Kurtis Malecha
Chem 451 Final Report
4/30/12
NH Molecule
NH
Minimal (STO-3G) Basis Set
Total
-1473.11
Energy
(eV)
Bond
107.921
Length
(pm)
Bond
N/A
Angle
(Degrees
)
LUMO
5.863184
Energy
(eV)
HOMO
Energy
(eV)
-9.299334
Medium (6-31G*) Basis Set
-1492.54
101.944
N/A
1.335357
-11.80637
HOMO- -12.42862
1 Energy
(eV)
-15.21593
HOMO- -26.25516
2 Energy
(eV)
-28.74976
HOMO- -417.1312
3 Energy
(eV)
Molecule (All in Gas Phase)
NH = N + H
OH = O + H
HF = H + F
-425.6237
ΔHf (kJ mol-1)
1064.26
506.19
24.1
These not very consistent with the bond orders determined in question #1. If we were to use the
enthalpy values determined above, the dissociation of HF would require the “least” energy to
convert to H and F. Also, if we look at Table 4.3, HF is to have the highest bond energy. Since
the bond order is predicted to be 1 for all the molecules, we cannot accurately assess the bond
energy based on the bond orders for these types of molecules.
CO2H2 Molecule
CO2H2
Total
Energy/
eV
C-H
Bond
Length
(pm)
C=O
Bond
Length
(pm)
C-O
Bond
Length
(pm)
O-H
Bond
Length
(pm)
H-C=O
Bond
Angle
(Degrees
)
H-C-O
Bond
Angle
(Degrees
)
O=C-O
Bond
Angle
(Degrees
)
C-O-H
Bond
Angle
(Degrees
)
LUMO
Energy
(eV)
Minimal (STO-3G) Basis Set
-5067.06
Large Basis Set
-5136.43
110.757
109.157
121.153
117.604
139.256
132.709
98.8052
94.3939
124.183
123.115
114.473
113.904
121.344
122.981
105.756
111.71
8.098211
5.113092
HOMO
Energy
(eV)
-9.661871
-12.53241
HOMO- -9.874241
1 Energy
(eV)
-13.27407
HOMO-
-16.1626
-13.18634
2 Energy
(eV)
HOMO- -14.45419
3 Energy
(eV)
-17.34674
HOMO- -14.85919
4 Energy
(eV)
-18.15959
HOMO- -18.64665
5 Energy
(eV)
-21.73983
3.) For the minimal basis, we have 12 filled MOs, so column “12” is the HOMO and column
“13” is the LUMO. The dominant contributions come from O2Px (-.83890) and a slight
H4s (-.35796). This, along with looking at the HOMO diagram above, leads to an overall
non-bonding environment between the C=O (The Hydrogen is in a bonding environment,
though). The diagram above has the nodes for the Oxygen at the nucleus, not between
the O and C, also meaning it is nonbonding. For the LUMO, C1Pz (.84), O2Pz(-.72867),
O3Pz(-.303) we have expected antibonding for the C=O bond and C-O bond. This is due
to the sign changes and also the nodes in the diagrams being between the nuclei, not at
the nuclei.
For the large basis, the results are nearly identical for the HOMO, with only the
relative coefficients magnitude (not sign) changing slightly. As for the LUMO, we once
again arrive at antibonding behavior like before, but the relative signs on each atom have
“switched.” (i.e. C1Pz = -.46, -.769) This does not affect the overall behavior of the
molecule, though.
This is somewhat similar to what is given for a “standard” description of the
carbonyl bonding. According to: http://131.104.156.23/Lectures/331/331_chapter_6.htm,
we expect to have, “ two degenerate LUMOs with p-symmetry, one HOMO with sigma
symmetry (but nevertheless antibonding) and two degenerate second HOMOs of p symmetry.” We only observe major contributions from the pi symmetry for the HOMO,
and not the sigma symmetry. (An online source was used here since the Organic Book is
not readily available – it is packed for moving.)
4.)
Energy Spacing
eV
Wavelength (nm)
HOMO to LUMO (Minimal)
17.76
69.82
HOMO to LUMO (Large)
17.65
70.25
Here we observe a * transition from the HOMO to the LUMO. According to
http://szerves.chem.elte.hu/oktatas/ea/Perczel/UV-VIS.pdf, the shorter wavelength (more
energetic) transitions correspond to the above transition. It is even more energetic than table
13.6!
Aniline Molecule
Ph-NH2
Total
Energy/ eV
C1-C2 Bond
Length (pm)
(Going
clockwise)
C2-C3 Bond
Length (pm)
C3-C4 Bond
Length (pm)
C4-C5 Bond
Length (pm)
C5-C6 Bond
Length (pm)
C6-C1 Bond
Length (pm)
C1-N Bond
Length (pm)
N-H Bond
Length (pm)
C-H
Representati
ve Bond
Length (pm)
C1-C2-C3
Bond Angle
(Degrees)
C2-C3-C4
Bond Angle
(Degrees)
C3-C4-C5
Bond Angle
(Degrees)
C4-C5-C6
Bond Angle
(Degrees)
C5-C6-C1
Bond Angle
(Degrees)
C6-C1-C2
Bond Angle
(Degrees)
Minimal (STO-3G) Basis Set
-7679.22
Large Basis Set
-7775.52
139.805
139.575
138.218
138.238
138.66
138.551
138.654
138.556
138.654
138.234
138.215
139.575
140.411
137.36
101.196
98.9534
108.338
107.77
120.111
120.368
120.786
121.107
119.177
118.521
120.779
121.105
120.122
120.371
119.025
118.529
H-C-C
Representati
ve Bond
Angle
(Degrees)
C-N-H
Representati
ve Bond
Angle
(Degrees)
LUMO
Energy (eV)
120.412
120.011
120.888
120.973
7.572148
4.221138
HOMO
Energy (eV)
-5.964339
-7.537912
HOMO-1
Energy (eV)
-7.614344
-8.927464
HOMO-2
Energy (eV)
-10.35992
-11.88697
HOMO-3
Energy (eV)
-11.54013
-13.03812
HOMO-4
Energy (eV)
-12.02189
-13.62713
HOMO-5
Energy (eV)
-13.09693
5.)
Energy Spacing
eV
Wavelength (nm)
-14.34545
HOMO to LUMO (Minimal)
13.536
91.608
HOMO to LUMO (Large)
11.759
105.451
Here we observe a n → σ*transition from the HOMO to the LUMO for the –NH2 substituent.
The nitrogen is only singly bonded to the aromatic ring, so a pi transition is not possible.
(Source: http://opencourseware.kfupm.edu.sa/colleges/cs/chem/chem303/files%5C3Lecture_Notes_CHEM-303_UV_Spectroscopy.pdf)
6.) For this molecule, the –NH2 functional group does not lie in the same plane as the
aromatic ring. Looking at the different HOMOs, we readily see that the electron density
is opposite in sign of the adjoining carbon atom. With some MOs, it is even antibonding
(node between the nuclei electron density). With the VSEPR prediction, we learn that
electron densities repel one another, and the two hydrogens from the functional group
would be expected to be perpendicular to the plane of the aromatic hydrogens. The
minimal and large basis sets both agree here.
7.) With the variational principle, we use a trial wave function, then minimize the energy.
As we use more basis functions, we get an even “truer” view of the actual molecular
orbitals. In our case, we used a minimal and large basis set, which means that we had
more of a “true” view of the MOs.
8.) (This question will be answered from the standpoint of the NH molecule, since we
utilized a Minimal and Medium basis set for it, and a Minimal and Large basis set for the
other two molecules.) The minimal basis set focuses on the spherical nature of the atom,
which utilizes the s and p functions. The 3G stands for three Gaussian functions, which
are then expanded for the basis functions. With the 6-31G* “medium” basis set, it takes
into account the shortcomings of the STO-3G basis set, namely incorporating that not all
atoms are spherical, and that the basis functions should be centered between the atoms
instead of at them (using polarizations functions – think hybrid orbitals). Utilizing these
two properties allows for a medium basis set (hopefully) gives a more accurate picture of
what occurs at the molecular level.