additions A + B --> C H-Cl + CH2=CH2 --> CH3-CH2-Cl eliminations X --> Y + Z CH3-CH2-Cl --> CH2=CH2 + H-Cl substitutions A-B + C-D --> A-C + B-D CH4 + Cl2 --> CH3-Cl + H-Cl rearrangements X --> Y cyclopropane --> propene

HCl plus Ethene

CH2=CH2 + H-Cl --> CH3-CH2-Cl an electrophilic addition reaction type: addition reagent type: an electrophile HCl, actually H+, a strong Lewis acid

Addition Mechanism


pi bond is relatively reactive, especially towards electrophiles it provides a good source of electrons addition of H+ to CH2=CH2 forms a new C-H sigma bond the electrons for the new bond came from the pi bond the other C is left with only 6 e-

Carbocation Intermediate

an intermediate is formed in the reaction mechanism CH2=CH2 + H+ --> CH3-CH2+ carbocation: a carbon atom with only 3 bonds (6 e-) và a positive charge structure: sp2 hybridized (trigonal)

Formation of Chloroethane

the reaction is completed as chloride anion (a nucleophile) adds khổng lồ the carbocation (an electrophile) CH3-CH2+ + Cl- ---> CH3-CH2-Cl

Alkene Addition Reactions

pi bonds undergo addition reactions CH2=CH2 + HCl --> CH3CH2Cl in general, C=C + HX --> H-C-C-X alkenes react with hydrogen halides to khung alkyl halides

Addition of HX khổng lồ Alkenes


cyclohexene + HBr --> bromocyclohexane 1-methylcyclohexene + HBr --> 1-bromo-1-methylcyclohexane (not 1-bromo-2-methylcyclohexane)

Reaction Notation

reactants -------> products focus on the organic reactants & products show reagents over the arrow show solvent and conditions under the arrow (or show full balanced reaction)

Orientation of Addition

regiochemistry: specific orientation of addition (which C gets H, which gets X?) alkene additions are regioselective: one direction of addition is usually preferred

Markovnikov"s Rule

the original: add H khổng lồ the C with more H"s (or to the C with fewer alkyl groups) the reason: showroom H+ to size the more stable cation CH3CH=CH2 + HCl ---> CH3CH+CH3 (not CH3CH2CH2+) ---> CH3CHClCH3 (not CH3CH2CH2Cl)



structure: trigonal (sp2) stability: 3° > 2° > 1° more alkyl groups stabilize a cation by electron donation to lớn the electron-deficient (6-electron) carbocation hyperconjugation: electron donation from adjacent C-H sigma bond khổng lồ empty p orbital of teh carbocation

Markovnikov Addition

Carbocation Rearrangements

carbocations easily rearrange to more stable forms e.g., 1° --> 2° , 1° --> 3° , or 2° --> 3°

Hydration of Alkenes

alkene + water --> alcohol CH2=CH2 + H2O --(H+)--> CH3CH2OH mechanism: step 1: addition of H+ electrophile to pi bond step 2: addition of H2O nucleophile to lớn cation

Hydration Mechanism

Halogenation of Alkenes

CH2=CH2 + Cl2 ---> Cl-CH2-CH2-Cl

mechanism: Cl2 is an electrophile (adds Cl+) then Cl- is a nucleophile

Anti Addition

anti stereochemistry: two new groups are added khổng lồ opposite sides of the original pi bond

cyclopentene + Br2 ---> trans-1,2-dibromocyclopentane (no cis)

anti - describes the process trans - describes the product

Bromonium Ion

carbocations can be stabilized by bonding lớn a neighboring Br (also works with Cl, but less favorable)


addition of halogens in water adds X & OH to lớn the pi bond water is the nucleophile that adds anti khổng lồ X


addition of BH3 followed by H2O2 adds H và OH "anti-Markovnikov" addition completely syn addition consider B as the electrophile that adds first to the pi bond addition of B và H is concerted (simultaneous)

Reduction of Alkenes

reduction - addition of H2 (or removal of O)

CH2=CH2 + H2 ---> CH3-CH3

R-O-H + H2 ---> R-H + H2O

Catalytic Hydrogenation

CH2=CH2 + H2 ---> CH3-CH3

requires an active catalyst, typically Pt, Pd, Ni, PtO2 reaction occurs on the surface both Hs are delivered khổng lồ the same side of the pi bond

Syn Addition

syn stereochemistry: two new groups are added khổng lồ the same side of the original pi bond

1,2-dimethylcyclohexene + H2 --(cat)-->cis-1,2-dimethylcyclohexane(no trans)

syn - describes the process cis - describes the hàng hóa

Oxidation of Alkenes

oxidation - addition of O (or removal of H2) RCH2OH ---> RCH=O ---> RCOOH there are a wide variety of oxidizing agents: O2, O3, KMnO4, CrO3, Na2Cr2O7 metals in high positive oxidation states