Chem2O6 - 1997/98

1. Write the following condensed formulas as Lewis structures:

(i) (CH₃)₃SO+     (ii) CH₂N₂     (iii) CH₃NHCONH₂     (iv) CH₃CH₂N₃     (v) CHCCHNCH₃

2. Write resonance structures for the following, indicating major and minor contributors (C₆H₅ is a phenyl ring).

(i) [CH₃CHOCHCH₂]+     (ii) [CH₃CH₂OCHCHCH₂]+     (iii) [C₆H₅CH₂]-     (iv) [CH₃COCH₂]-

(v) [CH₂CHCHCHCH₂]+     (vi) [C₆H₅CHNH₂]+     (vii) [CH₂CHCH₂]

3. Draw a molecular orbital diagram for carbon tetrachloride (CCl₄), using sp³ hybrid atomic orbitals for carbon and a 3p atomic orbital for each of the chlorines. Fill the MO's with the eight electrons involved in sigma-bonding in the molecule. Draw pictorial representations of one of the bonding and one of the antibonding MO's.

(a) Irradiation of a solution of CCl₄ in cyclohexane C₆H₁₂) with UV light results in the formation of the following products:

Suggest a mechanism for the reaction, and explain what the role of the UV light is, using your MO diagram for assistance.

(b) Reduction of carbon tetrachloride with sodium metal leads to the formation of hexachloroethane (C₂Cl₆) and sodium chloride. Suggest a mechanism for this reaction, again using MO diagrams to help explain why the reaction occurs.

4. Draw a molecular orbital diagram for water (H₂O), using two hydrogen 1s atomic orbitals and four oxygen sp³ hybrid orbitals. Fill the MO's with the eight electrons.

Why would it be incorrect to construct the MO's using sp hybrid atomic orbitals for the O-H bonds, and two pure p-orbitals for the lone pairs?

19sep97; wjl