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.