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Photochemistry Assignment #2

This assignment covers material from Chapter 2 section 1 to Chapter 2 Section 14.

1) According to the principles of quantum mechanics, what is the wave function?

2) What is the Born-Oppenheimer approximation?

3) Under what two types of interactions does the approximation given in equation 2.4 break down?

4) (a) What is the four-letter abbreviation for the highest energy occupied molecular orbital? (b) What is the four-letter abbreviation for the lowest energy unoccupied molecular orbital?

5) To what does the square of a wave function relate?

6) What is an expectation value?

7) What is meant by an electronic configuration?

8) An alkene like ethylene will usually have only one low-energy electronic transition. What is it?

9) An organic molecule which contains a carbonyl functional group, like formaldehyde, typically has two relatively low-energy electronic transitions. What are they?

10) What are the two possible spin states for the configurations shown for ethylene and formaldehyde in Figure 2.1-b?

11) A single electron configuration is often adequate to approximate the electronic characteristics of an electronic state. In some cases, however, a combination of two or more configurations are required to achieve a good approximation of a single state. When does this occur?

12) (a) What is Hund’s rule for organic photochemistry? (b) What is the physical basis for this rule?

13) (a) What is the symbol for the Coulomb integral? (b) What is the symbol for the electron exchange integral? (c) Are both of these integrals positive quantities? Why? (d) Which integral is purely a quantum mechanical phenomenon?

14) According to equation 2.18, the difference in the electronic energy between singlet and triplet states derived from the same electron orbital configuration (ΔEST) is equal to what?

15) In Section 2.14, the text says that the

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e r term can be factored out of the electron

exchange integral leaving the overlap integral. The text then states that the quantum mechanical mathematical overlap integral corresponds to the degree of physical overlap of the orbitals in space. Thus, the smaller the overlap, the smaller the value of the overlap integral; and the larger the overlap, the larger the value of the overlap integral. (a) So, in a carbonyl containing compound, which is larger: , *nJ  which is proportional to , *n  or , *J  which is proportional to , *  ?

(b) Since the value of ΔEST is related to the value of the electron exchange integral J, which is larger: ΔEST from a , *  configuration in ethylene or ΔEST from a , *n  configuration in formaldehyde?

16) Does increasing conjugation increase or lower ΔEST from the , *  configuration in alkenes? (Refer to Table 2.3.)