Structure of benzene help !!

for this question I am uncertain about why 2 is also right. I know the bond length of benzene is an intermediate of a single & a double bond. So I am confused about what bond benzene has? The kekule structure has double bonds but I thought that is the wrong structure? Thus why can benzene still be described as unsatured? Also I am not quite sure why 3 is wrong either, is it because there is only 1 hydrogen on each C?

Thanks

(edited 6 years ago)

Reply 1

RoadToGradeA

11

1 is right, so is 2 because if benzene was saturated it would be c6h12, however, it is c6h6 which is unsaturated as carbon has potential to have 4 bonds.

Reply 2

_NMcC_

15

Original post by coconut64

for this question I am uncertain about why 2 is also right. I know the bond length of benzene is an intermediate of a single & a double bond. So I am confused about what bond benzene has? The kekule structure has double bonds but I thought that is the wrong structure? Thus why can benzene still be described as unsatured? Also I am not quite sure why 3 is wrong either, is it because there is only 1 hydrogen on each C?

Thanks

The true model of benzene is best represented by the 'circle in the middle' structure because it's what is between the two kekule resonance structures (shown below) is where the true structure of benzene can be found.

So the structure in benzene is best described as a ''delocalised pi-cloud of electrons'' because there are 6 delocalised pi-electrons (in P orbitals) flying around inside the ring. Which is why the circle is used as the structure really is like a 'circle of delocalisation'.

So think of the electrons are flying around the ring instead of bonding to hydrogen atoms, so just like a double or triple bond, they are accepted to make the ring very unsaturated.

Reply 3

coconut64

OP

16

Original post by _NMcC_

The true model of benzene is best represented by the 'circle in the middle' structure because it's what is between the two kekule resonance structures (shown below) is where the true structure of benzene can be found.

So the structure in benzene is best described as a ''delocalised pi-cloud of electrons'' because there are 6 delocalised pi-electrons (in P orbitals) flying around inside the ring. Which is why the circle is used as the structure really is like a 'circle of delocalisation'.

So think of the electrons are flying around the ring instead of bonding to hydrogen atoms, so just like a double or triple bond, they are accepted to make the ring very unsaturated.

Why can't it be classed as an alicylic then? Thanks

Original post by coconut64

Why can't it be classed as an alicylic then? Thanks

For hydrocarbons you have:

aliphatic
alicyclic
aromatic

benzene is categorised as aromatic

Reply 5

coconut64

OP

16

Original post by charco

For hydrocarbons you have:

aliphatic
alicyclic
aromatic

benzene is categorised as aromatic

So a hydrocarbon can only have one of those category, not both ? I thought it could also be alicyclic as it has a ring structure also

Reply 6

S.G.

22

Original post by coconut64

So a hydrocarbon can only have one of those category, not both ? I thought it could also be alicyclic as it has a ring structure also

All alicyclics are also aliphatic but not all aliphatics are alicyclics.

Reply 7

coconut64

OP

16

Original post by SGHD26716

All alicyclics are also aliphatic but not all aliphatics are alicyclics.

All alicyclics are also aliphatic -> are you sure about this because aliphatic only applies to straight chain molecule, no?

Reply 8

_NMcC_

15

Original post by coconut64

Why can't it be classed as an alicylic then? Thanks

'Alicyclic' - is really just a combination of 'Aliphatic' and 'Cyclic'

Cyclic is anything in a ring.
Aliphatic refers to anything that isn't aromatic - Benzene is Aromatic!

So alicyclic is wrong for benzene.

Reply 9

coconut64

OP

16

Original post by _NMcC_

'Alicyclic' - is really just a combination of 'Aliphatic' and 'Cyclic'

Cyclic is anything in a ring.
Aliphatic refers to anything that isn't aromatic - Benzene is Aromatic!

So alicyclic is wrong for benzene.

If you have cyclohexane, is it only an alicyclic as I thought aliphatic can only be used to describe a molecule that is not in a ring.. Thanks

Reply 10

_NMcC_

15

Original post by coconut64

If you have cyclohexane, is it only an alicyclic as I thought aliphatic can only be used to describe a molecule that is not in a ring.. Thanks

Alicyclic is a better name for it. It is still technically an Aliphatic as it's really just composed of Hydrogen and Carbon, non-aromatic however Alicyclic is far better.

Think of Alicyclic hydrocarbons as a branch of Aliphatic hydrocarbons, the other being 'Straight-chain' Aliphatics.

I say Aliphatic is anything that's non-aromatic, which is true, however by convention it refers only really to hydrocarbons.

(edited 6 years ago)

Reply 11

S.G.

22

Original post by coconut64

All alicyclics are also aliphatic -> are you sure about this because aliphatic only applies to straight chain molecule, no?

All alicyclics are aliphatics. I'm pretty sure. Aliphatic is everything bar aromatic. Alicyclics is a type of aliphatic effectively, making the distinction it contains a ring structure