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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