UNIT 4. ORGANIC CHEMISTRY

point, and index of refraction. Qualitative properties include odor, consistency, solubility, and
color.
Synthetic organic chemistry is an applied science as it borders engineering, the
"design, analysis, and/or construction of works for practical purposes". Organic synthesis of a
novel compound is a problem solving task, where a synthesis is designed for a target molecule
by selecting optimal reactions from optimal starting materials. Complex compounds can have
tens of reaction steps that sequentially build the desired molecule. The synthesis proceeds by
utilizing the reactivity of the functional groups in the molecule. For example, a carbonyl
compound can be used as a nucleophile by converting it into an enolate, or as an electrophile;
the combination of the two is called the aldol reaction. Designing practically useful syntheses
always requires conducting the actual synthesis in the laboratory. The scientific practice of
creating novel synthetic routes for complex molecules is called total synthesis.
Strategies to design a synthesis include retrosynthesis, popularized by E. J. Corey,
starts with the target molecule and splices it to pieces according to known reactions. The
pieces, or the proposed precursors, receive the same treatment, until available and ideally
inexpensive starting materials are reached. Then, the retrosynthesis is written in the opposite
direction to give the synthesis. A "synthetic tree" can be constructed, because each compound
and also each precursor has multiple syntheses.
Organic reactions are chemical reactions involving
organic compounds. Many of these reactions are
associated with functional groups. The general theory of
these reactions involves careful analysis of such properties
as the electron affinity of key atoms, bond strengths and
steric hindrance. These factors can determine the relative
stability of short-lived reactive intermediates, which
usually directly determine the path of the reaction.
 
The basic reaction types are: addition reactions,
elimination reactions, substitution reactions, pericyclic reactions, rearrangement reactions and
redox reactions. An example of a common reaction is a substitution reaction written as: 
Nu
−
+ C-X → C-Nu + X
− 
,where X is some functional group and Nu is a nucleophile.
The number of possible organic reactions is basically infinite. However, certain
general patterns are observed that can be used to describe many common or useful reactions.
Each reaction has a stepwise reaction mechanism that explains how it happens in sequence—
although the detailed description of steps is not always clear from a list of reactants alone.
The stepwise course of any given reaction mechanism can be represented using arrow
pushing techniques in which curved arrows are used to track the movement of electrons as
starting materials transition through intermediates to final products.
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