Jan., 1948
ULTRAVIOLET SPECTRA OF NAPHTHALENES AND DIPHENYLS [ CONTBDVTION FROM TRE u.s. BWAU
199
OF MINES, CENTRAL EXPERIMENT STATION]
Steric Hindrance and Short Wave Length Bands in the Ultraviolet Spectra of Some Naphthalene and Diphenyl Derivatives’ BY R. A. FRIED EL,^ MILTONORCI-IIN~ AND LESLIEREGGEL* ture is diminished, and bands are considerably Introduction The aromatic cyclodehydrogenation studies broader than in (I). being conducted in this Laboratory have provided I I I I I a series of compounds that exhibit interesting re5.0 lationships between ultraviolet absorption spectra and steric hindrance. Most of the work on the correlation of steric hindrance with ultraviolet 4.5 spectra has been done on diphenyl^,',^.^ but J o n e ~ has ’ ~ ~studied ~ ~ more complex aromatic systems. He observed, for example, that in 9-phen4.0 ylanthracene and 9,10-diphenylanthraceneJ the phenyl groups cannot be coplanar with the anthracene nucleus because of hindrance between neigh\ \! 3.5 boring hydrogen atoms. The resultant lack of coplanarity is manifested by the similarity of the spectra to that of anthracene. Jonesa has noted the general effects of steric hindrance on the spec3.0 tra of conjugated ring systems, such as increased 1,l’- Dinophlhyl fine structure, hypsochromic band shifts, and decreased intensity. The present paper discusses 2.5 these effects as observed for several naphthalene e, 2’. and diphenyl derivatives, which were investigated down to 206 mp. 2.0 (Y
3
XX
&
A Discussion and Results I,Z‘-Dinophthyl .In)------Dinaphthy1s.-The spectra of the three di1.5 naphthyls’O are shown in Fig. 1. 1,l’-Dinaphthyl (I)shows the greatest effect of steric hindrance as its spectrum is closest to that of naphthalene (Fig. 200 240 280 320 3) ; however, some resonance structures involving Wave length in millimicrons. coplanarity probably exist, since fine structure is Fig. 1. diminished. 2,2’-Dinaphthyl (11)should be free of steric hindrance; its spectrum shows a type of The spectrum of a dinaphthyl derivative,” structure radically M e r e n t from that of naphtha- 2,2’7,7’-tetramethyl-l,l’-dinaphthyl(IV)(Fig. 2), lene with a very strong band a t 254, a weaker indicates very strong steric hindrance. Fine strucbroad band a t 305,and a short wave length band ture is developed, including the appearance of the a t 212 mp. 1,2‘-Dinaphthyl (111) is, as expected, typical naphthalene band a t 319 mp, and intensiintermediate between the other two. Its spec- tiesare approximately double those of naphthalene. trum is more similar to that of l,l‘-dinaphthyl Also shown is the spectrum of a hydrogenated de(I); however, intensities are greater, fine struc- rivative, 3,4,3’,4’-tetrahydro-lJl‘-dinaphthyl (V), Coplanarity is probably lacking in this compound (1) Published by permission of the Director, U. S. Bureau of Mines. Presented before the Organic Division a t Atlantic City, also since the spectrum is very similar to that of 1047. Not copyrighted. 1,2-dihydronaphthalene. (2) Physical chemist, Research and Development Division, Phenylnaphtha1enes.-The spectra1*of naphO 5 c e of Synthetic Liquid Fuels, U. S. Bureau of Mines, Central thalene (VI),1-phenylnaphthalene (VII),and Experiment Station, Pittaburgh, Pennsylvania. (3) Organic chemist, Research and Development Division, O l c e 2-phenylnaphthalene (VIII)are shown in Fig. 3. of Synthetic Liquid Fuels, U. S. Bureau of Mines, Central RxpufThe 1-phenylnaphthalene (VII) spectrum rement station, Pittsburgh. Pennsylvania. sembles that of naphthalene, indicating strong (4) O’Shaughnessyand Rodebush, THISJOURNAL, 64,2906 (1940). steric hindrance; howev.er, bathocbromic shifts (6) Pickett. Walter and France, ibid., 66, 2296 (1936). (6)Pestemer and Mayu-Pitsch. Moratssh.. TO, 104 (1937). and greatly decreased fine structure indicate ap(7) R. N. Jones, THB JOWRNU, 68, 313, 1658 (1941). preciable contribution from coplanar resonance (8) R. N. Jones, ibid.. 67, 2137 (1945).
(9) R. N. Jones,Chcm. Rev., 88, I (1943). 60, 2180 (1938), (10) Mama and.Kirkpatrick, THIS JOURNAL, determined the apectrrr of 1,l’- and 2,2’-dinaphthyl t o 230 mp. They found a band at 287 in 2,Y- which we do not 5ad. Their low wave lengtb band f a 1J’- la at 288, rhereaa OW liea a t 236.
(11) Jones, THB JOORNAI., 6T, 2127 (1946), determined the ipectrum of 2,2’-diamino-1.1 ’-dinaphthyl. (12) Jacobs, Craig and Lavin, J . Bwl. Chm., 14l, 51 (1941). determined the spectra of 1- and 3-phenylnaphtholene d o m to 256 mp.
K. A.
200
LESLIEKEGGEL
F R I E D E L , B l I L T O N ORCHIN AND
Vol. 70
naphthalene. The same bands observed by Jacobs, et al., for (VIII) are found a t 250 and 285; in addition a short wave length band appears a t 212 mp. Thus the general form of the spectrum of (VIII) is the same as that of unhindered 2,2’dinaphthyl(I1) (Fig. 1). 5.0
200
240 280 Wave length in millimicrons. Fig. 2.
320 I
structures. The aromatic rings of f-phenylnaphthalene (VIII), on the other hand, can assume a coplanar structure; accordingly the spectrum of this compound is quite different from that of I
1
I
I
I
I
5.0
4.5 4.0
3.5
’ u;
M
3.0 2.6
2.0
1.5
200
240 280 Wave length in millimicrons. Fig. 3.
t ‘
320
1
h
(CyClOh*iOM
I
200
I
I
Miwnll
I
I
240 280 Wave length in millimicrons. Fig. 4.
I
320
The spectra in Fig. 4 of 1-phenylnaphthalene (VII) and three of its derivatives, 2’-methyl-lphenylnaphthalene (1-o-tolylnaphthalene) (IX), 2’-methoxy-l-phenylnaphthalene(X) and 2’-hydroxy-1-phenylnaphthalene(XI), show the effects of substituting the groups -CHI, -0CHs and -OH, respectively, in the ortho position of the phenyl group of 1-phenylnaphthalene (VII). The methyl group in 1-o-tolylnaphthalene (IX) appreciably increases steric hindrance since its presence produces in the 280 mp region a weaker, narrower band with typical naphthalene fine structure, including the band a t 314 mp. The methoxyl (X) and hydroxyl (XI) groups apparently cause only slight additional hindrance over that already present in 1-phenylnaphthalene (VII); the bands as a whole are somewhat narrower and definite peaks are produced a t 282 and 283, respectively, giving band structures similar to that of the strongly hindered methyl derivative (IX). All of these spectra were determined in both 95% alcohol and cyclohexane. Differences are very slight if any, but the spectra shown were obtained in cyclohexane in order to remove any effect of a polar solvent. The spectra of 2-phenylnaphthalene (VIII)and two of its derivatives, 2’-methyl-2-phenylnaptha-
ULTRAVIOLET SPECTRA OF NAPHTHALENES AND DIPHENYLS
Jan., 1948 I
l
I
l
,
201
I
5.0
6.0
4.5
4.6
4.0
4.0
3.5
3.5
' u;
Y
M
3.0
s" 3.0
2.5
2.5
2.0
2.0
1.5
1.5 Icyclohwm* solnnll
I
200
I
I
I
I
240 280 Wave length in millimicrons. Fig. 5.
320
lene (2-o-tolylnaphthalene) (XII) and 2'-hydroxy2-phenylnaphthalene (XIII) are given in Fig. 5 to permit comparison of the relative degrees of steric hindrance produced by the groups
