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Collision Induced Fragmentation of Alkylideneammonium Ions.

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with the appropriate buffer. After transfer to a chromatography column, the polymer was washed with water or buffer
solution until no absorption was observed at 256 nm in the
eluate. The protein mixture was then applied.
Fig. 2. Protein pattern of the fractions obtained from the crude Jack bean extract
(Fig. 1b). A, crude extract. B. fraction eluted by i>-glucose; C. commercially
available Concanavalin A (Pharmacia. Tubingen) The protein pattern was determined by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate (SDS). Polyacrylamide concentration 8%.
Binding of lectins: The binding was determined by incubation of the polymer (10 mg) with increasing concentrations of
the lectins (0.13 mg/ml-2.6 mg/ml) in ammonium acetate
(0.1 mol/l, pH 6.5) for 2 h a t 22 "C. After the incubation, the
polymer was sedimented and the protein content of the supernatant was determined. Bovine serum albumin was used
as control for unspecific adsorption: this adsorption was negligibly small.
Received: May 22, 1979
supplemented- July 27, 1979 and
April 8, 1980 (2 492 IE]
German version: Angew Chem. 92. 547 (1980)
[ I ] de Konmck, Justus Liebigs Ann. Chem. 15. 258 (1835).
[21 C Zemplen. R. Bognur, Ber. Dtsch. Chem. Ges. 75, 1040 (1942).
131 R. Kinne. Curr. Top. Membr. Transp 8. 209 (1976); R. Kinne, H. Murer. E.
Kinne-Suffrun. M. Thees. G. Sachs, J. Membr Biol. 21. 375 (1975): A. Klip. S.
Grinstein. G Semenra. ibid 51, 47 ( 1979).
141 M. Dubois. K. A. Giles, J. K. Hamilton, P. A . Rebers. E Smirh, Anal. Chem.
2s. 350 (1956).
IS] H:G. Eltas. Makromolekule. Huthig & Wepf, Base1 1972, pp. 714ff. 733ff
Collision Induced Fragmentation of
Alkylideneammonium Ions[**]
tion to their molecular weights, structural details of alkylideneammonium salts can be determined.
Previously, such salts could not be investigated mass spectrometrically since the ionic structure does not remain intact
on transfer of the salt into the gas phase (cf. [Ih1). With the
field desorption (FD) method, however, alkylideneammonium ions can be generated intact in the gas phase from the
corresponding salts. While the masses of the cations can thus
be determined directly, and the occurrence of cluster ions
permits determination of the molecular weights of the salts,
no structural details are obtained from the FD-mass spectrum, since the field-desorbed alkylideneammonium ions d o
not decompose within the mass spectrometric time scale owing to the low excitation energyl2I.
A possibility of producing fragmentation is offered by the
collisional activation (CA) method. The highly accelerated
ions collide inelastically with a neutral target gas, thereby
experiencing a n excitation separated in space and time from
the actual ion-formation process, which leads to fragments of
the ions to be investigated (cf. l3]). These fragment ions are
generated in the first field-free region of a double-focusing
mass spectrometer and recorded with a linked-scan deThe FD-CA mass spectra of the three isomeric alkylideneammonium ions (1)-(3) (Fig. l), generated by field desorption from the t e t r a f l u o r o b o r a t e ~differ
~ ~ ~ , primarily in the intensity ratios of the main fragmentations. The ion (1) decomposes, predominantly by heterolysis of the N-Chenlyl bond,
into a C7@ ion ( m / e = 9 1 ) . This charge transfer from the N
atom to the aromatic ring is also observed in ion (2). but the
formation of the C,HY ions from (2) and from (3) is associated with a hydrogen migration. Apparently, less energy is
required for the elimination of N-methylmethyleneamine
from ( I ) than in the case of the ions (2) and (3) since the proportion of competing decompositions in (2) and (3) increases
considerably. In the CA spectrum of (2) the [ M e - CH,] ion
( m / e = 118) reaches cu. 60% of the intensity of the C,Hp ion
and appears as base peak in the spectrum of the ion (3).
The N,N-dimethylaminotropylium structure, both in the
case of ion (3) as well as partially after isomerization of (2), is
proven by the occurrence of more intense signals at m / e = 90
and 89 in comparison to the C A spectrum of ( 1 ) . The formation of these ions can be explained in terms of homolysis of
the C-N bond and N,N-dimethylamine elimination, respectively. As in the case of phenylalkyl-substituted ammonium
ions[41the elimination of 52 mass units ( m / e = 82) is observed
with ions (1) and (2) and of 26 mass units (m/e=108) with
ion (3). Despite the low signal intensity these fragments provide information about the charge localization. Positively
charged aromatic systems eliminate one molecule of acetylene, both as is well-known under electron-impact as well as
under CA conditions; uncharged benzene rings, on the other
hand, directly lose two acetylene molecules in the form of a
neutral fragmentation under CA conditions.
By Hans J. Veifhl-1
Alkylideneammonium ions play a special role in organic
synthesis and as natural products (cf. ""1). We report here on
a mass spectrometric method (FD-CA) with which, in addi-
['I
Dr. H. J. Veith
Institut fur Organische Chemie und Biochemie der Technischen Hochschule
Petersenstrasse 22. D-6100 Darmstadt (Germany)
[**I
Collision Induced Fragmentations of Field Desorbed Cations. Part 4. This
work was supported by the Deutsche Forschungsgemeinschaft; we thank Herr
M. Fischer for help with the experiments.-Part 3: H. J. Veirh, Adv Mass Spectrom. K. in press.
Angew. Chem. Inf. Ed Engl. I9 (1980) No. 7
121
Ill
131
Besides its use in structural analysis, the FD-CA method
opens up new entries to comparative studies on gas-phase
fragmentations of alkylideneammonium ions, which are gen-
0 Vedug Chemie, GmbH. 6940 Weinheim, 1980
0570-0833/80/0707-0541
$ 02.50/0
541
134
91
118
I00
1.) I
So m/e
-
I
91
loo
4
100
Fig. 1. FD-CA mass spectrum a ) of the N-benzyl-N-methylmethyleneammonium
ion (1). b) of the N.N-dimethylbenzylideneammonium ion (2). c) of the N,N-dimethylaminotropyliumion (3).
BF,o
Table I . Section of the E l mass spectrum (70 eV) of (4) and of the FD-CA mass
spectrum of (6): intensities in [%I.
m/e
148
146
134
132
105
98
91
84
FD-CA-MSof(6)
€1-MS of (4) [a]
15
49
16
0.5
31
3
I3
16
I0
1
7
8
100
II
I00
07
[a] The abundances are normali7,ed to m / e = 105e 100'fi. m / e = 1 9 0 s 140%.
R = n-C*H@
( h ) , m l e = 105
Scheme 1. Main fragmentation of the methyleneammonium ion a and (6). which
was generated by u-cleavage in an electron-impact ionized molecular ion of (4)
or from the tetrafluoroborate (5) under FD-CA conditions.
erated from the molecular ions of alkylamines by a-cleavage
after electron impact (EI) excitation or under FD conditions
from alkylideneammonium salts.
Under EI conditions a-cleavage of the molecular ion of
N,N-bis(6-phenylethy1)butylamine (4) affords the methyleneammonium ion a (m/e= 190), which, after homobenzylic
heterolysis with loss of N-methylenebutylamine, decomposes
into the ion b ( m / e = 105) (cf. Scheme 116]).This reaction, accompanied by a charge transfer from the N atom to the benzene ring, is likewise the main reaction in the collision-induced decomposition of the ion (6) liberated under FD conditions from the salt (5). From the intensities of the C7H7
ions (m/e=91) generated from (4) and (6), which are consistent within the experimental error, it follows that the C7H7
ions recorded in the EI mass spectrum of compound (4)are
formed by secondary fragmentation from the methyleneammonium ion Q and not, as would appear at first sight, by
cleavage of a benzyl bond in the molecular ion of (4). Further agreement between the EI and the FD-CA spectrum has
been established for the propene and butene eliminations
(m/e = 148 and 134, resp.), well-known in electron-impact
mass ~pectrometry"~
(cf. Table 1).
In contrast to the electron-impact fragmentations, in the
CA spectrum of (6) signals appear for the elimination of propane ( m / e = 146), butane (m/e= 132), toluene ( m / e = 98).
and ethylbenzene ( m / e = 84), the more intense signals hcirrg
recorded for the cleavage of ally1 bonds. As D-labeling experiments show, the H atom to be eliminated with the leaving
542
0 Verlug Chemie. CmbH. 6940 Weinherm, 1900
group for a n alkane elimination does not originate from the
alkylideneammonium function. On the basis of findings with
alkyl-substituted methyleneammonium ions[x1,a cycloalkylmethyleneammonium structure is postulated for the ions
formed in the alkane elimination. While alkane eliminations
under EI conditions are only observed to a small extent-if
at all-as secondary fragmentations of alkylamines, they occur as collision-induced main fragmentations in field desorbed alkylideneammonium ions. Furthermore, alkane
eliminations are also recorded as collision induced main
fragmentation reactions in other "closed shell" ions, e. g. in
quaternary ammonium i o n ~ ' ~ . ' "and
~ in the protonated amineslYblaccessible by chemical ionization.
Received: October 3. i979 [Z 493 IEJ
revised: April 24, 1980
German version: Angew. Chem. 92. 548 (1980)
Ill a) H. Bohme, H G. Viehei Iminium Salts in Organic Chemistry. Wiley, New
York 1976 b) R. Merenyr in [la], Part I, p. 23.
[2] H. J. Veith, Org. Mass Spectrom. 11, 629 (1976).
[3] a ) K. Leusen, H. Schwarz. Angew. Chem. 88, 589 (1976); Angew. Chem. Int.
Ed. Engl. 15, 509 (1976); K. Leusen: Fundamental Aspects of Organic Mass
Spectrometry. Verlag Chemie. Weinheim 1978.
141 M. Fischer, H. J. Veirh, Helv. Chim. Acta 61, 1038 (1978).
IS] The methyleneammonium salts are obtained by condensation of the corresponding sec-ammonium tetrafluoroborates with gaseous formaldehyde; for
the preparation of N,N-dimethylbenzylideneammonium tetrafluoroborate
see: T. R. Keenan. N . J. Leonard, J. Am. Chem. SOC.93.6576 (197 I): the preparation of N,N-dimethylaminotropyliumtetrafluoroborate: E Haug, B.
Fohlisch, Chem. Ber. 104. 2338 (1971).
[6] a ) W. J. Richter. W. Verrer, Org. Mass Spectrom. 2, 781 (1969): b) P. A. Weibe/, M. Hesse. Helv. Chim. Acta 56. 2460 (1973).
[71 a ) R. S. Cohlke. F. W McLnfferty. Anal. Chem. 34, 1281 (1962); h) C. Djerassi, C Fenselau. J. Am Chem. SOC.87. 5752 (1965).
[8] H J. Meyer, Staatsexamensarbeit, Technische Hochschule Darmstadt 1979
H . J. Veifh,unpublished.
191 a) H. H. Gierlrch, F. W. RoJIgen, I;. Borchers. K.Levsen, Org. Mass Spectrom.
12, 387 (1977); b) M L. Sigsbv. R. J. Day, R. G. Cooks, ibid. 14. 556
(1979).
0570-0833/R0/0707-0542
S 02.50/0
Angew. Chem. I n l . Ed. Engl. 19 (1980) No. 7
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