Introduction
Organic
Chemistry
The
chemistry of the compounds of carbon
The
human body is largely composed of organic compounds
Organic
chemistry plays a central role in medicine, bioengineering etc.
Vitalism
It
was originally thought organic compounds could be made only by living things by
intervention of a “vital force”
Fredrich
W?hler disproved vitalism in 1828 by making the organic compound urea from the
inorganic salt ammonium cyanate by evaporation:
Isomers
Isomers
are different molecules with the same molecular formula
Three
Dimensional Shape of Molecules
Virtually
all molecules possess a 3-dimensional shape which is often not accurately
represented by drawings
It
was proposed in 1874 by van’t Hoff and le Bel that the four bonds around carbon
where not all in a plane but rather in a tetrahedral arrangement i.e. the four
C-H bonds point towards the corners of a regular tetrahedron
Example
Consider
two compounds with molecular formula C2H6O
These
compounds cannot be distinguished based on molecular formula; however they have
different structures
The
two compounds differ in the connectivity of their atoms
Constitutional
Isomers
Constitutional
isomers are one type of isomer
They
are different compounds that have the same molecular formula but different
connectivity of atoms
They
often differ in physical properties (e.g. boiling point, melting point,
density) and chemical properties
Isomerism:
Constitutional Isomers and Stereoisomers
Stereoisomers
are isomers with the same molecular formula and same connectivity of atoms but
different arrangement of atoms in space
Enantiomers:
stereoisomers whose molecules are nonsuperposable mirror images
Diastereomers:
stereoisomers whose molecules are not mirror images of each other
Example:
cis and trans double bond isomers
Example:
cis and trans cycloalkane isomers
Chiral
molecule
A
molecule with a single tetrahedral carbon bonded to four different groups will
always be chiral
A
molecule with more than one tetrahedral carbon bonded to four different groups
is not always chiral
Switching
two groups at the tetrahedral center leads to the enantiomeric molecule in a
molecule with one tetrahedral carbon
Stereogenic
center
An
atom bearing groups of such nature that an interchange of any two groups will
produce a stereoisomer
Carbons
at a tetrahedral stereogenic center are designated with an asterisk (*)
Example:
2-butanol
