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UB CHE 202 ir values

IR Stretching Frequencies

QuestionAnswer
C-C 1200 cm-1
isolated C=C 1640-1680 cm-1
conjugated C=C 1620-1640 cm-1
aromatic C=C approx 1600 cm-1
C=-C just below 2200 cm-1, usually does not appear for internal, only terminal appears
C=-N just above 2200 cm-1
in general C=C and variations 1660cm-1, conjugation lowers frequency, aromatic is around 1600cm-1
distinguishing between C=-C and C=-N nirtogen form is just above 2200cm-1 while carbon only is just below 2200cm-1. There is a greater polarity and stronger bond so nitrogen form is higher
sp3 C-H 2800-3000 cm-1 (just below 3000cm-1)
sp2 C-H 3000-3100 cm-1(just above 3000 cm-1)
sp C-H 3300 cm-1 sharp, usually strong
O-H, alcohol 3300 cm-1 broad
O-H, acid 3000 cm-1, broad - stronger H bonding makes it lower than an alcohol, probably shoulder/spikes around 2500-2700cm-1
C-O 1060 cm-1 usually in 1000-1200 cm-1 range, unreliable because other things absorb there too
distinguishing an ether Look for 1000-1200 cm-1 absorption and absence of 1700cm-1 and broad 3300/3000cm-1 absorptions
N-H, primary amine 3300cm-1, 2 sharp spikes
N-H, secondary amine 3300cm-1, 1 sharp spike
typical C=O 1700cm-1, overtones usually seen around 3400 cm-1
ketone C=O 1710 cm-1
aldehyde frequencies C=O at 1725cm-1, 2 lowered C-H frequencies around 2700cm-1 and 2800 cm-1
Carboxylic acid C=O 1710 cm-1
conjugated C=O 1685 cm-1, resonance stabilization lowers typical C=O stretch. It is a good way to know there is a C=C even if the C=C stretch does not appear
C=O of amides 1640-1680cm-1, exhibits resonance. DO NOT MISTAKE FOR AN ALKENE. It will be stronger and broader than alkene.
Distinguishing between a C=O of an amide and an Alkene C=O of amide is stronger and broader. Amide has N-H stretches and spikes. Alkene will have C-H above 3000cm-1
C=O of an ester 1735cm-1
strained cyclic ketones C=O (5 membered or smaller) Will absorb above 1725 b/c of increased e- density
C-N 1200cm-1, rarely useful
C=N 1660cm-1, much stronger than C=C although same region
Created by: HugsAndKisses