Lecture Organic chemistry - Chapter 15: Benzene and aromaticity. In this chapter, we will explore the structural implications of the stabilizing effects of aromaticity. The discussion will introduce the key ideas by focussing on the unique properties of benzene, the prototypical aromatic molecule. One new chemical reaction appears, electrophilic aromatic substitution, of benzene (using a variety of reagents, leading to different products). This reaction is elaborated in the next chapter, where the substrate is a substituted benzene.
Polychlorinated biphenyls (PCBs) are a family of chemical
compounds which do not exist in nature but which are manmade.
Commercial mixtures are clear, pale yellow liquids
manufactured by the replacement of hydrogen atoms on the
biphenyl molecule by chlorine. The reaction is controlled
according to the percentage replacement of hydrogen and
results in a product which contain chlorobiphenyls with one
or, more usually, several chlorine atoms attached to each
“There’s Plenty of Room at the Bottom” ⎯ this was the title of the lecture Prof. Richard Feynman delivered at California Institute of Technology on December 29, 1959 at the American Physical Society meeting. He considered the possibility to manipulate matter on an atomic scale. Indeed, the design and controllable synthesis of nanomaterials have attracted much attention because of their distinctive geometries and novel physical and chemical properties.
Single crystal X-ray crystallography is the most common and easily accessible way to
determine the molecular structure of any crystalline material. This method provides
two kinds of information which are needed for understanding both single molecule
properties and bulk material properties:
1. Molecular Structure - Single Molecules:
Unambiguous and three-dimensional information about the structure of the molecular
Bioremediation strategies use microorganisms to remove hazardous sub-stances, such as aromatic molecules, from polluted sites. The applicability
of these techniques would greatly benefit from the expansion of the cata-bolic ability of these bacteria in transforming a variety of aromatic com-pounds.
BASICS OF CRUDE OIL
Crude oils are complex mixtures containing many different hydrocarbon compounds. An average crude oil contains about 84% carbon, 14% hydrogen, 1 ÷ 3% sulfur and less than 1% each of nitrogen, oxygen, metals and salts. Simple crude oil assays are used to classify crude oils as paraffinic, naphthenic, aromatic or mixed, based on the predominant proportion of similar hydrocarbon molecules. The comprehensive crude assays determine the value of the crude: its yield and quality of useful products.
To be classified as aromatic, a compound must
meet both of the following criteria:
It must have an un-interrupted cyclic p cloud
above & below the plane of the molecule.
The p cloud must contain (4n + 2) p electrons (n
= 0, 1, 2…).
However, from an energetic point of view, it has been
debated that phenolics favour hydrogen atom transfer mechanisms, in which lower energies
are involved (Leopoldini et al., 2011). The radicals derived from oxygen represent the most
important class of radical species generated in living systems. However the term antioxidant
is often used to describe the scavenging activity of all reactive radicals including e.g. RNS
Several in vitro studies have shown that polyphenols are the major contributors with respect
to the total antioxidant activity of the majority of fruits and vegetables. Over 8.000
polyphenolic molecules have been identified and can be classified into flavonoids and non-
flavonoid phenolics. Certain authors consider (poly)phenols to be all secondary
phytochemicals that have at least two phenol subunits.