Some rules regarding the writing of resonance forms 1

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Some rules regarding the writing of resonance forms:1.Structures with a maximum number of octets are “most important” (contribute the most to the hybrid’s structure)2.Charges are best accommodated on atoms with appropriate electronegativity characteristics
3.Less separation of charge is more important than greater separation of charge
5.Reactive Intermediatesa.RadicalsA neutral species with an unpaired electron:-sp2hybridization-Trigonal planar geometry-The carbon is not charged-Electron can be delocalized via resonance-Reactive intermediate in radical halogenations of alkanes-Order of Stability is 3o> 2o> 1o> CH3Main Modes of Reactivity for Radicalsb.Carbonium IonsA positively charged species (cation) with an empty carbon 2p orbital:-sp2hybridization-Trigonal planar geometry-The carbon bears a +1 charge-The charge can be delocalized via resonance-Reactive intermediate in many chemical reactions-Order of Stability is 3o> 2o> 1o> CH3Main Modes of Reactivity for Carbonium Ions
c.Alkyl oxonium and Dialkyl oxonium ionsA positively charged species (cation) with a protonated alcohol or ether group:-sp3hybridization on oxygen-Tetrahedral geometry of oxygen-The oxygen bears a +1 charge-The charge cannot be delocalized via resonance-Reactive intermediate in chemical reactions-Requires a strong acid to protonate oxygenMain Modes of Reactivity for Alkyl oxonium and Dialkyl oxonium Ions6.Classes of Compoundsa.AlkanesHydrocarbons made up of only C and H – no multiple bondsCnH2n+2Prefer to “stretch out” in a zigzag form:Very unreactiveUsed as fuels and solvents for the most partb.CycloalkanesCyclic compounds made up of only C and H
CnH2n Small rings (3 and 4-membered) are angle strained and torsionally strained5- and 6-membered rings can assume conformations to minimize angle and torsional strain5-membered – envelope form6-membered – chair form
c.Alkyl halidesContain a polar C-halogen bond responsible for reactivityEndows R-X with electrophilic properties (that is, R-X is an electrophile)Nucleophilic Substitution is a main reactivity modeSN2 – concerted mechanism where leaving group departs as the nucleophile start to form a bondSN1 – two step mechanism where a carbonium ion is produced by departure of the leaving group followed by capture of the carbonium ion by a nucleophileElimination is a main reactivity modeE2 – concerted mechanism where the hydrogen is removed by a base while the C-X bond is breakingE1 – two step mechanism where a carbonium ion is produced by departure of the leaving group followed by removal of an adjacent hydrogen to form the alkeneGenerally, only Cl, Br and I can participate as leaving groups in these reactions.d.AlcoholsAlso contain polar bondsThe structure of alcohols in the liquid and solid state is dominated by hydrogen bonding:Hydrogen bond strength is about 1- 5 kcal/mole.The acidity of alcohols is similar to that of water.
The pKaof alcohols is around 17 so they are weak acids.“Inductive effects” contribute to the acidity of alcohols.Inductive Effect-

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