Chem3D 8.0 Manual - CambridgeSoft

Form ofglycine∆H(kcal/mole)SolventAccessibleThe following table contains the keywordsautomatically sent to MOPAC and those you can useto affect this property.Administratorzwitterion(H2O)neutral (gas) -92.75386zwitterion (gas) -57.83940-126.93974 52.37133From this data you can reason that the glycinezwitterion is the more favored conformation inwater and the neutral form is more favored in gasphase.Hyperfine Coupling ConstantsHyperfine Coupling Constants are useful forsimulating Electron Spin Resonance (ESR) spectra.Hyperfine interaction of the unpaired electron withthe central proton and other equivalent protonscause complex splitting patterns in ESR spectra.ESR spectroscopy measures the absorption ofmicrowave radiation by an unpaired electron when itis placed under a strong magnetic field.Hyperfine Coupling Constants (HFCs) are related tothe line spacing within the hyperfine pattern of anESR spectra and the distance between peaks.Species that contain unpaired electrons are asfollows:• Free radicals• Odd electron molecules• Transition metal complexes• Rare-earth ions• Triplet-state moleculesFor more information see the MOPAC onlinemanual, page 34.Surface Å 2 Keyword DescriptionUHFHyperfineGEO-OKMMOKHyperfine Coupling Constantsfor the Ethyl RadicalTo build the model:1. From the File menu, choose New Model.2. Click the Text Building tool.3. Click in the model window.A text box appears.4. Type “EtH” and press Enter.5. Click the Select tool.Automatically sent to MOPACif you choose “Open Shell(Unrestricted)” wave functionsto specify the use of theUnrestricted Hartree-Fockmethods.Automatically sent to MOPACto specify the hyperfinecomputation.Automatically sent to MOPACto override checking of theZ-matrix.Automatically sent to MOPACto specify MolecularMechanics correction foramide bonds. Use theadditional keyword NOMM toturn this keyword off.170 • Chapter 11: MOPAC Computations CambridgeSoftCompute Properties