This document discusses infrared spectroscopy and its use in identifying unknown organic compounds. Infrared spectroscopy analyzes the vibrations of chemical bonds when exposed to infrared radiation. Different functional groups like C-H, N-H, and O-H bonds vibrate at different frequencies. An unknown sample was analyzed and its peaks were observed and compared to reference data to identify it as a secondary amide.

1. Infrared Spectroscopy
By Dr. Robert D. Craig, Ph.D

2. Abstract
The presence of functional groups in organic molecules can be identified using
infrared spectroscopy. As this experiment allows us to explore, we use infrared
spectroscopy to analyze and identify an unknown organic compound. Infrared radiation
consists of wavelengths, when absorbed by molecules; radiation of this wavelength
increases the amplitude of vibrations of the chemical bonds joining atoms.
Introduction
Infrared spectroscopy is a study of which specific mode of interactions with added
radiation by molecules called vibrations. Infrared spectra are measured in units of
frequency or wavelength. The positions of absorbed bands are measured in frequency
units by wavenumbers, ῡ, which are expressed in reciprocal centimeters, cm ̄ ¹,
corresponding to the number of cycles of the wave in each centimeter.
cm ̄ ¹ = 10,000
μm
Wavenumbers, cm ̄ ¹, are proportional to frequency: ῡ (cm ̄ ¹) = v/c
Molecular vibrations that interact with infrared light can be described as saying
that the frequency of a stretching vibration is directly proportional to the strength of the
bond and inversely proportional to the masses connected to the bonds. Therefore, we
may find; C--H, N--H, and O--H bond stretching vibrations are high frequency (short
wavelength) compared to C--C and C--O bonds because of their low mass of the
hydrogen compared to that of carbon or oxygen. A double bond will yield a stronger
bond so we can see C=C and C=O vibrations at higher frequency than C—C and C—O

3. stretching vibrations. Triple bonds such as, C≡C and C≡N stretch at a higher frequency
than double bonds; C=C and C=O, but lower frequencies than; C—H, N—H, and O—H.
Procedure
While wearing proper personal protective equipment; gloves and goggles, the
following procedure is performed under the fume hood at all times. The given NaCl disk
is handled with tongs and added to it are several drops of CHCl3 onto the disk. The NaCl
is allowed to evaporate to ensure the disks are dried completely. Only one drop of the
unknown labeled C is added onto the NaCl disk. The two NaCl disks are placed together
with the compound in between the two disks. The NaCl disk is then placed into the
liquid sample holder. The liquid-sample is removed from the fume hood and placed into
the spectrometer, ensuring correct positioning. Using the computer, the data attached is
collected.
Results and Observations
(See Attached Graph)
Unknown Sample C had the following observed peaks:
-Strong-Medium intensity at 3342.11 cm ̄ ¹
-Stron-Medium intensity at 2970.26 cm ̄ ¹
-Medium intensity at 2933.48 cm ̄ ¹
-Medium intensity at 2884.45 cm ̄ ¹
-Weak intensity at 2651.53 cm ̄ ¹
-Medium intensity at 1470.60 cm ̄ ¹

4. -Strong-Medium intensity at 1380.70 cm ̄ ¹
-Medium intensity at 1311.24 cm ̄ ¹
Conclusion
Following the Step-by-Step Analysis of Infrared Spectra and comparing the
collected data to Table 12.2: Characteristic Infrared Carbonyl Stretching Peaks, we can
assume the following. The infrared spectra collected displays weak peaks between 1820
– 1625cm ̄ ¹ with a medium intensity N—H band between 3520 – 3070 cm ̄ ¹ of 3342.11
cm ̄ ¹ producing only one N—H stretch absorption, we may note the observed functional
group as a secondary amide.