nmr: proton, carbon, dept

principle behind NMR

apply a strong magnetic field and determine amount of energy needed to spin flip a proton

2 spin states of protons in presence of magnetic field

align with magnetic field (alpha), align against magnetic field (beta)

proton shielding/deshielding

electrons shield and need more energy spin flip, lower frequency; vice versa

NMR can only be used with nuclei of an even/odd number of protons or neutrons

odd

number of signals in H NMR and C NMR

how many differernt H/C is present

chemical shift in H NMR

info about chemical/magnetic environment of H

integration of H NMR

number of H that give that signal

H NMR splitting

# of H on neighboring C’s, n-1 = neighbors, n+1 = multiplicity (s, d, t…)

what is H NMR chemical shifts measured relative to and why

TMS (tetramethyl silane) C is more EN than Si, so H in TMS are more shielded and resonate at higher field than other organic H

coupling constant (J value)

distance between individual peaks of a signal; coupled H have same coupling constant

(when any H is replaced with X to determine if 2 H are equivalent or not) and constitutional isomers result

H are non equivalent

(when any H is replaced with X to determine if 2 H are equivalent or not) and same compound results

H are homotopic; equivalent

(when any H is replaced with X to determine if 2 H are equivalent or not) and enantiomers result

H are enantiotopic; equivalent

(when any H is replaced with X to determine if 2 H are equivalent or not) and different diasteromers result

H are diastereotopic; not equivalent

NMR of alcohols

must be done in DMSO instead of D2O bc proton exchange is slower in DMSO and OH peak can be observed (trace amts of acid catalyze proton transfer faster than NMR can measure)

carbonyl C NMR range

230-150

sp2 C; C NMR range

150-11

deshielded sp3 C; C NMR range

EWG deshields; 100-50

sp3 C; C NMR range

50-0

DEPT-90

only shows CH (methyne) signals

DEPT-135

CH3 and CH positivel CH2 negative