Rep:Mod:michellesimon
NH3
Calculation method: RB3LYP
Basis set: 6-31G(d,p)
E(RB3LYP) -56.55776873 a.u.
RMS Gradient Norm 0.00000323 a.u.
Point Group: C3V
Optimised angle: 105.7
Optimised length: 1.018 Angstroms
Item Value Threshold Converged?
Maximum Force 0.000006 0.000450 YES
RMS Force 0.000004 0.000300 YES
Maximum Displacement 0.000014 0.001800 YES
RMS Displacement 0.000009 0.001200 YES
Predicted change in Energy=-1.141618D-10
Optimization completed.
-- Stationary point found.
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! Optimized Parameters !
! (Angstroms and Degrees) !
-------------------------- --------------------------
! Name Definition Value Derivative Info. !
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! R1 R(1,2) 1.018 -DE/DX = 0.0 !
! R2 R(1,3) 1.018 -DE/DX = 0.0 !
! R3 R(1,4) 1.018 -DE/DX = 0.0 !
! A1 A(2,1,3) 105.7446 -DE/DX = 0.0 !
! A2 A(2,1,4) 105.7446 -DE/DX = 0.0 !
! A3 A(3,1,4) 105.7446 -DE/DX = 0.0 !
! D1 D(2,1,4,3) -111.8637 -DE/DX = 0.0 !
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NH3 |
Gaussian log file can be accessed here: Media:MICHELLESIMON_NH3_OPT_FPOP.LOG
Vibrations
How many modes do you expect from the 3N-6 rule? 6
Which modes are degenerate (ie have the same energy)? 2&3 and 5&6
Which modes are "bending" vibrations and which are "bond stretch" vibrations?
Bending: 1, 2, 3
Bond stretch: 4, 5, 6
Which mode is highly symmetric? 4
One mode is known as the "umbrella" mode, which one is this? 1
How many bands would you expect to see in an experimental spectrum of gaseous ammonia? 2
Charge distribution
H: 0.375
N: -1.125
N is expected to have a slightly negative charge because it has more protons in its nucleus and should draw bonding electrons closer to itself, and H should have a slightly positive charge as it it poorer at attracting bonding pairs. ie. N is more electronegative than H
N2
Calculation Method RB3LYP
Basis Set 6-31G(d,p)
E(RB3LYP) -109.52359111 a.u.
RMS Gradient Norm 0.02473091 a.u.
Point group D∞h
Bond length 1.10 Angstroms
Item Value Threshold Converged?
Maximum Force 0.000001 0.000450 YES
RMS Force 0.000001 0.000300 YES
Maximum Displacement 0.000000 0.001800 YES
RMS Displacement 0.000000 0.001200 YES
Predicted change in Energy=-3.401047D-13
Optimization completed.
-- Stationary point found.
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! Optimized Parameters !
! (Angstroms and Degrees) !
-------------------------- --------------------------
! Name Definition Value Derivative Info. !
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! R1 R(1,2) 1.1055 -DE/DX = 0.0 !
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N2 |
Gaussian log file can be accessed here: Media:MS4516_N2_OPT.LOG
Vibrations
H2
Calculation Method RB3LYP
Basis Set 6-31G(d,p)
E(RB3LYP) -1.17853936 a.u.
RMS Gradient Norm 0.00000017 a.u.
Point group D∞h
Bond length 0.743 Angstroms
Item Value Threshold Converged?
Maximum Force 0.000000 0.000450 YES
RMS Force 0.000000 0.000300 YES
Maximum Displacement 0.000000 0.001800 YES
RMS Displacement 0.000001 0.001200 YES
Predicted change in Energy=-1.164080D-13
Optimization completed.
-- Stationary point found.
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! Optimized Parameters !
! (Angstroms and Degrees) !
-------------------------- --------------------------
! Name Definition Value Derivative Info. !
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! R1 R(1,2) 0.7428 -DE/DX = 0.0 !
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H2 |
Gaussian log file can be accessed here: Media:MS4516 H2 OPT.LOG
Vibrations
Reactivity
E(NH3)= -56.55776873 a.u.
2*E(NH3)= -113.11553746 a.u.
E(N2)= -109.52359111 a.u.
E(H2)= -1.17853936 a.u.
3*E(H2)= -3.53561808 a.u.
ΔE=2*E(NH3)-[E(N2)+3*E(H2)]= -0.05632827 a.u.
Which is -147.89 kJ/mol. (This is for 2 molecules of NH3)
The ammonia product is more stable because the reaction is exothermic (negative energy change), which means that in converting N2 and H2 into NH3, excess energy was released from the system into the surroundings. Therefore ammonia is at a lower energy than the reactants.
Molar ΔE = -73.945 kJ/mol
This molar ΔE compared to its literature value is higher (-41kJ/mol) [1] . This is likely to be due to the inaccuracies in calculations of the energy. Experimentally there are many more small effects on the energy of the molecule that have not been considered in RB3LYP calculations, especially since the processing power of the computer used is quite low. Therefore this causes a discrepancies in the two values.
- ↑ T. Lister, J. Renshaw, in New Understanding Chemistry for Advanced Level, Nelson Thornes, 2000, ch. 11, pp. 137
Own molecule 1: BH4-
Calculation Method RB3LYP
Basis Set 6-31G(d,p)
Charge -1
E(RB3LYP) -27.24992701 a.u.
RMS Gradient Norm 0.00000589 a.u.
B-H bond length 1.23940A
H-B-H bond angle 109.47
Point group Td
Item Value Threshold Converged?
Maximum Force 0.000011 0.000450 YES
RMS Force 0.000006 0.000300 YES
Maximum Displacement 0.000057 0.001800 YES
RMS Displacement 0.000030 0.001200 YES
Predicted change in Energy=-1.299237D-09
Optimization completed.
-- Stationary point found.
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! Optimized Parameters !
! (Angstroms and Degrees) !
-------------------------- --------------------------
! Name Definition Value Derivative Info. !
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! R1 R(1,2) 1.2394 -DE/DX = 0.0 !
! R2 R(1,3) 1.2394 -DE/DX = 0.0 !
! R3 R(1,4) 1.2394 -DE/DX = 0.0 !
! R4 R(1,5) 1.2394 -DE/DX = 0.0 !
! A1 A(2,1,3) 109.4712 -DE/DX = 0.0 !
! A2 A(2,1,4) 109.4712 -DE/DX = 0.0 !
! A3 A(2,1,5) 109.4712 -DE/DX = 0.0 !
! A4 A(3,1,4) 109.4712 -DE/DX = 0.0 !
! A5 A(3,1,5) 109.4712 -DE/DX = 0.0 !
! A6 A(4,1,5) 109.4712 -DE/DX = 0.0 !
! D1 D(2,1,4,3) -120.0 -DE/DX = 0.0 !
! D2 D(2,1,5,3) 120.0 -DE/DX = 0.0 !
! D3 D(2,1,5,4) -120.0 -DE/DX = 0.0 !
! D4 D(3,1,5,4) 120.0 -DE/DX = 0.0 !
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BH4- |
Gaussian log file can be accessed here: Media:MS4516_BH4 OPT.LOG
Charge distribution
H: -0.096
B: -0.615
B and H have very similar electronegativities, therefore charges on the atoms are fairly similar.
Vibrations
-Two peaks should be seen on the infrared spectrum for BH4-.
- One at 1122.0cm-1 and another at 2283.9cm-1
MOs
| 1. | 
|
-This is the 1s core non-bonding MO
-It is significantly deeper in energy than the other orbitals, with an energy of -6.42131 a.u. -This value shows that these aren't involved in bonding -It is made up using a 1s orbital from H and from B. |
| 2. | 
|
-This shows the sigma (2s) valence bonding MO. -It is much higher in energy than the 1s non bonding MO at -0.22587 a.u. but is also tenfold more negative than the following 2p orbitals. -It is made up using a 1s orbital from H and 2s from B. |
| 3. | 
|
-This is one of the 2p valence bonding MOs. -It is degenerate with two other orbitals, which can be seen in the screenshot of the orbital energies. -It is made from a 1s atomic orbital from H and 2p from B. -Any of these 2p MOs are the HOMO of this molecule. -It is instrumental in the chemical bonding of BH4-. |
| 4. |  |
-This is another one of the 2p valence bonding MOs. -It is identical to the above orbital but is made from another 2p atomic orbital from B. - It can also be a HOMO and contributes fully to the chemical reactivity/bonding of the molecule. -These degenerate bonding MOs are all filled. |
| 5. | 
|
-This is a 2p antibonding orbital. -It has two other degenerate antibonding orbitals, which are shown as 6 and 8 in the above image. -These degenerate antibonding MOs are all LUMO as none of them are filled. -They are made from the same 1s H orbital and 2p B orbital. -It is also important in the chemical bonding of the molecule, being the lowest energy empty orbital a nucleophile could theoretically attack. -All these MOs are high in energy, having a positive value of 0.41615a.u. compared to the previous exclusively negative values. |
Own molecule 2: CN-
Calculation Method RB3LYP
Basis Set 6-31G(d,p)
Charge -1
E(RB3LYP) -92.82453153 a.u.
RMS Gradient Norm 0.00000704 a.u.
C-N bond length 1.18409A
Point group C∞v
Item Value Threshold Converged?
Maximum Force 0.000012 0.000450 YES
RMS Force 0.000012 0.000300 YES
Maximum Displacement 0.000005 0.001800 YES
RMS Displacement 0.000008 0.001200 YES
Predicted change in Energy=-6.650389D-11
Optimization completed.
-- Stationary point found.
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! Optimized Parameters !
! (Angstroms and Degrees) !
-------------------------- --------------------------
! Name Definition Value Derivative Info. !
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! R1 R(1,2) 1.1841 -DE/DX = 0.0 !
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CN- |
Gaussian log file can be accessed here: Media:MS4516_CN OPT.LOG
Charge distribution
C: -0.246
N: -0.754
- As with NH3, the nitrogen atom is more electronegative than carbon is.
- Therefore it pulls electrons closer to its nucleus than carbon does, resulting in a more negative charge distributed onto the N atom.
Vibrations
- Although CN- is also a linear molecule (like H2 and N2 previously explored), there is one peak observed on the infrared spectrum for CN- at 2139.1cm-1.
- This is due to a change in dipole moment during the vibration, which differs from H2 and N2 homodiatomic molecules because CN- is composed of two different atoms (heterodinuclear).
MOs
| 1. | 
|
-This is the 1s core non-bonding MO for Nitrogen
-It is also significantly deeper in energy than the other orbitals, with an energy of -14.00393 a.u. -This value shows that these aren't involved in bonding - It looks very similar to the 1s atomic orbital, further corroborating this point. |
| 2. | 
|
-This shows the sigma (2s) valence bonding MO (head on overlap of the orbitals). -It is much higher in energy than both nitrogen and carbon 1s non-bonding MOs at -0.56195 a.u. -The electron density overlaps over both carbon and nitrogen atoms. - On the left end of the carbon atom, a region without electron density can be seen as a hole; this molecular orbital is exhibiting some p character from the double bond - This is involved in the chemical bonding of the molecule |
| 3. | 
|
-This is a sigma (2p) valence bonding MO. -It is lower in energy than the other 2p valence bonding MOs, unlike BH4- shown earlier because it is a sigma overlap rather than a pi overlap. -It is made from a 2p orbital from N and one from C. -It is instrumental in the chemical bonding of this moleucle. - Some electron density can be seen to be drawn from the carbon towards the nitrogen atom, which makes sense because the nitrogen is more electronegative and should bring the bonding pair of electrons closer to itself. |
| 4. |  |
-This is one of the pi (2p) valence bonding MOs. -It is a sideways overlap of 2p orbitals from N and C. - It is degenerate with another orbital (5 and 6), and these two MOs make up the triple bond (on top of the sigma 2p MO). - They are very important in chemical bonding and reactivity -These degenerate bonding MOs are both filled. |
| 5. | 
|
-This is a sigma* (2p) antibonding orbital; it is the last filled MO in this molecule and is therefore the HOMO. - The more electronegative atom contributes less to the antibonding orbital (as its atomic orbital is lower in energy and will be more prominent in the bonding orbital), which is why the red lobe coming out from the carbon atom is larger. -It is also important in the chemical bonding/reactivity of the molecule, being the HOMO of the molecule -This is the first orbital to have a positive energy value, of 0.01857a.u. |
| 6. | 
|
-This is another pi* (2p) antibonding orbital. - It is degenerate with another pi* antibonding orbital (8&9) - These two MOs are LUMOs and are therefore involved in chemical bonding and reactivity of the molecule. - Again, the lobes on the carbon atom are larger as it contributes more to this antibonding orbital. |