Spectroscopic Applications for Structure Elucidation of Organic Compounds

IR

Infrared (IR) Spectroscopy- Is a simple and rapid instrumental technique that can give evidence for the presence of

various functional groups.Infrared (IR) region of the electromagnetic spectrum covers the range from just above the visible (7.8 x 10 -7 m) to approximately 10-4 m, but only the midportion from 2.5 x 10 -6 m to 2.5 x 10 -5

m is used by organic chemistry.

Wavelengths w/in IR regiono Given in micrometers

(1µm=10-6m)

Frequencieso Given in wavenumbers

Wavenumbers: v (cm-1)=1/λ(cm)

Useful IR region is from 4000 to 400 cm-1

INTREPETING INFRARED SPECTRA

Fingerprint region (Complex region)1500 -400 cm-1

INFRARED SPECTRA OF SOME FUNCTIONAL GROUPS

IR spectrum of an alkane is fairly uninformative because no functional groups are present and all absorptions are due to C-H and C-C bonds.

C-H 2850 – 2960 cm-1

C-C 800 – 1300 cm-1

Show several characteristic stretching absorptions.

terminal alkyne (intense)

CARBONYL COMPOUNDS

Characteristic IR Absorptions of Some Functional Groups