Categories of Organic Categories of Organic

ReactionsReactionsThereThere areare soso manymany typestypes ofof organicorganic reactionsreactions..

We’reWe’re goinggoing toto focusfocus onon justjust aa fewfew..

�� AdditionAddition ReactionsReactions

�� SubstitutionSubstitution ReactionsReactions

�� EliminationElimination ReactionsReactions�� EliminationElimination ReactionsReactions

�� OxidationOxidation –– ReductionReduction ReactionReaction

�� RearrangementRearrangement ReactionsReactions

�� PericyclicPericyclic ReactionsReactions

�� PhotochemicalPhotochemical ReactionsReactions

�� NuclearNuclear ReactionReactionss

Bond Breaking:Bond Breaking:Polar and NonPolar and Non--polar polar

Bond Forming:Bond Forming:Polar and NonPolar and Non--polarpolar

II-- Addition Addition ReactionsReactions

InIn alkenesalkenes andand alkynesalkynes

•• IInn additionaddition reactions,reactions,reactantsreactants areare addedadded totothethe carboncarbon atomsatoms inin thethedoubledouble oror tripletriple bondbond..doubledouble oror tripletriple bondbond..

•• TheThe doubledouble oror tripletriple bondbondiiss easilyeasily broken,broken, sincesince itit isishighlyhighly reactivereactive..

InIn hydrogenationhydrogenation,,

•• HydrogenHydrogen atomsatoms addadd toto thethe carboncarbon atomsatoms ofof aa doubledouble bondbond oror tripletriplebondbond..

•• convertsconverts unsaturatedunsaturated moleculemolecule toto saturatedsaturated

•• alkenealkene oror alkynealkyne ++ HH22 →→ alkanealkane

•• AA catalystcatalyst suchsuch asas PtPt oror NiNi isis usedused toto speedspeed upup thethe reactionreaction..

11-- HydrogenationHydrogenation(addition of Hydrogen)(addition of Hydrogen)

•• AA catalystcatalyst suchsuch asas PtPt oror NiNi isis usedused toto speedspeed upup thethe reactionreaction..

�� UnsaturatedUnsaturated vegetablevegetable oilsoils reducedreduced toto produceproduce saturatedsaturated fatsfats usedused ininmargarinemargarine andand cookingcooking productsproducts

H C C H + 2 H 2

N iH C C H

H H

H H

H 2C C H 2

H HPt

H 2H 2C C H 2 +

22-- HydrationHydration(addition of water H(addition of water H22O)O)

•• anan acidacid HH++ catalystcatalyst isis requiredrequired..

•• waterwater (HOH)(HOH) addsadds toto aa doubledouble bondbond..

•• anan HH atomatom bondsbonds toto oneone CC inin thethe doubledouble bondbond..

•• anan OHOH bondsbonds toto thethe otherother CC..

HH OHOH

HH++ ││ ││HH++ ││ ││CHCH33──CH=CHCH=CH──CHCH33 ++ HH──OHOH CHCH33──CHCH──CHCH──CHCH33

HydrationHydration

WhenWhen hydrationhydration occursoccurs withwith aa doubledouble bondbond thatthat hashas ananunequalunequal numbernumber ofof HH atomsatoms,,

•• thethe HH atomatom bondsbonds toto thethe CC inin thethe doubledouble bondbond withwith thethemoremore HH..

•• thethe OHOH bondsbonds toto thethe CC inin thethe doubledouble bondbond withwith thethe fewerfewer•• thethe OHOH bondsbonds toto thethe CC inin thethe doubledouble bondbond withwith thethe fewerfewerHH atomsatoms..

OHOH HHHH++ ││ ││

CHCH33──CH=CHCH=CH22 ++ HH──OHOH CHCH33──CHCH──CHCH22

33-- HalogenationHalogenation

In In HalogenationHalogenation,,

�� halogen atoms add to the carbon atoms of halogen atoms add to the carbon atoms of double bond or triple bond.double bond or triple bond.

�� Addition of BrAddition of Br22 and Cland Cl22 to alkenes to yield 1,2to alkenes to yield 1,2--�� Addition of BrAddition of Br22 and Cland Cl22 to alkenes to yield 1,2to alkenes to yield 1,2--dihalidesdihalides

A A colourcolour test for c=c Bondtest for c=c Bond

C C + Br2 C C

Br

Br

HalogenationsHalogenations

44-- HydrohalogenationHydrohalogenation

InIn hydrohalogenationhydrohalogenation,,

�� thethe atomsatoms ofof aa hydrogenhydrogen halidehalide addadd totothethe carboncarbon atomsatoms ofof aa doubledouble bondbond orortripletriple bondbond..

Br H H Br

CH3 CH=CH2 HBr CH3 CH-CH2

Br H

CH3 CH-CH2

H Br

1-Bromopropane (not observed)

2-BromopropanePropene

++

MarkovnikovMarkovnikov’’ss RuleRule

InIn thethe additionaddition ofof HX,HX, HH22O,O, oror ROHROH toto anan alkenealkene,, HH addsadds totothethe carboncarbon ofof thethe doubledouble bondbond havinghaving thethe greatergreater numbernumberofof hydrogenshydrogens..

II- Substitution Reactions

� Are characteristic reaction of saturatedcompounds such as alkanes.

� In a substitution reaction, one atom, ion orgroup is replaced (substituted) by anothergroup is replaced (substituted) by another

CH4 + Cl2 CH3Cl + HCl

CH3Cl + Cl2 CH2Cl2 + HCl

CH2Cl2 + Cl2 CHCl3 + HCl

CHCl3+ Cl2 CCl4 + HCl

�� Needs Needs ultraviolet lightultraviolet light to initiate the to initiate the reaction.reaction.

Nucleophilic Nucleophilic Substitution Substitution RReactionseactions�� EachEach stepstep involvesinvolves thethe substitutionsubstitution ofof oneone nucleophilenucleophile

(chloride(chloride ion,ion, ClCl--,, oror hydroxidehydroxide ion,ion, HOHO--)) byby anotheranother� Nucleophile: a molecule or ion that donates a pair of

electrons to another molecule or ion to form a new covalentbond

� To be a good leaving group the substituent must be able toleave as a relatively stable, weakly basic molecule or ion

� In alkyl halides the leaving group is the halogen substituent-� In alkyl halides the leaving group is the halogen substituent-it leaves as a halide ion

� Because halide ions are relatively stable and very weakbases, they are good leaving groups

� Substitution of alkyl halides with nuclophiles can occur by anSN2 or SN1 path, a fundamental difference between them isthe timing of bond breaking and bond forming steps

The SThe SNN22 ReactionReaction

SSNN2 2 reactionreaction

�� SubstitutionSubstitution,, NucleophilicNucleophilic,, Bimolecular.Bimolecular.

�� Essential features of the SEssential features of the SNN22 Reaction Reaction

–– Takes place in a single step without Takes place in a single step without intermediatesintermediatesintermediatesintermediates

–– Incoming Incoming nucleophilenucleophile reacts with the alkyl reacts with the alkyl halide or (the halide or (the substratesubstrate) from a direction ) from a direction opposite the group that is displaced (the opposite the group that is displaced (the leaving group)leaving group)

The SThe SNN22 ReactionReaction

TheThe mechanismmechanism ofof thethe SSNN22 reactionreaction whenwhen((SS))--22--bromobutanebromobutane reactsreacts withwith ––OHOH totogivegive ((RR))--butanbutan--22--olol

�� TheThe reactionreaction takestakes placeplace inin aa singlesingle stepstep

�� IncomingIncoming nucleophilenucleophile approachesapproaches fromfrom aadirectiondirection 180180ºº awayaway fromfrom thethe leavingleavingdirectiondirection 180180ºº awayaway fromfrom thethe leavingleavinghalidehalide ion,ion, therebythereby invertinginverting thethestereochemistrystereochemistry atat carboncarbon

Substitution, Nucleophilic, Bimolecular Substitution, Nucleophilic, Bimolecular –– SSNN22

C Xδ−δ+

Nuc : C XNuc CNuc + Xδ− δ−

C XNuc : C XNuc CNuc + X

transition state

δ−

CarbocationsCarbocations�� CarbocationCarbocation:: aa speciesspecies inin

whichwhich aa carboncarbon atomatom hashas onlyonlysixsix electronselectrons inin itsits valencevalenceshellshell andand bearsbears positivepositive chargecharge

�� CarbocationsCarbocations areare

–– classifiedclassified asas 11°°,, 22°°,, oror 33°°dependingdepending onon thethe numbernumberdependingdepending onon thethe numbernumberofof carbonscarbons bondedbonded toto thethecarboncarbon bearingbearing thethe positivepositivechargecharge..

–– electrophileselectrophiles;; thatthat is,is, theytheyareare electronelectron--lovingloving..

–– LewisLewis acidsacids..

–– OrderOrder ofof stabilitystability::

33°° ›› 22°° ›› 11°°›› methylmethyl..

The SThe SNN1 1 ReactionReactionUnimolecularUnimolecular nucleophilicnucleophilic substitution reactionsubstitution reaction

�� Mechanism of the Mechanism of the SSNN1 1 reaction of reaction of 22--bromobromo--22--methylpropane methylpropane with Hwith H22O involves O involves three stepsthree steps

–– The first step The first step –––– The first step The first step ––spontaneous, spontaneous, unimolecular unimolecular dissociation of dissociation of the alkyl the alkyl bromide to yield bromide to yield a carbocation a carbocation ––is rateis rate--limitinglimiting

SSNN1 1 mechanism mechanism 11stst step is rate determiningstep is rate determining

IIIIII-- Elimination ReactionsElimination Reactions

�� EliminationElimination:: removalremoval ofof atomsatoms oror groupgroup ofof atomsatoms fromfromadjacentadjacent carboncarbon toto formform aa carboncarbon--carboncarbon doubledouble bondbond

�� TheseThese areare thethe oppositeopposite ofof additionsadditions

�� ThisThis usedused toto prepareprepare alkenesalkenes

�� AnAn importantimportant eliminationelimination reactionreaction isis DehydrohalogenationDehydrohalogenation�� AnAn importantimportant eliminationelimination reactionreaction isis DehydrohalogenationDehydrohalogenation

DehydrohalogenationDehydrohalogenation ((--HX)HX)

strong

base+ " "C C

X

H XC C

H

X = Cl, Br, I

X

CombustionCombustion

AA reactionreaction inin whichwhich aa compoundcompound

(often(often carbon)carbon) reactsreacts withwith oxygenoxygen

CC ++ OO22 COCO22CC ++ OO22 COCO22

CHCH44 ++ 22OO22 COCO22 ++ 22HH22OO

CC33HH88 ++ 55OO22 33COCO22 ++ 44HH22OO

CC66HH1212OO66 ++ 66OO22 66COCO22 ++ 66HH22OO

IVIV-- Oxidation/ReductionOxidation/Reduction

�� Oxidation:Oxidation: the loss of electronsthe loss of electrons

–– alternatively, the loss of H, the gain of O, or alternatively, the loss of H, the gain of O, or bothboth

�� Reduction:Reduction: the gain of electronsthe gain of electrons�� Reduction:Reduction: the gain of electronsthe gain of electrons

–– alternatively, the gain of H, the loss of O, or alternatively, the gain of H, the loss of O, or bothboth

Oxidation and ReductionOxidation and Reduction3 3 hydrocarbon oxidation levelshydrocarbon oxidation levels

CH3CH3 CH2=CH2 HC CH[O] [O]

oxidation # -3 -2 -1oxidation # -3 -2 -1of carbon

Oxidation Oxidation -- ReductionReduction

�� Oxidation of AlcoholsOxidation of Alcohols

–– Oxidation of Primary Alcohols to AldehydesOxidation of Primary Alcohols to Aldehydes

�� A primary alcohol can be oxidized to an aldehyde A primary alcohol can be oxidized to an aldehyde or a carboxylic acidor a carboxylic acid

–– The oxidation is difficult to stop at the aldehyde stage The oxidation is difficult to stop at the aldehyde stage and usually proceeds to the carboxylic acidand usually proceeds to the carboxylic acid

–– Oxidation of Secondary Alcohols to KetonesOxidation of Secondary Alcohols to Ketones

�� Oxidation of a secondary alcohol stops at the Oxidation of a secondary alcohol stops at the ketoneketone

OxidationOxidation--ReductionReductionReactions involve electron transfersReactions involve electron transfers

�� OxidationOxidation ofof biomoleculesbiomolecules oftenoften occursoccurs asasdehydrogenation,dehydrogenation, electronelectron acceptoracceptor –– whichwhich areareusuallyusually coenzymescoenzymes –– areare neededneeded forfor suchsuchreactionsreactions toto occuroccur..

Practice Exercises:Classify the following rxns as substitution, elimination, or addition.

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