13.4 Electrophilic Addition In Alkenes Flashcards
What is electrophilic addition?
Addition reactions where the first step is attack by an electrophile on a region of high electron density
What is an electrophile?
An electrophile is an atom or group of atoms that is attracted to an electron rich centre and accepts an electron pair - usually positive ion or a molecule containing an atom with a partial positive charge
What in an alkene attracts electrophiles?
The high electron density of the pi electrons
Mechanism for reaction between But-2-ene and Hydrogen Bromide
Bromine is more electronegative than Hydrogen, so molecule is polar and contains dipoles
Electron pair in the pi bond is attracted to the partially positive hydrogen atom, causing double bond to break
Bond forms between hydrogen atom of H-Br molecule and carbon atom that was part of the double bond
H-Br bond breaks by heterolytic fission, electron pair goes to Bromine atom
A Bromine ion and carbocation are formed
Br- ion reacts with carbocation to form the product
How do alkenes react with non polar molecules?
The high electron density of the pi bond creates induced dipoles in the non polar molecule
What happens when an unsymmetrical alkene reacts with hydrogen halide?
Two isomeric products are formed
According to Markownikoff what happens when a Hydrogen halide reacts with an unsymmetrical alkene?
The hydrogen in the hydrogen halide attaches to the carbon atom of the alkene with the most number of hydrogen atoms and lowest number of carbon atoms
What is a carbocation?
An ion that contains a positively charged carbon atom
Which carbocation is more likely to form?
The more stable carbocation
Which carbocation forms the major product?
The more stable carbocation
Which carbocations are most stable?
Tertiary carbocations
How are carbocations classified?
With the number of alkyl groups attached to them
Why are tertiary carbocations more stable?
Each alkyl group donates and pushes electrons towards the positive charge of the carbocation
Positive charge is spread over the alkyl groups
More alkyl groups - charge is spread out more
