible conformers because their
lifetimes are especially long. Such rotamers have been
[*] Doz. Dr. G . E. Herberich, Dip].-Chem. G. Greiss, and
Dip1.-Chem. H. F. Heil
Anorganisch-chemisches Laboratorium
der Technischen Hochschule
8 Miinchen 2, Arcisstrasse 21 (Germany)
[**I This work was supported by the Deutsche Forschungsgemeinschaft.
[lI S . Katz, J . F. Weiher, and A . F. Voigt,J. Amer. Chem. SOC.
80, 6459 (1958); M . L . H . Green, L . Pratt, and G. Wilkinson,
J. Chem. SOC.1959, 3753.
[2] G. E. Herberich and E . Bauer, J. Organometal. Chem. 16,
301 (1969); G . E . Herberich, E . Bauer, and J . Schwarzer, ibid.
17, 445 (1969).
[3] G . E . Herberich and J . Schwarzer, Angew. Chem. 81, 153
(1969); Angew. Chem. internat. Edit. 8, 143 (1969).
[4] G. E. Herberich and J . Schwarzer, Chem. Ber. 103, 2016
( 1 970); G . E. Herberich, G . Creifi, and H . F. Heil, J. Organometal.
Chem. 22, 723 (1970).
151 H . Noth and H . Vahrenkamp, J . Organometal. Chem. 11,
399 (1968).
[6] Presumably of the intermediate ( 5 ) . which has not yet
been isolated on account of its extreme sensitivity.
[7] Measurements by Dip1.-Chem. Schmidt-Sudhoff, Universitat Munchen. We thank Dr. H . Noth for his valuable suggestions.
[8] X-ray structure analysis ought to provide direct proof of
such a structure. Measurements are at present being carried
out on CO(C~HSBOCH&;G. Huttner and B. Krieg, unpublished.
[9] Cf: M . L . Maddox, S . L . Stafford, and H. D . Kaesz, Advan.
Organometal. Chem. 3, 1 (1965); J. W. Emsky, J . Feeney, and
L . H . Sutcliffe: High Resolution Nuclear Magnetic Resonance
Spectroscopy, Vol. 2, Pergamon Press, London 1968.
[lo] P . H . Bird and M . R . Churchill, Chem. Commun. 1967,
777; M . R . ChurchiII and F. R . Scholer, Inorg. Chem. 8, 1950
(1969).
[ l l ] For such a structure having tricovalent boron an I l B resonance would be expected at 8 = -50 to -80ppm; the
signals of the dienyl protons should appear in the range T = 2.5
to 6.0; cf. [3,9].
Conformations of ortho-Disubstituted Aniline and
Toluene Derivatives. Proton Magnetic
Resonance and Semiempirical Energy
Calculation[1l [**I
By Albrecht Mannschreck, Ludger Ernst, and Elmar Keck [*I
Compared to the situation at sp3-sp3 and sp2-sp2 valences,
little is known about the conformations resulting from
rotation about spz-sp3 bonds o r about their relative ener-
R'
Kt
I
described for N,N-dibenzylanilinium ions ( 1 ) (21 and for
9-arylfluorenes 131, which may be regarded as toluene
derivatives (2). I t has repeatedly been suggested 12-61 that
those conformations are most favored in which the proton
a t the sp3 center eclipses a n ortho substituent. This assumption is now strongly supported by semiempirical energy
calculations on toluenes (2) for which we also determined,
for the first time, the most unfavorable conformation, i.e.
the transition state of the sp2-sp3 rotation. Moreover our
calculations reproduce the rotamer equilibria which we
were able to measure for the structurally simple toluenes
( 5 ) and ( 6 ) and for the isoelectronic N,N-dimethylanilinium
ions ( 3 ) and ( 4 ) .
Reaction of 6-chloro-2-methylaniline and 6-bromo-2,4dimethylaniline, respectively, with dimethyl sulfate yielded
the corresponding N , N-dimethyl compounds (b.p. 84-85 "C/
1 2 torr, n g 1.5248, and b.p. 65-67 "Cj0.001 torr, n g 1.5433,
resp.) which o n dissolution in CF3C02H gave the anilinium
ions (3) and ( 4 ) . We obtained ( 5 ) from 5-chloro-1,3dimethylbenzene and isopropanol/H2S04; after purification
by G L C the sample of ( 5 ) still contained 5 % of 5-chloro1,3-dimethyl-2-isopropylbenzene.Bromination of 4-nitro2-methyl-l-isopropylbenzene[7l in the presence of
Ag~SO4/H$304 yielded ( 6 ) which, after separation by
GLC, was still contaminated by 25 % of 5-bromo-4-nitro2-methyl-1-isopropylbenzene (m.p. 50-52 "C). The absorptions of this by-product, however, did not interfere
with those of (6).
For ( 3 ) and ( 4 ) in CF3C02H a t +27 'C as well as for ( 5 )
and (6) in CS2 a t -55 "C we found two sets of I H - N M R
signals which are due to rotamers ( E ) and ( Z ) (Table) and
coalesce upon raising the temperature [*I. The assignment
of signals t o rotamers will be explained for the case of
( E ) - ( 5 ) and ( Z ) - ( 5 ) .The a-CH septet a t T = 6.69 (CH) is
due to isomer ( Z ) - ( 5 ) where the methine proton and the
ortho methyl group experience the same environment as
in the symmetrical toluene (7) showing 7 = 6.81 (CH)
(CS2, -60 "C)[51. In ( E ) - ( 5 ) ,however, the methine proton
is adjacent t o the chlorine atom, which causes a deshielding
through space and shifts the a-CH resonance to T = 6.18
(CH) (septet). The a-methyl protons of ( E ) - ( 5 ) and ( Z ) - ( 5 )
give rise to doublets a t T = 8.74 and 8.65, respectively,
which were correlated in the same way.
The energy E of a conformation was calculated by addition
of the following partial energies [Sl: a) stretching energy
+ 27°C)
Table. Rotamer percentages P and chemical shifts T in mihiurn-ions (X=N@, CF~COZH,
and toluenes (X=C, CS2, -55'C) as determined by 'H-NMR.
1
-(5)
(6)
C
C
NO2
54
6.74
6.58
6.65
8.50
1
7.72
7.42
8
[a] Doublets by coupling with the NH-proton ( J = 5 Hz) of the anilinium ions (X-NO) and with the
CH-proton (J = 7 Hz) of the toluene derivatives (X=C), resp.
806
Angew. Chem. internat. Edit. / Vol. 9 (1970)
/ No.
10
of the bond between the a-C atom a n d the benzene ring;
b) bending energy of the angles at the a-C atom a n d the
angles formed by the bonds of the ortho substituents and the
7 =
8.74
7.63
= 8.65
H
6.81
Me 7.82
C-C bonds of the benzene ring; c) nonbonded interactions 191 between each ortho substituent and the neighboring meta proton o n the one hand a n d the three a-substituents CH3, CH3, and H o n the other. The specific
geometry of a conformation was found by varying the
C-aryl bond length a n d the above mentioned angles in
small steps and by calculating the energies of all resulting
combinations. The lowest energy combination was regarded
as representing the geometry of that conformation.
[**I This work was supported by the Deutsche Forschungsgemeinschaft and the Fonds der Chemischen Industrie.
[ l ] Part 7 of the series “Protonenresonanz-Untersuchungen
zur inneren Rotation”. - Part 6: A . Jaeschke, H . Miinsch,
H . G. Schmid, H . Friebolin, and A . Mannschreck, I. Mol.
Spectrosc. 31, 14 (1969).
[ 2 ] A . Mannschreck and H. Mnnsch, Tetrahedron Lett. 1968,
3227.
[3] T . H . Siddall, IIIand W . E. Stewart, J. Org. Chem. 34, 233
(1969); K . D . Bartle, P . M . G. Bnvin, D . W. Jones, and R .
L’Amie, Tetrahedron 26, 911 (1970). See also R . D. Chambers,
J . A . Jackson, W. K . R . Miisgrave, L . H . Sutcliffe,and G . J . T .
Tiddy, ibid. 26, 71 (1970).
[4] P . C . Myhre, J . W . Edmonds, and J . D . Kruger, J. Amer.
Chem. SOC.88, 2459 (1966); E. A. Chandros and C . F. Sheley j r . ,
ibid. 90, 4345 (1968); H. Kessler, A . Moosmayer, and A . Rieker,
Tetrahedron 25, 287 (1969).
[5] Cf. A . Mannschreck and L . Ernst, Tetrahedron Lett. 1968,
5939; Chem. Ber., submitted.
[6] Cf. B. J . Fuhr, B. W . Goodwin, H . M . Hutton, and T . Schaefer, Can. J. Chem. 48, 1558 (1970).
[7] M.p. 33-34 “C. Prepared by NaBH4 reduction of 4-nitro2-chloromethyl-1-isopropylbenzene in dimethyl sulfoxide.
[8] Review: J . E . Williams, P . J . Stang, and P . v. R . Schleyer,
Annu. Rev. Phys. Chem. 19, 531 (1968).
[9] H. A . Scheraga, Advan. Phys. Org. Chem. 6, 103 (1968).
“Single Vessel Reaction” for the Synthesis of
Various Types of Substituted Phosphanes PR1R2R3
By Max Schmidt and Wolf-Ruiner Neeff [*I
i 7cl
17.6
I1
,
l
, ..... Me
M e ....
H,C
CH,
(7dl
21.6 k c a l / m o l e
T h u s for n,a,2,4,6-pentamethyltoluene (7) we found that
conformation (7a) indeed shows the lowest energy. Compared t o ( 7 a ) , ( 7 b ) is destabilized both by additional bond
angle deformations and by a more unfavorable Me/CH3
interaction. As shown by our calculation, this Me/CH3
interaction (dihedral angle 0 ”) is less repulsive in (7c) than
the corresponding interaction via ca. 30 in ( 7 d ) which has
t o be counted twice. The transition state of the spz-sp3
rotation is thus represented by (7d). We obtained analogous results for a,a,2,4,6-pentachlorotoluene
[61 a s well
a s for ( 5 ) a n d ( 6 ) .
The calculation for these two toluene derivatives yielded
energy differences between the ( E ) - and (2)-rotamers. From
these differences we obtained (with A S = 0) rotamer
equilibria (33 % ( E ) - ( S ) and 50 % ( E ) - ( 6 ) , resp.) which
agree fairly well with the N M R results (Table). As t o the
corresponding anilinium ions ( 3 ) and ( 4 ) , their (,??)-isomers
are somewhat more favorable (Table) than ( E ) - ( 5 ) and
( E ) - f 6 ) . This is perhaps due t o weak intramolecular
hydrogen bonds N - H . . . Y in ( E ) - ( 3 ) and ( E ) - ( 4 ) which,
however, have still t o be proved.
Received: July 30. 1970
[ Z 266 IE]
German version: Angew. Chem. 82, 840 (1970)
[*I Priv.-Doz. Dr. A. Mannschreck, Dipl.-Chem. L. Ernst, and
Dip1.-Chem. E. Keck
Institut fur Organische Chemie der Universitat
69 Heidelberg, Im Neuenheimer Feld 7 (Germany)
Angew. Chem. infernat. Edit.
1 Yol. 9 (1970) / No. 10
lssleih and Krech (11 have recently investigated the nucleophilic cleavage of “phenylphosphorus” with phenyllithium
and, on the basis of their findings, quite justifiably postulated the existence of a n analogy between elemental sulfur
(--S-)x,
and cyclopolyphosphanes (-PR-)x.
Such a
working hypothesis served as a starting point for investigations which we have been carrying o u t for some time
now [2J on the degradation reactions of cyclopolyphosphanes with Lewis bases as a parallel t o the many examples
already known in the case of s u l f u r W According t o this
hypothesis one would expect the cyclic phosphanes (RP),
to react with organolithium compounds as follows:
T h e lithium phosphides then formed could react with
organohalides according to:
LiPRIRz -C R3X
+ LIX
+ PRIR2R3
In fact we have been able t o show that various types of
organophosphanes can be prepared quite easily, and in
manageable yields according t o this principle in a “single
vessel reaction” with exclusion of air and moisture, if solutions of a n organolithium compound LiR2 and a n organochloride R3Cl a r e added simultaneously t o a solution of
cyclopolyphosphane (RIP),:
+ n LiR2+
n R3CI
+ n PRIRzR3+
N
LiCl
T h e phosphanes thus obtained react as expected with
methyl iodide t o give the corresponding phosphonium
salts (with R1, R2, and R3 CH3, completely unsymmetrical). If triorgano-silyl, -germyl, or -stannyl chlorides are
used instead of RCI the analogous phosphanes containing
P-Si, P-Ge, or P-Sn bonds respectively a r e obtained.
+
Obvious side reactions, which lower the yields of the mononuclear phosphanes (some of which - depending o n the
substituents a r e difficult t o handle and occasionally ignite
807
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conformational, toluene, aniline, calculations, magnetic, disubstituted, energy, proto, resonance, semiempirical, derivatives, ortho
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