HALOGEN DERIVATIVES bimolecular reaction - substitution SN 2 reaction is charakteristic for non-branched halogenderivatives SN2 HALOGEN DERIVATIVES SN2 Nucleophilic substitution SN2 HALOGEN DERIVATIVES monomolecular reaction - substittution SN1 reaction is characteristic for branched halogen derivatives SN1 HALOGEN DERIVATIVES SN1 HALOGEN DERIVATIVES SN1 Nucleophilic substitution SN1 Substitution reactions examples Nucleophilic substitution examples •The course of the reaction is influenced: •structure: non-branched ---- SN2 • branched --- SN1 •during SN2 different derivatives differ by reaction rate: • •methyl>prim. halogenid>sek. hal.>terc. hal • 30 1 0,02 rel. rate • the reason is sterical hindrance •during SN1 electronic influence is plaing main role • they are limited to terciary derivatives, allyl and benzyl derivatives The course of the reaction is influenced: •influence of strenght and concentration • influence only at SN2 (at SN1 in rate equation the concentration is not included) • • -nucleophility in the periodic table is growing from left to right and from top down • -charged atom(ion) is more nucleophilic than its conjugated acid (neutral molecule) • • •-nucleophility is paralel with basicity • Course of the reaction is influenced: •solevent • types of solvents: • nonpolar • polar protic • • aprotic • • • • Course of the reaction is influenced : •nucleophility is changing with polarity of solvent • •-in polar solvent the bigger atom is more nucleophilic •(polarisibility is higher – softer reagent; small atom is solvated by hydrogen bridges and this way its reactivity is decreased ) • • R-SH > ROH • J- > Br- > Cl- > F- • -in aprotic solvent is the dependence just opposite - -F- > Cl- > Br- > I- • • • The course of the reaction is influenced: •by leaving group • • - the more stabil is the leaving group, the easier is substitution • I- > Br- > Cl- > F- • • - in acidic medium we can support the substitution i.e. alcohols or ethers • • - very important group of leaving species are groups with sulfur (tosylates, mesylates, nosylates, brosylates etc.) •