Reaction Mechanisms

Nuc: with unpaired e- attaches to the alkyl group and X is displaced from alkyl group 2 mechanisms: Sn1 or Sn2

Simultaneous Nuc-C bind formation and C-X bond cleavage Rate = k[Nuc:][RX]

Heterolytic cleavage of the C-X bond, followed by the formation of a Nuc-C bond; carbocation formation Rate = k[RX]

Typical for aldehydes and ketones; the oxygen on carbonyl group get protonated m, which enhances partial (+) charge on carbonyl carbon and makes it more likely to be attacked by Nuc:

Nuc substitution when electron withdrawing group is on the ring 2 mechanisms

Addition of a Nuc: and formation of a carbanion intermediate, followed by the loss of the halide ion

In absence of electron withdrawing group substituents, very rare and proceeds through an enzyme intermediate

Initial attack by electrophile (on pi electron system) to form a carbocation, followed by reaction with the negative halide ion

Electron rich pi-electron clouds are attacked by electrophiles

When a molecule loses atoms or ions Two mechanisms: E2 and E1

Base removes a hydrogen atom; a C-H cleaves heterolytically; adjacent carbons form carbon-carbon double bind by ejecting the leaving group; no carbocation intermediate Rate = k[base][substrate]

E2 obey this rule, which states that when more than one beta-carbon bears a hydrogen atom, it is the most substituted carbon that undergoes elimination

• ) formation of carbocation through the loss of X-, without cleavage of C-H bond • ) weak base removes and H+ ion from carbon adjacent to the positive carbon Rate = k[substrate]

A conjugated diene is heated and attacks an alkene or alkyne, called dienophiles to yield a six members ring

Usually contains an electron-withdrawing group; electron-poor species

electron rich species

Less substituted alkene predominates due to most commonly steric hinderance caused by the: size of the attacking base and size of the group surrounding the leaving group