Dr. Glaser's "Chemistry is in the News"
To Accompany Bruice, Organic Chemistry, 3/e.
Chapter 12. Mass Spectroscopy, Infrared Spectroscopy, and
Ultraviolet/Visible Spectroscopy.
Editorial Comments
The art of wine making is an old one. The University of Pennsylvania Museum of Archeology and Anthropology maintains a website on the Origins and Ancient History of Wines. There you can read that wine has been a part of human civilization for some 7,000 years. The art has been refined over the centuries and this evolution resulted in a great variety of delightful wines.
Today, the "art" of wine making is complemented by the "science" of wine making. Micro-climate monitoring and modification, soil assessment and fertilization, spectroscopic analyses and quality control - the modern day wine-maker needs to be competent in all of these issues in addition to having that golden nose.
LC-MS is the best method to analyze wines. In the LC-MS technique, complex mixtures are separated by liquid chromatography (LC) and the components are then analyzed by mass spectroscopy (MS). Both techniques are highly sensitive and LC-MS therefore allows for the detection of compounds that might be present in very small amounts. Thus, there now are quantitative data available for the characterization of wines.
Questions &
Chemistry
Online Exploratory.
Question 1:
The viscous character of German rieslings are due in part to glycol,
1,2-dihydroxyethane. Check the
Chemfinder if you are not sure
what the structure looks like. Which radical cation M+ is
formed upon ionization of glycol? Wha is the mass of M+? What
is the most likely fragmentation of M+?
Answer 1:
Ionization of O-lone pair electron generates M+.
alpha-Cleavage of M+ results in (H2COH)+
with mass 31. See the SDBS databank for the mass spectrum of
glycol.
Question 2:
Phenols provide wines with color and a bit of astringency. Let's look at
the parent phenol first.
Check the
Chemfinder if you are not sure
what the structure of phenol looks like.
Which radical cation M+ is formed upon ionization of phenol?
What is the mass of M+?
What is the most likely fragmentation of M+?
Answer 2:
Ionization of O-lone pair electron generates M+ or
ionization of the pi-system generates M+.
No typical fragmentations expected; strong M+.
See the SDBS databank for the mass spectrum of
phenol.
Question 3:
Hydroxycinnamics provide that golden color to the German Rulaender.
Let's look at one specific "hydroxycinnamic", the 4-hydroxycinnamic
acid. Cinnamic acid is Ph-CH=CH-COOH. Check the
Chemfinder if you are not sure
what the structures of cinnamic acid and cinnamic acid derivatives look
like.
Which radical cation M+ is formed upon ionization of
4-hydroxycinnamic acid?
What is the mass of M+?
What is the most likely fragmentation of M+?
Answer 3:
Ionization of pi-electron of the carboxylic acid group leads to
M+
followed by OH-radical elimination gives cation with mass M+ -
17 = 147. The cation can the loose CO and give a cation with mass 119.
The ionization of the hydroxyl group or of the benzene also are possible;
these ionizations do not lead to dominant fragmentations.
See the SDBS databank for the mass spectrum of
4-hydroxycinnamic
acid
Question 4:
Flavonoids are a special kind of phenols; the phenols that are derived
from flavone. Check the
Chemfinder to see what the
structures of flavone looks like.
Which radical cation M+ is formed upon ionization of flavone?
What is the mass of M+?
What is the most likely fragmentation of M+?
Answer 4:
Ionization of a carbonyl oxygen lone pair is most likely. The cation
M+ with mass 222 can undergo alpha-cleavage and the resulting
cation will loose CO and form a cation with mass 194.
See the SDBS databank for the mass spectrum of
flavone.
Chemistry
and Society.
Germany is famous for its law of 23. April 1516 regulating the purity of
German beer. This law causes all kinds of trouble in the EC since many
countries believe that the old German law serves to limit the import of
beer into Germany. A similar debate will eventually start about the
purity of wine. As "wine chemists" learn more and more about the
compounds that give wines those great flavors, sooner or later there will
be the temptation to manipulate the concentrations of these compounds.
Would such manipulation present the natural next step in the evolution
of wine? Or would such manipulation be undesirable?