Electrophilic Addition in Alkenes Flashcards
How many steps is electrophilic addition and what is the reaction similar to?
2 steps and reverse of an E1 reaction
What is the hybridization of the carbons involved in the double bond in the carbocation?
One that accepted hydrogen: sp3
One with positive charge: sp2
In electrophilic addition, what is always the electrophile source?
H+ from an acid
What is the difference between using concentrated sulfuric acid and diluted?
Concentrated created alkyl-hydorgensulphate however in diluted the water replaces the bisulphate ion (as water is a better nucleophile) and turns the molecule into an alcohol instead
Why is water a better nucleophile than the sulfate ion
sulfate ion is a weak base as it comes from a strong acid thus does not + the sulfate ion is very stable thus does not really need to react
What are the 2 steps in electrophilic addition?
- Protonation and formation of carbocation
- Nucleophile attacks positive carbon center to generate new single bond
What determines where the hydrogen is attacked in asymmetrical alkenes?
- positive charge should be on the more substituted carbon due to hyperconjugation
- resonance may help stabilize carbocation
- hydrogen should go to the carbon with the most hydrogens already
what are the 2 types of selectivity and what are their differences
regioselective: one product is formed in a greater amount than another (major minor)
regiospecific: only one possible product is formed
Is reaction under kinetic control? What does that mean?
It is under kinetic control because the major product is caused by the rate of reaction rather than the stability of the product
Is a carbon radical or carbocation more stable and why?
The carbocation is more stable because in creation of the 2 new MOs as a result of hyperconjugation carbocations have 2 electrons in the lower MO while radicals have an additional electron in the higher MO which destabilizes the molecule
Why does the nucleophile not attack the positive charge when it can be delocalized into the ring?
Loss of aromaticity if attack on the ring, HIGHLY UNFAVOURABLE (not thermodynamically liked)
Why can electrophilic addition and radical addition result in different products?
In each reaction a different species attacks first, for EA it is the positive hydrogen and in radical it is the radical substituent (still based on radical stability)
What is the stereochemistry of the electrophilic addition reactions?
Enantiomers (R and S) as the nucleophile has equal probability of attack from both sides of the planar molecule
