July, 1963
ELECTEOSIC SPECTEAAND STRUCTURE OF a- ASD @NAPHTHOL
ELECTROSIC SPECTRA AXD STRUCTURE OF
1443
ASD p-XAPIITHOL1
CY-
BY KICHISUKE NISHINOTO Department of Chemastry, Faculty of Science, Osaka Czty Unioersify, A'uniiyoshi-ku, O.saka, Japan Received November 16, 1962 A semi-empirical theory based on ASMO-CI method is applied to the electronic structure of a- and p-naphthol. The calculated results are, on the whole, in satisfactory agreement with the experiment. I n spite of the absence of D2hsymmetry, the nature of the electronic spectrum of a-naphthol is well correlated with that of naphthalene. The effect of substitution at the a-position of naphthalene causes a substantial red shift in the BO,, band, and a rather small shift in the Bau- band. On the other hand, in P-naphthol the characteristics of the naphthalene spectra are rompletely destroyed, because the configuration corresponding to naphthalene's Rlu band interacts strongly with the configuration corresponding to the Bsu- band. Our calculation can also explain other moleculw properties, such m hydrogen bond forming power and dipole moments in the various electronic states.
Introduction In a previous paper,2 a semi-empirical theory was applied to the calculation of the electronic spectra and electronic structure of phenol to study the effect of substitution on the parent hydrocarbon. According to the calculation, the polarizations of the excited states of benzene are still preserved by the substitution of a hydroxyl group, accompanied with the considerable change in the intensities and frequencies of the electronic transitions. Our next interest is to study the effect of substitution on the electronic structure of a more complicated molecule, such as naphthalene. I n naphthalene derivatives] the effect of substitution on the electronic spectra of naphthalene depends considerably upon the position where the substituent is attached to the m ~ l e c u l e . ~ - ~The near-ultraviolet spectra of naphthalene have three absorption maxima.8 The high frequency band in the region of 45,300 cm.-' has the greatest intensity; the medium intensity band in the 36,400 em.-.' region is assigned t o B2"; and the weakest band near 32,200 em.-', to B3-u. The substitution a t the a-position of naphthalene causes a substantial red shift in BzUband and a rather small shift in B3,,- band. On the other hand, the substitution a t the @-position leads apparently to slight blue shift in the former band and a rather larger red shift in the latter. The band intensities have a tendency to increase as band shifts to the red. Recently, a theoretical study has been made by Baba and Suzuki5 to elucidate this interesting phenomenon. The electronic spectra of a-naphthol were successfully explained by their theory, but those of ,&naphthol were still open to question. I n this paper, a semi-empirical calculation will be applied to the electronic spectra of naphthols to make clear this problem. I n addition, some molecular properties, such as hydrogen bond forming power and dipole moments in the various electronic states, of naphthols will be discussed. The Calculation In this paper the folloming approximations arc used : E'irst, differential overlap is neglected.".'" Second, the (1) Presented in part a t the Symposium on Electronic States in Molecules held by the Chem. SOC. of Japan, Oct., 1961. (2) K. Nishimoto and R. Fujishiro, Bull. Chem. Soc. Japan, 31, 1036 (1958). (3) R. A. Friedel and M.Orchin, "Ultraviolet Spectra of Aromatic Compounds," John Wiley and Sons, Xew York, N. Y., 1951. (4) D. M. Hercules and L. B. Rogers, Spectrochzm. Acta, 393 (1959). ( 5 ) H. Baba and S. Susuki, Bull. Chem. Soc. Japan, 34, 82 (1961). (6) C. J. P. Spruit, Rec. trav. chzm., 68, 309 (1949). (7) C. Daglish, J. Am. Chem. Soc., 71, 4859 (1950). ( 8 ) American Petroleum Institute Research Project 44, Ultraviolet Spectral Data, Serial No. 640, 65L.
integrals over atomic orbitals (AO) are est'imated by a semi-empirical procedure. Finally, the core structures of the naphthols are assumed as indicated in Fig. 1. All nearest carbon-carbon distances are assumed to be 1.390 8.,and the carbon-oxygen distance to be 1.460 A . These values of interatomic distances are the same as those used in the study of phenol.2 The procedure of calculation is as follows (1) We set up Huckel MO's, using the same parameters as those of phenoL2 The Huckel MO's, $i, arc expressed in the form $i
=
C CiP4p
(1)
P
where 4,, is the p-th 2pn A 0 and Ci, is the coefficient to be determined by variational procedure. A secular equation of the eleventh degree must be solved. (2) The configurational wave functions, xi, are built up as antisymmetrized products of these &IO'S. The wave function and the corresponding energy for the ground state are denoted by xo and Ho, respectively. The excited configuration which arises from the excitation of an electron from an occupied orbital $i to a vacant orbital $k! is written as 'xi-k' or 3Xi-k', where the superscripts 1 and 3 are associated with singlet and triplet, respectively. The configurational energy Hi+! associated with Xi-k' is calculated by two methods described in our previous papers. One (Method J) is given in ref. 2. Another one (Method 11) is found in ref. 11. Electron repulsion integrals are calculated by the methods proposed in our previous papers.2*12 (3) The electronic state functions, \kats, are represented by the linear combinations of configurational wave functions *a
=
Ci d a i x i
(2)
where d a i is a coefficient to be determined by the variation principle. In the present calculation, the excited state functions are expressed by the linear combinations of the four lowest singly excited configurations, ~ 1 - 1 ' ) XW', x1--2', and XZ-~.. We must therefore solve a secular determinant of fourth degree, in which the matrix elements have the form Hi-w,
j-it
=
J
Xi-ktHXj-1'
dv
(3)
where H is the total Hamiltonian for the system. (9) R. Pariser and R . G. Parr, J. Chem. Phys., 21, 466, 767 (1953). (10) R , Pariser, ibid., 1 4 , 250 (1956). (11) K. Nishimoto and R. Fujishiro, Bull. Chem. Soc. Japan. 35, 90.5 (1962).
(12) I
