Chemistry Reference
In-Depth Information
Scheme 1.1 Example of the Wittig reaction.
Scheme 1.2 Example of the Diels-Alder reaction.
Scheme 1.3 Example of a tin hydride dehalogenation.
Diels-Alder reaction (Scheme 1.2) is used for the formation of six-membered ring
systems, and treatment of alkyl halides with reagents such as tributyltin hydride
(Scheme 1.3) results in removal of the associated halides. However, by presenting these
reactions as illustrated in Schemes 1.1, 1.2, and 1.3, no explanation is provided as to
how the starting materials end up as their respective products.
By definition, the outcome of any chemical reaction is the result of a process resulting in
the breaking and formation of chemical bonds. Referring to material covered in most
general chemistry courses, bonds between atoms are defined by sets of two electrons.
Specifically, a single bond between two atoms is made of two electrons, a double bond
between atoms is made of two sets of two electrons, and a triple bond between atoms is
made of three sets of two electrons. These types of bonds can generally be represented
by Lewis structures using pairs of dots to illustrate the presence of an electron pair. In
organic chemistry, these dots are most commonly replaced with lines. Figure 1.1 illustrates
several types of chemical bonds in both electron dot notation and line notation. The list of
bond types shown in Figure 1.1 is not intended to be inclusive with respect to functional
groups or potential combinations of atoms.
While chemical bonds are represented by lines connecting atoms, electron dot notation is
commonly used to represent lone pairs (nonbonding pairs) of electrons. Lone pairs are
found on heteroatoms (atoms other than carbon or hydrogen) that do not require bonds
with additional atoms to fill their valence shell of eight electrons. For example, atomic
