The new energy data will overwrite the old energy data file. Rotate the structure on the screen to verify that the dihedral angle has indeed changed. Make sure you have clicked after each angle change but before each calculation. Conformational Analysis of Butane: Close the ethane file (File ( Close).
(Save now under a new file name or at least make sure you have the energy you need from the output.) 17. All you have to do to get the next energy value is Calculate ( Submit. Click [pic] (or File ( New) and make a model of vary the dihedral angle of butane from 0-360( at 20( increments (0(, 20(, 40( … Getting butane into a 0( C-C-C-C dihedral angle can be a little tricky. 60( (or -60(), you can change it to 180° to 0° and have a very strange conformation, close the file and build butane again.) Once you have constrained the dihedral angle in butane to 0(, follow the instructions listed above to setup your calculations (step 11) and obtain your first energy output.
The challenge is to describe this wavelike behavior in enough mathematical detail that we can accurately predict important features of the molecule such as bond lengths, bond energies, and force constants. For larger atoms (and molecules), the problem is so complicated that it cannot be solved. Years of research have shown that we need to retain the approximate 3-dimensional shapes of the orbitals, but that we can simplify considerably how we describe the wavelike behavior of the electron with respect to distance from the nucleus. An atom’s core electrons are closely held, while the atom’s valence electrons are shared among atoms.
We will concentrate on calculating the total energy of the molecule. If any calculations are being carried out, they will appear in the top half of the window.
Spartan ESl can be started by clicking the Windows “Start” button and then selecting the “Spartan ES V2.0.1” icon from the “Programs” menu. If the network connection fails, or if the network is particularly busy and does not respond to Spartan queries, Spartan will shut down.
You may wish to save your work at regular intervals to avoid loss of data. Then, take a closer look at gauche butane and answer questions. Open Spartan ES from the Start menu (Start ( Programs ( Spartan ES V2.0.1). Open a new file by either using the the chart on the right side of the screen. A carbon atom (gray) with four possible bonds (yellow) should appear.The program is smart enough to figure out that any unassigned bonds should be to hydrogen. That means we need to constrain the geometry of the molecule to a particular dihedral angle.To do this, either click [pic] or use the dropdown menu Geometry ( Constrain Dihedral. At the bottom right of the screen the word “Constrain” followed by “(, , ,) = ” should appear.The idea that energy in atoms occurs in discrete bundles is contrary to our everyday notion that energy flows smoothly into or out of a reaction.But on the atomic and molecular scale, our everyday notions must be set aside.To compute and graph the relative conformational energies of ethane and butane.One of the most successful theories of the 20th century is quantum mechanics, also called wave mechanics.Also, bring a model kit or at least models of ethane and butane.To download Spartan: While connected to the Wake Forest Network (from an on-campus site), choose “Run” from the Windows Start Menu. You will need to restart your PC to complete the installation.Click on any one of the yellow open bond sites to add a second sp3 hybridized carbon.You should have a gray bond between the two carbon atoms and six yellow lines/open valences in the molecule. Get a rough idea of the conformation of the molecule by program tell us the total energy of the molecule at the angle we designate.