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    Question 1
    Which of these molecules will absorb IR radiation
    H2O
    N2
    CH4
    O2
    CO2

    I said H2O and CH4 but apparantly CO2 does as well - I thought only polar molecules did????

    Question 2
    Which intermolecular forces exists between molecules of ethoxyethane (CH3CH2OCH2CH3)

    I said "Instantaneous dipole - induced dipole ONLY but apparantly permanent dipole-permanent dipole forces are there too. Why????


    Question 3
    Which of these will be the best solvent for cyclohexanol and why
    H2O
    CH3COCH3
    NaCl
    CH3CH2CH2CH2CH2CH3

    I said the last one but it is the second one. Why?
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    (Original post by jsmith6131)
    Question 1
    Which of these molecules will absorb IR radiation
    H2O
    N2
    CH4
    O2
    CO2

    I said H2O and CH4 but apparantly CO2 does as well - I thought only polar molecules did????
    IR absorption occurs when a change in a vibrational state produces a CHANGE in the molecules dipole moment.

    You are quite correct in saying that CO2 is not polar...

    ... BUT, if it flexes and bends the O-C-O bond angle it becomes polar. Hence the change in dipole moment and IR absorption

    (Original post by jsmith6131)
    Question 2
    Which intermolecular forces exists between molecules of ethoxyethane (CH3CH2OCH2CH3)

    I said "Instantaneous dipole - induced dipole ONLY but apparantly permanent dipole-permanent dipole forces are there too. Why????
    It may be symmetrical vertically but horizontally is has a dipole moment. Don't forget that the electronic arrangement at the oxygen is tetrahedral and you could represent the molecule as:

    R2O

    So it's basically the same shape as water (angular, bond angle 104º) and hence polar.

    (Original post by jsmith6131)

    Question 3
    Which of these will be the best solvent for cyclohexanol and why
    H2O
    CH3COCH3
    NaCl
    CH3CH2CH2CH2CH2CH3

    I said the last one but it is the second one. Why?
    Cyclohexanol is polar and able to form some hydrogen bonds. It is too bulky to dissolve in water, so propanone is the best bet with polarity and a largish size.
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    I still don't understand the answer for Question 2 can someone please elaborate / display diagramtically

    thanks
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    (Original post by jsmith6131)
    I still don't understand the answer for Question 2 can someone please elaborate / display diagramtically

    thanks
    I'm not sure, but I guess the oxygen would attract electron density from the two carbons next to it, giving it a negative dipole and the two carbons positive dipoles.
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    (Original post by jsmith6131)
    I still don't understand the answer for Question 2 can someone please elaborate / display diagramtically

    thanks
    Check this out:

 
 
 
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