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MCAT O Chem

Ch. 13 Spectroscopy

QuestionAnswer
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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