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E-2-benzylidenebenzocyclanones. II. IR and mass spectrometric investigations
Journal of Molecular Structure 520 (2000) 97–102 www.elsevier.nl/locate/molstruc
E-2-benzylidenebenzocyclanones. II. IR and mass spectrometric investigations Gy. Tarczay a, K. Ve´key b, K. Luda´nyi b, P. Perje´si c, P. Soha´r a,* a
Department of General and Inorganic Chemistry, Eo¨tvo¨s Lora´nd University, Pa´zma´ny se´ta´ny 1A, H-1117 Budapest, Hungary b Research Centrum of Chemistry, Institute of Chemistry, Hungarian Academy of Sciences, Budapest, Hungary c Department of Medical Chemistry, University Medical School, H-7643 Pe´cs, Hungary Received 28 April 1999; received in revised form 4 June 1999; accepted 18 June 1999
Abstract A series of E-2-benzylideneindanones (a) -tetralones (b) and -benzosuberones (c) with OCH3 (2–4), NO2 (5–7) and F (8–10) substituents in ortho, meta or para position was studied by IR and mass spectrometry. The most important IR bands were assigned and stated correlations between some frequencies and the stereostructure or conjugation feature of the molecules investigated. IR spectra were also analyzed in order to find frequencies characteristic of the size of the alkanone ring. The mass spectrometric investigation aimed at determining fragmentation pathways and finding correlations between them and the ring size of the alkanone ring or the position of the substituents. q 2000 Elsevier Science B.V. All rights reserved. Keywords: E-2-benzylidenebenzocyclanones; IR and mass spectrometry
1. Introduction In the first paper on our study [1] of benzylidenebenzocycloalkanones we reported the synthesis and the NMR investigation focused on the stereostructure (configurations and conformations) and the electronic properties (enone-conjugation). The conclusions drawn from NMR data were also supported by quantummechanical calculations: the scope of the recent paper, the second part of our study, is the IR and mass spectrometric investigations of our new compounds which are also expected to have valuable biological activity.
2. Materials and methods Compounds 1a–c to 10a–c were synthesized by * Corresponding author.
the methods given in Refs. [2,3]. The melting points of the compounds were given in our previous paper [1]. The IR spectra were recorded in KBr on a Bruker IFS-55 instrument controlled by Opus 2.0 software. All spectra have been treated similarly by a rubber band baseline correction, and have been normalized to 1–0.1 transmittance. Single stage electron impact (EI) ionisation mass spectra were recorded on a double focusing AEI MS-902 type mass spectrometer, using 70 eV electron energy. Metastable and collision induced decomposition (CID) spectra were observed using the mass analyzed ion kinetic energy spectroscopy (MIKES) technique on a reverse geometry VG ZAB-2SEQ instrument. For CID experiments argon collision gas was used, its pressure adjusted to result in 50% main ion beam transmission.
0022-2860/00/$ - see front matter q 2000 Elsevier Science B.V. All rights reserved. PII: S0022-286 0(99)00330-0
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Gy. Tarczay et al. / Journal of Molecular Structure 520 (2000) 97–102
Table 1 Assignments of charecteristic IR-frequencies of compounds 1a–c to 10a–c (in KBr discs (cm 21))
1a 2a 3a 4a 5a 6a 7a 8a 9a 10a 1b 2b 3b 4b 5b 6b 7b 8b 9b 10b 1c 2c 3c 4c 5c 6c 7c 8c 9c 10c
n CArOMe
n CArOMe
1021 1034 1025
1254 1254 1259
n sNO2
1357 1348 1340
n asNO2
n CArF
1517 1531 1510 1232 1231 1232
1022 1040 1034
1240 1249 1252 1347 1348 1345
1520 1534 1515 1226 1238 1228
1022 1037 1026
1243 1241 1256 1340 1346 1342
1519 1521 1513
3. Results and discussion The detailed analysis of IR data aimed, besides the firm assignment of the bands to characteristic vibrational modes, and above all, at recognizing correlations between the IR-frequencies and the ring size. The MS study was carried out to clear the pathways of fragmentation, the influence of ring size on these processes and to draw conclusions concerning bond stabilities. 3.1. IR spectroscopic investigations The characteristic vibrational frequencies can be seen in Table 1. There are two intense bands in each spectrum in the region 1600–1800 cm 21, corresponding to the n CyO and n CyC vibrations. The
1228 1226 1228
n CyO
n CyC
g CArH
g CArH
1693 1706 1691 1695 1704 1692 1695 1700 1700 1690 1661 1664 1666 1666 1672 1663 1666 1670 1667 1663 1663 1662 1661 1666 1665 1663 1663 1670 1664 1665
1625 1629 1627 1625 1635 1634 1630 1630 1630 1631 1605 1605 1601 1601 1623 1612 1611 1626 1607 1604 1605 1605 1600 1599 1611 1609 1613 1614 1605 1606
740 740 733 735 738 744 740 736 737 734 741 741 742 744 741 746 738 742 737 745 757 763 744 757 728 735 750 750 750 764
763 749 781 823 738 809 751 752 775 836 756 763 780 841 755 801 749 760 764 844 762 763 772 838 766 815 776 761 774 831
carbonyl IR-frequencies are discussed in detail in Ref. [1] (see also [4–6]). Briefly, as in series a, in contrast with series b and c, the enone moiety is planar and the aryl group is also coplanar with the former, the carbonyl frequencies are decisively determined by the conjugation, while the type and the position of the substituent have only a marginal effect on it. Similar to our statement on the n CyO frequencies the n CyC-type skeletal vibrations are also sensible to the ring size. While the n CyC band of indanones (series a) has a frequency in the interval 1625– 1635 cm 21, the same band of tetralones (series b) and benzo-suberones (series c) appears (with two exceptions for 5b and 8b, where n CyC is 1623 and 1626 cm 21, respectively) at lower frequencies between 1601–1612 (b) or 1599–1614 cm 21(c). Hence, the direction of the frequency-shift is the
Gy. Tarczay et al. / Journal of Molecular Structure 520 (2000) 97–102 Table 2 IR-frequencies charecteristic for ring size of compounds 1a–c to 10a–c (in KBr discs (cm 21)) n5
n6
n7
955 ^ 10 795 ^ 10 735 ^ 10 672 ^ 10 559 ^ 10 478 ^ 5
958 ^ 10 794 ^ 10 745 ^ 10 653 ^ 5 628 ^ 5 533 ^ 10 490 ^ 10
969 ^ 10 881 ^ 10 825 ^ 10 760 ^ 10 709 ^ 10 652 ^ 10 587 ^ 5 458 ^ 10
99
same, while the measure of it is only half than the effect of the ring size on the n CyO frequencies. Due to the numerous effects, which are about the same in magnitude, it is hard to interpret the characteristic frequencies of the substituents. These effects (see e.g. [7]) are the conjugation, the polarizabilizy of the aromatic ring in the benzylidene group, the conformation of the molecule and the intermolecular interactions in the crystal. In case of the n asNO2 vibration the most determining factor is the polarizability of the aromatic ring. According to this the n asNO2 frequency increases in the order of para , ortho , meta: Similarly, the n asCOC and n sCOC vibrations of the
Fig. 1. Part of the IR spectra of series a, b, and c n 5; 6, and 7) in the 450–1000 cm 21 interval for compounds 1–10 to identifying frequencies characteristic of ring size.
100
Gy. Tarczay et al. / Journal of Molecular Structure 520 (2000) 97–102
Fig. 2. Electron impact mass spectra of selected model compounds: unsubstituted (1b), para-methoxy (4b), ortho-methoxy (2b), para-nitro (7b) and para-fluoro (10b) derivatives.
Gy. Tarczay et al. / Journal of Molecular Structure 520 (2000) 97–102 O
OH
+
H
-H
Scheme 1.
C(Ar)–O–C(H3) groups are coupled stronger in series a (in fully planar structures) and in each series for the ortho and para isomers (2 and 4) are due to more significant interaction with the enone moiety: the frequency-differences are 218–234 cm 21 in contrast to meta isomers 3a–c, where it is 220, 209, and 204 cm 21. The value of these frequencies is higher in the order of ortho , para , meta (n sCOC) and ortho, meta , para (n asCOC), respectively. The n sNO2 and n C(Ar)F vibrations are not sensible either on the ring size or on the position of the substituents. In the interval of 450–1000 cm 21 there are frequencies characteristic of ring size, for one or other series a, b or c (Table 2). This is illustrated with Fig. 1, in which the part of spectra 1–10 of the series a, b, and c, whose ring sizes are different have been drawn superposed (upon one another). The number of accumulation intervals of absorption maxima is between 6 and 8 for the series and the simultaneous appearance of these ensembles of bands offers a firm base to differentiate molecules containing alkanone rings of different sizes. 3.2. Mass spectrometric investigations Mass spectra of compounds 1a–c to 10a–c were studied by electron impact ionization. The fragmentation pathways discussed below were supported in each case by a metastable ion and collision induced decomposition (CID) techniques. As an example, mass spectra of the unsubstituted, p-methoxy, omethoxy, p-nitro and p-fluoro substituted benzocyclohexanone derivatives (1b, 4b, 2b, 7b and 10b) are shown in Fig. 2. The common mass spectrometric characteristics of the compound class are an abundant molecular ion, only few low mass fragments due to cleavages of the molecular backbone, an abundant fragment corresponding to the loss of a hydrogen atom, and some fragmentation processes characterizing the substituent.
101
Methoxy substituted derivatives show abundant ions due to the loss of CH3 and OCH3 substitutes. Comparison among the compounds studied shows that the peak corresponding to methyl loss is abundant in the case of all methoxy substituted compounds, it is not characteristic for other substituents and does not depend significantly on the ring size. This suggests, that methyl loss originates from the methoxy group, and not from the cycloalkanone ring. Nitro derivatives predominantly show OH, NO and HNO2 loss. Fluoro derivatives loose the F substituent, very prominent in the case of ortho substitution. This process does not lead to abundant ions in the electron impact mass spectra of the meta and para isomers, but its mass (M—19 Da) is very characteristic. In the metastable √ and in CID spectra, however, F loss is a peak of very high abundance. The size of the cycloalkanone ring significantly influences the abundance of the [M–H] 1 ion. Provided that the phenyl substituent is the same, the abundance of this ion is similar in the case of cyclopentanone and cycloheptanone derivatives, while significantly larger for cyclohexanones. A likely reason for this feature is the formation of an extended aromatic ring structure by rearrangement (Scheme 1), which is possible only in the case of cyclohexanone derivatives (6-member rings). Note that the suggested product ion has an enol functional group. Such structures are typically favored to the keto forms for the gas-phase positive ions [8]. In the rearranged ion the positive charge is stabilized both by the phenyl and the newly formed naphtyl ring. The position of substitution on the phenyl ring has a large effect on fragmentation, independently on the type of substituent. Meta and para substituents show practically identical spectra. For ortho isomers the loss of the substituent (OMe, NO2 or F) becomes the dominant fragmentation process, and the stability of the molecular ion decreases. The size of the cycloalkanone ring has little effect on this process. As an example, this effect is clearly shown in Fig. 2, which compares para and ortho methoxy substituted derivatives (4b and 2b). The facility of this process can be characterized by the abundance ratio√of the product and precursor ions ([M–X] 1/[M] 1 ). For the p-OMe derivative (4b) it is 0.24, for the ortho isomer it is 45, a 200-fold increase! Nitro compounds
102
Gy. Tarczay et al. / Journal of Molecular Structure 520 (2000) 97–102
tures shown above do explain the fragmentation behavior observed. X
O
O
+
References
-X (CH2)n
(CH2)n
Scheme 2.
behave in a similar manner (NO2 and OH losses), and even the ortho-fluorine derivatives show an abundant [M–F] 1 peaks. Note that fluorine compounds only very rarely loose an F atom [9]. These suggest the occurrence of a very favorable rearrangement. Formation of a stable, condensed aromatic ring structure seems to be the likely explanation (Scheme 2). In conclusion, mass spectra of benzylidene benzocycloalkanones are easy to interpret, give information on the type and position of the substituent and the molecular mass. The spectra are dominated by hidden rearrangement processes—the gas-phase ion struc-
[1] P. Perje´si, T. Nusser, G. Tarczay, P. Soha´r, J. Mol. Struct. 479 (1999) 13–19. [2] A.T. Nielsen, W.J. Houlihan, The aldol condensation, Organic Reactions, 16, Wiley, New York, 1968, pp. 44–47. [3] A. Hassner, N.H. Cromwell, J. Am. Chem. Soc. 80 (1958) 893– 900. [4] S. Geribaldi, Y. Girault, P. Perje´si, J. Tortajada, Spectrochim. Acta A 48 (1992) 879–892. ´ . Somogyi, V. Galamb, Spectro[5] Z. Dinya, A. Le´vai, J. Scha´g, A chim. Acta A 48 (1992) 25–30. [6] O. Azzolina, G. Desimoni, V. Toro, V. Ghislandi, G. Tacconi, Gazetta Chim. Italiana 105 (1975) 971–983. [7] G. Varsa´nyi, Vibrational Spectra of Benzene Derivatives. Akade´miai kiado´, Budapest, 1969. [8] Fred W. McLafferty, F. Turee`ek, Interpretation of Mass Spectra, University Science Books, Sausalito, CA, 1993. [9] H. Budzikiewitz, C. Djerassi, D.H. Williams, Mass Spectrometry of Organic Compounds, Holden-Day, San Francisco, CA, 1967.
E-2-benzylidenebenzocyclanones. II. IR and mass spectrometric investigations Gy. Tarczay a, K. Ve´key b, K. Luda´nyi b, P. Perje´si c, P. Soha´r a,* a
Department of General and Inorganic Chemistry, Eo¨tvo¨s Lora´nd University, Pa´zma´ny se´ta´ny 1A, H-1117 Budapest, Hungary b Research Centrum of Chemistry, Institute of Chemistry, Hungarian Academy of Sciences, Budapest, Hungary c Department of Medical Chemistry, University Medical School, H-7643 Pe´cs, Hungary Received 28 April 1999; received in revised form 4 June 1999; accepted 18 June 1999
Abstract A series of E-2-benzylideneindanones (a) -tetralones (b) and -benzosuberones (c) with OCH3 (2–4), NO2 (5–7) and F (8–10) substituents in ortho, meta or para position was studied by IR and mass spectrometry. The most important IR bands were assigned and stated correlations between some frequencies and the stereostructure or conjugation feature of the molecules investigated. IR spectra were also analyzed in order to find frequencies characteristic of the size of the alkanone ring. The mass spectrometric investigation aimed at determining fragmentation pathways and finding correlations between them and the ring size of the alkanone ring or the position of the substituents. q 2000 Elsevier Science B.V. All rights reserved. Keywords: E-2-benzylidenebenzocyclanones; IR and mass spectrometry
1. Introduction In the first paper on our study [1] of benzylidenebenzocycloalkanones we reported the synthesis and the NMR investigation focused on the stereostructure (configurations and conformations) and the electronic properties (enone-conjugation). The conclusions drawn from NMR data were also supported by quantummechanical calculations: the scope of the recent paper, the second part of our study, is the IR and mass spectrometric investigations of our new compounds which are also expected to have valuable biological activity.
2. Materials and methods Compounds 1a–c to 10a–c were synthesized by * Corresponding author.
the methods given in Refs. [2,3]. The melting points of the compounds were given in our previous paper [1]. The IR spectra were recorded in KBr on a Bruker IFS-55 instrument controlled by Opus 2.0 software. All spectra have been treated similarly by a rubber band baseline correction, and have been normalized to 1–0.1 transmittance. Single stage electron impact (EI) ionisation mass spectra were recorded on a double focusing AEI MS-902 type mass spectrometer, using 70 eV electron energy. Metastable and collision induced decomposition (CID) spectra were observed using the mass analyzed ion kinetic energy spectroscopy (MIKES) technique on a reverse geometry VG ZAB-2SEQ instrument. For CID experiments argon collision gas was used, its pressure adjusted to result in 50% main ion beam transmission.
0022-2860/00/$ - see front matter q 2000 Elsevier Science B.V. All rights reserved. PII: S0022-286 0(99)00330-0
98
Gy. Tarczay et al. / Journal of Molecular Structure 520 (2000) 97–102
Table 1 Assignments of charecteristic IR-frequencies of compounds 1a–c to 10a–c (in KBr discs (cm 21))
1a 2a 3a 4a 5a 6a 7a 8a 9a 10a 1b 2b 3b 4b 5b 6b 7b 8b 9b 10b 1c 2c 3c 4c 5c 6c 7c 8c 9c 10c
n CArOMe
n CArOMe
1021 1034 1025
1254 1254 1259
n sNO2
1357 1348 1340
n asNO2
n CArF
1517 1531 1510 1232 1231 1232
1022 1040 1034
1240 1249 1252 1347 1348 1345
1520 1534 1515 1226 1238 1228
1022 1037 1026
1243 1241 1256 1340 1346 1342
1519 1521 1513
3. Results and discussion The detailed analysis of IR data aimed, besides the firm assignment of the bands to characteristic vibrational modes, and above all, at recognizing correlations between the IR-frequencies and the ring size. The MS study was carried out to clear the pathways of fragmentation, the influence of ring size on these processes and to draw conclusions concerning bond stabilities. 3.1. IR spectroscopic investigations The characteristic vibrational frequencies can be seen in Table 1. There are two intense bands in each spectrum in the region 1600–1800 cm 21, corresponding to the n CyO and n CyC vibrations. The
1228 1226 1228
n CyO
n CyC
g CArH
g CArH
1693 1706 1691 1695 1704 1692 1695 1700 1700 1690 1661 1664 1666 1666 1672 1663 1666 1670 1667 1663 1663 1662 1661 1666 1665 1663 1663 1670 1664 1665
1625 1629 1627 1625 1635 1634 1630 1630 1630 1631 1605 1605 1601 1601 1623 1612 1611 1626 1607 1604 1605 1605 1600 1599 1611 1609 1613 1614 1605 1606
740 740 733 735 738 744 740 736 737 734 741 741 742 744 741 746 738 742 737 745 757 763 744 757 728 735 750 750 750 764
763 749 781 823 738 809 751 752 775 836 756 763 780 841 755 801 749 760 764 844 762 763 772 838 766 815 776 761 774 831
carbonyl IR-frequencies are discussed in detail in Ref. [1] (see also [4–6]). Briefly, as in series a, in contrast with series b and c, the enone moiety is planar and the aryl group is also coplanar with the former, the carbonyl frequencies are decisively determined by the conjugation, while the type and the position of the substituent have only a marginal effect on it. Similar to our statement on the n CyO frequencies the n CyC-type skeletal vibrations are also sensible to the ring size. While the n CyC band of indanones (series a) has a frequency in the interval 1625– 1635 cm 21, the same band of tetralones (series b) and benzo-suberones (series c) appears (with two exceptions for 5b and 8b, where n CyC is 1623 and 1626 cm 21, respectively) at lower frequencies between 1601–1612 (b) or 1599–1614 cm 21(c). Hence, the direction of the frequency-shift is the
Gy. Tarczay et al. / Journal of Molecular Structure 520 (2000) 97–102 Table 2 IR-frequencies charecteristic for ring size of compounds 1a–c to 10a–c (in KBr discs (cm 21)) n5
n6
n7
955 ^ 10 795 ^ 10 735 ^ 10 672 ^ 10 559 ^ 10 478 ^ 5
958 ^ 10 794 ^ 10 745 ^ 10 653 ^ 5 628 ^ 5 533 ^ 10 490 ^ 10
969 ^ 10 881 ^ 10 825 ^ 10 760 ^ 10 709 ^ 10 652 ^ 10 587 ^ 5 458 ^ 10
99
same, while the measure of it is only half than the effect of the ring size on the n CyO frequencies. Due to the numerous effects, which are about the same in magnitude, it is hard to interpret the characteristic frequencies of the substituents. These effects (see e.g. [7]) are the conjugation, the polarizabilizy of the aromatic ring in the benzylidene group, the conformation of the molecule and the intermolecular interactions in the crystal. In case of the n asNO2 vibration the most determining factor is the polarizability of the aromatic ring. According to this the n asNO2 frequency increases in the order of para , ortho , meta: Similarly, the n asCOC and n sCOC vibrations of the
Fig. 1. Part of the IR spectra of series a, b, and c n 5; 6, and 7) in the 450–1000 cm 21 interval for compounds 1–10 to identifying frequencies characteristic of ring size.
100
Gy. Tarczay et al. / Journal of Molecular Structure 520 (2000) 97–102
Fig. 2. Electron impact mass spectra of selected model compounds: unsubstituted (1b), para-methoxy (4b), ortho-methoxy (2b), para-nitro (7b) and para-fluoro (10b) derivatives.
Gy. Tarczay et al. / Journal of Molecular Structure 520 (2000) 97–102 O
OH
+
H
-H
Scheme 1.
C(Ar)–O–C(H3) groups are coupled stronger in series a (in fully planar structures) and in each series for the ortho and para isomers (2 and 4) are due to more significant interaction with the enone moiety: the frequency-differences are 218–234 cm 21 in contrast to meta isomers 3a–c, where it is 220, 209, and 204 cm 21. The value of these frequencies is higher in the order of ortho , para , meta (n sCOC) and ortho, meta , para (n asCOC), respectively. The n sNO2 and n C(Ar)F vibrations are not sensible either on the ring size or on the position of the substituents. In the interval of 450–1000 cm 21 there are frequencies characteristic of ring size, for one or other series a, b or c (Table 2). This is illustrated with Fig. 1, in which the part of spectra 1–10 of the series a, b, and c, whose ring sizes are different have been drawn superposed (upon one another). The number of accumulation intervals of absorption maxima is between 6 and 8 for the series and the simultaneous appearance of these ensembles of bands offers a firm base to differentiate molecules containing alkanone rings of different sizes. 3.2. Mass spectrometric investigations Mass spectra of compounds 1a–c to 10a–c were studied by electron impact ionization. The fragmentation pathways discussed below were supported in each case by a metastable ion and collision induced decomposition (CID) techniques. As an example, mass spectra of the unsubstituted, p-methoxy, omethoxy, p-nitro and p-fluoro substituted benzocyclohexanone derivatives (1b, 4b, 2b, 7b and 10b) are shown in Fig. 2. The common mass spectrometric characteristics of the compound class are an abundant molecular ion, only few low mass fragments due to cleavages of the molecular backbone, an abundant fragment corresponding to the loss of a hydrogen atom, and some fragmentation processes characterizing the substituent.
101
Methoxy substituted derivatives show abundant ions due to the loss of CH3 and OCH3 substitutes. Comparison among the compounds studied shows that the peak corresponding to methyl loss is abundant in the case of all methoxy substituted compounds, it is not characteristic for other substituents and does not depend significantly on the ring size. This suggests, that methyl loss originates from the methoxy group, and not from the cycloalkanone ring. Nitro derivatives predominantly show OH, NO and HNO2 loss. Fluoro derivatives loose the F substituent, very prominent in the case of ortho substitution. This process does not lead to abundant ions in the electron impact mass spectra of the meta and para isomers, but its mass (M—19 Da) is very characteristic. In the metastable √ and in CID spectra, however, F loss is a peak of very high abundance. The size of the cycloalkanone ring significantly influences the abundance of the [M–H] 1 ion. Provided that the phenyl substituent is the same, the abundance of this ion is similar in the case of cyclopentanone and cycloheptanone derivatives, while significantly larger for cyclohexanones. A likely reason for this feature is the formation of an extended aromatic ring structure by rearrangement (Scheme 1), which is possible only in the case of cyclohexanone derivatives (6-member rings). Note that the suggested product ion has an enol functional group. Such structures are typically favored to the keto forms for the gas-phase positive ions [8]. In the rearranged ion the positive charge is stabilized both by the phenyl and the newly formed naphtyl ring. The position of substitution on the phenyl ring has a large effect on fragmentation, independently on the type of substituent. Meta and para substituents show practically identical spectra. For ortho isomers the loss of the substituent (OMe, NO2 or F) becomes the dominant fragmentation process, and the stability of the molecular ion decreases. The size of the cycloalkanone ring has little effect on this process. As an example, this effect is clearly shown in Fig. 2, which compares para and ortho methoxy substituted derivatives (4b and 2b). The facility of this process can be characterized by the abundance ratio√of the product and precursor ions ([M–X] 1/[M] 1 ). For the p-OMe derivative (4b) it is 0.24, for the ortho isomer it is 45, a 200-fold increase! Nitro compounds
102
Gy. Tarczay et al. / Journal of Molecular Structure 520 (2000) 97–102
tures shown above do explain the fragmentation behavior observed. X
O
O
+
References
-X (CH2)n
(CH2)n
Scheme 2.
behave in a similar manner (NO2 and OH losses), and even the ortho-fluorine derivatives show an abundant [M–F] 1 peaks. Note that fluorine compounds only very rarely loose an F atom [9]. These suggest the occurrence of a very favorable rearrangement. Formation of a stable, condensed aromatic ring structure seems to be the likely explanation (Scheme 2). In conclusion, mass spectra of benzylidene benzocycloalkanones are easy to interpret, give information on the type and position of the substituent and the molecular mass. The spectra are dominated by hidden rearrangement processes—the gas-phase ion struc-
[1] P. Perje´si, T. Nusser, G. Tarczay, P. Soha´r, J. Mol. Struct. 479 (1999) 13–19. [2] A.T. Nielsen, W.J. Houlihan, The aldol condensation, Organic Reactions, 16, Wiley, New York, 1968, pp. 44–47. [3] A. Hassner, N.H. Cromwell, J. Am. Chem. Soc. 80 (1958) 893– 900. [4] S. Geribaldi, Y. Girault, P. Perje´si, J. Tortajada, Spectrochim. Acta A 48 (1992) 879–892. ´ . Somogyi, V. Galamb, Spectro[5] Z. Dinya, A. Le´vai, J. Scha´g, A chim. Acta A 48 (1992) 25–30. [6] O. Azzolina, G. Desimoni, V. Toro, V. Ghislandi, G. Tacconi, Gazetta Chim. Italiana 105 (1975) 971–983. [7] G. Varsa´nyi, Vibrational Spectra of Benzene Derivatives. Akade´miai kiado´, Budapest, 1969. [8] Fred W. McLafferty, F. Turee`ek, Interpretation of Mass Spectra, University Science Books, Sausalito, CA, 1993. [9] H. Budzikiewitz, C. Djerassi, D.H. Williams, Mass Spectrometry of Organic Compounds, Holden-Day, San Francisco, CA, 1967.