Alkenes

Why is there no rotation about the C=C double bond?

Due to the pi orbitals, which hold the carbons in place

Are alkenes more or less reactive than alkanes? Why?

More reactive - due to high electron density of double bond and the fact that the pi-bond is slightly easier to break

What IM forces do alkenes have?

Only VdW forces due to non-polar bonds

Are alkenes soluble in water? Why?

No as they are non-polar

Name the 4 kinds of isomers alkenes can have?

• Chain isomerism

• Position isomerism

• Functional group isomerism

• E/Z isomerism

What’s the trend for mp and bp in alkenes?

Mp and bp increases with chain length as VdW forces are stronger

What shape are double bonds?

Planar

What is an electrophile?

An electron deficient species which accepts a pair of electrons

What is the most stable type of carbocation intermediate? Why?

Carbocations that are bonded the the most other carbon atoms as these have a positive inductive effect

What’s the positive inductive effect?

When atoms push electron density towards an electron deficient centre (eg a carbocation) in order to stabilise it

What are major and minor products?

• Major products are formed in greater proportion as they are formed via the most stable pathway (involves the more stable carbon cation intermediate)

• Minor products are formed in a smaller amount via a less stable carbocation

Major products will be formed from which kind of carbocations?

Secondary or tertiary (the most stable available)

Why are minor products formed less readily?

Primary carbocations require more energy to produce as they are less stable. If we need to put more energy in to make it, it’s less likely to form.