Organic Chemistry: Hydrocarbons

Many students find organic chemistry difficult – unnecessarily so, for it is a very logical and systematic branch of chemistry. Two things that will make it easier to learn are:

  1. To know and understand the various definitions and technical terms that are used.
  2. To know the relationships between the different homologous series of compounds.

A chart showing these relationships can be found in the introduction to Oxygen-containing Organic Compounds.

Definitions and Technical Terms

Homologous Series and Functional Groups

Alkane -C-C-
Alkene -C=C-
Alkyne -C≡C-
Alcohol R-OH
Aldehyde R-CHO
Ketone R-CO-R
Carboxylic acid R-CO-OH
Ester R-CO-OR’

It is important too, to know the structure of these various functional groups.


Types of Reaction and Processes

  • Substitution and addition reactions
  • Hydrogenation, hydration, dehydration
  • Homolytic fission, heterolytic fission

The Hydrocarbon Homologous Series

Series Characteristic
feature
General
formula
First
member
Compound
type
Characteristic
reaction
alkane —C —C — CxH2x+2 methane CH4 saturated substitutions
alkene —C= =C — CxH2x ethene C2H4 unsaturated additions
alkyne —C≡C— CxH2x-2 ethyne C2H2 unsaturated additions
The above three series of compound are closely related:
aromatics benzene ring benzene C6H6 substitution

Relationship
The three series of compounds, alkanes, alkenes and alkynes, are closely related.

Naming Compounds

The rules for doing this will be found in the textbooks. Follow the rules in their order. The generic names for the compounds containing the various numbers of carbon atoms need to be known.

  1. C atom = meth . . . .
  2. C atoms = eth . . . .
  3. C atoms = prop . . . .
  4. C atoms = but . . . .
  5. C atoms = pent . . . .


Experiments

You need to be able to describe the following:

  • Preparation of ethene
  • How to test for ethene
  • Preparation of ethyne


Reaction Mechanisms

The two reaction mechanisms on the syllabus are:

  1. The chlorination of methane (a substitution reaction initiated by the homolytic fission of chlorine by uv radiation)
  2. The bromination of ethene, which is an ionic addition across a double bond

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