20. R. C. Dougherty, H. H. Strain, W. A. Svec, R. A. Uphaus, and J. J. Katz, J. Am. Chem. Soc. 92, 2826 (1970).

21. T. Kitagawa, M. Abe, and H. 0goshi, J. Chem. Phys. 69, 4516 (197S).

22. W. D. Wagner, unpublished data.

23. P. M. Champion and A. C. Albrecht, Chem. Phys. Lett. 82, 410 (1981).

24. S. Hassing and O. Sonnich Mortensen, J. Chem. Phys. 73, 1078 (1980).

Infrared Group Frequency Correlations for Styrenes, a-Methylstyrenes, and Related Compounds*

R. A. NYQUIST The Dow Chemical Company, Analytical Laboratories, 574 Building, Midland, Michigan 48667

Infrared group frequency correlations are presented which aid in spec- tra-structure identification of styrenes, a-methylstyrenes, and related compounds. The vinyl and phenyl groups in styrene are coplanar in only those cases where atoms or groups such as CI and CH3 are not substi- tuted in the 2,6-positions, and the isopropenyl and phenyl groups in a- methylstyrenes are eoplanar in only those cases where atoms or groups such as CI and CH3 are not substituted in one ortho-position. Steric factors prevent the vinyl and phenyl groups from being eoplanar in styrene substituted with atoms or groups in at least the 2,6-positions, and sterie factors also prevent the isopropenyl and phenyl groups from being coplanar in 2-substituted a-methylstyrenes.

Index Headings: Infrared; Molecular structure; Group frequency cor- relations.

INTRODUCTION

Factors affecting the out-of-plane hydrogen defor- mation frequencies in olefins and their derivatives have been well discussed. ',2 The present study offers new spectra-structure correlations useful in the elucidation of molecular structure of styrenes, ~-methylstyrenes, and related compounds.

EXPERIMENTAL METHOD

Infrared spectra were recorded with the use of several spectrometers. Spectra were recorded in the vapor phase, neat, or in CC14 to CS~ solutions. Some of the data was published by Sadtler Research Laboratories and is in- dicated in the tables.

RESULTS AND DISCUSSION

Figure 1 is an infrared vapor-phase spectrum of sty- rene. Type-C IR bands are noted at 990, 911, 774, and 696 cm -1. The dipole moment change during the normal vibration takes place parallel to the c-axis for those fun- damentals exhibiting type-C bands. Therefore, the vinyl and phenyl groups in styrene are coplanar, since type-C

Received 18 June 1985. * These data were presented at the Williams-Wright Award Sympo-

sium, Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, Feb. 1985.

bands are exhibited by group frequencies for the vinyl group (990 cm-', vinyl twist and 911 cm -t, vinyl CH2 wag) and for the phenyl group (774 cm -1, in-phase 5-hydrogen out-of-plane deformation and 696 cm-', the alternating phenyl carbon atom out-of-plane deforma- tion). Figure 2 is an infrared vapor-phase spectrum of 2,4,6-trimethylstyrene. In this case, steric factors pre- vent the vinyl and 2,4,6-trimethyl phenyl groups from being coplanar. In fact, the vinyl group must be perpen- dicular to the 2,4,6-trimethyl phenyl group. In this case, the dipole moment change during the vinyl twist (~995 cm -1) and vinyl CH2 wag (~925 cm -1) vibrations must take place in a direction not exactly parallel to the a or b symmetry axis, since both of these fundamentals ex- hibit a type-AB band. The in-phase two-hydrogen out- of-plane deformation for the 2,4,6-trimethyl phenyl group is assigned to the 849 cm -~ type-C band, and the dipole moment change during this normal vibration must take place parallel to the c-axis. Thus, the vapor-phase IR band contours for styrene and 2,4,6-trimethylstyrene show that the vinyl and phenyl groups are coplanar in one case and are not coplanar in the case of 2,6-disub- stituted styrenes.

Infrared group frequencies for styrene and ring-sub- stituted styrenes are given in Table I. Table I also con- tains pKa values for some correspondingly substituted phenols. Figure 3 is a plot of the vinyl CH2 wag fre- quencies for styrene and ring-substituted styrenes vs. pKa values for phenol and correspondingly substituted phenols. The vinyl CH2 wag frequencies occur in the 900-940 cm -~ region, and the pKa values for the corre- spondingly substituted phenols are in the 5-11 range. Examination of Fig. 3 shows that styrenes substituted with atoms or groups in at least the 2,6-positions cor- relate in a manner different from styrenes not substi- tuted with atoms or groups in the 2,6-positions. The pKa values are affected by contributions from both inductive and resonance of the substituted atoms or groups. In the case of 2,6-substituted styrenes, the vinyl and 2,6-disub- stituted phenyl groups are not coplanar; therefore, it is not possible for the resonance effects of the atoms or groups substituted at least in the 2,6-positions of styrene to affect the vinyl CH2 wag frequencies. Thus, only in-

198 Volume 40, Number 2, 1986 0003-7028/86/4002-019652.00/0 APPLIED SPECTROSCOPY © 1986 Society for Applied Spectroscopy

8 C E

E'

100 t_~

80

60

40

20

0 4000 3500

I 3 0 0 0

I I I 1 I I I

t(,.)J H + ~ / + H v - " ' c - c ' " . 5 " ' " - I01

I 1 I I I I 2500 2000 1800 1600 1400 1200

cm -1

FIG. 1. Infrared vapor-phase spectrum of styrene.

t ¢

I÷

I , 1000 800

1 I I 1

I 600 400 200

ductive effects can affect the vinyl CH2 wag frequency in the case of 2,6-substituted styrenes (assuming that the effect of intramolecular forces between atoms or groups joined to the 2- and/or 6-positions and the vinyl group are negligible in affecting the CH2 wag frequencies for 2,6-substituted styrenes). Thus, the vinyl CH2 wag frequencies for coplanar styrenes are affected by both inductive and resonance effects of the atoms or groups joined to the ring, while only inductive effects affect the vinyl CH2 wag frequencies for styrenes where the vinyl and 2,6-substituted phenyl groups are not coplanar.

Figure 4 is a plot of the frequency separation between vinyl twist and vinyl CH2 wag for styrene and substi- tuted styrenes vs. the pKa values for correspondingly substituted phenols. Again, separate correlations for planar and noncoplanar styrenes are apparent.

Infrared group frequencies for a-halostyrenes, a-al- kylstyrenes, and related compounds are given in Table II.

Figure 5 is a plot of the CH2 wag frequencies for sty- rene and ring-substituted styrenes vs. the CH2 wag fre- quencies for a-methylstyrene and correspondingly sub- stituted a-methylstyrenes (see Tables II and III). This plot suggests that the factors which affect the vinyl CH2 wag frequencies for styrenes also affect the CH2 wag frequencies for a-methylstyrenes. However, the CH2 wag

frequencies for a-methylstyrenes occur at lower fre- quency than correspondingly substituted styrenes by 10- 18 cm -~ (see Table III).

The isopropenyl and phenyl groups are not coplanar for 2-substituted a-methylstyrenes (substituted with at- oms or groups such as C1 and CH3), while for styrenes both ortho-positions must be substituted with compa- rable atoms or groups in order to sterically prevent the vinyl and phenyl groups from being coplanar.

Several infrared group frequencies for 1-alkenes and the vinyl halides are compared in Table IV. The 1-al- kenes exhibit several infrared group frequencies. Some of these are:

olefinic carbon-hydrogen stretch, 3082-3090 cm-1; carbon-carbon double bond stretch, 1640-1650 cm-1; vinyl twist, 990-1007 cm-1; vinyl CH2 wag, 910-917 cm-~; first overtone of vinyl CH2 wag, 1829-1835 cm-1; and symmetric CH2 stretch, 2860-2880 cm-k

The absorbance ratios for vinyl twist/sym. CH2 stretch, for vinyl CH2 wag/sym. CH2 stretch, and for olefinic C-H stretch/sym. CH2 plotted vs. the number of carbon at- oms in the 1-alkene series show smooth relationships which are useful in spectra-structure indentification of unknown samples of 1-alkenes? ~

0 E

E

i=-

8

100 ..,..,.,...,,,....,....,.,.,.,.,.,,..,,,,__.~=.

80 -

60 -

40 -

20 -

0 . . , . . ~ , . _ . ~ L

4000 3500 3001

I 1 r I 1 1 [ ] I 1

H3C~cH3 c~3 I CH' 3 H 3C, ,~ .C . ~ . _ _

÷ H " ' ~ "~H+ I

2500 2000 1800 1600 1400 1200 1000

cm -1

FIG. 2. Infrared vapor-phase spectrum of 2,4,6-trimethylstyrene.

In

-½H~__c/H-

CH3

800 600 400 200

APPLIED SPECTROSCOPY 197

TABLE I. Infrared group frequency data for styrene and ring-substituted styrenes."

Compound

2=CH2 C=C CH=CH2 =CH~ CH=CH~ pKa for wag stretch twist wag twist corresponding

(CC14 soln.) (CC14 soln.) (CS2 soln.) (CS2 soln.) -CH~ wag substituted cm -~ cm ~ cm -~ cm ~ Acre -~ phenol

Styrene 1821 1632 989 907 82 9.93 1829 VP 1631 VP 985 VP 912 VP 73

4-Methylstyrene 1812 1631 987 903 84 10.254 1819 VP 1636 VP 989 VP 909 VP 80

4-Ethylstyrene 1812 1629 987 903 84 4 -Isopropylstyrene 1808 1629 981 898 83 4-Tert-butylstyrene 1810 1631 985 901 84 4-Chloromethylstyrene 1827 1631 986 908 76 4-Hydroxystyrene 1805 FM 1626 FM 990 NM 899 NM 91 4-Bromostyrene 1826 1631 986 909 77 9.344 4-Chlorostyrene 1815 1628 982 904 78 9.25 4-Fluorostyrene 1825 VP 1638 VP 990 VP 911 VP 79 9.956 4-Cyanostyrene 1833' 1627" 982 917 65 4-Vinylbenzoic acid 1833 FM 1634 FM 911 NM 912 NM 79 4-Vinylbenzamide 1830 FM masked 989 NM 915 NM 74 4-Sodium styrenesulfonate 1829 FM 1631 FM 991 NM 909 NM 82

3-Ethylstyrene 1818 1633 987 904 83 3-Isopropenylstyrene 1820 1629 986 907 79 3-Chlorostyrene 1831 1631 986 913 73 8.95 3-Hydroxystyrene 1815 1629 984 905 79 9.37 3-Acetylstyrene 1828 1637 987 910 77 9.187 3-Chloromethylstyrene 1832 1637 987 909 78 3,4-Dichlorostyrene 1824 1626 980 910 70 8.45 3,4-Dibromostyrene 1835 1626 985 915 70 3,4-Dimethylstyrene 1817 1628 989 903 86 10.178 3,5-Dimethylstyrene 1808 1626 984 903 81 10.13 2,4-Dimethylstyrene 1821 1626 987 907 80 10.498 2,6-Dimethylstyrene 1800 N 1629 N 990 N 920 N 70 2-Chlorostyrene 1833 1629 986 914 72 8.55 2-Bromostyrene 1835 1629 984 916 68 8.439 2-Methylstyrene 1832 VP 1630 VP 989 VP 914 VP 75 10.28 l°,H 2-Chloromethylstyrene 1845 1630 987 917 70 2-Vinylstyrene 1832 1629 983 912 71 2,3-Dichlorostyrene 1842 1626 986 919 67 7.4 ~ 2,4-Dichlorostyrene 1832 1623 983 917 66 7.83 2,4-Dibromostyrene 1629 982 919 63 2,5-Dichlorostyrene 1842 1624 986 921 65 7.35 2,5-Dibromostyrene 1844 1629 983 917 66 2,6-Dichlorostyrene 1872 1637 981 932 49 6.8 ~ 2,3,6-Trichlorostyrene 1876 1631 978 935 43 6.15 2,4,5-Trichlorostyrene 1845 1623 982 920 62 7.0 ~ 2,4,5-Tribromostyrene 1850 1626 981 921 60 2,4,5-Tribromostyrene 1857 KBr 1616 KBr 986 KBr 928 KBr 58 2,4,6 -Trichlorostyrene 1876 1631 978 933 45 6.46 2,3,4,5-Tetrachlorostyrene 1858 1627 974 925 49 7.06 2,3,4,6-Tetrachlorostyrene 1883 1633 978 937 41 5.226 2,3,4,5,6-Pentachlorostyrene 1883 1631 975 936 39 4.77 TM

2,3,4,5,6-Pentachlorostyrene 1899 KBr 1629 KBr 981 KBr 947 KBr 34 4.77 TM

2,4,6-Trimethylstyrene 1843 1632 991 919 72 10.83 ~ 2,4,6-Trimethylstyrene 1850 VP 1633 VP 993 VP 924 VP 69 2,3,4,5,6-Pentafluorostyrene 1872 N 1644 N 998 N 931 N 57 2,3,4,5,6-Pentamethylstyrene ~1842 N ~1632 N ~998 N ~918 N 80

' These data are recorded in CC14 soln. (3800-1333 cm -~) and CS2 soln. (1333-400 cm -1) unless indicated otherwise. KBr = KBr pellet data; NM = Nujol mull data; FM = fluorosoluble mull data; VP = vapor-phase data; * = CS2 solution data; N = neat liquid (Sadtler Research Laboratories, Philadelphia, PA).

There is another characteristic mode which aids in the spectra-structure identification of 1-alkenes, and this mode is called vinyl wag (see Table IV). The vinyl wag mode is affected by the atoms or groups joined to the 3-carbon atom in 1-alkenes, by the halogen atom joined to the 3-carbon atom in the allyl halide series, and by the halide joined to one carbon atom in the vinyl halide series. The normal coordinate for vinyl wag has been determined for vinyl bromide, 14 and a pictorial view of the vinyl wag mode for vinyl bromide is shown on the

198 Volume 40, Number 2, 1986

top of Fig. 6. Figure 6 demonstrates the frequency be- havior of the vinyl wag mode for vinyl halides, allyl ha- lides, and 1-alkenes. The vinyl halide, vinyl wag fre- quencies (495-711 cm -~) are plotted vs. the halogen atom, and the frequency increases in the order I through F (where the scale is F = 0, C1 = 1, Br = 2, and I = 3). Thus, the vinyl wag frequency increases with an increase in electronegativity, with a decrease in the c-x bond length, and with decreasing mass of the halogen atom. The allyl halides exist in cis and gauche configurations.

Vinyl CH 2 Wag Frequencies For Styrene And Substituted Styrenes Vs. pK. Values For Phenol And Corresponding Substituted Phenols.

Vinyl CH 2 Wag 940 F

I ~,~ ®Styrene Substituted With Atoms Or Groups ~ . ~ tn At Least The 2,6-Positions. 935 __1 X • Styrene Substituted With Atoms Or Groups 1 ~"~ In At Least The 2-Position, But Not In The

6-Position. 930 - ~ ~ Styrene Or Substituted Styrene Not Su bsti-

tuted In the 2 and 6 Positions.

Vinyl Group 925 - ~ ~ ~ Non Coplanar With

cm" ~ ~ h e n y l Group

920 o a k e ~®

915

910 ~ " ~

~ ~ Vinyl Group 905 ~ \==" CoplanarWith

\ ~ Phenyl Group

90O i I 1 I I I 5 6 7 8 9 10 11

pK.

FIG. 3. Vinyl CH2 wag frequencies for styrene and substituted sty- renes vs. pKa values for phenol and corresponding substituted phen- ols.

The vinyl wag frequencies for the gauche allyl halide isomers occur in the region 491-643 cm -1 region and for the cis allyl halide isomers (the less stable form) in the 540-552 cm -1 region. 1~ Figure 6 shows that the vinyl wag frequencies for the cis and gauche allyl halides correlate

(Vinyl Twist)-(Vinyl CH2 Wag) 90

Acm'l / 80 Vinyl Group

Coplanar With ,~ ,,~J Phenyl Group / '~

60

J Vin~ylGroup 50 ~ Non Coplanar With

_?,t,,f,,,~,, ~ Phenyl Group

40 •

30 1 f i I I I 6 7 8 9 10 11

pKa

FIG. 4. Vinyl twist frequencies minus vinyl CH2 wag frequencies for styrene and substituted styrenes vs. pKa values for phenol and cor- responding substituted phenols.

in essentially a linear manner when plotted in the same manner as used to plot the vinyl halides. The vinyl wag frequencies for the cis allyl halides differ in frequency by 12 cm ', while the vinyl wag frequencies for the gauche allyl halides differ in frequency by 152 cm-' .

A reasonable explanation for the frequency behavior between the cis and gauche vinyl wag frequencies in the allyl halides is as follows: The cis structure is planar while the gauche structure does not have a plane of sym- metry. It is theoretically possible for any of the funda- mentals to couple in the case of the nonplanar gauche

TABLE II. Infrared group frequency data for a-halostyrenes, a-alkylstyrenes, and related compounds, a

2(=CH2 wag) C=C stretch =CH~ wag Compound cm ' (CC14 soln.) cm 1 (CC14 soln.) cm I (CS2 soln.)

a-Chlorostyrene a-Bromostyrene a-Phenylstyrene

a-Methylstyrene a-Propylstyrene a(2-Hydroxyethyl)styrene 3-Vinyl-a-methylstyrene a,4-Dimethylstyrene 4-Chloro-a-methylstyrene 4-Bromo-a-methylstyrene 4-Hydroxy-a-methylstyrene 4-Acetyl-a-methylstyrene 3,4-Dichloro-a-methylstyrene 3,5-Dichloro-a-methylstyrene

4-Chloro-a-3-dimethylstyrene 2-Hydroxy-a-methylstyrene 2 -Chloro-a-methylstyrene 2,3-Dichloro-a-methylstyrene 2,4-Dichloro-a-methylstyrene 2-Chloro-a,5-dimethylstyrene 2-Nitro-a-methylstyrene a,2,4,5-Tetramethylstyrene 2,3,4,5,6-Pentafluoro-a-methylstyrene 1-Isopropenylnaphthalene 4-Isopropenylpyridine

1760 1626 877 1775 1617 882 1809 1616 896

(1803 VP) (1609 VP) (901 VP) 1797 1629 892 1801 1629 897 1799 1627 897 1792 1629 892 1783 1629 887 1790 1627 890 1789 1623 892 1772 1630 882 1795 1626 897 1802 1634 896 1810 1629 899

(1818 VP) (1635 VP) (908 VP) 1790 1631 892 1822 1632 911 1810 1642 904 1805 1640 902 1819 1642 905 1814 1642 902 1822 1643 902 1803 1642 899

~1830N ~1645N ~918N 1815 1634 904 1815 1634 904

"VP = vapor phase data; N = neat liquid data.

APPLIED SPECTROSCOPY 199

CH 2 WAG FREQUENCIES OF STYRENE AND~METHYLSTYRENE AND CORRESPONDING

RING SUBSTITUTED ANALOGS

935 l

930 -

-~2 H H+ • "c :<

925 ~ H+

Vinyl CH2 Wzg 92O

915

910

- / ~ 885

I I ] I I I

Vinyl CH 2 WIR for Styrene= Occurs 10--18 cm "1 Higher in Frequency than Vinylidine CH 2 Wag for Corresponding Ring SubstitutlKI a-met hytlt yrenes

C•?:C ~H+

890 895 g00 905 g10

¢m.I

915 920

FIG. 5. Vinyl CH2 wag frequencies for styrenes vs. the CH~ wag fre- quencies for corresponding ring-substi tuted a-methylstyrene.

structure, but in the case of the planar cis structure it is not possible for out-of-plane fundamentals to couple with planar fundamentals. Therefore, it appears that vi- nyl wag for the cis isomer is more of a "pure" vibration than in the case of the gauche isomer where the vinyl wag fundamental is considerably more complex because of coupling with other modes.

Figure 6 also shows the vinyl wag frequencies of 1-alkenes plotted vs. the number of protons on the 3-carbon atom. The vinyl wag fundamentals increase in frequency as the number of protons on the 3-carbon atom decreases from 2, 1, 0. The vinyl wag frequency for propene (3 protons on the a-carbon atom) occurs at a frequency intermediate between the cis and gauche iso- mers of R-CH2-CH=CH2.

Alkene cm-]

cis R-CH2-CH=CH2, 545-568 CH3-CH=CH2, 582

gauche R-CH2-CH =CH2, 611-635

(R-)2CH-CH=CH2, 661-672 (R-)3C-CH=CH2, 681-683

The vinyl CH2 wag frequencies for the cis isomer of 1-alkenes are comparable to those exhibited by the cis isomer of the allyl halides. The vinyl halides have C~ symmetry, and the vinyl wag mode exhibits a type-C band in the vapor phase. Propene also has a plane of symmetry, and the vinyl wag mode is assigned to the 582 cm- ' type-C band. The vinyl wag frequencies are useful in helping one to determine whether the 3-carbon atom is substituted with 1-, 2-, or 3-alkyl groups.

Infrared group frequencies for 2-alkyl- l-alkenes, 2-halopropenes, and 1, 1-dihaloethylenes are given in

TABLE III . Comparison of CH~ wag frequencies of correspondingly ring-substituted a-methylstyrene and styrene.

Ring substi tut ion

a-Methyl- styrenes

vinylidene Styrenes Vinylidene CH2 CH2 wag vinyl CH2 wag wag-vinyl CH~

cm ~ am-1 wag Acm -1

Unsubst i tu ted 892 907 - 17 4-CH~ 887 903 - 16 4-C1 890 908 - 1 8 4-Br 892 909 - 17 4-OH 882 899 - 17 3,4-C12 896 910 - 14 2-C1 904 914 - 10 2,3-C12 902 919 - 17 2,4-C12 905 917 - 12 2,5-C1~ 906 921 - 15 2,3,4,5,6-F 5 918 931 - 13

Table V. The CH2 wag vibrations for 2-methyl-l-alkenes occur 18-22 cm -1 lower in frequency than vinyl CH2 wag for 1-alkenes. The first overtone of CH2 wag for 2-meth- yl-l-alkene is also a good group frequency that exhibits negative anharmonicity (see Table V).

Table VI compares infrared group frequency data for 2-alkyl- l -a lkenes and a-methyls tyrenes . The C=C stretching vibration for 2-alkyl-l-alkenes (1644-1660 cm -1) and for a-methylstyrenes not substituted in the 2-position with atoms or groups (1623-1629 cm -1) sug- gests that conjugation of the vinylidene and phenyl groups lower the C=C stretching vibration frequency. Alpha-methylstyrenes with atoms or groups substituted in at least the 2-position exhibited a band in the 1640- 1645 cm- ' region, and occur in a region comparable to that exhibited by 2-alkyl-l-alkenes. This similarity in the C=C stretching frequencies is reasonable, because the isopropenyl and phenyl groups are not coplanar in 2-substituted-a-methyl styrenes. The C=C stretching frequency for 2-hydroxy-a-methylstyrene is an excep- tion, since it occurs at 1623 cm-L However, there is a plausible explanation for this exception. The O-H stretching frequency occurs at 3532 cm -1 (CC14 soln.), which indicates that the 0 -H group is intramolecularly hydrogen bonded to the at-system of the C=C bond. Thus, the C=C stretching frequency occurs at lower fre- quency for 2-hydroxy-a-methylstyrene than the other 2-substituted-c~-methylstyrenes because of intramole- cular hydrogen bonding between the OH group and the C=C bond.

In the series CH3(CH2)nC=CH2, the weak band as- signed as CH2 rocking decreases in frequency as the val- ue of n increases. For example, CH2 rock is assigned at 773, 740, 735, 729, ~722 cm- ' for n = 1-4, and 6, re- spectively.

Vinylidene-type compounds containing 1 or 2 halo- gens joined to the carbon-carbon double bond exhibit several characteristic group frequencies. The band as- signed as C=C stretching has high intensity and the fre- quency decreases in the order F, C1, Br, as shown below.

1,1-difluoroethylene 1,1-dichloroethylene

C=C CH2 stretching wagging

cm -1 cm '

1728 803 1616 872

200 Volume 40, Number 2, 1986

720

V I N Y L WAG ÷ H~ /H + ½

CzC -Ya H / .y,%XorR

(481--711 cm "1 )

700

cm -I

680

660

640 (611 --635 cm "1 ) H,, /H T ~c:c. ~ t

620 H •C .,3 H T R l "--"

gauche j

6O0 H x / H

C : C ,,H ~. H / '~'C <~ H -~'~"

580 H

560 H ~ = : c / H R [ cls

-H / ~'C~ H | -.t,.- -

~ / H 1 540 ¢is ~ {545-568cm" )

52O

50O

I I ! / t / / 0 1

H, x / X H ~ / H (681-683 cm "1) j =

C : C ~ /R H / "~4C ,~ R H/C C \H {495-711 cm "1 )

R

~ H~ / H

H; c : 1661--672 cm "11

gauche

(491 --643 cm "1 ) H\ /H \ C : C .H H / XC/,,~ H

gauche .._._..---.w

(.~0-552 r~n "1 ) H~ /H

C--C~ /X H / C,~H

2 3 F CI Br I No. Prolons On The 3-Carbon A t o m Halogen

FIG. 6. Viny l wag frequencies vs. the n u m b e r of protons on the 3-carbon a t o m of 1-alkenes and the v inyl wag frequencies of v inyl hal ides and allyl hal ides vs. the halogen atom.

C=C CH2 stretching wagging

cm-1 cm-1

1-bromo-l-chloroethylene 1609 872 1,1-dibromoethylene 1601 881 2-methyl- 1-propene 1660 893 2-chloro-l-propene 1645 878 2-bromo-l-propene 1638 883 ~-methylstyrene 1629 892 ~-chlorostyrene 1626 877 c~-bromostyrene 1617 882 In contrast, the CH2 wagging frequency and its first overtone increase in frequency in the order F, C1, and Br.

T A B L E IV. A comparison of infrared group frequency data for l - a i k e n e s and vinyl halides. ~

No.

hydrogen 2 v inyl CH2 C=C s tretch Viny l twist CH2 wag Viny l wag on 3

carbon wag cm -~ am -1 cm -1 cm -~ cm -~

C o m p o u n d atoms Vapor N e a t Vapor N e a t Vapor N e a t Vapor N e a t Vapor N e a t

Propene 3 1830 . . . 1650 . . . 991 . . . 911 . . . 582 . . . 1 -Butene 2 1835 . . . 1648 . . . 991 . . . 910 . . . 632 ,552 . . . 1 -Pentene 2 1835 (1828) 1640 (1643) 1000 (991) 915 (910) 627 (630, 556) 1 -Hexene 2 1829 (1822) 1640 (1641) 990 (990) 911 (907) 632, 545 (630, 551) 4 - M e t h y l - l - p e n t e n e 2 1834 . . . 1645 . . . 998 . . . 918 . . . 625 . . . 1 -Heptene 2 1830 1813 1642 1638 995 995 912 912 630 635, 545 4 - M e t h y l - l - h e x e n e 2 1830 . . . 1641 . . . 990 . . . 910 . . . 621 . . . 1 -Octene 2 1830 1834 1642 1651 994 995 912 913 630 632, 557 4 ,4 -Dimethy l - 1 -hexene 2 1832 1827 1646 1640 999 994 918 910 611 611 1 - N o n e n e 2 1829 1816 1643 1639 992 983 912 903 630 623, 545 1 -Decene 2 1830 1825 1642 1645 992 990 911 909 632 632 1 -Dodecene 2 1830 1815 1642 1635 993 989 911 905 635 632 1-Tridecene 2 1829 1820 1641 1640 994 985 911 902 630 630, 568 1 -Tetradecene 2 1829 1822 1641 1644 991 999 911 915 630 640, 552 1 -Hexadecene 2 1829 1822 1641 1641 991 990 910 909 629 630, 550 1-Octadecene 2 1829 1814 1641 1639 992 990 911 903 629 628, 545 3 - M e t h y l - l - b u t e n e 1 1830 . . . 1641 . . . 997 . . . 911 - . . 661 . . . 3 , 4 - D i m e t h y l - l - p e n t e n e 1 1831 1822 1642 1640 1000 997 917 910 672 672 3 , 3 - D i m e t h y l - l - b u t e n e 0 1834 . . . 1648 . . . 1002 . . . 915 . . . 682 . . . 3 , 3 - D i m e t h y l - l - p e n t e n e 0 1831 1821 1647 1640 1007 1001 915 909 681 682 3 , 3 - D i m e t h y l - l - h e x e n e 0 1830 1822 1644 1639 1005 1005 912 910 683 685 Viny l bromide 0 . . . . . . 1608 . . . 944 . . . 904 . . . 586 . . . V iny l chloride 0 1800 . . . 1610 . . . 943 . . . 898 . . . 621 . . . V iny l fluoride 0 . . . . . . 1654 . . . 930 . . . 862 . . . 711 . . .

a Frequenc ies in parentheses are recorded in CC14 solut ion in the 3800-1333 cm -1 region and in CS2 solut ion in the 1333-400 cm -1 region.

APPLIED SPECTROSCOPY 201

TABLE V. Infrared group frequency data for 2-alkyl-l-alkenes, 2-halopropenes and 1,1-dihaloethylenes."

Antisym. =CH~ 2(=CH2 C=C =CH2 Alkyl N u m b e r of s t re tch wag) s t re tch wag CH= rock ad jacent

C o m p o u n d cm 1 cm -~ cm -1 cm 1 cm i CH2 groups

2 -Methy l - l -p ropene 3090 1789 1660 893 2 - M e t h y l - l - b u t e n e 3071" 1783" 1650" 883" 2 -Methy l -4 -pheny l - l -bu tene masked 1800" 1651" 870* 2 -Me thy l - l - pen t ene 3082 1790 1652 890 2 -Me thy l - l - pen t ene 3072* 1785 1648 888 2 -Me thy l - l -hexene 3085 ~ 1778 1653 890 2 - M e t h y l - l - h e p t e n e 3084 ~ 1785 1651 890 2 - M e t h y l - l - h e p t e n e 3080* ~ 1785" 1650" 888 2 -E thy l - l -hexene 3080* 1781" 1647" 887* 2 ,4 ,4 -Tr ime thy l - l -pen tene 3082 1792 1648 896 2 -Me thy l - l - nonene 3080 1785 1652 890 2 ,4 ,4 -Tr imethy l - l -hexene 3082 ~ 1795 1644 893 2 ,6 -Dime thy l - l -hep tene 3082 1785 1648 890 2 ,5 -Dimethy l - l -hexene 3082 1785 1655 891 2 ,5 -Dimethy l - l -hexene 3075 .1 1778 .1 1650 .1 884 .1 2 ,4 -Dimethy l - l -hexene 3081 1791 1655 893 2 ,4 -Dimethy l - l -hexene 3075"~ 1780"1 1650"~ 888 2 ,4 -Dimethy l - l -hep tene 3083 1790 1655 893 2 ,4 -Dimethy l - l -hep tene 3078 .1 1781.1 1650 .1 889 .1 2 ,3 -Dimethy l - l -bu tene 3082 1790 1651 893 2 -Methy l -3 -pheny l - l -p ropene 3085 1804 1651 891 2-Chloro- l -propene 3090 1776 1645 878 2 -Bromo- l -p ropene 3085 1775 1638 883 1,1-Difluoroethylene 3103 1610 1728 803

(3060 ~ sym. CH=) 1,1-Dichloroethylene 3130 1741 1616 872

(3035 J, sym. CH2) 1-Bromo- 1-chloroethylene 3140 1752 1609 872

(3046 ~ sym. CH2) 1 ,1-Dibromoethylene 3112" ~1764 1601 881

(3027* v sym. CH2)

" ' " 0

773* 1 ? 2

740 2 740* 2 735 3 729 4 729* 4

745,729 1,3 760 1

~722 6 ~820, ~785 1,1

735 .1 3 - 7 6 5 2

760 .1 2 ? ,769 1,1

832"1,770 * 1,1 ? ,742 1,2

834"1,740 .1 1,2 • ' ' 0

822 1

"Frequenc ies no t ma rked with * or .1 are vapor -phase data. Frequencies marked with * in the 3800-1333 cm ~ region are for CC14 solut ions and in the 1333-400 cm ~ region are for CS2 solutions. Frequencies marked with ,1 are for nea t liquids.

TABLE VI. A comparison of infrared group frequency data for 2-alkyl-l-alkenes and a-methylstyrenes.

2(CH~ wag) C=C CH2 wag cm 1 s t re tch cm -~

R' H 1780-1804 1644-1660 884-896

~c__c / R' l,I

c\ /

• C=C ~ H

(×)n (where x is no t subst i -

t u t ed in the 2-posi- tion)

CH3 H

\c=c /

X

(where x = halogens alkyl groups nitro hydroxyl) X = 2-OH

1797-1810 1623-1629 882-899

1803-1822 1640-1645 899-918

1822 1632 911

202 Volume 40, Number 2, 1986

1. W. J. Potts and R. A. Nyquist, Spectrochim. Acta 15, 679 (1959). 2. L. J. Bellamy, Advances in Infrared Group Frequencies (Methuen

& Co. Ltd., London 1968) p. 38. 3. G. E. Blackman, M. H. Parke, and G. Garton, Arch. Biochem.

Biophys. 54, 55 (1955). 4. F. G. Bordwell and G. D. Cooper, J. Amer. Chem. Soc. 74, 1058

(1952). 5. J. W. Murray and N. E. Gordon, J. Amer. Chem. Soc. 57, 110

(1935). 6. R. O. Griffith, A. McKeown, and W. J. Shutt, Annual Tables of

Constants and Numerical Data, Vol. XIII, 22: Electrolytic Equi- libria, Chemical Equilibria (Hermann et CIE, Paris, 1938).

7. J. N. Vandenbelt, C. Henrieh, and S. G. Vandenberg, Anal. Chem. 26, 726 (1954).

8. F. Kieffer and P. Rumpf, Compt. Rend. 238, 360, 700 (1954). 9. C. M. Judson and M. Kilpatriek, J. Amer. Chem. Soc. 71, 3110

(1949). 10. A. I. Biggs, Trans. Far. Soc. 52, 35 (1956). 11. G. R. Sprengling and C. W. Lewis, J. Amer. Chem. Soc. 75, 5709

(1953). 12. Unpublished data, Dow Chemical Company, Main Laboratory

(1956). 13. R.A. Nyquist, The Interpretation of Vapor-Phase Infrared Spec-

tra: Group Frequency Data (Sadtler Research Laboratories, Phila- delphia, 1984), p. 94.

14. J. R. Scherer and W. J. Potts, J. Chem. Phys. 30, 1527 (1959). 15. R. D. McLachlan and R. A. Nyquist, Spectrochim. Acta 24A, 103

(1968).

A Spectrometric Technique for Monitoring [O2(a' Ag)l in the Gas Phase

J. A. COXON* and U. K. R O Y C H O W D H U R Y Department of Chemistry, Dalhousie University, Halifax, Nova Scotia B3H 4J3, Canada

The reaction of chlorine with alkaline hydrogen peroxide has been used to produce O2(a'A,) in a fast flow system at partial pressures up to about 0.5 Torr, and total pressures (mostly argon) in the range 0.8-2.5 Torr. Absolute concentrations of O2(a'A~) were determined from the intensity of absorption of hydrogen emission lines in the vacuum-UV at 144.095 and 148.66 nm, for which the cross sections are known. The intensity of the 02 (a ~ X) transition at 1270 nm, monitored simultaneously with a simple germanium detector, was found to vary linearly with [O2(a'A~)], as expected. The germanium detector was calibrated at 1270 nm with a readily reproducible standard, the air afterglow continuum due to NO2* at defined concentrations of O(3p) and NO. The ratio of k, for O2(a) ko O2(X) + hv, to k c for O + NO kc NO2 + hv, is (1.4 _+ 0.2) x 10 -7 mol L - ' at 1270 nm.

Index Headings: Spectroscopic techniques; Singlet oxygen.

INTRODUCTION

Metastable "singlet" oxygen, 02(a~A), has been of in- terest to spectroscopists and kineticists for more than two decades '-3 and is known to play an important role in many diverse fields. A partial listing of the areas of interest would include photophysical, photochemical, and photobiological processes, 4 photosensitized oxidation, 4 reversible quenching of excited states of polyatomic molecules, 4 one-photon/two-molecule processes due to oxygen molecule pair interaction, ~ and atmospheric chemical processes. ~'7 In addition, a more recent interest has arisen owing to the important role of the 'A state as a chemical energy storage medium. The I2/02 chemical laser system has been studied intensively 8-'2 and has rel- evance even in the field of controlled fusion research.~3In

Received 19 April 1985; revision received 10 June 1985. * Author to whom correspondence should be sent.

this system, as in any other potential laser system in- volving O2(a'A), it is essential to monitor the absolute concentration of the metastable species which would transfer energy to the lasing species.

Among the approaches that have been employed for measuring [02(alA)], the EPR technique 1~ is the most prominent in terms of reliability and accuracy. However, for routine concentra t ion-moni tor ing purposes, the method is limited in scope; in particular, an expensive and elaborate experimental setup is a prerequisite. Vac- aum-UV absorption spectroscopy is another accurate method that has a similar inherent limitation. Isother- mal calorimetry, 15 although experimentally simple, can lead to uncertain results owing to nonspecificity and variations in catalytic efficiency of the detector. The technique of emission spectrometry is, in principle, a simple and versatile technique for monitoring the con- centrations of electronically excited species. The avail- ability of small bandwidth interference filters at any de- sired optical wavelength precludes the need for a sophisticated spectrometer. The present work has been directed towards establishing the feasibility of spectro- metric monitoring of the a 'A -~ X~2~ system of O~ as a simple, reliable and routine technique for measurement of [02(alA)] in complex chemical systems.

The most intense among the known emissions of gas- phase 02(a'A) produced by a chemical generator are the dimol emissions at 634.4 and 703.0 nm, and the direct a -~ X emission (from v' = 0) at 1270 nm. TM Although the intensity of emission is proportional to [02(alA)] 2 for dimol emission, a linear relationship holds for direct emission. However, until recently, the lack of suitable detectors in the near-infrared has precluded the intrin- sically more straightforward approach of monitoring di- rect emission from 02(a'A). The principal objective of

Volume 40, Number 2, 1986 ooo3-7o2s/86/4oo2-o2o~2.oo/o APPLIED SPECTROSCOPY 203 © 1986 Society for Applied Spectroscopy