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    UV/Visible and IR spectroscopy

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    I have a few questions regarding Ir and UV-Vis,

    1. How do you determine if a molecule will be IR-Active?

    2. Why is CO2 IR active and N2 not? Is O2 IR-Active?

    3. Would the IR spectrum of polymer polystyrene have sharp or broad signals? Explain.

    4. Why are some compounds colored and others white?

    Thanks in advance for any help you can pass along. I have a general idea of what the answers are but want to make sure I am on the right track.

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    Solution Preview

    1. How do you determine if a molecule will be IR-Active?

    Linear molecules , whether they possess permanent dipole moment or not, are IR active if some of their vibrations produce an oscillating dipole moment. This means that molecules such as CO2, HCN and H2O are IR active whereas O2, N2 are not.

    2. Why is CO2 IR active and N2 not? Is O2 IR-Active?

    Carbon dioxide has two C=O bonds which are polar (due to high electronegativity difference between C and O) however, the net dipole moment is zero and the overall molecule is non-polar. These two polar bonds can produce ...

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