3.4 Alkenes Flashcards
What is the general formula for alkenes?
CnH2n
The double bond means there is…
…restricted rotation.
Which type of isomerism forms due to the restricted rotation of the double bonds between carbons?
Geometric (E-Z)
What is stereoisomerism?
When a molecule has the same structural formula, but the atoms/groups have different spacial arrangements.
If two alkyl groups are opposite each other across a C-C double bond, is it a Z isomer or an E isomer?
E isomer.
If there are things other than alkyl groups, for example halogens, attached to the carbons with the double bond, how would you know whether the alkene was a Z or E isomer?
On each side of the double bond, pick the atom with the largest Ar. This atom has the highest priority. The two atoms with the highest priority on each side will then show whether it is a Z or E isomer.
Which mechanism involves producing haloalkanes from alkenes?
Electrophilic addition
What are the three electrophiles involved in electrophilic addition?
Br2, HBr and sulphuric acid (H2SO4)
What is the reactant in electrophilic addition?
The alkene
Why are the electrophiles attracted to the double bond?
The electrons in the double bond cause repulsion in the electrophiles, causing an induced dipole.
What happens in the intermediate stage of electrophilic addition?
A carbocation is formed, which attracts a lone pair on a nucleophile.
What is the product of using Br2 as an electrophile with ethene?
1,2-dibromoethane
Why is 2-bromopropane the major product of a reaction between HBr and propane rather than 1-bromopropane?
The carbocation produced is attached to more alkyl groups and is therefore more stable.
What is it called when a carbon is attached to one alkyl group?
Primary
What is it called when a carbon is attached to four alkyl groups?
Quaternary - it cannot go higher than this since carbon can only bond to four atoms.
