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Bonding in thiirene dioxides
IJettere
Tatnhedron
No* 13,
pp 1209 - 1212, 1974.
BONDING IN THIIRENE
F.
de Jong,
A.J.
Noorduin,
Departmentof
Organic
Miss
Pe.r@ullon
Prees.
Pcirdd
in
Great
Britain.
DIOXIDES
!I?. Bouwman
Chemistry,
The
and M.J.
.Janssen,
University,
Zernikelaan,Groningen,The Netherlands. (Receivedin UK 1 Wbruary 1974; rccepted'forpublication'15Febru~
1974))
Our continuinginterest in unsaturatedsulfones',led us into a study of the properties of thiirene-l,l-dioxides (1). The structuralresemblancewith cyclopropsnones(2) has induced the
pO.¶+pO 2
idea2-4
that
2r
thiirene-dioxides ars stabilizedby the same typs of cyclopropsniumresonancestruc-
tures (la - and -lb) as are cyclopropenones(a). The participationof w-orbitals of sulfur is often thought to be responsiblefor this analogy. Indeed one does obtain a conjugatedsystem as in cyclopropenones,when the 3d -orbital (fig. 1) of sulfur is used. This Hffckelsystem demands the Y= presence of 2 n electronsfor aromaticityand stabilizationis obtainedby a weakeningof the SO
bond and sn increasein charge density on oxygen (as depictedby resonancestructures&and
2).
However,participationof the sxy orbital creates a M8bius-systemwith exactly oppositedemands for stabilizatiod, namely the presence of 4 n electronsin the ring. This is achievedby a dscrease in charge on oxygen and a strongerSO bond. Obviouslythe total effect of $I orbital resonance on the SO2 group is difficultto estimate. In order to have a more quantitativemeasure for the (in)validityof ketone-sulfone 1209
1211
No. 13
(FX-I values in cm-' given in parenthesis):
whereas for ketones:
MOO)
to be a In good agreementwith theory, we find cyclopropenoneto be a strong, thiirene-dioxide weak acceptorin hydrogenbonding. Interestinglyenough, the smaller calculatedpolarity of the SO bond in thiirenediaxider is accompaniedby a decreasein bondorder (TableI). This property causes thiirenedioxidesto be a unique class of sulfones,since in a series of dialkyl sulfonesa less polar SO bond (as judged from dipole moments or from hydrogen bonding ability)is accompaniedby a strengtheningof the SO bond" (as judgedfromthe SO stretchingfrequency) (fig.2). The relationshipbetween AvoH and lb that we used before to distinguishbetween dialkyl sulfones end thi@mne dioxides,clearly so2 demonstratesthe differentelectronicconfigurationof the S02-groupin thiirenedioxides,resulVasP
ting in abnormallylow values of vso . 2 Fig. 2 Plot of AVoH versus $s;"" for 2 a: dialkyl and diary1 sulfones b: thiophenedioxides c: thiirenedioxides X 110 YP
4H
so2
1m 1: X=H; ECH f 160
3
2: X=Y=C6H5
160
3: X=Y=C6H4.pCH3
'La
4: X=Y=C6H4.pC1
Ho. 13
1212
The origin of the small SO bondordercan be traced by breakdownof the calculatedtotal bondorder into the syknnetry ccnrponents of the C2v symmetry group (TableII). The Hackel-typeresonance (b2) and the 3d orbitals.Considering is subdividedinto the contributionsinvolvingthe sulfur 2 PY Ya the sulfur d orbitals,it follows that the decrease of the SO bondorderby the Hffckel-type of Table II SO bondorderdecomposedinto symmetryccnnponents
Compound
bl
pY CH3SO-CH
3
total
b2 dYa
0.856
0.292
0.329
0.450
0.30
2.196
0.844
O.Y5
0.344
0.449
0.249
2.191
0.837
0.319
0.350
0.409
0.197
2.113
0.852
0.278
0.351
0.450
0.262
2.!93
resonance (b2) is opposed by an increasedue to MBbius-typeof resonance (a,).The Hffckel-type of resonance of the sulfur 3py orbital gives rise to a further decrease in SO bondindexfor thiirene-
dioxide.As can be seen frcm the values for dimethylsulfoneand thiiranedioxide,differencesin CSC angle hardly effect the SO bondorder. In conclusionwe can state that a comparisonof cyclic unsaturatedsulfonesand ketones orbital of the sulfur atcducan -and does- promote resonance is of little value. Althoughthe d Y= orbital structuresanalogousto the predominantpolar resonancestructuresin ketones, the d xy has a contraryeffect of comparablemagnitude.The effect is a nice demonstrationof the importance of M8bius aromaticityas comparedto the more popular Hflckelaromaticity. References: la. F. de Jong, M.J. Janssen,J.Chem.Soc.Perkin Trans II, 572 (1972). b. Ibid., Rec.Trav.Chim.'$& 1073 (1973). 2. M.E. Volpin, Yu. D. Koreshkov,V.G. Dulova, D.N. Kurssnov,Tetrahedron&. 107 (1962). 3. L.A. Carpino, L.V. McAdams. III, J.Amer.Chem.Soc. 87, 5804 (1965). 4. L.A. Paquette,L.S. Wittenbrook,Ibid. &, 4483 (137). 5. M.J.S. Dewar, Angew.Chem.8 859 (1971). 6. K.B. Wiberg, Tetrahedron2_, z 1083 (1968). 7. F. Ijima, Bull.Chem.Soc.Jap. 9, 1049 (1970). 8. H.L. bon, J.Amer.Chem.Soc. s, 7093 (1973). 9. R.C. Benson,W.H. Flygare,M. Oda, R. Braslow,Ibid. , 2'772 (1973). 10. D.J. Bertelli,T.G. Andrews, Jr., Ibid. yl_,5280 (1969 7 . 11. J.A. Pople, G.A. Segal, J.Chtm.Phys.&, 3289 (1966). 12. L.A. Carpinc, L.V. McAdams, III, R.H. Rynbrandt,J.W. Spiewak,J.Amer.Chem.Soc. 2, 476 (1971). 13. P. Biscarni,G. Galloni,S. Ghprsetti,SpectrocL.im. Act. g, 26., (1964).
Tatnhedron
No* 13,
pp 1209 - 1212, 1974.
BONDING IN THIIRENE
F.
de Jong,
A.J.
Noorduin,
Departmentof
Organic
Miss
Pe.r@ullon
Prees.
Pcirdd
in
Great
Britain.
DIOXIDES
!I?. Bouwman
Chemistry,
The
and M.J.
.Janssen,
University,
Zernikelaan,Groningen,The Netherlands. (Receivedin UK 1 Wbruary 1974; rccepted'forpublication'15Febru~
1974))
Our continuinginterest in unsaturatedsulfones',led us into a study of the properties of thiirene-l,l-dioxides (1). The structuralresemblancewith cyclopropsnones(2) has induced the
pO.¶+pO 2
idea2-4
that
2r
thiirene-dioxides ars stabilizedby the same typs of cyclopropsniumresonancestruc-
tures (la - and -lb) as are cyclopropenones(a). The participationof w-orbitals of sulfur is often thought to be responsiblefor this analogy. Indeed one does obtain a conjugatedsystem as in cyclopropenones,when the 3d -orbital (fig. 1) of sulfur is used. This Hffckelsystem demands the Y= presence of 2 n electronsfor aromaticityand stabilizationis obtainedby a weakeningof the SO
bond and sn increasein charge density on oxygen (as depictedby resonancestructures&and
2).
However,participationof the sxy orbital creates a M8bius-systemwith exactly oppositedemands for stabilizatiod, namely the presence of 4 n electronsin the ring. This is achievedby a dscrease in charge on oxygen and a strongerSO bond. Obviouslythe total effect of $I orbital resonance on the SO2 group is difficultto estimate. In order to have a more quantitativemeasure for the (in)validityof ketone-sulfone 1209
1211
No. 13
(FX-I values in cm-' given in parenthesis):
whereas for ketones:
MOO)
to be a In good agreementwith theory, we find cyclopropenoneto be a strong, thiirene-dioxide weak acceptorin hydrogenbonding. Interestinglyenough, the smaller calculatedpolarity of the SO bond in thiirenediaxider is accompaniedby a decreasein bondorder (TableI). This property causes thiirenedioxidesto be a unique class of sulfones,since in a series of dialkyl sulfonesa less polar SO bond (as judged from dipole moments or from hydrogen bonding ability)is accompaniedby a strengtheningof the SO bond" (as judgedfromthe SO stretchingfrequency) (fig.2). The relationshipbetween AvoH and lb that we used before to distinguishbetween dialkyl sulfones end thi@mne dioxides,clearly so2 demonstratesthe differentelectronicconfigurationof the S02-groupin thiirenedioxides,resulVasP
ting in abnormallylow values of vso . 2 Fig. 2 Plot of AVoH versus $s;"" for 2 a: dialkyl and diary1 sulfones b: thiophenedioxides c: thiirenedioxides X 110 YP
4H
so2
1m 1: X=H; ECH f 160
3
2: X=Y=C6H5
160
3: X=Y=C6H4.pCH3
'La
4: X=Y=C6H4.pC1
Ho. 13
1212
The origin of the small SO bondordercan be traced by breakdownof the calculatedtotal bondorder into the syknnetry ccnrponents of the C2v symmetry group (TableII). The Hackel-typeresonance (b2) and the 3d orbitals.Considering is subdividedinto the contributionsinvolvingthe sulfur 2 PY Ya the sulfur d orbitals,it follows that the decrease of the SO bondorderby the Hffckel-type of Table II SO bondorderdecomposedinto symmetryccnnponents
Compound
bl
pY CH3SO-CH
3
total
b2 dYa
0.856
0.292
0.329
0.450
0.30
2.196
0.844
O.Y5
0.344
0.449
0.249
2.191
0.837
0.319
0.350
0.409
0.197
2.113
0.852
0.278
0.351
0.450
0.262
2.!93
resonance (b2) is opposed by an increasedue to MBbius-typeof resonance (a,).The Hffckel-type of resonance of the sulfur 3py orbital gives rise to a further decrease in SO bondindexfor thiirene-
dioxide.As can be seen frcm the values for dimethylsulfoneand thiiranedioxide,differencesin CSC angle hardly effect the SO bondorder. In conclusionwe can state that a comparisonof cyclic unsaturatedsulfonesand ketones orbital of the sulfur atcducan -and does- promote resonance is of little value. Althoughthe d Y= orbital structuresanalogousto the predominantpolar resonancestructuresin ketones, the d xy has a contraryeffect of comparablemagnitude.The effect is a nice demonstrationof the importance of M8bius aromaticityas comparedto the more popular Hflckelaromaticity. References: la. F. de Jong, M.J. Janssen,J.Chem.Soc.Perkin Trans II, 572 (1972). b. Ibid., Rec.Trav.Chim.'$& 1073 (1973). 2. M.E. Volpin, Yu. D. Koreshkov,V.G. Dulova, D.N. Kurssnov,Tetrahedron&. 107 (1962). 3. L.A. Carpino, L.V. McAdams. III, J.Amer.Chem.Soc. 87, 5804 (1965). 4. L.A. Paquette,L.S. Wittenbrook,Ibid. &, 4483 (137). 5. M.J.S. Dewar, Angew.Chem.8 859 (1971). 6. K.B. Wiberg, Tetrahedron2_, z 1083 (1968). 7. F. Ijima, Bull.Chem.Soc.Jap. 9, 1049 (1970). 8. H.L. bon, J.Amer.Chem.Soc. s, 7093 (1973). 9. R.C. Benson,W.H. Flygare,M. Oda, R. Braslow,Ibid. , 2'772 (1973). 10. D.J. Bertelli,T.G. Andrews, Jr., Ibid. yl_,5280 (1969 7 . 11. J.A. Pople, G.A. Segal, J.Chtm.Phys.&, 3289 (1966). 12. L.A. Carpinc, L.V. McAdams, III, R.H. Rynbrandt,J.W. Spiewak,J.Amer.Chem.Soc. 2, 476 (1971). 13. P. Biscarni,G. Galloni,S. Ghprsetti,SpectrocL.im. Act. g, 26., (1964).