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Electron impact studies—XLII
~m,ddn~
VolZ6,pp.l163t01166.
papmOnRcu1970.
PdedinOmtbith
ELECTRON TMPACT STUDIES-XLTT’ PERI-EFFECTS IN THE MASS SPECTRA OF ALKOXYQUINONES J. H. BOWIE,P. J. HOFFMANN and P. Y. WHITE Department of Organic Chemistry, University of Adelaide, Adelaide, South Australia, 5001 (Received in the UK 2 June 1%9; Acceptedfor publication 3 July 1969) tie&-The mass spectra of certain I-alkoxyanthraquinones, 5-alkoxynaphthaquinones and 1,8dialkoxyanthraquinones exhibit diignostic fragmentations which are absent in the spectra of other alkoxyquinones. These fragmentations are characteristic of the peri-alkoxyquinonc moiety, and may be used BP)useful aids to structure dettrminations.
basic fragmentations in the mass spectra of benzoquinones,2* ’ naphthaquinone$* 4-7 anthraquinones2 and certain higher quinones2* **g have been desctibed. Ortho-effects’” have been noted in the spectra of naphthaquinones”, l2 and anthraquinones.11-‘3 In connection with our studies “* I2 of the ortbeffects which occur in the mass spectra of aromatic carbonyl compounds containing adjacent alkoxyl groups, we observed large differences between the spectra of l- and 2-ethoxyanthraquinone. As it seem@ that mass spectrometry may usefully complement the use of IR14 and W” spectroscopy for the determination of the oxygenation pattern of an hydroxyquinone, we examined the mass spectra of I-XXI. This paper describes the diagnostic perieffects which are observed in many of these spectra. THE
I
R’
II III N V VI VII VIII IX X XI XII XIII XN XV XVI XVII
0
R’
R’ CDs0 Et0 CD&H10 H H nPr0 H isoR MexCDO Me0 Me0 Me0 Me0 CDs0 H Et0 Et0
R’ H H H Et0 CD&H20 H nFV0
H H
R3 H H H H H H H H H H Me0 H H H H H H
R4 H H H H H H H H H H H Me0 H H H Et0 H
R’ H H H H H H H H H H H H H H Me0 H H
0 R’ Et0 H
1163
RZ H Et0
R6 H H H H H H H H H H H H Me0 CD,0 H H Et0
J. H. Bow,
P. J. HOFFMANN and P. Y. WHITE
RZ H Me0
R’ Et0 Me0
TABU 1. ~WTMI ABUNDANCES OFbit--X’
IONS IN THE
SFWTRA
OF COMFQUNIX
OF TNJI
TYFTJ
0 o( 3 Y)
M? -X’
Compound
hf?
I II III IV
loo 98 88 93
6 100 81 -
V VI VII
94 18 10
-
M? -X’
Compound
Mf
VIII XVI XVII
15 13 100 1
12 10 31 -
XVIII XIX
100 88
75 -
Ix
9
-
b"
(II I)
I
I 237
_
169
L FIG. 1
Electron impact studies-XL11
1165
-Me*
t
187 174
140
=2H4
180
FIG.2
The mass spectra of l- and 2-alkoxyanthraquinones are very different. The major differences are summarised in Table 1, and are illustrated [for the cases of l- and 2-(2,2,2+ethoxy)anthraquinone (III and V)] in Fig. 1. The pronounced loss of CD; from the molecular ion of III is absent in the spectrum of V. This effect is characteristic of the spectra of l-alkoxyanthraquinones (when X 2 Me, see a), and is most pronounced for l-ethoxyanthraquinone. The peti-effect may be rational&d by the formation of the stabilised oxonium species b and its formation is always substantiated by a metastable peak (represented by an asterisk in a Figure or the text). It is of interest to note that this effect is minor in the spectrum of o-ethoxybenzophenone (M+ - Me’ = 100 and 12% in the spectra of I and XX respectively)
-CHO
7
C,oHsOzt m/e 158
c, m/e 18?
1166
J. H. Bowra, P. J. H~NN
and P. Y. Wm
The spectrum (Fig. 2) of Sethoxynaphthaquinone also shows a pronounced Mt - Me’ ion. In marked contrast, Z~~oxynaphthaquinone does not eliminate a Me radical upon electron impact. The fragmentation of the oxonium species c is indicated in Fig. 2. Loss of a formyl radical from c produces a species which fragments in the same way as the 1,rGnaphthaquinone molecular ion.4 However, this species may not correspond to the 1,4aaphthaquinone radical ion because of the large differences between the abundance ratios of m/e 158 and its daughter ions in the spectra of 1,4naphtbaqu~one2 and XIX. The same situation occurs for III (Fig. 11where the process M~-CI&--CHO’ produces a species which may not correspond to the anthraquinone molecular ion. The spectra of the labelled derivatives III, IV and IX show that no hydrogen randomisation in the alkoxyl groups precedes the M* - X process at 70 eV.
(60
200
240
Fra. 4
Electron Impact Studie\-XLII
1167
The mass spectra of the isomeric dimethoxyanthraquinones (X-XII and XV) are reasonably similar and are typified by that (Fig. 3) of 1,Sdimethoxyanthraquinone (XII). The spectrum (Fig. 3) of 1,8dimethoxyanthraquinone (XIII) is easily distinguishable from that of XII in that the process M+-Me’ produces the base peak for XIII but only a peak of 5 % relative abundance in the spectrum of XIL This distinction is even more apparent in the spectra (Fig 4) of the isomeric diethoxyanthraquinones (XVI and XVII). Although these spectra are complex, they can be easily differentiated, because the base peak in the spectrum of 1,8-diethoxyanthraquinone is an M* -Et’ ion, whereas the corresponding peak in that of l,Sdiethoxyanthraquinone is only 19% of the base peak. It is of interest to note that a major fragmentation in the spectrum of XVI proceeds through the Mt -Me’ ion, and that this peri-effect is completely absent in the spectrum of XVII which is dominated by the second peri-effect discussed above. Although mass spectrometry can be used to determine the presence of l,&dialkoxyl substitution in an anthraquinone, it is not obvious why this peri-effect occurs. The tricyclic aromatic system is a prerequisite for the elimination, as the spectrum of o,o’dimethoxybenxophenone (XXI) does not contain an M t -Me’ ion. There seems to be no obvious reason why the M-15 ion in the spectrum of XIII should be any more stable than a similar species which could be produced from other isomeric dimethoxyanthraquinones unless a cyclic structure is involved. Whatever the structure of the M* --R’(R = Me or Et) ion is, it is unusual, in that it decomposes by loss of water (see Figs 3 and 4). The process M?-Me’-Hz0 in the spectrum (Fig. 3) of 1,8dlmethoxyanthraquinone becomes M* -CD; -DzO in that of l,&di(& methoxy)anthraquinone (XIV). In summary, mass spectrometry will allow the determination of the 1-hydroxyl and l,&dihydroxyl substitution pattern in an anthraquinone and a 5-OH group in a naphthaquinone if the OH groups are first converted into ethoxyl substituents. In this way mass spectrometry complements the use of other spectroscopic methods for the structure determination of hydroxyquinones. EXPERIMENTAL All spectra were demrmined with an Hitachi Perkin-Ehner RMU 6D double focusing mass spectrometer operating at 70 eV. Samples were introduced through an all glass heated inlet system at 200”. The compositions of species indicated by schematic arrows in a Figure were determined by exact mass measwbments at a resolution of lO,OfNI (40% valley definition) using heptacosafiuorotributylamine to provide referencemasses. All unlabelfed compounds were available from previous studies.r r*tz The hbelled ethers were prepared by alkylation of the appropriate hydroxyquinone with the required labelled alkyl iodide. Acknowledgement-The Hitachi Perkin-ELmer RMU 6D mass spectrometer was purchased with the aid of a graot from the Australian Research Grants Committee.
REFERENCES r Part XL.1.J. H. Rowie, M. T. W. Hearn and A. D. Ward, Auatrol. J. Chem. 22,175 (1969) 2 J. H. Reynon and A. E. Wilhams, Appf. Spectroscopy 14,156 (1960) 3 J. H. Bowie,D. W. Cameron, R. G. F. Gilea and D. H. WiRiams, J. Chem. Sec. (R), 335 (1966) l J. H. Bowie,D. W. Cameron and D. H. WiUiams, J. Am. CJrem. Sot. 87.3094 (1965) r S. J. Di Mari, J. H. Supple and H. Rapoport, Ibid. 88.1226 (1966) 6 D. Becker, C. Djemssi, R. E. Moore, H. Singh and P. J. Scheuer, J. Org. Chem. 31,365O (1966)
1168
J. H. BOWIE,P. J. HOFFMANNand P. Y. WHIIX
‘I R. W. A. Olivar and R. M. Ra&mau, 1. Chem. Sot. (B), 1141(1968) s J. H. Bowis and D. W. Cameron, Ibid. (B), 684 (1966) ’ H. Brockmauu, J. Nicmeyer, H. Brockmauu, Jr., and H. Budzikiawia, C/tent. J&r. 96,378s (1966) and Rds therein lo F. W. McLatKxty and R. S. Gohlkc, AM&. Cheat. 31,2079 (1957) I1 J. H. Bowie aud P. Y. White, J. Cheat. Sot. (B), 89 (1969) I2 J. H. Bowie and P. Y. White. ‘FetraAedrm U. 1629 (1969) I3 E S. Waight, Symposium on “Newer Methodsin Structural Chemistry”. Oxford (1966) See also D. R Buckle and E S. Waight Org. Mass Spectrmeh?, 1,273 (1968) l* H. Bloom, L. H. Briggs and B. Cloverley, J. C/tent. Sot. 178 (1959) I5 L. H. Briggs, G. A. Njcholls and R. M. L. Paterson, Ibid. 1718 (1952)
VolZ6,pp.l163t01166.
papmOnRcu1970.
PdedinOmtbith
ELECTRON TMPACT STUDIES-XLTT’ PERI-EFFECTS IN THE MASS SPECTRA OF ALKOXYQUINONES J. H. BOWIE,P. J. HOFFMANN and P. Y. WHITE Department of Organic Chemistry, University of Adelaide, Adelaide, South Australia, 5001 (Received in the UK 2 June 1%9; Acceptedfor publication 3 July 1969) tie&-The mass spectra of certain I-alkoxyanthraquinones, 5-alkoxynaphthaquinones and 1,8dialkoxyanthraquinones exhibit diignostic fragmentations which are absent in the spectra of other alkoxyquinones. These fragmentations are characteristic of the peri-alkoxyquinonc moiety, and may be used BP)useful aids to structure dettrminations.
basic fragmentations in the mass spectra of benzoquinones,2* ’ naphthaquinone$* 4-7 anthraquinones2 and certain higher quinones2* **g have been desctibed. Ortho-effects’” have been noted in the spectra of naphthaquinones”, l2 and anthraquinones.11-‘3 In connection with our studies “* I2 of the ortbeffects which occur in the mass spectra of aromatic carbonyl compounds containing adjacent alkoxyl groups, we observed large differences between the spectra of l- and 2-ethoxyanthraquinone. As it seem@ that mass spectrometry may usefully complement the use of IR14 and W” spectroscopy for the determination of the oxygenation pattern of an hydroxyquinone, we examined the mass spectra of I-XXI. This paper describes the diagnostic perieffects which are observed in many of these spectra. THE
I
R’
II III N V VI VII VIII IX X XI XII XIII XN XV XVI XVII
0
R’
R’ CDs0 Et0 CD&H10 H H nPr0 H isoR MexCDO Me0 Me0 Me0 Me0 CDs0 H Et0 Et0
R’ H H H Et0 CD&H20 H nFV0
H H
R3 H H H H H H H H H H Me0 H H H H H H
R4 H H H H H H H H H H H Me0 H H H Et0 H
R’ H H H H H H H H H H H H H H Me0 H H
0 R’ Et0 H
1163
RZ H Et0
R6 H H H H H H H H H H H H Me0 CD,0 H H Et0
J. H. Bow,
P. J. HOFFMANN and P. Y. WHITE
RZ H Me0
R’ Et0 Me0
TABU 1. ~WTMI ABUNDANCES OFbit--X’
IONS IN THE
SFWTRA
OF COMFQUNIX
OF TNJI
TYFTJ
0 o( 3 Y)
M? -X’
Compound
hf?
I II III IV
loo 98 88 93
6 100 81 -
V VI VII
94 18 10
-
M? -X’
Compound
Mf
VIII XVI XVII
15 13 100 1
12 10 31 -
XVIII XIX
100 88
75 -
Ix
9
-
b"
(II I)
I
I 237
_
169
L FIG. 1
Electron impact studies-XL11
1165
-Me*
t
187 174
140
=2H4
180
FIG.2
The mass spectra of l- and 2-alkoxyanthraquinones are very different. The major differences are summarised in Table 1, and are illustrated [for the cases of l- and 2-(2,2,2+ethoxy)anthraquinone (III and V)] in Fig. 1. The pronounced loss of CD; from the molecular ion of III is absent in the spectrum of V. This effect is characteristic of the spectra of l-alkoxyanthraquinones (when X 2 Me, see a), and is most pronounced for l-ethoxyanthraquinone. The peti-effect may be rational&d by the formation of the stabilised oxonium species b and its formation is always substantiated by a metastable peak (represented by an asterisk in a Figure or the text). It is of interest to note that this effect is minor in the spectrum of o-ethoxybenzophenone (M+ - Me’ = 100 and 12% in the spectra of I and XX respectively)
-CHO
7
C,oHsOzt m/e 158
c, m/e 18?
1166
J. H. Bowra, P. J. H~NN
and P. Y. Wm
The spectrum (Fig. 2) of Sethoxynaphthaquinone also shows a pronounced Mt - Me’ ion. In marked contrast, Z~~oxynaphthaquinone does not eliminate a Me radical upon electron impact. The fragmentation of the oxonium species c is indicated in Fig. 2. Loss of a formyl radical from c produces a species which fragments in the same way as the 1,rGnaphthaquinone molecular ion.4 However, this species may not correspond to the 1,4aaphthaquinone radical ion because of the large differences between the abundance ratios of m/e 158 and its daughter ions in the spectra of 1,4naphtbaqu~one2 and XIX. The same situation occurs for III (Fig. 11where the process M~-CI&--CHO’ produces a species which may not correspond to the anthraquinone molecular ion. The spectra of the labelled derivatives III, IV and IX show that no hydrogen randomisation in the alkoxyl groups precedes the M* - X process at 70 eV.
(60
200
240
Fra. 4
Electron Impact Studie\-XLII
1167
The mass spectra of the isomeric dimethoxyanthraquinones (X-XII and XV) are reasonably similar and are typified by that (Fig. 3) of 1,Sdimethoxyanthraquinone (XII). The spectrum (Fig. 3) of 1,8dimethoxyanthraquinone (XIII) is easily distinguishable from that of XII in that the process M+-Me’ produces the base peak for XIII but only a peak of 5 % relative abundance in the spectrum of XIL This distinction is even more apparent in the spectra (Fig 4) of the isomeric diethoxyanthraquinones (XVI and XVII). Although these spectra are complex, they can be easily differentiated, because the base peak in the spectrum of 1,8-diethoxyanthraquinone is an M* -Et’ ion, whereas the corresponding peak in that of l,Sdiethoxyanthraquinone is only 19% of the base peak. It is of interest to note that a major fragmentation in the spectrum of XVI proceeds through the Mt -Me’ ion, and that this peri-effect is completely absent in the spectrum of XVII which is dominated by the second peri-effect discussed above. Although mass spectrometry can be used to determine the presence of l,&dialkoxyl substitution in an anthraquinone, it is not obvious why this peri-effect occurs. The tricyclic aromatic system is a prerequisite for the elimination, as the spectrum of o,o’dimethoxybenxophenone (XXI) does not contain an M t -Me’ ion. There seems to be no obvious reason why the M-15 ion in the spectrum of XIII should be any more stable than a similar species which could be produced from other isomeric dimethoxyanthraquinones unless a cyclic structure is involved. Whatever the structure of the M* --R’(R = Me or Et) ion is, it is unusual, in that it decomposes by loss of water (see Figs 3 and 4). The process M?-Me’-Hz0 in the spectrum (Fig. 3) of 1,8dlmethoxyanthraquinone becomes M* -CD; -DzO in that of l,&di(& methoxy)anthraquinone (XIV). In summary, mass spectrometry will allow the determination of the 1-hydroxyl and l,&dihydroxyl substitution pattern in an anthraquinone and a 5-OH group in a naphthaquinone if the OH groups are first converted into ethoxyl substituents. In this way mass spectrometry complements the use of other spectroscopic methods for the structure determination of hydroxyquinones. EXPERIMENTAL All spectra were demrmined with an Hitachi Perkin-Ehner RMU 6D double focusing mass spectrometer operating at 70 eV. Samples were introduced through an all glass heated inlet system at 200”. The compositions of species indicated by schematic arrows in a Figure were determined by exact mass measwbments at a resolution of lO,OfNI (40% valley definition) using heptacosafiuorotributylamine to provide referencemasses. All unlabelfed compounds were available from previous studies.r r*tz The hbelled ethers were prepared by alkylation of the appropriate hydroxyquinone with the required labelled alkyl iodide. Acknowledgement-The Hitachi Perkin-ELmer RMU 6D mass spectrometer was purchased with the aid of a graot from the Australian Research Grants Committee.
REFERENCES r Part XL.1.J. H. Rowie, M. T. W. Hearn and A. D. Ward, Auatrol. J. Chem. 22,175 (1969) 2 J. H. Reynon and A. E. Wilhams, Appf. Spectroscopy 14,156 (1960) 3 J. H. Bowie,D. W. Cameron, R. G. F. Gilea and D. H. WiRiams, J. Chem. Sec. (R), 335 (1966) l J. H. Bowie,D. W. Cameron and D. H. WiUiams, J. Am. CJrem. Sot. 87.3094 (1965) r S. J. Di Mari, J. H. Supple and H. Rapoport, Ibid. 88.1226 (1966) 6 D. Becker, C. Djemssi, R. E. Moore, H. Singh and P. J. Scheuer, J. Org. Chem. 31,365O (1966)
1168
J. H. BOWIE,P. J. HOFFMANNand P. Y. WHIIX
‘I R. W. A. Olivar and R. M. Ra&mau, 1. Chem. Sot. (B), 1141(1968) s J. H. Bowis and D. W. Cameron, Ibid. (B), 684 (1966) ’ H. Brockmauu, J. Nicmeyer, H. Brockmauu, Jr., and H. Budzikiawia, C/tent. J&r. 96,378s (1966) and Rds therein lo F. W. McLatKxty and R. S. Gohlkc, AM&. Cheat. 31,2079 (1957) I1 J. H. Bowie aud P. Y. White, J. Cheat. Sot. (B), 89 (1969) I2 J. H. Bowie and P. Y. White. ‘FetraAedrm U. 1629 (1969) I3 E S. Waight, Symposium on “Newer Methodsin Structural Chemistry”. Oxford (1966) See also D. R Buckle and E S. Waight Org. Mass Spectrmeh?, 1,273 (1968) l* H. Bloom, L. H. Briggs and B. Cloverley, J. C/tent. Sot. 178 (1959) I5 L. H. Briggs, G. A. Njcholls and R. M. L. Paterson, Ibid. 1718 (1952)