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organic

Naming & isomerism, mechanisms (radical, SN1/SN2, addition, aromatic substitution), functional-group chemistry, reaction map.

naming · isomerism · mechanism language · substitution · alkenes & arenes · functional groups · reaction map

Formulae & naming

Formula types. Empirical, molecular, full/condensed structural, skeletal, stereochemical.

Nomenclature. Longest chain containing the principal functional group; lowest locants; substituents alphabetical; multiplying prefixes di/tri; suffix priority often acid > ester > aldehyde > ketone > alcohol > amine > alkene/alkyne > alkane; halogen and nitro always as prefixes.

Homologous series. Same functional group, successive \(\ce{CH2}\); similar chemistry, gradual physical trends.

Isomerism

Structural. Chain, position, functional-group.

Stereoisomers. Same connectivity, different 3D arrangement. Geometric: restricted rotation; cis/trans or E/Z assigned by CIP priority around \(\ce{C=C}\) or rings.

Optical. Chiral center = tetrahedral atom with 4 different groups; enantiomers are non-superimposable mirror images that rotate plane-polarized light equally and oppositely; a racemate is optically inactive. Enantiomers share identical physical properties except optical rotation and reaction with chiral reagents. Diastereomers: stereoisomers that are not mirror images.

Mechanism language

Bond fission. Homolytic: one electron to each fragment, giving radicals — \(\ce{A-B -> A. + B.}\). Heterolytic: both electrons to one atom, giving ions — \(\ce{A-B -> A+ + B-}\).

Curly arrows. Show electron-pair movement from source to sink. Trap: an arrow starts at an electron pair (bond or lone pair), never at a positive charge.

Species. Nucleophile = electron-pair donor (Lewis base); electrophile = electron-pair acceptor (Lewis acid).

Leaving groups. Better leaving group = weaker base, more stable anion. Halogenoalkane rates usually RI > RBr > RCl ≫ RF: the \(\ce{C-X}\) bond is weaker and more polarizable.

Carbocations. Stability 3° > 2° > 1° > \(\ce{CH3+}\); resonance-stabilized allylic/benzylic cations are strongly stabilized.

Substitution

Radical substitution of alkanes. Conditions UV/heat. Initiation: \(\ce{Cl2 ->[h\nu] 2Cl.}\). Propagation: \(\ce{Cl. + CH4 -> HCl + .CH3}\); \(\ce{.CH3 + Cl2 -> CH3Cl + Cl.}\). Termination: radical + radical → molecule. Products are a mixture; further substitution possible; regioselectivity follows radical stability.

Halogenoalkane substitution. \(\ce{R-X + OH- -> R-OH + X-}\) (aqueous NaOH/KOH, heat); \(\ce{R-X + CN- -> R-CN + X-}\) (ethanolic KCN, reflux; adds one carbon); \(\ce{R-X + NH3 -> R-NH2}\) (excess ethanolic \(\ce{NH3}\), pressure/heat); \(\ce{R-X + H2O -> R-OH + H+ + X-}\) (slow).

S_N2. One-step backside attack; rate \(=k[\ce{RX}][\ce{Nu^-}]\); inversion of configuration; favored by methyl/1° substrates, strong nucleophile, polar aprotic solvent.

S_N1. Two-step via carbocation; rate \(=k[\ce{RX}]\); racemization; favored by 3° substrates, weak nucleophile, polar protic solvent.

Elimination. Competes with ethanolic \(\ce{OH-}\), heat: \(\ce{RCH2CH2X + OH- -> RCH=CH2 + H2O + X-}\).

Alkenes & arenes

Electrophilic addition. The \(\pi\) bond attacks an electrophile → carbocation intermediate → nucleophile attacks. Hydrogenation \(\ce{C=C + H2 -> C-C}\) (Ni/Pt); halogenation with \(\ce{Br2}\) decolorizes bromine; hydrohalogenation with \(\ce{HX}\); hydration with steam (\(\ce{H3PO4}\)/\(\ce{H2SO4}\)) gives the alcohol; cold dilute alkaline \(\ce{KMnO4}\) gives a diol; ozonolysis/strong oxidation cleaves the double bond.

Markovnikov. H adds to the carbon with more H, giving the more stable carbocation; anti-Markovnikov possible with peroxides for HBr.

Addition polymerization. Alkene monomers → saturated backbone.

Benzene. Delocalized aromatic \(\pi\) system; resists addition. General mechanism: generate the electrophile \(\ce{E+}\); ring attack → sigma complex; deprotonation restores aromaticity.

Electrophilic substitutions. Nitration: \(\ce{HNO3/H2SO4}\), 50–60 °C, electrophile \(\ce{NO2+}\), product nitrobenzene. Halogenation: \(\ce{Br2/FeBr3}\) or \(\ce{Cl2/AlCl3}\). Friedel–Crafts alkylation/acylation: \(\ce{RCl/AlCl3}\) or \(\ce{RCOCl/AlCl3}\); acylation avoids rearrangement and polyalkylation.

Directing effects. EDG activate, ortho/para-directing; EWG deactivate, meta-directing; halogens deactivating but ortho/para-directing.

Functional groups

Organic redox. Oxidation increases bonds to O/N/halogen or decreases C–H; reduction is the reverse / adds H.

Alcohols. Combustion; substitution with HX/\(\ce{PCl5}\); dehydration \(\ce{RCH2CH2OH -> RCH=CH2 + H2O}\) (conc. \(\ce{H2SO4}\), heat); esterification with a carboxylic acid + conc. \(\ce{H2SO4}\), reversible.

Oxidation ladder. 1°: \(\ce{RCH2OH -> RCHO -> RCOOH}\); 2°: \(\ce{R2CHOH -> R2CO}\); 3° resistant. Mild oxidant + distil off the aldehyde; reflux + excess oxidant for the acid. Oxidants: acidified \(\ce{K2Cr2O7}\) orange → green; \(\ce{KMnO4}\) purple → colorless/brown.

Reductions. Aldehyde/ketone → alcohol with \(\ce{NaBH4}\)/\(\ce{LiAlH4}\)/\(\ce{H2}\)-Ni; alkene → alkane with \(\ce{H2}\)/Ni; nitro/nitrile/amide reductions possible.

Carbonyl nucleophilic addition. Aldehyde/ketone + \(\ce{NaBH4}\) gives the alcohol; + HCN/KCN gives a hydroxynitrile (chain extension; chiral mixture, since the carbonyl is planar).

Aldehyde tests. Tollens silver mirror; Fehling/Benedict brick-red \(\ce{Cu2O}\).

Carboxylic acids. Weak acids; react with bases/carbonates/metals; reduced to primary alcohols.

Esters. Acidic hydrolysis reversible, to acid + alcohol; alkaline hydrolysis irreversible (saponification), to carboxylate + alcohol; often fruity odors.

Reaction map

Map. One line per interconversion:

• alkane →(X₂/UV) haloalkane
• haloalkane →(aq. OH⁻) alcohol
• haloalkane →(alcoholic OH⁻) alkene
• haloalkane →(CN⁻) nitrile
• alkene →(HX/X₂/H₂O) haloalkane
• alkene →(H₂/Ni) alkane
• alcohol (1°) →(oxid.) aldehyde
• aldehyde →(oxid.) acid
• alcohol (2°) →(oxid.) ketone
• aldehyde →(red.) alcohol
• ketone →(red.) alcohol
• acid →(ROH/H⁺) ester
• ester →(hydrolysis) acid

Conditions.