infrared study of β-propiolactone in various solvent systems and other lactones

Infrared Study of/ -Propiolactone in Various Solvent Systems and Other Lactones

R . A . N Y Q U I S T , * H . A . F O U C H E A , G . A . H O F F M A N , a n d D . L . H A S H A Analytical Sciences, 1897 Building, Dow Chemical Company, Midland, Michigan 48667

Many lactones exhibit two significant bands in the carbonyl stretching region which result from Fermi resonance interaction between J,C=O and a combination or overtone of a lower-lying fundamental (or funda- mentals). However, for ~-propiolactone, three significant bands in the carbonyl stretching region of the spectrum are observed. These bands result from ~,C=O in Fermi resonance between the combination tone v6 + p~3,A' and 2V~o,.4'. The extent of Fermi resonance interaction between vC=O and the combination and/or overtone is dependent upon the solvent system. Approximate unperturbed pC=O frequencies have been calculated, and these ~C=O frequencies decrease in frequency in the solvent order n-hexane, carbon tetrachloride, and chloroform. The unperturbed vC=O frequencies were also calculated with the use of reported frequencies and band intensities for many other lactones, and the unperturbed ~,C=O frequencies decrease significantly as the amount of ring strain is reduced in the lactone structures. An equation, based on perturbation theory for obtaining approximate unperturbed ~,C=O frequencies for situations where three modes are in Fermi resonance, was developed and used to assign the unperturbed vC=O frequencies for ~-propiolactone in various solvent systems. This method assumes that all or nearly all of the intensity in the three bands in Fermi resonance arises from the vC=O mode. Index Headings: Infrared; Molecular structure; Solvent effects; Fermi resonance.

I N T R O D U C T I O N

Durig has assigned the vibrational spectrum of B-propiolactone using infrared and Raman spectroscopy. 1 However, in his vibrational assignment no mention was made of the possibility of the carbonyl stretching mode being in Fermi resonance with combination and overtones belonging to the A' species. Jones e t a l . 2 studied the infrared and Raman spectra of unsaturated lactones. They noted two significant bands in the region expected for carbonyl stretching and attributed the presence of these two bands to the carbonyl stretching mode being in Fermi resonance with an overtone of a lower-lying fundamental. Bond e t a l . , s in their study of terpenoids containing a, B-unsaturated ,y-lactone functional groups, observed split bands in the carbonyl stretching region of the IR spectrum and attributed the cause to Fermi resonance. We have studied the effects of solvents and mixed solvent systems on a variety of carbonyl- and nitro-containing compounds. 4-t4 In the case of phthalic anhydride in various solvent systems, it was shown that the degree of Fermi resonance interaction between the out-of-phase (C=O)2 stretching mode and a combination tone changed with a change in the solvent system2 ° After correction for Fermi resonance, the out-of-phase (C=O)2 stretching mode exhibited the same frequency behavior with solvent systems as observed for ketones and open-chain

Received 30 December 1991. * Author to whom correspondence should be sent.

carboxylic acid esters. Our interest in solvent effects upon group frequencies has been extended to B-propiolactone. The development of the equation to correct for Fermi resonance for cases involving three vibrational modes is discussed in the appendix.

EXPERIMENTAL

Infrared spectra were recorded of 1% solutions of B-propiolactone placed in a 0.1-mm KBr cell with the use of a Nicolet 60 SX FT-IR spectrometer. IR spectra in the region 1600 to 1900 cm -~ were also recorded with a Perkin-Elmer 983 spectrometer. Mixed 1% solutions of B-propiolactone were prepared as follows: 0.I, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, and 1.0 mL aliquots of each 1% B-propiolactone solution were added, respectively, to 1 mL of the other 1% B-propiolactone solution (for ex- ample, a 1% solution of B-propiolactone in CC14 solution and a 1% solution of fl-propiolactone in CHC13 solution).

RESULTS AND DISCUSSION

The carbonyl region of the infrared (IR) solution spectra for 1% B-propiolactone in CC14, 52 mole % CHClJ CC14, and CHC13 are shown in Fig. 1. For each solution spectrum three bands are observed. In CC14 solution IR bands are detected at 1850.54, 1833.09, and 1816.29 cm-L In the 52 mole % CHCls/CC14 solution the corresponding IR bands occur at 1844.57, 1832.82, and !814.82 cm -1. In CHC13 solution the corresponding IR bands occur at 1845.02, 1831.70, and 1813.04 cm-L In each solution spectrum of B-propiolactone these IR bands decrease in intensity in the order of decreasing frequency. The most intense IR band is the one having the most contribution from carbonyl stretching, uC=O. The other two IR bands are more intense than would be expected for combination or overtones, and it is reasonable to attribute their high intensity to Fermi resonance with the uC=O fundamental. It is certain that for/~-propiolactone, which is a rigid 4-membered ring, the multiple IR bands do not result from rotational isomers. As mentioned in the introduc- tion, certain lactones yield a doublet in the region expected for ~C=O, and this doublet was attributed to uC=O being in Fermi resonance with the first overtone of a lower-lying fundamental. 2,3 In the case of B-propiolactone there are apparently two modes in Fermi resonance with ~C=O, or to be more exact, all three modes are in Fermi resonance with each other. The vC=O fundamental be- longs to the A' species, and any mode in Fermi resonance with uC=O must also belong to the A' symmetry species. The most likely modes in Fermi resonance with vC=O are ~6 + ~3 =A' and 2vl0=A '. The approximate description of us,A' is B-CH2 wagging, of u~a,A' is C=O in-phase bend-

860 Volume 45, Number 5, 1991 ooo3-7o28/91/45o5-o~o$2.oo/o APPLIED SPECTROSCOPY © 1991 Society for Applied Spectroscopy

ee-~

i!i

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195~ I SSG

FIG. 1. T h e s p e c t r u m on the left is t ha t for 1%/3-propiolactone in CC14 solution, the middle spec t rum is t h a t for 1% /3-propiolactone in 52 mole % CHC13/CC14 solution, and the spec t ra on the r ight is t h a t for 1% ~-propiolactone in CHC13 solution.

ing, and of ~lo,A' is ring C-C stretching} Table I gives the assignments of ~s, v~3, rio, P6 + ~3, and 2~o for /3- propiolactone in the neat phase and in several solvents. Table II gives IR data for ~-propiolactone in several solvents as well as relative absorbance values for vC=O, ~s + ~3, and 2~1o. Study of the data in Tables I and II shows that the strongest band in this series is not always the highest frequency band, and in some solvents it is the center band in this set of three bands. This observation is reasonably explained on the basis that, when unperturbed ~6 + rio occurs at a lower frequency than unperturbed vC=O, the higher-frequency band has the most intensity. And in the case when unperturbed ~s + ~o occurs at higher frequency than ~C=O, the middle band has the most intensity. This explanation is reasonable since ~6 and ~3 are also affected by the various solvents (see Table I).

Langseth and Lord 15,1s have developed equations which yield approximate corrections for Fermi resonance when two bands are anharmonically coupled. In the case when three bands are in Fermi resonance, the situation be- comes extremely complex. 17,1s Using perturbation theory we have obtained approximate corrections for the three- band Fermi resonance problem. The derivation of the expressions used to calculate the unperturbed frequencies is presented in the appendix. The data in Table II show that the observed frequency difference between the outer bands is larger than the corresponding difference in unperturbed frequencies. This behavior is analogous to two-band Fermi resonance in which the anharmonic coupling, between bands ~A and vB, results in a repulsion of the unperturbed frequencies; i.e., I~A - ~ I > I~,~ - PSI. It is also observed that the unperturbed frequency of the central band falls between its observed position

T A B L E I. Solvent effects of modes which affect the amount of Fermi resonance between v C = O and a combination and overtone.

(~ + v13)A' 2v,o,A' Observed v6,A' ~13,A' Calc. Obs. v,0,A' Calc. Obs. vC=O,A '

Solvent a m - ' cm -~ a m - ' cm- ' cm -1 am ' c m - ' a m - '

Nea t 1321.6 516.9 1838.5 1847.9 910.73 1821.4 1807.19 1826.36 CHC13 1319.54 513.39 1832.9 1831.7 911.87 1823.7 1813.04 1845.02 CH2C12 1318.96 514.43 1833.4 1844.9 910.24 1820.5 1812.36 1831.46 CC14 1316.11 507.40 1823.5 1833.1 912.67 1825.3 1816.28 1850.50 CS2 1313.17 512.44 1825.6 1829.7 910.05 1820.1 1812.12 1848.31

APPLIED SPECTROSCOPY 861

T A B L E II. Infrared data for ~-propiolactone in 1% solutions.

In Fermi resonance

~6 + ~ C = O , A ' ~q3=A ' 2v,0=A '

Solvent am 1 am-1 cm-' (A,) a

Corrected for Fermi resonance

u6 + ~,C=O,A' ~3=A ' 2~o=A '

(A2) b (A3)" cm -~ cm -~ am-' AN

Hexane 1857.18 1832.01 1817.52 0.673 Diethyl ether 1852.24 1838.04 1814.14 0.489 Carbon tetrachloride 1850.50 1833.08 1816.28 0.896 Nitrobenzene 1830.93 1843.31 1808.44 1.144 Acetonitrile 1832.18 1845.07 1810.23 1.035 Benzonitrile 1830.77 1843.31 1812.78 0.795 Methylene chloride 1831.46 1844.86 1812.36 1.090 Chloroform 1845.02 1831.70 1813.04 0.783 Nitromethane 1831.80 1845.07 1809.80 0.988 Tert-butyl alcohol 1832.02 1845.66 1813.40 0.922 Isopropyl alcohol 1833.07 1845.72 1810.82 0.641 Ethyl alcohol 1833.81 1845.72 1810.37 0.324 Methyl alcohol 1834.23 1843.96 1809.89 0.289

0.136 0.074 1850.21 1830.69 1826.81 0 0.350 0.061 1843.80 1834.65 1825.97 3.9 0.447 0.223 1841.78 1831.62 1826.46 8.6 0.664 0.689 1828.74 1830.62 1823.33 14.8 0.448 0.423 1830.55 1832.56 1824.37 19.3 0.435 0.404 1829.72 1831.92 1825.23 15.5 0.930 0.480 1830.87 1832.43 1825.38 20.4 0.775 0.476 1834.70 1829.67 1825.39 23.1 0.370 0.410 1830.12 1832.48 1824.07 - - 0.628 0.691 1830.79 1833.28 1821.01 (29.1) d 0.471 0.482 1830.84 1832.72 1826.05 33.5 0.234 0.241 1831.14 1832.78 1825.99 37.1 0.179 0.221 1830.72 1832.01 1825.35 41.3

a (A,) Absorbance for v C = O , A ' in Fermi resonance. b (A0 Absorbance for u6,A' + v,3,A' = A ' in Fermi resonance.

(A3) Absorbance for 2Ul0,A'=A' in Fermi resonance. d Est imated (see Ref. 8).

a n d t h e l o w e s t - f r e q u e n c y b a n d , 2Vlo. F o r e x a m p l e , w h e n v C = O o c c u r s a t l o w e r f r e q u e n c y t h a n vs + ~13, t h e n ~ C = O is t h e c e n t r a l b a n d a n d i t s u n p e r t u r b e d f r e q u e n c y is b e t w e e n t h e o b s e r v e d f r e q u e n c i e s f o r ~ C = O a n d 2~10.

T h e d a t a i n T a b l e I I s h o w t h a t t h e u n c o r r e c t e d ~ C = O f r e q u e n c y f o r / ~ - p r o p i o l a c t o n e o c c u r s a t 1 8 5 7 . 1 8 c m -1 i n h e x a n e s o l u t i o n , w h i l e i t s u n p e r t u r b e d f r e q u e n c y a f t e r c o r r e c t i o n fo r F e r m i r e s o n a n c e is 1850 .21 c m -1. T h e o b - s e r v e d ~ C = O f r e q u e n c i e s v a r y b e t w e e n 1 8 5 7 . 1 8 a n d 1830 .77 c m -1 a n d t h e u n p e r t u r b e d v C = O f r e q u e n c i e s v a r y b e t w e e n 1850 .21 a n d 1 8 2 8 . 7 4 c m -~ i n t h i s s e r i e s o f so l - v e n t s . T h e ~6 + ~la c o m b i n a t i o n t o n e a f t e r c o r r e c t i o n f o r F e r m i r e s o n a n c e is a s s i g n e d i n t h e r e g i o n 1 8 3 4 . 6 5 - 1 8 2 9 . 6 7 c m -~ i n t h i s s e r i e s o f s o l v e n t s . T h e 2~,0 o v e r t o n e a f t e r c o r r e c t i o n f o r F e r m i r e s o n a n c e is a s s i g n e d i n t h e r e g i o n o f 1 8 2 7 . 0 1 - 1 8 2 3 . 3 3 c m - L

The absorbance of the pC=O fundamental, v6 + /-/13

combination, and 2P10 overtone are A1, A2, and A3, respectively. For the solvents listed in Table II--with the exception of the alcohols, nitromethane, and nitrobenzene--the absorbance for the three bands decreases in the order A1 < A2 < A~. In the alcohols, nitromethane, and nitrobenzene the absorbance is A 1 < A 3 < A 2. As mentioned earlier, the ~C=O fundamental is assigned to the most intense band with absorbance A 1.

The acceptor number (AN) for each solvent used is given in Table II. Wohar et al. have reported that the vC=O frequency for tetramethylurea in various solvents correlates with the AN value for each of these solvents. 19 The data in Table II show that the AN values do not correlate with observed or unperturbed ~C=O frequencies. In a study of acetone in various solvents it was shown

T A B L E III . Infrared data for B-propiolactone in hexane and/or CCL 4 solutions.

In Fermi resonance

Mole % ~C=O v6 -~- v,3 2~1o CClJHexane cm-' cm-' cm -1 (A,) (A2) (A3)


vC=O v6 + u13 2Ulo am-' am-' cm-'

0 1857.18 1832.01 1817.52 0.637 0.136 0.074 1850.21 1830.69 1825.81 11.91 1856.24 1832.99 1818.69 0.502 0.111 0.067 1849.35 1831.61 1826.96 21.29 1855.65 1833.03 1818.26 0.542 0.132 0.076 1848.52 1831.62 1826.80 28.26 1855.49 1833.44 1818.38 0.582 0.153 0.085 1848.20 1832.01 1827.10 35.10 1855.53 1833.31 1818.13 0.611 0.171 0.092 1847.96 1832.00 1827.01 40.34 1855.32 1833.32 1818.00 0.639 0.189 0.102 1847.53 1832.05 1827.06 44.79 1855.11 1833.29 1817.92 0.661 0.204 0.110 1847.17 1832.07 1827.08 48.63 1854.74 1833.22 1817.68 0.683 0.220 0.119 1846.66 1832.00 1826.98 51.96 1854.70 1833.29 1817.63 0.695 0.227 0.124 1846.55 1832.05 1827.02 54.89 1854.57 1833.25 1817.62 0.711 0.240 0.130 1846.31 1832.07 1827.05 57.49 1854.59 1833.33 1817.69 0.712 0.242 0.132 1846.30 1832.16 1827.15 60.04 1854.56 1833.30 1817.74 0.715 0.245 0.132 1846.27 1832.16 1827.16 62.83 1854.26 1833.31 1817.92 0.741 0.266 0.141 1845.91 1832.27 1827.32 65.89 1854.11 1833.28 1817.89 0.735 0.259 0.140 1845.84 1832.18 1827.26 69.27 1853.67 1833.19 1817.28 0.723 0.267 0.141 1845.27 1831.98 1826.90 73.01 1853.69 1833.29 1817.48 0.784 0.305 0.159 1845.11 1832.20 1827.15 77.17 1853.36 1833.29 1817.27 0.811 0.330 0.172 1844.66 1832.17 1827.09 81.84 1853.02 1833.33 1817.07 0.891 0.392 0.200 1844.10 1832.22 1827.10 87.12 1852.65 1833.26 1816.95 0.864 0.392 0.202 1843.66 1832.14 1827.05 93.11 1851.34 1833.27 1816.49 1.059 0.536 0.273 1842.29 1831.97 1826.84

100 1850.57 1833.19 1816.37 0.994 0.493 0.251 1841.84 1831.71 1826.58 A cm-' -6.61 1.18 -1 .15 -8.37 1.02 0.77

8 6 2 V o l u m e 45, N u m b e r 5, 1991

T A B L E IV. Infrared data for ~-propiolactone in CHCI 3 and/or hexane solutions.

In Fermi resonance Mole %

CHC1Jn- vC=O p8 + ~,3 2V,o Hexane cm -~ cm-' cm-' (A,) (A2)


~,C=O ~,~ + v,3 2~,,o (A3) cm -1 cm ' cm

0 1857.23 1833.35 1818.69 0.637 0.136 13.95 1848.56 1832.91 1818.76 0.518 0.272 24.49 1847.59 1832.64 1818.03 0.553 0.320 32.72 1847.14 1832.51 1817.97 0.589 0.356 39.34 1847.10 1832.30 1817.20 0.608 0.385 44.77 1846.80 1832.22 1816.75 0.629 0.420 49.31 1846.67 1832.31 1816.60 0.643 0.438 53.16 1846.42 1832.12 1816.22 0.658 0.461 56.47 1846.32 1832.12 1816.50 0.663 0.472 59.34 1846.15 1832.04 1816.27 0.673 0.492 61.85 1846.05 1831.98 1816.15 0.680 0.502 64.31 1846.07 1832.00 1816.08 0.682 0.511 66.96 1845.85 1831.88 1815.78 0.702 0.531 69.85 1845.76 1831.84 1815.59 0.705 0.535 72.99 1845.67 1831.78 1815.27 0.714 0.563 76.43 1845.48 1831.69 1814.98 0.724 0.584 80.21 1845.39 1831.63 1814.74 0.742 0.612 84.39 1845.79 1832.33 1814.39 0.753 0.641 89.02 1845.64 1832.22 1814.43 0.767 0.675 94.19 1845.51 1832.09 1814.03 0.783 0.722

100 1845.11 1831.78 1813.19 0.794 0.794 A cm ~ -12.12 -1.57 -5 .50

0.074 1850.53 1831.82 1826.92 0.163 1840.35 1831.96 1827.92 0.191 1839.23 1831.55 1827.48 0.212 1838.77 1831.43 1827.42 0.225 1838.43 1831.16 1827.01 0.245 1837.97 1830.99 1826.81 0.258 1837.80 1830.99 1826.79 0.270 1837.45 1830.76 1826.54 0.277 1837.39 1830.84 1826.71 0.288 1837.15 1830.73 1826.58 0.297 1837.00 1830.65 1826.53 0.299 1836.97 1830.66 1826.51 0.310 1836.73 1830.48 1826.29 0.319 1836.59 1830.39 1826.22 0.334 1836.34 1830.29 1826.09 0.348 1836.06 1830.15 1825.94 0.367 1835.87 1830.05 1825.84 0.382 1836.10 1830.41 1826.00 0.406 1835.87 1830.36 1826.06 0.433 1835.55 1830.20 1825.89 0.485 1834.78 1829.78 1825.52

-15.75 -2.04 -1 .40

t h a t t h e A N v a l u e s a r e n o t a p r e c i s e m e a s u r e o f t h e s o l u t e / s o l v e n t i n t e r a c t i o n , s i n c e t h e m o l e c u l a r g e o m e t r y a n d t h e s i t e s o f s o l u t e / s o l v e n t i n t e r a c t i o n c a n v a r y c o n - s i d e r a b l y f r o m ( C 2 H s ) 3 P O / s o l u t e i n t e r a c t i o n , s

T a b l e I I I s h o w s I R d a t a f o r ~ - p r o p i o l a c t o n e i n n - h e x - a n e a n d / o r c a r b o n t e t r a c h l o r i d e s o l u t i o n s . T h e d a t a s h o w t h a t , i n h e x a n e s o l u t i o n , t h e o b s e r v e d v C = O f r e q u e n c y o c c u r s a t 1 8 5 7 . 1 8 c m -1 a n d i n CC14 s o l u t i o n i t o c c u r s a t 1 8 5 0 . 5 7 c m - L I n a d d i t i o n , t h e o b s e r v e d ~ C = O f r e q u e n c y r a n g e d e c r e a s e s a s t h e m o l e % C C 1 4 / n - h e x a n e i n c r e a s e s . A f t e r c o r r e c t i o n f o r F e r m i r e s o n a n c e , ~ C = O is a s s i g n e d a t 1850 .21 c m - ' i n n - h e x a n e s o l u t i o n a n d a t 1 8 4 1 . 8 4 c m -~

i n CC14 s o l u t i o n . T h e u n p e r t u r b e d v C = O f r e q u e n c y d e - c r e a s e s m o n o t o n i c a l l y w i t h i n t h i s r a n g e as t h e m o l e % C C 1 4 / n - h e x a n e i n c r e a s e s . T h e v6 + p,~ c o m b i n a t i o n a f t e r c o r r e c t i o n f o r F e r m i r e s o n a n c e is a s s i g n e d i n t h e r e g i o n 1 8 3 0 . 6 4 - 1 8 3 2 . 2 2 c m -1 a n d t h e u n p e r t u r b e d 2rio is a s - s i g n e d i n t h e r e g i o n 1 8 2 5 . 8 1 - 1 8 2 7 . 3 2 c m -1.

T a b l e I V s h o w s I R d a t a f o r / 3 - p r o p i o l a c t o n e i n n - h e x - a n e a n d / o r c h l o r o f o r m s o l u t i o n s . T h e d a t a s h o w t h a t , i n h e x a n e s o l u t i o n , t h e o b s e r v e d ~ C = O f r e q u e n c y o c c u r s a t 1 8 5 7 . 2 3 c m -1 a n d i t o c c u r s a t 1845 .11 c m -I i n C H C l ~ s o l u t i o n ( t h e d i f f e r e n c e o f 0 .05 c m -~ b e t w e e n ~ C = O i n h e x a n e s o l u t i o n p e r h a p s r e f l e c t s t h e p r e c i s i o n o f t h e m e a -

T A B L E V. Infrared data for B-propiolactone in CHCI 3 and/or CC14 solutions.

In Fermi resonance Mole % CHClJ vC=O v6 + v13 2v,0

CCI4 cm-' cm ' cm-' (A1) (A2) (A3)


~C=O v6 + ~13 2~o cm -~ cm ~ cm -~

0 1850.54 1833.09 1816.29 0.945 0.487 0.250 1841.61 1831.69 1826.61 10.8 1847.01 1832.66 1815.96 0.915 0.597 0.337 1838.19 1831.00 1826.44 16.9 1846.59 1832.43 1816.14 0.904 0.617 0.355 1837.73 1830.90 1826.53 26.7 1846.28 1832.29 1815.81 0.900 0.575 0.375 1843.37 1832.75 1828.27 32.6 1845.99 1832.13 1815.54 0.900 0.664 0.388 1836.91 1830.54 1826.22 37.7 1845.84 1832.05 1815.42 0.890 0.666 0.394 1836.71 1830.45 1826.16 42.1 1845.72 1831.95 1815.17 0.888 0.682 0.403 1836.48 1830.33 1826.03 45.9 1845.62 1831.89 1815.06 0.879 0.685 0.405 1836.34 1830.26 1825.97 49.2 1845.54 1831.87 1814.98 0.875 0.690 0.412 1836.22 1830.22 1825.95 52.2 1845.47 1831.82 1814.82 0.885 0.701 0.419 1836.12 1830.14 1825.86 55.7 1845.39 1831.75 1814.73 0.864 0.696 0.419 1835.97 1830.08 1825.83 57.4 1845.41 1831.74 1814.72 0.866 0.701 0.420 1835.97 1830.08 1825.82 60.2 1845.32 1831.70 1814.62 0.865 0.706 0.425 1835.85 1830.02 1825.77 63.4 1845.27 1831.65 1814.47 0.854 0.705 0.425 1835.74 1829.95 1825.70 66.9 1845.69 1831.61 1814.29 0.805 0.656 0.391 1836.00 1829.97 1825.63 70.8 1845.62 1831.53 1814.56 0.834 0.719 0.430 1835.80 1830.05 1825.86 75.2 1845.50 1832.17 1814.38 0.845 0.745 0.449 1835.77 1830.29 1825.99 80.2 1845.43 1832.12 1814.14 0.825 0.736 0.449 1835.60 1830.19 1825.90 85.8 1845.32 1832.02 1813.91 0.824 0.754 0.459 1835.39 1830.07 1825.78 92.4 1845.17 1831.88 1813.53 0.827 0.785 0.476 1835.09 1829.89 1825.59

100 1845.02 1831.70 1813.04 0.783 0.775 0.476 1834.70 1829.67 1825.39 A cm -1 -5 .52 -1 .39 -3 .25 -6.91 -2 .02 -1.22


T A B L E VI. Infrared data for unsaturated iactones in CCI 4 and CHCI 3 solution 2 and correction for Fermi resonance.

(1) (2) Compound Structure Solvent cm -~ cm ~ (A~) (As)


~C=O ~C=O (CC1,-CHC13) cm -~ am ' A am -~

A~,_Butenolide ~u, .... , . CCI4 1784.5 1742 1240 ., ~ o CHC13 1777.5 1745 790

B-n-Butyl- , c,.. . CC14 1785 1752 1075 A-'-butenolide . ~ o CHC13 1784 1748 335

..C.H,, H fl-n-Hexyl- CC]4 1787 1754 1000

A"~-butenolide , T o CHCI~ 1785 1750 330

B-Cyclopentyl-cyclo- oyo~o c., H CC14 1785 1756 1175 A"~-butenolide . ~ o CHC13 1784 1750 335

~3-Cyclohexyl-cyclo . . . . . . . c., . CC14 1785 1764 695 A'-butenolide . ~ o CHC13 1782 1748 225

B-Phenyl- c,., . CC14 1786 1758 1805 A'-butenolide ~ o CHC13 1789 1751 335

H H B-Angelica lactone c.~o.~ °~ CC14 1782 1765 900

CHC13 1783 1759 270

~-Dimethy l - " " CC14 1776 1764 635 A,~_butenolide ,c,,~,~o CHC13 1774 1754 295

(2-Hydroxy- 1 - cyclohexylidine) ~ o ~'° CC14 1779 1764 855 acetic acid lactone CHC13 1755 1740 640

6UR-2,3,4,5

a-Pyrone " CC14 1752 1716 1480 : ~ o ~ CHCI~ 1739 1721 1080

5-Methyl c~-pyrone c .~ ,~ . CCI4 1753 1731 1505 .koAo CHCI3 1750 1719 404

Coumarin ~ CC14 1757 1743 1100 o CHC13 1757 1731 275

,~-Pyrone ,uR~ ...... CC14 1678 1657 1270 CHC13 1674 1661 980

98 1781.39 1745.11 565 1763.95 1758.55 17.44

430 1775.57 1761.43 900 1757.77 1774.23 17.80

405 1777.49 1763.51 915 1759.28 1775.72 18.21

495 1776.40 1764.60 920 1759.08 1774.92 16.32

540 1775.82 1773.18 850 1755.12 1774.88 20.70

975 1776.18 1767.82 1400 1758.34 1781.66 17.84

470 1776.17 1770.83 940 1764.36 1777.64 11.83

650 1769.93 1770.07 975 1758.65 1769.35 11.28

605 1772.78 1770.22 830 1746.53 1748.47 26.25

115 1749.40 1718.60 920 1730.72 1729.28 18.68

445 1747.98 1736.02 990 1728.54 1740.46 19.44

1290 1749.44 1750.56 1000 1736.61 1751.39 12.83

320 1673.77 1661.23 1210 1666.82 1668.18 6.95

surement). After correction for Fermi resonance, ~C=O is assigned at 1850.53 cm -1 in hexane solution and at 1834.78 cm -1 in CHCI~ solution. The unperturbed ~C=O frequencies are assigned in the region 1850.53-1834.78 cm -1 and decrease in frequency as the mole % CHC13/ n-hexane increases. The unperturbed ~s + ~3 combination tone is assigned in the region 1831.96-1829.78 cm -1, and unperturbed 2v10 is assigned in the region 1827.92- 1825.52 cm-L

Table V lists the IR data for fi-propiolactone in CClt and/or CHC13 solutions. The observed vC=O frequency occurs at 1850.54 cm -1 in CC14 solution and at 1845.02 in CHC13. The corresponding unperturbed ~C=O frequencies are at 1841.61 cm -~ in CClt solution and 1834.70 cm -~ in CHC13 solution. Moreover, the unperturbed ~C=O frequency decreases monotonically from 1841.61 to 1834.70 cm -~ as the mole % CHClJCC14 increases. The unperturbed ~6 + Vlo combination tone is located in the region 1832.75-1829.67 cm -~, and the first overtone of rio, corrected for Fermi resonance, is assigned in the region 1826.61-1825.39 cm-L

Other Lactones and a Comparison of Their vC=O Fre- quencies with Those for/~-Propiolactone after Correction for Fermi Resonance. In order to compare ~,C=O frequencies for different lactones it is useful to use symbols

such as 4SR (4-membered saturated ring) in the case of fi-propiolactone,

r ° O

5UR-2, 3 (5-membered unsaturated ring where the C=C is in the 2,3-position relative to the C=O group) for lactones containing the

~ O

group; and 6UR-2,3,4,5 (6-membered unsaturated ring where the C=C's are in the 2,3- and 4,5-positions relative to the C=O group, and a-pyrone and coumarin are ex- amples containing this group,

(see Ref. 20).

~L 0

864 Volume 45, Number 5, 1991

TABLE VII. Terpenoids containing 'y-lactone sWucture2

(1) Compound Structure Solvent cm-'


(2) vC=O cm-' (A,) (A~) cm-' cm -'

5SR

y-Butyrolactone Do CC14 1796

Dehydrodrimenin ~ o CHCi3 1770

Drimenin ~ o n-Hexane 1789 A -

Trans-dihydro- A . ~ - ~ ° CHC13 1782 confertifolin Vo

" "o CC14 1797

~ _ ~ o CHCI~ 1777 H H

o CC14 1796

. . CHCI~ 1780

Campholenolactone ~u~-~.~ n-Hexane 1786

" , ~ ° ° CC14 1783

1784 415 570 1789.06 1790.94

1760 480 500 1764.90 1765.10

1772 595 170 1785.22 1775.78

1770 420 620 1777.85 1777.15

1787 820 610 1792.73 1791.27

1766 530 370 1772.48 1770.52

1786 800 520 1792.06 1789.94

1772 560 520 1776.15 1775.85

1758 1300 190 1782.43 1761.57

1759 760 575 1772.66 1769.34 CC14

Jones e t a l . 2 found that for several 5- and 6-membered ring lactones, two bands were present in the carbonyl stretching region. Additional "doubling" was observed by Bond e t a l . 3 in the vC=O region of o-lactone-containing terpenoids. Although the presence of two bands was attributed to Fermi resonance of vC=O with an overtone of a lower-lying fundamental, the unperturbed vC=O frequencies were not determined. Using the expressions of Langseth and Lord, 15 we have calculated the unperturbed vC=O frequencies from the reported data (see Tables VI-VIII). Comparison of the data in these tables shows that the unperturbed ~C=O for the lactones (and y-lactones) always occurs at lower frequency in CHC13 than in CC14 solution. The 5UR-2,3 lactones yield unperturbed vC=O 51-63 cm -1 lower in frequency than unperturbed vC=O for 4SR lactone (B-propiolactone) in CC14 solution and 68-86 cm -~ lower in frequency in CHC13 solution. The behavior of lactone vC=O frequencies with changes in chemical structure has been discussed pre- viously. 2° In lactones, the amount of ring strain decreases in the order of lactones with the 4SR, 5UR-2,3 and 6UR- 2,3,4,5 structures. With a reduction in ring strain it be-

TABLE VIII. A comparison of lactone carbonyl stretching frequencies after correction for Fermi resonance.

Unperturbed vC=O

Type CC14 soln. lactone cm -~

Unperturbed vC=O vC=O vC=O CC1, soln. - CHC1 a

CHC13 soln. soln. cm -1 A am -1

4SR 1841.8 1834.7 7.1 5SR 1789.1-1792.7 1764.9-1776.2 16.5-24.2 5UR-2,3 1769.9-1781.4 1746.5-1764.4 17.9-23.4 6UR-2,3,4,5 1748.0-1749.4 1728.5-1736.1 13.3-19.5

comes easier for the carbonyl carbon atom to vibrate into the ring during a cycle of C=O stretching. Consequently, the vC=O mode occurs at increasingly lower frequency with decrease in ring strain. In addition, conjugation of the C=O group in lactones containing 5UR-2,3 results in an unperturbed gC=O lower in frequency in comparison to ~-butyrolactone (5SR) (8-20 cm -1 in CC14 solution). In the case of lactones containing the 6UR-2,3,4,5 structure, reduced ring strain and conjugation both con- tribute to lowering of the vC=O frequency. However, the presence of the double bond in the 4,5 position has a

TABLE IX. Infrared data for/%n-hexyl-A~'-butenolide. 2

(a) (b) Solvent cm -~ cm -1


vC=O (Aa) (Ab) cm-' cm -1

CC14 1787 1754 CHC13 (20%)/CC14 (80%) 1785 1751 CHC13 (50%)/CC14 (50%) 1785 1752 CHC13 1785 1750 CC14 (Satd. with HC1) 1786 1752 CHC13 (Satd. withHC1) 1785 1749 CS2 1782 1750 CH3OH 1783 1741 CH3CN 1783 1750

1000 405 1777.49 1763.51 695 785 1766.97 1769.03 470 865 1763.62 1773.38 330 915 1759.28 1775.72 980 460 1775.14 1762.86 310 880 1758.38 1775.62

1120 410 1773.42 1758.58 185 750 1749.31 1774.69 325 1050 1757.80 1775.2


contribution from the canonical form, -C-C-O-C=O, which stiffens the C=O bond, and raises ~C=O frequencies. These competing factors yield unperturbed ~C=O frequencies similar to those for open-chain aliphatic carboxylic acid esters. The ~C=O frequency for isopropyl acetate occurs at 1738 cm - ' in CCl~ solution, ~ and the lactones containing the 6UR-2,3,4,5 exhibit unperturbed ~C=O frequencies in the region 1748-1749.4 cm -1.

Jones et al. studied/~-n-hexyl-Aa/~ butenolide in several solvents and in mixed solvents, 2 and we have calculated the unperturbed ~C=O frequencies using their data (see Table IX). This compound contains 5UR-2,3 structure. The unperturbed ~C=O frequency for this butenolide derivative decreases as the concentration of CHCla to CC14 is increased, and this observation is com- parable to what was observed for/~-propiolactone in solution with these two solvents. Saturating the CCI~ and CHCI~ solutions of this butenolide solution with HC1 lowers unperturbed ~C=O by 2.35 and 0.9 cm -', respectively.

APPENDIX

An Approximate Correction for Fermi Resonance Based on Perturbation Theory for Cases Involving Three Modes. Fermi resonance results from anharmonic coupling between a fundamental vibration, ~0A, and an overtone (or combination), ~$, of a molecule. In the presence of this anharmonic coupling the observed frequencies are given by ~

p~ po + ~ + 1 _ _ . o - ( - - )~V(PA-- pp~)2+ 4[WA~[2 (A1)

(PPB) 2

where W ~ is the energy of interaction between the two bands and we have assumed that the fundamental, P~, is the higher-frequency band. The corresponding observed intensities are governed by the square of the magnitude of the dipole transition moment

I~ ~ (~i~l~o)l ~ (A2)

where # is the dipole moment, ~0 is the ground-state wavefunction, and ~I,~ are the perturbed wavefunctions due to Fermi resonance. If the perturbed wavefunctions are described as a linear combination of the unperturbed wavefunctions and, assuming that in the absence of Fer- mi resonance the intensity of the overtone (combination) band is negligible, I~ >> I~, then the observed intensities are approximately

0 a,~(/~ + Is) (A3) I~ ~ aaAI~ Is ~ a,~I~ ~ a,~(I~ + Is)

where aa~ and a ~ are the normalized coefficients defined by

~I', = ~ ai,~/. (A4) J

The above coefficients can be written in terms of observed (perturbed) and unperturbed (P~) frequencies

866 Volume 45, Number 5, 1991

• (V~ -- ~ ) + VA -- ~S)] 1/2

aaa = (Pa - PB) (A5)

(~A Ps) "

Substituting Eq. A5 into Eq. A3, examining the intensity difference, Ia - Is, and using the identity (P,~ + p~)/2 = (Pa + Ps)/2 (~-P), we obtain the equations developed by Langseth and Lord ~,'~

(p~) - 2 (-+) 2 L& + IsJ (A6)

where P~ > P~. The above expressions yield approximate frequencies corrected for Fermi resonance (unperturbed frequencies) from the observed intensities and frequencies.

In the present case there are three vibrational bands in Fermi resonance: the fundamental vibration, PP,~, the overtone vibration, ~ , and the combination mode, ~ . Exact expressions for the perturbed wavefunctions and frequencies proved to be unmanageable. However, approximate corrections for Fermi resonance can be obtained with perturbation theory. The wavefunctions, correct to first order, are:

( 1 y;'[ W~ ~A = \ ~ ] . ~ + (~ - ~) @s +

'~s ~ \ ~ - ] (~g _ ~ ) ~ + '~s +

~ ~ \ N - c ] ( ~ - ~)

W A c ,I~ ] (~,~ - ~)

W.c ] (~g - ~)

W s c ] ~ + (~ - ~g) ~g + ~

(A7)

where the normalization constants are:

i w ~ i ~ iWAcl ~ N A = I + + (~ - ~ ) ~ (~.I, - ~)2

t W ~ l ~ I W s c l ~ N B = I + + (~ - ~)~ (~i - ~)~

IWAcl ~ IWBcl ~ N c = l + + (~,~ - ~)~ (~ - ~)~" (AS)

The frequencies are unaffected by the anharmonic perturbation in first order, W, = 0. Thus, frequencies, cot- rect to second order, are:

i W ~ l 2 iWAcl 2 (~% - ~ i ) (~I, - ~)

I w ~ i 2 I W s c l 2 ~s ~ ~i (~I, - ~ i ) + (~i - ~ )

IWA~I ~ I W s c I ~ PPc~ PP~+ ( ~ - ~ ) ( ~ - ~ ) "

(A9)

If it is assumed that, in the absence of Fermi resonance, the intensities of the overtone and combination bands are negligible, I~ >> I~ ~ I~, then the obseved intensities are:

I~ + Is + I~

[ I .] 1 + (p~ _ p~)2 + (p~ _ p~)2j

Is ~- (IA + Is + Ic) × I W ~ l 2

I 12 !ws 2_ .] _ p )2 1 + ( ~ _ ~g)2 + (pg _ ~ ) 2 j

Ic ~ ( 5 + Is + Ic) x I WAcl 2

i WAci 2 i WBcl2 ] (~ _ ~,)2.

( t l 0 )

T h e a b o v e e q u a t i o n s can be r e w r i t t e n to give s e c ond - o r d e r c o r r e c t i o n t e r m s in t h e f r equenc i e s :

w h e r e

I W~BI 2 (~ _ po)

I W , cl ~ • r ( ~ - p~)

• Z(p~ - ~) ( ~ - p~)

CI ~ IB + I c [ (IA + IC~_I-1 =---5-- L1 + \ ~ ~ ] I B ]

K ~ IA + Ic, (IA + I c ~

( A l l )

(Ai2)

S u b s t i t u t i n g Eq. A l l i n to Eq. A9 y ie lds :

~A ~- P.~ + ~(P.~. -- P~) + ~ r ( ~ - ~)

(A13)

W i t h t h e use of Eq. A14, s h o w n below, t h e t h r e e un - p e r t u r b e d f r e q u e n c i e s can be o b t a i n e d . W i t h t h e use o f t h e s e e q u a t i o n s , a 5% e r r o r in t h e I R b a n d i n t e n s i t y m e a s u r e m e n t s a n d a 0.1 c m -1 e r ro r in t h e o b s e r v e d f re- q u e n c y m e a s u r e m e n t s wil l p r o d u c e a v a r i a t i o n in t h e c a l c u l a t e d f r e q u e n c i e s o f ± 0 . 3 c m -I.

1. J. R. Durig, Spectrochim. Acta 19, 1225 (1963). 2. R. N. Jones, C. L. Angell, T. Ito, and R. J. D. Smith, Can. J. Chem.

37, 2007 (1959). 3. R. P. M. Bond, T. Cairns, J. D. Connolly, G. Eglinton, and K. H.

Overton, J. Chem. Soc. (London) 3958 (1965). 4. R. A. Nyquist, Appl. Spectrosc. 40, 79 (1986). 5. R. A. Nyquist, V. Chrzan, and J. Houck, Appl. Spectrosc. 43, 981

(1989). 6. R. A. Nyquist, C. L. Putzig, and L. Yurga, Appl. Spectrosc. 43, 983

(1989). 7. R. A. Nyquist, C. L. Putzig, and D. L. Hasha, Appl. Spectrosc. 43,

1049 (1989). 8. R.A. Nyquist, T. M. Kirchner, and H. A. Fouchea, Appl. Spectrosc.

43, 1053 (1989). 9. R. A. Nyquist, V. Chrzan, T. M. Kirchner, L. Yurga, and C. L.

Putzig, Appl. Spectrosc. 44, 243 (1990). 10. R. A. Nyquist, Appl. Spectrosc. 44, 426 (1990). 11. R. A. Nyquist, Appl. Spectrosc. 44, 433 (1990). 12. R. A. Nyquist, Appl. Spectrosc. 44, 438 (1990). 13. R. A. Nyquist, Appl. Spectrosc. 44, 594 (1990). 14. R. A. Nyquist, Appl. Spectrosc. 44, 783 (1990). 15. A. Langseth and R. C. Lord, Kgl. Dnaske Videnskab. Mat-fys.

Medd I5, 6 (1938). 16. R. A. Nyquist and W. J. Potts, Spectrochim. Acta 17, 679 (1961). 17. E. V. Chisler, V. Y. Davydov, I. N. Goncharuk and E. A. Ivanova,

Phys. Stat. Sol. 78, 359 (1976). 18. F. Winther, Z. Naturforsch. 2Sa, 1912 (1970). 19. M. M. Wohar, J. K. Seehra, and P. W. Jagodzinski, Spectrochim.

Acta 44A, 999 {1988). 20. R. A. Nyquist, The Interpretation of Vapor-Phase Infrared Spec-

tra: Group Frequency Data (Sadtler Research Laboratories, Di- vision of Bio-Rad Laboratories, Inc., Philadelphia, 1984), Vol. 1, pp. 346-350.

21. G. Herzberg, Molecular Spectra and Molecular Structure H In- frared and Raman Spectra of Polyatomic Molecules (D. Van Nos- trand Company, Princeton, New Jersey, 1945).

(K - r ) ( 1 - r ) ~ 2 ] -1

PP~ ~ 1 - {1 + ~(2 + F )}{~(2K + F) - 1}

. [ p A + 3 ~ _ ( P c + 3 ~ K ) ( l - r ) ~ ]

1 + ,I~(2 + F) {1 + ~(2 + F)} {,I)(2K + F) - 1}

p~ Pc + 3P,I~K - P ~ ( K - F)

,I~(r + 2K) - 1

~ ~ = 3~ - po _ p~; (3p --- PA + P. + PC). (A14)


infrared study of β-propiolactone in various solvent systems and other lactones

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