Interpreting the infrared spectrum of 3-methylbut-1-ene (3-methyl-1-butene)

Doc Brown's Chemistry Advanced Level Pre-University Chemistry Revision Study Notes for UK IB KS5 A/AS GCE advanced A level organic chemistry students US K12 grade 11 grade 12 organic chemistry courses involving molecular spectroscopy analysing infrared spectra of 3-methylbut-1-ene (3-methyl-1-butene)

email doc brown

Spectra obtained from a liquid film of 3-methylbut-1-ene (3-methyl-1-butene). The right-hand part of the of the infrared spectrum of 3-methylbut-1-ene (3-methyl-1-butene), wavenumbers ~1500 to 400 cm^-1 is considered the fingerprint region for the identification of 3-methylbut-1-ene (3-methyl-1-butene) and most organic compounds. It is due to a unique set of complex overlapping vibrations of the atoms of the molecule of 3-methylbut-1-ene (3-methyl-1-butene).

Interpretation of the infrared spectrum of 3-methylbut-1-ene (3-methyl-1-butene)

The most prominent infrared absorption lines of 3-methylbut-1-ene (3-methyl-1-butene)

The most characteristic absorption is ~1660 cm^-1 due to the C=C vibration (stretching).

You don't find this C=C absorption band in the infrared spectra of saturated alkanes.

There are also characteristic lines due to various C-H vibration absorptions group at wavenumbers ~3100, ~2900, ~1290-1420 and ~800 to 900 cm^-1.

The absence of other specific functional group bands will show that particular functional group is absent from the 3-methylbut-1-ene (3-methyl-1-butene) molecular structure.