SOLVENT EFFECT IN ABSORFTION SPECTRA AND CHEMICAL STRUCTURE
Jan. 20, 1955
n such chromophores are coupled together so that the whole conjugated system vibrates as a simple harmonic oscillator with a restoring force constant k , then the wave length of the light which this system absorbs is XO = 2 ? r c / m i e . , i o 2 = 47r2c2nz/K
If we assume that when n is an even number
1-= K
;
+f
(1
+f2
+ . . . +-f5 -
If- 1
1
- + .. . +
f f 2
center f2
+f
+ 1)
If-,
1,f,f2. . . . . , f 2
If-1
,f2
, , . . . , f 2 , f r1
and =
A0
As the value off (Le., Cz) is almost 1, C should still be close to 1; it is possible to substitute equation 4 for 4'with negligible error. Conjugation Series with Heterochromophores at a- and w-Positions (a,w-Diphenylpolyenes) .-Two heterochromophores are conjugated a t the a- and w-position in the case of a,w-diphenylpolyenes. Therefore, the following equation pertains to these compounds instead of 2
--l
-K _-L+.fh.t( 1+f+f2+ khet k
. . . +f;
,
n + ? - I +
center 1
(2)
(the factor of the force constant f is always very close to 1 but never larger than 1). Thus, the reciprocal of the force constant of each chromophore contributes to 1 / K with the weight of
379
+ 1) + kh,,
+f' + f
(5)
where khet is the restoring force constant of the unit vibrating phenyl chromophore, and fhet is the factor of the restoring force constant exerted on the ethylene chromophore by the phenyl chromophore. If equation 5 is rewritten as
2 7rc
f l m 2 HC
ZZ
1
we obtain the expression for 3
fz,
If b = 8rr2c2m/k,C = B = b / ( l - Cz),A = a B and a is the intercept value when n = 0 =u
(Amax)'
= Q
+ b 11 -- C"C' + B(l - C")
+
~-
=
- BC"
A
where b and C have the same values, respectively, as in 3 and a" is the intercept value when n = 0.
(4)
If
bhet =
8?y2c2m/khet,and
Chst
= filet*/2
When n is an odd number, the equation corresponding to 2 is
+c+ n-1
yK l
+k f
+
f
2
+
.....
..... +f2+
center SO
(Amax)* = A
-B
Cn-1
f + 1)
(A,,,jz (2')
+ Cnfl 2
This equation can be expressed in a functional form similar to that for the homoconjugation series.
(4')
where B" B".
= A"
bChet2/(1 -
=
- B"Cn
(6)
c2)and A ' = a" + bhet -/-
OSAKA,JAPAN
[CONTRIBUTION FROM INSTITUTE O F POLYTECHNICS, OSAKA CITY UNIVERSITY]
Absorption Spectra and Chemical Structure.
11. Solvent Effect
BY K E N ZHIRAYAMA ~ RECEIVED JULY 16, 1953
+
Previously it was stated that the A, of polyenes is given by '),X( =a B ( l - C N ) . I n the present paper, it is shown that the solvent modifies B , and that there is a linear relationship between B and the refractive index n2% of the solvent.
It was pointed out in part I' that the Xma, of polyenes containing conjugated homochromophoric groups and auxochromic substituents may be expressed by (Amax)* =
=a
A
- BCN
+ B(1 - C N )
(1) (2)
where N is the homoconjugation index, which is determined by substituent and structural effects ( 1 ) K . Hirayama,
T H I S JOURNAL,
17, 373 (1955).
as well as by the number of conjugated chromophoric groups. Thus, the following equation was given for alcholic solutions of polyene derivatives with auxochromic substituents =
= (36.98 - 39.10 X 0.92W) X lo4 mMz -2.12 39.10 X (1 - 0.92ON)t X lo4 mp2
+
(3) (4)
We shall discuss the influence of the solvent on i.e., which parameters are effected by a change in solvent.
Amax,
380
KENZGHIRAYAMA
Vol. 77
TABLE I ARSORPTION MAXIMA OF POLYENE DERIVATIVES IN VARIOUS SOLVENTS (mp)" No Compound 1 H-(CH=CH)-H 2 Ph-CHr-(CH=CH)a-CHz-Ph 3 H-(CH=CH)r-H 4 CHI-(CH=CH)~-CH;OH 5 {CH~CH=CH)~-CHOH)S 6 CHa-(CH=CH)r-CHOHCHOH-CHI 7 CHr(CH=CH)r-CHa 8 CHr(CH=CH)-CH, 9 Dihydrocrocetin 10 1,1,20,20-Tetramethyldihydrobixinol 11 Dihydronorbixin 12 Dihydrobixin 13 Dihydromethylbixin 14 6-Dihydrocarotene 15 Dihydro-@-carotenone 16 Dihydro-5-carotenone oxime 17 a-Apo-2-carotenol 18 C H d C H = C H ) v C H i 19 5,6-Dihydro-a-carotene 20 st-Carotene 21 Dihydroxy-a-carotene 22 Lycopene 23 Lycoxanthin 24 Lycophyll 25 Decapreno-el-carotene 26 Rhodoviolascin 27 Dehydrolycopene 28 a-Carotene monoepoxide 29 Eloxanthin (xanthophyll epoxide ?)
Substituent and structure R A E p rl 0 0 0 0 2 0 0 0 0 0 0 0 1 1 0 0 1 1 0 0
n 3 3 4 4 4
IV
3.0 3.2 4.0 4.2 4.2
4 5 6 6
1 2
1 0
0
2
0
0
0 0 0
4
0
0
0
4.2 5.2 6.2 6.4
8
6 6 6
0 0 0 0
0
0
8.fi
0 0 0
0 0 0 0
0
0
0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0
0 0
0 0
0 0 1 1
0 0 0
8.8 8.f: 8.6 8.6 8.6 8.6 8.6 9.2 9.6 9.8 9.6 11.8 11.8 11.8 13.8 13.8 16.0 9 7 9.7
8 8
8 8 8 8
6 6 6 6 5 2 6 6 5 8
8 9 9 9 9 11 11 8 11 8 13 8 13 8 15 10 9 5 9 5
0
0 0 1 0 0 0 1 0
0 0 0 0 0 0
0
0
0
0
No. 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 40 50 51 52 53 54 55 56 57
Substituent and structure R A Ep r l
Compound n Isoantheraxanthin 9 Rubixanthin monoepoxide 10 &Carotene diepoxide 9 Cryptoxanthin diepoxide 9 Violaxanthin (zeaxanthin diepoxide 7) 0 Vitamin AI 5 ,9-Apo-2-carotenol 9 5,6-Dihydro-@-carotene 10 a-Carotene 10 Xanthophyll (Lutein) 10 Helenien (xanthophylldipalmitate) 10 Capsanthol 10 Dihydroxy-@-carotene 10 @-Carotene monoepoxide 10 Cryptoxanthin monoepoxide 10 Antheraxanthin 10 Gazaniaxanthin 11 Gaznniaxantbin acetate 11 y-Carotene 11 Kubixanthin 11 Myxoxanthol I1 Celaxanthin 13 @-Carotene 11 Cryptoxanthin 11 Zeaxanthin 11 Physallien (zeaxanthin dipalrnitate) 11 Decapreno-@-carotene 15 Dodecapreno-@-carotene 19
5 6 4 4
4 5 7 8 8 8 8 7 7 7 7 7 9 9 9 9 8
0 0 0 0
1 1 2 2
0 0
0 1
2 0 0 0 0 0
0
1 0 0 0
0 1
0 0 1
10
1 0 0 0 0 0 0 0 1 0 0 0 0
0 0 0
10
0
12 14
0 0
10
10 10
0
1 1
0 0 0
0 0
0
0 0
1 1
1 1 1 1
1 1 1 1 1
N 9.7 10.8 9.8 9.8 9.8 4.8 9.0 10.0 10.0
10.0 10.0 10.0 10.0 10.1 10.1 10.1 11.1
1 1 1 1 . I 1 11.1 1 11.1 1 11.1 1 13.3 2 IO,*
a
10.4
2
10.4
0
2
0
2
0
2
104 I 4 (i 18.8
ABSORPTION MAXIMA C p d Calcd. Obsd. Alcohol 1
3 4 7 12 13 16 17 I9 22 23 24 25 26 29 33 34 35 36 37 39 40 41 44 45 46 49 F,1
53 54 56 57
256 299.5 307 341 423 423 423 423 441 473 473 473 498 496 442 444 444 328 430 447 447 447 447 449 449 463.5 463.5 490 453 453 504 537
257* 302* 310' 343d 425 424 426 423 443 472 474 474 494' 491 445 442 442.5 328' 426 448 446.5 448 448 449 450 462 463 488 452 451.5 606'" 536'
Cpd. Calcd. Obsd. C hlorolorm
8 10 11
12 13 15 19 22 25 26 27 28 32 33 34 37 38 39 40 41 42 43 44 45 48 49 50 52 53 54 56
378 432 432 432 432 432 451 483.5 507 507 528 552 454 454 454 457 457 457 457 457 457 459 459 459 474 474 474 464 464 464 515
375b 435 435 435 435 435 452 480 518' 507 528 554 456 453 451.5 457 454 456 456 456 456 459 456 460.5 475 474 474 466 463 462 617m
Cpd. Calcd. Petroleum 15 421.5 17 421.5 22 471 23 471 25 494 29 441 31 457 36 429 37 446 43 447 46 462 49 462 50 462 51 488 56 502 5 7 535
Obsd. ether 424 420 475.5 473l 4950 442 461 423 447.5 447 462.5 463 465 486.5 498"' 531'
Light ligroin 15 423 429 16 423 429 22 473 474 23 473 472 24 473 473 30 443 442 34 444 443 3 8 447.5 447.5 39 447.5 447.5 40 447.5 447.5k 42 447.5 448 44 449 449 48 464 462 52 454 452 53 454 452 54 454 451
Cpd. Calcd. Obsd. Carbon disulfide 10 453 455 11 453 454 12 453 454 13 453 454 14 453 461 15 453 454.5 16 453 4.54 5 17 433 448 19 471 486.5 20 471 470' 21 471 471 22 505 507 5 23 505 501; 24 505 50ii 25 530 5320 26 530 534 27 552 557 28 473 471 29 473 472 32 475 472 33 475 473 34 475 470 36 460 450 37 478 476l 38 478 477 39 478 475 40 478 477 41 478 477 42 478 473 43 480 479 44 480 479 45 480 478 46 495.5 494.5 47 495.5 494' 48 495.5 496
Cpd. Calcd. Obsd. Carbon disulfide 49 495.5 494 50 4 9 5 . 5 404 51 523 521 52 48.5 485 53 485 483 54 485 482 55 48.5 484 5,14m 56 538 57 573 5774 Benzene 436 436 18 447 436d 453.5 19 454 487 22 487 487 23 487 487 24 487 518' 25 511 511 26 511 ,531 27 532 45.5 28 456 453 29 456 456 32 4.58 495 33 458 37 461 438 461 456.5 39 40 4(il 462 41 4G1 462 4.57 42 461 460 43 463 461 44 463 476 46 478 477 48 478 522" 56 519 555' 57 553 13
Cpd. Calrd. Obsd. Methanol 5 304 3(Ud 6 304 29gd 34 440 440 39 443 444 54 449 449.5
2 9 14 13
19 20 22 26 27 28 32 3,; 38 39 42 48 49 52 53 54
Hexane 27OC 264 373 37!) 421 41'0 421 4% 438 438 438 4306 470.5 472 494 491 514
501
440 442 326.5 445 445 445 4631 461 451 451 451
442 443 320* 445 446 446 462 462
4JO 431
4,51
I, Experimental data from P. Karrer and E. Jucker, "Carotenoids," Elsevier Publishing Co., Inc., Houston, Texas, 1950, K. Dimroth, Angew. Chem., 52, 545 (1939). L. N. Ferguson, Chem. Revs., 43, 385 (1948). unless otherwise indicated. d F. Bohlman, Chem. Ber., 85, 386 (1951). e P. Karrer and C. H. Eugster, Helv. Chim. Acta, 34, 1805 (1951). f L. Zechmeister and L. V. Cholnoky, Ber., 69,422 (1936). 0 P. Karrer, C. H. Eugster and M. Faust, Helv. Chim. Acta,.34,823 (1951). * L. F. Fieser, J . Org. Chem., 15,930 (1950). A. E. Gillam and M. S. El Ridi, Biochem. J . , 32,820 (19.78). 1 P . Karrer and R. Kuhn and H. Brockmann, Z . physiol. Chem., 206, 41 (1932). K. Schon, W. Biirgi, Helv. Chim. Acta, 34,832 (1951). P. Karrer and C. H. Eugster, Helu. Chim. Acta, 3 4 , 2 8 (1951). Biochem. J., 3 2 , 1566 (1938).
SOLVENT EFFECTIN ABSORPTION SPECTRA AND CHEMICAL STRUCTURE
Jan. 20, 1955
The parameters, (a, B and C) for carbon disulfide solutions of carotenoids were computed from the observed wave lengths; a and C are the same for alcohol and carbon disulfide solutions (-2.12 and 0.920, respectively), and only B is characteristic of the solvent. Formulas for the calculation of Xma, in various solvents were determined from the observed values with a = -2.12 and t = 0.920. (Xmax), mpz X IO-'
Solvent
Methanol Hexane Petroleum ether Light ligroin Chloroform Benzene Carbon disulfide
(36.30 (36.62 (36.70 (37.05 (38.60 (39.20 (42.06
- 38.42 X - 38.72 X
- 38.82 X - 39.17 X - 40.72 X - 41.32 X
- 44.18 X
0.920N) 0.920'"') 0.920"') 0.920N) 0.920N) 0.920"') 0.920N)
(5) (6) (7) (8) (9) (10) (11)
The calculated values of Xmax in Table I are based on these formulas, which differ only with respect to B which is characteristic for each solvent; the agreement between the calculated and observed values is good except for compounds 14 in carbon disulfide, 25 in chloroform and in benzene and 27 in hexane. In the case of rhodoviolascin 26, i t was assumed that Nmethoxy = 0; the agreement between the observed values and those calculated with N m e t h o x y = 0 indicates that this substituent exerts practically no bathochromic effect.
1.6
-
1.5
-
1.4
-
formulas 5-1 1 agree well with the values calculated by the equation (see Table 11) B::;Zd = 12.976 f 19.019 X nmD (12) TABLE I1 B ~ O ' ~ / I VARIOUS N SOLVENTS
Solvent
nab
Methanol Hexane Petroleum ether Ether Alcohol Light ligroin Cyclohexane Chloroform Benzene Pyridine Carbon disulfide
1,3288 1.3751 1.37 1.3556 1.3633 1.38 1.4264 1.4486 1.5017 1.5085 1.6319
fpl.
I
I
I
40
1
42
I
I
44
B. Fig. 1-1, methanol; 2, hexane; 3, petroleum ether; 4 , alcohol; 5, light ligroin; 6, chloroform; 7, benzene; 8, carbon disulfide.
Figure 1 shows that there is an approximately linear relationship between Bsolvand the refractive index of the solvent.2 The values for Bsolv in (2) Regarding t h e solvent as a continuous dielectric medium, N. S. Bayliss (J. Chem. Phys., 18, 292 (1950)) shows t h a t t h e solvent effect on t h e absorption of light by solute molecules must be expressed in
...
39.10 39.17
... 40.72 41.32
...
44.18
TABLE I11 ABSORPTIONMAXIMA I N ETHER, CYCLOHEXANE PYRIDINE Xmax
38
m
d
38.25 39.13 39.03 38.76 38.91 39.22 40.10 40.53 41.54 41.67 44.01
38.42 38.74 38.82
Because the number of observations made in ether, cyclohexane and pyridine was insufficient for the determination of B s o l v , computed from equation 12 was used in the calculation of hmaxin these solvents (Table 111) ; the good agreement between the calculated and experimental values indicates the reliability of relation 12.
N0.a
8:
381
Compound
N
(in mp)
CycloE t h e r hexane
ANI)
Pyridine
... 25 Decapreno-q13.8 Obsd. 497* 5Wb 503 carotene Calcd. 494 . . . . 535c 27 Dehydrolycopene 16.0 Obsd. Calcd. 534.5 40 Helenien (xan10.0 Obsd. .. . . 463c thophyll dipalCalcd. 463 mitate) 41 Capsanthol 10.0 Obsd. .. . . 463" Calcd. 463 56 Decapreno-814.6 Obsd. . . 50Qd . . . carotene Calcd. 511 57 Dodecapreno-8- 18.8 Obsd. 536e 541E . , . carotene Calcd. 534 544 The numbers of compounds are the same as in Table I. P. Karrer, C. H. Eugster and M. Faust, Helv. Chim.Acta., 34, 823 (1951). a P. Karrer and E . Jucker, "Carotenoids," Elsevier Publ. Co., Inc., Houston, Texas, 1950. d P . Karrer and C. H. Eugster, Helv. Chim.Acta, 34,28 (1951). * Ibid., p. 1805. OSAKA.TAPAN terms of t h e electronic polarization part of its dielectric constant, K = )I) (n is t h e refractive index of the solvent); and using methods based both on quantum theory and on classical dispersion theory, he shows t h a t t h e red shift of absorption in solution depends directly on j,the oscillator strength, and inversely either on a8 (a is the radius of the spherical solute molecule) or the polarizability T h e expression is Au = const. C f / v d ) [ ( n *- 1)/(2n' 4- l)] alternatively with t h e substitution of a: for a'.
(I.
