- Email: [email protected]
Magnetic circular dichroism spectra of 1,5-naphthyridine
23 July 1982
CHEhfICAL PHYSICS LETTERS
Volume 90, number 2
MAGNETIC CIRCULAR DICHRDISM SPECTRA OF 1,5-~APHTHYRID~E M. ATA, 0. SEDOYAMA and H YAMACUCHI Department of
Chemistry, Faculty of Science, Kumamoto
Umkersity. 2-39-l
Kurokami,
Kumnmoto
860, Japan
Received 8 May 1982; m final Form 24 May 1982
The absorptron and MCD spectra of I$-naphthyridmc (1) WCrcportcd. The transitIon cncrgres, oscIlfator strcngthsand Faraday E terms computed withm the PPP SCF T MO CI method NC m reasonable agrccmcnt with cvpcrlmcnt. The Faraday B terms of two bands m the mlddlc wavenumber rcglon [(30.0-45.0) X lo3 cm-’ ] or 1 arc larger than lhosc m quinotinc.
1. Introduction
2. Experimental
Many papers concerning the electromc structure and spectra of azanaphthalenes have been reported [l-9] _ The electronic spectra of ~anaphthalenes were invess @ated by the semiemp~ical SCF MO method [l-4, 7-91. The ordering of the ftied x orbitals and the nrtrogen lone-pair orbitals was interpreted on the basis of the photoelectron spectra and the semiempirical MO calculations [5,6] _ Recently, magnetrc circular dichrolsm (MCD) spectra of n~phthalene and seven of its aza anaIogues have been reported [ IO,1 11, but the MCD spectra of I ,5naphthyridlne (1, see fig. 1) has not been publIshed. The MCD technique, which has been shown to be very useful in resolving complicated absorption bands into their components, is used for our purpose, and reasonable assignments for the absorption bands have been aided by LCAO SCF MO CI calculations [IO-181. The purpose of this paper is to assign the absorption spectra of 1 by using the MCD spectra and the results of variable bond-length SCF n MO CI calculatlons and to compare the Faraday B term extracted from the MCD spectra with those c~culated by the vrlnable bond-length SCF 7~MO CI method [19,20].
The sample was purified by rccrystalhwtion from petroleum ether. Spectrograde cyclohexane was used as a solvent. The MCD spectra were recorded with a JASCO J-500C recording circular dichrometer equipped with a 1.33 T electromagnet. In order to obtain adequat’ signal-to-noise ratios, multiple scanning and averaging were accomplished with the use of a DP-SOIN data processor. The absorption spectra were measured on a Hitachi ZOO-20recording spectrop~lotomcter_ All measurements were made at room te~lperature_ The Faraday B values were extracted from the MCD spectra by use of the formula
*
where Yis the frequency in cm-’ and [BJ hf the molar elliptlclty per unit field in units of deg lz m-l mol-1 G-l [13] The absorption spectra were analyzed by a curve-fitting procedure usmg gausslan functions [ 141 The dipole strengths and the Faraday B terms were obtamed by use of the m&hod of moments [I4] _
3. Calculation
Fig I. CoordiWc system of i,S-rwphthyridmc.
0 009.2614/82/0000-0000/S
02.75 0 1982 North-Holland
We have calculated the electronic transition energies (A& the dipole strengths (D) and the FaradayB v&es by use of the variable bond-length SCF JI MO CI 133
CHEMICAL PHYSICS LETTERS
Volume 90, number 2
method [19,20]. For C-C bonds, the bond-order bondlength relationship cited in ref. [19] was used. The bond lengths for the C-N bonds were calculated by use of the equatron cited in ref [20]. Standard parameters were used within the PPP approximation 1201. AlI singly excited configurations were included in the configuration interactrons. The magnetic moments were computed according to the procedure described by Kaito et al. (161 and the electric moments evaluated by use of a dipole length operator. Lowdin-orthogonalized atomic basis functions were used for the calcu. lation of both quantities [21] The bond lengths and bond angles were taken from the experimental values of azabenzenes [22] In all calculations, the origin was set at the center of gravity of 1.
0
23 July 1982
4
0
4. Results and discussron The absorptton and MCD spectra of 1 are shown m fig. 2. The computed transition energies (AL?),dipole s~ren~lls (D) and Faraday B values for 1 are summa~zed in table I along with the experimental results. Table 1 shows that the agreement between the calculated and exper~ental values for AE, B and D is not very good. However, the predrcted sign of8 agrees wth the sign of B extracted from the MCD spectra. In the lower wavenumber region, (25 O-30 0) X 103 cm-‘, compound 1 exhibits no MCD bands, hke quinohne and isoquinoline [ lo,11 J . We have measured the absorption spectrum of 1 in polar solvents such as methylacetate, 1-butanol, ethano1 and methanol. With increasing polartty of the solvent, the band I smfts to-
Table 1 Trnns~tron cncrgies (A_!?),dlpolc swxgtbs state
cml’f
ward the blue and all other absorption bands (2,3 and toward the red. On the basts of the usual conceptron that n -+ x* abso~tion bands are blue-shifted in polar solvents, tt is concluded that band 1 may be asslgned to an n + d transrtion and all other bands (2,3 and 4) to E+ II* transttions. Table 1 also supports this The investigation of the photoelectron spectra has shown that the symmetry of the nitrogen Ionempair orbital n+ is ag and the energy of n_ (bu) is lower than that of n, [5,6] AS the predicted symmetry of the lowest II* orbttal is bg and the s~rnet~ of the n +s* transitron is 4)
(0) and Faraday R values
Calculated AE (lo3
Fig. 2. The mqnetic circular dichroism spectrum (top) and the absorption spectrum (bottom) of l,5-nnphlhyrldine in cyclohexznc at rwm temperature.
Evpcrrmcntal D 3
I.+@)
104
-194
5E(i03
cm’)
L?3
3 b,
21.5
‘)D’(l
134
Bu
33.4
&I
39 5
991
% %I
46 9
forb
D=3.3356x
49 6
1f3’Cm)
05.1
b, lam4p D* cm.
62.7
forb.
28.0
32 3
4.39
400
S-11
47.5
48.3
-10.2 38.5
Volume 90, number 2
CHLhIICAL
B,, it can be considered that the n * 7~*transition is the forbidden tranntion. It is difficult to observe the Faraday l3 term of a forbidden transitIon in MCD spectra. In the middle wavenumber region, (30 O-45.0) X lo3 cm-l, two MCD bands (bands 2 and 3) with opposite sign can be identified. The vibrational structure v&h a progression of ==7OOcm-l IS observed in the MCD and absorption spectra of band 2 Band 3 shows the MCD and absorption spectra consisting of a nbrational progression of ~1400 cm-l. The signs and magnitudes of the Faraday L?terms of bands 2 and 3 are closely related to the position at which the aza substitution OCcus As shown by Vasak et al. [I l] , the I-aza replacement makes the Faraday B term of band 2 more negative and the Faraday B term of band 3 more positive. Adexpected, the FaradayE term (-10.2 X lo4 0 D2 cm) of band 2 of 1 is more negative than that (-9.0 X lo4 0 D2 cm) [lo] of band 1 of quinoline and the Faraday B term (38 5 X lOA /3D* cm) of band 3 of 1 is more positive
23 July 1982
PHYSICS LETTERS
than that (21 X IO4 p D* cm) [lo]
of band 2 of quinoline. In the higher wavenumber region, (45 O-SO 0) X lo3 cm-lthe intense band (log E = 4.47) is observed. As the MCD spectra measured in the wavenumber region above 47.6 X 103 cm-1 are noisy, we cannot extract the Faraday B term from the MCD spectra, which are not shown in fig. 1. Table 1 shows that the intense band is composed of two n--f n* transItIons (one is the forbidden transition and the other the allowed transition)
Acknowledgement
One of the present authors (HI’) thanks the Computer Center, Kyushu University, for the use of the FACOM M-200 computer_
References
[I] 8. Tmhnd, Thcorct. Chum. Acta 8 (1967) 361. [2] H. Baba and I. Yamawkl,
I. hfol. Spcctry.
44 (1972)
118
[3] J E Rldlcy and h! C. Zcrncr, I. hlol. Spcdry 50 (1974) 457.
[4] A D. Jordan, I C. Ross, R. Hoffmann, J R. Stvcnsbn and R. Glc~tcr, Chcm. Phys. Lcttcrs IU (1971) 572. [5] D.M.W van den Ham and D van dcr Mccr, Chcm Phys Letters 12 (1972) 447. [6] F. BrofiL, E. Hellbronncr and T. Kobayaql, Hclv. Chum. Acta 55 (1972) 274 [7] Z Yoshlda and T. Kobayarhl, Thcorct. Chim. Acta 20 (1971) 216. [a] E-C. Lim and A. Tanin, Spcctry. Lcttcrs 5 (1972) 35. [9] R W. Wagner, P. Hochmnnn and h1.A. El-Bayounn. J hlol Spectry 54 (1975) 167. [LO] A K~IIOand hl Hatano, J Am Chcm Sot. 100 (1978) 4037. [I I ] hl. Vauk, hl R. Wlupplc and 1 hllchl. J Am. Chcm. Sot. 100 (1978) 6838. [IZ] A D. Buckmgham and P J. Stcphcns, Ann. Rev. Phys Chcm. 17 (1966)
399.
[IS] P.N. Schatz and AJ hIcCaffcry,
Qu;lrt. Rev. Chcm. Sot. 23 (1969) 552. [ 141 J Badoz. hf. Ddhrdor,. AC Boccara and B. Elriat, Symp. Faraday Sot. 3 (1969) 27 [ 151 P J. Slcphcns, R.L hlowcry and P N Schltz, J. Chcm. Phys 55 (197 1) 224. [16] A Kaito, A TaJIri and hf. Hatano, J. Am. Chcm Sot. 97 (1975)5059.98(1976)384 1171 hf Higashi and H. Yamaguchi, J Chcm. Phys. 70 (1979) 2198. [ 181 H Yamaguclu and hl. Higashi, Chcm. Phys. Lcttcrs 68 (1979) 77 [ 191 H. Yamagucbi, T Nakqlma and T.L. Kurm, Thcoret. Ctum Acla 12 (1968) 349. [20] H. Yamaguchl, T. Ikcda and H. hfamctsukJ, Bull. Chcm. Sot Japan48 (1975) 1118. [21] P 0 Lowdin, J. Chcm. Phys. 18 (1950) 365. [22] K. Kimura and hl. Kubo. I. Chcm Phys. 32 (1960) 1776.
135
CHEhfICAL PHYSICS LETTERS
Volume 90, number 2
MAGNETIC CIRCULAR DICHRDISM SPECTRA OF 1,5-~APHTHYRID~E M. ATA, 0. SEDOYAMA and H YAMACUCHI Department of
Chemistry, Faculty of Science, Kumamoto
Umkersity. 2-39-l
Kurokami,
Kumnmoto
860, Japan
Received 8 May 1982; m final Form 24 May 1982
The absorptron and MCD spectra of I$-naphthyridmc (1) WCrcportcd. The transitIon cncrgres, oscIlfator strcngthsand Faraday E terms computed withm the PPP SCF T MO CI method NC m reasonable agrccmcnt with cvpcrlmcnt. The Faraday B terms of two bands m the mlddlc wavenumber rcglon [(30.0-45.0) X lo3 cm-’ ] or 1 arc larger than lhosc m quinotinc.
1. Introduction
2. Experimental
Many papers concerning the electromc structure and spectra of azanaphthalenes have been reported [l-9] _ The electronic spectra of ~anaphthalenes were invess @ated by the semiemp~ical SCF MO method [l-4, 7-91. The ordering of the ftied x orbitals and the nrtrogen lone-pair orbitals was interpreted on the basis of the photoelectron spectra and the semiempirical MO calculations [5,6] _ Recently, magnetrc circular dichrolsm (MCD) spectra of n~phthalene and seven of its aza anaIogues have been reported [ IO,1 11, but the MCD spectra of I ,5naphthyridlne (1, see fig. 1) has not been publIshed. The MCD technique, which has been shown to be very useful in resolving complicated absorption bands into their components, is used for our purpose, and reasonable assignments for the absorption bands have been aided by LCAO SCF MO CI calculations [IO-181. The purpose of this paper is to assign the absorption spectra of 1 by using the MCD spectra and the results of variable bond-length SCF n MO CI calculatlons and to compare the Faraday B term extracted from the MCD spectra with those c~culated by the vrlnable bond-length SCF 7~MO CI method [19,20].
The sample was purified by rccrystalhwtion from petroleum ether. Spectrograde cyclohexane was used as a solvent. The MCD spectra were recorded with a JASCO J-500C recording circular dichrometer equipped with a 1.33 T electromagnet. In order to obtain adequat’ signal-to-noise ratios, multiple scanning and averaging were accomplished with the use of a DP-SOIN data processor. The absorption spectra were measured on a Hitachi ZOO-20recording spectrop~lotomcter_ All measurements were made at room te~lperature_ The Faraday B values were extracted from the MCD spectra by use of the formula
*
where Yis the frequency in cm-’ and [BJ hf the molar elliptlclty per unit field in units of deg lz m-l mol-1 G-l [13] The absorption spectra were analyzed by a curve-fitting procedure usmg gausslan functions [ 141 The dipole strengths and the Faraday B terms were obtamed by use of the m&hod of moments [I4] _
3. Calculation
Fig I. CoordiWc system of i,S-rwphthyridmc.
0 009.2614/82/0000-0000/S
02.75 0 1982 North-Holland
We have calculated the electronic transition energies (A& the dipole strengths (D) and the FaradayB v&es by use of the variable bond-length SCF JI MO CI 133
CHEMICAL PHYSICS LETTERS
Volume 90, number 2
method [19,20]. For C-C bonds, the bond-order bondlength relationship cited in ref. [19] was used. The bond lengths for the C-N bonds were calculated by use of the equatron cited in ref [20]. Standard parameters were used within the PPP approximation 1201. AlI singly excited configurations were included in the configuration interactrons. The magnetic moments were computed according to the procedure described by Kaito et al. (161 and the electric moments evaluated by use of a dipole length operator. Lowdin-orthogonalized atomic basis functions were used for the calcu. lation of both quantities [21] The bond lengths and bond angles were taken from the experimental values of azabenzenes [22] In all calculations, the origin was set at the center of gravity of 1.
0
23 July 1982
4
0
4. Results and discussron The absorptton and MCD spectra of 1 are shown m fig. 2. The computed transition energies (AL?),dipole s~ren~lls (D) and Faraday B values for 1 are summa~zed in table I along with the experimental results. Table 1 shows that the agreement between the calculated and exper~ental values for AE, B and D is not very good. However, the predrcted sign of8 agrees wth the sign of B extracted from the MCD spectra. In the lower wavenumber region, (25 O-30 0) X 103 cm-‘, compound 1 exhibits no MCD bands, hke quinohne and isoquinoline [ lo,11 J . We have measured the absorption spectrum of 1 in polar solvents such as methylacetate, 1-butanol, ethano1 and methanol. With increasing polartty of the solvent, the band I smfts to-
Table 1 Trnns~tron cncrgies (A_!?),dlpolc swxgtbs state
cml’f
ward the blue and all other absorption bands (2,3 and toward the red. On the basts of the usual conceptron that n -+ x* abso~tion bands are blue-shifted in polar solvents, tt is concluded that band 1 may be asslgned to an n + d transrtion and all other bands (2,3 and 4) to E+ II* transttions. Table 1 also supports this The investigation of the photoelectron spectra has shown that the symmetry of the nitrogen Ionempair orbital n+ is ag and the energy of n_ (bu) is lower than that of n, [5,6] AS the predicted symmetry of the lowest II* orbttal is bg and the s~rnet~ of the n +s* transitron is 4)
(0) and Faraday R values
Calculated AE (lo3
Fig. 2. The mqnetic circular dichroism spectrum (top) and the absorption spectrum (bottom) of l,5-nnphlhyrldine in cyclohexznc at rwm temperature.
Evpcrrmcntal D 3
I.+@)
104
-194
5E(i03
cm’)
L?3
3 b,
21.5
‘)D’(l
134
Bu
33.4
&I
39 5
991
% %I
46 9
forb
D=3.3356x
49 6
1f3’Cm)
05.1
b, lam4p D* cm.
62.7
forb.
28.0
32 3
4.39
400
S-11
47.5
48.3
-10.2 38.5
Volume 90, number 2
CHLhIICAL
B,, it can be considered that the n * 7~*transition is the forbidden tranntion. It is difficult to observe the Faraday l3 term of a forbidden transitIon in MCD spectra. In the middle wavenumber region, (30 O-45.0) X lo3 cm-l, two MCD bands (bands 2 and 3) with opposite sign can be identified. The vibrational structure v&h a progression of ==7OOcm-l IS observed in the MCD and absorption spectra of band 2 Band 3 shows the MCD and absorption spectra consisting of a nbrational progression of ~1400 cm-l. The signs and magnitudes of the Faraday L?terms of bands 2 and 3 are closely related to the position at which the aza substitution OCcus As shown by Vasak et al. [I l] , the I-aza replacement makes the Faraday B term of band 2 more negative and the Faraday B term of band 3 more positive. Adexpected, the FaradayE term (-10.2 X lo4 0 D2 cm) of band 2 of 1 is more negative than that (-9.0 X lo4 0 D2 cm) [lo] of band 1 of quinoline and the Faraday B term (38 5 X lOA /3D* cm) of band 3 of 1 is more positive
23 July 1982
PHYSICS LETTERS
than that (21 X IO4 p D* cm) [lo]
of band 2 of quinoline. In the higher wavenumber region, (45 O-SO 0) X lo3 cm-lthe intense band (log E = 4.47) is observed. As the MCD spectra measured in the wavenumber region above 47.6 X 103 cm-1 are noisy, we cannot extract the Faraday B term from the MCD spectra, which are not shown in fig. 1. Table 1 shows that the intense band is composed of two n--f n* transItIons (one is the forbidden transition and the other the allowed transition)
Acknowledgement
One of the present authors (HI’) thanks the Computer Center, Kyushu University, for the use of the FACOM M-200 computer_
References
[I] 8. Tmhnd, Thcorct. Chum. Acta 8 (1967) 361. [2] H. Baba and I. Yamawkl,
I. hfol. Spcctry.
44 (1972)
118
[3] J E Rldlcy and h! C. Zcrncr, I. hlol. Spcdry 50 (1974) 457.
[4] A D. Jordan, I C. Ross, R. Hoffmann, J R. Stvcnsbn and R. Glc~tcr, Chcm. Phys. Lcttcrs IU (1971) 572. [5] D.M.W van den Ham and D van dcr Mccr, Chcm Phys Letters 12 (1972) 447. [6] F. BrofiL, E. Hellbronncr and T. Kobayaql, Hclv. Chum. Acta 55 (1972) 274 [7] Z Yoshlda and T. Kobayarhl, Thcorct. Chim. Acta 20 (1971) 216. [a] E-C. Lim and A. Tanin, Spcctry. Lcttcrs 5 (1972) 35. [9] R W. Wagner, P. Hochmnnn and h1.A. El-Bayounn. J hlol Spectry 54 (1975) 167. [LO] A K~IIOand hl Hatano, J Am Chcm Sot. 100 (1978) 4037. [I I ] hl. Vauk, hl R. Wlupplc and 1 hllchl. J Am. Chcm. Sot. 100 (1978) 6838. [IZ] A D. Buckmgham and P J. Stcphcns, Ann. Rev. Phys Chcm. 17 (1966)
399.
[IS] P.N. Schatz and AJ hIcCaffcry,
Qu;lrt. Rev. Chcm. Sot. 23 (1969) 552. [ 141 J Badoz. hf. Ddhrdor,. AC Boccara and B. Elriat, Symp. Faraday Sot. 3 (1969) 27 [ 151 P J. Slcphcns, R.L hlowcry and P N Schltz, J. Chcm. Phys 55 (197 1) 224. [16] A Kaito, A TaJIri and hf. Hatano, J. Am. Chcm Sot. 97 (1975)5059.98(1976)384 1171 hf Higashi and H. Yamaguchi, J Chcm. Phys. 70 (1979) 2198. [ 181 H Yamaguclu and hl. Higashi, Chcm. Phys. Lcttcrs 68 (1979) 77 [ 191 H. Yamagucbi, T Nakqlma and T.L. Kurm, Thcoret. Ctum Acla 12 (1968) 349. [20] H. Yamaguchl, T. Ikcda and H. hfamctsukJ, Bull. Chcm. Sot Japan48 (1975) 1118. [21] P 0 Lowdin, J. Chcm. Phys. 18 (1950) 365. [22] K. Kimura and hl. Kubo. I. Chcm Phys. 32 (1960) 1776.
135