Chemistry*2*Notes!Organic(Chemistry(

Lecture(1(

Broad&reaction&types&

• First&order&reaction&–&rate&is&dependent&on&the&concentration&of&one&reactant&and&there&is&a&distinct&

break.&There&is&a&distinct&intermediate&that&forms&–&it&is&a&stepwise&reaction.&

• Second&order&reaction&–&rate&is&dependent&on&the&concentration&of&both&reactants&and&a&collision&

occurs.&There&is&no&distinct&intermediate,&the&reaction&is&fluid.&

Bond&breaking:&

• Heterolytic&bond&cleavage&–&both&electrons&of&a&bond&go&to&one&species&

• Homolytic&bond&cleavage&–&one&electron&from&the&bond&goes&to&each&species&

Lecture(2(

Species:&

• Nucleophile&–&nucleus&loving&–&usually&has&lone&pair&or&negative&charge&

• Electrophile&–&electron&loving&–&usually&lacks&lone&pairs&or&has&positive&charge&

• Strong&acid&–&has&a&stable&conjugate&base&

• Weak&acid&–&has&an&unstable&conjugate&base&

• Most&reactions&occur&between&a&nucleophile&and&an&electrophile,&the&nucleophile&donates&electrons&to&

form&a&bond&

AcidsGBases:&Acids&are&electrophiles,&bases&are&nucleophiles&

Hybridization:&sp3&& sp2& & sp&

Acidity:& &&&&&&&&&&least<& & <& & <greatest&

&& &&&&&&&&&CH3&CH3&&&& &&&&&&&H2C=&CH2&& &&&&&&&&&&HC≡CH&

pKa:& & ~70& & ~44& & ~25&

So,&lower&pKa&=&stronger&acid&!&therefore&a&more&stable&conjugate&base&

Electronegative&atoms,&such&as&chlorine,&have&the&ability&to&increase&acidity&of&species&by&pulling&electron&

charge.&

Species&

&pKa& &&&&&&4.76& &&&&&2.86& &&&&&&1.29& &&0.85&&

&

&

&

Resonance:&

• The&more&resonance&structures,&the&more&stable&a&compound&is&

• If&there&is&a&charge&or&lone&pair&next&to&a&π&bond,&resonance&will&occur&

• Example&of&resonance:&Phenol&

&

Lectures(3512(

Reaction(Mechanisms:(

The&best&nucleophiles&have&conjugate&acids&with&high&pKa&

Nucleophilic&substitution:&

SN2&reaction:&1&step&

H

H H

LGNu

- C LGNu-

H

HH

C LGNu

H

HH

CNu

H

HH

LG-+

&

H

CH3

ClCH3

OH-

C ClOH

H

CH3CH3

C Cl-OH

H

CH3CH3

COH

H

CH3

CH3

Cl-+

(R) (S)&

• Nucleophile&attacks&carbon&via&backside&attack&trajectory&and&leaving&group&leaves&in&a&single&step&

• If&carbon&that&reacted&was&asymmetric&then&the&absolute&configuration&is&reversed&

• The&reaction&is&more&likely&to&be&SN2&if&there&is&little&steric&crowding&from&surrounding&groups,&so&

likelihood&of&SN2&occurring&follows:&

• methyl&>&primary&>&secondary&>>>&tertiary&

&

&

&

&

&

SN1&reaction:&2&steps&

CH3

CH3 CH3

Cl

CH3

C+

CH3 CH3

Cl-

OH-

OHCH3CH3CH3

OH

CH3

CH3

CH3

&

• Leaving&group&leaves&and&carbon&becomes&planar&carbocation&

• Nucleophile&attacks&from&either&side,&producing&a&racemic&mixture&of&both&R&and&S&isomers&

• Reaction&is&more&likely&to&be&SN1&if&the&carbocation&formed&is&more&stable:&

• Tertiary&>&Secondary&>&Primary&>>>&Methyl&

Elimination&reactions:&Nucleophile&acts&as&a&base&and&reacts&with&nearby&hydrogen&

E2:&1&step&

LG

H

HH

HH

B-

+H

H

H

HBH

&

• Base&reacts&with&Hydrogen&that&MUST&be&antiGperiplanar&to&the&leaving&group&and&forms&an&alkene&

• Reactants&can&be&strong&bases&yet&be&weak&nucleophiles,&and&vice&versa&

• Always&gives&E&as&the&geometric&isomer&

Zaitsev’s&rule:&Elimination&gives&the&most&substituted&alkene&as&the&major&product&

E1:&2&steps&

LG

H

HH

CH3CH3

+H

H

CH3

CH3BH

CH3

CH3HH

H

+

B-

&

• Leaving&group&leaves&first&to&create&a&carbocation&

• Base&reacts&with&one&of&the&neighbouring&hydrogens&(depends&on&Zaitev’s&rule)&

• Mainly&E&isomer&formed,&but&also&some&Z&

&

&

&

Comparing&SN1,&SN2,&E1,&E2&

Reaction( Methyl( Primary( Secondary( Tertiary(SN2& Will&react& Will&react& May&react& Wont&react&E2& ?& React(str&base)& React(str&base)& React(str&base)(SN1& Wont&react& Wont&react& May&react& Will&react&E1& Wont&react& Wont&react& May&react& Will&react&&

Electrophilic&Addition:&

• Double&bond&becomes&single&bond&and&species&is&added&

• Usually&occurs&when&reacting&with&halogenoalkanes&or&polarisable&halogens&(not&F2)&

Markovnikov’s&rule:&when&HGX&is&added&across&a&double&bond,&the&X&adds&to&the&most&substituted&carbon,&and&

the&H&goes&to&the&least.&

This&rule&may&break&down&if&the&products&are&resonance&stabilised&

CH2CH3

CH3 +H+ Cl

-

CH3

CH3

CH3

+CH3 CH3

CH3

Cl

&

• Electrons&from&double&bond&instead&bond&with&proton,&forming&a&carbocation&

• Nucleophile&reacts&with&carbocation&to&form&product&

• Carbocations&form&on&the&carbon&with&the&most&substituents&

• Both&R/S&can&form&

Hydration&

H+ +

OH2

O+H

H

OH

&

Electrophilic&Aromatic&Substitution&

• Groups&attached&to&aromatic&rings&can&change&the&products&formed&

• Electron&Donating&groups&will&cause&ortho&and&para&products&

• E.g.&CH3,&NH2,&halogens&

• Electron&withdrawing&groups&will&cause&meta&products&

• E.g.&CO2H,&NO2,&CN,&C=O,&CO2R&

• (halogens&count&as&EWG&but&produce&ortho/para)&

EWG

CHCH

..δ−

δ− EDG

CH

CH

CH

δ−

δ+

δ+

δ+

&

&

&

Halogenation&

XX

FeX3 FeX4-

XC+

H

HX+

X

&

Acylation&

R

O

ClAlCl3

R

O

+R

O

(Hydrogens&omitted)&

Alkylation&

CH3Cl

CH3 AlCl3

R

CH3

+R

CH3

&

Sulphonation&

H2SO4+SO2+ OH2

SO

OH

&

Nitration&

H2SO4+HNO3 N+

O-

O

&

&