(A)
Explain the main criteria you use to predict the properties of organic
compounds based on structure
The properties of organic compounds are largely related to their polarity. It is the
intermolecular forces that are most important in explaining variation in boiling point,
melting point, solubility and state at room temperature. Stronger intermolecular
forces result in higher m.p. / b.p, thus compounds are more likely to be solids or
liquids at room temperature. To determine the polarity of a molecule, two factors
must be considered, the presence of polar bonds and the symmetry of the molecule.
To be polar it must contain polar bonds and it must be asymmetrical so that polarities
do not cancel each other out. Hydrocarbons are non-polar (weak intermolecular
forces) while alcohols and carboxylic acids are much more polar. They are able to form
hydrogen bonds which are among the strongest intermolecular forces. Weaker
intermolecular forces like van der Waal forces only become significant as molecules
get bigger. Even large alkanes may be solid at room temperature due to these forces
alone. Some molecules may have both polar and non-polar regions. Such
amphipathic molecules are excellent solvents as they can dissolve both polar and nonpolar solutes.
(B)
Explain the similarities between natural and synthetic polymers with
examples
Synthetic and natural polymers are extremely similar in terms of their chemistry.
Though it may not be immediately evident, nylon and proteins are both polyamides.
They both form by the dehydration of amino groups with carboxyl groups to form
amide linkages between monomers. The only difference between them is that nylon
uses the same two monomers over and over again, while proteins form more complex
combinations of 20 different monomers called amino acids. Even synthetic polyester
has a natural equivalent. DNA is a polyester composed of repeating nucleotides. Even
starch at its chemical level is a polymer of glucose linked by ether linkages. The end
result is that all polymers, natural or synthetic form long chains of repeating subunits
whose properties are largely determined by the resulting 3D shape.
(C)
Discuss the advantages and disadvantages between addition vs.
substitution reactions. You may choose to use an example
Chemists are able to synthesize a seemingly limitless number of organic compounds in
lab. By creating the right conditions, the products of many organic reactions can be
quite predictable even with large molecules. For example, organic chemists can have
specific control over where substituent groups will be added to a molecule when
performing addition reactions. If the desired product is an alkylhalide, simply adding
the halogen by substitution could attach it at any location in exchange for any
appropriate hydrogen. If the same reaction were performed as an addition reaction
using an alkene, the halogenation will occur ONLY at the location of the double bond.
Still further, Markovnicov’s rule can be exploited to attach the halogen predominantly
to just one side of the double bond. This same principle can be applied to the addition
of other substituent groups as well. In this course we studied similar reactions
resulting in the addition of hydroxyl groups by addition reactions with alkenes.