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    Right, what differences are there in the Infrared Spec between a Ketone and an Aldeyhde with a Molecular formula of C5H10O? And also, what differences are there in the Mass Spectormetry??
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    I suppose the most obvious difference in the mass spec would be that a peak would be present at 29 in the aldehyde spectra from the CHO fragment. Some IR to follow.

    EDIT: There seems to be a very distinctive aldehyde C-H stretch up near 3000 cm-1 that's obviously not present in the ketone.
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    The guys above are right. The stretches due to the C=O would be very similar for both compounds at around 1700 - 1750 cm-1. They way you can clearly tell them apart is from the presence or absence of a peak at around 2700 - 2800 cm-1, due to the aldehyde C-H stretch in the CHO group. Assuming you know it's an aldehyde or a ketone, if you see this peak it's an aldehyde. If not, it's a ketone.
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    (Original post by Kyri)
    The guys above are right. The stretches due to the C=O would be very similar for both compounds at around 1700 - 1750 cm-1. They way you can clearly tell them apart is from the presence or absence of a peak at around 2700 - 2800 cm-1, due to the aldehyde C-H stretch in the CHO group. Assuming you know it's an aldehyde or a ketone, if you see this peak it's an aldehyde. If not, it's a ketone.
    Ah you genius.. Yea, I only really noticed that today when I was looking more closely.. So to distinctively tell if its an Aldehyde or a Ketone from an IR Spec, is basically if there is this aldehyde C-H stretch in the CHO group.. Which appears around 2850-3100 according to my Datasheet. And yea, in the Mass Spec, you can tell if its an Aldehyde or Ketone due to the CHO+ fragment at 29..

    Thankyou both of you guys! Much appretiated!
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    (Original post by Haz Shah)
    Ah you genius.. Yea, I only really noticed that today when I was looking more closely.. So to distinctively tell if its an Aldehyde or a Ketone from an IR Spec, is basically if there is this aldehyde C-H stretch in the CHO group.. Which appears around 2850-3100 according to my Datasheet. And yea, in the Mass Spec, you can tell if its an Aldehyde or Ketone due to the CHO+ fragment at 29..

    Thankyou both of you guys! Much appretiated!
    That is correct. However the 2850 - 3100 cm-1 range which your book quotes sounds rather broad to me. If you see peaks appearing above 2900 cm-1 I wouldn't take take that as evidence of an aldehyde since aliphatic C-H stretchs are in the 2900 - 3000 cm-1 region and aromatic C-H stretches appear around 3000 - 3100 cm-1. If you don't see an aldehyde peak at around 2700 - 2850 cm-1 then you should look at other data for confirmation, such as mass spec as mentioned, or the presence of a singlet which integrate to one proton at around 9 - 9.5 ppm in the 1H-NMR.
 
 
 
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