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The Structure of Triaminoazacyclobutadiene.

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amino group migrates in an open-chain intermediate. Compounds (3), (5), and (probably) (6) can be excluded
because of the red color.
2. I R spectra: V ~ of(i)
=
~151ocm-1 (cH,c~,), 1520cm-'
(SO,); v C r N of (CH,),N--CN: 2206 in both solvents.
From the red solution new bands appear at 1630cm-'
(CHzCI,) or 1652cm-' (SO,). The structures ( 3 ) , (4),
(51,and (6) are thus excluded: aminoazirines comparable
] ; (5)
with ( 4 ) have a C=N band a t ' 1 7 6 0 ~ m - ' ~ ' ~from
one would expect a C r N band at 2190 cm-' (cf. [15,
16]), and for ( 6 ) , as a ketene imine derivative["], a band
at 2000cm-'. Of the structures proposed the only one
remaining is thus (2) (in 2-alkoxyazetine~['~]
vC=N has
been observed at 1620cm-').-The
band at 1630cm-'
is not to be found in the IR spectrum of a pyrolyzate
solution that has been kept for 2 days at room temperature,
is colorless, and no longer shows an ion of m/e= 182
in the mass spectrum.
3. U Vspectra: The UV spectrum of a methylene chloride
solution of the pyrolyzate, measured at -40 C, shows
an intense absorption maximum at 527 nm with ~-2OO00
[ C I ): h,,, = 352 nm]. The disappearance of this maximum
at 3 0 C follows second order kinetics with a half-life of
56 min (initial absorption 1.100 OD). From theoretical
consideration^^'^^ a maximum would be expected for (2)
at 670nm; one would predict shorter-wave absorptions
for the other structures considered.
4. N M R spectra: The 'H-NMR spectra of the pyrolyzate
in mixtures of CH2CI2 and CD2Cll show signals in the
range 6 = 2.5-3.5 ppm. Singlets at 6 = 2.75 and 2.9 ppm
can beassigned to the triazine ( I ) , and a singlet at 2.85 ppm
to dimethylcyanamide. A 60 MHz 'H-NMR spectrum,
measured at -60'C, shows, besides these signals, two
singlets at 6=3.22 and 2.94ppm. An intensity ratio of
1 :2 can be found from the 220MHz spectrum. If the
sample in the spectrometer is allowed to warm up to
room temperature these two singlets disappear simultaneously, being no longer present after ca. 12h, whilst
at the same time new signals appear at 6=2.31 and
3.35ppm; the solution then has only an extremely faint
red color.
As in the 'H-NMR spectrum, so in the 13C-NMR spectrum
two new signals arise, at 138.29 and 128.28ppm (relative
to TMS); these can be assigned to olefinic C atoms.
According to the conditions of the pyrolysis and working
up, further signals of lower intensity can be observed in
the 'H-NMR spectra of the pyrolyzate; some of them
decrease in intensity with increasing temperature.
The following properties can thus be assigned to the red
compound in the pyrolyzate solution: molecular weight
182; UV:h,,,=527
nm ( ~ ~ 2 0 0 0 0I)R; : vC=N=1630
cm-'; 'H-NMR: singlets at 6=3.22 and 2.94 ppm (1 :2).
Thence we conclude that tris(dimethy1amino)azacyclobutadiene (2) is formed on pyrolysis of ( I ). From the 'H-NMR
spectrum the yield can be estimated as approximately
30 Yo.
The relatively high thermal stability and the NMR spectra
of the product indicate that (2) should be described as
the resonance hybrid ( 7 a ) - ( 7 d ) , where especial irnpor-
RzNGNRz
0
R 2 N g R 2 - R 2 N E N R 2
R?N
7 ci:
K
=
848
CH,
R2n'
17b)
R2N
( 7 ~ j
0
RzN$NR2
(81
R2N
5. Chemical behavior: Experiments inwhich (2) was treated
with methyl iodide, tetracyanoethylene, acetylenedicarboxylic ester, phenyl isothiocyanate, tosyl isocyanate, or
Fe(COj5 led to inseparable mixtures of products. The difficulties in working up were partly due to the fact that
the triazine ( I ) , which is present in the pyrolyzate in
excess of (2) (>40%), reacts with electrophiles to give
deeply colored, as yet unidentified
Protonation of (2) also seems to take a complicated course.
Received: June 22, 1973 [Z 886a IE]
German version: Angew. Chem. 85, 918 (1973)
[ I ] M . J . S. Dewar, M . C. Kohn, and N . Trinujst~i,J. Amer. Chem.
SOC.93, 3437 (1971).
[ 2 ] M . J . S. Dewar and N . Trinujstii. Theor. Chim. Acta 17, 235 (1970).
[3] R. Hoffann, Chem. Commun. 1969, 240.
[4] Th. Curtius and K . Thun, J. Prakt. Chem. 44, 175 (1891).
[ 5 ] M . Or.starreich, Ber. Dtsch. Chem. Ges. 30, 2255 (1897).
[6] E. Ahderhalden and M . Puyuin, Ber. Dtsch. Chem. Ges. 53, 1129
( 1920).
[7] L. A. Paquertr. T Kakihuna, and J . F. Kelly, J. Org. Chem. 36,
435 (1971)
[8] E. A. Chandross and G. Smolinsky, Tetrahedron Lett. 1960, 19.
[9] G. L. Closs and A. M. Harrison, J. Org. Chem. 37, 1051 (1972).
[lo] B M . Adyer. M . Krating, C. 19: Rees, and R. C. Storr, J. C. S .
Chem. Commun. 1973, 19.
[I I ] R. Gompprr and G. Srpbold, Angew. Chem. KO, 804 (1968): Angew.
Chem. internat. Edit. 7 , 824 (1968).
[I21 Cf. [8, 91 and H. Neunhoeffer, H.-D. Vdtter. and H . Oh/, Chem.
Ber. 105, 3695 (1972).
1131 R. Gomppcr. U . Jersak, and K . Schiinafnger, unpublished results.
[I41 M . Rens and L. Ghost-, Tetrahedron Lett. 1970, 3765.
[15] R . Gompprr, E . Kutter, and W Tiipfl, Chem. Ber. 95, 2871 (1962).
[16] R . Kunz, Dissertation, Technische Hochschule Stuttgart 1964, p. 28
1171 C. L. St<W!7,Sand J . C. French, J. Amer. Chem. Soc. 75, 658 (1953).
[I81 G. Pfleri, P. Cousonni, G. Prlrzzn, and E. Tesfa, J . Heterocycl.
Chem. 4, 619 (1967).
[ 191 H.-U. Wagner, Angew. Chem. 85,920 ( I 973), Angew. Chem. internat.
Edit. 12, 848 (1973).
1201 H.Q U U S ~ ,E. Schmirt, and R. Frank, Angew. Chem. 83, 728 (1971);
Angew. Chem. internat. Edit. 10, 651 (1971).
The Structure of Triaminoazacyclobutadiene[**]
By Hans-Ulrich Wagner"]
Cyclobutadiene ( 1 ) is antiaromatic; it can be stabilized
by push-pull substitution''? Substitution as in compounds
of type (2) has been found especially advantageous in
this respect12].Analogously, azacyclobutadiene ( 3 ) , which
0
-R2N@NR2
c)
tance attaches to the structure ( 7 d ) [ " J . Provisionally the
possibility cannot be excluded that the product has one
of the angular structures derived from (7d), e.y. (a),
although the IR spectrum contraindicates this (cyclopropanimine has C=N bands at 1 7 7 0 ~ m - ' [ ~ ~ ~ ) .
R2N
( 7~1)
[*] Dr.
Institut
H -U.
furWagner
Orgdnische Chemie der Universitdt
8 Munchen 2. Karlstrasse 23 (Germany)
[**I This work was supported by the Deiitcche For~chunesgemeinschaft.
We are particularly grateful to the Leibniz-Rechenzentrum of the Bayrische Akademie der Wissenschaften.
Anyew. Chem. internat. Edit. 1 Vol. 12 ( 1 9 7 3 ) / No. 10
is energetically favored in comparison with ( I ) by introduction of the ring-nitrogen that acts as acceptor, can
be further stabilized by two donor groups at positions
2 and 4 [see (4)].
From this point of view a third donor group, as in ( 5 ) ,
has an unfavorable effect. Introducing a donor group at
position 3 relative to the acceptor position, as in ( 6 ) ,
however. causes distortion of the ring to a rhombus[3'
by increasing the bonding interaction and bringing positions 2 and 4 closer together.
COOR
2
6
i 2)
1)
P13 = O P24 =
0
N
R,NQ,,,
.
O-
C OOR
-0.40
+0.29
+0.46
NRZ
R2N& N
NIZz
(4)
(31
-0.16
Lt2NN
dkNR2
( 5)
x
N
(61
p13 = -0.35
-0.34
-0.39
pZ4 = +0.25
+0.35
+0.51
The transannular interaction of atoms at opposite corners
of the four-membered ring can certainly no longer be
neglected since thedistance between them of approximately
2 A comes in the region of normal bond lengths. The
energy change including the effect of the diagonal interaction can be estimated to a first approximation from the
bond orders in the H M O scheme (see the values under
the
Even in the push-pull-stabilized cyclobutadiene (2) closer
approach of centers 2 and 4 und further separation of
centers 1 and 3 should bring an increase in energy. As
shown by X-ray structure analysis[51of ( 2 ) the measured
angles (1-2-3
=93, 263-4= 87") and bond lengths
(2-4=2.00,1-3=2.11
A)indicate that the four-membered
ring is in fact distorted to a rhombus[61.
Although such a distortion does not lead to an energy
gain in unsubstituted cyclobutadiene ( I )['I, considerable
stabilization is to be expected for (3) in view of the bond
orders shown. In the language of resonance theory this
distortion favors the polar resonance structure ( 7).
In (7) it can be clearly seen how introducing a donor
group at position 3 buttresses the transannular interaction
between centers 2 and 4 by stabilizing the positive charge
[resonance structure (8)]. This effect can also be deduced
from the changes in H M O bond orders on going from
(3) to ( 6 ) and from (4) to ( 5 ) .
The unstable red product of molecular formula C9HL8N4
obtained on flash pyrolysis of 4,5,6-tris(dimethylamino)1,2,3-triazine (9u)['] can have one of the structures ( I O U )
to (15 a). To aid clarification of the structure the electronic
spectra to be expected for ( 1 0 ) to (15) were calculated
Aiigew.
Chem. intrmaf. Edif. 1 Vol. 12 (1973) / N o . 10
by a CNDO-Cl procedure[9] (Table I); but since it can
be assumed that the methyl groups have no appreciable
influence on the chrornophore of the red compound, the
CH3 groups were replaced by H for the calculations["'].
Table I . Calculated wavelengths of the longest-wave electronic transitions
for various structures C3H6N4(CoH,,NI).
__
Structure
L [nm]
(9hi
386
flOhl
670
f1lhl
737
f l 2 h ) f13hi
194
393
f14h)
282
-
fljh)
440
In hexane solution the longest-wave absorption maximum
for the triazine ( 9 u ) that was used as reference molecule
appears at 352 nm'"]. The calculated value is shifted to
longer wavelength from the experimental value['21.With
this trend in mind it is clear from Table 1 that the red
compound in question (k$y:c'2= 527 nm) can have only
structure (10) or ( I 1).
The structures ( 1 0 ) and ( 1I ) are topologically closely
related. On minimization of the energy of ( 1 0 ) and ( I I )
with respect to ull the coordinates by the MINDO/2 proced ~ r e [ ' ~the
' , most favorable structure with topology close
to that of (10) is found to be a symmetrical planar fourmembered ring with strongly distorted diagonal distances
as required by the considerations above (1-3 =2.07, 2 to
4 = 1.84A) but approximately equal lengths for the sides:
Minimization starting from the geometry of the less stable
structure ( I 1 ) discloses a tendency towards planarity, giving a planar rhombus (10). A planar structure ( 1 0 ) with
localized single and double bonds is also energetically
less favorable than a symmetrical delocalized structure.
Bond fixation of the second order appears to play no part
in (1o)[l41.
According to these results the unstable red compound
should have structure (10),as assigned also from the
physical data[''. However, the MIND0/2 calculation gives
Q
an astonishingly low bond index of 0.962 for the C=NH,
849
Specific Heat and Formation of Kinks in Bimolecular
Films of Long-Chain n-Alkyl Compoundsr**]
By Go.htrrr/ L L I < / LSfr,p/itrri
I/~..
Fir:. and 4rn7ir7 W,r.ss[*]
bond of (11 h ) ;comparing this value with the bond indices
of 1.507 for ( 1 6 ) and 1.537 for ( 1 7 ) shows that the IR
wave number of the C=N stretching vibration of ( 1 1 )
is not necessarily so high as for (16) and ( 1 7 ) .
Received: June 28. 1973 [ Z 886b IE]
German verslon: Angew. Chem. X5, 920 (1973)
[ I J J . D. Rohwrrs, cited in J. Chem. Soc. Spec. Publ. No. 12, I I I (1958).
[2] R. Gonipper and G. Seyhold, Angew. Chem. 80, 804 (1968): Angew.
Chem. internat. Edit. 7. 824 ( 1968); M. Nt,iirn.s~h~,urider
and A. NirdcrIiuirirr. Helv. Chim. Acta 53, 519 (1970); R. Hofiiiuiin, Chem. Commun.
1969. 240.
Alkyl chains may change their conformation via rotation
about C-C bonds. Among these isomerizations, the simultaneously occurring transformation of two trans bonds
(t) into +gauche (8) and -gauche bonds (g), for example
...ttt ... + ...gtg ... or ...ttttt ... + ...gtttg ... etc., appears to
be important in crystalline, paracrystalline, or partially
crystalline compounds. In these cases the two parts of
chain beyond the ...gt _..S... conformation remain parallel
to each other.
Conformations arising in this way were termed “kinks” by
Pechhold’! They have been discussed as structural elements in polymersE2];their formation and rearrangement
were assigned to definite relaxation regions (cf. e. g. Ref. [31).
n
l!j
v
H
6,
ttttt tttt t it
a l l - trans
tttgtttttttt
tttqtqtttttt
isolated
gauche -bond
igi- kinks
M
2s 1
tttgtgtgtttt
3 9 2 - kmks
26,
tttgtttgtttt
292-kinks
3 6:
tttgtttttgtt
293 -kinks
[28871/
Fig. I . Conformations of alkyl chains with isolated g u d 7 e bonds and kinks (6,= 1.78, 6,= 1.27, 6;= 1.27 A).
[3] If the lengths of the C-N
form corrcsponds t o a kite.
and C-C sides are different, the distorted
[4] F o r summands of the first order 6t=2pp,,Ppv: cf E. Nrilhroriricr
and H. Boc h . Das HMO-Model1 und seine Anwendung. Verlag Chemie,
Weinheim 1968, p. 146.
[ S ] H. J . L i ~ l t i ~ ,and
r
5 . roii Grus\, Angew. Chem. X3, 489 (1971);
Angew. Chem. internat. Edit. 111, 490 (1971).
[6] T h e antibonding interaction in the cyclobutadiene ( 2 ) is further
diminished by the facts that the acceptor substituents d o not lie in
the plane ofthe ring and that 2- -4 overlap is thus reduced by transhybridization.
[7] In alternant hydrocarbons all bond orders to second nearest neighbors are zero
dd. U . J m a h . and R. &mpp<,r, Angew. Chem. X i , 918 (1973);
m. internat. Edit. I?. 847 11973).
[Y] R. L. Ellis, G. K u c h i l m z . and H . H. Juffc;, Theor. Chim. Acta 26,
131 (1972); J . Kroiirr and D. Proch. Tetrahedron Lett. IY72. 2537, and
literature cited therein.
[lo] Standard coordinates were used for all the molecules. It was found
that for ( 1 0 ) the position of the longest-wave band was not appreciably
altered by use of minimum coordinates. As an analytical method the
calculations give only qirulirutice information about the spectra t o be
ex pectcd.
[ I I ] R. Gonipprr, C . Jersuk. and K . Sdiijiiufi~iyer,personal communication.
[ 121 An exact analysis of this electronic spectrum is in progress.
[I31 MINDO:2: N . Bodor, M . J . S. DLwar, A. Harqer, and E . Hu\elbuc/i,
J . Amer. Chem. Soc. 92,3854 (1970). Minimization by the QCPE program
of A . Komornicki and J . W M c I w r , Jr.. Chem Phys. Lett. 10, 303
( I 97 1 ).
1141 The largest eigenvaluecalculated by us for the bond-bond polarirability matrix is relatively small. For the theory see: G . Biiisch, I . Tumir,
and R. D. Hill, J. Amer. Chem. Soc. 9 / , 2445 (1969).
850
We succeeded in proving the existence of kinks experimentally by measurements of the shortening of the overall chain
length upon kink formation141.As models we have used bimolecular films of n-alkylammonium ions and n-alkanols
spread out between silicate layers. Kink formation was
shown by a stepwise decrease of the film thickness with
increasing temperature, measured by X-ray methods. Kink
formation is a cooperative process in which the number
of kinks per alkyl chain increases by 1 within a relatively
small temperature range. For steric reasons, the kinks must
be assigned to neighboring chains, so that kink blocks are
formed. The cause of kink formation is the increasing thermal energy.
We have now been able to elucidate kink formation by
measuring the specific heat of the same models (e.g. ntetradecylammonium-beidelliteln-tetradecanol)
in an adiabatic calorimeter. A small flask containing the sample
was immersed in paraffin as bath fluid, and the specific
heat was determined from the change in temperature of
the paraffin (measured by an NTC resistance), while a definite amount of heat was supplied by electrical heating.
The sensitivity of the calorimeter was better than 20mcal/h.
The experimental results are shown in Fig. 2: curve a)
[*] Priv-Doz. Dr. G. Lagaly, DipLChem. S . Fitz, and Prof. Dr. A.
Weiss
Institut f ~ Anorganische
r
Chemie der Universitiit
8 Munchen 2. Meiserstrasse I (Germany)
[**I This work was supported by the Deutsche Forschungsgemeinschaft.
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