ELECTRONIC STRUCTURE OF ETHYNYL SUBSTITUTED CYCLOBUTADIENES
Frank Lee Emmert III, Stephanie Thompson, and Lyudmila V. Slipchenko
Purdue University, West Lafayette, IN 47907
Fullerene formationBergman
CyclizationRing
Closure
Retro [2+2]
Coalescence and
Annealing
Hunter, J. M.; Fye, J. L.; Roskamp, E. J.; Jarrold, M. F. J. Phys. Chem. 1994, 98, 1810−1818.
Proposed mechanism for the formation of fullerenes.
H H
HH
1,2,3,4-tetraethynylcyclobuta-1,3-diene
Fullerene formation
HH
H
H
1,2,3-triethynylcyclobuta-1,3-diene
H
H
H
H
1,2-diethynylcyclobuta-1,3-diene
H
H H
H
1,4-diethynylcyclobuta-1,3-diene
H
H
H H
1-ethynylcyclobuta-1,3-diene
HH
H H
cyclobuta-1,3-diene
H
H
H
H
1,3-diethynylcyclobuta-1,3-diene
We cut the alkyne tails and looked at ethynyl substituted cyclobutadienes.
H H
HH
1,2,3,4-tetraethynylcyclobuta-1,3-diene
Fullerene formation
We calculated:equilibrium geometries adiabatic S-T gap energiesvertical S-T gap energiesstabilization energy of the ethynyl
substituentsspin densities (not discussed)natural charges (not discussed)
H
H
H H
1-ethynylcyclobuta-1,3-diene
HH
H H
cyclobuta-1,3-diene
H
H
H
H
1,3-diethynylcyclobuta-1,3-diene
Cyclobutadiene orbitalsSinglet cyclobutadiene undergoes Jahn-Teller distortion and becomes
rectangular.
1.34211.3676
1.56861.5679
1.43911.43961.4516
MP2EOM-SF-CCSD
ROMP2UMP2EOM-SF-CCSD
Triplet
Singlet
Singlet cyclobutadiene undergoes Jahn-Teller distortions to make a rectangular structure. Spin Flip variant of the Equation of Motion Coupled Cluster with single and double excitations was
emplolyed. Accuracy of Møller-Plesset 2nd order perturbation theory was tested employing both a restricted open shell
and unrestricted reference
SingletTriplet
L. V. Slipchenko and A. I. Krylov J. Chem. Phys. 2002, 117, 4694
Optimized singlet geometries
1 2
34
56
EOM-SF-CCSD/cc-pVDZ
Singlet Bond Lengths (Å)
Molecule 1 2 3 40-c 1.567 1.367 1.567 1.3671-c 1.557 1.353 1.557 1.371
2-c short 1.551 1.368 1.551 1.3702-c long 1.563 1.374 1.554 1.3742-c trans 1.564 1.377 1.564 1.377
3-c 1.542 1.385 1.546 1.3794-c 1.558 1.388 1.558 1.388
Ethynyl Substituents (Å)
bond 5 6average 1.42 1.22
Main pattern of alternating bond lengths does not change with substituent addition.
The singlet geometries become more square with increased diradical character.
Substituent bond lengths remain nearly constant.
Optimized triplet geometries
1 2
34
56
EOM-SF-CCSD/cc-pVDZ
Triplet Bond Lengths (Å)
Molecule 1 2 3 40-c 1.451 1.451 1.451 1.4511-c 1.466 1.466 1.438 1.4382-c 1.455 1.483 1.455 1.423
2-c trans 1.453 1.453 1.453 1.4533-c 1.456 1.442 1.442 1.4564-c 1.456 1.456 1.456 1.456
Ethynyl Substituents (Å)
bond 5 6average 1.42 1.22
Square structure is maintained when substituents are added symmetrically.
The triplet geometries have increasing bond lengths; decreasing the aromaticity.
Substituent bond lengths remain nearly constant.
Adiabatic energies
0-c 1-c 2-c short 2-c trans 2-c long 3-c 4-c0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
1.1
1.2
EOM-SF-CCSD UMP2
ROMP2 ROCCSD(T)
Ene
rgy
(eV
)
The singlet triplet gap decreases with substituent addition.UMP2 does not follow the trend of decreasing singlet-triplet gap energy.Main source of error is spin contamination of the triplet state.
MP2 vertical energies
Vertical S-T gaps should be larger at singlet geometries and smaller at triplet geometries.
MP2 cannot properly describe the diradical singlet state at the triplet geometries where the two π-orbitals of the ring are degenerate.
-0.50
0.00
0.50
1.00
1.50
2.00
2.50
0-c 1-c 2-c short 2-c long 2-c trans 3-c 4-c
Ene
rgy
(eV
)
RMP2//UMP2 UMP2//RMP2
-0.50
0.00
0.50
1.00
1.50
2.00
2.50
0-c 1-c 2-c short 2-c long 2-c trans 3-c 4-c
Ene
rgy
(eV
)
RMP2//ROMP2 ROMP2//RMP2
Adiabatic S-T Gap
Vertical S-T gap at triplet geometry
Vertical S-T gap at singlet geometry
S
T
EOM vertical energies
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
0-c 1-c 2-c trans 2-c long 2-c short 3-c 4-c
Ene
rgy
(eV
)
EOM-SF-CCSD Singlet
EOM-SF-CCSD TripletAdiabatic S-T Gap
EOM-SF-CCSD shows correct vertical behavior for all substituents.Vertical S-T gap energies decrease with substituent addition at the singlet
geometries while remaining almost constant at the triplet geometries.
MP2 had a lot of trouble and CCSD(T) would have a lot of trouble because it is mostly a problem of the HF reference.
S
T
EOM vertical energies
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
0-c 1-c 2-c trans 2-c long 2-c short 3-c 4-c
Ene
rgy
(eV
)
EOM-SF-CCSD Singlet
EOM-SF-CCSD TripletAdiabatic S-T Gap
Adiabatic S-T Gap
The triplet surface is becoming flatter or the singlet geometry is becoming more like the triplet geometry.
S
T
ST
Isodesmic Reactions
CH3 H C4H(4-n)(CCH)n + nCH41. C4H4 + n
H C4H(4-n)(CCH)n + n2. C4H4 + n
H C4H(4-n)(CCH)n + n3. C4H4 + n
H C4H(4-n)(CCH)n + n4. C4H4 + n
H C4H(4-n)(CCH)n + n5. C4H4 + n
CH3 H C4H(4-n)(CCH)n + nCH41. C4H4 + n
H C4H(4-n)(CCH)n + n2. C4H4 + n
H C4H(4-n)(CCH)n + n3. C4H4 + n
Isodesmic
Homodesmotic
Isodesmic reactions preserve the number and type of bonds (single, double, triple).
Homodesmotic reactions preserve the hybridization, the number and types of bonds of the carbon atoms, and the number of hydrogen atoms bonded to individual carbon atoms.
Wheeler, S.E., et al., J. Am. Chem. Soc., 2009. 131(7): p. 2547.
Stabilization energiesProduct Eqn. 1 Eqn. 2 Eqn. 3. Eqn. 4 Eqn. 5
Singlet RMP2
1-c -11.74 -3.73 -4.26 -2.40 -1.712-cs -24.73 -8.69 -9.77 -6.05 -4.662-cl -24.17 -8.14 -9.22 -5.49 -4.102-ct -23.08 -7.04 -8.12 -4.40 -3.013-c -36.75 -12.70 -14.32 -8.73 -6.654-c -50.01 -17.95 -20.11 -12.66 -9.88
Triplet ROMP2
1-c -12.07 -4.05 -4.59 -2.73 -2.042-cs -26.38 -10.35 -11.42 -7.70 -6.312-cl -26.38 -10.35 -11.42 -7.70 -6.312-ct -23.48 -7.45 -8.53 -4.80 -3.413-c -37.92 -13.87 -15.49 -9.91 -7.824-c -51.70 -19.63 -21.79 -14.34 -11.56
Both the triplet and the singlet are stabilized with substituent addition.The triplet is more stabilized then the singlet.Each reaction gives the same pattern and S-T differences.
ConclusionsS-T gaps are decreased with ethynyl substituent addition
but the singlets are always lower in energy.
Results are effected by spin contamination of the triplet states; UMP2 fails to properly describe the system.
Based on isodesmic reactions, triplet states becomes more stabilized then the singlet states as substituents are added.
Acknowledgements:Thank you:
Professor McMahon – University of WisconsinLevi Haupert
Visualization Software:MacMolPltChemBioDraw12
Packages:Q-ChemGAMESSCFOUR
Funding provided by:ACS-PRFPurdue University
Thank you
H H
HH
Graphene and fullerene formation
Bergman Cyclization
Ring Closure
Retro [2+2]
Coalescence and
Annealing
Hunter, J. M.; Fye, J. L.; Roskamp, E. J.; Jarrold, M. F. J. Phys. Chem. 1994, 98, 1810−1818.
Cyclobutadiene orbitals
Cyclobutadiene undergoes Jahn-Teller distortions.
SingletTriplet
Optimized Geometries1.43911.43961.4516
1.43501.46131.4385
1.44731.42171.4666
1.44731.42171.4666
1.43501.46131.4385
1.45511.40661.4830
1.44081.44011.4553
1.43681.49331.4239
1.44081.44011.4551
1.44451.44411.4536
1.44471.47291.4563
1.44471.47291.4564
1.44991.42441.4427
1.44981.42441.4426
1.45221.45091.4562
Singlet Triplet
1.35341.3724
1.58161.5578
1.55101.5576
1.34211.3717
1.34211.3676
1.56861.5679
1.35471.3749
1.59991.5631
1.35471.3749
1.53021.5546
1.56211.5510
1.34241.3707
1.36871.3859
1.56441.5559
1.35281.3779
1.54271.5453
1.36881.3855
1.57991.5467
1.35281.3798
1.36891.3884
1.55871.5478
Adiabatic energies
0-c 1-c 2-c short 2-c trans 2-c long 3-c 4-c0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
1.1
1.2
UEOM ROEOM UMP2
ROMP2 UCCSD(T) ROCCSD(T)
Ene
rgy
(eV
)
The singlet triplet gap decreases with substituent addition. UMP2 does not follow the trend of decreasing singlet-triplet gap energy. Main source of error is spin contamination.
Natural Charges Singlets-0.072
-0.187
-0.097
-0.146
-0.209
-0.076
-0.067
-0.173
-0.147
-0.040
-0.175
-0.078
-0.176
-0.075
-0.161
-0.079
-0.011
-0.040
-0.011
-0.081
-0.205
-0.181
( -0.837) ( -0.629) ( -0.428)
( -0.430)
( -0.426)
( -0.234)
( -0.045)
-0.169
-0.094
-0.119
-0.080
-0.157
-0.118
-0.066
-0.077
-0.165
-0.151
Natural Charges Triplets
-0.210
-0.184
-0.085
-0.082
-0.170
-0.085
-0.168
-0.047-0.165
-0.127
-0.079
-0.050
-0.021
-0.161
-0.012
-0.205
( -0.841) ( -0.627) ( -0.421)
( -0.430) ( -0.235) ( -0.048)
-0.173
-0.076
-0.089
-0.079
-0.159
-0.115
-0.148
-0.080
Spin Densities
0.4990.530
0.1220.831
0.5270.663
0.003-0.652
0.5000.596
0.003-0.665
0.1250.836
0.5370.651
0.3330.239
0.4050.425
0.001-0.571
0.4060.468
0.4290.614
0.0920.691
0.4020.414
0.3450.088
(1.999, 2.123)
(1.873, 1.944)
(1.741, 1.783)
(1.623, 1.703)
(1.714, 1.738)
(1.609, 1.659)
0.0920.662
0.002-0.545
0.4060.426
0.001-0.649
0.0940.807
0.4720.186
0.0950.705
0.001-0.578
0.0050.010
0.0410.267
0.018-0.035
-0.065-0.294
0.0150.107
-0.067-0.316
0.0440.310
0.0280.047
0.003-0.014
0.0070.298
-0.051-0.247
0.014-0.154
0.0190.252
0.0360.202
0.0190.017
-0.003-0.104
(0.020, 0.040)
(0.048, 0.075)
(0.062, 0.066)
(0.052, 0.178)
(0.066, 0.100)
(0.076, 0.068)
0.0340.170
-0.051-0.227
0.019-0.209
-0.056-0.340
0.0370.395
0.0190.156
0.0380.279
-0.053-0.277
HF Triplet
ROEOM Triplet
Spin Densities-0.067-0.314
0.0570.330
0.019 0.083
0.009-0.035
0.0050.009
-0.071-0.320
0.0230.039
0.0580.323
-0.002-0.016
0.0220.074
-0.005-0.065
-0.060-0.294
0.0470.298
-0.054-0.274
0.0530.347
-0.063-0.325
0.021-0.054
0.0200.120
0.0140.012
-0.053-0.272
-0.001-0.032
0.001 0.012
(0.021, 0.038) (0.029, 0.028) (0.041, 0.047)(0.033, 0.017)
(0.033, 0.003) (0.045, 0.013) (0.054, 0.047)
0.0510.312
0.016 0.101
0.000-0.100
-0.066-0.304
0.0540.288
-0.010-0.221
0.0140.169
-0.045-0.272
0.0380.312
0.0430.278
Optimized singlet geometries
1 2
34
56
EOM-SF-CCSD/cc-pVDZ
Singlet Bond Lengths (Å)
Molecule 1 2 3 40-c 1.5679 1.3676 1.5679 1.36761-c 1.5578 1.3534 1.5576 1.3717
2-c short 1.5510 1.3687 1.5510 1.37072-c long 1.5631 1.3749 1.5546 1.37492-c trans 1.5644 1.3779 1.5644 1.3779
3-c 1.5427 1.3855 1.5467 1.37984-c 1.5587 1.3884 1.5587 1.3884
Ethynyl Substituents (Å)
bond 5 6average 1.42 1.22
Main pattern of alternating bond lengths does not change with substituent addition.
The singlet geometries have decreasing single bond lengths and increased double bond lengths; becoming more square.
Substituent bond lengths remain nearly constant.
Optimized triplet geometries
1 2
34
56
EOM-SF-CCSD/cc-pVDZ
Triplet Bond Lengths (Å)
Molecule 1 2 3 40-c 1.4516 1.4516 1.4516 1.45161-c 1.4666 1.4666 1.4385 1.43852-c 1.4553 1.4830 1.4551 1.4239
2-c trans 1.4536 1.4536 1.4536 1.45363-c 1.4563 1.4426 1.4427 1.45644-c 1.4562 1.4562 1.4562 1.4562
Ethynyl Substituents (Å)
bond 5 6average 1.42 1.22
Square structure is maintained when substituents are added symmetrically.
The singlet geometries have decreasing single bond lengths and increased double bond lengths, becoming more square.
Stabilization energiesProduct Eqn. 1 Eqn. 2 Eqn. 3. Eqn. 4 Eqn. 5
Singlet RMP2
1-c -11.74 -3.73 -4.26 -2.40 -1.712-cs -24.73 -8.69 -9.77 -6.05 -4.662-cl -24.17 -8.14 -9.22 -5.49 -4.102-ct -23.08 -7.04 -8.12 -4.40 -3.013-c -36.75 -12.70 -14.32 -8.73 -6.654-c -50.01 -17.95 -20.11 -12.66 -9.88
Triplet ROMP2
1-c -12.07 -4.05 -4.59 -2.73 -2.042-cs -26.38 -10.35 -11.42 -7.70 -6.312-cl -26.38 -10.35 -11.42 -7.70 -6.312-ct -23.48 -7.45 -8.53 -4.80 -3.413-c -37.92 -13.87 -15.49 -9.91 -7.824-c -51.70 -19.63 -21.79 -14.34 -11.56
Product Eqn. 1 Eqn. 2
Singlet RCCSD(T)
1-c -10.71 -3.422-cs -22.05 -7.482-cl -21.67 -7.102-ct -21.16 -6.583-c -32.74 -10.884-c -44.21 -15.06
Triplet ROCCSD(T)
1-c -12.34 -5.052-cs -26.85 -12.272-cl -26.85 -12.272-ct -22.65 -8.073-c -37.03 -15.164-c -49.12 -19.97
CH3 H C4H(4-n)(CCH)n + nCH41. C4H4 + n
H C4H(4-n)(CCH)n + n2. C4H4 + n
H C4H(4-n)(CCH)n + n3. C4H4 + n
H C4H(4-n)(CCH)n + n4. C4H4 + n
H C4H(4-n)(CCH)n + n5. C4H4 + n