Transcript Chemistry 59-330 Lecture 5

Aromatics
Prominent (strong) features:
C-H stretch 3100-3000
in-plane C-H bend 1300-1000
out of plane C-H bend 900-675
C=C ring stretches 1600-1585 and 1500-1400
out of plane C=C bend 450-400
combination bands
IR of Alcohols
O-H H-bonded
3331
O-H bend overlaps
C-H bend 1209
C-O stretch
1023
IR of Alcohols
cyclohexylcarbinol
O-H non-hydrogen bonded
or free OH 3650-3584
(sharp bands in gas phase)
Intermolecular H-Bonding
in solution increase with
concentration gives bands
at 3550-3200 (broader)
Ethers and Epoxides
Ethers: C-O-C asymmetric stretch 1150-1085 (strong)
C-O-C symmetric stretch is usually weak at 1075-1000
Epoxides: ring stretch near 1250 and 950-810
O
Carbonyl Groups
Ketones, aldehydes, carboxylic acids, carboxylic esters,
lactones, acid halides, anhydrides, amides, lactams
all show C=O stretch 1870-1540
O
O
O
C
C
C
R
R
R
R
O
O
C
C
R
R
H
OH
O
OR
O
O
O
O
C
C
C
C
Cl
R
O
R
R
NH2
IR of 2-Pentanone
C=O stretch 1717
C-CO-C stretch 1171
Carbonyl Groups
normal aliphatic ketones (acetone, cyclohexanone)
1715
replacement of alkyl group by heteroatom (G)
+
G
G
shifts
C
C=O stretch
C O
R
direction depends on inductive
or resonance effect
inductive: increases C=O freq.
resonance: decreases
R
O-
Effect of G
Inductive
G
C
O
R
Resonance
+
G
C
R
O-
G
C=O
Cl
F
Br
OH (monomer)
OR
1815-1785
1869
1812
1760
1750-1735
NH2
SR
1695-1650
1720-1690
Aldehydes
Aldehydes slightly higher freq. than methyl ketones
C-H bend
C(O)-H stretch
C=O stretch 1724
760
2825, 2720
overtone band
combination bands
Carboxylic Acids
Broad OH absorption due to H-bonding 3300-2500
C=O stretch near 1760 ( aliphatic monomer)
reduced to 1700 (aliphatic dimers)
intramolecular H-bonding is usually stronger
C=O stretch can be reduced to 1680
Acid Halide
C-H stretch
3065
C=O stretch 1774
Fermi Resonance
overtone of 872
Esters
C-H stretches
C=O stretch
1765
O-C=C asymmetric
stretch 1193
N-H Stretch
(as) 3372,
(ss) 3290
Amines
N-H Bend C-N stretch
1617
1073
N-H wag
900-700
octylamine
Aliphatic C-H bands
Nitriles
CN stretch
2226
Aromatic C-H bands
IR of Benzylthiol
S-H Bend
2565
Aliphatic C-H bands
Aromatic overtones
Aromatic C-H bands
IR of p-toluenesulfonate
S=O stretch
1355, 1177
S-C-O
stretch
Sample 1a
Solution
Band at 2200 suggests CC
bands at 3300 suggest H-CC
bands around 3000 aliphatic C-H
one possibility:
C3H3Cl
H
C
C
H2
C
Cl
Sample 1b
Solution
High frequency bands suggest aromatic C-H
and aliphatic C-H
bands around 1600 suggest substituted aromatic
one possibility:
C10H14
Sample 1c
Solution
High frequency bands suggest N-H, aromatic C-H
and aliphatic C-H
bands around 1600 suggest substituted aromatic
one possibility:
NH2
C7H9N
Sample 1d
Solution
High frequency bands suggest O-H, aromatic C-H
and aliphatic C-H
bands around 1600 suggest substituted aromatic
one possibility:
OH
C7H8O
Sample 1e
Solution
High frequency bands suggest N-H, aromatic C-H
and aliphatic C-H
Note: N-H band is sharp…
bands around 1600 suggest substituted aromatic
one possibility:
C8H11N
H
N
Sample 1f
Solution
High frequency bands suggest aromatic C-H
and aliphatic C-H
bands around 1600 suggest substituted aromatic
one possibility:
Cl
C7H7Cl
Sample 1g
Solution
High frequency bands suggest H-bonding and O-H
and aliphatic C-H
O2 suggest acid? But band at 1728 suggests strong
C=O ….perhaps inductive effect of Cl
one possibility:
C3H5O2Cl
Cl
O
OH
Sample 1h
Solution
High frequency bands suggest H-bonding and O-H
and aliphatic C-H
O suggest alcohol?
Note: no unsaturation
one possibility:
C5H12O
OH
Sample 1i
Solution
High frequency bands suggest aliphatic C-H
band at 1718 suggests ketone
band at 1650 suggest some unsaturation
one possibility:
C6H10O
O
Sample 1j
Solution
High frequency bands suggest aromatic and
aliphatic C-H
bands at 1500-1400 suggest aromatic
one possibility:
C10H12
Sample 1k
Solution
High frequency bands suggest aliphatic C-H
bands at 2300 suggest CN
second N; note no evidence of N-H
one possibility:
N
C5H10N2
C
N