Lecture 1: Introduction
Wednesday, September 04, 2013
I. The Importance of Spectroscopy: Identification of unknown organic compounds
Did the reaction work?
Why did it work?
What else is in the reaction mixture? (impurities, other compounds?)
Did the purification method work?
The goal is to be able to put all of the obtained data together and correctly interpret it.
As the number of data increases, the complexity or the size of the molecule being analyzed increases.
A. Traditional Methods of Analysis:
Melting point, boiling point, optical rotation
Combustion analysis (for purity)
Taste, smell, color (obsolete and quite dangerous!)
These methods work, but there are obvious drawbacks, such as the destruction of the sample.
B. Modern Methods (extensive field):
Mainly the elucidation of the structures of organic compounds, but also of inorganic and
This analysis is done on dilute samples (solutions) or small amounts of the compound in vapor
phase to minimize the interaction between molecules.
1. Main Methods:
Nuclear Magnetic Resonance (NMR): 10mm-100m, generally insensitive method of detection.
(Bell and hammer analogy).
Infrared Spectroscopy (IR): 10 nm - 1mm
Mass Spectrometry (MS): 3
Ultraviolet/Visible (UV/Vis): 10nm - 10 nm. Will not ionize the sample, but will excite electrons
(which may cause isomerization to occur). Need super pure solvent!
X-ray Crystallography (not covered in this course!!!) 2. Advantages:
Obtain detailed information
Small amounts of material are required
C. Requirements to Determine the Structure of an Unknown Compound:
Use "chemical common sense" , or the knowledge of general principles structure and bonding in
Use an organ