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Introduction:
1-amino-4-nitronaphthalene (AhTN) is derived from naphthalene which is the
largest single constituent of coal tar. It consists of two benzene rings fused together and
two of the hydrogen atom is replaced by one amino and one nitro group. It exists in solid
form at room temperature. Its melting point is around 191-193° C. The geometrical
structure of the molecule is shown in the fig 1. ANN is used as an insecticide.
Commercially it is used for making dyes.
Paul et a1 [I]. recorded the FT-Raman spectra and FTIR spectra of three
naphthazarin polymorphs. Using these spectra they established that at room temperature
static synlnletry point group of naphthazarin is Czv, rather than Dzh
Resonance Raman spectra have been obtained for the naphthalene and
naphthalene-ds amines in tetrahydrofuran and seven of the nine totally symmetric
vibrational modes have been assigned by Christesen et al. [2 ] . Normal modes analysis
was perfomled for the planar modes to obtain stretching force constants for the C-C bonds,
which was found to be different form neutral naphthalene. The changes in the force
constants resulting from sodium reduction of naphthalene were found to be proportional to
change in 7c bond orders obtained form ab initio Hartree - Fock SCF calculation at the
STO-3G level.
'I'llc polarized 1R and Raman spectra of 2-naphthol was studied by Szostak et al.
[3] in different medium. The increase in band intensities in the IR spectra and Raman
spectra of 2-naphthol as compared with naphthalene spectra was interpreted as being due
to couplings between the intermolecular charge transfer and vibrations. These interaction
also found to be medium dependent.
The Raman intensities of lattice vibrations in naphthalene in the oriented gas
approximation were calculated by Burgos et al. [4]. and the relative intensities were
comp:lrccf with t l lc liaman spectrum it1 polarized light nleasurcd by Suzuki et a1 [ S ] . The
agreement with experiment was only fair. The potential model used by Burgos et a1
consists of atom-at0111 interaction and the fit to the lattice frequencies is not particularly
good in soiile cases. This would produce errors in the eigen vecton to be used in intensity
calculations. A better potential nod el for naplahalene i~icluding quadrupole -quadiapole
interactions was worked out by Califano et a1 [ 6 ] This model give a very satisfactory
explanation of the lattice dynamics of the naphthalene crystal. Cardini et al. [7]
recalculated the RanIan intensities at room temperature using the model proposed by
Califanao et a1 [6] . The results are found to be similar to those obtained by Burgos [4] et
a]. They have also discussed the contribution of the local field and the effect of two -
ce~lter representation of the molecular polarizability.
Thc k>lioto acoustic spectra of naphthalene in powder foonn and in boric acid glass
h : ~ bccn 1 ~ i 7 0 r t ~ d in the region 250 - 300 nm by Kumar ct n l [8]. The spectrum of
naphthalene in powder for111 is found to be identical to the spectrum taken in boric acid
glass, indicating that naphthalene is dispcrscd as a monomcr in the boric acid glass. The
photoacoustic spectra provides additional infolmation about non-radiative transitions such
as additional bands, intelisity and the shape of the bands observed in the convent~onal
optical spectrum. The electronic energy levels have been calculated by SCF-MO method.
A good i~gscemcnt is found bctwccn the esperimzntal and calculated results. Assignemnts
of the observed electronic transitions are made. The structure attached to these electronic
transitions are attributed to the ground state vibrational modes of naphthalene.
Nyulaszi and Veszpremi [9] reported adiabatic and vertical ionization energies for
naphthalene, five membered rings and ammonia calculated by density functional method.
Thc structure of the ionic ground stntc and that of the neutral was optilllised scpcratcly.
The calculated ionization energies and harmonic frequencies were in good agreement with
the observed values. The calculated geometrical changes was in good agreement with the
information from photoelectron spectra.
Jas and Kuczera [lo] reported the non~ial mode calculations for the lowest singlet
excited states S1 of benzene, naphthalene and anthracene. Optimized geometries and
cartesian ham~onic force constants of the excited states are obtained from ab initio
calculutions. Noriilal nloile analysis is pcrfonned in internal co-ordinates, yielding
vibrational frequencies and fonlls of normal nlodes for the parent molecules and their
dcutcratcci Jcrivntivcs. Thc results are compnrcd with So calculated at the Hartree-Fock
levcl and with nvailablc espcriine~ltal data. The overall changes in nlolecular geometry
and vibrational spectra upon So to S I esc~tation are snlall. For naphthalene and ai~thracene
the calculated vibrational frequencies are In good agreement w ~ t h llrerature data. This
method also helpful to predict new frequencies and types of normal modes for these
molecules.
Reaction dynamics of hot naphthalene inolecules in the gas phase with ArF laser
excitation has been reported by Susuki et a1 [ l l ] . Highly vibrationally excited 'hot'
naphthalen in the ground state was formed through rapid internal conversion after 193 nm
laser excitation. Hot naphthalene was effectively deactivated by nitrogen molecules and
the energy transferred per collision was similar to that of azulene or hexafluorobenzene.
The molecule was found to absorb a second photon under high photon density conditions
to undergo an illter~nolecular chenlical reaction.
S111cc ANN is biologici~lly slid coiiii~icrclally ilnportani collipo~lnd, an niternpt
made to record and analyse the vibrational spectra of this molecule using FTIR and FT-
Rarnan spectroscopy in the present work.
Experimental details :
The compound I-amino-4-nitronaphthalen (CloHsNzOz) was obtained from MIS
Fluha chc~nicnl coillpaily Switzerland which was used as such without further purification
(purity > 96%) to record FTIR and FT-Raman spectra. The FTIR spectrum of this
molcculc ~vrts rccorded in solid phrtsc in the region bctwcon 3000 - 400 c111.' using Bruker
IFS 66V spectrometer. The FT-Raman spectrum was also recorded in the same instrument
with FRA 106 Raman module equipped with Nd:YAG laser source operating at 10.6 pm
line with 200 mW power. The spectrum was recorded with a scanning speed of 30 cm-'
min-' of spectral width 2.0 cm-I. The frequencies for all sharp bands were accurate to + 2
cm-I. The observed FTIR and FT-Raman spectra of ANN is shown in fig. 2 and 3
Normal Coordiante Analysis :
Since the vibrational motion of ANN molecule is complicated, a modes of vibrations of this molecule can be resolved using symmetry considerations and group
theory. Wilson's group theoretical method of analysis of molecular vibrations has been of
great service in the study of n~olecular forces. The accepted theoretical approach for
intelpretation of the spectral data is normal coordinate analysis based on a simple valence
force field (SVFF). It consists In selecting of as many diagonal and a few off-diagonal
force constants from the general valence force field equal to the number of fundamental
frequencies. Two reduction criteria are used to select the relevant force constants. That is
the interaction force constants between distinct internal co-ordinates are neglected and
sym~iietry reasoning are used for setting equality between force constants belonging to
coordinates to bc cquivnlcnt. 'fliis rough approximation hiis givcn bcttcr results than
expected at first sight. The fittcd force fields reproduce quite satisfactorily the
esl~crimcntal f r c q ~ ~ c n c ~ c s of the studied compound for t l ~ c purpose of the vibrational
assignmerits. The computer program developed by Fuhrer eta1 [12] for the normal
coordinate analysis was suitably modified in this laboratory and applied to the molecule
under investigation in the present work. The observed spectra are explained on the basis of
C, symmetry assuming amino and nitro group as point masses. Thus the 60 fundamental
vibrations are distributed as
T, ,b - 43 a ' (inplanc ) + 17 a"(out of'planc)
Results and Discussion:
The observed frequencies of ANN together with the relative intensities, probabl
assignments. calculated frequencies and potential energy distribution is presented in the
Table (1).
Carbon vibrations
Eleven bands are expected from the ring of the molecule for the C-C stretching
vibrations. We have observed five bands at higher frequency and six at lower frequency.
Table 1 shows that the medium intensity bands correspond to asymmetric vibrations while
the lower intensity bands correspond to symmetric vibrations of carbon atoms. There is no
significant lnodificatioll of the ring stretching vibration due to the presence of nitro or
amino groups.
In aromatic molecules the C-H inplane bendings are observed in the region 1000-
1300 c m ' and are usually ureak. The C-H out of plane modes with medium intensity
arises in the region 600-900 cm" [13]. In the present case C-H inplane bending are
observed at 956 (predicted from NCA), 1161, 1199, 1265, 1279 and 1250 c m - b n d the out
ofplane bendings are observed at 648, 821, 940 and 959 cm-'.
We have assigned the characteristic frequency observed at 779 cm-' to the ring
breathing mode of the molecule. The other modes of vibration of carbon atom in the ring
such as CCC inplane and CCC out of plane vibrations are presented in the Table (1). The
above assignments agree well with the literature values 1141.
NOz Gmup y/Brat/uns:
'I'ilc stretching vibration of nitro group is csactly analogous to the CIIz or NIi2
groupx;111~i hence we can expect a doublet. As the Nitrogen in the NOz group exhibits
resonance hybrid with the oxygen atoms, there is a possibility of inter and intra molecular
hydrogen bonding in the molecules. In saturated aliphatic nitrocompounds the symmetric
and asymmetric bands are observed at 1550 and 1370 cm-I and are usually very intense
because of large dipole moment present. Conjucation lowers these frequencies to an
extent which is detem~ined by the electron denoting or attracting power of the attached
group [13, 151. In nitroaniline due to the presence of electron donating group (NHS the
N-0 stretching frequency appears at 1480 and 1319 cmbl whereas in 4-nitrobenzaldehyde
due the presence of electron attracting group the stretching frequency of the nitro group is
incrcascd co~lsidcrably. 111 ~litrobc~~xcnc the doublct ariscs at 1520 and 1355 cm'l.
Gigcrmanska ct a1 [I61 assigned the antisymmetric N - 0 stretching of In-
nitroplienol in CCIj solution at 1535 cm-' as a medium intensity and in the crystal it was
observed at 1526 cn1-' with diminishing intensity. The syn~metric Pi-0 stretching was
observed by him at 1345 cm-' as a strong band both in CC14 and crystal spectra. He
explained the difference in intensity on the basis of hydrogen bonding. Muralidhar Rao et
a1 1171 assigned the doublet around 1520 cm-I and 1350 cm-' in monohalogeneted
nitrobenzenes. Based on the above conclusions we assigned the doublet at 1525 and 1350
c ~ ' to nitro group in the present work. The absorption band at 1350 cm" is a mixed band
due to 68% of sytnmetric stretching character of NOz group and contribution from C H
stretching modes. Similarly the band at 1525 crn-' is due to 69% of asymmetric stretching
character of nitro group.
The band around 481 cm-' is due to the out of plane deformation (wagging) of nitro
group to the extent of 52%. The band near 532 cm" is mainly due to rocking mode of
nitro group. However it has to be described as a mixed mode due to PED contribution
from modes such as CH stretching and CCC out of plane bending modes. The above
assignlllerlts agree well with the literature values [I 71.
The twisting and deformation modes are assigned to the bands at 756 and 827 ern-' respectively which is in agreement with the value reported by ~'igermanska [16]. The
b;,nd ol>sc~.vcd a t 1153 cm" is assigneci to C-NO2 stretching vibration. The weak bands
obscr\~eci at 114 cm-' and 325 cm-' in Iiaman are nssigncd to C-NO, inplane and out of
plane bending vibrations and these are in agreement with calculated values as seen from
the Table (1).
N& Group Vibrations:
The molecule under consideration possesses only one amino group and hence we
expect only one symmetric and asymmetric N-H stretching vibrations. In all the primary
aromatic amines the stretching fi-equency occurs in the region 3300 - 3500 cm-'. In the
present casc thc bands at 3239 and 3336 cm-' are assigned to N-M symmetric and
asynlnlcti-ic stretching vibratiolls rcspectivcly. Thls observation agrees well with the
eal.licr workers [18,19]. The prcsence of intern~olecular or i~ltranlolecular hydrogen
bonding considerably affects the N-H stretching modes.
Thc fi-cqucncy at 1622 cm-' obscrved in IR and 1630 cm" in Rarnan has been
assigned to symmetric deformation (rocking) of NH2 group. The NH2 twisting mode
which was expected at 1048 cni ' was seen in our spectrum at 1049 crn-'. Similarly the
NHI out of plane wagging mode which was expected in the region 550 - 700 cm-' was
seen in our spectra at 599 cm'l. The above assignments agree with Shukla et a1 [20]. We
have assigned the C-NH2 stretching vibration at 950 cm-l. A literature survey [21, 221
reveals that the NH2 deformation mode appears a t about 290 cm". In the present case it was seen at 238 cm-'.
potential energy distribution :
To check whether chosen set of assignments contribute maximum to the potentiaI
energy associated with normal coordinates of the molecules, the potential energy
distribution (PED) has been calculated using the relation
Fii ~ i k ~
PED =
hk
Where F,, are the force constants defined by damped least square technique, Lik the
normaliscd amplitude of the associated elenlent (i,k) and hk the eigen value corresponding
to thc vibrational frequency of the element k. The higher PED contribution corresponding
to each of the observed frequencies are listed in the present work.
Conclusion
A complete vibrational spectra and analysis is available in the present work for 5-
a~llinoindole and i-aminoindane molecuIes. The close agreement between the observed
and calculated frequencies confirm the validity of the present assignment. The purity of
the modes are ascertained by the potential energy distribution associated with each
frequency of vibrations.
l'ablc -I Observed and calculated wave~lunlbers a11d Potential energy distribution (PED) for
1 -Amino-4-nitronaphthalene
V] 0
'3 a
V)
a'
a"
CCC in plane bending
Observed wavenumberht.
Cal. wave- number
12 1
224
FTIR FTR
83vw
1 14w
2 1 5vw
Assignments
Lattice modes
C-NO, out of plane bending
C-NH, out of plane bending
PED
48yC.,,, t 29yc,
3 9yc,,,+2 1 yc,,,t 1 5yc,
- a'
a"
a''
a'
a"
a'
a ' '
a'
a''
a'
a'
a'
9'
3'
3'
1'
3'
1'
1'
1'
1'
1'
1'
1'
i' -
NO, deformation
CH out of plane bending
CH out of plane bending
C-NH, stretching/
CH out of plane bending
CH inplane bending
CH out of plane bending
CCC trigonal bending
NH, twistlng
CH inplane bend~ng
C-NO2 stretch~ng
Ull ~npl~unc bcndlng
ZH inplane bend~ng
2H ~nplane bendlng
:H ~nplane bending
2-C stretching
N - 0 symmetric stretch~ng
.I1 NOz
Z-C stretching
Z-C stretching1
3 1 In plane bending
C-C stsctching
C-C stretching
2-C stretching
N-0 asymmetric stretching
m NO2
C=C stretching
*Predicted from Nonnal co-ordinate analysis; vs-very strong, s-strong, m-medium,
w-wcuk, vw-vely weak
v - stretching, 6 - deformation, P - inplane bending, y - out-of--plane bending, o - wagging z - twisting.
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