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Infrared spectra and structure of substituted unsaturated carbonyl compounds
JotmnaI
of Molecular
Strurture
Elsevier Publishing Company, Amsterdam, Printed in the Netherlands
INFRARED SPECTRA AND STRUCTURE OF SUBSTITUTED UNSATURATED CARBONYL COMPOUNDS XVI. COMPLEXES OF LEWIS ACIDS WITH NJ+DIALKYL VINYLOGUES
AMIDE
JANUSZ D$BROWSKI AND MAGDALENA KqTCKA Institute of Organic
Chemistry,
Polish Academy
of Sciences,
Warsaw 42 (Poland)
(Received 10 January 1972)
ABSTRACT
N,N-Dialkyl amide vinylogues form coordinative complexes with Lewis acids. The lowering of the carbonyl stretching frequency points unambiguously to an 0-complexation.
INTRODUCTiON
In our preceding paper’ we reported on the infrared spectra of complexes of Lewis acids with vinyiogues of acyl chlorides. The complexes were found to be of coordinative type with a linkage to the carbonyl oxygen. Coordinative complexation resulted in a marked lowering of the carbonyl stretching frequency; the olefinic stretching frequency was also lowered which was explained by mesomeric changes in bond orders of the conjugated system. With amide vinylogues, an ionic complex is not feasible; on the other hand two different coordinative complexes can be formed as two centres of comparable basicity, i.e. the oxygen and the nitrogen atoms, are present in the molecule. Since a totally different distribution of electron density should occur upon complexation at these two centres one can expect the spectroscopic data to be conclusive with regard to the structure of the complexes. A similar problem was faced in the case of amides2 and ureas3 and resolved in favour of O-complexation. The above results cannot simply be extended on amide vinylogues, however, as the latter exhibit two different carbonyl bands due to rotational isomerism thus posing the problem of the direction of the frequency shift. This diffi~uIty was overcome by investigating several complexes of rigid amide vinylogues. f. MoI. Structure, 12 (1972)
179
EXPERIMENTAL
/3-Dimethylaminovinyl aldehyde (I) was obtained by addition of dimethylamine to propargylic aldehyde4; /3-dialkylaminovinyl ketones were prepared from dialkylamines and the appropriate chlorovinyf ketones (II-VI)‘, ZhydroxymethyIene-cycIohexanI-one (VII)” or 1,3-cyclohexandione (WIK)‘. Compounds I-V and VII were purified by twofoId vacuum distiliation, VI by recrystallization from methanol and VIII by thin layer chromatography on silica gel. Aiuminium trichloride was purified by vacuum sublimation, titanium tetrachloride and tin tetrachloride by distillation. The formation of complexes and the preparation of samples for the infrared measurements were carried out in a dry-box. The com-
plexes were prepared by adding a solution of Lewis acid in carbon tetrachloride to an equimolar amount ofp-dialkyIaminoviny1 aldehyde or ketone in the same solvent. The liquid, viscous complexes of j?-dialkylaminovinyl ketones with AlCI, were investigated as a capillary film. The solid complexes of ~-diaIkyIaminoviny1 ketones with TiCI, and SnCI, were washed with CC&, dried, and examined as a suspension in Nujol. Infrared measurements were carried out using a Hilger H-800 double-beam spectrophotometer equipped with a rock-salt prism. The spectra were calibrated with polystyrene and are believed to be accurate to t-2 cm-’ in the double-bond stretching region. RESULTS
DISCUSSION
AND
AlI spectral data are presented in Table I which includes assignments made according to the discussion. Representative spectra are given in Fig. 1. It should be remembered that aliphatic open-chain /3-dialkylaminovinyl ketones and aldehydes exhibit three absorption bands in the double-bond stretching region. The band occurring at highest frequency was assigned6 to the S-&Y rotamer’s skeletal vibration dominated by C-0 stretch, vcZo (s-c’s); the middle band and that occurring at lowest frequency were assigned to a similar vcZo (s-frans) and v,-, type of vibration frequency, respectively. Upon complex formation with al1 Lewis acids examined here a new band arises in pIace of the two carbonyl bands, its frequency being intermediate between them. It is not possible to decide, in advance, whether the new band is a result of a low frequency shift of the vcZo (s-r%) band or rather of an opposite shift of the vcZo (s-trans) band. In the former case the observed spectroscopic change would clearly indicate an Ocomplexation whereas N-compIexation would account for the enhanced frequency; this point is iIIustrated by the following formulae:
1
180
2
J. MoL S&&we,
12 (1972)
TABLE
1
THE MAIN IR ABSORPTION BANDS 1750650 cm-l REGION
OF AMIDE
VINYLOGUES
AND
THEIR
COMPLEXES
WITH
LEWIS
ACIDS
IN THE
Conwounii
Assignment /H l’c=o
l’czo
s-cis
s-tram
LHCOCH-CHN(CH,), Ia(I - AICIJ) Ib (I - Tic&) Ic (I - SnC1.d
1668 w
II. IIa IIb IIc
1658 s
CHJCOCH-CHN(C2H& (11 - AI&) (II - TiCI,) (II * SnC14)
IV. C2HSCOCH-CHN(&H& 1Va (IV - AICIJ) IVb (IV - TiC14) IVc (IV - SnC14)
1657 s
V. Va Vb Vc
1657 s
VI. C6HSCOCH-CHN(CH& Via (VI - AICIB) VIb (VI - TiCI.+) WC (VI - SnCI,)
VII_
a
1568 vs 1553 vs 1544m 1563 s
1324 w 1316 m 1326 m
986 m 1004 m 995 m 999 m
1613 sh 1575 vs 1549 vs 1549 s 1537m
1314 m 1309 m 1325m
985 m 1014 m 1003 m 1005 w
1568 vs 1549 vs 1549 s 1528m
1330 m 1321 w 1330m
986 m 992 m 1010 s 1002 m
1577 vs 1547 vs 1545 s 1535 s
1317 m 1305 m 1312 m
983 w 965 m 957 m 974 m
1632 s 1629 s,
1648 s 1639 s
1612 s 1628 vs
1634 vs 1627 s 1610 sh 1642 vs 1646 s 1634 vs 1586 vs 1584m 1591 m 1584m
1640 vs 1636 s 1634 m 1634 s
961 m
971 w 1001 w 1007 m
1606 vs
1642 vs
H
1330 w 1337 m 1334 s
1630 vs
1658 s
%Z=N(?) ~,C=d
1585 m 1582 m 1568 s 1574 vs
1654 m 1653 s 1655 s
III. C2H5COCH-CHN(CH& IIIa (III - AM&) Illb (III - TiCL) 111~(III - SnCI,)
(CH&CHCOCH-CHN(CH& (V - AIf&) (V - TiCI*) (V - SnCld
1625 vs
l'C=C
1550 vs 1548m 1536m 1530m
1310 w 1300~
1002 w 998 w 998 w 982 w
CHN(C2H5)2
1542 s
1647 s 0
1514 vs 1349 s 1506 s 1337 m 1530 sh 1323 s
1622 s 1617 s 1596 s
VIIa (VII - AICIJ) VIIb (VII - TiCI&) VIIc (VII - SnC1.d NKH$2
VIII.
1605 s
I q
1549 vs
0
VIIIa (VIII - AIC.13) VIIIb (VIII - TiC14) VIIIc (VIII - SnCld
J. Mol. Structure,
12 (1972)
1578 s 1572 s 1528 s
1545 vs 1314 5 1546 sh 1341 m 1530 s 1341 m
181
1750
1500
1250
1000
750
Fig. 1. Infrared spectra of ethyl- fi- diethylaminovinyl ketone (IV) and its complexes. IV in liquid fiIm, IVa (= IV - AK&) in liquid film, IVb (IV * Tit&) in Nujol, IVc (IV * SnCL) in Nujol.
In order to make the choice between the above alternatives the complexes with rigid s-cis gnd s-tram enamino ketones (compounds VII and VIII, respectively) were examined. In both cases large low-frequency shifts were observed thus unambiguously pointing to an O-complexation. The yczc band, which is common to both rotamer&‘* 8 in 411 cases was
shifted to lower frequencies, this result being more readily -explained by scheme 1 rather than 2 because O-coordination augments the mesomeric changes already existing in the parent molecufe. The most interesting of the remaining absorption bands would be the stretching C-C and C-N’ bands which are expected to shift towards higher wave numbers upon complexatiou. Gerrard et aL2 found the amide III band, dominated by the C-N &retch, at 1299 cm-’ in N-ðyl ac&aniide &nd & i332-cm-’ in its 182
J. Mol. Structure,12 (1972)
complex with boron trichloride. A shift in the same direction was observed by Paul and Chadha in ureas3 and hydrazidesg and by Kuhn and Mc1ntyre.m amides (ref. 10). As for the amide vinylogues investigated here, there is a band.of medium intensity in the 13051330 cm-l region in the spectra of their complexes, but it is not clear which band is related to this vibration in the spectra of the parent .bases. The vc_c band was also hardly assignable. The only band of diagnostic value in the fingerprint region seems to be that due to the trans-olefinic out-ofplane vibration occurring at 961-1002 cm- I in the spectra of the parent compounds I-VI and at 957-1010 cm-’ in those of their complexes. The vaIue above 1000 cm-’ may seem somewhat high, but, as in the majority of cases, there are no other bands in the vicinity, this assignment appears to be correct.
NOTE
This work is a part of the Polish Academy of Sciences Programme for Structural Research (PAN-3)
REFERENCES
1 J. D~BROWSKIAND M. K~TCKA, J. Mol. Structzrre, 7 (1971)179. 2 W. GERRARD, M. F. LAPPERT, H. PYSZORA AND J. W. WALLIS, J. Cjzem. Sot.,
(1960)2144; R. C. PAUL AND S. L. CHADHA, .l. Izzurg. Nzzcl. Chem., 28 (1966)1225. 3 R. RIPEST,Can. J. Chem., 40 (1962)2234; R. C. PAUL AND S. L. CHADHA, SpectrocIzinz. Acta, 23A (1967)1243. 4 S. S. MALHOTRA AND M. C. WHITING, J. Chetzz. SOL, (1960)3812. 5 N. K. KOCHETKOV, IZV.Akad. Nauk SSSR., Otd. Hzitn. Nauk, (1953) 991. 6 J. D_~BROWSKI AND K. KAMIIX&KA-TRELA, Spectroclzitn. Acta., 22 (1966) 211. 7 F. HOFFMANN-LA-ROCHE, German Patent, 7 June 1935.,614 195. 8 J.D_~BROWSKIAND K.KAMIE&SKA-TRELA,ROCZ. Chem.,40 (1966)831. 9 R. C. PAUL AND S. L. CHADHA, Spectrochinz. Acta, 23A (1967) 1249. 10 Sr.J. KUHN AND J. S. MCINTYRE, Can. J. CIzetn., 43 (1965) 375.
J. Mol.
Structure,
12 (1972)
183
of Molecular
Strurture
Elsevier Publishing Company, Amsterdam, Printed in the Netherlands
INFRARED SPECTRA AND STRUCTURE OF SUBSTITUTED UNSATURATED CARBONYL COMPOUNDS XVI. COMPLEXES OF LEWIS ACIDS WITH NJ+DIALKYL VINYLOGUES
AMIDE
JANUSZ D$BROWSKI AND MAGDALENA KqTCKA Institute of Organic
Chemistry,
Polish Academy
of Sciences,
Warsaw 42 (Poland)
(Received 10 January 1972)
ABSTRACT
N,N-Dialkyl amide vinylogues form coordinative complexes with Lewis acids. The lowering of the carbonyl stretching frequency points unambiguously to an 0-complexation.
INTRODUCTiON
In our preceding paper’ we reported on the infrared spectra of complexes of Lewis acids with vinyiogues of acyl chlorides. The complexes were found to be of coordinative type with a linkage to the carbonyl oxygen. Coordinative complexation resulted in a marked lowering of the carbonyl stretching frequency; the olefinic stretching frequency was also lowered which was explained by mesomeric changes in bond orders of the conjugated system. With amide vinylogues, an ionic complex is not feasible; on the other hand two different coordinative complexes can be formed as two centres of comparable basicity, i.e. the oxygen and the nitrogen atoms, are present in the molecule. Since a totally different distribution of electron density should occur upon complexation at these two centres one can expect the spectroscopic data to be conclusive with regard to the structure of the complexes. A similar problem was faced in the case of amides2 and ureas3 and resolved in favour of O-complexation. The above results cannot simply be extended on amide vinylogues, however, as the latter exhibit two different carbonyl bands due to rotational isomerism thus posing the problem of the direction of the frequency shift. This diffi~uIty was overcome by investigating several complexes of rigid amide vinylogues. f. MoI. Structure, 12 (1972)
179
EXPERIMENTAL
/3-Dimethylaminovinyl aldehyde (I) was obtained by addition of dimethylamine to propargylic aldehyde4; /3-dialkylaminovinyl ketones were prepared from dialkylamines and the appropriate chlorovinyf ketones (II-VI)‘, ZhydroxymethyIene-cycIohexanI-one (VII)” or 1,3-cyclohexandione (WIK)‘. Compounds I-V and VII were purified by twofoId vacuum distiliation, VI by recrystallization from methanol and VIII by thin layer chromatography on silica gel. Aiuminium trichloride was purified by vacuum sublimation, titanium tetrachloride and tin tetrachloride by distillation. The formation of complexes and the preparation of samples for the infrared measurements were carried out in a dry-box. The com-
plexes were prepared by adding a solution of Lewis acid in carbon tetrachloride to an equimolar amount ofp-dialkyIaminoviny1 aldehyde or ketone in the same solvent. The liquid, viscous complexes of j?-dialkylaminovinyl ketones with AlCI, were investigated as a capillary film. The solid complexes of ~-diaIkyIaminoviny1 ketones with TiCI, and SnCI, were washed with CC&, dried, and examined as a suspension in Nujol. Infrared measurements were carried out using a Hilger H-800 double-beam spectrophotometer equipped with a rock-salt prism. The spectra were calibrated with polystyrene and are believed to be accurate to t-2 cm-’ in the double-bond stretching region. RESULTS
DISCUSSION
AND
AlI spectral data are presented in Table I which includes assignments made according to the discussion. Representative spectra are given in Fig. 1. It should be remembered that aliphatic open-chain /3-dialkylaminovinyl ketones and aldehydes exhibit three absorption bands in the double-bond stretching region. The band occurring at highest frequency was assigned6 to the S-&Y rotamer’s skeletal vibration dominated by C-0 stretch, vcZo (s-c’s); the middle band and that occurring at lowest frequency were assigned to a similar vcZo (s-frans) and v,-, type of vibration frequency, respectively. Upon complex formation with al1 Lewis acids examined here a new band arises in pIace of the two carbonyl bands, its frequency being intermediate between them. It is not possible to decide, in advance, whether the new band is a result of a low frequency shift of the vcZo (s-r%) band or rather of an opposite shift of the vcZo (s-trans) band. In the former case the observed spectroscopic change would clearly indicate an Ocomplexation whereas N-compIexation would account for the enhanced frequency; this point is iIIustrated by the following formulae:
1
180
2
J. MoL S&&we,
12 (1972)
TABLE
1
THE MAIN IR ABSORPTION BANDS 1750650 cm-l REGION
OF AMIDE
VINYLOGUES
AND
THEIR
COMPLEXES
WITH
LEWIS
ACIDS
IN THE
Conwounii
Assignment /H l’c=o
l’czo
s-cis
s-tram
LHCOCH-CHN(CH,), Ia(I - AICIJ) Ib (I - Tic&) Ic (I - SnC1.d
1668 w
II. IIa IIb IIc
1658 s
CHJCOCH-CHN(C2H& (11 - AI&) (II - TiCI,) (II * SnC14)
IV. C2HSCOCH-CHN(&H& 1Va (IV - AICIJ) IVb (IV - TiC14) IVc (IV - SnC14)
1657 s
V. Va Vb Vc
1657 s
VI. C6HSCOCH-CHN(CH& Via (VI - AICIB) VIb (VI - TiCI.+) WC (VI - SnCI,)
VII_
a
1568 vs 1553 vs 1544m 1563 s
1324 w 1316 m 1326 m
986 m 1004 m 995 m 999 m
1613 sh 1575 vs 1549 vs 1549 s 1537m
1314 m 1309 m 1325m
985 m 1014 m 1003 m 1005 w
1568 vs 1549 vs 1549 s 1528m
1330 m 1321 w 1330m
986 m 992 m 1010 s 1002 m
1577 vs 1547 vs 1545 s 1535 s
1317 m 1305 m 1312 m
983 w 965 m 957 m 974 m
1632 s 1629 s,
1648 s 1639 s
1612 s 1628 vs
1634 vs 1627 s 1610 sh 1642 vs 1646 s 1634 vs 1586 vs 1584m 1591 m 1584m
1640 vs 1636 s 1634 m 1634 s
961 m
971 w 1001 w 1007 m
1606 vs
1642 vs
H
1330 w 1337 m 1334 s
1630 vs
1658 s
%Z=N(?) ~,C=d
1585 m 1582 m 1568 s 1574 vs
1654 m 1653 s 1655 s
III. C2H5COCH-CHN(CH& IIIa (III - AM&) Illb (III - TiCL) 111~(III - SnCI,)
(CH&CHCOCH-CHN(CH& (V - AIf&) (V - TiCI*) (V - SnCld
1625 vs
l'C=C
1550 vs 1548m 1536m 1530m
1310 w 1300~
1002 w 998 w 998 w 982 w
CHN(C2H5)2
1542 s
1647 s 0
1514 vs 1349 s 1506 s 1337 m 1530 sh 1323 s
1622 s 1617 s 1596 s
VIIa (VII - AICIJ) VIIb (VII - TiCI&) VIIc (VII - SnC1.d NKH$2
VIII.
1605 s
I q
1549 vs
0
VIIIa (VIII - AIC.13) VIIIb (VIII - TiC14) VIIIc (VIII - SnCld
J. Mol. Structure,
12 (1972)
1578 s 1572 s 1528 s
1545 vs 1314 5 1546 sh 1341 m 1530 s 1341 m
181
1750
1500
1250
1000
750
Fig. 1. Infrared spectra of ethyl- fi- diethylaminovinyl ketone (IV) and its complexes. IV in liquid fiIm, IVa (= IV - AK&) in liquid film, IVb (IV * Tit&) in Nujol, IVc (IV * SnCL) in Nujol.
In order to make the choice between the above alternatives the complexes with rigid s-cis gnd s-tram enamino ketones (compounds VII and VIII, respectively) were examined. In both cases large low-frequency shifts were observed thus unambiguously pointing to an O-complexation. The yczc band, which is common to both rotamer&‘* 8 in 411 cases was
shifted to lower frequencies, this result being more readily -explained by scheme 1 rather than 2 because O-coordination augments the mesomeric changes already existing in the parent molecufe. The most interesting of the remaining absorption bands would be the stretching C-C and C-N’ bands which are expected to shift towards higher wave numbers upon complexatiou. Gerrard et aL2 found the amide III band, dominated by the C-N &retch, at 1299 cm-’ in N-ðyl ac&aniide &nd & i332-cm-’ in its 182
J. Mol. Structure,12 (1972)
complex with boron trichloride. A shift in the same direction was observed by Paul and Chadha in ureas3 and hydrazidesg and by Kuhn and Mc1ntyre.m amides (ref. 10). As for the amide vinylogues investigated here, there is a band.of medium intensity in the 13051330 cm-l region in the spectra of their complexes, but it is not clear which band is related to this vibration in the spectra of the parent .bases. The vc_c band was also hardly assignable. The only band of diagnostic value in the fingerprint region seems to be that due to the trans-olefinic out-ofplane vibration occurring at 961-1002 cm- I in the spectra of the parent compounds I-VI and at 957-1010 cm-’ in those of their complexes. The vaIue above 1000 cm-’ may seem somewhat high, but, as in the majority of cases, there are no other bands in the vicinity, this assignment appears to be correct.
NOTE
This work is a part of the Polish Academy of Sciences Programme for Structural Research (PAN-3)
REFERENCES
1 J. D~BROWSKIAND M. K~TCKA, J. Mol. Structzrre, 7 (1971)179. 2 W. GERRARD, M. F. LAPPERT, H. PYSZORA AND J. W. WALLIS, J. Cjzem. Sot.,
(1960)2144; R. C. PAUL AND S. L. CHADHA, .l. Izzurg. Nzzcl. Chem., 28 (1966)1225. 3 R. RIPEST,Can. J. Chem., 40 (1962)2234; R. C. PAUL AND S. L. CHADHA, SpectrocIzinz. Acta, 23A (1967)1243. 4 S. S. MALHOTRA AND M. C. WHITING, J. Chetzz. SOL, (1960)3812. 5 N. K. KOCHETKOV, IZV.Akad. Nauk SSSR., Otd. Hzitn. Nauk, (1953) 991. 6 J. D_~BROWSKI AND K. KAMIIX&KA-TRELA, Spectroclzitn. Acta., 22 (1966) 211. 7 F. HOFFMANN-LA-ROCHE, German Patent, 7 June 1935.,614 195. 8 J.D_~BROWSKIAND K.KAMIE&SKA-TRELA,ROCZ. Chem.,40 (1966)831. 9 R. C. PAUL AND S. L. CHADHA, Spectrochinz. Acta, 23A (1967) 1249. 10 Sr.J. KUHN AND J. S. MCINTYRE, Can. J. CIzetn., 43 (1965) 375.
J. Mol.
Structure,
12 (1972)
183