close

Вход

Забыли?

вход по аккаунту

?

Conformation of acyclic -unsaturated aldehydes and ketones deduced from their infrared and Raman spectra- results and limitations of model calculations.

код для вставкиСкачать
frequencies of a number of unsaturated enones and its depen-
This manuscript is
to be cited as
Angew. Chem. Suppl.
1982,1404-1415
Dieses Manuskript ist
zu zitieren als
Angew. Chem. Suppl.
1982,1404-1415
0 Verlag Chemie GmbH. 0-6940Weinheim,
dence on the pattern of substitution /3-5/ showed that the
or v(C=C) frequency is a poor
absolute value of thev(C.0)
means for the determinazion aP the conformation. The frequen-
1982
cy differencei;
0721 422718210808~14Mfi
02.5010
between t h e v (C.0)
and the
(C=C) vibrations
I
is, however, more meaningfull: The model calculations showed
t h a t A 7 varies with the angle P , f o r P =
O O A ~ =7 3
cm-l and
Conformation of acyclic d,B-unsaturated aldehydes and
ketones deduced pFOm their infrared and Raman Spectra
-
~~
~
-_
A Y = 58 cm-' f o r 1 = 180'.
-
This is in good accordance with
earlier experimental investigations /3-5/ and should allow a
results and limitations of model calculations**
Fig. 1 shows the
first estimate of the dihedral angle&'.
calculated relation together with experimental values. By
By Hans-Joachim Oelichmann, Daniel Bougeard, and Bernhard
applying this relation one has to keep in mind, however,
Schrader.
that tt is only a first guide for the determination of the
dihedral angle sinceA? is strongly dependent on the pattern
The a,8-unsaturated aldehydes ( R
i
H) and ketones
(R
of substitution on the C=C double bond:Aii is larger for
alkyl) 1 may exist in two planar confcrmations, the
unsubstituted enones than for trisubstituted ones /5/.
___-_
Dr. H.-J.
The IR- as well as the Raman-intensities of these two
Oelichmann+, Priv.-Doz. Dr. 0. Bougeard,
vibrations are more reliable in determining the conformation.
Prof. Dr.-Ing.
B. Schrader, Institut fur Physikalische
und Theoretische Chemie, Universitat Essen
- CHS.
Mecke and Noack /3/ related the conformation to the
UniversitBtsstraBe 5-7, D-4300 Essen
absolute integral IR-intensity of the
v
(C.0)
and the
v
(C=C)
vibration. The difficulties of absolute intensity measure+
present address: Carl Zeiss, Zentralbereich Fcrschung,
ments may be clrcumventad by taking the intensity ratio
P.O. Box 1369/1380, D-7082 Oberkochen
**
AC=O/AC.C
as a characterlstic value. Our calculations for
the smallest unsaturated ketone, methylvinylketone, showed
This work was supported by the Deutsche Forschungsgemeinschaft and the Fonds der Chemischen Industrte.
- 1406 -
- 1404 -
s-cis-
( 9 = 001, and the s-trans conformation ( V
=
1aoo),
and non-planar forms additionally.
R3
r5
r6
551
The spatial arrangement of the two double bonds of
these compounds has been investigated by various spectroscopic methods /1-lo/. The most prominent results were deFig. 1. Calculated dependence of the frequency difference
duced from the vibrational spectra. Several empirical re-
(C-0) a n d v (C:C)
vibrations,A;
on the dihedral
lations were developed in order to relate the frequencies
between the
as well as the IR and Raman intensities of the C-0 and C-C
angle
stretching vibrations to the conformations of the conjuga-
experimental values for 1 isopropenylmethylketcne, 2 3-pen-
ted system in
l
/1-8/.
We used a new procedqre / 1 1 /
(p
\I
for 1. R, R,
...R3
= point masses with
tene-2-one*, 3 (?)-2-decenal
for
/la/,
m
= 15; x
4 (Z)-2-dcdecenal /la/,
the simulation of the infrared and Raman spectra of several
5 (Z)-2-heptenal />a/, 6 t.r~n2-3-hexene-Z-one
/3/*, 7
trans-
conjugated enones: acrolein (s-trans and s-cis), trans-
3-heptene-2-one /3/*, 0 molecular mechanical calculation
and cis-crotonaldehyde, methacrolein, and methylvinylke-
of the dihedral angle 7
tone (s-trans and 8-cis) /12,13/. These calculattons en-
values of 8 mesityloxide, 9 G-3-methyl-3-pentene-2-one
abled us to develop a transferable set of force constants
/3/*, 10 3,4-dimethyl-3-pentene-2-one
/a/,
and experimental frequency
/3/.
f o r conjugated enones /12/, which was used in order to cal-
*This compound exists as a mixture of both conformers.
culate the frequencies of model molecules uith different
dihedral angles V = 0, 30')
...,
180'
(R, R 1 , R2, R 3 in
1
were taken as point masses, m = 15). The comparison of the
- 1405 -
- 1407 -
in accordance with experimental results that the infrared intensity of the CsC stretching vibration is much more affec-
0 0
2 0-
ted by the dihedral angle than that of the C=O vibration.
0
o
The absolute integral IR-intensity of the -t(C=C) vibration
0
15-
Q O
is much greater for the s-cis conformer.than for the s-trans
0
form, so that the infrared intensity ratio AC=O/AC=C
is lar-
10-
0
ger (40.33) for the s-trans than for the s-cis (1.84) con-
0
050 0 o
former / & / . For a larger ensemble of molecules recommended
values for a decision between the s-cis and the s-trans
0
conformation are given in table 2.
L.
0
.PI"]
$0
#)
90
120
180
1 9
-
Fig. 2 . Calculated dependence of the intensity ratio Icz0/
v(C=C) as a function of the dihedral angle 9 for methylvinyl-
1C.C in the Raman spectrum of methylvinylketone on the di0
'
.
which is apparently
hedral angle. (The value for 'p I 3
ketone yielded that the intensity of the C=C stretching
too small, depends on a non-linear relationship between the
vibration is nearly unaffected by the a n g l e q , whereas the
polarizability and the normal coordinate of the v (C=C) vibra-
The calculation of the Raman intensities of v(C=O) and
The saddle of the curve for 9 = 90'
is due to the
intensity of the C=O stretching vibration is much larger
tion /ll/.
for the s-trans conformer. Therefore the.ratio of the inte-
complete orbital decoupling for this spatial arrangement).
gral intensities Ic=o/Ic=c in the Raman spectrum may be used
in addition to the infrared intensity ratio for the determination of the dihedral angle9
(fig. 2 ) . As a general result
the Raman intensity ratio Ic~o/Ic=c is, in accordance with
01
'V(C.0)'
' v k . c 1'
'v(c.0)'
'vlc-cl'
experimental results, smaller than 0.5 for s-cis and larger
than 0,5 for s-trans conformers (table 2). Additionally the
depolarization ratio of thev (C-0) band can be used for a
further support of the conformation. The data for s-trans
conformers are somewhat smaller
s-cis conformers (9- 0.4)
(
9-0.2)
bl
than those for
Fig. 3 . Normal coordinates of the #(C=O) and v(C=C) vibra-
/a/.
tions of a) s-trans and b) s-cis acrolein.
- 1408 -
- 1410 -
Noack and Jones /7/ as well as Sobolev and Aleksanyan
Table 1: Frequencies of the C=O and C=C Stretching vibra-
- v (C=C), and their
/17/ suggested, that the dependences in band frequencies
tions, frequency differenceb:
and intensitles described above are due to partial coupling
intensity ratio in the spectra for some&,&-unsaturated
of the C=O and C=C stretching modes. Our normal coordinate
aldehydes and ketones as well as their application for the
calculations on s-trans and s-cis acrolein /12,13/ yielded
determination of the dihedral angle9
rv(C=O)
.
that these vibrations are indeed coupled to some degree
(less than 10 % ) , although the PED-values amount to 65
-
85 %
For the C-0 and C = C force constants 112,131. The normal co-
ordinates (fig. 3 ) show, however, that to some extend both
0
0
9
--
m
4
0
m
0
0
0
- 2 s
9 3 3
t-
l n . - I n & t -
0
m,
o
vibrations may be understood as in-phase and out-of-phase
0
0
s
vibrations of the two double bonds. This effect is somewhat
I
:
og o
m o
.
r
0
r
smaller for the s-cis conformer leading to a greater separa-
L
Y
W
D
e
tion between these two vibrations.
Y
0
0
.-I
Y
In the s-trans conformation the in-phase vibration is
0
L
located at higher wavenumbers than the out-of-phase vibration,
whereas the reverse is true for the s-cis form. An equivalent
N
t-
0
v)
O
N
m
t
-
t
-
- + l n l n l n
L
L.
relationship holds for conjugated dienes, too 1151. As the
0
changes in dipole moment as well as in polarizability of the
4
el
s
molecules are expected to be greater for the in-phase modes,
L.
these vibrations give rise to more intense IR and Raman bands
0
.d
than the out-of-phase modes.
Y
4
Y
x
."
m
In order to check the reliability of the relations
C
0
in fig. 1 and 2 these results have been used for the esti-
U
mation of the dihedral angles of somea,B-unsaturated
9,:
c
.
c - 0
C
5 . E
-
aldehydes and ketones (table 1).
-
1409
t
-
- 1411 -
All relations yield that mesityloxide exists as a
probably slightly twisted
-
References
- 5-cis conformer, whereas the
conformation of isopropenylmethylketone is s-trans, slightly
/I/ I. Naito, A. Kinoshita, T. Yonemitsu, &tll,Chem,-go~,
twisted, too. E-3-pentene-2-one subsists in two forms, s-cis
and 8-trans, both slightly twisted. All the three investiga-
(1976) 339.
&
J
J
/2/ H.H. Perkampus, I. Sandeman, C.J. Timmons, DHS UV-Atlas
ted 2-isomeres of the aldehydes /14,18/ exhibit the s-trans
Organischer Verbindungen, Verlag Chemie, Weinheim 1966.
9: (1960) 210.
conformation. These results are in good agreement uith those
/3/ R. Hecke, K. Noack, Chem.
of experimental investigations /3,9,10/.
/4/ F.H. Cottee, B . P . Straughan, C.J. Timmons, W.P. Forbes,
Be_t-,
A. Shilton, Chem. SOC: ( B ) 19_6_1
1146.
,
A relation between the dihedral angle in conjugated
Montnme, P. Arnaud, a
e
_
c
_
&
,.A.
o
_
ta_
~
?
i
_
m
/5/ R. Barlet, .!-I
25A (1969) 1081.
dienes and the frequency difference between the in-phase
and out-of-phase vibrations of the double bonds was already
/6/ A. Bienvenue, J.&.Chem_l_~_o_c_,
established /15/. The results can be applied to the inter-
/7/ K. Noack, R.N. Jones, Can,_J,-ch~m_,
19 (1961) 2201;
2225.
pretation of the spectra of larger molecules, for,example
the steroids /16/. The relations compiled in table 2 enable
the estimate of the conformation ofn ,&unsaturated
/8/ S.K. Freeman, Application of Laser Raman Spectroscopy,
John Uiley, New YOrk 1974.
alde-
/g/ T. Liljefors, N.L. Allinger, J.&a,Lh<?,-%?& @
hydes and ketones in general by measurement of characte-
(1976) 2745.
riztics easy to determine in the I R and Raman spectra. However, the accurate determination of the dihedral angle by
/lo/
means of the coupled frequency and intensity calculations
/ 1 1 / P. Bleckmann,
is not yet possible f o r large molecules at the present state.
This is due to the approximations required for the treatment
of molecules of that size by semiempirical methods and the
at the present time
- unbearable expence of ab-initio me-
thods. Nevertheless the simulation of vibrational spectra
is
z
pouerful tool in solving conformational problems by
(1973) 7345.
-
D. Iszak, R.J.W.
( B ) 1%66_251.
Le Fevre, J-Ch?$,-S'Z,
Z.Nat_u_~'f_o_c%ck..
zF! (1974) 1485;
M. Spiekermann, D. Bougeard, H.-J. Oelichmann,
5% (1980) 301.
B. Schrader. Theor. Chim,-Py2t_+-Ck&,)_
/12/ H.-J.
Oelichmann, Dissertation, UniversitZ4t Dortmund
1979.
1131 H.-J. Oelichmann, D. Bougeard, 8 . Schrader, J. Hol.
--Struct.
- -- 7_7_
(1981) 149; 179.
model calculattons.
- 1414 -
- 1412 -
Table 2: General infrared and Raman characteristics for
the estimation of the conformation ofa,B-unsatUrated ke-
/14/ B.J. Bestmann, K. Roth, M. Ettlinger, AnReY. Chem.
(1979) 748; Anaew. Chem. Int. Ed. Bnnl.
/15/ B. Schrader, A. Ansmann, Angew. Chem.
tones of aldehydes /3,7,8,12,13/.
(1979) 687.
9 (1975) 345;
AnEeY. Chem. Int. Ed. EnRl. 14 (1975) 364.
/16/ E. Steignsr, B. Schrader, LiebiRS Ann. Cham.
a-cis
8-trans
/17/ E.V.
Sobolev, V.T.
Ser. Khim.
Infrarad iqtensity
(1970)
1, 15.
Aleksanyan, Izv. Akad. Nauk SSSR,
1336.
/18/ The authors are indebted to Prof. Dr. H.J. Bestmann
for supplying the aldehydes.
Received April 6,
1981,
revised June 7. 1982 /z 164 s/
ntiog(C.0)
(Raman)
- 1413 -
- 1415 -
Документ
Категория
Без категории
Просмотров
1
Размер файла
217 Кб
Теги
ramana, mode, calculations, unsaturated, deduced, infrared, conformational, aldehyde, ketone, acyclic, results, limitations, spectral
1/--страниц
Пожаловаться на содержимое документа