- Email: [email protected]
The vibrational spectra of phthalic anhydride
Journal of Molecular 0 Elsevier Scientific
THE VIBRATIONAL
YOSHIYUKI SALA
Instituto
HASE.
de Quimica,
(Received
30 (1976) 37-44
Structure,
Publishing Company, Amsterdam -
SPECTRA
CELSO
OF PHTHALIC
U. DAVANZO*,
Universidade
KIYOYASU
de Stio Pa&o.
Printed in The Netherlands
AN-HYDRIDE
KAWAI**
Caixa Postal
20780,
and OSWALD0
Sdo Paul0
(Brazil)
16 January 1975)
ABSTRACT The IR and Raman spectra of phthalic anhydride have been reported for the polycrystalline sample and the polarized Raman spectrum for the molten sample. The observed frequencies have been assigned tentatively to the C:, molecular symmetry and a normal coordinate analysis has been carried out for a modified valence force field.
INTRODUCTION
The IR and Raman spectra of phthalic anhydride have not been studied, but the characteristic doublet in the C=O stretching frequency region has been extensively examined [l- -6]_ The C-O stretching vibration has been also studied in relation to the O=C-O-C=0 group [ 7 ] _ Recently, the IR and Raman spectra of pyromellitic dianhydride have been reported [ 81, and the frequency shifts of the skeletal stretching vibrations of this molecule have been discussed as compared with those of phthalic anhydride, considering the n-bonding characters. In order to examine these frequency shifts in more detail, it seems desirable to ascertain the vibrational assignment and carry out the normal coordinate analysis for a series of molecules such as phthalic anhydride, trianhydride.
pyromellitic
dianhydride and mellitic
In the present paper, the IR and Raman spectra of phthalic anhydride have been investigated. A normal coordinate analysis has been carried out for the modified valence force field and the potential energy distribution has been also calculated. The fundamental frequencies of pyromellitic dianhydride [ 81, maleic anhydride [9, lo] and benzene derivatives [ 111 have been considered in the assignment of the observed frequencies of phthalic anhydride. The observed frequencies for the molten sample have been *Permanent address: Paula, Brazil. **Permanent address: Japan.
Faculty
of Philosophy,
Faculty
of Literature
Science and Letters, and Science,
Toyama
Ribeirtio Preto, SHo University,
Toyama,
38
compared with those for the polycrystalline have been discussed.
sample and the frequency
shifts
EXPERIMENTAL
Phthalic anhydride was obtained commercially and recrystallized from benzene solution. The IR spectrum of the polycrystalline sample was recorded in the frequency region from 4000-170 cm-’ on a Perkin-Elmer IR 180 spectrophotometer, using the Nujol and hexachloro-1,3-butadiene mulls. The Raman spectra were recorded in the frequency region from 4000-40 cm-’ for the polycrystalline sample and from 4000-100 cm-i for the molten sample on a Jarrell-Ash Model 25-300 spectrometer, using the 5145 ,& radiation of an argon ion laser, 200 mW, for excitation. ASSIGNMENT
According to the X-ray diffraction study [12], phthalic anhydride belongs to the Cq, space group and to the C, site group with four molecules per unit cell. However, the CZV molecular symmetry can be assumed in the vibrational treatment for the free molecule model as the first approximation. So, there are thirty-nine fundamental vibrations in which fourteen of Q:I, six of b, and thirteen of b2 species are active in both the IR and Raman spectra, while six of cl2 species are only Raman active. The fundamental vibrations of the a, and b2 species are the in-plane vibrations and those of the a, and b , species are the out-of-plane vibrations_ The observed frequencies are given in Table 1 with tentative assignments. The observed polarized Raman spectrum of the molten sample permitted the thirteen polarized bands to be assigned to the a, species. Twelve of them are the fundamental bands and one is a combination band. Two bands at 3093 and 3073 cm-* are assigned to the C-H stretching vibrations. A strong band at 1850 cm-l is undoubtedly assigned to the in-phase C=@ stretching vibration and a weak band at 1600 cm-’ to the benzene ring stretching vibration. The bands at 1357 and 1334 cm-’ can be considered as a Fermi resonance splitting between the benzene ring stretching vibration v6 and the combination band v,,, + v,,+ The corrected frequency of v6 is 1337 cm-’ for the molten sample. The C-H in-plane bending and the skeletal ring stretching vibrations, except for the vibrations assigned above, are expected in the frequency region from 1300-700 cm-i [ll]. The four bands at 1256,1107, 1010 and 735 cm-l are assigned to the C-O stretching, C-H in-plane bending C-C stretching and skeletal ring breathing vibrations, respectively. The remaining three polarized bands at 638, 537 and 344 cm-l are assigned to the two skeletal ring bending and C=O in-plane bending vibrations, respectively. There are two more fundamental vibrations for the a, species. One is the benzene ring stretching vibration and the band at 1517 cm-’ is assigned to this vibration. Another is the C-H in-plane bending vibration and is expected
39
TABLE1 Observed frequencies(in cm-')andassignments Infrared
Solid
Solid
3099 3090 3069 3059 3049
3093 w
ww ww ww
3073m 3061~~ 3051vw 3036~~ 2934ww
2728~~ 2719ww 2165~~ 2097 ww 2027 ww 2017 ww
2097
Liquid
ww
w
3033ww
Assignment
Raman
v,
V 17, "(C-W
b2
3052~~
v =, “(C-H)
bz
vvw
1852~s 1827 ww 1806ww 1792m 1773ww 1762~s 1745ww 1735ww 1707 ww 1646~~ 1617 ww 1610~~ 1599m 1517 VW 1471s 1447 VW 1419w 1383~ 1360m 1336m 1288~ 1284~~
VII
1932ww 1902vw 1888ww 1874~~ 1854vvw 1845~s 1828~~ 1813w 1802~ 1793vw 1778~~ 1764s 1747 VW 1735ww 1704ww 1698~~ 1645~~ 1620~ 1612~~ 1602s 1518~~ 1476~~ 1472~ 1457 ww 1420~~ 1382~~ 1359w 1336~ 1289~
a, aI
2”s “29 + “33 “7 + “31 “9 + “30 “6 + “3.5 v. + vx “9 + “2, 2” 10 “13 + "31
VW
1931ww 19Olvw 1886ww
“7
v,,u(C--HI v,,u(C--HI
2006~~ 1983
l
3093vw,P 3073vw,P
"7
+
"37
"II
1850 s,P
"32
+ f
"33
V,
+
VIZ
"6
+
"13
"4
+
"39
v,,
Y (C=O)
"14
+
"31
viz
+
v>,
zv3,
1789w
"9
+
"13
1772~
"37 +
",f
1612~~ 16OOw.P 1471vw
"32
vr),v(C=O)
"IO
+
"II
VI3
+
"33
"22
+
"35
"IO
+
"IS
"=I+
"35
"30.
"(C-c)
"4,
"(C-c)
"5,
"(C-c)
"22
+
"312
b,
"13
Y17
"(C-C)
"13
+
"21
"II
+
vz3
+
"37
b,
2",, "23
1357 vw,P 1334 vw,P
VI0+ "14 "6,,(C--c) "19+ v2l VI9+ v35
a,
40 TABLE
1 (continued) Assignment
Infrared
Raman
Solid
Solid
Liquid
1257 s 1245 VW 1212vw 1208 ww 1171 m
1256 1242
s,P w
1169
VW
1258 1243 1213 1207 1175 1171 1126 1115 1107 1093 1070 1014 1006
vs m w ww m VW ww VW s ww w ww w
906
vs
893
w
887 vvw 839 m
800 w 734 VW 714 vs 679 m 643
m
540 ww 536 s
355 m 348 vuw 300 ww 256 w 212w
4c--0)
“7,
u,z, a(C--HI v.w fi(C--H)
a1
b, a,
VI3 + v37
4C-c)
1J33,
b,
vr2 + VI3 “21 + “24 “24
1109 1093 1071
m ww ww
1107
1008 976 922 906 894 887 840 817 800 796 737 714 679 662 641 608 585
vs vvw VW w VW ww w vvw ww VW vs ww w VW s ww ww
1010
m,P
“3,
vs,P
vvw
353 m
v35,
v
2-l
162~s 114 vs 58 VW 49 w 42 w
a2
dC---HI 4c-0)
b, b, a,
L’,,
6 cc=01
2v3, v r(C=O) 17,
794 735
VW
V&P
680 ww
“22,
r(C=O)
”
4c-3
I,,
~=a, AC--H) I’,,, h (CCC)
b, a, b, a, b, b2
VIR + v39
638 vs,P
VIZ,
b(COC)
uz. + v,, 588 ww 537 vs,P 410 ww 377 VW 344 w,P
253
w
fJ(CCC)
L’,R, “,3,
a:
+ u-5
&CC)
aI
“I9 + v20 U,R, fJ(CCC)
b,
VI91
a2
VIJ)
VIS-+
188 m 173 m
a,
+
“3*,
%
258 m 211 w 202 w
4C--c) -AC--W
~,clI “,s,
u ie.. -AC--H) 841 VW
a1
+ v39
“2,.
908
v,<
(C--H)
~,a, a(C--HI lJ ,a + v,-
“,.I
541 s 534 ww 409 VW
+
“9, fi
4
(C-C)
a(C=O)
al
TO
114
“39.
5 (CCC)
b,
“141
,(CCC)
b,
+ 42 “25, @(C--c) v:b, @(C-C) v20, @(C-C) lattice vibration lattice vibration lattice vibration lattice vibration vzo
193 VW 177 ww 143 m
b, b, a2
41
about 1200 cm-* [ll ]_ Because the band at 1242 cm-’ is a depolarized band, a weak band at 1213 cm-’ for the polycrystahine sample may be assigned to
this last vibration of the Q, species. For the b2 species, there are thirteen fundamental vibrations, and the characteristic bands above 1000 cm-l, except for the bands already assigned to the fundamental vibrations of the EL) species, may be assigned to the b, species. The bands at 3061 and 3052 cm-l are assigned to the C-H stretching vibrations. In the out-of-phase C=O stretching frequency region, two weak bands at 1789 and 1772 cm-’ are observed for the molten sample. These two bands may be considered as the doublet arising from a Fermi resonance splitting between the out-of-phase C=O stretching vibration V~ and the combination band vg + v37,considering the band intensities in the IR spectrum The corrected frequency for the out-of-phase C=O stretching vibration is 1774 cm-l in the Raman spectrum of the molten sample. The bands at 1612, 1471 and 1169 cm-’ are assigned to the two benzene ring stretching and C-C stretching vibrations, respectively. Two bands at 1242 and 1071 cm-’ are assigned to the C-H in-plane bending vibrations. The very strong band at 906 cm-’ in the IR spectrum can be assigned without a doubt to the out-ofphase C-O stretching vibration [9, lo]. Three skeletal ring bending and one C=O in-plane bending vibrations are expected below 1000 cm-’ and the bands at 680, 410, 253 and 841 cm-l are assigned rather tentatively to these vibrations, respectively. The vibrations belonging to the a2 species of the C,, molecular symmetry are essentially inactive in the IR spectrum and active in the Raman spectrum. However, the distorted molecules in the crystal field cause the lowering of the molecular symmetry. In the case of phthalic anhydride, the molecular symmetry is lowered from C,, to C, in the crystal field [12], and the vibrational bands of the Q, species can be observed in the IR spectrum of the polycrystalline sample. Comparing with the fundamental vibrations of benzene derivatives [ll] , two bands at 976 and 894 cm-’ are assigned to the C-H wagging vibrations of the CL? species. A band at 800 cm-l is assigned to the C=O wagging vibration. For the a2 species, three more fundamental vibrations are expected, and the observed bands at 588,377 and 143 cm-l are assigned rather tentatively to the skeletal ring out-of-plane bending or torsional vibrations. For the b, species, two bands at 922 and 714 cm-’ are assigned to the C-H wagging vibrations, and a band at 794 cm-l to the C-0 wagging vibrations. The skeletal ring outof-plane bending and torsional vibrations are expected in the low frequency region, and the bands at 211,193 and 177 cm-’ are assigned to these vibrations rather tentatively. For the vibrational spectrum of the polycrystalline sample, twelve rotational and nine translational lattice vibrations are expected for phthalic anhydride, in which three rotational and three translational vibrations are inactive in the IR spectrum because they belong to the a2 species of the Cg, factor group 1121. The observed bands at 114,58,49 and 42 cm-’ can be assigned to the lattice vibrations.
42 NORMAL
COORDINATE
ANALYSIS
A normal coordinate analysis of phthalic anhydride was carried out to ascertain the vibrational assignment and to obtain the force constants, using the computer programs reported previously [13] and an electronic computer IBM 360/44 at the Institute of Physics of the University of Go Paulo. A modified valence force field was assumed. The values of force constants were taken from those of related molecules [9,14-161 and adjusted to reproduce the observed fundamental frequencies, on the harmonic oscillator approximation. The potential energy distribution was alsc calculated to ascertain the vibrational assignment.* The tentative assignment of the fundamental vibrations are well-confirmed by the agreement between the observed and calculated frequencies (average error 1.4%) and by the matrix elements of the potential energy distribution. DISCUSSION
The in-phase and out-of-phase C=O stretching vibrations, v3 and vB, give a frequency separation of about 80 cm-‘. Such a large band splitting is generally observed in the vibrational spectra of the carboxylic [S-lo, 17,181, and attributed mainly to the interaction of
anhydrides
these C=O stretching vibrations with the resonance structures such as O=C-O’=C-Oand 0--C=O+-C=O. Comparing the Raman spectrum of the molten sample with that of the polycrystalline sample, it is found that’the observed frequencies agree within 5 cm-‘, except for the three fundamental vibrations, v,~, vu)and vzg. No remarkable band splittings due to the crystal field were observed either in the IR spectrum or in the Raman spectrum of the polycrystalline sample. Accordingly, the intermolecular interactions of phthalic anhydride in the crystal field may be considered to be negligible. The frequency shift of the out-of-phase C!=O stretching vibration vZ9amount! to 8 cm-’ for the observed frequencies and 5 cm -’ for the corrected frequencies. If this shift is attributed to a difference in the nature of the C=O bonding character arising from the electron migration from the benzene ring to the O=C-O-C=O group, a slight frequency shift can be also expected for the skeletal ring stretching vibrations. However, the frequency shifts on the skeletal ring stretching vibrations amount to 1 or 2 cm-‘, and these values are within the experimental error in this study. On the other hand, the shift of the in-phase C=O stretching vibration v3 amounts to 5 cm-‘. Therefore, the slight frequency shifts on the GO stretching vibrations may be due to the difference of the electron distribution on the C=O bonds
arising from
the weak
intermolecular
interaction.
*The values of the force constants and the potential energy distribution request from B.L.L. as sup. %b. No. 26012 (9 pages).
are available on
43
The shift of the in-phase C=O in-plane bending vibration Y,~ amounts to 9 cm-i, and may be explained in terms of the vibrational coupling, because the shift of the out-of-phase C=O in-plane bending vibration V% amounts only to 1 cm-‘. The large frequency shift of the ring torsional vibration LJ~ associated with the physical states amounts to 19 cm-‘, and may be explained in terms of the mechanical coupling with the lattice vibrations. The normal coordinate calculation for maleic anhydride [9] showed that the interaction force constants on the O=C-O-C=O group stretching vibrations are very important, through the delocalized electrons. On the other hand, it is well known that the benzene ring is also stabilized by the delocalized electrons and the interaction force constants on the benzene ring stretching vibrations cannot be neglected in the calculation. In the normal coordinate calculation of phthalic anhydride the interaction force constants between the benzene ring and the O=C-O-C=O group stretching vibrations are also considered to be effective. Accordingly, the electron migration may occur to the whole molecule of phthalic anhydride. In the vibrational assignment, the C-H stretching vibrations were easily assigned considering the Raman polarization, and they are v ,, v2, v 27 and Us in order of higher frequency. But, the normal coordinate analysis gave in the assignment may be due to that v2, is higher than v2, and this difference a hydrogen bond with the C=O bond. ACKNOWLEDGEMENTS
This work de Sao Paul0 FAPESP for Organization
was supported by Fundacao de Amparo a Pesquisa de Estado (FAPESP) and Conselho National de Pesquisas. Y. H. thanks his fellowship grant, and K. K. thanks FAPESP and the of American States for financial assistance.
REFERENCES
1 H. Tschamler and R. Leutner, Monatsh. Chem., 83 (1952) 1502. 2 W. G. Dauben and W. W. Epstein, J. Org. Chem., 24 (1959) 1595. 3 L. J. Bellamy, B. R. Connelly, A. R. Philpotts and R. L. Williams, Z. Elektrochem., 64 (1960) 563. 4 N. P. Buu-Hoi’ and P. Jacquignon, Bull. Sot. Chim. Fr., (1960) 1712. 5 E. M. Popov, A. Kh. Khomenko and P. P. Shorygin, Izv. Akad. Nauk. Kaz. SSR, Ser. Khim., (1965) 51. 6 F. H. Marquardt, J. Chem. Sot., B, (1966) 1242. 7 R. G. Cooke, Chem. Ind., (London), (1955) 142. 8 Y. Hase, K. Kawai and 0. Sala, J. Mol. Struct., 26 (1975) 297. 9 C. D. Lauro, S. Califano and G. Adembri, J. Mol. Struct.. 2 (1968) 173. 10 A. Rogstad, P. Klaboe, H. Baranska, E. Bjamov, D. H. Christensen, F. Nicolaisen, 11
0. F. Nielsen, B. N. Cyvin and S. J. Cyvin, J. Mol. Struct., 20 (1974) 403. G. Varstiyi, Vibrational Spectra of Benzene Derivatives, Academic Press, New York,
1969. 12 K. C. Banerji, Proc. Nat. Acad. Sci., India, Sect. A, 25 (1956)
115.
44 13 Y. Hase and 0. Sala, Computer Programs for Normal Coordinate Analysis, Institute de Quimica da Universidade de Sso Paula, Sao Paula, 1973. 14 K. Radcliffe and D. Steele, Spectrochim. Acta, Part A, 25 (1969) 597. 15 N. D. Patel, V. B. Kartha and N. A. Narasimham, J. Mol. Spectrosc., 48 (1973) 185. 16 N. D. Patei, V. B. Kartha and N. A. Narasimham, J. Mol. Spectrosc., 48 (1973) 202. 17 A. Rogstad, P. Klaboe, B. N. Cyvin, S. J. Cyvin and D. H. Christensen, Spectrochim. Acta, Part A, 28 (1972) 111. 18 A. Rogstad, P. Kiaboe, B. N. Cyvin, S. J. Cyvin and D. H. Christensen, Spectrochim. Acta, Part A, 28 (1972) 123.
THE VIBRATIONAL
YOSHIYUKI SALA
Instituto
HASE.
de Quimica,
(Received
30 (1976) 37-44
Structure,
Publishing Company, Amsterdam -
SPECTRA
CELSO
OF PHTHALIC
U. DAVANZO*,
Universidade
KIYOYASU
de Stio Pa&o.
Printed in The Netherlands
AN-HYDRIDE
KAWAI**
Caixa Postal
20780,
and OSWALD0
Sdo Paul0
(Brazil)
16 January 1975)
ABSTRACT The IR and Raman spectra of phthalic anhydride have been reported for the polycrystalline sample and the polarized Raman spectrum for the molten sample. The observed frequencies have been assigned tentatively to the C:, molecular symmetry and a normal coordinate analysis has been carried out for a modified valence force field.
INTRODUCTION
The IR and Raman spectra of phthalic anhydride have not been studied, but the characteristic doublet in the C=O stretching frequency region has been extensively examined [l- -6]_ The C-O stretching vibration has been also studied in relation to the O=C-O-C=0 group [ 7 ] _ Recently, the IR and Raman spectra of pyromellitic dianhydride have been reported [ 81, and the frequency shifts of the skeletal stretching vibrations of this molecule have been discussed as compared with those of phthalic anhydride, considering the n-bonding characters. In order to examine these frequency shifts in more detail, it seems desirable to ascertain the vibrational assignment and carry out the normal coordinate analysis for a series of molecules such as phthalic anhydride, trianhydride.
pyromellitic
dianhydride and mellitic
In the present paper, the IR and Raman spectra of phthalic anhydride have been investigated. A normal coordinate analysis has been carried out for the modified valence force field and the potential energy distribution has been also calculated. The fundamental frequencies of pyromellitic dianhydride [ 81, maleic anhydride [9, lo] and benzene derivatives [ 111 have been considered in the assignment of the observed frequencies of phthalic anhydride. The observed frequencies for the molten sample have been *Permanent address: Paula, Brazil. **Permanent address: Japan.
Faculty
of Philosophy,
Faculty
of Literature
Science and Letters, and Science,
Toyama
Ribeirtio Preto, SHo University,
Toyama,
38
compared with those for the polycrystalline have been discussed.
sample and the frequency
shifts
EXPERIMENTAL
Phthalic anhydride was obtained commercially and recrystallized from benzene solution. The IR spectrum of the polycrystalline sample was recorded in the frequency region from 4000-170 cm-’ on a Perkin-Elmer IR 180 spectrophotometer, using the Nujol and hexachloro-1,3-butadiene mulls. The Raman spectra were recorded in the frequency region from 4000-40 cm-’ for the polycrystalline sample and from 4000-100 cm-i for the molten sample on a Jarrell-Ash Model 25-300 spectrometer, using the 5145 ,& radiation of an argon ion laser, 200 mW, for excitation. ASSIGNMENT
According to the X-ray diffraction study [12], phthalic anhydride belongs to the Cq, space group and to the C, site group with four molecules per unit cell. However, the CZV molecular symmetry can be assumed in the vibrational treatment for the free molecule model as the first approximation. So, there are thirty-nine fundamental vibrations in which fourteen of Q:I, six of b, and thirteen of b2 species are active in both the IR and Raman spectra, while six of cl2 species are only Raman active. The fundamental vibrations of the a, and b2 species are the in-plane vibrations and those of the a, and b , species are the out-of-plane vibrations_ The observed frequencies are given in Table 1 with tentative assignments. The observed polarized Raman spectrum of the molten sample permitted the thirteen polarized bands to be assigned to the a, species. Twelve of them are the fundamental bands and one is a combination band. Two bands at 3093 and 3073 cm-* are assigned to the C-H stretching vibrations. A strong band at 1850 cm-l is undoubtedly assigned to the in-phase C=@ stretching vibration and a weak band at 1600 cm-’ to the benzene ring stretching vibration. The bands at 1357 and 1334 cm-’ can be considered as a Fermi resonance splitting between the benzene ring stretching vibration v6 and the combination band v,,, + v,,+ The corrected frequency of v6 is 1337 cm-’ for the molten sample. The C-H in-plane bending and the skeletal ring stretching vibrations, except for the vibrations assigned above, are expected in the frequency region from 1300-700 cm-i [ll]. The four bands at 1256,1107, 1010 and 735 cm-l are assigned to the C-O stretching, C-H in-plane bending C-C stretching and skeletal ring breathing vibrations, respectively. The remaining three polarized bands at 638, 537 and 344 cm-l are assigned to the two skeletal ring bending and C=O in-plane bending vibrations, respectively. There are two more fundamental vibrations for the a, species. One is the benzene ring stretching vibration and the band at 1517 cm-’ is assigned to this vibration. Another is the C-H in-plane bending vibration and is expected
39
TABLE1 Observed frequencies(in cm-')andassignments Infrared
Solid
Solid
3099 3090 3069 3059 3049
3093 w
ww ww ww
3073m 3061~~ 3051vw 3036~~ 2934ww
2728~~ 2719ww 2165~~ 2097 ww 2027 ww 2017 ww
2097
Liquid
ww
w
3033ww
Assignment
Raman
v,
V 17, "(C-W
b2
3052~~
v =, “(C-H)
bz
vvw
1852~s 1827 ww 1806ww 1792m 1773ww 1762~s 1745ww 1735ww 1707 ww 1646~~ 1617 ww 1610~~ 1599m 1517 VW 1471s 1447 VW 1419w 1383~ 1360m 1336m 1288~ 1284~~
VII
1932ww 1902vw 1888ww 1874~~ 1854vvw 1845~s 1828~~ 1813w 1802~ 1793vw 1778~~ 1764s 1747 VW 1735ww 1704ww 1698~~ 1645~~ 1620~ 1612~~ 1602s 1518~~ 1476~~ 1472~ 1457 ww 1420~~ 1382~~ 1359w 1336~ 1289~
a, aI
2”s “29 + “33 “7 + “31 “9 + “30 “6 + “3.5 v. + vx “9 + “2, 2” 10 “13 + "31
VW
1931ww 19Olvw 1886ww
“7
v,,u(C--HI v,,u(C--HI
2006~~ 1983
l
3093vw,P 3073vw,P
"7
+
"37
"II
1850 s,P
"32
+ f
"33
V,
+
VIZ
"6
+
"13
"4
+
"39
v,,
Y (C=O)
"14
+
"31
viz
+
v>,
zv3,
1789w
"9
+
"13
1772~
"37 +
",f
1612~~ 16OOw.P 1471vw
"32
vr),v(C=O)
"IO
+
"II
VI3
+
"33
"22
+
"35
"IO
+
"IS
"=I+
"35
"30.
"(C-c)
"4,
"(C-c)
"5,
"(C-c)
"22
+
"312
b,
"13
Y17
"(C-C)
"13
+
"21
"II
+
vz3
+
"37
b,
2",, "23
1357 vw,P 1334 vw,P
VI0+ "14 "6,,(C--c) "19+ v2l VI9+ v35
a,
40 TABLE
1 (continued) Assignment
Infrared
Raman
Solid
Solid
Liquid
1257 s 1245 VW 1212vw 1208 ww 1171 m
1256 1242
s,P w
1169
VW
1258 1243 1213 1207 1175 1171 1126 1115 1107 1093 1070 1014 1006
vs m w ww m VW ww VW s ww w ww w
906
vs
893
w
887 vvw 839 m
800 w 734 VW 714 vs 679 m 643
m
540 ww 536 s
355 m 348 vuw 300 ww 256 w 212w
4c--0)
“7,
u,z, a(C--HI v.w fi(C--H)
a1
b, a,
VI3 + v37
4C-c)
1J33,
b,
vr2 + VI3 “21 + “24 “24
1109 1093 1071
m ww ww
1107
1008 976 922 906 894 887 840 817 800 796 737 714 679 662 641 608 585
vs vvw VW w VW ww w vvw ww VW vs ww w VW s ww ww
1010
m,P
“3,
vs,P
vvw
353 m
v35,
v
2-l
162~s 114 vs 58 VW 49 w 42 w
a2
dC---HI 4c-0)
b, b, a,
L’,,
6 cc=01
2v3, v r(C=O) 17,
794 735
VW
V&P
680 ww
“22,
r(C=O)
”
4c-3
I,,
~=a, AC--H) I’,,, h (CCC)
b, a, b, a, b, b2
VIR + v39
638 vs,P
VIZ,
b(COC)
uz. + v,, 588 ww 537 vs,P 410 ww 377 VW 344 w,P
253
w
fJ(CCC)
L’,R, “,3,
a:
+ u-5
&CC)
aI
“I9 + v20 U,R, fJ(CCC)
b,
VI91
a2
VIJ)
VIS-+
188 m 173 m
a,
+
“3*,
%
258 m 211 w 202 w
4C--c) -AC--W
~,clI “,s,
u ie.. -AC--H) 841 VW
a1
+ v39
“2,.
908
v,<
(C--H)
~,a, a(C--HI lJ ,a + v,-
“,.I
541 s 534 ww 409 VW
+
“9, fi
4
(C-C)
a(C=O)
al
TO
114
“39.
5 (CCC)
b,
“141
,(CCC)
b,
+ 42 “25, @(C--c) v:b, @(C-C) v20, @(C-C) lattice vibration lattice vibration lattice vibration lattice vibration vzo
193 VW 177 ww 143 m
b, b, a2
41
about 1200 cm-* [ll ]_ Because the band at 1242 cm-’ is a depolarized band, a weak band at 1213 cm-’ for the polycrystahine sample may be assigned to
this last vibration of the Q, species. For the b2 species, there are thirteen fundamental vibrations, and the characteristic bands above 1000 cm-l, except for the bands already assigned to the fundamental vibrations of the EL) species, may be assigned to the b, species. The bands at 3061 and 3052 cm-l are assigned to the C-H stretching vibrations. In the out-of-phase C=O stretching frequency region, two weak bands at 1789 and 1772 cm-’ are observed for the molten sample. These two bands may be considered as the doublet arising from a Fermi resonance splitting between the out-of-phase C=O stretching vibration V~ and the combination band vg + v37,considering the band intensities in the IR spectrum The corrected frequency for the out-of-phase C=O stretching vibration is 1774 cm-l in the Raman spectrum of the molten sample. The bands at 1612, 1471 and 1169 cm-’ are assigned to the two benzene ring stretching and C-C stretching vibrations, respectively. Two bands at 1242 and 1071 cm-’ are assigned to the C-H in-plane bending vibrations. The very strong band at 906 cm-’ in the IR spectrum can be assigned without a doubt to the out-ofphase C-O stretching vibration [9, lo]. Three skeletal ring bending and one C=O in-plane bending vibrations are expected below 1000 cm-’ and the bands at 680, 410, 253 and 841 cm-l are assigned rather tentatively to these vibrations, respectively. The vibrations belonging to the a2 species of the C,, molecular symmetry are essentially inactive in the IR spectrum and active in the Raman spectrum. However, the distorted molecules in the crystal field cause the lowering of the molecular symmetry. In the case of phthalic anhydride, the molecular symmetry is lowered from C,, to C, in the crystal field [12], and the vibrational bands of the Q, species can be observed in the IR spectrum of the polycrystalline sample. Comparing with the fundamental vibrations of benzene derivatives [ll] , two bands at 976 and 894 cm-’ are assigned to the C-H wagging vibrations of the CL? species. A band at 800 cm-l is assigned to the C=O wagging vibration. For the a2 species, three more fundamental vibrations are expected, and the observed bands at 588,377 and 143 cm-l are assigned rather tentatively to the skeletal ring out-of-plane bending or torsional vibrations. For the b, species, two bands at 922 and 714 cm-’ are assigned to the C-H wagging vibrations, and a band at 794 cm-l to the C-0 wagging vibrations. The skeletal ring outof-plane bending and torsional vibrations are expected in the low frequency region, and the bands at 211,193 and 177 cm-’ are assigned to these vibrations rather tentatively. For the vibrational spectrum of the polycrystalline sample, twelve rotational and nine translational lattice vibrations are expected for phthalic anhydride, in which three rotational and three translational vibrations are inactive in the IR spectrum because they belong to the a2 species of the Cg, factor group 1121. The observed bands at 114,58,49 and 42 cm-’ can be assigned to the lattice vibrations.
42 NORMAL
COORDINATE
ANALYSIS
A normal coordinate analysis of phthalic anhydride was carried out to ascertain the vibrational assignment and to obtain the force constants, using the computer programs reported previously [13] and an electronic computer IBM 360/44 at the Institute of Physics of the University of Go Paulo. A modified valence force field was assumed. The values of force constants were taken from those of related molecules [9,14-161 and adjusted to reproduce the observed fundamental frequencies, on the harmonic oscillator approximation. The potential energy distribution was alsc calculated to ascertain the vibrational assignment.* The tentative assignment of the fundamental vibrations are well-confirmed by the agreement between the observed and calculated frequencies (average error 1.4%) and by the matrix elements of the potential energy distribution. DISCUSSION
The in-phase and out-of-phase C=O stretching vibrations, v3 and vB, give a frequency separation of about 80 cm-‘. Such a large band splitting is generally observed in the vibrational spectra of the carboxylic [S-lo, 17,181, and attributed mainly to the interaction of
anhydrides
these C=O stretching vibrations with the resonance structures such as O=C-O’=C-Oand 0--C=O+-C=O. Comparing the Raman spectrum of the molten sample with that of the polycrystalline sample, it is found that’the observed frequencies agree within 5 cm-‘, except for the three fundamental vibrations, v,~, vu)and vzg. No remarkable band splittings due to the crystal field were observed either in the IR spectrum or in the Raman spectrum of the polycrystalline sample. Accordingly, the intermolecular interactions of phthalic anhydride in the crystal field may be considered to be negligible. The frequency shift of the out-of-phase C!=O stretching vibration vZ9amount! to 8 cm-’ for the observed frequencies and 5 cm -’ for the corrected frequencies. If this shift is attributed to a difference in the nature of the C=O bonding character arising from the electron migration from the benzene ring to the O=C-O-C=O group, a slight frequency shift can be also expected for the skeletal ring stretching vibrations. However, the frequency shifts on the skeletal ring stretching vibrations amount to 1 or 2 cm-‘, and these values are within the experimental error in this study. On the other hand, the shift of the in-phase C=O stretching vibration v3 amounts to 5 cm-‘. Therefore, the slight frequency shifts on the GO stretching vibrations may be due to the difference of the electron distribution on the C=O bonds
arising from
the weak
intermolecular
interaction.
*The values of the force constants and the potential energy distribution request from B.L.L. as sup. %b. No. 26012 (9 pages).
are available on
43
The shift of the in-phase C=O in-plane bending vibration Y,~ amounts to 9 cm-i, and may be explained in terms of the vibrational coupling, because the shift of the out-of-phase C=O in-plane bending vibration V% amounts only to 1 cm-‘. The large frequency shift of the ring torsional vibration LJ~ associated with the physical states amounts to 19 cm-‘, and may be explained in terms of the mechanical coupling with the lattice vibrations. The normal coordinate calculation for maleic anhydride [9] showed that the interaction force constants on the O=C-O-C=O group stretching vibrations are very important, through the delocalized electrons. On the other hand, it is well known that the benzene ring is also stabilized by the delocalized electrons and the interaction force constants on the benzene ring stretching vibrations cannot be neglected in the calculation. In the normal coordinate calculation of phthalic anhydride the interaction force constants between the benzene ring and the O=C-O-C=O group stretching vibrations are also considered to be effective. Accordingly, the electron migration may occur to the whole molecule of phthalic anhydride. In the vibrational assignment, the C-H stretching vibrations were easily assigned considering the Raman polarization, and they are v ,, v2, v 27 and Us in order of higher frequency. But, the normal coordinate analysis gave in the assignment may be due to that v2, is higher than v2, and this difference a hydrogen bond with the C=O bond. ACKNOWLEDGEMENTS
This work de Sao Paul0 FAPESP for Organization
was supported by Fundacao de Amparo a Pesquisa de Estado (FAPESP) and Conselho National de Pesquisas. Y. H. thanks his fellowship grant, and K. K. thanks FAPESP and the of American States for financial assistance.
REFERENCES
1 H. Tschamler and R. Leutner, Monatsh. Chem., 83 (1952) 1502. 2 W. G. Dauben and W. W. Epstein, J. Org. Chem., 24 (1959) 1595. 3 L. J. Bellamy, B. R. Connelly, A. R. Philpotts and R. L. Williams, Z. Elektrochem., 64 (1960) 563. 4 N. P. Buu-Hoi’ and P. Jacquignon, Bull. Sot. Chim. Fr., (1960) 1712. 5 E. M. Popov, A. Kh. Khomenko and P. P. Shorygin, Izv. Akad. Nauk. Kaz. SSR, Ser. Khim., (1965) 51. 6 F. H. Marquardt, J. Chem. Sot., B, (1966) 1242. 7 R. G. Cooke, Chem. Ind., (London), (1955) 142. 8 Y. Hase, K. Kawai and 0. Sala, J. Mol. Struct., 26 (1975) 297. 9 C. D. Lauro, S. Califano and G. Adembri, J. Mol. Struct.. 2 (1968) 173. 10 A. Rogstad, P. Klaboe, H. Baranska, E. Bjamov, D. H. Christensen, F. Nicolaisen, 11
0. F. Nielsen, B. N. Cyvin and S. J. Cyvin, J. Mol. Struct., 20 (1974) 403. G. Varstiyi, Vibrational Spectra of Benzene Derivatives, Academic Press, New York,
1969. 12 K. C. Banerji, Proc. Nat. Acad. Sci., India, Sect. A, 25 (1956)
115.
44 13 Y. Hase and 0. Sala, Computer Programs for Normal Coordinate Analysis, Institute de Quimica da Universidade de Sso Paula, Sao Paula, 1973. 14 K. Radcliffe and D. Steele, Spectrochim. Acta, Part A, 25 (1969) 597. 15 N. D. Patel, V. B. Kartha and N. A. Narasimham, J. Mol. Spectrosc., 48 (1973) 185. 16 N. D. Patei, V. B. Kartha and N. A. Narasimham, J. Mol. Spectrosc., 48 (1973) 202. 17 A. Rogstad, P. Klaboe, B. N. Cyvin, S. J. Cyvin and D. H. Christensen, Spectrochim. Acta, Part A, 28 (1972) 111. 18 A. Rogstad, P. Kiaboe, B. N. Cyvin, S. J. Cyvin and D. H. Christensen, Spectrochim. Acta, Part A, 28 (1972) 123.