Infrared Spectra of FuIvenes J. C. W O O D , R. M. ELOFSON, and DORA M. SAUNDERS Research Council of Alberta, Edmonton, Alberta, Canada
b The infrared spectra of a number of fulvenes in carbon disulfide and carbon tetrachloride solution are presented. Dimethylfulvene is characterized by an unusually intense absorption in the double-bond region at 1642 cm.-' Fusion of benzene rings to the five-membered ring and particularly substitution of phenyl groups for the methyl groups on the exocyclic carbon atom lowers the frequency of the strongest peak and decreases its intensity. The fulvenes have a strong absorption at about 1360 ern.-', which is tentatively assigned to nuclear vibrations of the five-membered ring. Some correlations for out-of-plane carbon-hydrogen vibrations are suggested.
F
.i S r U D Y of the ultraviolet absorption spectra of extracts of the carbonaceous deposits froni diffusion flame< of a variety of hydrocurbon fuels, Thorp, Long, and Garner (26, 27) concluded that fulvenes and fulvenic ketones were present. Bec:iu>e of the present authors' intercst in the chemistry of carbonaceous inaterial. particularly the strong infrared absorption band a t 1600 cm-'for example. van Vucht, Rietveld, and v:tn Krevelen (28)-it seemed desirable tci prepare a number of fulvenes t o we if their infrared spectra sho\Ted iiitcn>e all-orption in this region. This p:tpc" is :i w i i m a r y of this norb. KO extended study of tlie infrared +tetra of the fulvenes has appeared in tlie literature. After the present work n :iq finished Schmidt (19) presented the infrared qpectra of furylfulvene, and Kresze ani1 Goetz (14) presented those of wnie phenylfulvenes. I n conjuiiction n itli a ctudy of cuniulenef. the spcctrum of dibiphenylencethylene TI-as r~ orded hy Otting ( 1 7 ) and reference liaq heen made t o the spectrum of dinietliylfulvene by S a h u n i (16). Fulvene itself has been prepared in the pure itnte and its infrared spectra measured by Thiec and Kiemann ( 2 2 ) . An impure solution of iiiethylfulvene \\ :ib prepnred for this investigation and a fen- of its absorption characteristics in the 1600 to 1650 ciii.-' range have h e m noted. The reniainder of the spectra 11x1 e been prepared froni isolatctl fulyenes starting n-itli diniethylfulrene and adding benzene rings either R03I
by fusion to the five-membered ring or substitution on the exocyclic carbon atom. One halogenated fulvene has also been examined. EXPERIMENTAL
Infrared analyses were performed on a Perkin-Elmer Model 21 double-beam recording spectrophotometer. The spectra of fulvenes from 4000 to 1250 cm.-' were run as 1% solutions in carbon tetrachloride; froni 1250 to 660 cm.-l they were run in 1% carbon disulfide solutions. These concentrations were doubled for 1, 2, 3, 4-tetrabromo-6,6diphenylfulvene. Utraviolet spectra were obtained with a Beckman DK2 double-beam recording spectrophotometer. Carbon and hydrogen analyses were carried out by the Micro-Tech Laboratories, 8000 Lincoln Aye., Skokie, Ill. Materials. Fulvenes were prepared b y t h e classical methods, generally b y condensation of cyclopentadiene, its benzo- or dibenzo-derivative with a ketone under t h e influence of a n alkaline catalyst (22-24), or by the use of Grignard reagents (5, IO). D a y (6)has reviewed the fulvene literature up to 1952. 6-LfETHYLFCLVEXE. Sodium (2.0 grams) was dissolved in 100 nil. of d r r ethylene glycol. Acetaldehyde (2.34 grams), and 0.9 gram of freshly distilled cyclopentadiene were dissolved in 50 ml. of dry ethylene glycol. The two glycol solutions were cooled to about 25' C. and mixed quickly. After the reaction proceeded for 2 hours, the mixture was extracted with 25 ml. of pentane and a deterniination of the infrared spwtrum carried out on the resulting solution. Thiec and Kiemann (22) have recently prepared pure 6-methylfuh-ene, but they did not publish its infrared spectrum. ~IISCELLAKEOUS. The remaining niaterials were prepared by procedures found in the literature, with slight niodifications in some cases. They were redistilled or recrystallized until their physical properties and infrared spectra n ere satisfactory. The distillations w r e pcrfornied in a 10-inch S'igreux column operated between 1 and 25 mm. with a receiver changer. A summary of these preparations is tabulated in Table I.
-
DISCUSSION
Infrared spectra of fulvenes are shon-n in Figures 1 and 2 .
The 1600-Cm.-1 Vibrations. Tlie simplest fulvene prepared in the pure s t a t e in this series was dimethylfulvene, rrhich has a strong absorption band a t 1642 cni.-' and apparent niolecular extinction coefficient [ E (a)]equal to 55. Fulvenes have a perinanent dipole [dimethylfulvene = 1.48 debyes, (2, S ) ] with the ring negative and the exocyclic carbon atom positive. The strong infrared absorption at 1642 cm.-1 is consistent with the fact. Methylfulvene shows absorption a t 1645 cm.-l This vibration frequency is lowered only slightly upon the fusion of benzene rings of the five-membered rings-e.g., dimethylbenzofulvene 1637 cni.-l [ € ( a ) , 1121; 3-hydroxyisopropyldiniethylbenzofulvene 1637 em.-' [€(a), 921 ; and dimethyldibenzofulvene 1629 em.-' [€(a), 581. The main peaks in this series of conipounds are acconipanied by a much smaller peak a t about 1600 cm.-' Replacing one methyl group by a phenyl group loxers the frequency somewliat more than fusion of a benzene ring to the five-membered ring; compare methylphenylfulrene 571 with dimethyl1626 c n - 1 [~(a), benzofulvene 1637 cni.-', and compare niethylphenylbenzofulvene 1613 em. [ € ( a ) , 571 rrith dimethyldibenzofulvene 1629 cni.-l Replacing both methyl groups on the exocyclic carbon atom causes a considerable lowering of the frequency of the band of maxiniuni intensity and with the exception of diphenylfulvene results in very marked reduction in intensity-e.g. diphenylfulvene 1597 cm.-' [ € ( a ) ,981:diphenylbenzofulvene 1605 em.-' [ e ( n ) , 261; diphenylbenzofulvene 1597 cni.-l [€(a), 201 and dibiphenyleneethyleiie 1605 cni.-l [€(a),201 and dibiphenyleneethylene 1605 cm.-' [ € ( a ) , 361. Tetrabroniodiphenylfulvene has no peak in this region but instead has a small band a t 1504 cm.-l, n-hose height is difficult to measure because of interference from other bands. Construction of Stuart and Briegleb niodels showed that the last four conipounds could not exist in the planar form, and this may explain the lack of strong absorption in this region. The observed absorption could be due merely to the aromatic rings. Strangely enough, benzofulrene does not fit into this pattern. It has the main absorption band a t 1604 em.-' [ € ( a ) , 181 with only a very weak ahVOL. 30, NO. 8, AUGUST 1958
a
1339
sorption a t 1629 em.-' Fulvene has a moderate absorption in this region a t 1664 em.-' (91). Because highly hindered fulvenes and fulvenes unsubstituted on the exocyclic carbon atom lack the characteristically intense absorption in this region, it seems best to ascribe the intense absorption of the other compounds t o resonance coupling of the cross-conjugated system rather than to specific ring vibrations comparable to the 1 6 0 0 - ~ m . -bands ~ in aromatic systems (4). The occurrence of a fundamental a t 903 cm.-l in benzofulvene seems to confirm the fact that the fulvene system can be represented b y conventional conjugated structures. Measurements of the heats of combustion of dimethylfulvene and diphenylfulvene by D a y and Oestreich ( 8 ) give values for the response energy of the fulvene moiety of 11.9 and 12.6 kcal. per mole, respectively. These values are low compared v-ith that of benzene (39 kcal. per mole), but midJTay between those of cyclopentadiene (3 kcal. per mole) and furan (23 kcal. per mole). The contribution of the exocyclic double bond of the fulvenes to the intense absorption in this range was confirmed by reducing dimethylfulvene (SO) and dimethylbenzofulvene (26) t o isopropylcyclopentadiene and isopropylindene, respectively. The spectra of these compounds lacked the intense absorption in the vicinity of 1640 mi.-', while the 1 6 0 0 - ~ n i . - ~band remained about the same in intensity, as in the corresponding fulvenes. The 1360-Cm.-1Band. T h e nonhalogenated fulvenes have sharp absorption bands a t 1340 to 1370 cm.-I, which can frequently be distinguished from the symmetrical methyl banding frequency in the region. The 1360em.-' band appears in both cyclopentadiene and indene. It appears a t slightly lower frequencies when aryl groups are substituted on the exocyclic carbon. It seems to be rather w a k in diphenyltlibenzofulvene [€(a), 111 in dimethyldibenzofulvene [€(a),10 approximately], when corrected for the contribution of the symmetrical methyl group vibration. These two compounds are colorless solids. I n diphenyltetrabromofulvene a band appears a t 1315 cni.-1, which may be due to the same vibration. This band appears t o be characteristic of the five-membered ring. especially in fulvenes-e.g., fluorene [n-eak band a t 1330 em.-', ( I s ) ] , tetraplienyl-
A
3
4
5
6
7
9
8
IO
II
13
12
14
15p
I
C
3
5
4
6
8
7
IO
9
II
12
I3
14
ISp
D
4000
I500
2000
1000
I200
900
800
100
z
80
0
Figure 1.
2 60
Infrared spectra of fulvenes
A . 6,6-Dimethylfulvene B . 6-hfethyl-6-phenylfulvene C. 6,6-Diphenylfulvene D. 1,2,3,4-Tetrabromo-6,6-diphenylfulvene E. Benzofulvene F. 8,8-Dimethylbenzofulvene
1340
ANALYTICAL CHEMISTRY
x
F
u)
5
E
40
* 20 0
3
4
5
6
7
8
9
IO
II
12
I3
14
15"
G
1
3
4
5
6
7
8
5
IO
1 II
L 12L _ _ \ 1141 315u 13
H
J
3
4
5
6
7
8
9
IO
I1
I2
13
I4
I5p
I
K
3
4
5
6
7
8
9
IO
II
12
I3
14
15p
ethylene (I?), and ferrocene (29) do not have this band. Fulvene itself has a strong band a t 1334 em.-', n-hich is too strong to be ascribed to a CH deformation vibration as done by Thiec and M'iemann ($1). This band is present in the spectra of furylfulvene presented by Schmidt (19) and of the phenylfulvenes presented by Kresze and Goetz (14). Isopropylcyclopentadiene has a somenhat ij-eaker band in this region. Apparently the band was absent for isopropylindene. It therefore appears to be a somewhat characteristic ring vibration, possibly analogous to the benzene-ring vibration a t 1500 cm.-' Out-of-Plane Carbon-Hydrogen Deformation Vibrations. Fulvenes with four nuclear ring hydrogens are characterized by strong absorption a t 762 cni.-l Fulrene itself has a strong abqorption of 765 ern.-' (21). Cyclopentadiene, on the other hand, has no qtrong absorption in this region. It is suggested that this frequency corresponds to the out-of-plane carbonhydrogen deformation vibrations. It occurs a t approximately the same freqiieiicy as the comparable vibrations involving the four nuclear hydrogens in o-disubstituted benzenes 735 to -t O cni.-l The nonappearance of this band in the spectrum of isopropylcj-clopentadiene confirms this assignment. The 6-phenylfulvenes prepared by Kresze and Goetz (14) and 6-furylfulvene prepared by Schmidt (19) alro have this band. The benzofulveiies which are substituted only in the exocyclic carbon atom are characterized by moderate absorption in the vicinity of 795 em.-'; 1)enzofulvene at 792 em.-'; dimethylbenzofulvene a t 790 cm.-'; methylphenylbenzofulvene at 793 crn.-l; diphenylbenzofulvene a t 797 cm.-l; and furylbenzofulvene a t 799 cm.-I This peak is very meak in indene (.4PI liO5) and absent in isopropylindene. It may correspond to the out-ofplane vibrations of the hydrogen atoms on the five-membered ring in this series of compounds. Benzofulvene is the only compound prepared in this laboratory in R hich the out-of-plane deformation frequencies of the hydrogen atoms on the exocyclic carbon can be studied. An intense band occurs at 903 em.-', which is outside the range 892 to 887 cni.-' quoted by Sheppard and Simpson (20)
Figure 2.
Infrared spectra of fulvenes
G. 3-Hylroxyisopropyl-8,8-dimethglbenzof ulvene H . 8-Methj-l-S-phen>-lbenzofulvene I . 8,s-Diphenylbenzofulvene J . 10,10-Dimethyldibenzofulvene K . 10,lO-Diphenyldibenzofulvene L . Dihiphenylenrethylene VOL. 30, NO. 8, AUGUST 1958
1341
Table 1.
Physical Properties and Preparation of Fulvenes
Physical Constants
Compound
Literature Values
Methylfulvene Dimethylfulvene
nL51.5404,b.p.
Methylphenylfulvene
nk51.6294, b.p 95-9"/1.4 mm.
Diphenylfulvene
L1.p. 79-82'
Tetrabromodiphenylfulvene
b1.p. 199-200"
1.5338, b.p. 46"/11 mm., b.p. 66"8"/25 mm. 1.5596, b.p. 14751"/25 mm., b.p. 130.5/010.5mm. R1.p. 82 R1.p. 81' R1.p. 200-1"
Benzofulvene
3f.p. 37"
M.p. 37"
Dimethylbenzofulvene
B.p. 93"/0.9 mm.
B.p. 142'/16 mm.
hlethylphenylbenzofulvene
b.p. h l . ~ . 68-9', b.p. 178-9"/5 mm., 14Go/0.9 mm., b.D. 204-5'/16 b.p. 144"/0.7 mm . mm . h1.p. 114 5" h1.p. 113-105° L1.p. 97-8" R1.p. 95-7
Diphenylbenzofulvene 3-Hydroxyisopropyldimeth-
52"/10 mm.
h1.p. 68-9.5',
ylbenxofulvene Dimethyldibenzofulvene
R1.p. 113-14.5'
R1.p. 89' L1.p. 113-17'
Diphenyldibenzofulvene
A1.p. 228.5-30'
R1.p. 229.5'
Dibiphen yleneethy lene
31.p. 187-8'
N.P. 187-8"
and Anderson and Seyfried ( 1 ) for iionconjugated structures. But it agrees with vibrations in styrene (API 170) and butadiene (API 379) a t the same frequency and is almost certainly due t o this vibration. The weaker band occurring at 1804 cm.-I is presumably a n overtone of the former frequency and serves as additional confirniation of the assignment. Corresponding bands were noted in the spectra of fulrene prepared by Thiec and Wiemann @ I ) , the fundamental being a t 925 em.-' ACKNOWLEDGMENT
LITERATURE CITED
\ - - - - ,
(1) Anderson, J. A., Jr., Seyfried, W.D., ANAL.CHERI. 20, 998 (1948).
1342
ANALYTICAL CHEMISTRY
Red oil. Had to be carefully distilled to free it from carbonyl-containing contaminants; probably acetophenone ( n y 1.5342) used in preparation Red plates from ligroin Dark violet-black shiny needles. I t was necessary to heat reaction mixture to 60" for 2 hours Pale yellow crystals, decomposed in 2 to 3 hours Formaldehyde gas used in preparation instead of solid trihydrosymethylene Yellow, unstable oil. Picrate was stable and had m.p. 114-16' from ethyl alcohol. (Literature m.p. 115-16') Yellow crystals from methanol
Orange crystals from ethyl alcohol Yellow crystals from n-hexane, decomposed readily Colorless needles from ligroin Calculated: carbon 93.15y0; hydrogen 6.847, Found: Carbon 93.16%, 93.19%; hydrogen 6.74%, 6.76% Colorless needles, yellow in solution. Purified bjchromatography on alumina using 1: 1 benzene and heptane. If preparation was on too small a scale 9,9'-bifluorene, m.p. 240-1 resulted, probably due to air oxidation of fluorene ( 1 2 ) Fine red needles from 5% benzene in ethyl alcohol, allowed to evaporate slo~vly
Bergmann, E. D., Fischer, E., Bull. SOC. chim. France 17, 1084 (1950). Zbid., 19,712 (1952). Blout, E. R., Fields, M.,Karplus, R., J . Am. Chem. SOC.70, 194 (1948). Courtot, C., Ann. chim. 4, 168 (1915). Day, J. H., Chem. Revs. 53, 167 (1958). Dav, J. H., Lukman, J. C., Ohio J . sei. 52, 335 (1952). Day, J. H., Oestreich, C., J . Org. Chem. 22. 214 (19571. Day, J. H.: Pidwerbesky, C., Zbid., 20,89 (1955). Grignard, V., Courtot, C., Compt. rend. 160, 500 (1915). Harpe, C. de la, Van Dorp, W. A , , Chem. Ber. 8, 1048 (1875). Je?nings, R. J. S., Fowler-Williams, A , J . Appl. Chenz. (London) 3, 426 (1953). Ilaufm ann, V., Chena. Ber. 29, 73 (1896). Kresze, G., Goetz, H., Zbid., 90, 2161 (1957). Maitland. P.. Tricker. S. H.. J . Chem. SOC.1929,'2559. ' Nahum, R., Compt. rend. 240, 1898 (1955). (17) Otting, W.,Chem. Ber. 87, 611 (1954). t
The authors wish to acknowledge their indebtedness t o Killiam Dammeyer for determination of the infrared spectra.
Description Yellow in solution Yellow oil, stable in sealed tubes
Richards. R. E.. Thomason. H. K.. Proc. Roy. Soc. (Lonhon)'A195,1 (1948). Schmidt, K. H., Chem. Ber. 90, 1352 (1957). Sheppard, S . , Simpson, D. l f . , Quart. Revs. (London) 6, 1 (1952). Thiec. J.. Wiemann. J.. Bull. SOC. chim. Fmnce 23, I f 7 (1956). Zbid., 24, 366 (1957). Thiele, J., Chem. Ber. 33, 666 (1900). Thiele, J., Balhorn, H., Ann. 348, 1 (1906). Thiele, J., llerck, K., Zbid., 415, 257 (19181. (26) Thorp, N. , Long, R., Garner, F. H., Fuel 32, 116 (1953). (27) Ibid., 34,S l(1955). (28) Vucht, H. A. van, Rietveld, B. J.. Krevelen. D. TT'. van. Zbid., 34, 50 (1955). Wilkinson. G.. Pauson. P. L., Cotton, F. '.k,J , Am. dhein. SOC.76, 1970 (1954). Ziegler, K., Gellert, H. G., Martin, H., Segel, K., Schneider, J., Ann. 589, 91-121 (1954). RECEIVED for review September 9, 1957. Accepted March 17, 1958. Division, of Gas and Fuel Chemistry, 132nd Meeting, ACS, Xew York, K, Y., September 1957.
