ch 16: aromatic compounds

Question 1

benzene

Answer 1

simple example of an aromatic compound

Question 2

are benzene rings saturated or unsaturated?

Answer 2

unsaturated

Question 3

how many p-orbitals overlap in a benzene ring?

Answer 3

6

Question 4

are benzene rings stable? why or why not?

Answer 4

very stable because of its aromatic characteristic, resonance and p-delocalization

Question 5

do benzenes do addition or substitution reactions?

Answer 5

only substitution
- cannot do addition because it would break the pi-bond system

Question 6

is benzene’s energy high or low?

Answer 6

low

Question 7

how many MOs are in benzene?

Answer 7

6: 3 bonding and 3 antibonding

Question 8

4 criteria for a compound to be aromatic

Answer 8

1. must be cyclic
   - each p-orbital must overlap with the p-orbitals on the adjacent atom
2. molecule must be planar
   - all p orbitals must be parallel
3. the ring must be completely conjugated
4. must satisfy Huckel’s Rule

Question 9

Huckel’s Rule

Answer 9

for a system to be aromatic, it must contain 4n + 2 pi e-

Question 10

what happens if a structure has 4n e-

Answer 10

it is antiaromatic and very unstable

Question 11

what does huckel’s rule refer to?

Answer 11

number of electrons not the number of atoms in the ring

Question 12

what is more stable: antiaromatics or non-aromatics?

Answer 12

non-aromatics

Question 13

annulenes

Answer 13

hydrocarbons containing a single ring with alternating C=C and C-C bonds

Question 14

can ions be aromatic?

Answer 14

yes, if they possess all the necessary features

Question 15

can radicals be aromatic?

Answer 15

usually no, because they always have an uneven amount of electrons

Question 16

polyaromatic hydrocarbons

Answer 16

two or more rings with alternating double bonds and single bonds fused together

Question 17

what happens as the number of fused rings increases?

Answer 17

the number of resonance forms increase

Question 18

can heterocycles be aromatic?

Answer 18

yes, but you have to consider whether the electrons are localized on the heteroatoms or part of the delocalized pi system

Question 19

what happens if heteroatom’s lone pair are apart of the pi system?

Answer 19

it is aromatic because it gives the pi system 2 electrons

Question 20

what happens if the lone pair is localized to the heteroatom?

Answer 20

not apart of the pi system, so would not be aromatic

Question 21

how to name monosubstituted benzene?

Answer 21

benzene is the parent name and the substituent is indicated by a prefix

Question 22

naming disubstitued benzenes

Answer 22

use the prefixes ortho, meta, and para
- also use numbers

Question 23

ortho

Answer 23

two substituents next to each other

Question 24

meta

Answer 24

two substituents one carbon away

Question 25

para

Answer 25

substituents equally across from each other

Question 26

what is another name for dimethylbenzenes?

Answer 26

xylene

Question 27

if two substituent groups are different, what must happen when naming?

Answer 27

alphabetize the names preceding the word benzene

Question 28

if one of the substituents is a "common-name benzene", what do you do?

Answer 28

name it is as a derivative of that parent and use o,p or m

Question 29

how do you name benzene rings with more than two substituents?

Answer 29

their positions must be indicated by the use of numbers - substituents get lowest possible numbers - alphabetize

Question 30

if the hydrocarbon chain is longer than the benzene, how is it named?

Answer 30

the chain is the parent carbon and the ring would be named a phenyl - have to use R or S

Question 31

another name for phenylmethyl group

Answer 31

benzyl

Question 32

what is the absorption value for aromatics on NMR spectrum?

Answer 32

6.5-8ppm

Question 33

what is the J-value for ortho?

Answer 33

7-9 Hz

Question 34

what is the j-value for meta?

Answer 34

0-2.5 Hz

Question 35

if phenyl is monosubstituted, how many H types will it have?

Answer 35

3 H types - 2 H are ortho - 2 H are para - 1 meta H

Question 36

draw out the common names for some aromatics

Answer 36

- phenol - toluene - aniline - anisole - styrene - acetophenone - benzaldehyde - benzoic acid