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An Extraordinarily Violent Molecular Dissociation The Unprecedented Kinetic Energy Release in the Decomposition of HONF+ a Singly Charged Metastable Ion.

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The mass spectrum was obtained for positive and negative secondary ions in a range
of 0-100. 5. The degree of substitution of the gel was monitored by adding pCimL-' n-[l-'4C]-butanethiol (NEN)[14] or n-[I-"TI-butylamine (Hoechst
AG) to the coupling mixture (as described in ref.[22]). The amount of coupled alkyl
residues was determined by liquid scintillation counting[22] after acid hydrolysis
of the n-[l-'4C]-butyl-labeled agarose (colorless hydrolysate). Analyses were done
in triplicate.
Received: July 6, 1993 [Z6200IE]
German version: Angen,. Chem. 1994, 106, 126
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An Extraordinarily Violent Molecular
Dissociation : The Unprecedented Kinetic
Energy Release in the Decomposition of
HONF', a Singly Charged Metastable Ion**
Fulvio Cacace, Felice Grandinetti,* and Federico Pepi
The kinetic energy associated with the separation of the fragments from the decomposition of a metastable species constitutes an integral component of the reaction dynamics and is
therefore of fundamental interest.['] In the case of charged species the translational energy of the fragments can be measured
with experimental techniques such as mass-analyzed ion kinetic
energy (MIKE) spectrometry,[' - whose application has provided a large amount of data and has proved a useful tool in the
determination of the structures of ions.[6'
The kinetic energy release (KER) spans over several orders of
magnitude, from a few hundredths of the one eV to large ener[*I
Dr. F. Grandinetti,"' Prof. Dr. F. Cacace, Dr. F. Pepi
Universita di Roma "La Sapienza"
P. le Aldo Moro, 5 1-00185 Roma (Italy)
Telefax: Int. code + (6)4991-3888
['I Permanent address:
Dipartimento di Scienze
Ambientali, Universita della Tuscia, V.S.C. De Lellis,
1-01100 Viterbo (Italy)
This work was supported by the Italian Minister0 dell'Universita e della
Ricerca Scientifica e Tecnologica (MURST) and Consiglio Nazionale
Ricerche (CNR).
Angew. Chem. Int. Ed. Engl. 1994, 33, No. 1
gies of 10eV and above, measured in the decomposition of
certain multiply charged ions. The latter, however, generally
undergo charge-separation reactions, and their KER is not simply related to the intrinsic dynamics of the dissociation reaction,
since most of the translational energy of the charged fragments
arises from their coulombic repulsion.[7] The KER associated
with the decomposition of a singly charged ion provides a more
direct insight into the ,potential energy hypersurface of the decomposing species.
A survey of the experimental results, customarily expressed
by the Tli2energy calculated from the metastable peaks widths
at their half heights, indicates that the KER associated with the
decomposition of singly charged ions falls in general well below
2 eV, rarely exceeding 1.5 eV. This is hardly surprising, since
large translational energies of the fragments require a combination of several factors, including a much higher stability of the
fragments with respect to their parent, a high barrier for the
dissociation, and a partition of the energy released that favors
the translational over the rotational and/or internal degrees of
freedom of the fragments.
The loss of HX from simple ions containing the (X-NY)H+ moiety (X, Y = 0 or F) which leads to metastable ions
(N-Y)' is characterized by an appreciable barrier for the reverse reaction and by a large KER, for example in the case of
protonated nitric acid,['] nitrogen trifl~oride,[~]
methyl" '1 and
ethyl nitrate.["]
A recent theoretical study of a closely related system has
pointed to the large exothermicity of the unimolecular dissociation (shown in [Eq. (a)]) estimated to be 68 kcalmol-' (2.95 eV)
HF + NOf
at the (CISD + Q) (CISD + Q = configuration interaction lirnited to single and double excitations corrected for unlinked
quadruple excitations) level of theory with a double-zeta plus
polarization quality basis set.["] This has prompted a reinvestigation of the system at the GAUSSIAN-1 level of theory,['31
aimed at evaluating the barrier for dissociation [Eq. (a)]. The
results summarized in Table 1, and illustrated in Figures 1 and
2 agree quite well with those from the previous theoretical study
with regard to the exothermicity of the dissociation [Eq. (a)] and
indicate, in addition, that the barrier for the dissociation process, which requires molecular reorganization, is as high as
24.2 kcalmol-'. The latter is an interesting finding, showing
that the total energy released in the decomposition of those
HONF' ions which are sufficiently excited to overcome the
barrier exceeds 80 kcalmol-', some 3.5 eV. Furthermore, the
nature of the NO' and HF fragments suggests that only a
limited fraction of the energy released should be partitioned in
Table 1. GAUSSIAN-I absolute energies [Hartree] and relative stabilities, A E
[kcalmol-'1 of the investigated (F,H,N,O)+ ions and their fragments.
Species ( n ) [a]
B E (298 K)
1 (0)
2 (0)
- 229.65430
3 (0)
4 (0)
TSI (1,
TS2 (1,
TS4 (1,
-1821 cm-')
- 229.6101 5
- 229.61143
- 229.57292
- 229.61207
- 100.34679
[a] n = number of imaginary frequencies; frequency.
Q VCH Verlagsgesellschaft mbH, 0-69451 Weinheim, 1994
0570-0833/94~0101-0123d 10.00+ ,2510
1 012
as required, excess internal energy. In fact, apart from the evidence provided by the formation route, the H-0-N-F connectivity of the ions obtained from Equation (d) is demonstrated by
their collisionally activated dissociation (CAD) spectrum, which
displays signals for the fragments NO' (56.2 YO),NF' (31 . l YO),
NOH+ (9.7%). OH+ (1.8 YO),
and N + (1.2%). The fact that the
HONF' ions are formed in an excited state is suggested by the
considerable (1.36 eV) KER of dissociation [Eq. (d)], since it is
most reasonable to assume that a proportionately large amount
of energy is deposited into the internal degrees of freedom of the
HONF' fragment. Moreover, a fraction of the energy of the
ionizating electrons may contribute to excited HONF' ions.
The MIKE spectrum of the HONF' ions obtained from the
sequence (b)-(d), displays the single transition [Eq. (a)], whose
KER (TIi2= 2.68 & 0.1 eV) fully meets, and perhaps exceeds,
the theoretically based expectations, being unprecedented for
the decomposition of a metastable monocation (Fig. 3). From
1.228 8,
TS 1
H 0.~u.8
Fig. 1. MP2(FU)/6-31G* optimized geometries (see Experimental Procedure) 01
the species of interest.
E [kcal mol-'1
Fig. 3. The NO' peak from the decomposition of the metastable HONF' [Eq. (a)].
The kinetic energy of the precursor ion IS 7921 eV. I = relative intensity.
Fig. 2 . Schematic energy profile of dissociation of HONF' [Eq. (a)]
their rotational and/or internal degrees of freedom, which justifies the expectation of an exceptionally large KER.
In order to verify the above-mentioned theoretical predictions
experimentally, a suitable route must be found to ions of the
required H-0-N-F+ structure, containing excess internal energy
sufficient to allow decomposition according to Equation (a).
HONF' ions have been successfully obtained upon ionization
of a NF,/H,O mixture, under chemical ionization (CI) conditions. A plausible explanation for the formation of HONF+ is
based on the reaction sequence summarized in Equations
NF: + F' + 2 e
+ H 2 0 * [H20-NF2]:x,
the study of a large number of simple ions, it has been found that
TI1 2 generally exceeds the mean kinetic energy release by 1520%.[51Under this assumption, the mean kinetic energy of the
fragments would account for 60 to 70% of the total energy
released from process (a) which in Figure 2 corresponds to the
energy difference of about 3.57 eV, between TS2 and the separate NO' and H F fragments; the remaining fraction is contained in their rotational and internal degrees of freedom. The
narrow gaussian component of Figure 3. centered at m / z = 30,
can be ascribed to the decomposition of metastable ions4
formed from the isomerization of HONF' ions, and stabilized
by collisional deactivation in the ion source. From Figure 2, and
consistent with the MIKE spectrum, the fragmentation of 4 into
NO+ and H F is a simple bond cleavage, occurring with no
energy barrier, for the reverse reaction.
In conclusion, apart from the intrinsic interest of (X-NY)H+ systems, several of which play an important role in such
fields as chemical reactivity and catalysis. environmental, flame,
and atmospheric chemistry, the present results underline the
powerful interplay between high-level calculations and MIKE
spectrometry in gathering direct insights into relevant details of
the potential energy hypersurface of simple ions in the gas
+ HF
Esperimenrul Procedure
The adduct from the highly exothermic reaction (c) dissociates yielding HONF' ions of the desired structure, containing.
VC H VeriagJgedisrhaft m b H , 0.69451 Weinhem, 19Y4
MIKE and CAD spectra of the (F.H.N.0)' ions were recorded by using a ZAB-2F
mass spectrometer from VG Micromass Ltd. Typical operating conditions of the CI
0570 .0833~94/0101-0124$ 10.00+ .25/0
Angcic. Chem. Int. Ed.
Enxi. 1994, 33. N o . 1
source were as follows: bulk gas pressure 0.1 -0.2 Torr, source temperature 180°C.
emission current 1 mA, repeller voltage 0 V, electron energy 100 eV. The MIKE
spectra were recorded by using an accelerating potential of 8 KeV at a typical energy
resolution of 8 x lo3, and represent the average of at least 100 scans. CAD spectra
were taken by admitting He into the collision cell at such a pressure to reduce the
main beam intensity to 30% of its initial value.
Compu/utronal Delaib: Ab initio quantum-mechanicalcalculations were performed
by using a RISC/6000 version of the GAUSSIAN 92 program package [14]. The
standard internal 6-31G* [ISa], 6-311G** [15b], 6-311 G** [16], and 6-311G**
(2df) [16] basis sets were employed. Geometry optimizationswere performed in the
full space of the coordinates by analytical gradient-based techniques [17], in the
framework of the second-order Meller-Plesset perturbation theory [lS], with the
6-31G* basis set. The MP2 method was used with full (FU) electron correlation
(including inner-shell electrons). The geometries obtained (Fig. 1) in this way are
denoted by MP2(FU)/6-31G*. The corresponding vibrational frequencies were
computed for all of the species investigated, in order to characterize them as true
minima, transition structures, or higher order saddle points on the potential energy
hypersurface. The zero-point energy of the various species was accounted for in this
way. The GAUSSIAN-1 procedure, as outlined in ref. [13]. was employed to obtain
the total energies of the investigated species.
(S)-2contain two salicylaldehyde residues in a chiral binaphthyl
~ y s t e m . [ ~The
. ~ ] synthesis of 2,2'-dihydroxy-I ,l'-binaphthyl3,3'-dialdehyde (2) proceeds by 1,l'-coupling of the commercially available 3-hydroxy-2-naphthoic acid, acetylation of the phenolic OH groups, reduction of the acid chloride, and cleavage of
Enanthe protecting groups, in an overall yield of about 20 YO.[~I
tiomeric resolution takes place at the 2,2'-dihydroxy-I ,I1-binaphthyl-3,3'-dicarboxylic acid stage.[51
Received: June 15, 1993 [Z 6143 IE]
German version: Angew. Chem. 1994, 106, 104
[l] K. C. Smyth, T. W. Shannon, J. Chem. Phys. 1969, 51. 4633.
[2] J. H. Beynon, R. G. Cooks, Res. Dev. 1971, 22, 26.
[3] J. H. Homes, A. D. Osborne, In/. .
Mass Spectrum. Ion Phys. 1979, 32, 35.
[4] J. E. Szulejko, A. Mendez Amaya, R. P. Morgan, A. G. Brenton, J. H. Beynon,
Proc. R. Soc. London A 1980, 373, 1.
[5] B. A. Runpf, P. J. Derrick, Int. J. Mass. Spectrum. Ion Processes 1988,82, 239.
161 J. L. Holmes, Org. Mass Spectrum. 1985, 20, 169.
[7] B. Brehm. G. De Frenes, Adv. Mass Spectrum. 1979, 8, 138.
[S] F. Cacace. M. Attind, G. de Petris, M. Speranza. J. Am. Chem. Soc. 1990, 112,
191 F. Grandinetti. J. HruSik, D. Schroder, S. Karrass, H. Schwarz, J. A m . Chem.
Soc. 1992, 114. 2806.
[lo] G. de Petris. Org. Mass Spec/rom. 1990, 25, 83.
[ l l ] G. de Petris. Orz. Mass Spectrum. 1990, 25, 557.
[12] C. Meredith, R. A. D a y , H. F. Schaefer 111, J. Chem. P h w . 1990, 93, 1215.
[I31 J. A. Pople, M. Head-Gordon, D. J. Fox, K. Raghavachari, L. A. Curtis, J.
Cliem. P h w . 1989, 90, 5622.
[141 M. J. Frisch. G. W. Trucks, M. Head-Gordon, P. M. W. Gill, M. W. Wong, J. B.
Foresman. B. G. Johnson, H. B. Schlegel, M. A. Robb, E. S. Replogle, R.
Gomperts, J. L. Andres, K. Raghavachari, J. S. Binkley, C. Gonzalez, R. L.
Martin. D. J. Fox, D. J. Defrees, J. Baker, J. J. P. Stewart, J. A. Pople, Gaussian
92. Revision A, Gausslan, Inc., Pittsburgh, PA, 1992.
[IS] a) P. C. Hariharan, J. A. Pople, Chem. Phjs. L e f t . 1972. 66, 217; b) R. Krishnann, J. S. Binkley. R. Seeger, J. A. Pople, ihid. 1980, 72, 4244.
[16] M . J. Frisch. J. A. Pople, J. S. Binkley, Chem. Phys. Lett. 1984, X U , 3265.
[17] H. B. Schle_eel,J1 Comput. Chen?. 1982, 3 , 214.
[18] C. M d e r , M. S. Plesset, Phys. Rev. 1934, 46, 86.
The condensation of salicylaldehyde (1) with the difunctionalized amine 1,2-diaminoethane yields the known tetradentate
salen ligand. In contrast to the monofunctionalized aldehyde 1,
the binaphthyl derivatives 2 are difunctionalized, and should
therefore react with (R,R)-1,2-diamino-l ,2-diphenylethaner6,71
(3) to give polymeric Schiff bases. This supposition is confirmed
by the reaction of (R)-2with 3, but not by the reaction of (S)-2
with 3, in which two molecules of dialdehyde undergo condensation with two molecules of diamine to form the 24-membered
macrocycle 4. Compound 4 is a yellow solid that may be purified
by chromatography on silica gel.ISIAn m/z value of 1037 in the
mass spectrum confirms the above formulation. Obviously during the condensation of (R)-2 with 3, the ends of the growing
chain are so far apart from one another that the anticipated
polymer forms, whereas in the reaction of ( 9 - 2 with 3, the
24-membered ring closes.
Ph ti H P h
i l ;/
2 tizN
Dialdehyde + DiaminePolymer or Macrocycle?
Henri Brunner* and Hubert Schiessling
Dedicated to Projessor Otto J. Scherer
on the occasion o j his 60th birthday
Schiff bases derived from salicylaldehyde (1) and primary
amines are common chelating ligands in complex chemistry."]
Optically active salicylaldiminates have, for some time, also
been employed successfully in enantioselective catalysis (e.g. cyclopropanation).[21The optically active compounds (R)-2 and
[*] Prof. Dr. H. Brunner, Dipl.-Chem. H. Schiessling
Institut fur Anorganische Chemie der Universitat
D-93040 Regensburg (FRG)
Tekfax: Int. code + (941)943-4439
Angew. Chem. I n / . Ed. EngI. 1994. 33, N o . 1
A simple enantiomeric separation exploits the observation
that with the given optically active diamine 3, only the S enantiomer of aldehyde 2 gives rise to a macrocycle, whereas the R
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