Aromatic Compounds

Question 1

What are the 4 things that need to be checked off for a molecule to be aromatic? (Huckel’s Rules)

Answer 1

cyclic
planar (sp2 hyrbdized)
conjugated p-orbitals
amount of pi electrons = 4n + 2

Question 2

Where would you find aromatic rings?

Answer 2

pharmaceutical drugs

DNA - nitrogenous bases somewhat resemble benzene but have a nitrogen
aromatic compounds are very stable, good for DNA because we dont want DNA to react which can cause cancer

Question 3

Explain the stability of benzene.

Answer 3

aromatic rings like benzene will not react with addition reactions because of its stability unlike other rings

Question 4

What are heats of hydrogenation?

Answer 4

Heats of hydrogenation are the amount of energy used to get from one molecule to another

the stability of aromatic rings make the energy needed to change less than a non aromatic ring

Question 5

What is the difference in the length of the bonds for conjugated pi orbitals?

Answer 5

You might think that the double bond is shorter than the single bond based off of previous knowledge, but that is not true

both the double and single bonds are the same length, this is due to resonance structures

Question 6

What is the equation for an anti-aromatic compound?

Answer 6

4n

Question 7

What does it mean if you have electrons in a non bonding or anti bonding orbital in a molecular orbital image?

Answer 7

you probably have an anti-aromatic compound

Question 8

What is the exception when it comes to aromaticity for cyclooctatetraene?

Answer 8

Although it does follow of Huckel’s rules on face value for an anti-aromatic compound (4n), it is not anti-aromatic due to the compound not being planar

it has a boat shape

Question 9

What is Lawrence’s rule for his test for compounds with 7 or less and greater than 8 carbons?

Answer 9

if a compound has 7 or less carbons, you can automatically assume it is planar

if a compound has greater than 8 carbons, you will be told whether the compound is planar or not

Question 10

What do frost circles help us determine?

Answer 10

if a compound is aromatic or anti aromatic, by observing if there are electrons in non bonding or anti bonding orbitals

Question 11

What is important when drawing frost circles?

Answer 11

a corner must be at the bottom, a dotted line through the middle to show where non bonding might be, each corner hitting the circle is a line representing energy level of molecular orbitals

Question 12

How are annulenes named?

Answer 12

based on the number of carbons

Question 13

When do you count the lone pairs on heteroatoms for aromatic compounds?

Answer 13

If the heteroatom has a double bond attached to it, then you DO NOT count the lone pair

If the heteroatom does not have a double bond attached to tit, then you DO count the lone pair

Question 14

What are benzylic carbons?

Answer 14

Carbons directly attached to the benzene ring

Question 15

What happens to benzylic carbons when they are oxidized by chromic acid? permanganate?

Answer 15

They turn the benzylic carbon into a carboxylic acid

BUT the benzylic carbon must have a proton/hydrogen attached to it

If they are treated with permanganate, they produce the same product except that it is a 2 step process, creating a carboxylate intermediate

Question 16

What happens when a benzylic carbon is treated with NBS?

Answer 16

You add a bromine to the benzylic carbon allowing the product to be used in SN1, SN2, E1, and E2 reactions

Question 17

How do you reduce benzene?

Answer 17

It can be reduced with a metal and pressure and heat along with hydrogens.

You can also be selective by the amount of pressure and heat you use

Question 18

What is the Birch Reduction?

Answer 18

When benzene is reduced with sodium metal, methanol (l), and ammonia (l)

the most stable structure is the hexane with double bonds left and right because it has more options to resonate

Question 19

What affects regioselectivity when a R group is attached to a benzene ring when treated with sodium metal, methanol, and ammonia?

Answer 19

When the R group is electron donating, the product observed is the one with the double bond attached to the R group in the ring

When the R group is electron withdrawing, the product observed is the one that looks similar to the regular observed product