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Isolation and Infrared Spectrum of Iodine Azide.

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dies. A “theoretical” estimate of this value can be obtained
by extrapolation from the linear relationship (1) between the
observed half-wave reduction potentials El of conjugated
rc-systems and the calculated energies of the lowest unoccupied
orbitals (LUMOs).
EI,2=
(1)
-0.92+2.37~ [volt]
The values E I l 2are polarographic data measured against
the saturated calomel electrode, and the numbers x characterize the HMO energies (cc+xP) of the LUMOs[’]. The
half-wave reduction potential of benzene (x= - 1.00) resulting
by extrapolation from eq. (1) is -3.29 V.
The finding[’] that benzene can also be electrolytically
reduced in an ethereal solvent to its radical anion suggests
an analogous, “experimental” procedure for the evaluation
of the half-wave potential. A prerequisite for such a procedure
is a linear relationship between the minimum voltages V,,
at which the ESR spectra of the radical anions appear during
the electroIysis, and the polarographic data E,
That this
prerequisite has been met is shown by the appearance voltages
V , measured in the present work for the radical anions of
20 hydrocarbons and plotted in Figure 1 us. the corresponding
values
The pertinent regression line has the equation
V ,=(I .92 f0.06) E l
~
(2)
2
with a correlation coefficient of 0.991 and a deviation from
the origin (0.007)which is far below the significance threshold.
perchlorate served as the solvent and supporting salt, respectively. The temperature was - 90°C. According to the original
quantity weighed in, the concentration of each hydrocarbon
ought to be 5 x
mol/liter. However, in the case of some
aromatics of poor solubility, the actual concentration was
lower, which may be one of the reasons for the deviation
of the corresponding data V , from the regression line in Figure
1. For each hydrocarbon several measurements were performed in order to determine the minimum value for the
appearance voltage V,. Such a value was considered as reliable
when it could be reproduced within an experimental error
of f0.05 V.
Extrapolation of the equation (2) to the appearance voltage
V , (Fig. 1) for the radical anion of benzene yields
Eli2= -3.31 *0.12V(90% confidence1imits)as an “expermental” estimate of the half-wave reduction potential of benzene
in excellent agreement with the “theoretical” result of - 3.29 V.
Obviously, values of E I I 2can be estimated in a similar way
for other compounds of low electron affinity, provided that
such compounds areelectrolytically convertible into their radical anions. An example is [2.2]paracyclophane for which equation (2) affords a half-wave reduction potential
El,,= -3.05k0.12 V (Fig. 1). It is worth mentioning that in
this case an extrapolation of equation (1) is not as straightforward as for benzene, since the HMO model is not directly
applicable to [2.2]paracyclophane. The values El ,2 found for
the two hydrocarbons are in accord with a previous report
which points to adistinctly higher electron affinity of [2.2]paracyclophane relative to that of benzene[’!
Received: July 21, 1976 [Z SO3 IE]
German version: Angew. Chem. 88,617 (1976)
CAS Registry numbers:
Benzene, 71 -43-2; [2.2]paracyclophane, 1633-22-3
I
I
I
I
I
10
15
20
m
2:5
[ I ] A . Streitwieser, J r . : Molecular Orbital Theory for Organic Chemists.
Wiley, New York 1961, Chapter 7.1.
[2] F . Gerson and G . Moshuk, unpublished work.
[3] We thank Prof. K . Ishizu, Ehime (Japan) for samples of several alkyl-substituted biphenyls.
[4] The polarographic measurements were performed by Drs. H. G . Seiler
and H . R . Schmutz of the Anorganisch-Chemisches Institut, Basel. For
biphenyl the value E , (-2.57V) determined by these workers was
used instead of that (-2.7OV) listed in ref. [I].
[ 5 ] R . D. Allendoerfer, C . A . Mnrrinchek, and S. Bruckenstein, Anal. Chem.
47, 890 (1975).
[6] F. Gerson and W B. Martin, Jr., J. Am. Chem. Soc. 91, 1883 (1969).
I
/
1
I
1
3.05
331
[volt]
Fig. 1. Plot of appearance voltages V. us. half-wave reduction potentials
E , ?. A=anthrdcene: Ac=acenaphthene; An =acenaphthylene; Az=azulene;
B = benzene: Bn = biphenylene: Bp= biphenyl: C =coronene; Ch =chrysene;
Dt =4,4’-di-ferfD b =4,4’-dimethylbiphenyl; Dn = 2,3-dimethylnaphthalene;
butylbiphenyl; F = nuoranthene: I =indeno[I,2,3-~d]fluoranthene;N= naphthalene: P = pyrene; Pc= [2.2]paracyclophane; Pe=perylene; Ph =phenanthT p = triphenylene.
rene; S =stilbene; T b = 3,3’,S,S‘-tetra-terf-hutylhiphenyl;
The half-wave reduction potentials E l ,2 in equation (2)
and Figure 1 were either taken from the compilation by Streitwieser“] or determined in a laboratory of our Departmentt3.‘1.
They refer to the saturated calomel electrode as standard.
On the other hand, the appearance voltages V , are not bound
to any conventional reference level and may thus be compared
only with data obtained under the same conditions. The electrolytic cell used throughout the entire series had a cylindrical
form and contained a helical cathode of amalgamated gold,
along with an anode of platinum wire placed along the cell
axis[5].1,2-Dimethoxyethane and 0.1 M tetrabutylammonium
Anyew. Chrm. I n f . Ed. Enyl.
1 Val. 15
(1976) No. 9
Isolation and Infrared Spectrum of Iodine Azide
3.0
By Kurt Dehnicker]
Far less is known about the chemistry of iodine azide than
about that ofchlorineazide and bromine azidec’]. The preparation of IN3 from iodine and silver azide in ether, which leads
to very readily decomposable solutions, has been reported[’],
as has the ability of IN3 to undergo stereospecific addition
to olefinic double bonds, for which IN3 generated from sodium
azide and iodine chloride in acetonitrile is employed in sitd31.
We have found that solutions of iodine azide in dichloromethane, carbon tetrachloride, and benzene are much more
stable than those in ether. 1 to 3 % solutions are obtained
by dropwise addition with stirring at 0°C of Iz solutions
of corresponding concentration to freshly precipitated silver
azide freed from water. Solutions of this concentration can
bemanipulated without danger, and can even be dried without
decomposition over phosphorus pentoxide.
[*] Prof. Dr. K. Dehnicke
Fachhereich Chemie der Universitat
Lahnberge, D-3550 Marburg (Germany)
553
Careful evaporation of solvent CHzClz leaves a residue
of golden yellow, hygroscopic, and somewhat light-sensitive
needle-shaped and extensively intermeshed crystals of IN3,
of which only very small amounts were prepared owing to
their explosive nature. Under normal pressure they can be
sublimed at room temperature on to a cold finger maintained
at -78°C. N o melting point can be recorded because the
sublimation point lies at 24"C/760 torr.
The IR spectrum of IN3 recorded both in solution and
in Nujol emulsion (Table 1 ) is compatible with the structure
( 1 ) which is bent at the a-N atom and has the molecular
symmetry C,.
Crystalline
[cm-I]
Intensity
Assignment
-~
3242
w
2058
1176
vs
m
578
338
m
W
3242
2460
2045
1240
648
580
338
VW
vw
vs
m
vw
W
m
Apart from the INN deformation vibration (A') to be
expected below the range of measurement (down to 250cm-')
all the fundamental vibrations can be assigned. Two special
features of the spectrum warrant attention:
1) The two N3 stretching vibrations having symmetric and
asymmetric character move apart significantly during the transition solid/dissolved. This might be connected with a favoring
of the diazonium structure of IN3 in the dissolved state. However, an intermolecular interaction is more likely and would
lead to deviation from linearity of the NNN group in the
crystalline state, as observed for some heavy metal azidesC41.
2) The I-N stretching frequency lies at 338cm-' and thus
at considerably longer wavelengths than to be expected from
the series FN, [~(FN)=869cm-'][~],CIN, [v(ClN)=719
cm'I, BrN, [v(BrN)= 687 cmThis result can be
explained by a pronounced polarity of the iodine-nitrogen
bond as shown in (2).
6+ 6 I-N
Received: l u l y 23, 1976 [Z 506 IE]
German version: Angew. Chem. 88,612 (1976)
CAS Registry numbers:
IN,, 14696-82-3
121
[3]
[4]
[S]
[6J
[7]
554
TI11
C5H?Na@
+
n-BuBr
NaH/THF
n-BuC H 5
- NdBr
7
Compounds ( I ) to ( 4 ) are highly air-sensitive, deeply
colored liquids. Elemental analyses confirm their purity, and
13C-NMR spectra their molecular structure (typical example
in Fig. 1). The precise 6(I3C) are listed in Table 1. Their
assignment follows from the chemical shifts, intensities, and
multiplicities, as well as from earlier findings[''.
(21
Iodine azide should therefore react with metal iodides via
substitution. Indeed boron triiodide and iodine azide immediately deposit I2 and form the unknown compound diiodine
borazide['].
[I]
By Karl Eberl, Frank Herwig Kohler, and Lothar Mayring[*]
O n the basis of Mulliken's concept of hyperconjugation''],
C-C hyperconjugation can be regarded as a particularly important variant of this phenomenon. It warrants attention in
the large number of organic and organometallic compounds
in which C-C CJ bonds. can interact with K orbitals of aromatic
systems or heteroatoms. The Baker-Nathan effect was considered to be an especially significant indication of hyperconjugation, C-C hyperconjugation being thought much smaller
than C-H hyperconjugati~n[~].
However, this effect was found
to arise rather from changes in s ~ l v a t i o n [ ~Very
? recent ab
initio calculations even show C-C hyperconjugation to make
an important contribution to the stability of acetyl cations[5!
This situation has long awaited experimental elucidation.
The development of paramagnetic 3C-NMR spectroscopy[61now permits study of C-C hyperconjugation with the
aid of a generally applicable method. Suitable molecules are
paramagnetic metallocenes. In these compounds part of the
spin density of the unpaired electrons is delocalized into the
K system of the ligand. From that position there exists the
possiblity of hyperconjugational transfer to the p-C atoms
of substituents located on the cyclopentadienyl groups. In
this way the unpaired spin density becomes an indicator of
C-C hyperconjugation. It causes exceptionally large ' 3C shifts
S(13C) which serve as a sensitive probe.
A versatile test is possible with n-butyl-substituted metallocenes. These compounds contain not only p-C but also y-C
and 6-C atoms, which are hardly affected by C-C hyperconjugation. The hitherto unknown 1 ,I/-di-n-butyl metallocenes of
vanadium ( I ), chromium (2), cobalt ( 3 ) , and nickel ( 4 )
can be obtained in 50 to 80 % yield by the following method
(yield of intermediates: 42 and 75 %)['I.
'
Table 1. IR spectrum of iodine a i d e (C, symmetry).
In benzene
[cm-'1
Intensity
A New Probe for C-C Hyperconjugation:
3C-NMR on Paramagnetic Metallocened'I
K. Deknicke, Angew. Chem. 79, 253 (1967); Angew. Chem. Int. Ed.
Engl. 6, 240 ( 1967).
A. Hanfzsch and M. Schumatin, Ber. Dtsch. Chem. Ges. 33, 522 (1900).
A. Hassner and L. A. Levy, J. Am. Chem. SOC. 87, 4203 (1965); G.
L'abbb and A. Hassner, Angew. Chem. 83, 103 (1971); Angew. Chem.
Int. Ed. Engl. 10, 98 (1971).
U . Muller, Struct. Bonding (Berlin) 14, 141 (1973).
D. E. Millignn and M . E. Jacox, J. Chem. Phys. 40, 2461 (1964).
W Kolirsch, Dissertation, Universitat Marburg 1974.
K. Dehnicke and 19: Siebert, unpublished.
200 ppm
H,
'I
-
/
C-31L
C-2/5
C-1
C-p
I\
C - 1 C-6
h
C-a
Fig. 1. "C-NMR spectrum O F ( ~ - B U C ~ H ~
(31
) ~atC309K.
O
L = [De]-toluene.
Concerning assignment, see Fig. 2.
In order to facilitate comparison of (1)-(4} we converted
the S(I3C)values in the known way['* *I into hyperfine interaction constants A . In connection with C-C hyperconjugation
we are interested in the magnitudes of A at the n-butyl C
atoms. The curves plotted in Fig. 2 reveal that IAl is excep-
1'1
Priv.-Dor. Dr. F. H. Kohler, K. Eberl, and L. Mayring
Anorganisch-chemisches lnstitut der Technischen Universitat
Arcisstrasse 21, 8000 Miinchen 2 (Germany)
Angrw. Chrm. Int. Ed. Engl. 1 Vol. 15 ( 1 9 7 6 ) No. 9
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