Theories of Covalent Bonding

Use MO diagrams and the bond orders you obtain from them to answer: 

(a) Is  ${{\mathbf{O}}_2}^{-}$ stable? 

(b) Is   ${{\mathbf{O}}_2}^{-}$ paramagnetic? 

(c) What is the outer (valence) electron configuration of  ${{\mathbf{O}}_2}^{-}$ ?      

There is concern in health-related government agencies that the American diet contains too much meat, and numerous recommendations have been made urging people to consume more fruit and vegetables. One of the richest sources of vegetable protein is soy, available in many forms. Among these is soybean curd, or tofu, which is a staple of many Asian diets. Chemists have isolated an anticancer agent called genistein from tofu, which may explain the much lower incidence of cancer among people in the Far East. A valid Lewis structure for genistein is NN

1. Is the hybridization of each  $\mathbf{C}$ in the right-hand ring the same? Explain.
2. Is the hybridization of the $\mathbf{O}$  atom in the centre ring the same as that of the $\mathbf{O}$  atoms in  $\mathbf{OH}$groups? Explain.
3. How many carbon-oxygen  $\mathbf{\sigma }$ bonds are there? How many carbon-oxygen  $\mathbf{\pi }$ bonds?
4. Do all the lone pairs on oxygens occupy the same type of hybrid orbital? Explain.

An organic chemist synthesizes the molecule below:

1. Which of the orientations of hybrid orbitals shown below are present in the molecule?
2. Are there any present that are not shown below? If so, what are they?
3. How many of each type of hybrid orbital are present?

Acetylsalicylic acid (aspirin), the most widely used medicine in the world, has the Lewis structure at the right.

1. What is the hybridization of each  $\mathbf{C}$  and each  $\mathbf{O}$ atom?
2. How many localized  $\mathbf{\pi }$ bonds are present?
3. How many  $\mathbf{C}$ atoms have a trigonal planar shape around them? A tetrahedral shape? 

Linoleic acid is an essential fatty acid found in many vegetable oils, such as soy, peanut, and cottonseed. A key structural feature of the molecule is the cis orientation around its two double bonds, where R1 and R2 represent two different groups that form the rest of the molecule.

1. How many different compounds are possible, changing only the cis-trans arrangements around these two double bonds?
2. How many are possible for a similar compound with three double bonds?

Tryptophan is one of the amino acids found in proteins:

(a) What is the hybridization of each of the numbered C, N, and O atoms? 

(b) How many sigma bonds are present in tryptophan? 

(c) Predict the bond angles at points a, b, and c.

Silicon tetrafluoride reacts with to produce the hexafluorosilicate ion, ${{\mathbf{SiF}}_6}^{2-}$ ;  ${\mathbf{GeF}}_4$behaves similarly, but ${\mathbf{CF}}_{\mathbf{4}}$ does not.

1. Draw Lewis structures for ${\mathbf{SiF}}_4$ , ${{\mathbf{GeF}}_6}^{2-}$ , and  ${\mathbf{CF}}_4$.
2. What is the hybridization of the central atom in each species?
3. Why doesn’t  ${\mathbf{CF}}_4$ react with $\mathbf{F}$ to form ${{\mathbf{CF}}_6}^{2-}$ ?

The compound 2,6-dimethyl pyrazine (below) gives chocolate its odor and is used in flavourings.

1. Which atomic orbitals mix to form the hybrid orbitals $\mathbf{N}$  ?
2. In what type of hybrid orbital do the lone pairs  $\mathbf{N}$   reside?
3. Is  $\mathbf{C}$ in  ${\mathbf{CH}}_{\mathbf{3}}$  hybridized the same as any $\mathbf{C}$  in the ring? Explain.