ORGANIC CHEMISTRY

INFRARED SPECTROSCOPY

REMEMBER:

VISIBLE SPECTRUM

ELECTROMAGNETIC SPECTRUM

INFRARED SPECTROSCOPY

MOLECULES ABSORB INFRARED RADIATION:

INCREASE IN VIBRATIONAL ENERGY.

{The following two simulations require QuickTime.}

BONDS BEND.

BONDS STRETCH.

TAKES A DIFFERENT ENERGY PHOTON FOR EACH BOND (in general).

GET ANABSORPTION OR TRANSMISSION SPECTRUM.

THREE TYPES OF INFORMATION:

1. FUNCTIONAL GROUP: CERTAIN BANDS ARE AT OR NEAR THE SAME FREQUENCY REGARDLESS OF THE STRUCTURE OF THE MOLECULE.

2-PENTANONE vs. 3-PENTANONE;

2-PENTANONE vs. 2-PROPANOL;

VIBRATIONAL ENERGY IS RELATED TO BOND ENERGY!.

BENDING REQUIRES LESS ENERGY THAN STRETCHING:

C-H (STR) = 3030-2860 cm^-1

C-H (BEND) = 1450 (ASYM), 1370 (SYM) cm^-1

2. FINGERPRINT: CERTAIN BANDS HAVE A FREQUENCY THAT IS VERY SENSITIVE TO THE STRUCTURE OF THE REST OF THE MOLECULE.

GET A UNIQUE SPECTRUM!

2-PENTANONE vs. 3-PENTANONE;

3. SEMIQUANTITATIVE.

SPECIFIC SPECTRA:

HEPTANE, 2960, 2925 cm^-1;

1-OCTENE, 3080, 2930, 1643 cm^-1;

BENZENE, 3036, 1481, 674 cm^-1;

TOLUENE, 3027, 1606, 1496, 760 cm^-1;

1-PROPANOL, 3335, 1057 cm^-1; 1-PROPANOL GAS PHASE;

2-PROPANOL, 3358, 1129 cm^-1;

1,4-DIOXANE, 1123 cm^-1

HEPTANAL, 2931, 2719, 1727 cm^-1;

2-PENTANONE, 1715 cm^-1;

3-PENTANONE, 1716 cm^-1;

n-PROPYL ACETATE, 1743, 1239 cm^-1;

HEXANOIC ACID, 3190 (broad), 1713 cm^-1;

CHARACTERISTIC INFRARED GROUP WAVENUMBERS.

IMPORTANT WAVENUMBERS!.

(ADDITIONAL SPECTRA ARE AVAILABLE ON THE WEB AT NIST. THESE SPECTRA ARE GAS PHASE. YOU WILL ALSO HAVE TO "CLICK" REVERSE X TO GET LARGE WAVENUMBERS ON THE LEFT.)