close

Вход

Забыли?

вход по аккаунту

?

Lone Pair Interaction in Pyridazine Pyrimidine and Pyrazine.

код для вставкиСкачать
petroleum (b.p. 80-lOO"C), in which ( I ) is less soluble
than ( 2 ) , affords (2) in crystalline form. ( I ) : m.p. 157OC.
( 2 j : m.p. 97 O C , IR absorption vco = 1840 and 1870 cm-1.
Received: September 7, 1970
[Z280 IEI
German version: Angew. Chem. 82, 935 (1970)
_~
[*I Prof. Dr. H.-D. Scharf and Dip1.-Chem. H. Seidler
Institut fur Organische Chemie der Technischen Hochschule
51 Aachen, Prof.-Pirlet-Strasse 1 (Germany)
[**I This work was supported by the Landesamt fur Forschung
des Landes Nordrhein-Westfalen.
[ l ] H . - D . Scharf, W . Droste, and R . Liebig, Angew. Chem. 80,
194 (1968); Angew. Chem. internat. Edit. 7, 215 (1968); H.-D.
Scharf, M . Feilen, and W . Pinske, Chem. Ber., in press.
[2] Pyrex glass immersion apparatus. Light source: HPK 125 W
(Philips).
[3] Correct elemental analyses have been obtained for compounds whose molecular formulas are cited.
[4] H.-D. Scharf, Fortschr. Chem. Forsch. 11, 216 (1969).
[5] Hydrolysis at 80 "C. M.p. 146 "C (decomp.) (acetone/
water), lit. [6] 140 "C.
[6] R . West, H . Y . Niu, and M . Ito, J. Amer. Chem. SOC.85,
2584 (1963).
[7] OH proton signals in the NMR spectrum ([D~lpyridine):
T = 4.02. The OH protons of all-cis-cyclobutanetetraol [ W .
Hartmann and R . Steinmetr, Chem. Ber. 100, 217 (1967)l in the
same solvent give signals at T = 4.15.
[81 Varian T-60 spectrometer, TMS as standard.
[9] Previous experience was that monocarbonates are readily
solvolyzed under these conditions (see [l]).
[lo] A1203-G and glacial acetic acid.
Lone Pair Interaction in Pyridazine, Pyrimidine,
and Pyrazine
By Rolf Gleiter, Edgar Heilbronner, and Volker Hornung [*I
The orbital diagram of Figure 1 correlates the energy levels
E(#J) of the highest occupied orbitals #J of benzene ( I ) ,
pyridine (21, pyridazine ( 3 ) , pyrimidine ( 4 ) , and pyrazine
( 5 ) . The orbital energies E(#J) correspond to the vertical
Table 1.
(1)
(2)
(3)
(4)
Vertical ionization potentials Iv(J) (in eV)
(D6h)
(CZV)
(CZ,)
(CzV)
( 5 ) (Dzh)
-I -10
>
a,
W
y.!
/
11
121
''1
1Zi
131
14/
I
151
@Ba
Fig. 1. Correlation diagram. It should be pointed out that (S) and (A)
do not refer to the true symmetry of the molecule but solely to the parent
orbital in ( I ) from which the respective x orbital is derived.
Assignment of the individual bands in the PE spectra to %
and n / s ionization processes is based o n the characteristic
shapes of x and n / o bands as well as o n model calculations.
It may be deduced from the fine structure of the two nbands of ( 5 ) that the first n-ban$(Iv(l) = 9.63 eV) corresponds to a n ionization process in which the photoelectron
stems from a n alg orbital containing the linear combination
n+, while the third bandiZv(3) = 11.35 eV) must be assigned
t o the bzu orbital containing the n- combination 151.
Interaction between the lone pair orbitals n l and n2 occurs
mainly via two mechanisms: a) Direct overlapping, i.e.
"through-space" interaction b) "through-bond" interaction
with other bonding and/or antibonding s orbitals of the
molecule[61. Mechanism a) always leads t o the sequence
E(#-)
above E(#+), while mechanism b) leads to the same
[31.
9.24 el&)
9.31 bz(n-)
9.73
10.61
9.73
10.41
9.59
9.63
a h 0 [a1
bz(n_)
aIg(n+)
10.18
az(rr, A)[al
az(x, S )
bl(z, S)
bzg(x,A)
10.50
10.9 [bl
1
11.23
11.35
b d x , S)
bdx. A)
ah+)
b&_)
ionization potentials Iv(J) (Table l), which were determined
from high-resolution photoelectron spectra 121: E(#)J =
-Zv(J). (For previous measurements see, e.g., ref. 141.) The
designation of the orbitals #J characterizes, in the usual
nomenclature, the symmetry behavior of the orbital with
regard to symmetry operations of the symmetry group to
which the molecule belongs. The letters S and A denote the
behavior of the two degenerate x orbitals eS = (2 @I
0 2 - @ 3 - 2 0 4 - (D5
@ 6 ) / 1 / u and eA = ( ( D 2 + , @ 3 @5@,5)/2 of benzene o n reflection in the x , z plane. I n
Figure 1, S and A are used solely in order t o correlate the
orbitals of the systems (2) to ( 5 ) with the "parent orbitals"
o f benzene from which they are derived. Linear combination of the atomic orbitals n l and n2 of the two lone pairs in
( 3 ) , ( 4 ) , and (51, which are regarded as localized, yields
initially the orbitals n+ = (nl + nZ)/l/2 and n- = (nl- nz)/1/2
of correct symmetry. Those molecular orbitals (JJ to which
n+ o r n- make the greatest contribution are marked (+) and
(-) respectively in Fig. 1.
+
+
Angew. Chem. internat. Edit. 1 Vol. 9 (1970)
1 No. I 1
11.31
11.39
11.77
al(n+)
a2(x, A)
big(x,S)
or to the reverse sequence, depending o n the relative positions of the orbitals nl and n2 in the molecule.
The molecules ( 3 ) , (4),and ( 5 ) yield the following values
for the splitting
Aexp
=
4+-) - d#+)= I,(#+, - L(#-)
which are compared with the theoretical values calculated
from a n EHT model[71.
As can readily be understood o n a qualitative basis, the
contribution to the value of A that is attributable to mechanism a) decreases along the series ( 3 ) , (41, ( 5 ) owing to
90 1
the increasing distance between n l and n2. In contrast,
mechanism b) contributes to about the same extent in all
three cases. Since $(n+) interacts primarily with the lowerenergy bonding 0 orbitals of the same symmetry, and +(n_)
mainly with the antibonding ones, mechanism b) has the
effect of raising E(G(n+)) and lowering E($(n-)). I n (5) this
leads to a n inversion of the sequence of the orbitals $(n+),
+(n..) relative to (3) and ( 4 ) and thus to a negative A
value. Direct interaction between nl and n2 (mechanism a))
dominates in ( 3 ) and ( 4 ) . Finally, the A values for transazomethane ( A = -3.3 eV) 181 and for 3,3-dimethyldiazirine
(A = 3.5 eV) [9J are given for the sake of comparison.
Received: July 27, 1970
[Z 281 IE]
German version: Angew. Chem. 82, 878 (1970)
Symmetry behavior
C2h
c2v
make the greatest contribution. We have now also studied
the interaction of nl and n2 in a diazirine derivative, which
contains the cis azo group.
Theoretically determined orbital energies E for the five
highest occupied MOs of cyclopropene ( I j , diazirine (21,
and 3,3-dimethyldiazirine ( 3 ) are listed in Table 1.
[*I Dr. R. Gleiter, Prof. Dr. E. Heilbronner, and
Dipl.-Chem. V. Hornung
Physikalisch-Chemisches Institut der Universitat
CH-4056 Basel, Klingelbergstrasse 80 (Switzerland)
[ l ] Applications of photoelectron spectroscopy, Part 15. This
work represents part of Project No. SR 2. 120.69 of the
Schweizerischer Nationalfonds. - Part 14: P . BischoL R .
Gleiter, E . Heilbronner, V . Hornung, and G . Schroder, Helv.
Chim. Acta 53, 1645 (1970).
[2] D. W . Turner, Proc. Roy. SOC.(London) A 307, 15 (1968).
[3] The photoelectron spectra were recorded on a modified
PS 15 spectrometer produced by Perkin Elmer Ltd. (Beaconsfield, England).
[4] (2): D. W . Turner, Tetrahedron Lett. 1967, 3419; (2) and
(5): A . D . Baker, D . Betteridge, N . R. Kemp, and R . E. Kirby,
Chem. Commun. 1970, 286; (5): L. Idsbrink, E. Lindholm, and
0. Edqvist, Chem. Phys. Lett. 5, 609 (1970); (2). ( 3 ) , ( 4 ) , and
( 5 ) : D. W. Turner, Advan. Phys. Org. Chem. 4, 31 (1966);
M. J. S. Dewar and S . D . Worley, J. Chem. Phys. 51, 263
(1969). The adiabatic ionization potentials given by these
authors agree with our la(J) values within the limits of experimental accuracy; however, the assignments of the bands differ
fundamentally, since Turner neglects the interaction between
nl and n2 and Dewar and Worlev consider it only in the case
of (3).
Note added in proof:
After submission of the present communication, a further
discussion of the PE-spectra of the diazines has appeared in
print: D. W . Turner, C. Baker, A. D . Baker, and C . R . Brundle:
Molecular Photoelectron Spectroscopy. Wiley-Interscience,
New York 1970, p. 327. Two correlation diagrams are given,
in which assignments are proposed which differ from that
shown in Fig. 1.
[5] E. Heilbronner and K . A . Muszkat, J. Amer. Chem. SOC.92,
3818 (1970).
[6] R . Hoffmann, A. Imamura, and J . W . Hehre, J. Amer. Chem.
SOC.90, 1499 (1968); R. Hoffmann, E. Heilbronner, and R .
Gleiter, ibid. 92, 706 (1970).
[7] R . Hoffmann, J. Chem. Phys. 39, 1397 (1963); 40, 2474,
2480, 2745 (1964); Tetrahedron 22, 521, 539 (1966).
[8] E. Haselbach, J. A . Hashmall, E. Heilbronner, and V.
Hornung, Angew. Chem. 81, 897 (1969); Angew. Chem. internat. Edit. 8, 878 (1969); E. Haselbach and E. Heilbronner,
Helv. Chim. Acta 53, 684 (1970).
191 E. Haselbach, E. Heilbronner, A. Mannschreck, and W.
Seitz, Angew. Chem. 82, 879 (1970); Angew. Chem. internat.
Edit. 9, 902 (1970).
Lone Pair Interaction in 3,3-Dimethyldiazirine[11
By Edwin Haselbach, Edgar Heilbronner,
Albrecht Mannschreck, and Werner Seitz [*I
The photoelectron-spectroscopic determination of the interaction
A
=
d+(n-)) - 4+(n+))
Table 1. Calculated orbital energies ( - E ) for cyclopropene ( I ) , diazirine ( 2 ) , and 3,3-dimethyldiazirine (3) [in eVI.
(1)
ab iniro
MINDOR
8.97
10.58
12.39
15.11
17.12
9.54
9.95
10.86
14.55
14.72
bl(n)
b2(0)
al(o)
bl(r;)
al(o)
bl(x)
b2(0)
a](.)
al(rJ)
bl(rr)
I
(2)
ab inifio
MINDO/2
10.46
12.31
14.46
16.73
17.44
10.47
11.17
11.76
13.45
15.65
b2(n-)
bi(n)
al(n+)
ai(o)
bi(tr)
b2cn-l
bi(n)
al(a)
al(n+)
bl(n)
9.72
10.51
11.46
11.95
12.25
bz(n_)
bl(;r)
al(o)
al(n+)
bl(rr)
The orbital sequence for ( 2 ) calculated by the MIND012
technique 141 differs from that obtained by Robin, Basch,
Kuebler, Wiberg, and Ellison 151 from a n ab initio model in
the order of the orbitals al(n+) and al(c). Experience shows
that for unsaturated systems MIND0/2 yields 0 orbitals at
too high orbital energies, so that the appearance of al(o)
between bl(x) and al(n+) in the case of ( 2 ) and ( 3 ) should
be regarded as a n artefact of the method. For a n extended
Hiickel model of (2) the reader is referred to a paper by
Hofmann 161 and for a detailed discussion of the electronic
structure of cycIopropane, ( I ) ,and (2) to a publication by
Kochanski and Lehn 171.
Table 2. Vertical ionization potentials Zv(J) of the first three bands in
the photoelectron spectrum of cyclopropene ( I ) and 3,3-dimethyldiazirine (3) [in eV1.
(I)
(3)
1
9.86
(A? % l2SOcm-1)
9.76
1 1
11.02
12.11
12.7
(A: % I100 cm-1)
13.31
Table 2 lists the vertical ionization potentials Iv(J) as
determined by P E spectroscopy 181, i.e. the maxima of the
first three bands in the spectrum of (I) and (3). The assignment is based o n the theoretical data listed in Table 1 and
o n the following arguments: The form of band 1 a t 9.9 eV
in the P E spectrum of ( I ) is typical for a x band (vibrational
fine structure; mean splitting 0.15 eV corresponding to
A; x 1200 cm-1). The next two 0 bands (at 11.0 and 12.7
eV) correspond to the orbitals b*(a) and al(a) which arise
from the Walsh e’ orbitals[gl of cyclopropane (D3h) o n
removal of their degeneracy when the distance between
centers 1 and 2 is reduced by introduction of a double
bond:
between the lone pairs n l and n2 of the trans azo group in
azomethane has been reported previously[zJ ( A = -3.3 eV;
cf. ref. [3J). The functions +(n-) and $(n+) are those molecular orbitals to which the linear combinations
902
Angew. Chem. internat. Edit.
Vol. 9 (1970j
/ No.
11
Документ
Категория
Без категории
Просмотров
3
Размер файла
227 Кб
Теги
pyrazines, loner, interactiv, pyridazine, pairs, pyrimidine
1/--страниц
Пожаловаться на содержимое документа