Infrared spectra of the monomethyl and dimethyl naphthalenes

Speetrochimics Acta, 1966,Vol. 22,pp. 1485to 1473.PergamonPressLtd. Printedin Northern Ireland

Infrared spectra of the monomethyl and dimethyl naphthalenest H. M. FRIEDMAN Emkay Chemical Company, Elizabeth, New Jersey (Received

13 December

1965)

Abstract-The infrared spectra of the ten isomeric dimethyl naphthalenes end the two monomethyl naphthaleneshave been observed in the C-H stretch, 2000-1650 and the 700-400 cm-r regions. The effect on the aromatic C-H stretchingvibrations due to the position of the methyl groups on the nephthalene nucleusis outlined. The position of the methyl groups can be established from data obtained from the 2000-1650 end the 700-400 cm-l regions. Effect on band frequencies and intensities by replacement of methyl by phenyl group in the monosubstituted naphthalene is discussed. INTRODUCTION DURING the course of a continuing investigation concerning the composition of various alkylated naphthalenes [l], it was necessary to determine the specific mono and dialkyl isomers present in the various mixed alkylates obtained. The infrared spectra of the ten isomeric dimethyl naphthalenes published in the API Catalogue of Spectra [2] are in the range of 3-15 ,u; the resolution in these spectra in the C-H stretching region and the 5-6 ,u region containing overtone and combination bands is not sufficient to reveal some of the available fine detail. Correlation of specific bands for disubstituted naphthalene compounds have been postulated in the 10.5-14 p region [3-lo]. During a study of the infrared spectra of the twelve monomethyl benzanthracenes and four dimethyl-1,2_benzanthracenes [ll], correlation with the bands obtained with a and p methyl naphthalene and naphthalene in the C-H stretching region as well as the 2000-1650 cm-l were made. Using the in-plane and out-of-plane C-H deformation frequencies (700-1300 cm-l), correlations between absorption frequency and ring hydrogen position have been reported [12]. In the course of a study of di-, tri- and tetra-alkyl naphthalenes [13], infrared spectra (liquid films) were divided into six main regions in the range

* Presented in part at the Ottawa Symposium on Applied Spectroscopy (1965). [l] H. M. FRIED~N, 1lQ7th InternationalCongresson &rjace ActiveSubetancesSeptember (1964). [2] Am. Petrol. Inst. Res. Proj. 44, Cat. of Infrared Spectra. [3] J. LECOMT&Bull. Sot. Chim. France 5, 731 (1945). [4] E. E. VA~O, E. M. TANNERend K. C. BRYANT,J. In&. Petrol. 85, 293 (1949). [5] C. G. CANNONand G. B. B. M. SUTHERLAND, Spectrochim. Acta 4, 373 (1951). [6] R. F. EVANSend J. C. SMITH,J. Inat. Petrol. 39, 724 (1953). [7] R. F. EVANS, J. C. SMITHand F. B. STRATJSS, J. In.&. Petrol. 40, 12 (1954). [8] J. FEnausoN and R. L. WERNER,J. Chem. Sot. 3645 (1954). [9] L. CENCELJand D. HAD%, Spectrochim. Acta 7, 274 (1955). [lo] H. KAMADAand S. TANAKA,Bun8eki Kugaku 5, 98 (1956). [ll] N. FUSONend M. L. JOSIEN,J. Am. Chem. Sot. 78, 3049 (1956). [12] J. G. HAWKINS,E. R. WARD and D. H. WIFFEN, Spectrochim. Acta 10,105 (1957). [13] W. COCKERet al., J. Chem. Sot. 448, 2230 (1960). 1465

H. M. FRIEDMAN

1466

of 700-3200 cm-l. The far infrared spectra have been measured of seven a naphthalenes and two p naphthalenes in the 300-650 cm-l region [la]. Spectra of the C-H stretching frequencies [15, 161 and the effect in this region of substitution in the l-position and the 2-position of naphthalene and the 2,3dimethyl naphthalene is discussed. It might be possible that mono- and d&substituted methyl naphthalenes may give characteristic patterns in the regions that we have investigated. We have made a detailed study of the infrared spectra of the ten dimethyl naphthalenes in the 3100-2700 cm-l, 2000-1650 cm-l and 700-400 cm-l regions and report here the results obtained. EXPERIMENTAL The naphthalene, monomethyl naphthalenes and 1,7-dimethyl naphthalene were shown by gas chromatography to be -99 per cent pure. The infrared spectra of the other purified dimethyl naphthalene isomers (K & K Laboratories and Aldrich Co.) compared favourably with the recorded API Spectra [2]. The infrared spectra were measured on a Beckman IR-10 recording infrared spectrophotometer equipped The wavenumber reproducibility was 3 cm-i from 400 to with two gratings. 2000 cm-l, and 5 cm-i from 2000 to 4000 cm-l. The spectra were run in solution (0.4 mm cells) in the 400-700 cm-l region, O-2 mm cells in the 1600-2000 cm-i and 2700-3100 cm-l regions. RESULTS AND DISCUSSION The 400-700 cm-l region For n systems, as found in benzene and naphthalene, the energy for vibration has a and 7~bond components. The B value for the bond will be altered as a change in bond distance occurs. The effect of the change in @ on the 7r component of the vibration energy is shown to be a function of the bond order p [17]. The C-C bond distances at the different positions of the naphthalene nucleus vary in length, this is in contrast to benzene where the C-C bond lengths are equal on all six carbon atoms [18]. Since the force constant for a bond is influenced by the bond order (as well as bond polarization), it was of interest to compare the position of adsorption bands we found in the corresponding dimethyl naphthalenes with those found in dimethyl benzenes. Figure 1 shows the strong and medium absorbing bands of the 1,2-, 1,3- and 1,4-dimethyl naphthalenes and those reported [14] for the dimethyl benzenes. For the analogous dimethyl naphthalene isomers, the richness of bands is retained in all three of the dimethyl naphthalenes (i.e. 1,2-,1,3- and 1,4-). The fairly strong band of the l,2- and 1,3dimethyl benzenes at about 407 cm-l is found in all three of [la]

[15] [16] [17] [18]

F. F. BENTLEY and E. F. WOLRARTH, Spectrochim. Acta 15, 165 (1959). S. E. WIBERLEYand R. D. GONZALEZ, J. Appl. Spectroscopy 16,174(1961). S. E. WIBERLEY,S. C. BUNCEcLndW. H. BAUER,And. Chem. 99, 217 (1960). C. A. COULSON, H. C. LONQUET-HI~QINS, Proc. Roy. Sot. Al98, 456 (1948). A. STREITWIESER, Molecular Orbital Theory for Organic Chemists p. 170, John Wiley, New York (1961).

Infrared spectra of the monomethyl

and dimethyl naphthalenes

1467

the corresponding dimethyl naphthalenes at about the same frequency (407412 cm-l). The dimethyl benzene band at 510 cm-l is found shifted to 628 and 537 cm-l respectively for the 1,2- and l&dimethyl naphthalenes. The 660 cm-1 band in the 1,klimethyl naphthalene spectrum may be a ring mode possibly analogous to the yll frequency in para substituted benzenes [ 191.

/

, 600

,‘I i

i

500

Wovenumber,

1,

1.41

400 cm-’

Fig. 1. Absorption bands in the 400-700 cm-l region of dimethyl benzenes [14] (I) and of the corresponding dimethyl naphthalenes (i) The vibrational

frequencies

of the strong

and moderate

absorbing

bands

in the

400-700 cm-l region of the monomethyl and dimethyl naphthalenes are summarized in Table 1. The spectra can be grouped into five absorption areas (at 623, 561, 533, 472 and 409 cm-l). It was interesting to see if isomers with the same substitution pattern would have similar spectral configurations. Figure 2 lists the substituted naphthalenes and the absorption bands we found in the 400-700 cm-l region. Figure 3 indicates the Table 1. Absorption bands in the 700-400 cm-l region for naphthalene and the monomethyl and dimethyl derivatives” Substituted naphthalenes 0

B” 192 193 194 196 196 137 193 293 2,6 297

623b 617 m 618 m

561c

557 m

632 w 624 m

472e

524 s

472 s 469 468 sw

528 s 537 s 560 m 664 m

617 m 628 s 565 m 614 m 622 m 624 w

533d

528 535 533 542

m m 8 m

536 m

409f

428 m

402 400 w 8

450 m

412 m 417 m 407 s

460 w 480 w 492 w 483 8 492 469 s 464 s 467 s

407 s 409 8 403 m

a The symbols s, m, w, indicate bands of strong, moderate and weak intensity. b k9 cm-l. c &4cm-r. d +9 cm-‘. e &12cm-l. f *9cm- l. The additional band in a-methyl naphthalene at 428 cm-l, also reported in [14] as an additional band, is not found in the dimethyl isomers. [19] H. W. WILSON and J. E.B~~~~,Spectrochim. Acta 21,45 (1965).

1468

H.

M. FRIEDMAN

band positions we obtained with monosubstitution on benzene with phenyl and naphthalene groups as compared with the monomethyl naphthalene isomers. The monosubstituted benzenes with reduced symmetry, changed from D,, to C, point group, the degeneracy of the benzene-forbidden Ye,, (es,) vibration being split into an allowed b, and forbidden a2 mode. The spectra of the biphenyl, 1-phenyl and 2-phenyl naphthalenes show the v4 (b,) ring deformation mode at 698 cm-l. The 1-phenyl naphthalene shows this frequency as a strong doublet at 697 and 702 cm-l. Microns, Subs1 *ituted no h thalenes

p

18 20

15 16

0

' I

P

I

'

Q

'1

II I

1.2

I

I I

I.3 2.3

1.5 I.8

700 Wavenumber,

16

p

20 I

16 I

25 I

I

I I

II

I

I

Ill

I

I

I

I I I

I I

I

II

I

2.7

MmJns, 15 II

I

II I I

2.6

I I

I

I

I.7

1

I I

I I

I.6

I

II

I

1.4

,

25 1

I

I

I

600

500

400

cm-1

I

II

00

I

I

II

II

J 7

I

I

I II

I

I 600

1

500

Wavenumber,

Fig. 2. Absorption bands from 700400 cm-l of the monomethyl and dimethyl naphthalenes.

I

41 cm-l

Fig. 3. Absorption bands in the 400-700 cm-1 region of benzene, biphenyl, naphthalene and its monosubstituted phenyl and methyl isomers.

The l-methyl naphthalene shows a weak absorption in this region. The v&b,) benzene vibration fundamental due to in-plane ring deformation might be assigned to the band found at 608 and 612 cm-l in biphenyl and I-phenyl naphthalene, respectively. Naphthalene and 2-methyl naphthalene show a moderate band at about this frequency. In the vibration fundamentals for monosubstituted benzenes, the band observed around 547 cm-r is usually associated with the I mode. This band appears at 546, 552 and 542 cm-i in biphenyl, l-phenyl and 2-phenyl naphthalene, in that order; a second band is also seen in 1-phenyl and 2-phenyl naphthalene at 564 and 557 cm-l, respectively. The band correlated with the benzene vi2(ul) frequency at 462 cm-l is apparently shifted to 488 cm-l in biphenyl, and at 477 cm-l in 2-phenyl naphthalene, not being observed in the I-phenyl naphthalene. The 1650-2000 cm-l region The absorption spectra in this region obtained from substituted benzenes has been shown to be characteristic of the type of substitution [20]. Recently, spectra of the mono-substituted naphthalenes have been reported to give two characteristic [20] C. W. YOUNG, R. B. DWAL

and N. WRIGHT, Anal. Chem 23, 709 (1951).

Infrared spectra of the monomethyl and dimethyl naphthalenes

1469

patterns for each type of substitution [21]. The spectra we obtained are shown in Fig. 4, and the band positions in Table 2. This region apparently may be used as a guide to the points of substitution for The absence of the band at 1946 cm-l the ten isomeric dimethyl naphthalenes. for isomers not containing four adjacent hydrogens, and presence of this band in those isomers with this hydrogen pattern may be of value. The double band of Microns,

p

6

5

1900

I600

5

6

1700

Wovenumber,

cm-’

Fig. 4. Solution spectra in 2000-1650 cm-l region of naphthalene, 0: and j3 methyl naphthalene and the ten isomeric dimethyl naphthalenes.

weaker intensity in the 1800-1900 cm-l region for the 1,5- and I,% isomers, and the single band in this region for the 2,6- and 2,7-dimethyl naphthalenes are distinguishing characteristics. 2,6-di-tertiary butyl naphthalene (spectrum not shown) exhibits the same weaker single band at 1842 cm-l and stronger bands at 1912 and 1770 cm-l as does the 2,6dimethyl naphthalene, both spectra being quite alike. Further studies of this type are in progress with other disubstituted naphthalenes to determine whether similar patterns can be applied as a means of identification of the points of substitution on the naphthalene nucleus. [21] W. Cox, M. A. KEENAN, R. D. TOPSOMmd G. J. WRICEIT,Spectrochim. Acta 21,1663

(1965).

1470

H. M. FRIEDMAN

Table 2. Absorption

bands in the 2000-1660 cm-l region for naphthelene and the monomethyl and dimethyl derivative@

Points of substitution 0 i 1,2 1,4 1,3 2,3 196 1,7 195 198 216 2,7

1946 1946 1941 1942 1941 1940 1939

1933 1927

1930 1932 1928

1922

1917 1913 1016 1920 1919 1917 1917 1919 1921 1918 1912 1010

1903 1898 1904 1902 1898 1897 1897 1907

1898

o Other work on naphthalene spectra [ll,

The 3100-2700

1848 1863 1840 1854 1855 1862 1865 1869 1859

1853 1842 1845 1855

1833 1830 1822 1835 1828 1833 1835

1810 1793

1772 1788

1802 1800 1816 1806 1795 1795

1783 1787 1767 1782 1787 1783

1750 1756 1752 1743 1742 1752 1735 1742 1735 1758 1728

1722 1718 1722 1728 1724 1706 1710 1717 1710 1708

1667 1680 1687 1692 1693 1685 1685

1678 1685

1650 1652 1665 1676

1655 1662

15a, 15b].

cm-l region

It has been noted [22], that the aromatic C-H stretching vibrations occur above 3000 cm-l usually near 3050 cm-l and that most unsubstituted aromatic hydrocarbons exhibit no strong absorption bands in the 3000-2700 cm-l region. In a series of aromatic compounds which included naphthalene, l- and 2-methyl naphthalene, C-H aromatic stretching vibrations produced generally three bands close to 3038 cm-l in carbon tetrachloride solution [23-251. It became apparent during the course of our investigation that the aromatic C-H stretching vibrations were markedly influenced by the substitution pattern on the naphthalene nucleus when the hydrogens were replaced with methyl groups. It was of interest to observe what effect might be obtained in the 3000-3100 cm-1 region when substitution of hydrogen by a phenyl group was made. All five molecules shown in Fig. 6 (band positions listed in Table 3), have two strongly absorbing bands at approximately 3030 and 3070 cm-l, and except for the unsubstituted benzene molecule also show an intense band at about 3050 cm-i; the naphthalene and both its monophenyl derivatives having additional bands at 3010 cm-l as well as one band between 3080 and 3100 cm-l. Absorption spectra of the ten isomeric dimethyl naphthalenes that we obtained in the 3100-2700 cm-l region (Fig. 6, Table 4), show characteristic differences in the bands found in the aromatic C-H stretch region. It has been well established [22, 25, 261 that the methyl group C-H stretching vibrations are found just below Our data show that, except for the 1,8dimethyl naphthalene, all the 3000 cm-l. dimethyl naphthalenes exhibit bands near 2925, 2945 and 2975 cm-l. Intensity of these bands show marked variation with the position on the naphthalene nucleus, [15a] G. C. PIMENTAL and A. L. MCCLELLAN, J. Chem. Phye. 20,270 (1952). [lBb] S. S. MITRA and H. J. BERNSTEIN, Cm. J. Chem. 3’7, 553 (1959). [22] L. J. BELLAMY, The Infrared Spectra of Complex Molecdee (2nd Ed.), Chap. 5, Methuen (1958). [23] J. J. Fox and A. E. MARTIN, J. Chem. Sot. 318 (1939). [24] J. J. Fox and A. E. MARTIN, Proc. Roy. Sot. A167, 257 (1938). [26] J. J. Fox and A. E. MAFUTN, Proc. Roy. Sot. Al%, 208 (1940). [26] G. M. BADGER and A. G. MORITZ, Spectrochim. Acta 9, 672 (1959).

Infrared spectra of the monomethyl

1471

and dimethyl naphthalenes

v 1 1 D

A

B

C

E

i

y

I

I

3100 3000

3100 3000 Wovenumbor,

cm-’

Fig. 5. Solution spectra in the 3000 cm-l region of: (A) naphthalene; 2-phenyl naphthalene; (C) 1-phenyl naphthalene; (D) Phenyl benzene; benzene. Table

,

3. Absorption

Nephthaleneb 1 -Phenyl2-PhenylBenzened Phenyl BenzeneC

bands in the 3100-3000 cm-r region for naphthalene, mono phenyl derivatives” 3080 w 3090

3100 w 3090 s 3105 m

3070 3070 3070 3070 3075

s m m s s

3050 8 3050 8 3050 8 3045 s

3030 3030 3030 3030 3035

(B) (E)

benzene and the

m s m 8 8

3000 w 3000 m 3000 w * 3005 w*

a The symbols s, m, w, indicate bands of strong, moderate and weak intensity. b Bands are reported elsewhere with slight variation in positions [16, 15b]. c Other reported work [27]. d Discussed in further detail [16]. * Weak bands not shown in Fig. 6.

permitting ready isomer identification when utilizing the additional information obtained from the aromatic C-H stretch region. The strong intensity of the 2975 cm-l absorption band CH, stretching frequency of the l,&dimethyl naphthalene gives rise to speculation as to the possible use of this frequency in w complex interactions similar to the studies with methyl substituted benzenes and naphthalenes with tetracyanoethylene [28]. Recently, the intensity of the ring stretching bands in six-membered aromatic rings which occur [27] D. STEELE and E. R. LIPPINCOTT,J. Mol. Spec. 6, 238 (1961). [28] A. R. LEPLEY, J. Org. Chmn. 29, 2545 (1964).

1472

H.

M. FRIEDMAN

Fig. 6. Solution spectra in the 3000 cm-l region for the monomethyl naphthalenes: A-a; B-p; and the dimethyl naphthalenes: C-1,2-; D-1,3-; E-1,4-; F-1,5-; G-l,&; H-1,7-; I-1,8-; J-2,3-; K-2,6-; L-2,7Table

4. Absorption

bands in the 3100-2700 cm-’ region for the monomethyl derivatives of naphtha.lene a

and dimethyl

Compound 30759

i

I,2 193 194 1,5 196 197 18 2,3 2,6 2,7

307ow 307ow 30708 3070m 3070m

30508 30558 30508 305ow 30558 30508 3050s 3060a

301ow

3040s 3020~

30358 3030s 3035s

3020s 30201x1

3040s

3050s 30509

30201x1 30208

8

w 2970 m 2970 m 2975

3OlOw 3OlOw 30108 3015w

30708

2975

3010m 3010s 3005w

2970

8

2975

8

2975

8

2975

8

2980

9

29758 2975m 2970

m

2945

8

2925

w

2945

w

2925

m

2945

I3

2925

8

2920

8

29408 29408 29458 29458 29458 29408 29408 2945m 2945

m

a The symbols 8, m, w indicate bands of strong, moderate and weak intensity.

2920

8

2920

8

2920

I3

2925s 2910m 29258 2925s 2920s

2875w 2870~ 2865w 2865~ 287Ow 2865~ 2865~ 2860~ 2865~ 2860~ 2865~ 2860~

Infrared

spectra of the monomethyl

and dimethyl naphthalenes

1473

at 1585 and 1600 cm-i have been used to measure in a quantitative way the resonance interactions of substituent groups attached to an aromatic ring [29]. It would appear that the marked influence on the aromatic C-H stretching vibrations in the 3000-3100 cm-l region by the substitution pattern on the naphthalene skeleton would merit investigation for possible similar correlations in naphthalene as well as benzene chemistry. CoNCLUsIoN

The spectra of the two monomethyl and the ten isomeric dimethyl naphthalenes have been measured in the C-H stretch, 2000-1650 and the 700-400 cm-l regions. Characteristic patterns have been found in these three regions which establish the position of the methyl groups. [29] R. T. C. BROWNLEE, A. R. KATRITZKY and R. D. TOPSOM, J. Am. Cl&em.Sot.

6

87,326O (1965).