MASS SPECTROMETRY OF SOME POLYPHENYLS
1647
Mass Spectrometry of Some Polyphenyls
by E. J. Gallegos Chevron Research Company, Richmond, Californk (Re5eived August 17, 1966)
The mass spectra, including metastable transitions and appearance potentials for the principal positive ions, were measured for several polyphenyls by a hgh-resolution mass spectrometer. The parent molecule-ion beam gave the most intense peak in the spectra for all of the polyphenyls. The doubly charged parent is generally second in intensity in the spectra of the m- and p-polyphenyls studied. The o-polyphenyls show that the doubly charged molecular ion makes a minor contribution to the mass spectra. The doubly charged parent increased in abundance, whereas their appearance potentials decreased with an increasing total number of T electrons. Resonance effects in ionization and dissociation of the polyphenyls are discussed in light of this study. The measured values for the parent ions are: m-octaphenyl, 8.28 ev; p-hexaphenyl, 7.67 ev; m and p-quinquephenyl, 8.45 and 8.18 ev; o-, m-,and p-quarterphenyl, 8.52, 8.51, and 8.08 ev; o-, nz-, and p-terphenyl, 8.64, 8.80, and 8.78 ev; and biphenyl, 8.95 ev.
Introduction Systematic electron-impact studies have recently been made on a number of polynuclear aromatic hydrocarbons.'V2 However, little informationa is found in the literature on the mass spectra and energetics of polyphenyls other than biphenyl.2 The lack of information of this kind on the higher molecular weight conjugated molecules provided an incentive to undertake this study. Two unique features of the mass spectra of higher molecular weight, highly conjugated compounds are the low abundance of fragment ions and the relatively high abundance of multiply charged ions. The purpose of this paper is to present data for a series of polyphenyls. Experimental Section The data were obtained with an AEI MS-9 highresolution mass spectrometer equipped with an automatic voltage scanner which decreases the electron accelerating voltage in increments of 0.05 or 0.2 v in the range of 80-3 v. This system has been described el~ewhere.~Partial mass spectra reported here were obtained at 70 ev with a 100-pa ionizing current using a rhenium filament. Source temperature was 240". Appearance potentials were obtained using a 20-pa ionizing current. In the polyphenyl nomenclature, o, m, or p refers
to the type of linkage throughout the molecule. Unsubstituted polyphenyls do not exhibit stereoisomerism. The polyphenyls were obtained from K & K Laboratories. o-, m, and p-terphenyls showed no impurities in the gas chromatogram. Of the polyphenyls of higher molecular weight, p-hexaphenyl and m-octaphenyl showed impurities. These were further purified by micr~sublimation~ under nitrogen. Ultraviolet spectra of the purified polyphenyls show only one absorption maximum each. Infrared spectra obtained also show no trace of impurities. Mass spectra of the polyphenyls, as purified or as received, show only negligible impurities of higher molecular weight in the mass spectrum. Appearance potentials of 1,4-bis(trifluoromethy1)benzene parent and selected fragments of perfluorotributylamine were determined using noble gases as a standard and these fragments were subsequently used as secondary standards for ionization potential de(1) M. E. Wacks, 13th Annual Conference on Mass Spectrometry and Allied Topics, St. Louis, Mo., May 16-21, 1965. (2) P. Natalis and J. L. Franklin, J . Phye. Chem., 69, 2935 (1965). (3) . 'E Bradt and F. L. Mohler, J . Res. Natl. Bur. Std., 60, 143 (1958). (4) E. J. Gallegos and R. F. Klaver, presented at the 14th Annual Conference on Mass Spectrometry and Allied Topics, Dallas, Texas, May 22-27, 1966. (5) W. H. Melhuish, Nature, 184, 1933 (1959).
Volume 71,Number 6 May 1967
1648
Table I:
E. J. GALLEGOS
Partial Mass Spectra of Several Polyphenyls (Source Temperature 240", Pressure 2 X lo-' Torr) Type
m/e
29 36 39 43 50 51 55 57 63 75 76 77 88 89 91 94.5 99 100 101 101.5 102 106.5 107.5 112 112.5 113 113.5 114 229 115 115 115.5 119.5 125 126 128 130.5 131.5 137 138 138.5 139 143.5 144 144.5 145 145.5 150 150.5 151 151.5 152 153 153.0 307 165 168.9 171.4 178 4
of ion5
o-Phs
m-Phs
p-Pha
o-Phr
Relative abundance8 at 70 ev m-Phc p-Phc
m-Phs
p-Phs
p-Phs
2.2 1.0 1.4 2.8
1.3 2.4 2.2 2.3 1.7 4.2 1.7 d
d d d d d
d d d
1.0 4.3 12.7 3.8 1.4 1.9 8.0 2.6 1.9 13.2 4.3 14.4 4.6 1.0 3.0 0.6 1.1
2.9
1.2
2.1 4.7
1.9
1.3 1.3 3.6 2.0
3.2 2.5 3.0 3.1 2.6 2.2
1.5 1.4 2.3 1.6 2.3 2.0
1.2
1.2
1.7 5.2 1.0 2.6
1.3
1.8
2.1
2.8
2.2
1.6
5.3 1.1 1.7
1.1 3.1
1.9
1.9
3.8 1.2 2.1
1.7 6.9 1.4
4.0 9.5 1.9
1.1
1.7 3.0
1.2 2.3 2.0
d
1.3 d d d 1.5
1.6
1.0
1.9
3.4
2.5
2.5
6.9 2.5
4.8 2.2
d d
d
2.3
1.4
1.5 1.2
1.0 3.6 2.3 7.3 2.3 2.7 3.4 2.4 10.6 13.0 4.2 4.9 1.7 6.5 2.2 3.6 2.2
1.4
1.2
2.4
d
2.8
1.4 2.0 2.0
d
m m
3.0
