ch 11 aromaticity and benzene reactions

rules for aromatic compound

1. The compound must be cyclic.

2. The ring must be fully conjugated and planar (none of the atoms comprising the ring are sp3 hybridized).

3. The system must satisfy Huckel’s rule (# of pi electrons = 4n+2; n is any integer).

does carbocation contribute to electron in the pi system

no

does lone pairs contribute to electron in the pi system

yes

If a compound satisfies all the rules except Huckel’s rule?

anti-aromatic

If a compound satisfies first 2 rules?

non-aromatic

What is the Birch reaction?

converting an aromatic benzene molecule into a non-aromatic ring with two pi bonds located on opposite sides of the ring

reagents for Birch reaction

1) Na, NH3

2) EtOH

When an electron donating group is present on aromatic ring + undergoes Birch reaction…

the carbon it is attached to is not reduced

When an electron withdrawing group is present on aromatic ring + undergoes Birch reaction…

the carbon it is attached to is reduced

if deprotonation of the compound makes it aromatic, is the compound acidic or basic?

acidic

If the loss of a leaving group makes the compound aromatic, what reaction is the compound inclined to undergo?

SN1 reaction

If the loss of a leaving group makes the compound aromatic, what reaction is the compound not inclined to undergo?

SN1 reaction

What is Electrophilic Aromatic Substitution (EAS)?

substitution of a hydrogen atom attached to an aromatic compound with an electrophile

what is the intermediate of a EAS reaction?

sigma comlex or an arenium ion

what is EAS halogenation?

substitution of an aromatic hydrogen atom with chlorine or bromine

reagents for EAS halogenation

1) Br2 or Cl2

2) Lewis acid catalyst

name the Lewis acid catalyst for EAS halogenation

FeBr3, AlBr3, FeCl3, AlCl3

What is the Friedel-Crafts Alkylation?

attach an alkyl group to a benzene ring

Friedel-Crafts Alkylation reagents

1) alkyl halide (e.g. CH3CH3CCl)

2) Lewis acid catalyst

Which reaction breaks the aromaticity of the ring and forming the sigma complex?

EAS halogenation 

(Friedel-Crafts Alkylation does not break aromaticity)

What happens to the carbocation intermediate of Friedel-Crafts Alkylation?

it can move to form a more stable carbocation and result in more stable product

What is Friedel-Crafts Acylation?

1. add carbons to an aromatic compound

2. attaches the carbonyl carbon of an acid halide

reagents Friedel-Crafts Acylation?

1) acid halide

2) Lewis acid catalyst

Friedel-Crafts Acylation can be reduced to alkane via what reactions?

Clemmensen reduction or Wolff-Kishner reduction

Friedel-Crafts alkylation/acylation does not occur in what group? Why?

electron withdrawing group such as NO2

electron donating group like NH2, NHR, NR2

EAS Halogenation reagents and what product is stuck to the aromatic ring?

1) X2

2) AlX3 or FeX3

product: X

EAS sulfonation reagents and what product is stuck to the aromatic ring?

1) SO3

2) H2SO4

product: SO3H

EAS nitration and what product is stuck to the aromatic ring?

1) HNO3

2) H2SO4

product: NO2

EAS FC Alkylation reagents and what product is stuck to the aromatic ring?

1) R-Cl

2) AlCl3

product: R (Cl doesnt do anything)

EAS FC acylation reagents and what product is stuck to the aromatic ring?

1) R-COCl

2) AlCl3

product: COR (Cl doesnt do anything)

EAS formylation reagents and what product is stuck to the aromatic ring?

1) CO, HCl

2) AlCl3

product: COH

electron withdrawing (deactivating)group is what director?

meta director

electron donating (activating) group is what director?

ortho/para director

what groups are electron withdrawing (deactivating) but are ortho/para directors?

halogens (—F/Cl/Br/l)

name 7 electron withdrawing groups

nitrile (CN), NR3, NO2, aldehyde, ketone, ester (on the nothing side), carboxylic acid, SO3H

name 9 ortho/para directors

NH2/NRH/NR2, SH, OH, C-OR-NH, SR, OR (ether), ester (on the O side), R, CH3

reagents for Nitro groups

1) Sn 2) HCl

1) H2 2) Pd or Pd/C or Pt

1) Zn(Hg) 2) HCl, heat

nitrobenzene (there is NO2 on benzene) + 1) Sn 2) HCl

aniline (NH2 replacing NO2)

nitrobenzene (there is NO2 on benzene) + 1) H2 2) Pd or Pd/C or Pt

aniline (NH2 replacing NO2)

nitrobenzene (there is NO2 on benzene) + 1) Zn(Hg) 2) HCl, heat

aniline (NH2 replacing NO2)

what happens in Benzylic Oxidation?

R R H 1)KMnO ,NaOH,heat HO O carboxylic acid using a strong oxidizing agent

Benzylic Oxidation reagents

1) KMnO4, NaOH, heat

2) H3O+ 

or

1) Na2Cr2O7

2) H2SO4, H2O

When will Benzylic Oxidation not happen?

If the benzylic carbon is not bound to at least one hydrogen

aromatic amine (aniline) + NaNO2 and HCl

diazonium salt

What is aryl diazonium ion composed of?

aryl diazonium ion consists of benzene attached to an N2

What is Diazonium Salt Reactions?

diazonium ion yielding different functional groups

diazonium salt + H3PO2 (weak acid)

benzene

diazonium salt + KI

I attaches to benzene

diazonium salt + HBF4

benzene attaches to F

diazonium salt + H3O+ and heat

benzene attaches to OH

diazonium salt + CuCN 

benzene attaches to CN

diazonium salt + CuBr

benzene attaches to Br

diazonium salt + CuCl

benzene attaches to Cl