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The structure of dinitrogen pentoxide
Volume
87, number -1
CHEMICAL
THE STRUCTURE OF DINITROCEN John E. CARPENTER
PHYSICS
LE-I’TCRS
2 Apsl
1982
PENTOXIDE
and Gerald M. MAGGIORA
Deparrmennrs of Chemistry and Lahvrence. Kansas 66045. USA
Bioclrenrisrr) . Unirersi~
of h’atrsas.
Reccned 8 January 1982
Ab initio restricted Harrree-rock sclf-consistcnt-Iield molecular orbits1 calculations at the STO-3G and J-31C baas set levels have been used to determme the mimmum-rnergy ~IIUC~UICoiduorrogen pcntokidc, NzOj- The c~cuht~oos~ho~v that NaOs has an anhydride-type structure wth its mtro groups rotated 42’ out of the ccnkd N-O-N plane m 3 conrotatory bsh1on.
1. Introduction
NO? into rntric actd, a component of acid rain [?I. The basrc structure of N,Os
The chemtstry of nitrogen oxides IS extremely
com-
IS gtven m fig. I, IIOW-
ever, the most stable conformation
of the molecule is
plex and as a result is still not fully understood. Due
the SubJcct of some controversy particularly
mainly to their Importance
tatton of the nttro groups wrth respect to the N-O-N
tion of photochemical
smog, the smaller nitrogen ox-
ides NO, NO?, N1O, etc.,
btle eshaust,
as key agents m the formafound primarily
have been studied
m automo-
extensively
[I].
ever, this is not the case in the larger nitrogen NzOj.
N204
and N205
whose
resctlvlty
Howoxides
and instabil-
ity has made their study particularly difficult. For exthe anhydride of
ample, dinitrogen pentoxide, N,Oj, nitric acid thermally
decomposes to NO2 and NO-, and
reacts readily with water to form two molecules of nitnc acid. This latter reactton may be an important hnk in the chain of reactions that convert atmospheric
the ortcn-
plane of the anhydrtde bond. An early electron difiracnon study [3] suggests that the mtro groupsare rotated 90” abour the O-N anhydnde bonds and rhus ore perpendlculnr
to the central
N-O-N
plane. H~satsune et
al. [J] assumed that the molecule was planar wlth Czv m order to assign the normal modes of vibration of its IR spectrum. Turner and Ames [5] determined the photoelectron spectrum and performed ab mitio self-consistent-field molecular-orbital (SCF MO) calculations on several dtiferenr conformers m an efsymmetry
fort to correlate the structure of N205
with Its photo-
electron spectrum. From then studies they also con-
Fig. 1. Ceometnc paramelers of NzOz optlmlzcd. See section 2 for a discussion of addihonal parameters studied.
cluded that the molecule was planar. Addrtronal calculations were carrted out by Julg and Oznts [6] on the planar conformer suggested by Hisatsune et al., while Okada et al. [7] constdered both the planar and perpendicular conformers. On the basts of their calculations, the latter investigators found the planar conformer to be most stable. In none of the above cited studtcs were all posstble orientations of the nitro groups considered. However, in a recent electron dtffraction study, McClelland [S] suggested that the nitro groups are rotated, in a conrotatory manner, about the central O-N bonds and lie 349
Voiume 97. numtw 4
7 ApnI 1981
CHCMICAL PHYSICS LIZMERS
at an an$e of =-@ wrb respect IO the N-O-N plane. Such an lnlern?edlate col~formation IS not entirely unexpected due to repulsive interactions between the
3. Results and discussion
nitro groups m 111eplanar confomw
yIelded the non-planar structure shown in fig. 7, where
and the apparent
loss of conlugdtion in the pcrpendwlx
conformer.
In an effort I0 furlher charactari7e lhc Slructure
and resolve 111~qucstlon of mtro group OrIcntatron, we have cdrried out an e\tenslvc scr~esof ab mirlo SCF MO cslculatlons IO determme lhe minimum-energy structure
Of
NzOj dnd to mvesngate its relationship to
other low-energy c0ni0rmatI0n
2. .Computational
5.
methodolo~
All calculstions described in the present work were camed out wth
the GAUSSIAN
70 SCF h10 program
and 4-3 IG [I I] basis sets. Optimrzations were performed with the standard algorithm contamed in the program. Due to the earlier work of Okada et al. [7] wllicll suggested that a hrghly polarized spm distribution ellsted m the singlet ground state of Nz05, all preliminary calculations employed the unrestricted Hnrtrce-Fock method [ 111. However, e~arnlnation of the results of these calculatrons indlcsted the absence of any spin polarization, the results bemg identical to thos: obf lined from the usual resrncrrd Hat-tree-Fock nletr,od [ 131.Thus, a11subsequent calculations were carned out with the latter method. ImtiaI optimizattons were carried out at the [9] m both the STO-3C
[IO]
basis set level, and selected points were optmzed at the 3-3 1G Icvel.
STO-3C
A Cz symmetry ws bisecting the central N-O-N which were based on the followmg types of geometric parameters: bond lengths R,_, and RN_0 and bond angles Q, I( and y as shown in fig. I. and angIes # 1, B,, and Q, angle ivaj assumed in all optimizations.
which are not depxied
350
the mtro groups are rotated conrotatorily
ti?“,
m
excellent agreement wit hlcClclfand’selectron dlffraction results [8]. Thn structure is *5 kcal n&-I mow stnble than either the perpendicular or the planar conformers,
the latter considered to be the most stable
conformer by most earlier workers (vide supra). In the planar and perpendicular casesall structurd parameters were optimized except Ot and 81, whrch were both fixed at 0” or 90”. respectively. Detatls of the structural parameters For all three confo~ers are given in table I. Eaaminatmn of table I shows that the nttro group structural parameters,RI,,_t, and 7, are essenri@ unchanged with respect to all three conformers and very smldar to the calculated values found for nitrogen dloxide itseff(RI+_O = 1.19 A,0 = 134O [I4]). Thus, the adiabatically relaxed potential energy curves for conrotatory and clisrotatory nitro group rotations were determined by fixing Ro_N,RN_o, p and 7 at their values m the planar conformer and varying a and fl for each set of B values. The curves obtamed by thus process are grven m fig. 3A. the conrorato~ curve is rep resented by the solid hne, the disrotatory curve by the dashed Ime and the fully rend partiaIly optimized STO-3G based SCF MO calculations by filled cl&es and open circles, respectively. Fig. 3B Illustrates the magnitude of changes in a and /3 for the more stable conrotatory nitro group rotarion. Not unexpectedly, a undergoes approxunately three times as large a change as that experienced by 0 (Z 15” as opposed to MO), although the change in fl is still significant.
m fig. 1. Angles 0, and B2
describe nitro group stations about the central O-N bonds (taken in a clockwise sense looking from the nitro groups towards the central oxygen atom) whrch can be rotated m a coupled fashron either conrotatory (0, = 02) or disrotatorily (Ot = -02). Angle q describes the orientation of the nitro group plane and the plane formed by the central ohygenatom and an oxygen and nitrogen atom of the mtro group and approximates a “wagging” matron of the mtro group. All bond lengths are given m &gstr6ms
Full optln~ization at the STO-3G basis set fever
and angles in degrees.
Kg. 2. IMly optunized structure of N205. See table 1 for the value5of the geometnc parameters.
Volume 81, number 4
CHEMICAL PHYSICS LflTTCRS
2 Aprd I982
Table 1 Geometric parameters oi N7_0sa1 Perpendrcular
Parametcrb.C) Pkxxtr STO-3G
; Y 01 & lo-N RN-O
energy
4-31G
STO-3G
117.4363 119 6733 132 0909 o.oooo* o~oooo*
123.9746 119.1724 13 I.6979 0 oooo* o.~o~*
102.5150 113.2468 131.1078 87 8809 87 8809
019699 0000” 1 2669 -476.030 13
0.0000’ I 4527 1.1909 -482 03013
176.7242 1 4901 1 2670 -476 33.515
C\penment3l 181
IWly optim~ed -t-31G
STO-3G
J-31G
109 I145153 8522 131 8496 90 oooo= 90.0000w
I08 116 2117 33J i 32.0909 39.1281 39.1281
113 116.1374 75.52 131.9571 4 I 4507* 3145075
114 35t 113 133 3 4s tx$) 4.5 ood)
~77.0000~ I .-lb49 1 1923 -482 02804
175I 3699 4077 1 2699 -476.3319I
I 77I oaoo* 499
lSO_O~~ 1AS36
1.1917 -482.03665
I 188
a) Parameters held constant durmg an optlm~atton are marked by an astcrts!. (=I; p~~rnet~r values assumed are m~ked by a dagger fi) b) All bond m&s are grven in degrees. bond lengths in &gsCr6ms. and energy tn hattrees Cl See fig 1 and se&on 2 of te\t for a full desctiptton of the geometrx parameters d) AdditIonal structural rcfinemcnt gax 6t = 29.S?’ and 8:! = 49.87” 181. although the cffecr on the Of.tJ2 values of certain geometric constratnts tmposed by hfcCIrbnd ISdtificult IOassess
In order to increase the reliabtIrty of the theoretml were ctrrted out to redet~rnllnc the structure of the planar, perpendrcular and mjntmum-ener~ conformers. All structural parameters for ilie mininlum-ener~ conformer were fully optimized while 0 t , e2 and q were fixed in the planar and perpendicular conformers, all other parameters being fully optrmized. In the latter two cases q was constrained based on prel~~na~ calculations which showed that the total energy was msensttmc to Q over a reasonably broad range about tts constrained value. Appropriate STO-3G optimtzed structures were used as mttial guesses for the 4-3 ICi calcuIstions. prcdlctio~s, 43 IG level c~cui~tlons
ftg 3 (A) The encr~cttcsofa~ta~~tcni~ refixed nitro group rotations The fried rucles (*) and tnangle (A) represent fully optimKed STO-3G and 4-31G ~~~i~~tons, wlule the open cw firs (o) and utangles (6) represent parttally optimucd STO-3G and 4-31G ~cu~tions The soltd line (-1 inchutes a conrotatory mtro group Matron and the dashed lmc (---Is disroCato~ nttro group rotation (B) The t&o curves represent the chuges undergone by angles a and 13(see fig 1) during the ad~bati~ily relaxed conrotaCory nitro group rotation. The calculttlons wete carried out at the STO-3G basts set 1eW and as XI(A) above the Tied circles or squires represent full structural optCm~atCon,whale the open nrcks or squares repreSc’ntpart131opt~~tron-
351
Volume 57, number 1
CHEMICAL PHYSICS LETTERS
Fig. 3A clearly shows that both basrs sets predtct similar minimum.energy geometries with respect to nitro group orientation, and the relative energetics of
2 Apnl 1982
of N,Os are underway, and the results will be reported presently.
the 4.3IG opmized conformers(denotedin fig. 3 by filled and open t~angles) are qualltatNety stmrtar to those obtamed in the STO-3G basrs. However, the greater srabdny of the planar over the perpendicular
Acknowledgement
[6,71 proposals. while the STO-3C results predtct just the opposite order.
Support for the calculations from the Academic Compuler Center of the University of Kansas ISgratefully acknowledged. J.C. also wishes to acknowledge parttal support from NSF Unde~raduate Research Parttcipation Award SP1802663 I.
Table 1 provides a detaded comparison of the structural parameters obtained by McClelland [El],who used an electron diffraction method, with those ob-
References
conformer predicted by the 4.31G results accords better with earlier experimental [4,5] and theoretical
tained in the present work. Examination of table 1 indicates that overall the 4-3 lG results are in closest
agreement with McClelland’s values, particularly with respect to the values obtained for a! and RN_O. How-’ ever, III comparing the electron diffraction derived datawrth that obtained quantum mechanically, it must be emphasized that more geometric constraints were used in the antiysrs of the eiecrron drffraction data
than were used tn the optimlzatrons carned out
in this work. For example, m the electron dlffraction study the geometry of the nitro group was constramed IO marntain C,, symmetry with respect to the central O-N bond (see table 1 for additions details). The effect of such constramts is diflkult to quantitate,but a re-interpretatron of the electron diffraction results m hght of the current findings may be helpful m thus regard. The prel~ina~ structural study reported here represents the first in a series of studies designed to characterrze fully the structure and properties, mcluding reactivity, of NzOj and related nitrogen oxides. Studies designed to elucidate the vtbrational properties
352
[ 1 f 81 J. McEwan and L.F. Phdhps, Chemistry of the atmosphere (Wiley. New York. 1975) ch. 7, and I~C~FXUXS therein. [21 C.C. Likens and I-H. Bormuln. Science 184 (1973) 1176. f3] P.A. Akrshin. L-V. Vtidov and V.Y. Rosolorskir, Zh. Strukt Khym. I (1960) 1 [4] 1-C. Htntsune. J P. Devhn and Y. Wada. Spectrochim. Acta 18 (1962) 1641 [Sl 5.L. Ames and D.W. Turner, Proc. Roy. Sot. A348
(1976) 175. [ti] A. Julg and Y. Otis, Rev. Chim. hlmcr. 6 (1969) 101. 17) K 0kada.S. Yabushita, K. Yamaguchi and T. lkeno. Chem. Lettets(l977) 1247. 181 B.W McClelland. D’iss.Abstr. inr. B 32 (1971) 2099. i9i \V.J. Hehre,W A. Lathan, R Dltchfirld. hi D-Newton and J.A. PO& QCPE I1 (1974) 236. IlOJ W J. Hchre,*R.F.-Stewart and J.A. Pople. J. Chem. Phys. 5 I (1969) 2657. 1111 R. 5ttch~eld, WJ. Hahre and J.A. Pople, 1. ~hem.Phys. 54 (19711724. [ 121J.A. Pople and RX. Nesbet, J. Chem. Phys. 22 (1953) 571. ~13JCCJ.Rooth~n,Rev.hiod.Phys.23(2)(1951)69. [ 141 G. Herrberg. Molecular spectra and molecular structure, Vol. 3 (Van Nostrand, Pnnceton. 1966).
87, number -1
CHEMICAL
THE STRUCTURE OF DINITROCEN John E. CARPENTER
PHYSICS
LE-I’TCRS
2 Apsl
1982
PENTOXIDE
and Gerald M. MAGGIORA
Deparrmennrs of Chemistry and Lahvrence. Kansas 66045. USA
Bioclrenrisrr) . Unirersi~
of h’atrsas.
Reccned 8 January 1982
Ab initio restricted Harrree-rock sclf-consistcnt-Iield molecular orbits1 calculations at the STO-3G and J-31C baas set levels have been used to determme the mimmum-rnergy ~IIUC~UICoiduorrogen pcntokidc, NzOj- The c~cuht~oos~ho~v that NaOs has an anhydride-type structure wth its mtro groups rotated 42’ out of the ccnkd N-O-N plane m 3 conrotatory bsh1on.
1. Introduction
NO? into rntric actd, a component of acid rain [?I. The basrc structure of N,Os
The chemtstry of nitrogen oxides IS extremely
com-
IS gtven m fig. I, IIOW-
ever, the most stable conformation
of the molecule is
plex and as a result is still not fully understood. Due
the SubJcct of some controversy particularly
mainly to their Importance
tatton of the nttro groups wrth respect to the N-O-N
tion of photochemical
smog, the smaller nitrogen ox-
ides NO, NO?, N1O, etc.,
btle eshaust,
as key agents m the formafound primarily
have been studied
m automo-
extensively
[I].
ever, this is not the case in the larger nitrogen NzOj.
N204
and N205
whose
resctlvlty
Howoxides
and instabil-
ity has made their study particularly difficult. For exthe anhydride of
ample, dinitrogen pentoxide, N,Oj, nitric acid thermally
decomposes to NO2 and NO-, and
reacts readily with water to form two molecules of nitnc acid. This latter reactton may be an important hnk in the chain of reactions that convert atmospheric
the ortcn-
plane of the anhydrtde bond. An early electron difiracnon study [3] suggests that the mtro groupsare rotated 90” abour the O-N anhydnde bonds and rhus ore perpendlculnr
to the central
N-O-N
plane. H~satsune et
al. [J] assumed that the molecule was planar wlth Czv m order to assign the normal modes of vibration of its IR spectrum. Turner and Ames [5] determined the photoelectron spectrum and performed ab mitio self-consistent-field molecular-orbital (SCF MO) calculations on several dtiferenr conformers m an efsymmetry
fort to correlate the structure of N205
with Its photo-
electron spectrum. From then studies they also con-
Fig. 1. Ceometnc paramelers of NzOz optlmlzcd. See section 2 for a discussion of addihonal parameters studied.
cluded that the molecule was planar. Addrtronal calculations were carrted out by Julg and Oznts [6] on the planar conformer suggested by Hisatsune et al., while Okada et al. [7] constdered both the planar and perpendicular conformers. On the basts of their calculations, the latter investigators found the planar conformer to be most stable. In none of the above cited studtcs were all posstble orientations of the nitro groups considered. However, in a recent electron dtffraction study, McClelland [S] suggested that the nitro groups are rotated, in a conrotatory manner, about the central O-N bonds and lie 349
Voiume 97. numtw 4
7 ApnI 1981
CHCMICAL PHYSICS LIZMERS
at an an$e of =-@ wrb respect IO the N-O-N plane. Such an lnlern?edlate col~formation IS not entirely unexpected due to repulsive interactions between the
3. Results and discussion
nitro groups m 111eplanar confomw
yIelded the non-planar structure shown in fig. 7, where
and the apparent
loss of conlugdtion in the pcrpendwlx
conformer.
In an effort I0 furlher charactari7e lhc Slructure
and resolve 111~qucstlon of mtro group OrIcntatron, we have cdrried out an e\tenslvc scr~esof ab mirlo SCF MO cslculatlons IO determme lhe minimum-energy structure
Of
NzOj dnd to mvesngate its relationship to
other low-energy c0ni0rmatI0n
2. .Computational
5.
methodolo~
All calculstions described in the present work were camed out wth
the GAUSSIAN
70 SCF h10 program
and 4-3 IG [I I] basis sets. Optimrzations were performed with the standard algorithm contamed in the program. Due to the earlier work of Okada et al. [7] wllicll suggested that a hrghly polarized spm distribution ellsted m the singlet ground state of Nz05, all preliminary calculations employed the unrestricted Hnrtrce-Fock method [ 111. However, e~arnlnation of the results of these calculatrons indlcsted the absence of any spin polarization, the results bemg identical to thos: obf lined from the usual resrncrrd Hat-tree-Fock nletr,od [ 131.Thus, a11subsequent calculations were carned out with the latter method. ImtiaI optimizattons were carried out at the [9] m both the STO-3C
[IO]
basis set level, and selected points were optmzed at the 3-3 1G Icvel.
STO-3C
A Cz symmetry ws bisecting the central N-O-N which were based on the followmg types of geometric parameters: bond lengths R,_, and RN_0 and bond angles Q, I( and y as shown in fig. I. and angIes # 1, B,, and Q, angle ivaj assumed in all optimizations.
which are not depxied
350
the mtro groups are rotated conrotatorily
ti?“,
m
excellent agreement wit hlcClclfand’selectron dlffraction results [8]. Thn structure is *5 kcal n&-I mow stnble than either the perpendicular or the planar conformers,
the latter considered to be the most stable
conformer by most earlier workers (vide supra). In the planar and perpendicular casesall structurd parameters were optimized except Ot and 81, whrch were both fixed at 0” or 90”. respectively. Detatls of the structural parameters For all three confo~ers are given in table I. Eaaminatmn of table I shows that the nttro group structural parameters,RI,,_t, and 7, are essenri@ unchanged with respect to all three conformers and very smldar to the calculated values found for nitrogen dloxide itseff(RI+_O = 1.19 A,0 = 134O [I4]). Thus, the adiabatically relaxed potential energy curves for conrotatory and clisrotatory nitro group rotations were determined by fixing Ro_N,RN_o, p and 7 at their values m the planar conformer and varying a and fl for each set of B values. The curves obtamed by thus process are grven m fig. 3A. the conrorato~ curve is rep resented by the solid hne, the disrotatory curve by the dashed Ime and the fully rend partiaIly optimized STO-3G based SCF MO calculations by filled cl&es and open circles, respectively. Fig. 3B Illustrates the magnitude of changes in a and /3 for the more stable conrotatory nitro group rotarion. Not unexpectedly, a undergoes approxunately three times as large a change as that experienced by 0 (Z 15” as opposed to MO), although the change in fl is still significant.
m fig. 1. Angles 0, and B2
describe nitro group stations about the central O-N bonds (taken in a clockwise sense looking from the nitro groups towards the central oxygen atom) whrch can be rotated m a coupled fashron either conrotatory (0, = 02) or disrotatorily (Ot = -02). Angle q describes the orientation of the nitro group plane and the plane formed by the central ohygenatom and an oxygen and nitrogen atom of the mtro group and approximates a “wagging” matron of the mtro group. All bond lengths are given m &gstr6ms
Full optln~ization at the STO-3G basis set fever
and angles in degrees.
Kg. 2. IMly optunized structure of N205. See table 1 for the value5of the geometnc parameters.
Volume 81, number 4
CHEMICAL PHYSICS LflTTCRS
2 Aprd I982
Table 1 Geometric parameters oi N7_0sa1 Perpendrcular
Parametcrb.C) Pkxxtr STO-3G
; Y 01 & lo-N RN-O
energy
4-31G
STO-3G
117.4363 119 6733 132 0909 o.oooo* o~oooo*
123.9746 119.1724 13 I.6979 0 oooo* o.~o~*
102.5150 113.2468 131.1078 87 8809 87 8809
019699 0000” 1 2669 -476.030 13
0.0000’ I 4527 1.1909 -482 03013
176.7242 1 4901 1 2670 -476 33.515
C\penment3l 181
IWly optim~ed -t-31G
STO-3G
J-31G
109 I145153 8522 131 8496 90 oooo= 90.0000w
I08 116 2117 33J i 32.0909 39.1281 39.1281
113 116.1374 75.52 131.9571 4 I 4507* 3145075
114 35t 113 133 3 4s tx$) 4.5 ood)
~77.0000~ I .-lb49 1 1923 -482 02804
175I 3699 4077 1 2699 -476.3319I
I 77I oaoo* 499
lSO_O~~ 1AS36
1.1917 -482.03665
I 188
a) Parameters held constant durmg an optlm~atton are marked by an astcrts!. (=I; p~~rnet~r values assumed are m~ked by a dagger fi) b) All bond m&s are grven in degrees. bond lengths in &gsCr6ms. and energy tn hattrees Cl See fig 1 and se&on 2 of te\t for a full desctiptton of the geometrx parameters d) AdditIonal structural rcfinemcnt gax 6t = 29.S?’ and 8:! = 49.87” 181. although the cffecr on the Of.tJ2 values of certain geometric constratnts tmposed by hfcCIrbnd ISdtificult IOassess
In order to increase the reliabtIrty of the theoretml were ctrrted out to redet~rnllnc the structure of the planar, perpendrcular and mjntmum-ener~ conformers. All structural parameters for ilie mininlum-ener~ conformer were fully optimized while 0 t , e2 and q were fixed in the planar and perpendicular conformers, all other parameters being fully optrmized. In the latter two cases q was constrained based on prel~~na~ calculations which showed that the total energy was msensttmc to Q over a reasonably broad range about tts constrained value. Appropriate STO-3G optimtzed structures were used as mttial guesses for the 4-3 ICi calcuIstions. prcdlctio~s, 43 IG level c~cui~tlons
ftg 3 (A) The encr~cttcsofa~ta~~tcni~ refixed nitro group rotations The fried rucles (*) and tnangle (A) represent fully optimKed STO-3G and 4-31G ~~~i~~tons, wlule the open cw firs (o) and utangles (6) represent parttally optimucd STO-3G and 4-31G ~cu~tions The soltd line (-1 inchutes a conrotatory mtro group Matron and the dashed lmc (---Is disroCato~ nttro group rotation (B) The t&o curves represent the chuges undergone by angles a and 13(see fig 1) during the ad~bati~ily relaxed conrotaCory nitro group rotation. The calculttlons wete carried out at the STO-3G basts set 1eW and as XI(A) above the Tied circles or squires represent full structural optCm~atCon,whale the open nrcks or squares repreSc’ntpart131opt~~tron-
351
Volume 57, number 1
CHEMICAL PHYSICS LETTERS
Fig. 3A clearly shows that both basrs sets predtct similar minimum.energy geometries with respect to nitro group orientation, and the relative energetics of
2 Apnl 1982
of N,Os are underway, and the results will be reported presently.
the 4.3IG opmized conformers(denotedin fig. 3 by filled and open t~angles) are qualltatNety stmrtar to those obtamed in the STO-3G basrs. However, the greater srabdny of the planar over the perpendicular
Acknowledgement
[6,71 proposals. while the STO-3C results predtct just the opposite order.
Support for the calculations from the Academic Compuler Center of the University of Kansas ISgratefully acknowledged. J.C. also wishes to acknowledge parttal support from NSF Unde~raduate Research Parttcipation Award SP1802663 I.
Table 1 provides a detaded comparison of the structural parameters obtained by McClelland [El],who used an electron diffraction method, with those ob-
References
conformer predicted by the 4.31G results accords better with earlier experimental [4,5] and theoretical
tained in the present work. Examination of table 1 indicates that overall the 4-3 lG results are in closest
agreement with McClelland’s values, particularly with respect to the values obtained for a! and RN_O. How-’ ever, III comparing the electron diffraction derived datawrth that obtained quantum mechanically, it must be emphasized that more geometric constraints were used in the antiysrs of the eiecrron drffraction data
than were used tn the optimlzatrons carned out
in this work. For example, m the electron dlffraction study the geometry of the nitro group was constramed IO marntain C,, symmetry with respect to the central O-N bond (see table 1 for additions details). The effect of such constramts is diflkult to quantitate,but a re-interpretatron of the electron diffraction results m hght of the current findings may be helpful m thus regard. The prel~ina~ structural study reported here represents the first in a series of studies designed to characterrze fully the structure and properties, mcluding reactivity, of NzOj and related nitrogen oxides. Studies designed to elucidate the vtbrational properties
352
[ 1 f 81 J. McEwan and L.F. Phdhps, Chemistry of the atmosphere (Wiley. New York. 1975) ch. 7, and I~C~FXUXS therein. [21 C.C. Likens and I-H. Bormuln. Science 184 (1973) 1176. f3] P.A. Akrshin. L-V. Vtidov and V.Y. Rosolorskir, Zh. Strukt Khym. I (1960) 1 [4] 1-C. Htntsune. J P. Devhn and Y. Wada. Spectrochim. Acta 18 (1962) 1641 [Sl 5.L. Ames and D.W. Turner, Proc. Roy. Sot. A348
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