IR Spectroscopy

Alkanes

C-H

H-C-H

C-C

C-H: <3000

H-C-H: ~1465

C-C: can’t interpret

Alkenes

=C-H

C=C

C=C-C=C

Weaker signal

=C-H: sp2 >3000

C=C: 1600-1660

C=C-C=C: conjugation shifts carbon-carbon streches to lower frequencies

Alkanes

Alkynes

=-C-H

C-=C

=-C-H: sp ~3250-3350

C-=C: 2150

Nitriles

-C=-N

C=C-C=-N

-C=-N: ~2250

C=C-C=-N: decreases frequency of C=-N stretch (red shift)

Alkanes

Alkene

Alkynes

No C=-C stretch bc the alkyne is symmetrical

Nitrile

Aromatic compounds

=C-H: sp2

C=C:

isolated C=C:

conjugated C=C:

aromatic C=C:

=C-H: sp2: >3000

C=C:~1600 and ~1475

isolated C=C: 1640-1680

conjugated C=C: 1620-1640

aromatic C=C: ~1600

Aromatic

Aromatic

Alcohol

Ether

Primary amine

Secondary amine

Aldehyde

Aldehyde

Carboxlyic acid

Carboxlyic acid

ester

Amide primary 2 stretches

Primary amide 2 N-H stretches

Secondary amide 1 stretch

Teritary amide no stretches

Red shift

more single bond character so vibrates at lower frequences

due to resonance