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Lecture

Organic_1_6.1ed_2012_03rd_module_resonance_arrows_and_acid-base.pdf

17 Pages
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Department
Chemistry
Course Code
CHM136H1
Professor
Kris Quinlan

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Description
RESONANCE USING CURVED ARROWS AND ACIDBASE REACTIONSA STUDENT SHOULD BE ABLE TO1 Properly use curved arrows to draw resonance structures the tail and the head of every arrow must be drawn in exactly the proper locationThe tail shows where the electrons are coming from and the head shows where the electrons are goingRecognize bad arrowsIdentify insignificant resonance structuresWhen drawing resonance structures avoid breaking a sigma bond never exceed an octet for secondrow elements recognize and properly notate formal charges 2 Define terms resonance resonance stabilization delocalization and resonance hybridBe able to identify allylic and vinylic positions in a moleculeAlso identify delocalized lone pairs including allylic and differentiate them from localized lone pairs Identify lone pairs that appear to be allylic however they are not delocalized because of the geometry of their orbitals 3 Define BronstedLowry acids proton donors and bases proton acceptors conjugate acids and conjugate bases BronstedLowry acids are all protic have an ionizable protonBe able to draw a conjugate base for any acid and conjugate acid for any baseUse arrows to show how an acid loses a proton with the help of a baseNote that this process called proton transfer is shown with at least two arrows Proton transfers play an integral role in reaction mechanismsDefine pKa and be able to predict the acidity of different hydrogens using it4 Write acidbase reactions keeping in mind that reactions will proceed in the direction from a stronger to a weaker base formation Remember that the strongest acid would form the weakest conjugate base and the weakest acids would form the strongest conjugate baseConsider factors affecting the stability of negative charges 1 which Atom the charge is on more electronegative and larger atoms stabilize negative charge better 2 Resonance effect resonance stabilized bases are more stable and therefore weaker 3 Inductive effect electron withdrawing atoms and groups stabilize negative charge better and 4 hybridization Orbitals with more scharacter stabilize negative 23charge better that is negative charge is most stable on sporbital then sp then spPredict the position of an equilibrium based on comparative strength of acids or bases or using pKa valuesAlso be able to predict which base would be suitable for removal of a particular proton deprotonatingKeep in mind bases that are stronger than hydroxide cannot be used when the solvent is waterCounterions cations always accompany negatively charged bases and can be ignored NaOH LiOH KOH are all the same basehydroxide Use the following series for comparative strength of bases322323 5 Define Lewis bases electron pair donors and Lewis acids electron pair acceptorsLewis acids may be protic have an ionizable proton or aprotic do not have an ionizable protonBe able to show Lewis AcidBase reactions with curved arrowsDifferent from Bronsted AcidBase reactions Lewis AcidBase reactions can be shown with one arrow
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