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Molecular structure and conformation of some dihalogenodioxanes
TetrahedronLetters Wo. 10, pp. 16-20, 1959. Pergamon Press Ltd. Printed in Great Britain.
MOLECULAR STRUCTUREARD CONFORMATIOROF SOME DIRALOCENODIOXARFS1 C. Altona, C. Romera end E. Ravings Laboratoryof Organic Chemistry,The University,Leiden (Reoeived6 July 1959)
IN recent years the propertiesend the conformationalrelationshipsof some dihalogenocyclohexanes end dihalogenodecalins have been studied in 2,394 this laboratory.
In the present communicationwe mise
the
results obtained in extending the investigation8to halogeno-eubstituted dioxanes. Monochlorodioxane,the known dihalogenodioxanesand one 2,5,5,6tetraohlorodioxane were synthesized(see Table 1) and studied. The followingmethods were employed for the investigationof the conformationalcharacteristioeof the dihalogenodioxanea: (1) Dipole moments were calculatedfrom measurementsin dilute solutions
A Details will be published in the thesis of C. Altona, Leiden and in forthcomingpublicationsin Rec. Trav. Chim, The reeulte of the X-ray analysee will be published in Acta Cryat, 2 W, Kweatroo, F. A. Meyer and E. Ravinga, Rec. Trav. Chim, 12, 717 (1954). ' W. Kweetroo, Thesis, Leiden (1954). 4 J. A. ven der Linden, Thesis, Leiden (1956).
16
Holeoul8r etruoture and oonformationof some dih8logenodioxanes
17
TABLE 1, Dipole moments of some halogeno-substituted diox8nes
xx
compound 3
I
b¶onoohlorodiox8ne5
II
Txans-2,3-diehlorodioxane6
III Tr8ns-2,3-dibromodioxane7 IV
Cie-2,3-dichlorodioxane6
V
Trans-2,5-diohlorodiox8neS
VI
Trans-2,5-dibromodiox8ne9
VII
2 ,o 3
Melting
Dipole moment
point
in benwene
@byes) in CC1 4
2.24
2.28
31
1.63
1.62
74
1.90
1.86
3.06
3.00
124
0.6
0.6
86 - 100
0.0
54
(deoomp.)
5 6*- Tetraohlorodioxanelo
in benzene and carbon tetrachloride,using the ertrapolationformulas of 11 HalVerStadtand KUmler. (2) Inhrr-redabsorptionspectra were obtained from the oompounds in the solid state (K&-disks) and from solutions in carbon diaulphide;the spectrum of III w8s also measured in oyulohexsneand the spectrum of II in cyclohexaneand nitromethane. (3) Ram8n spectra were taken of solutionsof II, III snd IV in solvents with dielectric constantsvarying from 2.1 to 37.5.
5 R. K. Summerbelland L. N. Rauer, J. Amer. Chem. SOC,~,
2364 (1935).
6 R. K. Summerbelland A. E, Lunk, J. Amer. Chem. Sot, 12, 4802 (1957). 7 H. C. D&m, J. Org. Chem, I.47(1958). _ ' L. A. Brysn, W. 1. Smedley and R. K. Summerbell,J. Amer. Chem. Soo, 12, 2206 (1950). ' R. K. Summerbelland L. K. Rochen, J. Amer. Chem. Soo, $2, 3241 (1941). lo M. Udioke and W. Stumpf, Naturwiaeenschaften $2, 363 (1953). I.1I. F. Halverstadtand W. D. Kumler, J. Amer. Chem, Sot, 6& (1942).
2988
Moleoular atructureaud oonfonrrtionof eomedihalogenodioxanee
18
(4)X-rag diffraotionpatterns were taken of single oryatala of III, IV, V and VII (eee Table 2). TABLE 2, Mmenaions of the unit cells in ktrom
unita and apace-groupsof
rome halogenodioxanea Spaoe-
Moxane derivatives Tr&UU+2,3-
a
b
5.68
7.63
a
B
Y
16.02
90
90
90
p212121
4.52 10.75
13.12
90
90
90
P 21/n
4.58
5.46
6.56
06
102.5107
6.70
7.60
90
90
0
group
dibromo-
citb2,3diuhloro-
*8118-2,5-
Pi
dichloro-
2,3,5,6-
p 21/o
tetraohloro-
The analyses of the structure of III and V are in the stage of refinement; they confirm that both compoundsare trans-substitutedand that the dioxane ring haa the chair conformation.To our surprise the halogen atoms of both aompoundewere found to oocupy axial positions. As is well Imown, the trane-1,2-and the trans-l+dihalogenooyalohexanesocaur in solution as an equilibriummixture oonsiating mainly of two conformations,the diaxial (aa) and the diequatorial (ee) chair conformations.This equilibriumvaries with the solvent, as ia evident from the solvent-dependentdipole momenta in the oaee of the 1,2-trans-subetituted compoundsand from the solvent-dependent Raman 2,J,12-16 spectra and infra-redabsorption spectra of these substancea. l2
JCo5ime and T, Yoshino, J.Amer. Chem. Soo. Q, 166 (1953);K. Koeima, K. Sekeshita and S. Haeda, J. Amer. Chem. Soo. 25, 1965 (1954).
K.
Moleoular structureand conformationof some dihalogenodioxanes
19
The trans-substituteddihalogenodioxanesdiffer in these aspects from the cyclohexaneanalogues.The dipole moment appeared to be independentof the solvent. The infra-red spectra of these compoundsin solution regardlees of the solvent - are in all cases identicalwith those of the crystals.The Raman spectra were also found not to vary with the solvent and to be practicallyidenticalwith those obtained from the crystalline material. No indicationswere found, then, for the occurrenceof more than one conformation.We tentativelyconclude that the molcules of the transdihalogenodioxanesshow a strong preferencefor one of the possible conformations. Taking into oonsiderationthat, according to the X-ray analyses, in solid III and V the halogen atoms are in aa positions, that the dipole moments of II and III do not differ appreaiablyand that the infra-red spectra of V and VI beer a close resemblance,we feel safe in concluding that the trans-2,3_dihalogenoand the trans-2,5_dihalogenodioxanes occur in solution ae well as in the solid state in the diaxial &air conformation.
l3 A. Tulinekir,A. DiGiaoomo and C.P. Smyth, J. Amer. Chest.Soo. Q, 3552 (1953 > l
P. Render, D. L. Flowers 3463 (1955).
and 8.
L.
Goering, J. Amer. Chem. Sot, II,
l5 P. Klaeboe, J. J. Lothe and K. Lunde, Acta Chem. Stand, 11, 1677 (1957). 16 For sn early disouseion of infra-reddata see also; M. Lsrnaudie, C. R. Aaad. Sci., Purls 226, 909 (1953). The results of investigationson the oon.?&=matione of cyalohexanederivativesin the gaseous state by eleatron diffractionwere aummarised by 0. Raesel, Researoh 2, 504 (1950).
20
Molecular etructureand conformationof some dihalogenodioxanee
Cie-2,+dichlorodioxane(IV) probably haa the ea conformation,in accordance with the value for the dipole moment that is practicallythe same ae that found for tie-1,2_dichlorocyclohexane (3.13D'). The dipole moments of II and III are somewhathigher than might be expected for a purely diaxial conformation.More data will be needed before a choice can be made between the several poaeible causes for thia phenomenon, As to the reason8 why the halogen atome preferentiallyoccupy axial poeitione in the ease of dihalogenodioxanes , it
might be argued that with
such oompounds the interactionbetween the electronsof an equatorial halogen atom and those of the oqgen atom Is relativelyunfavourable. Furthermore,the number of axial hydrogen atome that cauee steric hindrance ie, of course, smaller in the derivativesof dioxane than in the eubatituted oyclohexanes.
MOLECULAR STRUCTUREARD CONFORMATIOROF SOME DIRALOCENODIOXARFS1 C. Altona, C. Romera end E. Ravings Laboratoryof Organic Chemistry,The University,Leiden (Reoeived6 July 1959)
IN recent years the propertiesend the conformationalrelationshipsof some dihalogenocyclohexanes end dihalogenodecalins have been studied in 2,394 this laboratory.
In the present communicationwe mise
the
results obtained in extending the investigation8to halogeno-eubstituted dioxanes. Monochlorodioxane,the known dihalogenodioxanesand one 2,5,5,6tetraohlorodioxane were synthesized(see Table 1) and studied. The followingmethods were employed for the investigationof the conformationalcharacteristioeof the dihalogenodioxanea: (1) Dipole moments were calculatedfrom measurementsin dilute solutions
A Details will be published in the thesis of C. Altona, Leiden and in forthcomingpublicationsin Rec. Trav. Chim, The reeulte of the X-ray analysee will be published in Acta Cryat, 2 W, Kweatroo, F. A. Meyer and E. Ravinga, Rec. Trav. Chim, 12, 717 (1954). ' W. Kweetroo, Thesis, Leiden (1954). 4 J. A. ven der Linden, Thesis, Leiden (1956).
16
Holeoul8r etruoture and oonformationof some dih8logenodioxanes
17
TABLE 1, Dipole moments of some halogeno-substituted diox8nes
xx
compound 3
I
b¶onoohlorodiox8ne5
II
Txans-2,3-diehlorodioxane6
III Tr8ns-2,3-dibromodioxane7 IV
Cie-2,3-dichlorodioxane6
V
Trans-2,5-diohlorodiox8neS
VI
Trans-2,5-dibromodiox8ne9
VII
2 ,o 3
Melting
Dipole moment
point
in benwene
@byes) in CC1 4
2.24
2.28
31
1.63
1.62
74
1.90
1.86
3.06
3.00
124
0.6
0.6
86 - 100
0.0
54
(deoomp.)
5 6*- Tetraohlorodioxanelo
in benzene and carbon tetrachloride,using the ertrapolationformulas of 11 HalVerStadtand KUmler. (2) Inhrr-redabsorptionspectra were obtained from the oompounds in the solid state (K&-disks) and from solutions in carbon diaulphide;the spectrum of III w8s also measured in oyulohexsneand the spectrum of II in cyclohexaneand nitromethane. (3) Ram8n spectra were taken of solutionsof II, III snd IV in solvents with dielectric constantsvarying from 2.1 to 37.5.
5 R. K. Summerbelland L. N. Rauer, J. Amer. Chem. SOC,~,
2364 (1935).
6 R. K. Summerbelland A. E, Lunk, J. Amer. Chem. Sot, 12, 4802 (1957). 7 H. C. D&m, J. Org. Chem, I.47(1958). _ ' L. A. Brysn, W. 1. Smedley and R. K. Summerbell,J. Amer. Chem. Soo, 12, 2206 (1950). ' R. K. Summerbelland L. K. Rochen, J. Amer. Chem. Soo, $2, 3241 (1941). lo M. Udioke and W. Stumpf, Naturwiaeenschaften $2, 363 (1953). I.1I. F. Halverstadtand W. D. Kumler, J. Amer. Chem, Sot, 6& (1942).
2988
Moleoular atructureaud oonfonrrtionof eomedihalogenodioxanee
18
(4)X-rag diffraotionpatterns were taken of single oryatala of III, IV, V and VII (eee Table 2). TABLE 2, Mmenaions of the unit cells in ktrom
unita and apace-groupsof
rome halogenodioxanea Spaoe-
Moxane derivatives Tr&UU+2,3-
a
b
5.68
7.63
a
B
Y
16.02
90
90
90
p212121
4.52 10.75
13.12
90
90
90
P 21/n
4.58
5.46
6.56
06
102.5107
6.70
7.60
90
90
0
group
dibromo-
citb2,3diuhloro-
*8118-2,5-
Pi
dichloro-
2,3,5,6-
p 21/o
tetraohloro-
The analyses of the structure of III and V are in the stage of refinement; they confirm that both compoundsare trans-substitutedand that the dioxane ring haa the chair conformation.To our surprise the halogen atoms of both aompoundewere found to oocupy axial positions. As is well Imown, the trane-1,2-and the trans-l+dihalogenooyalohexanesocaur in solution as an equilibriummixture oonsiating mainly of two conformations,the diaxial (aa) and the diequatorial (ee) chair conformations.This equilibriumvaries with the solvent, as ia evident from the solvent-dependentdipole momenta in the oaee of the 1,2-trans-subetituted compoundsand from the solvent-dependent Raman 2,J,12-16 spectra and infra-redabsorption spectra of these substancea. l2
JCo5ime and T, Yoshino, J.Amer. Chem. Soo. Q, 166 (1953);K. Koeima, K. Sekeshita and S. Haeda, J. Amer. Chem. Soo. 25, 1965 (1954).
K.
Moleoular structureand conformationof some dihalogenodioxanes
19
The trans-substituteddihalogenodioxanesdiffer in these aspects from the cyclohexaneanalogues.The dipole moment appeared to be independentof the solvent. The infra-red spectra of these compoundsin solution regardlees of the solvent - are in all cases identicalwith those of the crystals.The Raman spectra were also found not to vary with the solvent and to be practicallyidenticalwith those obtained from the crystalline material. No indicationswere found, then, for the occurrenceof more than one conformation.We tentativelyconclude that the molcules of the transdihalogenodioxanesshow a strong preferencefor one of the possible conformations. Taking into oonsiderationthat, according to the X-ray analyses, in solid III and V the halogen atoms are in aa positions, that the dipole moments of II and III do not differ appreaiablyand that the infra-red spectra of V and VI beer a close resemblance,we feel safe in concluding that the trans-2,3_dihalogenoand the trans-2,5_dihalogenodioxanes occur in solution ae well as in the solid state in the diaxial &air conformation.
l3 A. Tulinekir,A. DiGiaoomo and C.P. Smyth, J. Amer. Chest.Soo. Q, 3552 (1953 > l
P. Render, D. L. Flowers 3463 (1955).
and 8.
L.
Goering, J. Amer. Chem. Sot, II,
l5 P. Klaeboe, J. J. Lothe and K. Lunde, Acta Chem. Stand, 11, 1677 (1957). 16 For sn early disouseion of infra-reddata see also; M. Lsrnaudie, C. R. Aaad. Sci., Purls 226, 909 (1953). The results of investigationson the oon.?&=matione of cyalohexanederivativesin the gaseous state by eleatron diffractionwere aummarised by 0. Raesel, Researoh 2, 504 (1950).
20
Molecular etructureand conformationof some dihalogenodioxanee
Cie-2,+dichlorodioxane(IV) probably haa the ea conformation,in accordance with the value for the dipole moment that is practicallythe same ae that found for tie-1,2_dichlorocyclohexane (3.13D'). The dipole moments of II and III are somewhathigher than might be expected for a purely diaxial conformation.More data will be needed before a choice can be made between the several poaeible causes for thia phenomenon, As to the reason8 why the halogen atome preferentiallyoccupy axial poeitione in the ease of dihalogenodioxanes , it
might be argued that with
such oompounds the interactionbetween the electronsof an equatorial halogen atom and those of the oqgen atom Is relativelyunfavourable. Furthermore,the number of axial hydrogen atome that cauee steric hindrance ie, of course, smaller in the derivativesof dioxane than in the eubatituted oyclohexanes.