LECTURE 10 1. Write the Lewis Structure for the following compounds: (a) CH3F (b) NBr3 H (a) H (b) C Br N F Br Br H 2. Determine the formal charge on each atom and label all non-zero formal charges in the following molecules. Identify most stable (lowest energy) structure for each case. (a) acetic acid: -1 H O C C +1 H O H H H H O C C H lower energy (no FC separation) O H (b) nitrate ion: -1 1- O N 3. 1- O +2 1- O N +1 N O O O O -1 -1 -1 -1 O O -1 note: not a valid structure! N can't have 5 bonds! Are the molecules below a pair of resonance structures? Briefly explain. O HO P H HO P OH H C H H C H H H No. In order to be resonance structures, only the electrons can be rearranged. When atoms are in a different relationship to each other, the two structures are not resonance forms, they are different molecules. 1 LECTURE 10 4. Write the Lewis structure for the guanadinium ion, C(NH2)3+1, and include all relevant resonance forms. (Note that the C is bonded to three N atoms.) Note that you do not need to indicate FC for this problem, but you should always consider FC when writing Lewis structures. + H + H H N H N C H 5. + H H N H N H H N H C H N H N H H N C N H H H The skeletal structures of two amino acids, leucine and arginine, are drawn below. Non-zero formal charges are indicated. Provide the Lewis structure(s), including double bonds and lone pairs, for each of these molecules. If there are equivalent resonance forms (which may include moving the formal charge on N), include them. O O (a) H 2N CH (b) C H 2N CH CH2 leucine CH2 CH C OH OH arginine CH2 CH2 CH 3 NH CH 3 C H 2N (a) (b) O NH 2 O O H 2N H 2N OH OH NH NH H 2N OH H 2N NH 2 H 2N NH 2 2