Spectrochimica Acta, 1902, Vol. IS, pp. 1187 to 1194. Pcrgamon Press Ltd. Printed in Northern Ireland
Infra-red spectra of sodium salts of some primary nitroparaffins
Z.
B U C Z K O W S K I and
T.
URBAŃSKI
Warsaw Institute of Technology (Politechnika) Warszawa 10, P o l a n d
(Received 12 November 1961)
Abstract Infra-red spectra o f sodium salts of a few p r i m a r y nitroparaffins have been examined,
and compared w i t h spectra o f the nitroparaffins. The characteristic feature o f the spectra o f
sodium salts is lack o f both symmetric and asymmetric N 0 frequencies. T w o bands corresponding
to C = N vibrations (c. 1660 and 1600 c m ) and a band at approximately 1170 c m , presumably
N —*• О vibration, are present i n the spectra o f sodium salts.
A hypothesis is proposed that sodium salts of p r i m a r y nitroparaffins m a y exist i n two
isomeric cis and trans forms.
2
- 1
- 1
I T I S known that the generally admitted structure [1] of the aci-form of nitroparaffins
or "nitronium acids" (I) and that of the aci-anion (II) was in doubt for some time
(See Ref. [2]).
R
OH
R
O-
\
C=N
/
/
\
\
R'
C=N
/
O
\
R'
(I)
/
О
(И)
Although the investigations of K O R N B L U M and his co-workers [ 3 ] seemed to con­
firm the correctness of the formulae (I) and (II), we have tried to obtain more infor­
mation on the structure of the sodium salts of a few nitroparaffins using infrared
absorption.
So far only a few papers dealing with infra-red spectroscopy of aci-nitrocompounds and their O-acyl derivatives [4-11] have been published. In all of them a
[1] A . H A N T Z S C H , Ber. deut. Chem. Ces. 32, 575 (1899); 35, 210, 226, 1001 (1902): 39, 139,
1073 (1906).
[2] G . W . W H E L A N D , Advanced Organic Chemistry (3rd E d . ) p. 715. J o h n W i l e y , N e w Y o r k
(1960).
[3] N . K O R N B L U M , N . N . L I C H T I N , J . T . P A T T O N and
D . C . I F F L A N D , J. Am.
Chem. Soc.
69,
307
(1947); N . K O R N B L U M , J . T . P A T T O N and J . B . N O R D M A N N , Ibid. 70, 746 (1948).
[4] J . P . F R E E M A N and K . S . M C C A L L U N , J. Org. Chem. 21, 472 (1956).
[5] E . H . W H I T E and W . J . C O N S I D I N E , J. Org. Chem. 22, 1745 ( 1957) ; J. Am. Chem. Soc. 80,
(1958).
[6] H . E . Z I M M E R M A N N and T . E . N E V I N S , J. Am. Chem. Soc. 79, 6559 (1957).
[7] S . S . N O V I K O V , К . K . B A B I E V S K I I and I. S . K O R S A K O V A , Doklady Akad. Nauk S.S.S.R.
560 (1959).
[8] P . D . B A R T L E T T , E . R . W E B S T E R , С
E . D I L L S and
H . G . R I C H E Y , J r . , Ann.
Chem.
626
125,
Liebigs
623, 217 (1959).
[9] M . M . S H E M I A K I N , D . N . S H I G O R I N , L . A . S H C H U K I N A and E . P . S I O M K I N , Izvest. Akad.
S.S.S.R. Otdel. Khim. Nauk 695 (1959).
[10] J . H . BOYER and H . A L U L . J. Am. Chem. Soc. 81, 4237 (1959).
[11] Z . E C K S T E I N and T . U R B A Ń S K I , Bull. acad. polon. se/. 8, 579 (I960),
1187
Nauk
I ISS
Z . B U C Z K O W S K I and T . U R B A Ń S K I
1
frequency 1()S-1 Milo cm very characteristic of the aci-iht roparalHns lias been
reported. It is assigned to the C = N stretching vibration bands which obviously do
not exist in spectra of "normal" nitroparaffins. However most of the authors [ 4 , 5 ,
7 - 1 0 ] did not report bands characterizing the O H group present i n the structures
(1).
Only Z I M M E R M A N and N E V I N S [ 6 ] and E C K S T E I N and U R B A Ń S K I [ 1 1 ] observed
in some aci-nitrocompounds the presence of a broad band 3 4 4 8 - 2 6 3 2 c m and
3 4 2 2 c m , respectively. This should be assigned to a hydrogen bonded O H group.
The only papers of infra-red spectra of sodium salts of nitroparaffins were given
by M A T H I E U and M A S S I G N O N [ 1 2 ] who examined sodium salt of 1-nitropropane,
B E L I K O V et al. [ 1 3 ] who examined sodium and potassium salts of phenylnitromethane
and B R O W N [ 1 4 ] who examined potassium salts of grem-dinitroparaffins of general
formula R—С ( N 0 ) K .
B R O W N found two frequencies:
1 2 4 2 and 1 1 6 2 c m , which he assigned to the
nitro groups. Recently J O N A T H A N [ 1 5 ] published the results of examination of sodium
salts of nitromethane and similarly assigned two bands, 1 2 7 8 - 1 2 6 3 and 1 0 3 3 - 1 0 1 7
cm
to the asymmetric and symmetric N 0 vibrations respectively.
- 1
- 1
2
2
- 1
- 1
2
EXPERIMENTAL
Nitroethane. 1-nitropropane, 1-nitrobutane, 1-nitropentane, 1-nitrohexane (com­
mercial grade) were purified by distillation.
Sodium salts were prepared by the standard method, by allowing sodium ethoxide to react with the ethanolic solutions of nitroparaffins. The precipitated sodium
salts were separated and washed with anhydrous ether. The nitrogen content was
determined to check their purity.
Sodium salt of nitroethane. Found N , 1 4 - 7 ; C H 0 N N a requires N , 1 4 - 4 per cent.
Sodium salt of 1-nitropropane. Found N , 1 2 - 9 ; C H 0 N N a requires N , 1 2 - 6 per cent.
Sodium salt of 1-nitrobutane. Found N , 1 1 - 5 ; C H 0 N N a requires N , 1 1 - 2 per cent.
Sodium salt of 1-nitropentane. Found N , 1 0 - 3 ; C H O N N a requires N , 1 0 - 1 per cent.
Sodium salt of 1-nitrohexane. Found N , 8 - 9 ; C H 0 N N a requires N , 9-1 per cent.
Infra-red absorption spectra in the range from 1 8 0 0 to 7 5 0 c m were determined
by means of I K S - 1 2 (USSR production) single-beam and Hilger H - 8 0 0 double-beam
spectrophotometers with sodium-chloride optics. Liquid substances (all nitroparaf­
fins) were examined in layers of capillary thickness. The sodium salts were used in
form of Nujol mull. In the case of 1-nitropentane two thicknesses were used, a
thinner layer above ca. 1 3 5 0 c m and thicker below this point. Standard spectra of
gaseous ammonia and atmospheric moisture were used for calibration.
The frequencies are recorded in Table 1 and the spectra are given i n Figs. 1 - 5 .
2
4
3
e
4
8
3
1 0
6
1 2
2
2
2
2
2
- 1
4
DISCUSSION
The main feature of the spectra of sodium salts of aci-nitroparaffins is the
[ 1 2 ] J . P . M A T H I E U a n d D . M A S S I G N O N , Compt. rend. 211, 7 8 3 ( 1 9 4 0 ) .
[13]
W . M . B E L I K O V , S . G . M A I R A N O V S K I I , C . B . K O R C H E N N A Y A , S . S . X O V I K O V and W . A .
K L I M O V A , Izvest. Akad. Nauk S.S.S.R.
Otdel. Khim. Nauk
[ 1 4 ] J . F . B R O W N Jr., J. Am. Chem. Soc. 7 7 , 6 3 4 1 ( 1 9 5 5 ) .
[ 1 5 ] N . J O N A T H A N , J. Mol. Spectrosc. 5, 1 0 1 ( 1 9 6 0 ) .
1675
(19(H)).
Infra-red spectra o f sodium salts o f some primary nitroparaffins
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1190
Z . B U C Z K O W S K I and
T. URBAŃSKI
V
i
1
1750
,500
,250
,000
Wave number,
(if
L
u
i
1
n
1- Nitropropane
II
750
cm-'
W
F i g . 1. (top) Infra-red spectrum o f nit roethane.
(Bottom) I . R . spectrum o f N a salt o f nitroethane.
a
v
e
п
и
т
Ь
е
Г
|
c m
-.
F i g . 2 . (Top) Infra-red spectrum o f 1-nitropropane. (Bottom) I . R . spectrum o f N a salt o f
1-nitropropane.
disappearance of both frequencies of N 0 stretching vibrations in the spectra of
the salts and appearance of new bands: near 1600 c m and near 1170 c m .
2
- 1
Asymmetric,
N0
2
stretching
vibrations
Very strong bands were found at 1556-1550 c m
salts of aci-nitroparaffins gave this band.
symmetric
N0
2
stretching
- 1
- 1
in nitroparaffins. None of the
vibrations
Strong bands 1 3 6 0 - 1 3 4 4 c m
absent in their salts.
- 1
were shown by all the nitroparaffins. They were
Infra-red spectra of sodium salts o f some p r i m a r y nitroparaffins
1] A
1 Â
M
Л
'
1191
/1
1
If
* ¥
>*—
7^
i _
1
l-Nitropentane
I- Nitrobutane
I
1
1
n
Û / ГV
p
A
i
Na salt of
I - nitrobutane
1
1250
1000
1250
Wave number,
Wave
F i g . 3. (Top) Infra-red spectrum of 1-nitrobutane, (Bottom) I . R . spectrum o f N a salt o f
1-nitrobutane.
1
К
number,
F i g . 4 . (Top) Infra-red spectrum o f l-nitropentane. (Bottom) I . R . spectrum o f N a salt o f
1-nitropentane.
1
1605-1650 c m - and 1610-1599 c m "
Two bands, one of medium or low intensity near 1660 c m and another one of
very high intensity near 1600 c m , are present in the spectra of all the salts. They
are absent in nitroparaffins. Our assignment of these bands to C = N stretching
vibrations is in agreement with the data of other authors [4—11] as mentioned above.
It remains difficult however to explain why two bands are present in the spectra of
all salts so far examined. It might suggest that the double maximum of the band is
due to asymmetry of the crystal lattices. In order to examine this, we examined
the absorption of the sodium salt of 1 -nitropropane in alcoholic solution in this region.
Bands
at
- 1
- 1
1192
Z . B U C Z K O W S K I and
лл
li
T.
UIIBAŃSKI
4f~T
1
1 - Nitrohexane
1
1750
1500
1250
1000
Wave number,
cm
750
-1
F i g . 5. (Top) Infra-red spectrum o f 1-nitrohexane.
(Bottom) I . R . spectrum o f N a salt of 1-nitrohoxano.
There was no change of the absorption spectrum, two maxima being still present.
Thus the influence of the crystal lattice upon the absorption maxima of this band
seems to be ruled out.
Another possible cause of the two maxima in question could be the existence of
two isomeric sodium salts. A l l investigated samples of the salts would in this case
be composed of mixtures of two isomers.
So far it is difficult to find the answer to the structure of the isomers. We suggest
a tentative explanation that two geometrical isomers (la) and (lb) deriving from
primary nitroparaffins were possible.
Infra-red spectra o f sodium salts of some p r i m a r y nitroparaffins
H
O
\
R
/
C=N
H
\
0-Na+
\
/
0-Na+
R
(la)
1193
C=N
/
/
\
0
(lb)
Indeed it is known that C = C stretching vibrations in cis-trans isomers of the
compounds of a general formula C H R = C H R differ appreciably [16]. S H E P P A R D
and S I M P S O N [17] gave the values 1657 and 1673 c m for cis and trans isomers of
simple olefin derivatives respectively.
A special study will be carried out on the possibility of isomerism of the salts and
O-derivatives of aci-nitroparaffins.
1
2
- 1
Band
at 1178-1166 c m
- 1
This strong band exists in all the sodium salts. We suggest that it should be
assigned to N —*• 0 vibrations. This could be regarded as similar to N —>- 0 v i ­
brations in N-oxides. E.g. pyridine N-oxide has a group of atoms C = N — similar to
i
О
this in aci-nitroparaffins of the formula (I) and the frequency of it is 1270 c m . It is
subjected to large shifts under the influence of various substituents [16].
- 1
Band
at 875-848 c m "
1
We assign tentatively this band to the bond С—N vibration in nitroparaffins. It
is similar to that suggested by H A S Z E L D I N E [18]: 920-830 c m . The intensity of
the bands decreases with an increase of size of the alkyl group. The bands are absent
in the salts with an exception of the salt of 1-nitrobutane which shows a very weak
absorpt ion al S70 cm (possibly an overtone or combinai ion frequency), whereas 1 he
corresponding nitroparaffin gives a strong band at 861 c m .
- 1
1
- 1
Some other bands
1
The strong band 1450-1435 e n r is present only in nitroparaffins and absent in
their salts. It resembles the deformation frequency of C H group in paraffin chains
and the absence in sodium salt of nitroethane seems to suggest this assignment.
However it is absent in salts of 1-nitropropane and higher nitroparaffins, where C H
group (or groups) are present. In the light of these facts the assignment of the band
cannot yet be made.
As a conclusion of the discussion it can be pointed out that most experimental
facts recorded above agree with the formula (I) of the aci-nitroparaffins.
Thus:
(1) Both NO,-frequencies are absent in the spectra of nitroparaffins.
(2) Two frequencies C = N appear in the spectra of sodium salts and it is possible
that two geometric isomers are responsible for existence of the bands.
2
2
116] L . .1. B E L L A M Y , The Infra-red Spectra of Complex Molecules. M e t h u e n , London ( 1 9 6 8 ) .
I 1 7 ] N . S H E P F A R D and D . M . S I M P S O N , Quart. Revs. (London) 6, 1 ( 1 9 5 2 ) .
I 18] K . N . H A S Z E L D I N E , J.
Chem. Soc.
2525 (1953).
1194
Z . B U C Z K O W S K I and
T.
URBAŃSKI
(3) The frequency N —>- O is probably present in the spectra of sodium salts.
(4) The frequency С — N is absent in the spectra of sodium salts.
Note
When this paper was ready for publication, a new paper by J O N A T H A N [ 1 9 ] came
to our notice. His results do not affect our main conclusions although some assign­
ments are different.
Acknowledgement—We are m u c h indebted to M r . P . G L U Z I Ń S K I for measurement o f spectra i n a
H i l g e r H - 8 0 0 spectrophotometer.
[19]
N . J O N A T H A N , J.
Mol.
Spectrosc. 7 , 1 0 5 ( 1 9 0 1 ) .