Questions and Answers
What is the general formula for the alkene family?
Why are alkenes referred to as unsaturated hydrocarbons?
What is the type of bond formed by the overlap of p orbitals in alkenes?
What happens to the C─C distance in ethylene compared to ethane?
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What is the process by which alkenes are obtained from alkyl halides?
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What type of bond is stronger in a double bond?
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What is the typical reaction of an alkene?
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What is formed when alkenes react with cold, concentrated sulfuric acid?
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What is the rule that states the hydrogen of the acid attaches itself to the carbon atom that already holds the greater number of hydrogens?
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What is formed when water adds to the more reactive alkenes in the presence of acids?
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Study Notes
Alkene Family
- The general formula for the alkene family is CnH2n.
- Alkenes are unsaturated hydrocarbons, containing less than the maximum quantity of hydrogen.
- The simplest member of the alkene family is ethylene, C2H4.
Formation of Pi Bond
- The pi bond is formed by the overlap of p orbitals of two carbon atoms, resulting in an additional bond.
- The pi bond is weaker than the carbon-carbon σ bond.
- The overlap can only occur when all six atoms lie in the same plane, making ethylene a flat molecule.
Properties of Alkenes
- Alkenes are named by the IUPAC system.
- They possess physical properties similar to alkanes, such as being insoluble in water and soluble in nonpolar solvents.
- The boiling point of alkenes increases with increasing carbon number.
Preparation of Alkenes
- Alkenes can be prepared by dehydrohalogenation, involving the elimination of the elements of hydrogen halide.
- Dehydrohalogenation involves the removal of the halogen atom and a hydrogen atom from a carbon adjacent to the one bearing the halogen.
Reaction of Alkenes
- The typical reaction of an alkene is electrophilic addition, involving the breaking of the weaker pi bond.
- Alkenes react with electrophilic reagents, which are seeking a pair of electrons.
- Hydrogenation is the most useful method for preparing alkanes.
Markovnikov's Rule
- In the ionic addition of an acid to the carbon-carbon double bond of an alkene, the hydrogen of the acid attaches to the carbon atom that already holds the greater number of hydrogens.
- Addition of hydrogen chloride and hydrogen iodide to alkenes follows Markovnikov's rule.
- However, HBr adds to alkenes in the reverse direction, known as the peroxide effect.
Other Reactions of Alkenes
- Alkenes react with cold, concentrated sulfuric acid to form alkyl hydrogen sulfates.
- Alkyl hydrogen sulfates can be converted into alcohols by diluting with water and heating.
- Water adds to the more reactive alkenes in the presence of acids to yield alcohols.
- Addition of chlorine or bromine in the presence of water can yield halohydrins.
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Description
This quiz covers the properties and characteristics of alkenes, including their general formula, unsaturated hydrocarbons, and the formation of bonds. Learn about the alkene family and its simplest member, ethylene.
