[Crystal1137]

How could I determine that the IR above is for cyclohexanone by looking at the graph?

Thanks in advance!

[bolo]

At first you can notice a strong absorption caused by C=O bond in its usual range, here it'd be about 1720 cm^-1. There is nothing but simple C-H aliphatic range ca. 3000 cm^-1-2850 cm^-1 in the spectrum. All other differences, like the absorption ranges of methyl/methylene (here you have them only)/methine groups, you can see i.e. on Wikipedia:

  http://en.wikipedia.org/wiki/Infrared_spectroscopy_correlation_table