Solid-State Structure of Protonated Ketones and Aldehydes

Article abstract of DOI:10.1002/anie.201710263

Protonated carbonyl compounds have been invoked as intermediates in many acid-catalyzed organic reactions. To gain key structural and electronic data about such intermediates, oxonium salts derived from five representative examples of ketones and aldehydes are synthesized in the solid state, and characterized by X-ray crystallography and Raman spectroscopy for the first time. DFT calculations were carried out on the cations in the gas phase. Whereas an equimolar reaction of the carbonyl compounds, acetone, cyclopentanone, adamantanone, and acetaldehyde, with SbF₅ in anhydrous HF yielded mononuclear oxonium cations, the same stoichiometry in a reaction with benzaldehyde resulted in formation of a hemiprotonated, hydrogen-bridged dimeric cation. Hemiprotonated acetaldehyde was obtained when a 2:1 ratio of aldehyde and SbF₅ was used. Experimental and NBO analyses quantify the significant increase in electrophilicity of the oxonium cations compared to that of the parent ketones/aldehydes.

Full text of DOI:10.1002/anie.201710263

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Accepted Article
Title: Solid-State Structure of Protonated Ketones and Aldehydes
Authors: Michael Gerken, Stacey D. Wetmore, and Daniel Stuart
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10.1002/anie.201710263
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Solid-State Structure of Protonated Ketones and Aldehydes
Daniel Stuart, Stacey D. Wetmore, and Michael Gerken*
In memoriam George A. Olah
Abstract: Protonated carbonyl compounds have been invoked as
intermediates in many acid-catalyzed organic reactions. To gain key
structural and electronic data about such intermediates, oxonium salts
derived from five representative examples of ketones and aldehydes
are synthesized in the solid state, and characterized by X-ray
crystallography and Raman spectroscopy for the first time. DFT
calculations were carried out on the cations in the gas phase.
Whereas an equimolar reaction of the carbonyl compounds, acetone,
cyclopentanone, adamantanone, and acetaldehyde, with SbF5 in
anhydrous HF yielded mononuclear oxonium cations, the same
stoichiometry in a reaction with benzaldehyde resulted in formation of
a hemiprotonated, hydrogen-bridged dimeric cation. Hemiprotonated
acetaldehyde was obtained when a 2:1 ratio of aldehyde and SbF5
was used. Experimental and NBO analyses quantify the significant
increase in electrophilicity of the oxonium cations compared to that of
the parent ketones/aldehydes.
A small number of protonated ketones has been studied in the
solid state. Structural studies of monoprotonated ketones are
limited to a group of cyclopropylcarbinyl derivatives which were
part of investigations of the stabilization of a positive charge by
cyclopropyl groups and in homoaromatic systems.[2] In one
attempt to isolate the 2-hydroxyhomotropylium benzannelated
cation, the X-ray crystal structure showcased a hemiprotonated
cation consisting of two deuterium-bridged ketones.[3] In a study
involving the isolation of solvated protons in organic oxygen-
donor solvents, the X-ray crystal structure of hemiprotonated
benzophenone was determined.[4] Computational studies using
the B3LYP/6-31++G(d,p) level of theory have been carried out on
the carbonyl bases R2C=O (R = F, H, CH3), investigating the
changes in bond lengths and vibrational frequencies upon
protonation.[5] Semi-empirical studies in conjunction with mass
spectrometric measurements have been used to study the
geometric properties and stability of protonated acetone
clusters.[6]
Protonated ketones and aldehydes are key intermediates in
many organic reactions. Ground-breaking work by Gillespie and
Olah proved by NMR spectroscopy that these cationic
intermediates can be stabilized in superacidic solutions at low
temperatures (LT).[1] One of the first ketones to be studied by 1H
NMR spectroscopy was the conjugate acid of acetone, with a pKa
of −7.3, giving rise to a 1H resonance of the C=OH+ group at 14.45
ppm.[1a] Synthesizing these protonated compounds requires a
proton source from a superacidic medium such as HSO3F-SbF5
(“magic acid”) or HF/SbF5. Two resonance structures can be
written for protonated ketones and aldehydes: the oxonium and
hydroxycarbenium cation structures (Scheme 1). The highly
Currently, no solid-state studies of protonated aldehydes have
been reported. Infrared photodissociation spectroscopy along
with quantum-chemical calculations was used to probe
protonated benzaldehyde.[7] Excited state and optimized
geometry calculations showed the lowest-energy configuration to
be the E-configuration.[8] Mass spectrometry studies, along with
gas-phase calculations, have suggested that formaldehyde and
acetaldehyde form hydrogen-bridged dimers, (RCHO)2H+ (R = H
or CH3).[9] Attempts to synthesize protonated formaldehyde in the
solid state have been unsuccessful and instead
[H2C=O−CH2OH]+ salt was obtained in HF/SbF5 at −78 °C.[10]
a
While exploring the interactions of [SF3]+ with ketones in our
studies of the mechanisms of deoxofluorination reactions, an
equimolar reaction between [SF3][AsF6] and 2-adamantanone (1)
in anhydrous hydrogen fluoride (aHF) resulted in protonation of
the carbonyl group and the synthesis of the [AsF6]− salt of [1−H]+.
The protonation of the ketone can be explained by the superacidic
nature of the [SF3][AsF6]/aHF system [Eq. (1)].
1
deshielded H resonances between 13 and 15 ppm,[1b-d] as well
as the observation of the E- and Z-stereoisomers of protonated
aldehydes and unsymmetrically substituted ketones[1c,d] provides
strong evidence that the oxonium resonance structure is the
primary resonance existing in solution.
[SF3][AsF6] + 2HF ⇌ SF4 + [H2F][AsF6]
(1)
In targeted reactions, salts of protonated ketones and aldehydes
were isolated using stoichiometric amounts of either [SF3][AsF6]
or SbF5 in aHF. Reactions using AsF5 were attempted, but led to
inaccurate stoichiometric ratios, which resulted in reduced
stability of the product, likely due to oxidation of the organic
substrate by excess AsF5.
Reactions of [SF3][AsF6] with 1 and cyclopentanone (2) in aHF
at −78 °C yielded the hexafluoroarsenate salts of [1−H]+ and
[2−H]+, respectively, according to Eq. (2). The salt of [1−H]+ was
stable at room temperature (RT) for 20 min before turning pale
yellow, whereas [2−H][AsF6] was more stable and remained a
white powder for upwards of 1 h. The bands in the LT Raman
spectra showed no change in frequency; however, increasing
Scheme 1. Resonance structures for protonated ketones.
[*]
D. Stuart, Prof. Dr. S. D. Wetmore, Prof. Dr. M. Gerken
Canadian Centre for Research in Advanced Fluorine Technologies
and Department of Chemistry and Biochemistry
University of Lethbridge
4401 University Drive, Lethbridge, AB T1K 3M4 (Canada)
E-mail: michael.gerken@uleth.ca
Supporting information for this article is given via a link at the end of
the document.((Please delete this text if not appropriate))
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10.1002/anie.201710263
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fluorescence was observed in the spectral baseline the longer the
sample was left at RT.
[SF3][AsF6] + O=R + HF →aHF [HO=R][AsF6] + SF4
(R = C10H14 (1), C5H8 (2))
(2)
Hexafluoroantimonate salts can be obtained via the reaction
of ketones with 1 molar equivalent of SbF5 in aHF. The reaction
of 1, 2, and acetone (3) with SbF5 in aHF at −78 °C resulted in
immediate reactions producing white powders of [1−H][SbF6],
[2−H][SbF6], and [3−H][SbF6], respectively, according to Eq. (3).
[3−H][SbF6] proved to be the most stable salt among those
studied, lasting 24 h at RT before LT Raman spectroscopy
showed some fluorescence in the baseline.
SbF5 + O=R + HF →aHF [HO=R][SbF6]
(R = C10H14 (1), C5H8 (2), C(CH3)2 (3))
(3)
The crystal structures of [1−H][AsF6], [2−H][AsF6],
[2−H][SbF6], and [3−H][SbF6] (Figure 1) clearly show the
protonation of 2-adamantanone, cyclopentanone, and acetone,
which results in an increase in the C=O bond lengths ([1−H]+
1.274(2) Å; [2−H]+ 1.266(3)/1.267(2); [3−H]+ 1.271(3) and
1.273(3) Å) compared to their respective parent ketones (1
1.215(3) Å;[11] 2 1.21909(15) Å;[12] 3 1.208(3) Å[13]) (Table 1). The
C=O bond lengths of the protonated compounds, however,
remain significantly shorter than the average C−O single bond in
an alcohol (1.432(13) Å).[14] As confirmed by DFT calculations at
the B3LYP/aug-cc-pVTZ level of theory (Table 1), a significant
decrease in the CC=O−C bond lengths is observed for the
protonated ketones relative to the parent compounds.[11-13]
Whereas slightly longer CC=O−Ccis bonds are calculated than for
the CC=O−Ctrans bonds, the experimental CC=O−C bond distances
in each protonated ketone are the same within 3σ. The oxonium
cations [1−H]+ and [2−H]+ in the [AsF6]− salts exhibit strong
hydrogen bonds to a F atom of the [AsF6]− anion. The O---F
distance in [1−H]+ (O---F(1) 2.6233(16) Å) is larger than [2−H]+
(O---F(1) 2.560(3) Å), however, both are comparable to previously
reported hydrogen bonds in protonated cyclopropylcarbinyl
derivates (O---F 2.557(6) and 2.601(6) Å).[2d] These hydrogen
bonds result in an elongation of the As−F(1) distance and an
ensuing distortion of the idealized octahedral geometry of the
anion. Unlike [1−H]+ and [2−H]+ salts, the X-ray crystal structure
Figure 1. Thermal ellipsoid plots of a) [1−H][AsF6], b) [2−H][AsF6], c)
[3−H][SbF6]. Thermal ellipsoids are set at the 50% probability level.
Table 1. Selected Experimental and Calculated Bond Lengths (Å) of Oxonium
Cations [1−H]+, [2−H]+, and [3−H]+ as well as the Parent Ketones 2-
Adamantanone (1), Cyclopentanone (2), and Acetone (3).
1
[1−H]+
exptl [b]
calcd [e]
1.213
1.524
1.524
exptl
calcd [e]
1.285
1.468
1.464
C=O
CC=O−Ccis
1.215(3)
1.5176(16)
1.5176(16)
1.274(2)
1.469(2)
1.472(2)
2.6233(16)
[a]
[a]
CC=O−Ctrans
O---F
2
[2−H]+
exptl
[AsF6]−; [SbF6]−
exptl [c]
calcd [e]
calcd[e]
1.2109(15)
1.2148(15)
1.5078(18)
1.5103(14)
1.5111(15)
1.5103(14)
C=O
1.205
1.528
1.528
1.266(3); 1.267(2)
1.275
1.476
1.470
[a]
CC=O−Ccis
1.473(3); 1.481(2)
1.469(3); 1.477(2)
[a]
CC=O−Ctrans
O---F
2.560(3); 2.6043(16)
3
[3−H]+
exptl [d]
calcd [e]
exptl
calcd [e]
̅
of [3−H][SbF6] crystallized in the P 1 space group with two
1.208(3)
1.209(3)
1.478(4)
1.485(4)
1.485(4)
1.486(4)
1.271(3) O(1)−C(2)
1.273(3) O(2)−C(5)
1.467(3) C(2)−C(3)
1.469(4) C(5)−C(6)
1.459(4) C(1)−C(2)
1.464(4) C(4)−C(5)
2.597(2)
C=O
1.210
1.277
crystallographically unique cations and three different anion
environments in the unit cell. One of the three [SbF6]− anions does
not have any significant contacts with the oxonium cation,
whereas the other two anions accept one or two hydrogen-bonds
from [3−H]+ cations.
The DFT-optimized gas-phase geometries of the oxonium
cations [1−H]+, [2−H]+, and [3−H]+, as well as their parent ketones,
generally show excellent agreement with the experimental values.
The C=O bond lengths are slightly overestimated in the
protonated compounds. Hydrogen bonding in the solid state
contributes to the elongation of the O−H bond and shortening of
the C=O bond compared to the gas-phase structures.
[a]
CC=O−Ccis
1.514
1.514
1.470
1.466
[a]
CC=O−Ctrans
O---F
2.619(2)
[a] Refers to the carbon cis or trans to the proton on the oxygen. [b] from
Ref. 11; [c] from Ref. 12; [d] from Ref. 13; [e] DFT calculations at the
B3LYP/aug-cc-pVTZ level of theory.
Reactions of benzaldehyde (4) with SbF5 in aHF yielded the
[SbF6]− salt of the hemiprotonated, hydrogen-bridged dimeric
[4−H−4]+, even when a one molar equivalent of SbF5 was used
[Eq. (4)]. No evidence for the monoprotonated [4−H]+ cation was
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10.1002/anie.201710263
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obtained. Reacting acetaldehyde (5) with SbF5 in 2:1 and 1:1
molar ratios, the [5−H−5]+ and [5−H]+ cations were isolated,
respectively, in the solid state as the [SbF6]− salts [Eq. (4) and (5)].
The three salts, [4−H−4][SbF6], [5−H−5][SbF6], and [5−H][SbF6],
were isolated as white powders and characterized by Raman
spectroscopy at LT, proving to be unstable upon warming to RT.
The [5−H−5][SbF6] salt was only obtained in admixture with
[5−H][SbF6].
the two acetaldehyde moieties is reproduced by the geometry
optimization.
SbF5 + 2 O=CH(R) + HF →aHF [H(O=CHR)2][SbF6]
(R = C6H5 (4), CH3 (5))
(4)
(5)
Figure 2. Thermal ellipsoid plots of a) [4−H−4][SbF6] and b) [5−H−5][SbF6].
Thermal ellipsoids are set at the 50% probability level.
SbF5
+
O=CH(CH3) + HF →aHF [HO=CH(CH3)][SbF6]
The X-ray crystal structures of the [SbF6]− salts of
hemiprotonated aldehydes [4−H−4][SbF6] and [5−H−5][SbF6]
reveal the hydrogen-bridged dimeric nature of the oxonium
cations (Figure 2), which contrasts that of the protonated ketones.
Hydrogen-bridged dimeric cations were previously observed by
Table 2. Selected Experimental and Calculated Bond Lengths (Å) of Oxonium
Cations [4−H−4]+ and [5−H−5]+, as well as the Parent Aldehydes Benzaldehyde
(4) and Acetaldehyde (5).
4
5
[4−H−4]+
exptl [a]
calcd [c]
1.208
Exptl
calcd [c]
X-ray
crystallography
for
benzannelated
2-
C=O
C−C
O−H
O---O
1.20936
1.47768
1.248(3)
1.441(4)
1.213(3)
2.425(4)
1.256, 1.246
1.423, 1.433
1.140, 1.276
2.415
hydroxyhomotropylium[3] and [H(benzophenone)2]+ cations,[4] as
well as for acetone, according to IR spectroscopy.[15] The cations
[4−H−4]+ and [5−H−5]+ are isolated, having no contacts with the
anions in the unit cell. Cation [4−H−4]+ is comprised of two
symmetry-related hydrogen-bridged benzaldehyde molecules
(O(1)−H(1) 1.213(3) Å, O(1)---O(1A) 2.425(4) Å). The previously
synthesized [H(benzophenone)2]+ cation shows a similar O---O
distance (2.470(3) Å) to 4, however, the O−H−O moiety is
asymmetric in the crystal structure.[4] Upon hemiprotonation of
benzaldehyde, the C=O bond distance increases ([4−H−4]+
1.248(3) Å; 4 1.212(3) Å) and the CC=O−C bond length decreases
([4−H−4]+ 1.441(4) Å) when compared to the reported structural
data for 4 (1.479(4) Å) (Table 2).[16] Geometry optimization
reproduced the planar geometry of [4−H−4]+ and the E-
configuration of the C=O−H moiety; the hydrogen-bridge is shown
to be asymmetric in the gas phase, whereas the symmetric
hydrogen bridge in the crystal structure is imposed by
crystallographic symmetry. The calculated C=O bond distances
(1.256 and 1.246 Å) compare well with the experimental value for
[4−H−4]+, whereas the C−C bond distances are underestimated
by the calculations (by up to 0.018 Å), likely due to packing effects
in the solid state.
1.478
[5−H−5]+
exptl [b]
calcd [d]
Exptl
calcd [d]
C=O
1.208(3)
1.205
1.239(2) C(2)−O(1)
1.232(2) C(3)−O(2)
1.457(3) C(2)−C(1)
1.471(3) C(3)−C(4)
1.240
1.233
1.464
1.472
C−C
1.514(5)
1.501
O−H
0.88(4), 1.58(4)
2.4449(19)
1.167, 1.253
2.419
O---O
[a] from Ref. 16; [b] from Ref. 17; [c] DFT calculations at the B3LYP/cc-pVTZ
level of theory. [d] DFT calculations at the B3LYP/aug-cc-pVTZ level of
theory.
The low-temperature Raman spectra of the protonated ketone
and aldehyde salts were recorded at −100 °C (see Supporting
Information), and vibrational frequencies of the geometry-
optimized structures were calculated and used to aid in the
assignments of the Raman bands. Protonation of the ketones is
accompanied by a dramatic decrease in the characteristic C=O
stretching frequency. For [1−H]+, [2−H]+, and [3−H]+, the C=O
stretching frequencies decrease between 116 and 155 cm−1
relative to the neutral parent compounds (Table 3), which is in
agreement with a previous LT-IR study of [3−H][SbF6].[15] This
reflects a weakening of the C=O bond. DFT calculations
overestimate the decrease in the C=O stretching frequencies
upon protonation (194 to 224 cm−1), consistent with the absence
of H-bonding in the computed gas-phase structures.
Unlike the protonated ketones, the C=O stretching frequency
of [4−H−4][SbF6] (1639 cm−1) only decreases by 59 cm−1 relative
to 4. The Raman spectrum of [5−H−5][SbF6] shows two C=O
stretching frequencies (1629 and 1665 cm−1), which are
associated with protonated and H-bond accepting acetaldehyde
moieties, respectively, observed in the crystal structure of
[5−H−5][SbF6]. As expected, the decreases in C=O stretching
frequency is more dramatic for the monoprotonated acetaldehyde
cation [5−H]+ (108 cm−1).
The crystal structure of [5−H−5][SbF6] contains a protonated
acetaldehyde in the Z-configuration that is hydrogen-bonded to a
second acetaldehyde molecule in an E-configuration relative to its
methyl group. The configuration of the lowest-energy gas-phase
geometry of [5−H−5]+ is the reverse, suggesting packing effects
influence the configuration in the solid state. The Z-geometry of
the oxonium cation [5−H]+ was calculated to be only 3 kJ/mol
higher in energy than E-[5−H]+. The hydrogen-bond in [5−H−5]+ is
asymmetric, which contrasts with the symmetric hydrogen-bridge
in [4−H−4]+. The latter results in a significantly stronger bridging
interaction in [4−H−4]+. Similar to 1−4, the C=O bond distance
increases ([5−H−5]+ C(2)−O(1) 1.239(2) Å; 5 1.208(3) Å) and the
CC=O−C bond decreases ([5−H−5]+ C(2)−C(1) 1.457(3) Å; 5
1.514(5) Å) upon protonation (Table 2).[17] Interestingly, the
second acetaldehyde appears to be almost equally affected by
the hydrogen-bridge. The small difference in C=O bond lengths in
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10.1002/anie.201710263
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COMMUNICATION
Table 3. Observed and Calculated (CO) Frequencies (cm−1) for Protonated
Ketones and Aldehydes.
decrease in the C=O bond order from 5 (1.88) to protonated
acetaldehyde [5−H]+ (1.47), with that of hemiprotonated [5−H−5]+
being intermediate (1.61 and 1.65).
exptl [a]
1719(13)
1564(11)
calcd [b]
1779(17)[280]
1555(8)[184]
1
In conclusion, the cations presented in this study are the first
examples of representative protonated ketones and aldehydes to
be isolated and structurally characterized in the solid state. As a
result, the presented experimental and computational results
provide key data about a class of intermediates that are
ubiquitous in acid-catalysed organic reaction mechanisms.
Protonation significantly increases the electrophilicity of the
carbonyl carbon, as reflected by bond elongation, significant
decrease in the (CO) stretching frequencies, as well as
calculated charges, bond orders, and LUMO energies.
[1−H]+
1743(16)
1727(23)
1605(16)
2
1806(15)[264]
1591(9)[211]
[2−H]+
1751(3)
1709(16)
1593(10) [c]
3
1782(13)[195]
1588(4)[97]
[3−H]+
4
1698(46)
1639(66)
1767(113)[287] [d]
1712(11)[23], [d]
1678(125)[61] [d]
[4−H]+
1732sh
1712(33)
1665(15)
1629(18)
1604(18)
5
1805(13)[197]
Acknowledgements
1740(7)[117]
1715(15)[51]
1644(7)[137]
[5−H−5]+
[5−H]+
We thank the Natural Scienes and Engineering Research Council
of Canada (NSERC) for funding this research (Discovery Grants
for M.G. and S.D.W.). Computational studies were performed
using equipment funded through the Canada Foundation of
Innovation, as well as resources made available through Westgrid
and Compute/Calcul Canada
[a] Raman intensities, in Å4 u−1
, are given in parentheses. [b] DFT
calculations at the B3LYP/aug-cc-pVTZ level of theory. Unscaled Raman
intensities, in Å4 u−1, are given in parentheses; infrared intensities, in km
mol−1, are given in square brackets; [c] Previous LT-IR study from Ref. 15
shows (CO) 1590 cm−1; [d] DFT calculations at the B3LYP/cc-pVTZ level
of theory.
Natural bond order (NBO) analyses were carried out to
investigate the bonding in these protonated ketones and
aldehydes (Supporting Information). For acetone, the NPA charge
on the carbonyl carbon increases from 0.59 to 0.73 when
protonated, while the charge on oxygen does not change
appreciably (Table 4), suggesting that the hydroxycarbenium
resonance structure (Scheme 1) cannot be neglected. The energy
of the LUMO is dramatically lowered from −18 to −189 kJ/mol,
making acetone more accessible for nucleophilic attack upon
protonation, reflecting the increased reactivity of protonated
carbonyl compounds as proposed intermediates in acid-catalyzed
reactions. There is also a substantial decrease in the energy of
the HOMO from −162 to −376 kJ/mol, reducing the accessibility
to electrophilic attack upon forming the O−H bond.
Keywords: density functional calculations • oxonium cation •
reactive intermediates • superacidic systems • X-ray diffraction
[1]
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[2]
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C. J. L. Lock, J. Am. Chem. Soc. 1986, 108, 1694−1695; d) R. F. Childs,
M. D. Kostyk, C. J. L. Lock, M. Mahendran, J. Am. Chem. Soc. 1990, 112,
8912−8920.
Table 4. Selected NPA Charges, Valences and Wiberg Bond Indices of Cations
[3−H]+, [5−H−5]+, [5−H]+, and their Parent Compounds Acetone (3) and
Acetaldehyde (5).
[3]
[4]
R. F. Childs, R. Faggiani, C. J. L. Lock, A. Varadarajan, Acta Crystallogr.
Sect. C 1984, 40, 1291−1294.
D. Stasko, S. P. Hoffmann, K. C. Kim, N. L. P. Fackler, A. S. Larsen, T.
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E. S. Stoyanov, J. Am. Chem. Soc., 2002, 124, 13869−13876.
A. K. Chandra, M. T. Nguyen, T. Zeegers-Huyskens, Chem. Phys. 2000,
255, 149−163.
NPA Charges
NPA Charges
Wiberg Bond
Indices
(Valence [a]
)
(Valence [a]
)
O
C
CO
[5]
[6]
3
−0.55 (2.04)
−0.52 (2.23)
−0.52 (2.06)
−0.49 (2.26)
−0.52 (2.20)
−0.55 (2.17)
0.59 (3.87)
0.73 (3.71)
0.44 (3.83)
0.57 (3.61)
0.54 (3.84)
0.53 (3.70)
1.83
1.39
1.88
1.47
1.61
1.65
[3−H]+
5
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[5−H]+
[5−H−5]+
[7]
[8]
[9]
S. Chakraborty, A. Patzer, O. Dopfer, J. Chem. Phys. 2010, 133,
044307/1−044307/12.
[a] Sum of the Wiberg Bond Indices per atom.
I. Alata, R. Omidyan, C. Dedonder-Lardeux, M. Broquier, C. Jouvet, Phys.
Chem. Chem. Phys. 2009, 11, 11479−11486.
When protonated, the C=O bond order in acetone decreases
from 1.83 to 1.39 (Table 4), reflecting the significant weakening of
the bond, which is paralleled by the increase in C=O bond length
and lowering of the C=O stretching frequency. Similar trends are
found for the cyclopentanone and 2-adamantanone systems.
NBO analyses for 5, [5−H]+, and [5−H−5]+ showed the expected
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D. Stuart, S. D. Wetmore, and M.
Gerken
Page No. – Page No.
Solid-state Structure of Protonated
Ketones and Aldehydes
Layout 2:
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Daniel Stuart, Prof. Dr. Stacey D.
Wetmore, Prof. Dr. Michael Gerken
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Solid-State Structure of Protonated
Ketones and Aldehydes
Structures of Reactive Intermediates: Solid-state structures of protonated carbonyl
compounds are presented. Whereas protonation of ketones (acetone,
cyclopentanone and adamantanone) in superacidic solution yielded the mononuclear
oxonium ions, hemiprotonated hydrogen-bridged dinculear structures were observed
in the crystal structure obtained from reactions of benzaldehyde or acetaldehyde with
HF/SbF5.
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