alkenes

Question 1

general reactivity of alkenes towards electrophilic reagents/ electrophilies

Answer 1

-at least got 1 C=C bond(strong sigma bond + weaker pi bond)
-sp2 hybridised, unsaturated hydrocarbons, meaning got potential to bond one more atom
- CnH2n
- when got more than 1 C=C bond, write -diene/ -triene …
- pi e serves as a source to attract electrophiles or induce dipoles in approaching molecules to form electrophiles. since c=c unsaturated, alkenes undergo electrophilic addition rxns

Question 2

mp and bp of alkenes vs alkanes

Answer 2

alkenes slightly lower than alkanes cuz slightly smaller e cloud = less polarisable = weaker id-id = less energy needed to overcome weak intermolecular forces

Question 3

branch alkenes

Answer 3

lower bp than straight chain ones cuz smaller surface area of contact between branched isomers so less energy needed to overcome idid forces of attraction

Question 4

What is Markovnikov’s rule

Answer 4

• diff structures of carbonation have diff stability relative to one another (methyl < pri < sec < tertiary)
• e-donating effect of alkyl groups help to stabilise the carbonation by dispersing the positive charge of the carbon atom
• a carbonation with more alkyl groups is thus more stable and forms at a faster rate
• hence the more stable carbonation leads to the major product

Ans :
- it is a major product because A carbocation intermediate formed during electrophilic addition is more stable than B carbocation intermediate that leads to the minor product, __.
- A carbocation has more e-donating alkyl groups bonded to the +vely charged carbon that than the B carbocation hence its positive charge is dispersed to a larger extent

Question 5

oxidation of alkenes cannot take place with KCr2O7. why?

Answer 5

KCr2O7 is a weaker oxidising agent so not enough energy to oxidise alkenes

Question 6

what affects mild and strong oxidation

Answer 6

temperature. heat likely needed for strong oxidation to take place

Question 7

How rate of reaction changes from HCl to HI

Answer 7

• slow step in mechanism -> break H-X bond
• From Cl to I, atomic radius increases
• overlap of orbitals between H & X atoms becomes less effective (cuz they are more repelled?? cuz e size big? )
• From HCl to HI, bond strength decreases
• decreasing amt of energy needed to break the Hcl to HI bonds
• rate of rxn : HCl < HBr < HI