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Form of<br />

glycine<br />

∆H<br />

(kcal/mole)<br />

Solvent<br />

Accessible<br />

Surface Å 2<br />

The Ethyl Radical is displayed.<br />

neutral (gas) -92.75386<br />

zwitterion (gas) -57.83940<br />

From this data you can reason that the glycine<br />

zwitterion is the more favored conformation in<br />

water and the neutral form is more favored in gas<br />

phase.<br />

Example 6<br />

Hyperfine Coupling<br />

Constants for the Ethyl<br />

Radical<br />

To build the model:<br />

1. From the File menu, choose New Model.<br />

2. Click the Text Building tool.<br />

3. Click in the model window.<br />

A text box appears.<br />

4. Type EtH and press the Enter key.<br />

5. Click the Select tool.<br />

6. Select H(8).<br />

7. Press the Backspace key.<br />

If you have automatic rectification on, a message<br />

appears asking to turn it off to perform this<br />

operation.<br />

8. Click Turn Off Automatic Rectification.<br />

To perform the HFC computation:<br />

1. From the MOPAC Interface submenu of the<br />

Calculations menu, choose Minimize<br />

Energy.<br />

2. On the Theory tab, choose the PM3 potential<br />

function and the Open Shell (Unrestricted)<br />

wave function.<br />

3. On the Properties tab, choose Hyperfine<br />

Coupling Constants.<br />

4. Click Run.<br />

The unpaired electron in the ethyl radical is<br />

delocalized. Otherwise, there would be no coupling<br />

constants.<br />

Hyperfine Coupling Constants<br />

C1 0.02376<br />

C2 -0.00504<br />

H3 -0.02632<br />

H4 -0.02605<br />

H5 0.00350<br />

<strong>ChemOffice</strong> 2005/Chem3D MOPAC <strong>Com</strong>putations • 191<br />

<strong>Com</strong>puting Properties

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