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Energy Differences in the Inner Molecular Orbitals of tert-Butyl and Trimethylsilyl Phenyl Ketones.

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be accelerated by the addition of catalytic quantities of OH@,
and by the methylation of (3b) with CH31 under s N 2 conditions, the ambident anion (6) giving the S-methyl ether of
( 2 b ) , m.p. 88-89 'C. All the compounds were pure on thin
layer chromatography and o n analysis.
Table I . Melting points and I R spectra of thiacyclols and cyclothiodepsipeptides.
v (crn-1)
Amide I
Arnide I1
1 I
Sa-Hydroxy-6, 8.9-1 trahydro -5aH,I1 H-pyrido[Z,I - blbenzo[el-[I ,3]thiazin I-one (3a)
Ag acetate (955 mg, 5 % excess) is added under nitrogen to a
solution of (S-acetyl-o-mercaptobenzoy1)valerolactam
(1.50 g,
5.40 mmole) [m.p. 99-100 "C, synthesized according to
ref. 1311 in methanol (30 ml) and pyridine ( 2 ml). The mixture
is stirred for 30 min at room temperature, poured into water,
and the colloidally dissolved Ag thiolate is salted out with
H N 0 3 . The solid thus obtained is filtered off, dissolved i n
acetone/water (5: 1) (50 ml), and H2S is introduced into the
solution with stirring. Afier the AgS has been filtered off and
the acetone removed under vacuum, 950 mg (75 %) of the
crystalline thiacyclol (3a) (m.p. 129-130 "C) is obtained.
Compound (30) rapidly turns yellow to form (5a), but is
stable at -15 OC. (3a) (10.0 g) is recrystallized from a mixture of acetone (150 ml), water (75 ml), and triethylamine
(0.5 ml). 75 mg of (4a) (m.p. 195-196OC, from acetic acid)
in the crystalline state is obtained at room temperature.
excitation energy of the n + x S transition responsible for the
color: (a) "Through space" interaction dsi/no between the
free electron pair no of the carbonyl oxygen, which is orthogonal to the CO x-system, and unoccupied 3d atomic orbitals
of the silicon leads to a "superchromophore" Si-C=O [41.
(b) The x*co molecular orbital is lowered by dsi/x*co
splitting (51. (c) The a-donor and Tc-acceptor properties of R3Si
groups stabilize the n + x * excited state of the ketone x system relative to the ground state [61. (d) The strong inductive
effect of R3Si groups increases in particular the level &no) of
the free electron pair o n the oxygen[71. It should be possible
to decide between these interpretations on the basis of additional energy data for alkyl and silyl ketones.
Investigations on the substituent effects of R3C and R3Si
groups o n linear and cyclic x-electron systems have shown
that the following values can be used to determine the energy
differences between the inner molecular orbitals x , n, and x*:
According to Koopmans' theorem 181, vertical ionization
energies IE found by mass spectroscopy correspond to the
energy of the highest occupied molecular orbital E(n) or
E(x) in the ground state 191. Charge-transfer excitation
energies + z T of suitable donor-acceptor complexes are
proportional to the energy E(x) of the highest occupied x
molecular orbital [9,101. Half-wave reduction potentials ERed
can be correlated with the energy E(x*) of the lowest unoccupied T: molecular orbital [ I l l . With the aid of the electronic
and +n+n*, these energy values
excitation energies *
can be used to construct approximate energy level diagrams
for the inner molecular orbitals [I21 by introduction of simplifying assumptions concerning the differentiation of molecular orbitals and electronic states.
The approximate energy level diagrams (Fig. 1) for tertbutyl ( I ) and trimethylsilyl phenyl ketone ( 2 ) may be
deduced from the experimental values (Table 1).
Received: August 5, 1968
[Z 860b IE]
German version: Angew. Chem. 80, 909 (1968)
[*I Prof. Dr. M. Rothe and Dip1.-Chern. R. Steinberger
Organisch-Chemisches Institut der Universitat
65 Mainz, Johann-Joachim-Becher-Weg 18-20 (Germany)
[* *] We thank the Deutsche Forschungsgemeinschaft and the
Fonds der Chemischen Industrie for financial support, Farbwerke Hoechst AG for awarding the Karl-Winnacker grant to
M.R., and the Dr.-G.-Scheuing-Stiftungfor a grant to R.St.
[***I It has become common practice to use the name cyclol for
the grouping
Table 1.
Experimental values for rrrt-butyl ( I ) and trimethylsilyl
phenyl ketones ( 2 ) .
where X = 0, S, NH, etc. Representatives having X = 0 are
usually called just cyclols and are only rarely termed oxacyclols.
[l] Part 13 of Reactions with Activated Amides. - Part 12: M.
Rothe, Angew. Chem. 80, 245 (1968); Angew. Chem. internat.
Edit. 7, 233 (1968).
12) M . M . Shemyakin, V. K . Antonov, A. M . Shkrob,' V. J.
Shchelokov, and Z . E. Agadzhanyan, Tetrahedron 21,3537 (1965);
A . Hofmann, H . O f t , R. G . Griot, P . A . Stadler, and A. J . Frey,
Helv. chirn. Acta 46, 2306 (1963).
[31 M . Rothe, T . Tdfh,and R. Daser, Chern. Ber. 99, 3820 (1966)
I -0.27
I -2000
[ a ] Measured for methyl and trirnethylsilyl 9-naphthyI ketone [13].
AIE is due to the different energies E(n0) of the free electron
pair on the carbonyl oxygen, and is also reflected in the different p K values [I41 of the two compounds. The lowering of
the x * level in the silyl ketone ( 2 ) deduced from the large
is condifference in the n + x * excitation energies Ap**
firmed by the fact that the half-wave reduction potential
ERed of ( 2 ) is more positive. A similar lowering of the x
level suggested by the smaller difference in the x + x * excitation energy A+X+X* is confirmed by the different
Energy Differences in the Inner Molecular
Orbitals of teri-Butyl and Trimethylsilyl Phenyl
By H . Bock, H . Alt, and H. Seidl[*I
In contrast to the colorless alkyl ketones, monosilyl ketones
are yellow 12741 and disilyl ketones are violet [31. The following
interpretations are offered in the literature for the reduced
Angew. Chem. internat. Edit.
Val. 7 (1968) / No. I 1
charge-transfer excitation energies
of tetracyanoethylene
complexes of methyl and trimethylsilyl @-naphthylketone 1131.
The fact that the n + x* excitation energy of the yellow silyl
ketone is lower than that of the colorless tert-butyl ketone
can be explained (on the basis of a o / x separation) as follows:
The strong inductive effect of the trimethylsilyl group
~ + ICR, raises all the inner molecular orbitals.
However, this becomes observable only in the free electron
pair of the carbonyl oxygen, which is orthogonal to the x
[lo] H. Bock and H. Alt, Angew. Chern. 79, 934 (1967); Angew.
Chem. internat. Edit. 6 , 9 4 3 (1967); Chem. Commun. 1967,1299;
J. organometallic Chem. 13, 103 (1968).
1111 H. Bock and H. Alt, Angew. Chem. 79, 932 (1967); Angew.
Chert. internat. Edit. 6, 941 (1967); cf. also F. Gerson, J. Heinzer,
H . Bock, H. Alt, and H. Seidl, Helv. chim. Acta 51, 707 (1968).
[12] H. Bock and H. Seidl, J. organornetallic Chem. 13,87(1968);
J. chem. SOC. (London) ( B ) 1968,1158; J. Amer. chem. SOC.90,
5694 (1968).
[131 In the case of the phenyl ketone derivatives, the CT band is
situated in the self absorption region; it was therefore necessary
to use analogous substances.
1141 K. Yutes and F. Agolini, Canad. J . Chem. 44, 2229 (1966).
A New Test for the Determination of Pyruvate
Decarboxylase Activity
By A . Schellenberger, G . Hubner, and H . Lehmannc*J
The hydroxide ions formed in the pyruvate decarboxylase
reaction( PDC, 2-oxoacid carboxylase, EC in accordance with
Fig. 1. Approximate energy level diagrams for lert-butyl (Z) and trimethylsilyl phenyl ketone ( 2 ) .
permit the accurate determination of the reaction rate by pHstat titration. It can be seen from Figure 1 that the acid consumption increases linearly with time and that the slope of
the curves is proportional to the enzyme concentration.
system and is situated in the p poyition with respect to the
silicon. The energies of the ground state and the excited
states, on the other hand, are lowered by the possibility of
back-donation Si t C , from the x system into empty atomic
orbitals of the silicon, which is in the a-position in this case.
As expected, this interaction is greater in the excited states
because of the smaller energy difference in relation to the
unoccupied Si acceptor orbitals. The acceptor function of
trimethylsilyl groups, which must be of x symmetry, may
involve unoccupied 3d atomic orbitals of the silicon.
Received: August 5, 1968
12 861 IE]
German version: Angew. Chem. 80,906 (1968)
['I Priv.-Doz. Dr. H. Bock, Dip1.-Chem. H. Alt, and
Dr. H. Seidl
Institut fur Anorganische Chemie der Universitat
8 Munchen 2, Meiserstr. 1 (Germany)
[l] Lecture to the 2nd International Symposium on Organosilicon Compounds in Bordeaux, July 1968. Part 13 of d-Orbital
Effects in Silicon-substituted x-Electron Systems. - Part 12:
H. Bock and H . Seidl, J. chem. SOC.(London) ( B ) 1968,1158.
[2] A. G. Brook, J. Amer. chem. SOC.79, 4373 (1957); A. G.
Brook, J. M . Duff, P. F. Jones, and N. R . Davis, ibid. 89, 431
(1967); E. J . Corey, D. Seebach, and R . Freedman, ibid. 89, 434
[3] A. G. Brook and G . J . D. Peddle, J. organometallic Chem. 5,
107 (1966).
[4] A. G. Brook, M . A . Quigley, G . J. D. Peddle, N. V. Schwarz,
and C. M . Warner, J. Amer. chem. SOC.82, 5102 (1960); A. G.
Brook, and J. R . Pierce, Canad. J. Chem. 42, 298 (1964); cf. also
W. K . Musker and R . W. Ashby, 3. org. Chemistry 31, 4237
(1966); W. K. Musker and G. L. Lurson, J . organometallic Chem.
6, 627 (1966).
[5] D. F. Harnish and R. West, Inorg. Chem. 2, 1082 (1963);
R. West, J. organometallic Chem. 3, 314 (1965).
[6] L. E. Orgel in C. Eaborn: Volatile Silicon Compounds.
Pergamon Press, London 1963, p. 81.
[7] G. J. D . Peddle, J. organometallic Chem. 5, 486 (1966);
F. AgoIini, S. Klemenko, J. C. Csizmadiu, and K. Yates, Spectrochim. Acta 24 A, 169 (1968).
[8] Cf., e.g., L. Salem: Molecular Orbital Theory of Conjugated
Systems. Benjamin, New York 1966, p. 155.
[9] H. Bock and H . Seidl, Chem. Ber. 101, 2815 (1968).
Owing to the sensitivity of the test, the pyruvate conversion
is low, so that there is no inhibition of the reaction by the
acetaldehyde formed. The fact that investigations can be
carried out in buffer-free media, thus eliminating salt and
foreign-ion effects, represents a further advantage. The
enzyme activities found in the optical test described by
HoZzerLlJ and in the Warburg test agree to within a good
approximation with those found in the pH-stat test (Table 1).
Table 1.
Comparison of enzyme activity
Angew. Chem. internat. Edit. J VoI. 7 (I968) 1 No. I I
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trimethylsilyl, butyl, molecular, differences, inner, phenyl, ketone, energy, tert, orbital
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