HOMO-17: This natural bonding orbital has simply a core p orbital on aluminium. This was observed to be the highest energy orbital in which there was no interraction between the chlorine orbitals. All orbitals below this are core orbitals, either on aluminium or chlorine.
HOMO-13: We are beginning to see interaction between adjacent chlorine atoms. The spherical shape of the orbitals indicate that this natural bonding orbital is composed of mainly core s orbitals on each chlorine atom. Overall bonding orbital but a small antibonding interaction between the orbitals which are separated by a large distance.
HOMO-12: This natural bonding orbital indicates the presence of strong s type bonding interactions between orbitals on chlorine. None of the aluminium orbitals are involved in this natural bonding orbital. There is a slight antibonding interaction between the two lobes but overall this interaction is strongly bonding.
HOMO-12: This natural bonding orbital indicates the presence of strong s type bonding interactions between orbitals on chlorine. None of the aluminium orbitals are involved in this natural bonding orbital. There is a slight antibonding interaction between the two lobes but overall this interaction is strongly bonding.
HOMO-11: Strong bonding interactions are observed for this NBO composed of the s orbitals on aluminium overlapping with the p orbitals on each chlorine atom. This orbital is also has large bonding character.
4
(T2) The second of the triply degenerate bending modes.
161
145
Weak
5
(T2</sub)>) The third of the triply degenerate bending modes.
161
145
Weak
6
(A1) Simultaneous elongation or shortening of all Al-Cl bonds, which involves no change in dipole moment.
305
315
IR inactive
7
(T2) The first of the triply degenerate stretching vibrations which involves a large change in dipole moment. All four atoms move considerably during this vibration. Large change in dipole moment observed.
470
485
Strong
8
(T2) The second of the triply degenerate stretching vibrations which involves a large change in dipole moment.
470
485
Strong
9
(T2) The third of the triply degenerate stretching vibrations which involves a large change in dipole moment.
471
485
Strong
NBOs
HOMO-17: This natural bonding orbital has simply a core p orbital on aluminium. This was observed to be the highest energy orbital in which there was no interraction between the chlorine orbitals. All orbitals below this are core orbitals, either on aluminium or chlorine.HOMO-13: We are beginning to see interaction between adjacent chlorine atoms. The spherical shape of the orbitals indicate that this natural bonding orbital is composed of mainly core s orbitals on each chlorine atom. Overall bonding orbital but a small antibonding interaction between the orbitals whish are separated by a large distance. HOMO-12: This natural bonding orbital indicates the presence of strong s type bonding interactions between orbitals on chlorine. None of the aluminium orbitals are involved in this natural bonding orbital. There is a slight antibonding interaction between the two lobes but overall this interaction is strongly bonding. HOMO-11: Strong bonding interactions are observed for this NBO composed of the s orbitals on aluminium overlapping with the p orbitals on each chlorine atom. This orbital is also has large bonding character. HOMO-8: This diagram indicates the strong bonding interaction between the p orbitals on each chlorine atom. Two pairs of bonding interactions are clearly visible in this natural bonding orbital and the aluminium orbitals are uninvolved in this NBO. HOMO-7: This indicates the presence of bonding interactions between the p orbitals on chlorine which are large enough to enable these interactions to take place within this ion. HOMO-4: This NBO indicates the presence of bonding interactions between the chlorine p type orbitals. Two regions of bonding character above and below the plane of the aluminium atom are visible in this overall bonding orbital. No participation of aluminium orbitals is observed.HOMO-3: This orbital shows similar interactions as those seen in HOMO-4. Once again this bonding orbital arises primarily from bonding interactions between each of the p orbitals on chlorine. This NBO is slightly higher in energy than HOMO-4, which is expected to be due to the larger antibonding interaction between the vertical chlorine atom's p orbital lobe and those of two of the other chlorine atoms.HOMO-2: This orbital shows the overall non-bonding or slightly antibonding interaction between the filled p orbitals on chlorine atoms.HOMO: This has unequal contributions from each of the p orbitals as shown above and from analysis of the log file. This raises the total NBO energy as the 60% of the orbitals involved are of antibonding character but they are not well aligned for interaction. The remaining approximately 40% of orbital interaction comes from the two remaining p orbitals on chlorine which are well aligned and hence result in a strong bonding interaction. Overall this orbital has a slightly bonding character, which is expected to arise from the well aligned p orbital bonding interaction.HOMO: This is the second of the doubly degenerate HOMos. This raises the total NBO enrgy as the 60% of the orbitals involved are of antibonding character but they are not well aligned for interaction. The remaining approximately 40% of orbital interaction comes from the two remaining p orbitals on chlorine which are well aligned and hence result in a strong bonding interaction. Overall this orbital has a slightly bonding character, which is expected to arise from the well aligned p orbital bonding interactionLUMO: The LUMO has considerable antibonding character due to the overlap of the 4s orbital on Aluminium with the p orbitals of chlorine. The strong s-p interaction raises the energy of this NBO considerably. Yet there may be a slight bonding interaction with the ends of the chlorine p-orbital lobes due to the large size of the orbitals involved in bonding, resulting in the HOMO-LUMO gap being lowest for this ion as the interaction is between the largest orbitals and hence the splitting energy is lowest. LUMO+1: The antibonding character of this orbital is clearly depicted as the empty p orbitals on Aluminium engage in an antibonding interaction with the p orbitals on chlorine. As the aluminium orbitals in this case are large, the interaction is expected to be low, compared to that of the other ions studied. LUMO+6: This NBO indicates the large antibonding interaction resulting from p-type interactions between Aluminium and Chlorine atoms. It also shows the involvement of both 3p and 4p orbitals on aluminium in bonding.
Vibs AlCl4
Table of vibrational data for [AlCl4]-
Vibration number
Symmetry Label and Form of Vibration
Computed Frequency / cm-1
Literature Frequency / cm-1
Intensity
1
(E) symmetric bend. First of the doubly degenerate low frequency vibrational modes which is IR inactive as there is no change in dipole moment.
101
115
IR inactive
2
(E) symmetric bend. Second of the doubly degenerate low frequency vibrational modes which is IR inactive as there is no change in dipole moment.
101
115
IR inactive
3
(T2) The first of the triply degenerate bending modes. As one Cl-Al-Cl bond angle increases, the other decreases.
161
145
Weak
4
(T2) The second of the triply degenerate bending modes.
161
145
Weak
5
(T2</sub)>) The third of the triply degenerate bending modes.
161
145
Weak
6
(A1) Simultaneous elongation or shortening of all Al-Cl bonds, which involves no change in dipole moment.
305
315
IR inactive
7
(T2) The first of the triply degenerate stretching vibrations which involves a large change in dipole moment. All four atoms move considerably during this vibration. Large change in dipole moment observed.
470
485
Strong
8
(T2) The second of the triply degenerate stretching vibrations which involves a large change in dipole moment.
470
485
Strong
9
(T2) The third of the triply degenerate stretching vibrations which involves a large change in dipole moment.
471
485
Strong
MOs AlCl4
Molecular Orbitals of [AlCl4]-
Molecular Orbital
Symmetry Label and Form of Vibration
Computed Frequency / cm-1
Literature Frequency / cm-1
Intensity
HOMO-1
There is a rotation of the Mo-P bonds in opposite directions, Mo is stationary.
101
0
0
HOMO
There is a rotation of the Mo-P bonds in opposite directions and slight movement of the central Mo atom also occurs.
101
0
0
LUMO
There is a rotation of the Mo-P bonds in opposite directions and slight movement of the equatorial CO ligands atom also occurs, whilst the P atoms are stationary.
161
0
13
LUMO+1
There is a rotation of the Mo-P bonds in opposite directions and slight distortion of the vertical C-Mo-C axis occurs.
161
0
13
Vibs AlF4
Table of vibrational data for [AlF4]-
Vibration number
Symmetry Label and Form of Vibration
Computed Frequency / cm-1
Literature Frequency / cm-1
Intensity
1
T(E) symmetric bend.First of the doubly degenerate low frequency vibrational modes which is IR inactive as there is no change in dipole moment.
212
193
IR inactive
2
(E) symmetric bend. First of the doubly degenerate low frequency vibrational modes which is IR inactive as there is no change in dipole moment.
212
193
IR inactive
3
(T2) The first of the triply degenerate bending modes. As one F-Al-F bond angle increases, the other decreases.
308
308
Weak
4
(T2) The second of the triply degenerate bending modes. As one F-Al-F bond angle increases, the other decreases.
308
301
Weak
5
(T2) The third of the triply degenerate bending modes. As one F-Al-F bond angle increases, the other decreases.
308
301
Weak
6
(A1) Simultaneous elongation or shortening of all Al-F bonds, which involves no change in dipole moment.
460
450
IR inactive
7
(T2) The first of the triply degenerate stretching vibrations which involves a large change in dipole moment. All four atoms move considerably during this vibration. Large change in dipole moment observed.
637
621
Strong
8
(T2) The second of the triply degenerate stretching vibrations which involves a large change in dipole moment. All four atoms move considerably during this vibration. Large change in dipole moment observed.
637
621
Strong
9
(T2) The third of the triply degenerate stretching vibrations which involves a large change in dipole moment. All four atoms move considerably during this vibration. Large change in dipole moment observed.
637
621
Strong
Vibs BCl4
Table of vibrational data for [BCl4]-
Vibration number
Symmetry Label and Form of Vibration
Computed Frequency / cm-1
Literature Frequency / cm-1
Intensity
1
[(E) symmetric bend. First of the doubly degenerate low frequency vibrational modes which is IR inactive as there is no change in dipole moment.
178
191
IR inactive
2
(E) symmetric bend. Second of the doubly degenerate low frequency vibrational modes which is IR inactive as there is no change in dipole moment.
178
191
IR inactive
3
(T2) The first of the triply degenerate bending modes. As one Cl-B-Cl bond angle increases, the other decreases.
263
271
Very weak
4
(T2) The second of the triply degenerate bending modes. As one Cl-B-Cl bond angle increases, the other decreases.
263
275
Very weak
5
(T2) The third of the triply degenerate bending modes. As one Cl-B-Cl bond angle increases, the other decreases.
263
275
Very weak
6
(A1) Simultaneous elongation or shortening of all B-Cl bonds, which involves no change in dipole moment.
373
385
IR inactive
7
(T2) The first of the triply degenerate stretching vibrations which involves a large change in dipole moment. All four atoms move considerably during this vibration. Large change in dipole moment observed.
644
721
Medium
8
(T2) The second of the triply degenerate stretching vibrations which involves a large change in dipole moment. All four atoms move considerably during this vibration. Large change in dipole moment observed.
645
721
Medium
9
(T2) The third of the triply degenerate stretching vibrations which involves a large change in dipole moment. All four atoms move considerably during this vibration. Large change in dipole moment observed.
646
721
Medium
Vibs BF4
Table of vibrational data for [BF4]-
Vibration number
Symmetry Label and Form of Vibration
Computed Frequency / cm-1
Literature Frequency / cm-1
Intensity
1
(E) symmetric bend. First of the doubly degenerate low frequency vibrational modes which is IR inactive as there is no change in dipole moment.
326
341
IR inactive
2
(E) symmetric bend. Second of the doubly degenerate low frequency vibrational modes which is IR inactive as there is no change in dipole moment.
326
341
IR inactive
3
(T2) The first of the triply degenerate bending modes. As one F-B-F bond angle increases, the other decreases.
494
505
Weak
4
(T2) The second of the triply degenerate bending modes. As one F-B-F bond angle increases, the other decreases.
494
505
Weak
5
(T2) The third of the triply degenerate bending modes. As one F-B-F bond angle increases, the other decreases.
494
505
Weak
6
(A1) Simultaneous elongation or shortening of all B-F bonds, which involves no change in dipole moment.
733
743
IR inactive
7
(T2) The first of the triply degenerate stretching vibrations which involves a large change in dipole moment. All four atoms move considerably during this vibration. Large change in dipole moment observed.
1140
1102
Strong
8
(T2) The second of the triply degenerate stretching vibrations which involves a large change in dipole moment. All four atoms move considerably during this vibration. Large change in dipole moment observed.
1140
1102
Strong
9
(T2) The third of the triply degenerate stretching vibrations which involves a large change in dipole moment. All four atoms move considerably during this vibration. Large change in dipole moment observed.
1140
1102
Strong
Hello World
Mo
Table 8: Comparison of Bond Lengths With Literature
Bond
Computed Bond Length/Å
Literature Bond Length/Å
Difference/Å
% Difference
Al-Cl
2.25
2.15
0.1
4.65
Al-F
1.73
1.69
0.04
2.37
B-Cl
1.92
1.84
0.08
4.35
B-F
1.44
1.43
0.01
0.70
Trans Isomer
Cis Isomer
Cis Isomer
TransIsomer
TlBr3
TransIsomer
BH3
TransIsomer
Final
This schematic view of possible host-guest complexes formed when using compound 22 as catalyst shows the unfavourable orientation (d) due to OH---CH3 repulsion and the favourable orientation (c) leading to optimal guest activation, resulting in the 4:1 ratio of 19:20. The predominant configuration of 19 is explained by an endo attack of the diene 15 to the Re,Re face of the diketone 16 when bound to the chiral amidine. The Curtin-Hammett principle is respected as stronger H-bonds will stabilize the diketone while increasing its reactivity. Yet it is also important to remember that other interactions in the transition state may be decisive in controlling the high enantioselectivity of this reaction. Catalyst 22 not only gives high enantioselectivity, it also increases the rate of reaction by a factor of 550 when compared to the uncatalysed reaction.
Infrared spectral data and inferences for compound 18
Computed Frequency/cm-1
Literature Frequency/cm-1
Inference
3673
3346
O-H
3071
3076
=C-H asym
3121
3125
=C-H sym
2924
2927
aliphatic C-H
1781
1785
C=O
1737
1735
C=O
1692
1690
C=C
1631
1627
C=C
1568
1570
Enolate form C=O
1452
1450
Enolate form C=O
1216
1212
C-O
1167
1163
C-O
Infrared spectral data and inferences for compound 19
Computed Frequency/cm-1
Literature Frequency/cm-1
Inference
3671
3341
O-H
3079
3074
=C-H asym
3121
3127
=C-H sym
2926
2930
aliphatic C-H
1779
1789
C=O
1732
1738
C=O
1691
1688
C=C
1633
1629
C=C
1563
1567
Enolate form C=O
1451
1447
Enolate form C=O
1165
1163
C-O
Bw0810degrees.jpg
Bw50810degrees.jpg
yes
The MM2 molecular mechanics approach encounters difficulties when dealing with compounds containing a positively charged nitrogen atom, so the structure of compound 5 was also optimised using MMFF94 and MOPAC PM6 methods. The results are shown below.
Dihedral angles and energies calculated using MMFF94 and MOPAC PM6 methods
Method
Dihedral angle
Energy (kcal mol-1)
MMFF94
20.9o
57.55
MOPAC PM6
20.5o
93.6 (heat of formation)
These results showed higher overall energies for the ‘lowest energy’ conformations, but the dihedral angles obtained of 20.15o and 20.60o, respectively, are in good agreement with each other. In each case, these models show the lowest energy conformation as having the carbonyl group above the plane of the ring, reinforcing the proposed mechanism to account for the stereochemistry of the product.
Dihedral angles and energies calculated using MMFF94 and MOPAC PM6 methods
Method
Dihedral angle
Energy (kcal mol-1)
MMFF94
20.1517o
57.5375
MOPAC PM6
20.6034o
93.9079 (heat of formation)
Bw0822degrees.jpg
Results from MMFF94 and PM6 MOPAC analysis show a dihedral angle of approximately 40o below the plane of the quinolinium ring. The MMFF94 and PM6 results show quite high energies but they are in good agreement:
Dihedral angles and energies calculated using MMFF94 and MOPAC PM6
Method
Dihedral angle
Energy (kcal mol-1)
MMFF94
-40.9o
99.8
MOPAC PM6
-43.5o
156.4 (heat of formation)
These results are markedly different from those obtained using the MM2 analysis. Again, the MM2 results are not particularly accurate due to its inability to correctly process the N+ of the ring.
(NB. The MMFF94 force field does not permit a dihedral angle to be inputted, in order to calculate the energy of such a geometry.)
Molecular orbitals and their electron density distribution for compound 12
