Chem Unit - 1
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Hydrocarbons contain only carbon and hydrogen atoms. They are the simplest organic compounds, are generally very unreactive and are usually used as solvents.
- alkanes - which contain only carbon-carbon single bonds
- Eg. methane from methanogens (has a tetra hedral shape made from pair bond pair repulsion)
- alkenes - which contain one or more carbon-carbon double bonds
- resistance to rotation due to the presence of the extra C-C bond of the double bond.
alkynes - which contain one or more carbon-carbon triple bonds
Polymers are repeating units of a single molecule (the monomer). So for instance, polypropylene is made from propene starting material. However, in polymers like this, the double bond is no longer present, it has been used to form the bond to the next unit.
- Benzene is the prototypical aromatic compound. Its Kekulé structure (named after August Kekulé who formulated it) is a six-membered ring with alternating double and single bonds.
- Alternating double and single C-C bonds are an example of a conjugated system (there are other types of these systems as we will see later). These conjugated systems are much more chemically stable than non-conjugated systems, and aromatic systems, which have several other requirements, are more stable still.
- A benzene ring with a hydrogen removed is called a phenyl
- Alkyl groups are obtained by removing a hydrogen from an alkane. Often more than one alkyl group can be obtained from an alkane by removal of different kinds of hydrogens.
- R is the symbol used in diagrams to represent a generic alkyl groups. R is the equivalent of any alkyl group and is used as a shortcut instead of writing many different structures where the only variation is the alkyl group.
- In alkyl halides, halogen (F, Cl, Br, I) replaces the hydrogen of an alkane. They are classified according to which carbon the halogen is attached. For example, if the carbon is attached to:
- one other carbon that carbon is primary (1o) and the alkyl halide is also 1o
- two other carbons, that carbon is secondary (2o) and the alkyl halide is 2o
- three other carbons, the carbon is tertiary (3o) and the alkyl halide is 3o
- The hydrogen of the alkane is replaced by the hydroxyl (-OH) group in alcohols
- Alcohols are also classified according to the carbon to which the hydroxyl is directly attached.
- Much of the chemical reactivity of alcohols comes from the lone pair of electrons on the oxygen atom of the alcohol function.
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