Which compound would be expected to show intense IR absorption at 3363, 3185, 1660 cm-1? How do you know?

Question

#CH_3CH_2CH_2OH#
#(CH_3)_2CHNH_2 #
#CH_3CH_2CONH_2#
but-1-ene

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Answer 1 · 2016-05-16T01:29:36

#"CH"_3"CH"_2"CONH"_2# would be expected to show the observed peaks.

Let's eliminate the obvious culprits.

Propan-1-ol would show only a broad band from #"3200 - 3550 cm"^"-1"#.

2-Methylpropanamine would not show a peak at #"1660 cm"^"-1"#.

But-1-ene would show no peaks above #"3100 cm"^"-1"#.

The peak at #"1660 cm"^"-1"# could be either #"C=C" ("1620 – 1680 cm"^"-1")# or #"amide C=O" ("1640 – 1690 cm"^"-1")#.

The two peaks at #"3363 cm"^"-1"# and #"3165 cm"^"-1"# are definitive, however.

They must represent the symmetric (#"~3180 cm"^"-1"#) and asymmetric #("~3350 cm"^"-1")color(white)(l) "N-H"# stretches of an amide #"NH"_2# group.

The compound must be propanamide.