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Ch. 13 Spectroscopy

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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  


   





 
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Created by: adam87 on 2010-07-10



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