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Chemistry: Structural Differences and Formulae

Questions 1:
a) Why do alkanes react only by homolysis?
b) What happens with nucleophilic substitution of bromoethane with sodium hydroxide?
Explain the following terms: Addition reaction, homolysis and heterolysis, and nucleophile and electrophile.

Question 2:
What are the structural formulae of compounds A-H? Explain your reasoning. There are four compounds, A-D, all with molecular formula C4H8. Compound A is a cis-isomer and compound B is a trans-isomer. Both react with concentrated sulphuric acid, followed by water to yield a compound E of formula C4H10O. Compound C reacts with sulphuric acid followed by water, to yield mostly compound E, but also some compound F, also C4H10O. Compound D also reacts reacts with sulphuric acid and water to produce a major product G and a minor product H, both of formula C4H10O also.

Question 3:
Explain the difference in structure between a primary, secondary and tertiary alcohol (Alkanol). Outline, with equations, the product(s) of oxidation of each of the above three types of alcohol.

Question 4:
You are provided with a mixture which you suspect may consist of hexane, hexylamine and propanol.
a) How would you attempt to separate the mixture?
b) Suggest a chemical or physical test, which would help to confirm your suspicion as to the chemical nature of each of the three components?

Solution Preview

Question 1:
This question refers to the different types of reactions that organic molecules can endure. Two big groups of organic molecule reactions are classified into substitution and addition reactions. As their names tells us substitution reactions change an existing group for another. In addition reactions a whole new molecule is added to the organic molecule. For example the reaction of an alkene molecule with HBr is an addition reaction, all atoms of the HBr are added to the alkene molecule.

Homolysis and heterolysis are two words used to mean rupture reactions in organic molecules. The characteristics of homolysis are the following:
If I have a molecule XY the reaction is X-Y ---> X + Y
- produces neutral species
- open-shell species (octets are not satisfied)
- happens in gas phase
- happens with non-polar molecules
- happens with molecules constructed from atoms of
similar electronegativity

The characteristics of Heterolysis are the following
X-Y ---> Y(+) + X(-)
- produces neutral ions
- open-shell species and closed shell species (at this
point you should be able to tell me which ion has an
open shell and which has a closed shell)
- happens in solution phase
- ...

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