Carbocation Stability — Master Organic Chemistry

8/18/2019 Carbocation Stability — Master Organic Chemistry

1/15

HomeBlogOnline TutoringReaction GuideStudy GuidesContact »Members Login »

Master Organic Chemistry

New? Start HereStudy And Exam TipsOrganic 1 IndexOrganic 2 IndexFree “Cheat Sheets”Feedback

by James

Let’s talk about carbocations today. This is going to be really important going forward.

Carbocations are unhappy species. Why? Because they’re electron-poor: they have less than a full octet of electrons.

So how do we cheer a poor carbocation up?

Two ways:Donate electrons to itSpread the positive charge out

Donate electrons

If you’re poor, it helps to have rich neighbors.

So carbocations are stabilized by adjacent groups that can donate electron density. The most common exampleyou learn in Org 1 is alkyl groups . Alkyl groups are electron donating, since they have C-H bonds that can

cation Stability — Master Organic ChemistryCarbocation Stability — Master Organic ChemistryCarbocation Stability — Master Organic Chemistry

5


2/15

end up donating electrons to the adjacent carbocation.

For this reason, carbocation stability increases as we go from primary to secondary to tertiary.

[There’s a second situation that you generally don’t encounter until Org 2, but carbocations are also stabilized by adjacent atoms that have lone pairs. Even an atom like oxygen, which we normally think of as electronwithdrawing, can stabilize a carbocation – since it can donate a pair of electrons to carbon, giving it a fulloctet. This is called Pi-donation. ]Spreading out the chargeThe second way carbocations are stabilized is through resonance. Charge is stabilized by distributing it over alarger area (making it more diffuse).

Resonance helps to “spread out” the charge between multiple sites, which is going to decrease the chargedensity on the carbon. The effect on stability of the carbocation is tremendous. For this reason, the “allylcarbocation” is more stable than a normal secondary carbocation, even though it is technically “primary”.Here’s a summary:

Invert, always invert

It can also help to ask the opposite question. How do we destabilize a carbocation? Well, we can make it lessstable if we take electrons away. So adjacent electron-withdrawing groups destabilize carbocations. So doesmaking the charge more concentrated.


5


3/15

Tomorrow: let’s apply what we’ve learned, because we’re going to start talking about rearrangements.

Thanks for reading! James

P.S. Relevant posts:3 factors that stabilize carbocations.3 factors that destabilize carbocations

Sign Up To Get WeeklyOrganic Chemistry Tips

And get the free "How To Succeed In Organic Chemistry" E-book

Please enter your first name *

Please enter your email *

About Master Organic Chemistry

Imagine having a comprehensive online guide to help you solve your own problemsin organic chemistry. That's my mission with this site. After earning a Ph.D. at McGilland doing a postdoc at MIT, I applied to be a professor. That didn't work out. So Idecided to teach organic chemistry anyway. Master Organic Chemistry is the site Iwish I had when I was learning the subject.

Get The Latest Updates

facebook twitter rssemailRecent Posts

Popular PostsRecent Comments

New IUPAC Rules Make Molecular Names More Pronounceable, Friendlier Posted on:Apr 01, 2016

Liquid Gold: Pheromones In Doe Urine Posted on: Mar 24, 2016


5


4/15

Our New Book, "Practice Organic Mechanisms", Is Out Posted on: Mar 14, 2016

The Heck, Suzuki, and Olefin Metathesis Reactions (And Why They Don't Belong InMost Posted on: Mar 10, 2016

Gilman Reagents (Organocuprates): What They're Used For Posted on: Feb 05, 2016

Copyright © 2016 MasterOrganicChemistry.com. All rights reservedOrganic Chemistry Is Awesome

About JamesAccountAdvanced Substitution Topics – Sun Nov 10Alkene Mini Course – Thanks!Alkene Mini-CourseAlkene Webinar Alkenes: Common Exam Problems (With Solutions)Alkyne Webinar Sun Dec 15 at 9pm ESTAlkynes Are A Blank CanvasBlogCarbon Carbon BondsCommon Mistakes In Organic Chemistry: Pentavalent CarbonConfirming your email address…Crash Course On AlkenesCrash Course On Alkenes – Checkout

DashboardDon’t Be Futyl, Learn The ButylsElimination Webinar – Sunday Nov 24 at 9pm ESTFeedback Form Styling Sandbox PageFrom Gen Chem To Organic ChemGetting StartedHomeHome-2How To Draw A Cyclohexane Chair

How To Succeed In Organic ChemistryHow To Succeed In Organic ChemistryInitiation, Propagation, TerminationInterviewIntroduction To Spectroscopy Seminar (Including NMR)Introduction To Substitution Webinar Tuesday Nov 5Leah Nomenclature Guest PostManage SubscriptionMembers LoginMission


5


5/15

MOC EliteMy Organic Chemistry Story – What’s Yours?

New Acid-Base Webinar NEW! Reagents AppOctober 22 Acid-Base Webinar Online Organic Chemistry TutoringOrg 2 Post Index

Organic 1Organic 2Organic Chemistry Study AdvicePost IndexPost Index 2Post Index Draft

post index draft 2Products

Organic Chemistry Reagent GuideReaction Guide

1,4-addition of enolates to enones (“The Michael Reaction”)1,4-addition of nucleophiles to enones1,4-addition of organocuprates (Gilman reagents) to enonesAcidic cleavage of ethers (SN2)Addition Of Alcohols To Alkenes With AcidAddition of aqueous acid to alkenes to give alcoholsAddition of Dichlorocarbene to alkenes to give dichlorocyclopropanesAddition of dichloromethylene carbene to alkenesAddition of Grignard reagents to aldehydes to give secondary alcoholsAddition of Grignard reagents to esters to give tertiary alcoholsAddition of Grignard reagents to formaldehyde to give primary alcoholsAddition of Grignard reagents to ketones to give tertiary alcoholsAddition of Grignard reagents to nitriles to give ketones (after hydrolysis)Addition of HBr once to alkynes to give alkenyl bromidesAddition of HBr to AlkenesAddition of HBr twice to alkynes to give geminal dibromidesAddition of HCl once to alkynes to give alkenyl chloridesAddition of HCl to Alkenes to Give Alkyl ChloridesAddition of HCl to alkynes twice to give geminal dichloridesAddition of HI once to alkynes to give alkenyl iodidesAddition of HI twice to alkynes to give geminal diiodides

Addition of Hydroiodic Acid to Alkenes to Give Alkyl IodidesAddition of LiAlH4 to aldehydes to give primary alcoholsAddition of LiAlH4 to ketones to give secondary alcoholsAddition of NaBH4 to aldehydes to give primary alcoholsAddition of NaBH4 to ketones to give secondary alcoholsAddition of organocuprates (Gilman reagents) to acid chlorides to give ketonesAddition to alkenes accompanied by 1,2-alkyl shiftAdditions to alkenes accompanied by 1,2-hydride shiftsAldol addition reaction of aldehydes and ketonesAldol Condensation


5


6/15

Alkylation of enamines with alkyl halidesAlkylation of enolatesAllylic bromination of alkanes using NBSBaeyer-Villiger ReactionBase-promoted formation of enolates from ketonesBasic hydrolysis of esters (saponification)Beckmann Rearrangement

Bromination of alkenes with Br2 to give dibromidesBromination of aromatic alkanes to give alkyl bromidesBromination of Aromatics to give BromoarenesCannizarro ReactionChlorination of alkenes with Cl2 to give vicinal dichloridesChlorination of Arenes to give ChloroarenesClaisen Condensation of estersCleavage of ethers using acid (SN1 reaction)Clemmensen Reduction of Ketones/Aldehydes to AlkanesConversion of acid chlorides to aldehydes using LiAlH(O-tBu)3Conversion of acid chlorides to esters through addition of an alcoholConversion of alcohols to alkyl bromides using PBr3Conversion of alcohols to alkyl chlorides using SOCl2Conversion of alcohols to alkyl halides using HClConversion of Alkyl halides to ethers (SN1)Conversion of carboxylic acids into acid chlorides with SOCl2Conversion of carboxylic acids to carboxylates using baseConversion of carboxylic acids to esters using acid and alcohols (Fischer Esterification)Conversion of tertiary alcohols to alkyl bromides using HBr Conversion of tertiary alcohols to alkyl iodides with HIConversion of thioacetals to alkanes using Raney NickelCurtius Rearrangement of Acyl Azides to IsocyanatesDecarboxylation of beta-keto carboxylic acidsDehydration of amides to give nitrilesDeprotonation of alcohols to give alkoxidesDeprotonation of alkynes with base to give acetylide ionsDiels Alder Reaction of dienes and dienophilesDihydroxylation of Alkenes to give 1,2-diols (vicinal diols)Dihydroxylation of alkenes with cold, dilute KMnO4 to give vicinal diolsElimination (E1) of alkyl halides to form alkenesElimination (E1) with 1,2-alkyl shift

Elimination (E1) with hydride shiftElimination (E2) of alkyl halides to give alkenesElimination of alcohols to give alkenes using POCl3Elimination of water from alcohols to form alkenes using acidEnamine HydrolysisFormation of Acetals from Aldehydes and KetonesFormation of alkynes through double elimination of vicinal dibromidesFormation of amides from acid chlorides and aminesFormation of Amides Using DCCFormation of anhydrides from acid halides and carboxylates


5


7/15

Formation of Bromohydrins from alkenes using water and Br2Formation of bromohydrins from alkenes using water and NBSFormation of Carboxylic Acids from Acyl ChloridesFormation of carboxylic acids from Grignard reagents and CO2Formation of chlorohydrins from alkenes using water and Cl2Formation of Cyanohydrins from ketones and aldehydesFormation of cyclopropanes from alkenes using methylene carbene (:CH2)

Formation of Diazonium Salts from Aromatic AminesFormation of enamines from ketones/aldehydes and secondary aminesFormation of epoxides from alkenes using m-CPBAFormation of epoxides from bromohydrinsFormation of Gilman reagents (organocuprates) from alkyl halidesFormation of Grignard Reagents from Alkenyl HalidesFormation of Grignard Reagents from Alkyl HalidesFormation of hydrates from aldehydes/ketones and H2OFormation of imines from primary amines and ketonesFormation of organolithium reagents from alkyl halidesFormation of thioacetals from aldehydes and ketonesFormation of tosylates from alcoholsFree Radical Addition of HBr To AlkenesFree Radical Bromination of AlkanesFree Radical Chlorination of AlkanesFriedel Crafts alkylation of arenesFriedel-Crafts acylation of aromatic groups to give ketonesHalogenation of AlkynesHell-Vollhard-Zelinsky ReactionHofmann elimination of alkylammonium salts to give alkenesHofmann Rearrangement of Amides to AminesHydroboration of AlkenesHydroboration of alkynes using BH3 to give aldehydesHydrogenation of Alkenes to give AlkanesHydrogenation of Alkynes to Alkanes using Pd/CHydrolysis of acetals to give aldehydes and ketonesHydrolysis of esters to carboxylic acids with aqueous acidHydrolysis of imines to give ketones (or aldehydes)Hydrolysis of nitriles with aqueous acid to give carboxylic acidsIodination of alkenes to give vicinal diiodides (1,2-diiodides)Iodination of Aromatics with I2

Keto-enol tautomerismKiliani-Fischer Synthesis

Nitration of aromatic groups Nucleophilic Aromatic Substitution (SNAr) Nucleophilic Aromatic Substitution Via ArynesOpening of epoxides with acid and water to give trans diolsOpening of epoxides with nucleophiles under acidic conditionsOxidation of aldehydes to carboxylic acids using Cr(VI)Oxidation of aldehydes to carboxylic acids with Ag2OOxidation of aromatic alkanes with KMnO4 to give carboxylic acids


5


8/15

Oxidation of primary alcohols to aldehydesOxidation of Primary Alcohols to Aldehydes using PCCOxidation of primary alcohols to carboxylic acidsOxidation of secondary alcohols to ketones using PCCOxidation of thiols to disulfidesOxidative cleavage of 1,2-diols to give aldehydes/ketonesOxidative cleavage of alkenes to give ketones/carboxylic acids using ozone (O3) – (“oxidative

workup”)Oxidative cleavage of alkenes to ketones/carboxylic acids using KMnO4Oxidative Cleavage of Alkynes with KMnO4Oxidative Cleavage of Alkynes with Ozone (O3)Oxymercuration of Alkenes to form Ethers using Hg(OAc)2Oxymercuration of AlkynesOxymercuration: Alcohols from alkenes using Hg(OAc)2 and Water Ozonolysis of alkenes to ketones and aldehydes (reductive workup)Partial reduction of alkynes to trans alkenes using sodium and ammoniaPartial reduction of alkynes with Lindlar’s catalyst to give cis alkenesPinacol RearrangementPolymerization of dienes with acidProtection of alcohols as silyl ethersProtonation of alcohols to give oxonium ionsProtonation of Grignard reagents to give alkanesReaction of alkyl halides with water to form alcohols (SN1)Reaction of epoxides with nucleophiles under basic conditionsReactions of Diazonium SaltsReduction of aromatic ketones to alkanes with Pd/C and hydrogenReduction of aromatic nitro groups to amino groupsReduction of carboxylic acids to primary alcohols using LiAlH4Reduction of esters to aldehydes using DIBALReduction of esters to primary alcohols using LiAlH4Reduction of nitriles to primary amines with LiAlH4Reductive AminationSharpless EpoxidationSN2 of Cyanide with Alkyl Halides to give NitrilesSN2 reaction between azide ion and alkyl halides to give alkyl azidesSN2 Reaction of Acetylide Ions with Alkyl HalidesSN2 reaction of alkoxide ions with alkyl halides to give ethers (Williamson synthesis)SN2 reaction of alkyl halides with hydroxide ions to give alcohols

SN2 reaction of amines with alkyl chlorides to give ammonium saltsSN2 reaction of carboxylate ions with alkyl halides to give estersSN2 reaction of hydrosulfide ion with alkyl halides to give thiolsSN2 reaction of organocuprates (Gilman reagents) with alkyl halides to give alkanesSN2 reaction of thiolates with alkyl halides to give thioethers (sulfides)SN2 reaction of water with alkyl halides to give alcoholsStille ReactionSubstitution (SN1) with hydride shiftSubstitution with accompanying alkyl shiftSulfonylation of Arenes to give sulfonic acids


5


9/15

Suzuki ReactionThe Gabriel synthesis of aminesThe haloform reaction: conversion of methyl ketones to carboxylic acidsThe Heck ReactionThe Malonic Ester SynthesisThe Mannich ReactionThe Robinson Annulation

Transesterification promoted by alkoxidesWittig Reaction – conversion of ketones/aldehydes to alkenesWolff Kishner Reaction – conversion of ketones/aldehydes to alkanesWolff Rearrangement

Resource GuideResourcesShare Your Organic Chemistry StorySign Up For The Reaction GuideSign Up To Be A Flashcards Beta Tester!Signup for the Reaction GuideSomething Has Gone WrongSpectroscopy Video – Thanks!Spectroscopy Video CheckoutStereochemistry Webinar Sunday Nov 3Store ActionStudy and Exam TipsSummary SheetsTest PagetesttypgThanks for Joining!Thanks! You’re signed up for the newsletter.Thanks! You’re Signed Up For The Reaction GuideThe Cat Line DiagramThe Web of ReactionsThoughts On O-ChemTips

#9109 (no title)Conjugation

“Initial Tails” and “Final Heads”3 Ways To Make OH A Better Leaving GroupA Simple Formula For 7 Important Aldehyde/Ketone Reactions

AcetoaceticAcids (Again!)Activating and DeactivatingActors In Every Acid Base ReactionAddition – EliminationAddition Pattern 1 – CarbocationsAddition pattern 2 – 3 membered ringsAddition ReactionsAlcohol Personality AdjustmentAldehydes And Ketones – Addition


5


10/15

Alkene Pattern #3 – The “Concerted” PathwayAlkyl RearrangementsAlkynes – 3 PatternsAlkynes: Deprotonation and SN2AminesAromaticity: Lone PairsAvoid These Resonance Mistakes

Best Way To Form AminesBulky BasesCarbocation StabilityCarbocation Stability RevisitedCarboxylic Acids are AcidsChair FlipsCis and TransConformationsConjugate AdditionCurved Arrow Refresher Curved ArrowsDecarboxylationDetermining AromaticityDiels Alder Reaction – 1Dipoles: Polar vs. Covalent BondingE2 ReactionsElectronegativity Is Greed For ElectronsElectrophilic Aromatic SubstitutionElectrophilic Aromatic Substitution – Directing GroupsElimination ReactionsEnantiocats and DiastereocatsEnolatesEpoxides – Basic and AcidicEvaluating Resonance FormsFiguring Out The Fischer Find That Which Is HiddenFormal ChargeFrost CirclesGabriel SynthesisGrignardsHofmann Elimination

How Acidity and Basicity Are RelatedHow Are These Molecules Related?How Stereochemistry mattersHow To Stabilize Negative ChargeHow To Tell Enantiomers From DiastereomersHybridizationHybridization ShortcutHydroborationImines and EnaminesImportance of Stereochemistry


15


11/15

Intramolecular ForcesIntro to ResonanceKetones on AcidKinetic ThermodynamicMaking Alcohols Into Good Leaving GroupsMarkovnikov’s ruleMechanisms Like Chords

Mish MashamineMore On The E2 Newman Projections Nucleophiles & Electrophiles Nucleophilic Aromatic Substitution Nucleophilic Aromatic Substitution 2Order of Operations!Oxidation And ReductionOxidative CleavagePapedPi DonationPointers on Free Radical ReactionsProtecting GroupsProtecting GroupsProton Transfer Putting it together (1)Putting it together (2)Putting it together (3)Putting the Newman into ACTIONReaction MapsRearrangementsRecognizing Endo and ExoRedraw / ModifyReturn of The SN2Robinson AnnulationRobinson Annulation MechSecond Most Important Reactions of Alkynes: Lindlar – Na/NH3Sigma and Pi BondingSN1 vs SN2sn1/sn2 – Putting It Together sn1/sn2/e1/e2 – Exceptions

sn1/sn2/e1/e2 – Nucleophilesn1/sn2/e1/e2 – Solventsn1/sn2/e1/e2 – Substratesn1/sn2/e1/e2 – TemperatureStereochemistryStrong Acid Strong BaseStrong And Weak OxidantsStrong and Weak ReductantsStronger Donor WinsSubstitution


15


12/15

Sugars (2)Synthesis (1) – “What’s Different?”Synthesis (2) – What Reactions?Synthesis (3) – Figuring Out The Order Synthesis Part 1Synthesis Study BuddySynthesis: Walkthrough of A Sample Problem

Synthesis: Working Backwardst-butylTautomerismThe Awesomeness Of The SN2The Claisen CondensationThe E1 ReactionThe Inflection PointThe Meso TrapThe Michael ReactionThe Nucleophile Adds Twice (to the ester)The One-Sentence Summary Of ChemistryThe Second Most Important Carbonyl MechanismThe Single Swap RuleThe SN1 ReactionThe SN2 ReactionThe Wittig ReactionThree Exam TipsTips On Building Molecular OrbitalsTop 10 SkillsTry The Acid-Base Reaction FirstTwo Key Reactions of EnolatesWelcomeWhat makes a good leaving group?What Makes A Good Nucleophile?What to expect in Org 2Work BackwardsZaitsev’s Rule

Tuesday Oct 22 Acid Base Webinar at 9pm ESTVideos

A Simple Trick For Determining R/SApplying E2 Reactions with Newman Projections

Bond Rotations: Exercise 1Bond Rotations: Exercise 2Bond Rotations: Exercise 3Bond Rotations: Exercise 4Bond Rotations: Exercise 5Bond Rotations: The “Steering Wheel” AnalogyBronsted and Lewis AcidityBulky Bases in Elimination ReactionsCarbocation StabilityComparing E1 and E2 Mechanisms


15


13/15

Comparing E1 and E2 StereochemistryComparing the E1 and SN1Comparing the SN1 and SN2Converting a Fischer Projection To A Line DiagramConverting a Line Diagram to a Fischer ProjectionConverting a Newman Projection to a Line DiagramCurved Arrows

Determining R/S on a Fischer ProjectionE1 with RearrangementE1 With Rearrangement (2)Elimination Exercise: Zaitsev’s RuleElimination Reactions in CyclohexanesElimination Reactions in Cyclohexanes (2)Evaluating Resonance Forms (1) ChargesEvaluating Resonance Forms (2) OctetsEvaluating Resonance Forms (3) Negative ChargeEvaluating Resonance Forms (4) Positive ChargeEvaluating Resonance Forms (5) AromaticityExercise: Condensed Formula (1)Exercise: Condensed Formula (2)Factors that affect acidity – AromaticityFactors That Affect Acidity (1) Charge DensityFactors That Affect Acidity (2) ElectronegativityFactors That Affect Acidity (3) PolarizabilityFactors That Affect Acidity (4) Electron Withdrawing GroupsFactors That Affect Acidity (4) ResonanceFactors That Affect Acidity (6) – OrbitalsFormal Charge (1) – Atomic ChargeFormal Charge (2) – Introduction to Formal ChargeFormal Charge Exercise: Allyl CarbocationFormal Charge Exercise: CH2N2Formal Charge Exercise: CH3NO2Formal Charge Exercise: CNFormal Charge Exercise: CO3Formal Charge Exercise: Hidden HydrogensFormal Charge Exercise: Hidden Lone PairsFormal Charge Exercise: N3Formal Charge Exercise: NH4

Formal Charge Exercise: O3Formal Charge Exercise: Radicals and CarbenesHidden HydrogensHow Formal Charge Can MisleadHow Heat Affects Elimination ReactionsHow to draw an enantiomer How To Use A pKa TableIn Summary: ResonanceIntroduction to EliminationIntroduction to pKa


15


14/15

Introduction to RearrangementsIntroduction to ResonanceIntroduction to the E2 ReactionIntroduction to the SN1: ExperimentsIntroduction to the SN2: ExperimentsKey Patterns in Formal ChargeLine Drawings

Making OH Into A Good Leaving GroupRearrangement Reactions: Alkyl ShiftsRearrangement: Hydride ShiftRearrangements: Carbocation StabilityResonance – Common Mistakes (1)Resonance – Common mistakes (2)SN1 Exercise: The SubstrateSN1 Reaction Energy DiagramSN1 vs. SN2 OverviewSN1 With Alkyl Shift (1)SN1 With Alkyl Shift (2)SN1 With Hydride ShiftSN1: Applying the SN1 ReactionSN1/SN2/E1/E2 – SubstrateSN1/SN2/E1/E2 Decision – OverviewSN1/SN2/E1/E2 Decision – SolventSN1/SN2/E1/E2 Decision – TemperatureSN1/SN2/E1/E2 Decision – The Nucleophile/BaseSN2 Exercise: Apply the SN2SN2 Exercise: Leaving GroupsSN2 Exercise: The SubstrateSolvents in SN1 and SN2 ReactionsStereochemistry Exercise 1Stereochemistry Exercise 2Stereochemistry Exercise 3Stereochemistry Exercise 4Stereochemistry Exercise 5Strong and Weak AcidsSubstitution: What is Substitution?The 4 Components of Every Acid Base ReactionThe E1 Reaction

The Golden Rule of Acid Base ReactionsThe Single Swap RuleThe SN1 MechanismThe SN2 MechanismThe SN2 Reaction Energy DiagramUnderstanding R/S RelationshipsUnequal Resonance FormsUsing Electronegativity to Find Reactive Sites on a MoleculeWhat Makes A Good Leaving Group?What Makes A Good Nucleophile? (1)


15


15/15

What Makes A Good Nucleophile? (2)What Makes A Good Nucleophile? (3)What’s A Nucleophile?Zaitsev’s Rule

You’re Almost Subscribed To The Reaction Guide!


Carbocation Stability — Master Organic Chemistry

Documents

Transcript of Carbocation Stability — Master Organic Chemistry