Problem Set 1
Problem Set Due no later than 26 September
Do any 12 of the following problems. Be prepared to defend your answers in in class.
- Write Lewis structures, including formal charges, for each of the following species; show all significant contributing "resonance" structures. Use curly arrows to move electrons appropriately to create each resonance structure from its predecessor. In some cases multiple structures that are not resonance structures may be possible. Write them all. When multiple structures are possible, whether resonance or otherwise, select the most stable and justify your choice.
Need a review of writing Lewis structures?
- Write structures for all molecules of formula C5H8. Be alert for stereoisomers, and include all stereoisomeric pairs. Think in three dimensions, and organize. Not counting enantiomers, 28 isomers are possible.
- Carey/Sundberg, Problem 1.2; also think about how you would determine experimentally the site of protonation
- Carey/Sundberg, Problem 1.11
- Carey/Sundberg, Problem 1.12, parts (a) and (b); you will note that we have already done these in class, but try them on your own, anyhow.
- (a) Combine the H2 MOs with another 1s orbital to make linear H3 (that is, H-H-H). How would the set of MOs you made for H3 be occupied in neutral H3? In H3+? Which is more stable, the linear arrangement or the triangular (which we described in class)? Why?
(b) Combine the orbitals of two H2 molecules to make the orbitals of H4.
- Combine the orbitals of H4 with the 2s, 2px, 2py, and 2pz orbitals of carbon to make methane, CH4.
- Bronsted-Lowery acid base reactions may be diagrammed in orbital interaction theory as the interaction between an orbital on the base and the s* orbital of the HX bond. Use orbital interaction diagrams to predict the relative acidities of HF, HCl, and HBr.
- The hydroperoxyl anion, HOO- is as much as 105 better a nucleophile than is hydroxyl, HO-, a difference that is attributed to the unshared pairs on the nonnucleophilic oxygen. Use frontier orbital theory to explain.
- Use the Huckel MO program to compute the orbital energies, coefficients, bond orders, and electron densities for the cyclopentadienyl anion and for furan. Rationalize any differences.
- Identify the symmetry elements of the molecules below. Then determine whether symmetry permits orbital interactions between orbitals of the starred atoms or groups. Where interactions are possible, identify them.
- Assign each of the molecules below to its point group.
Here is some help with this problem:
|This Molecule Has D3 Symmetry
- Assign configurations to any chiral axes or planes in the following molecules.
- Draw structural formulas including stereochemistry for the product(s) described for each reaction:
- Addition of Br2 to Z- and E-cinnamic acid
- Syn-elimination of acetic acid from 1R, 2S-diphenylpropyl acetate
- OsO4 dihydroxylation of Z- and E-3-hexene
- Carey and Sundberg, Problem 2.1 (Translate the Fischer projections in part (a) into real stereochemical drawings)
- Carey and Sundberg, Problem 2.25
- Carey and Sundberg, Problem 2.9
Just in case anyone would like to draw some chemical structures to include in their work, here are links to some free structure-drawing programs:
This page last modified 9:34 AM on Friday September 23rd, 2011.
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