b Describe the different ways to calculate charges on atoms There are 4 classes

B describe the different ways to calculate charges on

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properties and behavior of the molecule. b. Describe the different ways to calculate charges on atoms. There are 4 classes of methods to calculate charges on atoms. Class I methods use experimental data. Class II come from quantum mechanics. Class III come from physically observable properties. Class IV mix several of these methods. c. Describe the different techniques to include solvation effects in molecular modeling. The polarizable continuum model (PCM) or a discrete polarizable model (DPM) are two different techniques to include solvation effects in molecular modeling.
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5. Calculate the atomic charges for formaldehyde using the following methods: Mulliken population analysis, CHelp, and NBO. Try several theories: AM1, HF, B3LYP. The default charges displayed in Webmo are Mulliken charges listed as “Partial Charges”. Add the keyword “pop=CHelp” (or pop=NBO) to get the other charges. CHelp will be listed as ESP charges, while NBO will be listed as Natural Population Analysis. NBO for AM1 theory failed. HF mulliken and AM1 CHelp had the same values. The different theories and method had different values of charges. Atom Mulliken Chelp NBO C 0.135 0.518 0.335 H 0.14 -0.026 0.123 H 0.14 -0.026 0.123 O -0.416 -0.466 -0.416 Atom Mulliken Chelp NBO C 0.159 0.135 n/a H 0.052 0.14 n/a H 0.052 0.14 n/a O -0.263 -0.416 n/a Atom Mulliken Chelp NBO C 0.082 0.514 0.239 H 0.117 -0.056 0.126 H 0.117 -0.056 0.126 O -0.315 -0.402 -0.492 AM1 B3LYP HF
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6. If we have a molecule such as CH3-R, the R group may influence the number of electrons on the other atoms since different R groups will have different electronegativities. Model the molecules below and calculate the charges (Mulliken is fine) on the C and H atoms for different R groups. Use B3LYP/Routine for these calculations. How does the R group influence the electrons on the other atoms? Did you find anything unexpected? The R-group that cause C to be the lowest is H. The R-group that cause C to be the lowest is OH. The R-group that cause H to be the lowest is OH. The R-group that cause H to be the lowest is Cl. I was surprised that the -Cl R-group didn t cause the C atom to be higher because it has a high electronegativity. Molecule R Group C H CH3-H H -0.63 0.157 CH3-OH OH -0.203 0.143 CH3-Br Br -0.402 0.195 CH3-Cl Cl -0.526 0.199 CH3-CH3 CH3 -0.434 0.145
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  • Summer '20
  • Computational chemistry

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