Aromatic compounds

Question 1

Benzene formula

Answer 1

C6H6

Question 2

C-C bonds in benzene are all equal =

Answer 2

1.4Å (single C-C 1.54Å, double C=C 1.33Å)

Question 3

Resonance hybrid of the two Kekulé structures: the pi electrons are _________

Answer 3

delocalised

Question 4

Aromatic compound:

Answer 4

be a cyclic compound containing some number of conjugated double bonds and having an unusually large resonance energy

Question 5

Aromatic compounds meet the following criteria:
[4]

Answer 5

1] Structure must be cyclic, containing some number of conjugated pi bonds

2] Each atom in the ring must have an unhybridized p orbital. Usually sp2 or occasionally sp hybridised

3] Unhybridized p orbitals must overlap to form a continuous ring of parallel orbitals (conjugated). Structure must be planar (or nearly planar) for effective overlap to occur

4] Delocalisation of the pi electrons over the ring must lower the electronic energy

Question 6

Antiaromatic compound:

Answer 6

meets the first three criteria, but delocalisation of the pi electrons over the ring increases the electronic energy

Question 7

Aromatic structures are _____ stable than their open-chain counterparts

Answer 7

more

Question 8

What is a Nonaromatic compound (aliphatic)?

Answer 8

cyclic compound that does not have a continuous, overlapping ring of p orbitals. Its electronic energy is similar to that of its open-chain counterpart

Question 9

Aromatic or antiaromatic: a cyclic compound must have

Answer 9

a continuous ring of overlapping p orbitals, usually in a planar conformation

Question 10

Benzene (4N+2) = N=1. How many pi electrons can the benzene obtain?

Answer 10

6 pi e-

Question 11

sp3 carbon is nonaromatic because

Answer 11

no unhybridized p orbital and no continuous ring of p orbitals

Question 12

4N the system is

Answer 12

nonaromatic

Question 13

sp3 present

Answer 13

nonaromatic

Question 14

When carbon have -ive charge it is sp2 instead of sp3

Answer 14

antiaromatic

Question 15

when a carbon is +ive NOT sp3 but sp2

Answer 15

aromatic

Question 16

4 pi e- system with N=1 obtains

Answer 16

4N = 4 pi e-

Question 17

Derivative of benzene:

Answer 17

substituents named just as they were attached to an alkane

Question 18

Disubstituted benzenes:

Answer 18

prefixes ortho- (o), meta- (m), and para- (p).
Numbers can also be used

Question 19

Three or more substituents

Answer 19

give the lowest possible numbers to the substituents. Carbon atom bearing the functional group that defines the base name

(as in phenol or benzoic acid) is assumed to be C1

Question 20

Benzene ring named as a substituent:

Answer 20

prefix- phenyl group.
Often abbreviated Ph in drawing a complex structure

Question 21

Nomenclature of Benzene Derivatives

Answer 21

Benzyl group:
benzene ring + methylene (-CH2-) group (7 carbons)
Do not confuse with the phenyl group (six carbons)

Question 22

aromatic hydrocarbons can be called

Answer 22

arenes

Question 23

Aryl group (Ar):

Answer 23

Aromatic group after the removal of a H atom from an aromatic ring. The phenyl group, Ph, is the simplest aryl group.

Question 24

what are the 6 steps of Aromatic Compounds Reactions?

Answer 24

1. Electrophilic aromatic substitution
2. Nucleophilic aromatic substitution
3. Organometallic Couplings
4. Addition reactions
5. Side-chain reactions
6. Oxidation of phenols to quinones

Question 25

Electrophilic Aromatic Substitution

Answer 25

Benzene has clouds of pi electrons above and below its sigma bond framework
Attack a strong electrophile to give a carbocation

Question 26

2 steps of electrophilic aromatic substitution

Answer 26

Step 1: Attack on the electrophile forms the sigma complex (a resonance-stabilised carbocation)

Step 2: Loss of a proton regains aromaticity and gives the substitution product

Question 27

Overall reaction of e- substitution is a sub of:

Answer 27

electrophile (E+) for a proton (H+) on the aromatic ring

Question 28

Electrophilic Aromatic Substitution (electrophiles)

Answer 28

a. Bromination of Benzene
b. Nitration of Benzene
c. Sulfonation of Benzene
d. The Friedel–Crafts Alkylation
e. The Friedel–Crafts Acylation

Question 29

Activating, Ortho, Para-Directing Substituents
What is the role of methyl group?

Answer 29

electron-donating (ED): stabilises the sigma complex

Question 30

Inductive stabilisation:

Answer 30

donate electron density through the sigma bond to the benzene ring

Question 31

Resonance stabilisation:

Answer 31

[Alkoxy groups] oxygen atom is called resonance-donating or pi-donating because it donates electron density through a pi bond in one of the resonance structures

Question 32

in AMINE GROUPS

Answer 32

Resonance stabilisation: Nitrogen’s lone pair electrons provide resonance stabilisation to the sigma complex if attack takes place ortho or para to the position of the nitrogen atom.

Question 33

Any substituent with a lone pair of electrons on the atom bonded to the ring can provide resonance stabilisation to a _____ complex

Answer 33

sigma

Question 34

Is nitro a strong or weak deactivating group?
(Deactivating, Meta-Directing Substituents)

Answer 34

Strong - 1. Nitrobenzene: 100,000 times less reactive

Question 35

2nd step;
Deactivating, Meta-Directing Substituents

Answer 35

2. One product: meta-directors, deactivate the meta position less than the ortho/para positions, allowing meta substitution

Question 36

Inductively withdraws electron density from the aromatic ring, which is less electron-rich, so

Answer 36

DEactivated

Question 37

Deactivating substituents: groups with _____ _______ (or a partial positive charge) on the atom bonded to the aromatic ring

Answer 37

positive charge

Question 38

Halogen Substituents

Halogens: deactivating groups but ortho, para-directors

Answer 38

1) Strongly electronegative: withdrawing electron density from a carbon atom through the sigma bond (inductive withdrawal)

2) Nonbonding electrons donate electron density through pi bonding
(resonance donation)

Question 39

_________ reacts at ortho/para and the positive charge of the sigma complex is shared by the carbon atom bearing the halogen.

Answer 39

Eloctrophile

Question 40

Directing effects of substituents
1) e- donating and 2) e-withdrawing

Answer 40

1) activating = pi donors and sigma donors
2) deactivating = halogens, carbonyls and others

Question 41

Effects of Multiple Substituents
Activating groups are usually stronger directors than deactivating groups

Answer 41

1. Powerful ortho, para-directors that stabilise the sigma complexes through resonance. -OH, -OR, and -NR2 groups
2. Moderate ortho, para-directors, such as alkyl groups and halogens
3. All meta-directors

Question 42

Nucleophilic Aromatic Substitution
SN1 and SN2 mechamisms

Answer 42

SN2 mechanism: NO. The aromatic ring blocks approach of the nucleophile to the back of the carbon bearing the halogen

SN1 mechanism: NO. Strong nucleophiles are required and the reaction rate is proportional to the concentration of the nucleophile

two can be involved - depending reactants

Question 43

Organometallic coupling: Heck reaction

Answer 43

Coupling of an aryl or vinyl halide with an alkene to give a new C-C bond at the less substituted end of the alkene, usually with trans stereochemistry

Question 44

Organometallic coupling; The Suzuki Reaction (Suzuki Coupling)

Answer 44

Palladium-catalysed substitution that couples an aryl or vinyl halide with an alkyl, alkenyl, or aryl boronic acid or boronate ester