This question is due Monday, October 31 st by 12:00 pm (noon) in my office. If I

Question

This question is due Monday, October 31 st by 12:00 pm (noon) in my office. If I am not in my office, please put it under the door. Late take home questions will not be graded. You may use additional resources to answer this question excluding other students and faculty. You must to get full credit. One very useful application of group theory is its use in predicting the number of IR and Raman vibrational frequencies of molecules. Consider the following isomers Would you be able to distinguish all of the Isomers of Fe(CO)_3(PPh_3)_2 with a combination of IR and Raman spectroscopy? Explain your reasoning. You must for full credit.

Explanation / Answer

There are three possible isomers of Fe (CO)3(PPh3)2as shown in fig. D3h Cs and C2v.

In D3h Phosphines are in Tran’s position, in Cs symmetry one phosphine is axial and one is on equatorial position. In C2v both phosphines are equatorial.

In D3h the CO stretches transform like a1' and e'. Both are allowed in the Raman spectrum, but only the e' stretch is IR allowed. In Cs the CO stretches transform like 2a' + a'', while in C2v they are 2a1 + b1. Unfortunately, in the lower symmetry point groups all three stretches are allowed in both the IR and Raman spectroscopy, so it is not possible to distinguish all possible geometric isomers of Fe(CO)3(PPh3)2 with a combination of infra-red and Raman spectroscopy.

Only vibrational spectroscopy can be used to distinguish the D3h isomer from the other two.

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