Beaker is a low-cost commercial student "expert system" for organic chemistry. In this course, we use only a fraction of this program's capabilities: to draw the 2D structure of any molecule whose IUPAC name is typed in by the student and to give the IUPAC name of a structure drawn by the student, using this set of drawing tools on the left of the screen, and to give the Lewis dot structures of simple molecules. Here is the assignment done by the students using the Beaker program:
Chemistry 121/122 Name______________________________________ Oct. 5, 1994 Beaker: The Structure and Naming of Simple Carbon Compounds This activity must be done in the Chemistry Macintosh Room, Chem 2305, just one flight up from our laboratory. (The WAM labs don't have the required software). This computer room is a public facility that you can use anytime during its open hours (9 am - 5 pm weekdays). It has word processors and other common software but not the same software that the WAM labs have. 1. Dot structures in Beaker Double-click on the Beaker icon. Click on the opening screen to clear it, then pull down the Struct menu and select Lewis Dot Diagrams. Beaker knows the electron configuration of the elements up to Ne and will attempt to draw the "Lewis dot structures" of simple formulas you type in the box at the bottom of the window. In drawing these structures, the computer will use the correct total number of valence electrons for all atoms and will attempt to "obey the octet rule" insofar as possible (it's not always possible, as you will see). a. Referring to your periodic table, type in the element symbols for each element from H to Ne and press return after each one. The computer draws the element symbol with dots around it representing the valence shell electrons. b. Try typing the formulas for O2, N2, Cl2, H2O, H2O2 (hydrogen peroxide), CH4, NH3 (ammonia), C2H6 (ethane) and determine whether the dot structures drawn by the computer are correct, that is, do they have the correct number of electrons and do they obey the octet rule if possible. c. Now try to make the series CH, CH2, CH3, CH4, CH5. Which is the only one that the program will draw that obeys the octet rule? Why won't it draw a dot structure for CH5? d. Use the program to predict the likely structure of a compound of boron and chlorine. Is it possible for this compound to obey the octet rule? Why not? e. What dot structure does the program draw for carbon monoxide. Does it obey the octet rule? Why do you think the program puts -1 and +1 signs on the structure? (Hint: compare this dot structure with that for N2, which has the same number of total valence electrons, 10, and the same dot structure, yet does not have the -1 and +1 signs). f. What dot structures does the program draw for ozone, carbon dioxide and nitrous oxide N2O? What does the double line represent? (Don't worry about the resonance structures for the time being). g. What dot structures does the program draw for nitrogen oxide (NO) and nitrogen dioxide (NO2). Is it possible for these compounds to obey the octet rule? Why not? h. Have the program draw the series C2Hn, where n = 1 through 7 Which are the only ones that obey the octet rule? 2. Drawing and Naming Organic Compounds in Beaker a. Click on the Cancel button to get out of the Lewis Dot structure mode and return to the main program mode. In this mode the program "knows" some of the simple rules for the structure and naming of organic compounds (compounds of carbon). You can draw an organic compound and the program will try to give it a chemical name according to the naming conventions of the International Union of Pure and Applied Chemistry (IUPAC). To draw a compound, select the arrow tool (upper left-most tool), click on an atom symbol, then click on the main window area. To make a bond between two atoms, click on the bond icon (single, double or triple), and drag the pointer between the two atoms you wish to bond. To erase an atom, select the arrow tool, click on the atom, and pull down the Edit menu and select Clear. b. Draw methane (CH4). Then pull down the Struct menu and select Find IUPAC Name. The program should print out "This is methane." Click the OK button. Erase the methane structure by selecting Select All and then Clear from the Edit menu. c. Try to draw the hydrocarbons C2H6 and then C3H8 and find out what name does the program give for them? After each structure is named, click the OK button and erase the structure by selecting Select All and then Clear from the Edit menu. d. With the structure for C3H8 still on the screen, pull down the Redraw menu and select Lewis Structure. This will cause the programs to redraw your structure more neatly, so you can draw messily and have the computer clean it up. Now pull down the Redraw menu and select Line Segment. This displays the molecule in a shorthand notation that is widely used by chemists. Can you explain how the shorthand notation works? Hint: go back to the Lewis Structure, add another methyl group (-CH3) and see what that looks like as a line segment drawing. e. You can use this shortcut in your own drawings. For example, try using the line (single bond) tool to draw seven line segments connected end-to-end in a zig-zag pattern. What name does the program give for that compound? Convert it to a Lewis structure. How many carbons does it have? f. Try using this shortcut to draw a branched hydrocarbon, such as this isomer of butane: What name does Beaker give for this compound? Did you expect this name? g. Try drawing some other branched hydrocarbons and see if you can figure out how the IUPAC names for such compounds are derived. Hint: What's the longest chain of carbons in the structure? i. Can you draw a branched hydrocarbon so complicated that Beaker can't name it? Try it!