Welcome To Organic Chem Flashcards
Homologous series
A homologous series is a family of organic compounds with the same functional group, but different carbon chain length.
Each member of the series differs
• The length of the carbon chain has little effect on chemical reactivity . The length of the carbon chain affects physical properties, like melting point, boiling point, and solubility. Melting points and boiling points increase by a small amount as the number of carbon atoms in the chain increases. This is because the intermolecular forces increase.
Chain branching generally reduces melting points because the molecules pack together less well.
Isomers and the two types
Isomers are molecules that have the same molecular formula but whose atoms are arranged differently.
structural isomerism and stereoisomerism.
All parts of Structural isomers
the same functional groups attached to the main chain at different points - this is called positional isomerism
functional groups that are different - this is called functional group isomerism
a different arrangement of the hydrocarbon chain (such as branching) - this is called chain isomerism.
Stereoisomerism and the two types
Stereoisomerism is where two (or more) compounds have the same structural formula. They differ in the arrangement of the bonds
E-Z isomerism
• optical isomerism.
E-z isomerism
E-Z isomerism tells us about the positions of substituents at either side of a carbon-carbon double bond. Two substituents may either be on the same side of the bond Z or on opposite sides E.
Polarity of alkanes
Alkanes are almost non-polar because the electronegativities of carbon and hydrogen are so similar. As a result, the only intermolecular forces between their molecules are weak van der Waals forces, and the larger the molecule, the stronger the van der Waals forces.
Boiling point of alkanes
This increasing intermolecular force is why the boiling points of alkanes increase as the chain length increases. The shorter chains are gases at room temperature. At a chain length of about 18 carbons, the alkanes become solids at room temperature. The solids have a waxy feel.
Alkanes with branched chains have lower melting points than the same unbranched chains. This is because they cannot pack together as closely as unbranched chains and so the van der Waals forces are not so effective.
Solubility
Alkanes are insoluble in water. This is because water molecules are held together by hydrogen bonds which are much stronger than the van der Waal’s forces . However, alkanes do mix with other relatively non-polar liquids.
How do alkanes react
Alkanes are relatively unreactive. They have strong carbon-carbon and carbon-hydrogen bonds.
They do not react with acids, bases, oxidising agents, and reducing agents. However, they do burn and they will react with halogens under suitable conditions.
They burn in a plentiful supply of oxygen to form carbon dioxide and water
