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MCAT O Chem
Ch. 13 Spectroscopy
| Question | Answer |
|---|---|
| What is infrared spectroscopy used for | find functional groups |
| symmetric bonds and IR | do not show up because they involve no net change in dipole moment |
| IR carbonyls | sharp peak at 1,700cm-1 |
| IR hydroxides | broad peak at 3,300cm-1 |
| IR amines | sharper peaks at 3,300 and 3,400cm-1 for primary amines, secondary amines have one peak |
| H-NMR | useful to find the structure of a compound and can also reveal functional groups |
| what does H-NMR measure | how deshielded (how much electron density has been pulled away) protons are on a molecule. gamma=0-12 ppm. the more deshielded the proton is, the further down-field it will be. |
| H-NMR aldehyde | 9 to 10 ppm (highly deshielded) |
| H-NMR caroxylic acid | 10.5 to 12 ppp (highly deshielded) |
| H-NMR hydrogen aromatic ring | 6.5 to 8.5 ppm |
| how to tell how much deshielding | concept of electronegativity, the more electron density that is pulled away from the proton, the more deshielded in will be. |
| H-NMR coupling | protons three bonds apart experience coupling. If there is one proton three bonds away, its a doublet; if there are two, its a triplet; three, its a quartet |
| C-NMR | similar to H-NMR but gamma=0-210ppm |
| what is UV spectroscopy useful for | conjugated compounds |
| Mass spectroscopy | used to find the mass of the compound and the masses of fragments of the compound |
| compounds that will show absorption in the 1750 region | (carbonyls) ketones, aldehydes, carboxylic acids, any caboxylic acid derivative(acid anhydrides, acid halides, amides, esters) |
| acid, alcohol O-H peak | broad peak, above 3000 |
| Amine N-H peak | sharp peak, above 3000 |
| Alkane C-H peak | sharp peak, below 3000 |
| what does the area under the signal represent | the total area under the signal corresponds to the number of nuclei represented by that signal |
| NMR spec based on hybridization | H bonded to sp3 hybridized carbon shift between 0 and 5. if bonded to an sp2 hybridized carbon shift between 5-10. divide spectrum in half, sp3 right, sp2 left |
| what compounds are always conjugated | aromatic molecule |
| important peaks on mass-spec | base peak-tallest peak, most abundant ion, assigned relative abundance of 100. Molecular ion or parent peak (M+) peak furthest to the right, usually equivalent to molecular weight of original molecule |
| mass spectroscopy results in the separation of fragments according to | mass-to-charge ratio |
Created by:
adam87
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