Alkenes Flashcards
Are alkenes saturated or unsaturated hydrocarbons?
unsaturated
What is meant by the term unsaturated hydrocarbon?
They are made with carbon and hydrogen only, and have at least one carbon-carbon double bond. This means that they are not bonded to the maximum number of hydrogen atoms
Why are alkenes more reactive than alkanes?
They are more reactive due to the carbon-carbon double bond which provides an electron rich area (high electron density) between the two carbon atoms (they are more vulnerable to attack from a electrophile).
What is the general formula for an alkene?
CNH2N
Why cant alkenes rotate about the carbon-carboon double bond?
On each carbon atom there is a p orbital. As these carbon atoms create a double bond the two p orbitals overlap forming an orbital (pi orbital) with a cloud of electron density above and below the double bond, which prohibits it from rotating.
draw the structures of the p orbitals turning into a pi orbital between the double bonds of an alkene
Check page 217
What are the names of the two types of isomers that involve the double bond?
position isomers
geometrical isomers
What are positional isomers?
They are isomers where the double bond is places in different positions along the hydrocarbon chain
What are geometrical isomers?
A form of stereoisomer
What is a stereoisomer?
They have the same structural formula but the bonds are arranged differently in space (they occur only around the c-c double bond)
What is another name for geometrical isomers?
E-Z isomerism
What is the name of the type of isomer with the highest groups on the same side of the c-c double bond
z isomer
What is the name of the type of isomer with the highest groups on the opposite side of the c-c double bond
E isomer
What did E-Z isomerism used to be called?
cis-trans isomerism
How would you know weather an isomer was an E or a Z?
weather or not the atoms with the largest atomic number are on the same side of the c-c double bond.
What are the only intermolecular forces that act between alkene molecules?
van der Waals forces
How are the properties of alkenes similar to that of alkanes?
They are not soluble in water
Their melting and boiling points increase as the chain length increases
What is the bond enthalpy for a c-c single bond?
347 kJ mol-1
What is the bond enthalpy for a c-c single bond?
612 kJ mol-1
What is the definition of an electrophile?
They are an electron pair acceptors
